Advise on what Rock/mineral/glass wool to choose for basstraps

All about acoustics. This is your new home if you already have a studio or other acoustic space, but it isn't working out for you, sounds bad, and you need to fix it...

Which insulation product would you choose for bass traps ?

Poll runs till Sun, 2020-Nov-29, 18:23

Knauf Ultracoustic-p
0
No votes
Fibran b030
1
100%
Fibran b040
0
No votes
Fibran b050
0
No votes
 
Total votes: 1

musictracer
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Advise on what Rock/mineral/glass wool to choose for basstraps

#1

Postby musictracer » Mon, 2020-Feb-03, 18:23

Hello everyone and good luck with this beautiful new forum to you Stuart and your team! :D

I have "designed" and currently building a couple of Bass Traps for my room and I find it hard to decide which product of porous absorbing material I should use.
Unfortunately where I live I can't get owen's curning or Rockwool Safe n' sound.

Thus my choices are narrowed to this table:
products 2 - no isover or izifon.jpg
.

Preferably I'd like to avoid exceeding the 40kg/m3 in order to make the traps lighter.
According to the porous absorber calculator, the 5 kpa.s/m2 will work better for the lows, so the ultracoustic-p is on of my 2 top candidates here. Has anyone used that, and if yes how did it perform?

On the other hand my other top candidate is the b-040 which shows better absorption at the lowmid area, but in a conversation I had with Stuart in another forum some time in the past he recommended around 7 kpa.s/m2 for low freq absorption, while this one is 15 kpa.s/m2, so I would pick b-030 over this. Problem is the company hasn't published any absorption coefficient data for this product, but judging by the coefficient difference between the b050 and b040, I guess the b030 coefficient should be slightly greater than 0,22 @125hz which is the best choice of all for me. (By the way, b050, b040 and b030 correspond to 50, 40 and 30 kg/m3 densities respectively ;-) )

Also it is good to mention that Stuart's recommendations align with Porous Absorber Calculator which confirms that 5 kpa.s/m2 (ultracoustic p ) will work better than 10 kpa.s/m2 (b030) at the dimensions of my traps .


So right now I am in a dilemma between those two products.

I am making two corner traps (see pics), both on the front wall. Geometry and size of each one is due to the shape of my room (which you can see in the pictures bellow) and the lack of more space.

So, as the thread title states, I am having trouble picking the right product of insulation. Which one would you recommend and why?

Thank you beforehand!

Ps. The triangular bass trap will be including only one divider (in the middle), not 3. This means that each one of the 2 parts of insulation will be roughly 70cm tall.
Attachments
fibran b-040.jpg
knauf ultracoustic - p.jpg
triangular bass trap - fixed.jpg
rectangular bass trap - fixed.jpg
6. over front left side.jpg
5. over front right side.jpg
4. over back right side.jpg
3. above .jpg
2. over back left side.jpg
1. left side.jpg



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Re: Advise on what Rock/mineral/glass wool to choose for basstraps

#2

Postby Soundman2020 » Tue, 2020-Feb-04, 23:45

Hi there, and welcome to the new forum! :thu: :)

Hello everyone and good luck with this beautiful new forum to you Stuart and your team!
Thanks! Glad you found us, and glad you joined up too!

Regarding your choice of insulation, it looks like the Fibran 30 (or maybe the Fibran 40) would be the best for what you need.

Preferably I'd like to avoid exceeding the 40kg/m3 in order to make the traps lighter.
I wouldn't worry too much about weight: your traps are have a volume of less than 1 m3, so the weight is only going to be about 35 kg or so (including the wood). That's not so heavy. But if you are very concerned about weight, then yes, the Ultracustic would be the best from that point of view.

However.... ( :) ) I think your room layout could probably be improved a bit. It's a small room, so it would be beneficial to do as much as you can to improve it. Here's what I would suggest:

[list=]
[*]Rotate the orientation 90° to the right, so you are facing the double doors. I'm hoping that you don't need to use those doors?
[*]Get rid of the book case ad closet if you can: they are taking up a lot of space in the room. That might not be possible, I know, but it would help a lot if you could
[*]Get your speakers off the desk and onto stands behind the desk. Use heavy, tough stands, not light-weight ones.
[*]Get your speakers up against the front wall, as close as you possibly can.
[*]In addition to the bass traps in the corners, I would also put more trapping in some of the wall/ceiling corners
[*]You have a bed in there, and you are going to have lots of bass trapping too, so the room is going to end up sounding very "dry", with very short decay times. You will probably need to put plastic sheeting over the front of your bass traps to reflect back some of the highs into the room, and also broad wood slats, to reflect back some of the high-mids and highs.
[*]If there is carpet on the floor, consider removing that, since it is not doing good things to your room (see here: viewtopic.php?f=16&t=149 )
[*]Before you do anything in your room first do a test with REW, to see how it is doing right now (See here: How to calibrate and use REW to test and tune your room acoustics )
[/list]

Small rooms are the hardest to get good, but there's always somethings you can do to make it better! And you seem to be on the right path.

- Stuart -



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Re: Advise on what Rock/mineral/glass wool to choose for basstraps

#3

Postby musictracer » Wed, 2020-Feb-05, 08:35

Thanks! Glad you found us, and glad you joined up too!

You are welcome! Pleasure is mine of course! :D

Regarding your choice of insulation, it looks like the Fibran 30 (or maybe the Fibran 40) would be the best for what you need.

I was indeed leaning to b030 to be honest! I'm glad you recommended this one. But now you put me in a new dilemma between this and the b040 :( . Now I know that probably it isn't going to make much of a difference no matter which one I choose of the two since little differences in the absorption coefficients don't influence acoustic efficiency that much (ie. the bobgolds coefficient chart we all get advise from for years now whenever we need to clearly states in the 3d line of the 2nd sentence:

"Differences in coefficients of less than 0.15 are not significant."

https://www.bobgolds.com/AbsorptionCoefficients.htm )

Weight wise I would benefit from using the b030 since it would make the corner trap 5kg lighter.

Sagging wouldn't be a problem since when I spoke with them on the phone they assured me that it is unlikely to occur bellow a 2 meters stack. Though I can't recall if that info regards the 040 or the 030, I still believe I'll be fine with my 0,70m - 0,75m stacks no matter which one I choose!

But the factor I am mostly concerned about is the GFR of the two. The 030 is 10kPa.s/m2 while the 040 is 15kPa.s/m2 . And I remember you once recommended around 7 kPa.s/m2 or a little less for bass traps. Now, by "playing" a bit with the porous absorption calculator I can see that the 030 benefits with an around 0.6 - 0.8 larger coefficient at the lows. But probably, as stated above, that wouldn't make a significant difference, and the fact that the 030 lacks coefficient measurement by the company confuses thing even more.
Dunno, I need your thoughts with this!

As for your recommendations, they are much appreciated though I have thought most of them in the past and couldn't realize due to a few reasons:

[*]Rotate the orientation 90° to the right, so you are facing the double doors. I'm hoping that you don't need to use those doors?

This is the exit to my balcony. Not used so often indeed, but if I bring the desk with the speakers and the sbir panel against it I will lose 50% of the light coming in the room, while at the same time the other 50% will be coming directly to my face, forcing me to pull the curtains shut, thus having no light in the room. Also, none of the balcony doors would be able to open, since the desk should be right against the doors...

[*]Get rid of the book case ad closet if you can: they are taking up a lot of space in the room. That might not be possible, I know, but it would help a lot if you could

Correct! No can do, sorry! I know it would be beneficial but there is no room elsewhere in the house to put it. At least it provides some sort of diffusion (or maybe I should say scattering to be more accurate) which is good for me I suppose.

[*]Get your speakers off the desk and onto stands behind the desk. Use heavy, tough stands, not light-weight ones.

I am afraid neither that is possible. There is no room for that either.

[*]Get your speakers up against the front wall, as close as you possibly can.

This might be an option , but that would make the desk reflecting sound to the sweet spot, but even if I moved them, it wouldn't be more than 10cm since that is their distance from the sbir panel. Should I benefit from that, despite creating desk reflections? And speaking of sbir panels, I think I should make a new one covering the whole desk width wise, so that it is covering the back of the speakers too, do you agree? Also I will be using this product: https://alphacoustic.com/wp-content/uploads/2013/09/iZiFON-%CE%BC%CE%BF%CE%BD%CF%89%CF%84%CE%B9%CE%BA%CF%8C-%CE%B9%CE%BD%CF%8E%CE%BD-%CF%80%CE%BF%CE%BB%CF%85%CE%B5%CF%83%CF%84%CE%AD%CF%81%CE%B1.pdf
The coefficient plot of the one I'll be using is the blue one (see 2nd page), the one with the greatest absorption @125hz. It is a polyester product with a 20kg/m2 density, so it is very light and looks quite efficient for sbir panels. (I know what you might be thinking, it would be great for the traps too, but problem is it is quite costy compared to the other alternatives ;) ) I assume 20cm thickness should be fine for a sbir panel, right?

[*]In addition to the bass traps in the corners, I would also put more trapping in some of the wall/ceiling corners

That would be beneficial indeed, but I really don't want to hurt the walls even more. I know the room is not the best for what I want to do , so I will probably be moving some time in the future in an other one, so I don't want to leave many holes behind :lol: .

[*]You have a bed in there, and you are going to have lots of bass trapping too, so the room is going to end up sounding very "dry", with very short decay times. You will probably need to put plastic sheeting over the front of your bass traps to reflect back some of the highs into the room, and also broad wood slats, to reflect back some of the high-mids and highs.

Yes, I have thought that this is possible to happen also, this is why I am thinking of making the front face fabric of my traps removable (attached with velcro) so that I can edit the inside of it at will. I would just prefer not to edit the trap construction if possible, so I would like to avoid using lumber sluts for example. Our dear friend Gregwor once spoke to me about vapor barrier. It seems easier to attach. Do you think it might be enough if needed? (Probably impossible to answer without measurements, but I thought I might ask beforehand :) )

[*]If there is carpet on the floor, consider removing that, since it is not doing good things to your room (see here: viewtopic.php?f=16&t=149 )

I won't be using any, since I will be using an 1.60x1.20x0.40 m cloud too. . That will absorb a lot of hi freq energy, so putting a carpet as well will be suicidal I suppose :lol:

Sorry for not mentioning the cloud before, I have so much in my mind to deal with... I will be using the polyester product I mentioned before. Do you think it should cover only the ceiling first reflection, or should I consider covering the area above the speakers, or the listener - if possible ?

[*]Before you do anything in your room first do a test with REW, to see how it is doing right now (See here: How to calibrate and use REW to test and tune your room acoustics )

I had a few measurements a year ago, but I will take new ones since I lack the mic I used back then, and I have edited the settings of my sub a bit since then as well. Here is a comparison of the empty vs side+sbir panels in place measurements.

sbir + side.jpg


The red line is the empty space. I know it didn't seem to do anything significant, though I admit a saw some slight improvement with the RT60 times. Of course placement of the panels was done with the moving mirror method and it is as seen in the sketchup pics I uploaded. Insulation I used is this one: http://www.metaxiotis.gr/xml/pdf/NavisionLinks/Item%20Technical%20Data/FIBRAN/GEOLAN/TDS%20FIBRANgeo%20B-051%20%20gr.pdf . You can see that it is quite efficient (0.35 @125hz) though quite heavy (150kg/m3), but it didn't perform like I expected to... [Please bare in mind that it is likely (can't remember) that I had a carpet on the floor when taking these measurements, which of course I have removed already. ]

Small rooms are the hardest to get good, but there's always somethings you can do to make it better! And you seem to be on the right path.

Thanks so much for your encouragement and assistance! It is so valuable to me as well as the rest of us in here ! :D

P.S. Yesterday I got a spam p.m. from a user nicknamed "Robertvew". Probably you have already blocked him by now, but I thought it would be good to mention in case you haven't. :-)
Attachments
FR+SBIR (20 - 20000 hz).rar
m.dat file of the measurements
(2.51 MiB) Downloaded 60 times
FR+SBIR (20 - 20000 hz).rar
m.dat file of the measurements
(2.51 MiB) Downloaded 60 times



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Advise on what Rock/mineral/glass wool to choose for basstraps

#4

Postby Soundman2020 » Tue, 2020-Feb-11, 14:01

Now I know that probably it isn't going to make much of a difference no matter which one I choose of the two since little differences in the absorption coefficients don't influence acoustic efficiency that much (ie. the bobgolds coefficient chart we all get advise from for years now whenever we need to clearly states in the 3d line of the 2nd sentence: "Differences in coefficients of less than 0.15 are not significant."
True, but it's still better to go for the best you can get, in general.

Sagging wouldn't be a problem since when I spoke with them on the phone they assured me that it is unlikely to occur bellow a 2 meters stack. Though I can't recall if that info regards the 040 or the 030, I still believe I'll be fine with my 0,70m - 0,75m stacks no matter which one I choose!
You should be fine. Even if you do get a little sagging, it's not going to be a lot. Compression up to about 20% is usually still OK for most insulation.

But the factor I am mostly concerned about is the GFR of the two. The 030 is 10kPa.s/m2 while the 040 is 15kPa.s/m2 . And I remember you once recommended around 7 kPa.s/m2 or a little less for bass traps.
Around 5k to 15k rayls GFR is the "sweet spot" for bass trapping, for most types of porous absorber. That's why I mentioned 7k in that post you mentioned, as roughly the mid point.

Now, by "playing" a bit with the porous absorption calculator I can see that the 030 benefits with an around 0.6 - 0.8 larger coefficient at the lows. But probably, as stated above, that wouldn't make a significant difference, and the fact that the 030 lacks coefficient measurement by the company confuses thing even more.
You are probably "over-thinking! this a bit! :) Either of those products is going to give you good absorption in the low end. Make it thick, and floor-to-ceiling, and you'll have good results in both cases.

Not used so often indeed, but if I bring the desk with the speakers and the sbir panel against it I will lose 50% of the light coming in the room, while at the same time the other 50% will be coming directly to my face, forcing me to pull the curtains shut, thus having no light in the room. Also, none of the balcony doors would be able to open, since the desk should be right against the doors...
A conundrum indeed! :) Three things to consider here: 1) you might not need SBIR panels across the glass: it might be sufficient to just have them from the room corner up to the edge of the speaker. You could do some testing to see if that is effective or not. 2) Maybe you could set up your video screen directly in front of the window, so you don't have too much light straight into your face? 3) Are you going to be using your room for mixing mostly during the day, or mostly at night? If it will be at night, then you don't need to worry too much about daylight in your face...

Correct! No can do, sorry! I know it would be beneficial but there is no room elsewhere in the house to put it. At least it provides some sort of diffusion (or maybe I should say scattering to be more accurate) which is good for me I suppose.
Maybe.... But not that much. If you can't move the bookshelf, then just fill it with insulation. Put some of that 030 in all of the shelves. Also, take the doors off the closet and do the same: fill the interior with insulation. Those would make pretty good bass traps, filled completely with insulation.

I am afraid neither that is possible. There is no room for that either.
Then get a smaller desk! :) With your speakers on the desk as shown in your images, you are going to have several problems, such as:

1) SBIR: the speakers are too far away from the front wall. If you look at the diagram below, from Neumann, you can see that you need to have a distance of no more than about 20 cm between the FRONT face of your speaker (the woofer cone), and the front wall. That normally means that you need to have the speaker tight up against the front wall, with the rear corner almost touching the wall, then perhaps have some low-density porous insulation around the speaker, but taking care not to block good air circulation.
neumann_loudspeaker_boundary_location_v02-SBIR-TABLE-wall-bounce-distance.jpg


2) Vibrations: The speakers will induce vibrations in the desk itself, which will be re-radiated into the room. Using sponge pads to try to isolate this does not work very well. Ethan Winer did a series of tests on commercial "speaker isolators" and a couple of other things, and showed quite convincing that they don't do much: the vibrations still get into the desk.

3) "Early-early sound". In other words, sound that arrives at your ears BEFORE the direct sound from the speakers. This is related to #2 above. Sound travels much faster through the wood of your desk than it does through air, so any vibrations in your desk could be re-radiated from an area closer to your ears, and thus arrive at your ears before the direct sound does.

4) Reflections. Some of the sound will reflect off the desk, into your ears, which messes up your psycho-acoustic perception of the sound. Since the reflection arrives within just a couple of milliseconds of the direct sound, your brain is unable to determine that it is a reflections, and instead decides that the sound came from a different direction, and with a different frequency response...

5) Comb filtering. Relate to #4: When you have two copies of the same sound arriving at your ears, with slightly different timing (phase"). This causes a series of dips and peaks in the frequency response of the sound that you hear. This graph shows the general concept:
comb-filter-concept.jpg
That's the frequency response that you get from comb filtering. You can see that the shape of the waveform looks a bit like a comb, hence the name. Here's a comparison of the direct sound and the comb-filtered sound:
comb-filtering-1--direct-vs-combined.jpg
The flattish line at the top is the direct sound, as it came out of the speaker, the "bumpy" line is what you actually hear when that direct sound is combined with a delayed copy of itself. And here's a real-world example:
Comb-filtering-frequency-response-1ms.png
In this case, the reflected sound is delayed by about 1 millisecond. There are a few techniques for dealing with this, such as angling the desk surface a bit (so it is not flat any more). Doing that can produce this:
Desk-surface-comb-filtering-red-is-flat-blue-is-angled-toward-mix-pos-slightly.jpg
You can see the improvement: the red line is the original comb-filtered signal with the desk flat, and the blue line shows the result after angling he desk a little towards the mix position. Improved, but it is still not good. It's better to avoid this entirely (or at least reduce it as much as possible), by getting the speakers off the desk, onto stands behind the desk.

This might be an option , but that would make the desk reflecting sound to the sweet spot
You are getting that in any case! See above... Also, your speakers are probably too close to your ears if you have them in the position you show. The graph below is from Springer's "Handbook of Acoustics", in the section about speaker placement.
what-near-field-really-is.jpg
what-near-field-really-is.jpg (32.98 KiB) Viewed 2608 times
what-near-field-really-is.jpg
what-near-field-really-is.jpg (32.98 KiB) Viewed 2608 times
It shows how the frequency response varies according to how far you are away from the speaker. As you can see, being too close to a speaker is not a good thing! There are wild swings in frequency response...

but even if I moved them, it wouldn't be more than 10cm since that is their distance from the sbir panel.
Once again, you are up against a "conundrum"! :) As with most things in small studio design, you often have to "trade off" one thing for another. In your case, considering that the room is so small, I would suggesting pushing the speakers all the way up to the wall, so the rear corner is almost touching the wall, then setting up your SBIR panels vertically, not horizontally: two of them. One just next to the left of the left speaker, then other just to the right of the right speaker.
Should I benefit from that, despite creating desk reflections?
You already have desk reflections, vibrations, and comb-filtering....
And speaking of sbir panels, I think I should make a new one covering the whole desk width wise, so that it is covering the back of the speakers too, do you agree?
As above: I would create a sort of "C" shaped panel, where the speaker is in the middle of the "C", surrounded on three sides by the absorption, with the rear corner of the speaker almost touching the wall (or window! :) ).

The coefficient plot of the one I'll be using is the blue one (see 2nd page), the one with the greatest absorption @125hz. It is a polyester product with a 20kg/m2 density, so it is very light and looks quite efficient for sbir panels. (I know what you might be thinking, it would be great for the traps too, but problem is it is quite costy compared to the other alternatives ;) ) I assume 20cm thickness should be fine for a sbir panel, right?
With the speaker against the wall, as above, you could probably use 10cm thickness. When you make those new panels, do be careful that you leave some space for air to circulate behind the rear of the speaker, for cooling.

Yes, I have thought that this is possible to happen also, this is why I am thinking of making the front face fabric of my traps removable (attached with velcro) so that I can edit the inside of it at will.
:thu: Sounds like a good idea!

once spoke to me about vapor barrier. It seems easier to attach.
Welllll.... yes and no. Plastic can be useful, but it might not go down low enough. Technically, it is a "foil", and it reflects some frequencies while allowing others through. The frequency range is determined by the thickness, or rather the density, of the foil. Here's a graph that shows the effect for a few different densities of plastic, when used in front of a porous absorber:
effect-of-plastic-sheet-foil-on-porous-absorber-2.jpg
So you would need to to do some testing to find out what frequency range you are losing too much of, then add the right thickness plastic accordingly. However, you cannot do that on your first reflection point absorbers! Only on your bass traps and SBIR treatment.

Sorry for not mentioning the cloud before, I have so much in my mind to deal with... I will be using the polyester product I mentioned before. Do you think it should cover only the ceiling first reflection, or should I consider covering the area above the speakers, or the listener - if possible ?
Generally, for small rooms like yours I recommend using an "angled, hard-backed ceiling cloud", over the area between the speakers and the listening position. The angle and hard back help to redirect some of the sound towards the rear wall, where it can be absorbed more, and can also be beneficial for vertical modal problems.

I had a few measurements a year ago, but I will take new ones since I lack the mic I used back then, and I have edited the settings of my sub a bit since then as well. Here is a comparison of the empty vs side+sbir panels in place measurements.
That looks like you did the testing with both speakers on, and with the levels a bit too low. There is some comb-filtering evident there. Take a look at the tutorial I linked you to before, to see the full procedure.

P.S. Yesterday I got a spam p.m. from a user nicknamed "Robertvew". Probably you have already blocked him by now, but I thought it would be good to mention in case you haven't.
Right! I fixed him real quick, as soon as I found him. That was my fault, for not having turned off the ability to send PM's for spammers. I fixed that now. Over the last few days we have had some pretty intense attacks by spammers: hundreds of spam posts, many dozens of fake new members (mostly from Russia and the Ukraine!). The anti-spam measures and yours-truly managed to kill most of those, with forum members never even seeing the vast majority, but a couple did get through. Sorry about that! I also added some new anti-spam features to the forum. I'm trying to improve it all the time. If it happens again, please send me a PM (Private Message), as I will probably see that sooner than a comment in a thread.

- Stuart -



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Advise on what Rock/mineral/glass wool to choose for basstraps

#5

Postby musictracer » Thu, 2020-Feb-13, 19:05

Soundman2020 wrote:Source of the post True, but it's still better to go for the best you can get, in general.

And that's exactly what I hope I did! :) Today I got the b030 delivered to my home!

Soundman2020 wrote:Source of the post You should be fine. Even if you do get a little sagging, it's not going to be a lot. Compression up to about 20% is usually still OK for most insulation.

Great! To be honest I wasn't concerned too much about the performance due to sagging , but mainly for the aesthetic result .

Soundman2020 wrote:Source of the post Around 5k to 15k rayls GFR is the "sweet spot" for bass trapping, for most types of porous absorber. That's why I mentioned 7k in that post you mentioned, as roughly the mid point.

Nice! I went for the 10k eventually!

Soundman2020 wrote:Source of the post You are probably "over-thinking! this a bit! Either of those products is going to give you good absorption in the low end. Make it thick, and floor-to-ceiling, and you'll have good results in both cases.

It's true, I am over-thinking quite often. But it's just that I haven't got practical experience on acoustics despite having studied Music Technology and Acoustics Engineering. Once again, thanks for your valuable assistance! :D

Soundman2020 wrote:Source of the post A conundrum indeed! Three things to consider here: 1) you might not need SBIR panels across the glass: it might be sufficient to just have them from the room corner up to the edge of the speaker. You could do some testing to see if that is effective or not. 2) Maybe you could set up your video screen directly in front of the window, so you don't have too much light straight into your face? 3) Are you going to be using your room for mixing mostly during the day, or mostly at night? If it will be at night, then you don't need to worry too much about daylight in your face...

I appreciate your recommendation for moving the desk up against the balcony door, but I am afraid that it is not possible. I mean, it's true that not only would it help with delaying the reflections from the back wall, but it would also provide more stereo balance due to equidistant boundaries on either side of the sweet spot. So I spent some time sketching-up yesterday trying hard to find an efficient placement of the furniture to accomplish that but there were problems I couldn't resolve, like the fact that both balcony doors should remain permanently shut for example.

Soundman2020 wrote:Source of the post If you can't move the bookshelf, then just fill it with insulation. Put some of that 030 in all of the shelves. Also, take the doors off the closet and do the same: fill the interior with insulation. Those would make pretty good bass traps, filled completely with insulation.

Well, if I were able to fill them with insulation, I would rather remove them instead and make absorption panels anew. :D But maybe I never mentioned it and thus got you confused with the sketchup drawing. Both the bookshelf and the wardrobe are filled with books and clothes respectively. It's a real bedroom, aspiring to be a control room... :lol:

Soundman2020 wrote:Source of the post 1) SBIR: the speakers are too far away from the front wall.

Soundman2020 wrote:Source of the post 2) Vibrations

Soundman2020 wrote:Source of the post 3) "Early-early sound"

Soundman2020 wrote:Source of the post 4) Reflections.

Soundman2020 wrote:Source of the post 5) Comb filtering.

I am aware of all these issues you display, but I appreciate that you took the time to analyze them in such detail. The graphs and the tables you cite are very valuable, indeed!. (For instance, the Neumann table can be really handy for having an idea of how the sbir frequency is pushed upwards the closer the source (speaker) gets to the boundary! Thanks for sharing!.
Regarding the "1" in conjunction to "5" and "4" you guessed right that I preferred to avoid desk reflection comb filtering at the cost of a lower sbir frequency. Getting a new desk is rather impossible at the moment since I am tight on budget already. The cloud insulation alone + a few extra boards (18 boards in total) costed €100 while the rest (40 boards of b030) costed €73. These prices are just fine for the products of course, but if you add the lumber I used (€95) and the fabric which I haven't got yet the budget goes up quite a bit.

Thus regarding the separate speaker stands I am afraid it is impossible due to lack of space, despite owning a pair which I can't use.
But I'm curious about the "speaker surrounding" sbir panel you recommended. I'd be glad If you shared any pictures of this. :)

The nearfield pressure fluctuation is something I wasn't aware of. My sweet spot is roughly 1.2m away from each speaker, so that is not too close, but unfortunately that is the longest I can get. Maybe I could push the speakers 7cm further towards the sbir panel, but no more than that is possible, due to xlr/power cables on the back and angle towards the sweet spot.

Soundman2020 wrote:Source of the post You already have desk reflections, vibrations, and comb-filtering....

The way I have my setup I suppose I have diminished the desk reflections which only come from the small keyboard desk and not from the speaker desk. But probably that is not enough to fully eliminate them.

Soundman2020 wrote:Source of the post As above: I would create a sort of "C" shaped panel, where the speaker is in the middle of the "C", surrounded on three sides by the absorption, with the rear corner of the speaker almost touching the wall (or window! ).

As I mentioned before, I am having trouble understanding it. I mean I get the "either side of the desk" panels placement, but which one is the third size of absorption? Maybe I misunderstood your description but you mean the back of the speakers are almost touching the wall, right?

Soundman2020 wrote:Source of the post So you would need to to do some testing to find out what frequency range you are losing too much of, then add the right thickness plastic accordingly. However, you cannot do that on your first reflection point absorbers! Only on your bass traps and SBIR treatment.

Yes I understand. It makes sense that it shouldn't create directional (high frequency) first reflection to the sweet spot . Thanks for noting!

Soundman2020 wrote:Source of the post Generally, for small rooms like yours I recommend using an "angled, hard-backed ceiling cloud", over the area between the speakers and the listening position. The angle and hard back help to redirect some of the sound towards the rear wall, where it can be absorbed more, and can also be beneficial for vertical modal problems.

So that's why I see some angled models in some rooms. I thought it was just for coercing the first reflection sound beam to travel a longer distance into the insulation,thus being more absorbed.I never thought these would be hard backed.Thanks for the enlightenment! :D
In my case it wouldn't be beneficial though, since there is no room for decent absorption that behind me. I am only planning to put a board of insulation just as a slight high frequency reflection treatment (no gap behind it).

Soundman2020 wrote:Source of the post Sorry about that! I also added some new anti-spam features to the forum. I'm trying to improve it all the time. If it happens again, please send me a PM (Private Message), as I will probably see that sooner than a comment in a thread.

No need to apologize! I will send PM if it happens again!

I would like to thank you again for your will and time to assist me! I am really sorry that I can't do much of what you propose at the current time, but I definitely keep everything in mind for future improvements. I will come back with a few photos of the process!



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Advise on what Rock/mineral/glass wool to choose for basstraps

#6

Postby Soundman2020 » Sat, 2020-Mar-07, 01:39

musictracer wrote:Source of the post Maybe I could push the speakers 7cm further towards the sbir panel, but no more than that is possible, due to xlr/power cables on the back and angle towards the sweet spot.
You might want to consider using right-angle XLR and power connectors, to gain another few cm:
right-angle-XLR-connector.jpg
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right-angle-XLR-connector.jpg
right-angle-XLR-connector.jpg (8.8 KiB) Viewed 2385 times
right-angle-power-connector-2.jpg
right-angle-power-connector-2.jpg (8.36 KiB) Viewed 2385 times
right-angle-power-connector-2.jpg
right-angle-power-connector-2.jpg (8.36 KiB) Viewed 2385 times
It's not a big difference, but every cm helps! :)

musictracer wrote:Source of the post As I mentioned before, I am having trouble understanding it. I mean I get the "either side of the desk" panels placement, but which one is the third size of absorption? Maybe I misunderstood your description but you mean the back of the speakers are almost touching the wall, right?
Like this:

Link to video animation of C-shaped SBIR panels around speakers

:)

That's what I was trying to explain, but it seems like my explanation wasn't so good. "A picture is worth a thousand words", as they say, so I did that quick animation to show what I was suggesting.

musictracer wrote:Source of the post So that's why I see some angled models in some rooms. I thought it was just for coercing the first reflection sound beam to travel a longer distance into the insulation,thus being more absorbed.I never thought these would be hard backed.Thanks for the enlightenment!
:thu: Here's an example of such a cloud: Completed:
RDMOUS--cloud-done-image-01-ENH.jpg
RDMOUS--cloud-done-image-01-ENH.jpg (61.91 KiB) Viewed 2385 times
RDMOUS--cloud-done-image-01-ENH.jpg
RDMOUS--cloud-done-image-01-ENH.jpg (61.91 KiB) Viewed 2385 times
Under construction:
RDMOUS-BUILD-12th-construction-soffit-cloud-fully-framed-in.JPG
That one is a bit too big for your place, of course (!) , but the same principles apply.

musictracer wrote:Source of the post In my case it wouldn't be beneficial though, since there is no room for decent absorption that behind me. I am only planning to put a board of insulation just as a slight high frequency reflection treatment (no gap behind it).
The idea is to send the sound back behind you anyway, even if it can't be absorbed back there. It will still take a much longer path before it gets back to your ears, and that's what matters. You want to delay the reflections in time as much as possible: ideally more than 30ms, but even if you can get 15ms, or just 10ms, that's still good. Also, there is thick absorption below the "hard back" deck of the cloud, as you can see in the construction photo above. That attenuates the sound a bit already: at least a few dB. And the angle is also important: it needs to be fairly steep. If the angle of your cloud is not large enough to send the reflections behind you, roughly towards the middle of the rear wall, then the reflected sound will come right back down to your head, where it will mess up your psycho-acoustic ability to correctly discern both frequency and direction. That's the problem with early reflections: they mess with the way your ears and brain work, and they fool your brain into interpreting things the wrong way. Those reflections cause your brain to think that the sound came from a different direction from where it really came, and that it had a different frequency response from what it really was. It's a physical process that happens inside your ears, where the direct sound and reflected sound cause cancellations and phasing issues at various frequencies, which your brain then interprets as though it was one single but different sound that arrived, rather than two separate sounds, separated by just a few milliseconds. Your brain is not able to figure out that there were two separate sounds, unless the timing difference is about 20ms or so, and preferably 30ms. This is why its so important in studios to control the early reflections, and get them away from your ears. An angled, hard-backed cloud can help with that.

Here's a couple of articles I wrote recently, about speakers and setting them up in a studio: you might have seen them already, but if not, they might be useful for you, as you try to optimize things in your room:

The speaker triangle myth

Near field monitors: what they really are

I will come back with a few photos of the process!
:thu: Absolutely! We'd love to see what you accomplish: And please also measure with REW at each step, so you can see how much each part improves the sound.


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#7

Postby musictracer » Thu, 2020-Mar-19, 17:12

Thanks a lot for your detailed reply!
I am done with construction and placement.
-> 2 Bass traps in the front wall corners.
-> 1 Bass trap in the rear right corner
-> 1 Ceiling cloud

Unfortunately I had already completed the process before reading your reply, so I didn't measure at each step of the process, but I feel that generally the whole project was a failure, so maybe it doesn't matter that much.

Let me start by saying that I struggled hard to find a way to do as you suggested and move the speakers as close to the front wall as possible. I managed to get them roughly 20 cm closer, but that was possible only by removing the sbir panel and placing it vertically right behind the middle of the desk, eliminating the 10cm gap from the wall it had before. There was no other way to accomplish that without this compromise. Luckily there is still no desk reflection from the tweeter/woofer mid point to the sweet spot as I checked with the mirror trick.

Regarding the cloud it was made without a hard back , but with 15 cm thick insulation with another 15 gap from the ceiling. It is literally just within the limits of both being covering the first reflection of the right speaker as well as leaving enough room for the light fixture to come through it.

As I said, I am quite disappointed by the results. Although the decay times got better to my ears, and the sound generally got tighter indeed, the frequency response didn't get any better. Surprisingly even worse at some points. Measurements are attached within this post. Here are some photos of the process :

(Site allows only 18 attachments max so the rest is to follow in another post.)
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#8

Postby musictracer » Thu, 2020-Mar-19, 17:51

And here are the rest + measurement samples:

IMG_20200319_203131.jpg
IMG_20200319_203142.jpg
IMG_20200319_203235.jpg
IMG_20200319_203253.jpg
L+ R (BEFORE - AFTER).jpg
EMPTY
L+R - EMPTY (DECAY TIMES).jpg
TRAPS + CLOUD
L+R  TRAPS + CLOUD (DECAY TIMES).jpg
TRAPS + CLOUD
L+R  TRAPS + CLOUD (WATERFALL).jpg
EMPTY
L+R- EMPTY (WATERFALL).jpg


I really don't know what to say. I expected better results in frequency response. Or maybe I get something wrong, I don't know.
But really after having spent so much time in this project I don't have the energy to do something else.
At this point I was thinking about purchasing a measurement mic, since I used an omni condenser, considerably flat in the low / mid region, yet not a measurement type. I was thinking of this :
https://www.audiophonics.fr/en/measurement-microphones/minidsp-umik-1-low-noise-omnidirectional-usb-microphone-p-8269.html

I am sure you know it and I hope you approve it since it is a well known product / company. It would be beneficial for me to have a usb mic since it comprises a level calibration too, so that I won't have to use my untrusty smart phone spl meter anymore. My only concern is the max usb cable length it can work with, since it has to be fairly long in some situations. By the way, in case you 've had experience with such a product, what's the longest it can be?

To conclude, it seems that there is not much to expect with the acoustic treatment I applied, regarding even freq response. Most likely the scenario I was hoping to avoid seems to be the only way at this point. And that is DSP correction. I have tried it and I didn't like it because in my opinion it removes the character of the speakers. Maybe some would argue on this but to my experience speaker character doesn't necessarily mean not being usable as a studio monitor. Every monitor has a character, that's why a genelec differs from a focal, an ATC , a barefoot etc... But even uneven freq monitors are still a great tool for mixing. And I am pretty sure Mr. Akira Nakamura would agree with this statement :-) .
So what are your thoughts on DSP correction? Do you approve it?
Also, what do you think went wrong with my treatment?
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Advise on what Rock/mineral/glass wool to choose for basstraps

#9

Postby Starlight » Thu, 2020-Mar-19, 18:31

Hello musictracer. Congratulations aon what looks like a lot of hard work, rearranging your room and making and installing all those traps.

Stuart's comments on measurement mics - which one not to buy, which ones he recommends and his caution about USB mics are all here.

From your photos I would recommend stands for your monitors and getting them up to ear level. No doubt Stuart will be along shortly to answer all your questions.



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#10

Postby musictracer » Thu, 2020-Mar-19, 22:41

Starlight wrote:Source of the post Congratulations aon what looks like a lot of hard work, rearranging your room and making and installing all those traps.

Thank you very much, Starlight! I only wish it all worked better!

Starlight wrote:Source of the post Stuart's comments on measurement mics - which one not to buy, which ones he recommends and his caution about USB mics are all here.

Thank you, I had read it in the past, as well as at John Sayers forum but I had forgotten about it. Thanks for pointing out! It seems like a USB mic is a bad idea for the reason I feared and stated in my previous post: cable length limitations!
So, since I will have to buy a good spl meter too, I was looking at this one https://www.nsmarket.gr/gr/index/products/vibration?row=388 . Stuart approves it , so it must be a good pick for me. As for the mic, is there anything you'd recommend? (Preferably with cal. file)

Starlight wrote:Source of the post I would recommend stands for your monitors and getting them up to ear level.

Yes, we discussed that previously with Stuart. I already own a pair of stands, but the problem is that there is no room for it. Imagine that I had to displace the sbir panel just to be able to get the speakers 20 cm closer to the wall!

Anyway, thanks for your contribution! :-)



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#11

Postby Soundman2020 » Thu, 2020-Mar-26, 23:48

Hi again, Music tracer. Good work there, as Starlight said. You've put a lot into this so far... and to be honest, it shows! :)

but I feel that generally the whole project was a failure,
Not really! Keep reading....

Regarding the cloud it was made without a hard back , but with 15 cm thick insulation with another 15 gap from the ceiling. It is literally just within the limits of both being covering the first reflection of the right speaker as well as leaving enough room for the light fixture to come through it.
It looks pretty good, but I would still suggest making it hard-backed, angle it, and move the light fixture into the cloud itself. I have a fairly standard cloud design for small rooms,
SOUNDMAN--sample-standard-cloud--for--recording-studio.jpg
I often use that basic model for small rooms, just modifying the dimensions and details a bit, but you can see how there's a "light panel" built into the cloud itself. In this example, there's a few halogen spotlights in there, but you can use anything you want. Note that the light panel itself is angled more than the cloud, to help reduce unwanted reflections. I adjust the angles and sizes for each individual room for my clients, but the basic concept is there.

As I said, I am quite disappointed by the results.
You shouldn't be!! :) ...

I expected better results in frequency response. Or maybe I get something wrong, I don't know.
That's the problem! You were expecting results in the wrong place. You got results! Your ears told you about them. But your eyes were not looking at the right thing...

Although the decay times got better to my ears, and the sound generally got tighter indeed, the frequency response didn't get any better.
You are looking in the wrong place, and not trusting your ears! :) You say that you noticed a clear difference in both bass response and decay times, and those are very evident in the REW data you posted. But you won't find "bass tightness" or "decay times" in the frequency curves... because those are not frequency-domain issues: rather, they are time domain issues, so you have to look for them in the time-domain graphs that REW produces.

For example:

Here's the before and after waterfall plots for the low end of the spectrum:
Musictracer--REW--WF--20-500--LS--empty--vs--cloud-and-traps.png
This is the data for your "left+sub" combination. Red is before the treatment, blue is after. You can clearly, clearly see that you tamed some pretty big monsters there! Well done! You got the peaks at 58 Hz, 77 Hz, and 121 Hz really well. The ringing is way down on all of those. Here's the individual graphs, so you can see the details more clearly: Empty room:
Musictracer--REW--WF--12-500--LS--empty.png
Treated room:
Musictracer--REW--WF--12-500--LS--cloud-and-traps.png
I'd call that a pretty remarkable result, for a small room such as yours. You also smoothed out things above that, in the rest of the visible range there (up to 500 Hz, shown). The remaining modal issue at 50 Hz is likely on the side-to-side axis, where there isn't much bass trapping yet: You have treated the front-back axis and the up-down axis to a certain extent, but there's not much on the left-right axis. That mode at 50 Hz could probably be reduced a bit with some treatment on the side walls.

You can see similar improvements on the spectrograms. Before:
Musictracer--REW--SP--20-500--LRS--empty.png
And after:
Musictracer--REW--SP--20-500--LRS--cloud-and-traps.png
I this case, that's for all three speakers going at once: LRS in both cases. A significant improvement.

So yeah, your ears are not lying to you: You achieved much tighter bass control, and also a reduction in decay times! A pretty good job you did there, overall. The data doesn't lie, and neither do your ears. You didn't see these improvements, because you were looking at the frequency domain, which is a very common mistake: Speaker manufacturers love to publish wonderful looking frequency response ("FR") curves for their products, which misleads people into believing that FR is the most important aspect of a speaker or a room: it isn't. In fact, a speaker can have impressively flat frequency response and still sound awful. So can a room. FR is one aspect of speakers and rooms, but not necessarily the most important. As you just discovered for yourself, there are more important aspects to a room: how it behaves over time. That won't be reflected much in the FR curves. Sometimes I wish that REW would default to the IR display, or the waterfall display, rather than the FR display.... (another important aspect is phase response: but that's a little more difficult to explain in simple terms, so I'll leave that pending for now....)

OK, that's the good news: you tamed some of the modal monsters in the low end, smoothed out time-domain issues in the low mids nicely, and got your decay times more even, down overall from around 200 ms to around 140 ms. Now for the not-so-good news: You still have some large reflections that are messing things up. You can see that on the IR (Impulse Response) graphs, when you look at the ETC curves (ETC=Energy-Time-Curves.... Before:
Musictracer--REW--IR--150ms--LRS--empty.png
After:
Musictracer--REW--IR--150ms--LRS--cloud-and-traps.png
I have placed the cursor at the biggest issue, which is a very strong reflection at about 3.1ms after the direct sound, but you can see several other reflections around that area. The ideal is to have no reflections larger than -20 dB for the first 20 ms, and as you can see, you have several. Each vertical spike on that ETC graph is one specific reflection. That big one at 3.1 ms is nasty: just a couple of dB down from the direct sound, in fact. I mentioned this in an earlier post, and what it does to the psycho-acoustic ability of your ears and brain to correctly interpret sound.

So I would suggest that you try to identify that guy, and get rid of him! Fortunately, there's an easy way to do this, which I call the "string trick". You are going to need a long piece of string, some masking tape, and a marker pen. From looking at the REW data, it's clear that your reflection is arriving at very nearly 3.08ms after the direct sound. Since sound travels at 343m/s, that means that it must have traveled about 1100mm further than the direct sound did, to arrive at the mic 3.08ms later. So, all you need to do is to find out which surface in your room creates a path that is 1100mm longer than the direct path from the speaker to the mic! Simple. In other words, the reflection is traveling about a meter longer than the direct distance, which is why it is delayed by 3.08ms.

So, first carefully measure the distance from the acoustic center of the speaker to the tip of the mic, then get your piece of string and measure out that same distance PLUS 1100mm along the string! Leave a little bit of string free at one end so you can tape it to the speaker, make a mark on the string with your marker pen, then measure exactly the distance "speaker to mic + 1100mm", and make another mark. That distance is how far your nasty reflection is traveling. Now gently tape one end of the string to the front of your speaker as close to the acoustic axis as you can get, (gently! don't damage the speaker!!) such that the first mark on your string is right up against the front face of the speaker. Now attach the other end of the string to a mic stand (without the mic! Don't risk messing up your mic...), set up so that the second mark on your string is at the exact spot where the measurement mic was when you did the REW tests. So no you have your string danging down, with one mark on the speaker axis and the other where the mic was: all you need to do now is to take the middle of that dangling loop of string and move it around the room, to see what surface it touches. Bingo! That's your reflection point. It might be on the wall, or the ceiling, or some piece of furniture, or the desk... try many spots all over the place: you might even find that there are several spots that you can reach with the middle of the loop: put pieces of masking tape on all of those, with a visible mark at the point where the string just touches the surface. You might need help with this, so you don't accidentally pull over the mic stand, or pull the string off the speaker.

If you work carefully, you'll be able to identify the culprit easily. Let me know where it is, so we can figure out how to fix it.

Also, you can probably improve the low--end response even more by "walking" the sub around on the floor, in small increments (maybe 10cm or so for each "step"), measuring with REW each time, then comparing the measurements to see which one gets you the smoothest response. Walk it across the entire front wall, from left side wall to right side wall, in 10cm steps, and do a LRS test in REW at each location. The best spot should be clearly visible in REW... but do look at all the graphs to determine that! Not just the frequency response. You are juggling several things here, and for the this set of tests FR is important, but so are time-domain response and phase response. Check them all, at each location, and choose the best compromise. Oh, and try flipping the "phase invert" switch on the sub at each test location as well: that will make a BIG difference, always. So do a REW test at each spot with "phase=0°" set on the speaker itself, and another test with "phase=180°". You'll hear the difference here too.

It can sometimes also help to rotate the speaker in place at that best spot, so that it points in each of the four main directions, testing again at each one. Sometimes there's a useful change: sometimes not. And you can also try raising the sup up off the floor in small increments (use books under it), once again checking with REW. It's surprising just how much things can change from simply moving the sub around! The goal is to keep careful notes in REW and on paper, about exactly where you had the sub for each test, so that you can then compare the results to find the best spot.

But overall, as Starlight said: you did a good job, and got good results. You were just looking for them in the wrong place.

At this point I was thinking about purchasing a measurement mic, since I used an omni condenser,
Definitely get a proper measurement mic! Take a look at the article on how to calibrate REW: I mention some good ones in there, and what to look for.

It would be beneficial for me to have a usb mic since it comprises a level calibration too,
As Starlight also mentioned: I'm nto a big fan of USB measurements for several reasons. Some people love them, but for the way I work when testing rooms, they don't make a lot of sense to me.

To conclude, it seems that there is not much to expect with the acoustic treatment I applied, regarding even freq response.
I'm afraid I don't agree with your conclusion! :) You did a good job, and got good results. It's a common mistake to expect improvements in FR from adding room treatment, but that usually is not the case, unless you go crazy with major treatment, one careful step at a time... and even then, you will never get flat FR in a small room like this. The point of treatment is to tame the time-domain issues, and the reflections and other issues, to the point where it becomes possible to use digital tuning of the signal itself to fix some of the remaining FR issues. You aren't at that point yet, but you are getting there, and you are doing it right.

One final point here: trust your ears! If you can hear the improvement, then it is real. You just have to go looking around REW to find out "what" improved, to better understand what your ears are telling you.

And that is DSP correction. I have tried it and I didn't like it because in my opinion it removes the character of the speakers.
Right! That's because you are not yet at the point where DSP can be used successfully. And your ears told you that too! DSP can only change frequency response: it cannot change time-domain response in the room, nor can it change reflections or phase cancellations. Think of it this way: after the sound wave has left the speaker, there is nothing that EQ can do. EQ only works up to the point where the electronic signal becomes an acoustic signal: at the speaker cone. After that, the wave just bounces around the room, resonating and reflecting and cancelling and scattering and being absorbed... and there is NOTHING that EQ can do to change that! All of those issues are acoustic problems, not signal problems. They can only be fixed with treatment. If you try to fix them with DSP, you get even worse results, and it sounds terrible. That's like trying to fix a lousy steak by putting lots of salt on it: it won't make a bad steak taste any better, and all you get is a lousy steak that tastes very salty! But if you have a good stake, then a just a little salt can really bring out the flavor and make it taste great. DSP is salt. The steak is the treatment in the room. You first have to have a good steak (good treatment), then you can add a touch of salt (DSP) to get it tasting perfect.

As you already discovered, DSP in a bad room doesn't work. But in a GOOD room, it sure does, as long as you use it right: just a subtle touch, just enough to deal with the things that can be dealt with using DSP, and not trying to do things that it can't. So keep on working on the treatment, and sooner or later you'll get it to the point where DSP can help, then we can take a look at how to do that too.

So what are your thoughts on DSP correction? Do you approve it?
No! Yes! :) No, never, in an untreated or poorly treated room. Yes definitely in a fully treated room. But even then, done gently, and with understanding of what it is that you are doing, and only on things where it makes sense. I never recommend using the so-called "automated room correction" systems, that try to analyze the room then automatically apply filters to "correct" it. That seldom gives good results. Algorithms are not ears. Software is not brain power, or experience. I prefer to do it manually, one step at a time. Boring! Slow! Painful! But that's the way to get the best results. Such as this: viewtopic.php?f=8&t=14 Those final curves were achieved by careful, slow, manual adjustment, to get everything just right. We reached the limit of the equipment, and the room, in doing that. There's not even a fraction of a dB or a Hertz or a millisecond that can be improved further in that room. But first we treated it to the extreme... before we even started thinking about DSP, or "digital tuning" as I prefer to call it.

Also, what do you think went wrong with my treatment?
Nothing! In fact, it went very right! The only thing "wrong" with it, is that it is incomplete.... :)


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#12

Postby musictracer » Sat, 2020-Mar-28, 10:46

Thank you so much for your encouragement and detailed response, Stuart!
It is quite a relief having you saying that things worked at a good level with my project!

Regarding the cloud:
Soundman2020 wrote:Source of the post It looks pretty good, but I would still suggest making it hard-backed, angle it, and move the light fixture into the cloud itself.

The problem is that as I mentioned before, all the lumber work was done with the assistance of my father who currently has moved about 300 km away till next winter, so there is literally no way to do any changes or new constructions at this point. In addition, there is another issue. The house belongs to my parents and it was already a bit of difficult to convince them to allow me to make holes in the walls and ceiling. Thus I'm afraid it will be quite unlikely they will let me go further with this, so I only hope that any further modification will not demand making any more holes...

Soundman2020 wrote:Source of the post But you won't find "bass tightness" or "decay times" in the frequency curves... because those are not frequency-domain issues: rather, they are time domain issues, so you have to look for them in the time-domain graphs that REW produces.

No, not at all! this is not the case with my judgement. Of course I am aware that the "tightness" and "consistency" issues regard the time domain measurements! This is the reason why I posted the waterfall analysis as well in the first place. I know it is an important factor! The problem is that I thought that it is secondary compared to the FR analysis. I mean I thought it wouldn't make much sense as long as the FR was still a mess. But after reading your reply I realized that this is not really the case. Thanks a lot for clarifying!

Soundman2020 wrote:Source of the post You can see similar improvements on the spectrograms.

Yes indeed there is some improvement there indeed. But I have a technical question. What is the point of negative time values in the Spectrogram? I suspect it has something to do with phase, otherwise it makes no sense to me, since there is no point in having negative values. But maybe I am missing something here...

Also, how can you get the waterfall analysis to show you both before and after measurements simultaneously ? I was looking for that in REW before uploading the measurements, but couldn't find it. It helps a lot to see the two graphs overlapping each other! Thanks for posting!

Soundman2020 wrote:Source of the post The ideal is to have no reflections larger than -20 dB for the first 20 ms, and as you can see, you have several.

I thought -10db would be fine, but -20 is quite challenging! Is it really so much important to get it that low?

Soundman2020 wrote:Source of the post You can see that on the IR (Impulse Response) graphs, when you look at the ETC curves

Wow! I didn't know REW could present IR graph with just sweeping tone measurement analysis. I thought it demanded a momentary pulse tone or a "clap", "shot" etc... I remember doing such measurements back in the University days along with fourier transforms and moving from time to frequency domains, but I can't recall if we did any sweeps to get the IR graphs.
Thanks for showing this!

Soundman2020 wrote:Source of the post Since sound travels at 343m/s, that means that it must have traveled about 1100mm further than the direct sound did, to arrive at the mic 3.08ms later. So, all you need to do is to find out which surface in your room creates a path that is 1100mm longer than the direct path from the speaker to the mic!

Please forgive me if I am mistaken but I have an objection: According to my calculation the further distance travelled (assuming c=343m/s and 3.08ms time travelled) should be 1.056m , not 1.1m . Maybe 2'' won't make that much of a difference, but then again maybe it does, I don't know, so I thought maybe I should mention this... :-)

Also thank you very much for spending time to explain how to spot where the reflection comes from. I was aware of the way but I really appreciate that you described it in such a detail! At this point I can't assume where that might be coming from but I will follow the process soon and find out.

Soundman2020 wrote:Source of the post Also, you can probably improve the low--end response even more by "walking" the sub around on the floor, in small increments (maybe 10cm or so for each "step"), measuring with REW each time, then comparing the measurements to see which one gets you the smoothest response. Walk it across the entire front wall, from left side wall to right side wall, in 10cm steps, and do a LRS test in REW at each location. The best spot should be clearly visible in REW... but do look at all the graphs to determine that! Not just the frequency response. You are juggling several things here, and for the this set of tests FR is important, but so are time-domain response and phase response. Check them all, at each location, and choose the best compromise. Oh, and try flipping the "phase invert" switch on the sub at each test location as well: that will make a BIG difference, always. So do a REW test at each spot with "phase=0°" set on the speaker itself, and another test with "phase=180°". You'll hear the difference here too.

It can sometimes also help to rotate the speaker in place at that best spot, so that it points in each of the four main directions, testing again at each one. Sometimes there's a useful change: sometimes not. And you can also try raising the sup up off the floor in small increments (use books under it), once again checking with REW. It's surprising just how much things can change from simply moving the sub around! The goal is to keep careful notes in REW and on paper, about exactly where you had the sub for each test, so that you can then compare the results to find the best spot.


I had an idea of how things can improve by proper sub placement, but your words are much more enlightening. For instance, I didn't know that even 10cm can make such a great difference, mainly because we are talking large wave lengths here, significantly bigger than this distance (10cm). And of course, phase is an important issue , as you point out, since cancellation or any kind of coincidence is more obvious at this part of the spectrum.

But there are two limiting factors that make the process difficult. One is the lack of space in the room, where as you can see clearly things are quite squeezed. The other one is the lack of lengthy enough cables to get it moving around until I find the most beneficial spot. You see, as it often happens, the sub contains the crossover as well, which means that there are 5 cables in total connected to it: 2 audio ins, 2 audio outs and 1 power plug. None of it is currently long enough to make the test, and given the quarantine situation in my country due to Covid-19 it is quite inlikely I'll be able to get any within the next weeks or months. So this is postponed for now, but as I mentioned before, the room limitations are deterring anyways.

Soundman2020 wrote:Source of the post I'm afraid I don't agree with your conclusion! :) You did a good job, and got good results.

Thanks a lot for reminding me. It's quite encouraging
Soundman2020 wrote:Source of the post The point of treatment is to tame the time-domain issues, and the reflections and other issues, to the point where it becomes possible to use digital tuning of the signal itself to fix some of the remaining FR issues. You aren't at that point yet, but you are getting there, and you are doing it right.

Ok, didn't know that treatment was not meant to correct FR, that's why I felt dissapointed in the first place. Thanks for pointing out.

Soundman2020 wrote:Source of the post Right! That's because you are not yet at the point where DSP can be used successfully. And your ears told you that too! DSP can only change frequency response: it cannot change time-domain response in the room, nor can it change reflections or phase cancellations.

I think you misunderstood me. By "removing the character of ther speakers" I was speaking literally about the speaker it self, excluding the room interference. This is why I mentioned the speaker brands in my comment, meaning that every brand exhibits its own character, and that includes its own FR as well. NS-10s for instance, they exhibit quite a unique FR, yet they are still considered as an irreplaceable tool by many engineers. So why correct it with DSP? But that's another and long discussion to bring in here... :-)

Also the steak/salt example you introduced was really insightful! Couldn't have made things clearer in such simple representation!

Soundman2020 wrote:Source of the post Such as this: viewtopic.php?f=8&t=14 Those final curves were achieved by careful, slow, manual adjustment, to get everything just right.

Gosh!!! This is from another world!!! You definitely nailed it there, Stuart!!! Well done!!! :shock: :jammin:


Ok, so next I will track down that nasty first reflaction to see where it comes from and post again. It is quite possible it came from the sides , since I am afraid I had misplaced the side panels, but the problem is that the distance doesn't match the 1,056 extra distance travelled. Anyway, hopefully we'll know soon.

Thanks a lot once again for your assistance, Stuart!
Stay safe and we'll talk again soon!
Bye for now!



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Advise on what Rock/mineral/glass wool to choose for basstraps

#13

Postby musictracer » Sat, 2020-Mar-28, 10:46

Thank you so much for your encouragement and detailed response, Stuart!
It is quite a relief having you saying that things worked at a good level with my project!

Regarding the cloud:
Soundman2020 wrote:Source of the post It looks pretty good, but I would still suggest making it hard-backed, angle it, and move the light fixture into the cloud itself.

The problem is that as I mentioned before, all the lumber work was done with the assistance of my father who currently has moved about 300 km away till next winter, so there is literally no way to do any changes or new constructions at this point. In addition, there is another issue. The house belongs to my parents and it was already a bit of difficult to convince them to allow me to make holes in the walls and ceiling. Thus I'm afraid it will be quite unlikely they will let me go further with this, so I only hope that any further modification will not demand making any more holes...

Soundman2020 wrote:Source of the post But you won't find "bass tightness" or "decay times" in the frequency curves... because those are not frequency-domain issues: rather, they are time domain issues, so you have to look for them in the time-domain graphs that REW produces.

No, not at all! this is not the case with my judgement. Of course I am aware that the "tightness" and "consistency" issues regard the time domain measurements! This is the reason why I posted the waterfall analysis as well in the first place. I know it is an important factor! The problem is that I thought that it is secondary compared to the FR analysis. I mean I thought it wouldn't make much sense as long as the FR was still a mess. But after reading your reply I realized that this is not really the case. Thanks a lot for clarifying!

Soundman2020 wrote:Source of the post You can see similar improvements on the spectrograms.

Yes indeed there is some improvement there indeed. But I have a technical question. What is the point of negative time values in the Spectrogram? I suspect it has something to do with phase, otherwise it makes no sense to me, since there is no point in having negative values. But maybe I am missing something here...

Also, how can you get the waterfall analysis to show you both before and after measurements simultaneously ? I was looking for that in REW before uploading the measurements, but couldn't find it. It helps a lot to see the two graphs overlapping each other! Thanks for posting!

Soundman2020 wrote:Source of the post The ideal is to have no reflections larger than -20 dB for the first 20 ms, and as you can see, you have several.

I thought -10db would be fine, but -20 is quite challenging! Is it really so much important to get it that low?

Soundman2020 wrote:Source of the post You can see that on the IR (Impulse Response) graphs, when you look at the ETC curves

Wow! I didn't know REW could present IR graph with just sweeping tone measurement analysis. I thought it demanded a momentary pulse tone or a "clap", "shot" etc... I remember doing such measurements back in the University days along with fourier transforms and moving from time to frequency domains, but I can't recall if we did any sweeps to get the IR graphs.
Thanks for showing this!

Soundman2020 wrote:Source of the post Since sound travels at 343m/s, that means that it must have traveled about 1100mm further than the direct sound did, to arrive at the mic 3.08ms later. So, all you need to do is to find out which surface in your room creates a path that is 1100mm longer than the direct path from the speaker to the mic!

Please forgive me if I am mistaken but I have an objection: According to my calculation the further distance travelled (assuming c=343m/s and 3.08ms time travelled) should be 1.056m , not 1.1m . Maybe 2'' won't make that much of a difference, but then again maybe it does, I don't know, so I thought maybe I should mention this... :-)

Also thank you very much for spending time to explain how to spot where the reflection comes from. I was aware of the way but I really appreciate that you described it in such a detail! At this point I can't assume where that might be coming from but I will follow the process soon and find out.

Soundman2020 wrote:Source of the post Also, you can probably improve the low--end response even more by "walking" the sub around on the floor, in small increments (maybe 10cm or so for each "step"), measuring with REW each time, then comparing the measurements to see which one gets you the smoothest response. Walk it across the entire front wall, from left side wall to right side wall, in 10cm steps, and do a LRS test in REW at each location. The best spot should be clearly visible in REW... but do look at all the graphs to determine that! Not just the frequency response. You are juggling several things here, and for the this set of tests FR is important, but so are time-domain response and phase response. Check them all, at each location, and choose the best compromise. Oh, and try flipping the "phase invert" switch on the sub at each test location as well: that will make a BIG difference, always. So do a REW test at each spot with "phase=0°" set on the speaker itself, and another test with "phase=180°". You'll hear the difference here too.

It can sometimes also help to rotate the speaker in place at that best spot, so that it points in each of the four main directions, testing again at each one. Sometimes there's a useful change: sometimes not. And you can also try raising the sup up off the floor in small increments (use books under it), once again checking with REW. It's surprising just how much things can change from simply moving the sub around! The goal is to keep careful notes in REW and on paper, about exactly where you had the sub for each test, so that you can then compare the results to find the best spot.


I had an idea of how things can improve by proper sub placement, but your words are much more enlightening. For instance, I didn't know that even 10cm can make such a great difference, mainly because we are talking large wave lengths here, significantly bigger than this distance (10cm). And of course, phase is an important issue , as you point out, since cancellation or any kind of coincidence is more obvious at this part of the spectrum.

But there are two limiting factors that make the process difficult. One is the lack of space in the room, where as you can see clearly things are quite squeezed. The other one is the lack of lengthy enough cables to get it moving around until I find the most beneficial spot. You see, as it often happens, the sub contains the crossover as well, which means that there are 5 cables in total connected to it: 2 audio ins, 2 audio outs and 1 power plug. None of it is currently long enough to make the test, and given the quarantine situation in my country due to Covid-19 it is quite inlikely I'll be able to get any within the next weeks or months. So this is postponed for now, but as I mentioned before, the room limitations are deterring anyways.

Soundman2020 wrote:Source of the post I'm afraid I don't agree with your conclusion! :) You did a good job, and got good results.

Thanks a lot for reminding me. It's quite encouraging
Soundman2020 wrote:Source of the post The point of treatment is to tame the time-domain issues, and the reflections and other issues, to the point where it becomes possible to use digital tuning of the signal itself to fix some of the remaining FR issues. You aren't at that point yet, but you are getting there, and you are doing it right.

Ok, didn't know that treatment was not meant to correct FR, that's why I felt dissapointed in the first place. Thanks for pointing out.

Soundman2020 wrote:Source of the post Right! That's because you are not yet at the point where DSP can be used successfully. And your ears told you that too! DSP can only change frequency response: it cannot change time-domain response in the room, nor can it change reflections or phase cancellations.

I think you misunderstood me. By "removing the character of ther speakers" I was speaking literally about the speaker it self, excluding the room interference. This is why I mentioned the speaker brands in my comment, meaning that every brand exhibits its own character, and that includes its own FR as well. NS-10s for instance, they exhibit quite a unique FR, yet they are still considered as an irreplaceable tool by many engineers. So why correct it with DSP? But that's another and long discussion to bring in here... :-)

Also the steak/salt example you introduced was really insightful! Couldn't have made things clearer in such simple representation!

Soundman2020 wrote:Source of the post Such as this: viewtopic.php?f=8&t=14 Those final curves were achieved by careful, slow, manual adjustment, to get everything just right.

Gosh!!! This is from another world!!! You definitely nailed it there, Stuart!!! Well done!!! :shock: :jammin:


Ok, so next I will track down that nasty first reflaction to see where it comes from and post again. It is quite possible it came from the sides , since I am afraid I had misplaced the side panels, but the problem is that the distance doesn't match the 1,056 extra distance travelled. Anyway, hopefully we'll know soon.

Thanks a lot once again for your assistance, Stuart!
Stay safe and we'll talk again soon!
Bye for now!



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Advise on what Rock/mineral/glass wool to choose for basstraps

#14

Postby Soundman2020 » Tue, 2020-Mar-31, 17:47

It is quite a relief having you saying that things worked at a good level with my project!
:thu:

The problem is that as I mentioned before, all the lumber work was done with the assistance of my father who currently has moved about 300 km away till next winter, so there is literally no way to do any changes or new constructions at this point. In addition, there is another issue. The house belongs to my parents and it was already a bit of difficult to convince them to allow me to make holes in the walls and ceiling. Thus I'm afraid it will be quite unlikely they will let me go further with this, so I only hope that any further modification will not demand making any more holes
OK. Understood! So, maybe when your dad comes back for the winter, he could help you modify the cloud, and just us the same holes to hang it in the same place again? Just an idea... :)

The problem is that I thought that it is secondary compared to the FR analysis. I mean I thought it wouldn't make much sense as long as the FR was still a mess. But after reading your reply I realized that this is not really the case. Thanks a lot for clarifying!
Right! Tis is confusing for many people, because "frequency response" is just logical and easy to understand, and you see it all over the place, with graphs or specs for pretty much every type of studio gear, from speakers to mics to consoles to outboard gear: Everywhere you look, it's all about frequency response. And that's fine for purely electronic stuff, but for acoustics, the "time domain" response is just as important, and personally I think it is even more important. It's not intuitive for many people.

But I have a technical question. What is the point of negative time values in the Spectrogram? I suspect it has something to do with phase, otherwise it makes no sense to me, since there is no point in having negative values. But maybe I am missing something here...
It's more a mathematical oddity than a "real" thing, in the sense of something you could hear BEFORE the impulse, but it does have real world implications. If you look at the impulse response graph, for example, and zoom out a lot, you'll see that over on the left (negative time: before the impulse), there's a series of small "copies" of the impulse itself. That's a result of the way the mat works, and those actually are related to distortion in the system... but of course, they did note really happen before the impulse! That would be impossible. It's just an artifact of the way the math works. But REW does use that information in calculating the distortion graphs. Each of the "miniature compressed copies" of the impulse is actually one of the distortion harmonics, but working backwards from right to left. So the first one you see (closest to the impulse itself) is the second distortion harmonic, the next one to the left is the third harmonic, then the fourth, and so on. Another way of thinking of it is that the main impulse response shows the rooms linear response, and the others show it's non-linear response. The main impulse that starts at time zero is the response of the room without any distortion, and the distortion harmonics appear before that, out to the left "before" time zero... but only because that's the way the math works out.

It's complicated!

Also, how can you get the waterfall analysis to show you both before and after measurements simultaneously
This is a bit convoluted, but very useful! First, make sure that you have actually generated the waterfall plots for both of the data sets that you want to see. If you have not yet generated a graph for one of them, you won't be able to overlay it. Then, select one of the waterfalls that you want to use, and click on the "controls" button, on the far right hand side of the window, just above the end of the graph. It looks like a gear wheel. That opens up a sub-window with some controls you can use to change the way the graph appears. Down in the bottom left corner of that, there's three controls for handling overlays. The first time you see it, the top one will just say "overlay transparent", the second one tells you the percentage transparency, and the bottom one is where you can select the OTHER waterfall that you want to overlay here. IF you click on the down arrow next to that, you get a list of all of the data sets in the current REW session. The ones that have NOT been generated yet are shown in gray, and you cannot select those. The ones that HAVE been generated are shown in white, and you can select any one of those to overlay. Then you can adjust the other two controls above that one, to change the way it is displayed. When you don't want to see the overlay any more, then just go back to the bottom control, click on the down arrow again, and select "No Overlay".

I thought -10db would be fine, but -20 is quite challenging! Is it really so much important to get it that low?
There's some debate among acousticians about what is "acceptable" in a studio, but what the science actually shows is that it needs to be -20 dB down for the first 20 ms in order for it to not cause a problem, psycho-acoustically. -10 dB means that it is half as loud as the direct sound (subjectively), but one tenth of the intensity (objectively). -20 dB means that it is one quarter as loud as the direct sound (subjectively), and one one-hundredth of the intensity (objectively). That's a big difference in intensity, even though it doesn't seem that big subjectively. But your ear works on the absolute intensity if the sound waves BEFORE it gives you its subjective impression of how loud things are, so really its the intensity that matters here. So a reflection at -10 dB is actually ten times stronger than one at -20 dB. The stronger the reflection is, the more problematic the issue becomes.

There's also the issue of timing: Psycho-acoustic studies show that if the reflection arrives at least 30ms after the direct sound, your ear can probably already determine that it is a distinct, separate sound. Certainly, after 50ms the two sounds are distinguishable. going the other way, at 20ms it might still be possible to discern the direct and reflected sound as being separate and distinct, but for the majority of people, they hear both together as one single sound that is sort of "blurred" in time, comes form a different direction, and has a different frequency balance. As times get shorter, the problem gets bigger.

There's also the issue that the relationship between these two parameters is not fixed: A louder reflection will always cause a bigger problem, even for longer delays, while a softer reflection might not cause any problem at all, even if the delay is very short.

Add to that the issue of "masking", where a loud reflection can actually prevent you from hearing what comes right after it, under some circumstances, as well as "forward masking" where a very loud reflection can also suppress your perception of sounds that came just BEFORE the reflection did, which is a bit unexpected. It all has to do with the very complicated way that our ears and brains work. And some of this stuff is used in things like "MP3 compression": it removes sounds from the audio stream if w would not be able to hear them due to "masking", as well as other similar psycho-acoustic artifacts. If our ears did not work like this, then MP3 compression would not work either.

So, that's a long way of saying: it's complicated! :)

Here's a diagram that might help make it clearer. It shows how the various levels and delays affect our ability to determine all of this:
Reflection Audibility.jpg
Reflection Audibility.jpg (30.69 KiB) Viewed 1923 times
Reflection Audibility.jpg
Reflection Audibility.jpg (30.69 KiB) Viewed 1923 times
You can see where the "20-20" criteria comes from on that graph! If the reflection is -20 dB down,for delays up to about 20ms it is not audible. But if the level is -10dB, it registers for ALL time delays, and it fools your brain into hearing the sound as though it were more spacious than it really is. In your case, your reflection is very much in that area of "spaciousness", meaning that it is messing with your ability to determine direction and frequency, and giving you a false sense that the music is more "surrounding" than it really is.

Related to the above, there are several "philosophies" or "concepts" for building control rooms, with names like "NER", "RFZ", "CID", etc. Each of those precisely defines the acoustic response characteristics that the room must achieve. One of those is the ideal "20-20" criteria, which means "20ms delay, 20 dB down". (And that's also where my screen name comes from! "SOUNDMAN2020" has nothing at all to do with the year 2020.... I've been using it that name more than a decade now! It's all about this "20-20" criteria that a room must meet in order to be good: no reflections greater than -20 dB in the first 20ms). Now, that's the ideal situation: to not have any reflections at all for the first 20ms, but to do that properly means that you need a large room. Sound travels roughly one foot for every millisecond, so you need to have at least ten feet between your head and the closest reflective surface behind you, plus there's often a 3 foot deep bass trap behind that reflective surface, so you need at least 13 feet distance just behind your head, plus a corresponding distance in front of you... thus, a room that fully meets the 20-20 criteria needs to be abut 20 feet long. That's a bit more than 6m long. Most home studios are not big enough to do that, so we have to make do with shorter times. 15ms is reasonable, and down to about 12ms is still acceptable. Now, as I mentioned before, as the delay time gets shorter, the level needs to be lower in order to not produce serious psycho-acoustic artifacts. So, while a level of -10dB might be fine for a large room with a long 25ms delay, you do need more attenuation for a small room.

Unfortunately, there's no simple rule that says you need xx db for every zz ms... it would be nice if there were, but there isn't: people are different, rooms are different, perception is different. There are only guidelines. All I can suggest is measuring the distance from your head to the closest reflective surface behind you, and if that is less than 10 feet (3m), then make sure that there are no reflections at all for the time that it takes for sound to get back to your ears (ie, less than -20dB), then after that time, keep the level under -15 dB, and allow it to decay at the correct natural rate for your room, which is easy to calculate. If you happen to have a room that is large enough to allow more than 20ms for the first reflections, then you can relax that levels a little, and allow something slightly higher, but certainly not as high as -10 dB. That's too strong, even for a large room.

Wow! I didn't know REW could present IR graph with just sweeping tone measurement analysis. I thought it demanded a momentary pulse tone or a "clap", "shot" etc... I remember doing such measurements back in the University days along with fourier transforms and moving from time to frequency domains,
Exactly! And that exact sam Fourier transform is reversible! You did it one way, but it is also possible to go the other way: take the frequency response, and use the reverse Fourier transforms to get back to the impulse response. That's what REW does. Time and frequency are flip sides of the same coin, and it is simple to convert between them. Which is why REW can do a log frequency sweep, then convert that to the actual IR (Impulse response), which it then uses to calculate many of the other graphs.

The problem with trying to do measure a true impulse response, is that it is impossible! :) In theory, the impulse needs to be infinitely short, and therefore it has to be infinitely loud... which, of course, is impossible. All real-world impulses, such as a balloon bursting, or a gunshot, or wood planks slapped together, are non-zero (they do last for a certain time, even if it is very brief), and thus they are not true impulses. Also, they are not loud enough! Even though they are very loud, because the last a certain non-zero time, they are not loud enough. They would need to be something like 190 dB SPL (in other words, almost a shock wave) to create a true impulse. Once again, it is impossible to actually generate such a sound in real life. And even if you could, such extreme over-pressures would probably damage the room... :shock: So the only realistic way to derive the impulse response for a room, is by using some type of sound at a lower level, for a longer time, and covering all frequencies. There are various types of sound that can be used, such as white noise, pink noise, MLS, and swept sin waves. Each has its advantages and disadvantages. REW uses the swept sine technique, which is a good compromise between the limitations of the other methods.
Please forgive me if I am mistaken but I have an objection: According to my calculation the further distance travelled (assuming c=343m/s and 3.08ms time travelled) should be 1.056m , not 1.1m .
True... assuming that sound really is traveling at 343 m/s in your room! Did you take into account the air temperature? :) Also, the measurement can't be extremely accurate, because you are not measuring over a continuous unbroken time period, but rather a series of samples, separated by time (which depends on your audio interface), plus the reflection is not a sharp impulse but rater spread over time, and in fact your reflection is not just one single reflection, but two at nearly the same time! And the timing changes between measurements, and as the treatment changes. REW tries to estimate a correction for the timing differences, and in your case it says that the actual impulse is delayed by -0.053ms, which is 18mm. If you tell it to adjust for that presumed delay, and zoom in for higher level of detail, this is what you get:
Musictracer--REW--IR--9ms-zoom-LRS--cloud-and-traps.png
That's the actual reflection, and you can see that there are two, very close together, at different levels, with the adjusted time peak at 3.15ms. Assuming 343 m/s, that would be 1080mm, but the second peak is at 3.29ms, which is 1139mm. Average gives you 1109ms, but the first peak is larger magnitude, so the average deserves to be "weighted" a bit. So 1100ms is a "best guess" that should find the spot that is causing BOTH of those reflections. They will be very close to each other (just a few mm apart), so it really doesn't matter if the string only gets to one of those points, or the other one, or somewhere in between: once we find that spot and treat it, we will be treating BOTH of those issues, since the treatment will be much, much larger than the possible error in locating the point.

I had an idea of how things can improve by proper sub placement, but your words are much more enlightening. For instance, I didn't know that even 10cm can make such a great difference, mainly because we are talking large wave lengths here, significantly bigger than this distance (10cm).
That surprises a lot of people, but it is very real. Here's a real-world example:
Sample-walking-sub-test-STVNOUS.png
That's from a room that I'm in the process of precision-tuning right now for a client in the USA, and shows exactly what I'm talking about. The frequency range here is just the low end: 12 Hz to 500 Hz. In this case I am using two identical subs to create a plane wave bass array (which is a bit complex to explain right now), and that graphs shows a series of tests where we were sliding one of the subs in steps of just 2" (10cm) without moving the other one at all. The major differences are clearly visible. In this particular test I was looking for the spot that best eliminates the phase-related issue at 80 Hz, while also reducing the modal issue at 37 Hz. You can see that I did find a good spot for doing both of those... :)

This often comes as an eye-opener for many people, since you don't really expect to see any difference from moving a sound source by 2 inches (10cm) when it is generating waves 14 FEET long (430cm), but there's the proof! The reason this works is because of the interaction between the speaker and the room: if you did the same thing out in the open, with nothing at all around the speaker for 100 feet in any direction, then the changes would be miniscule. But because the speaker is inside a room, and is also not alone: there are other things in the room generating the same waves, but at different places (the main speakers, and the other sub in this case), all of those interact to create patterns of interference. So it's just a matter of moving the sub around to get the most beneficial pattern.

The room in question is in the final stages of tuning right now, and the owner is a forum member.... who I'm trying to persuade to create a thread about the design and construction of his place, as he has quite a story to tell! He says that maybe he'll do that one day, but for now he doesn't want to be identified... but I can still use data like this to demonstrate the principles of acoustics.

But there are two limiting factors that make the process difficult. One is the lack of space in the room, where as you can see clearly things are quite squeezed.
Fair enough. .... but there must be at least a FEW places you could try! Here's the data from another client, in the UK, whose room I am also doing precision tuning, and he has a similar situation: there's furniture and acoustic treatment in the way, so he could only get his sub to 6 specific positions in the room... as you can see, "position A" is by far the best. Before, he had it at "position D", so you can see why he said there was a lack of bass at the mix position. I fixed that very simply, just by moving the sub off to the side, to "A", and now the bass is roaring! There's also enough treatment in that room now, that I'll probably be using digital tuning to slightly reduce the peaks at 48 Hz, 76 Hz, and 100 Hz. , to smooth out the low end even more. However, there's also phase to take to account: I need to be sure that there are no phase issues at any of those frequencies, because if there are then it is not possible to apply EQ there...

But anyway, the point is that even if you can only get your speaker to half a dozen different spots in your room, try them all anyway.... as soon as you can buy longer cables! :)

Ok, didn't know that treatment was not meant to correct FR, that's why I felt dissapointed in the first place. Thanks for pointing out.
Some treatment can change frequency response yes, but mostly there isn't a lot of effect. Acosutically, everything effects everything! Here's a graph from an excellent book on acoustics, that shows how the modal response for a room shapes the entire frequency response for the room:
TICHY--Modal-contribution-to-room-response.jpg
TICHY--Modal-contribution-to-room-response.jpg (32.36 KiB) Viewed 1923 times
TICHY--Modal-contribution-to-room-response.jpg
TICHY--Modal-contribution-to-room-response.jpg (32.36 KiB) Viewed 1923 times
Here's another graph from the same book, showing what happens to that when you install bass trapping, to dampen the modal issues:
TICHY--Effect-of-damping-on-room-response.jpg
As you can see, even though the modes are being damped in the time domain, there's not much happening to the frequency response! The curve just smooths out a bit, with the peaks and dips getting a little lower in intensity, but the overall shape of the frequency response doesn't change much at all, just from damping (bass trapping). I'm not sure if you saw the article I wrote on this a while back, where I say that it is impossible to get rid of the modes in a room: this is why. You can damp them, and you can reduce the intensity, but you can't get rid of them, and they still shape the overall response of the room, even if they are damped.

I think you misunderstood me. By "removing the character of ther speakers" I was speaking literally about the speaker it self, excluding the room interference. This is why I mentioned the speaker brands in my comment, meaning that every brand exhibits its own character, and that includes its own FR as well. NS-10s for instance, they exhibit quite a unique FR, yet they are still considered as an irreplaceable tool by many engineers. So why correct it with DSP?
I did understand what you meant, yes, but I guess I didn't explain the point I was trying to make: if you use EQ at all in the signal chain, it will affect the room response! Even if the purpose was to correct a the deficient response of a not-so-great speaker (such as the NS-10, for example... :mrgreen: ), then that will ALSO have an affect on the room response, if the room is not treated. For example, let's say that you attempt to correct the notoriously "missing bass" of the NS-10 (which falls off the edge of a cliff below about 100 Hz) by adding just a little 6 dB boost at 70 Hz, to try to get at least some low end out of it.... Now, if your room happened to have a modal resonance at 70 Hz, you would be triggering that more strongly (even though you did not intend to do that! You only wanted to extend the low end of the NS-10...) So now you would have a frequency response peak there, sure, but you'd also have excessive modal ringing. On the other hand, if your room had a modal null at 70 Hz, then your EQ boost would do nothing at all! 70 Hz would not get louder, because you'd be pouring energy into a deep hole that you cannot ever fill.... However, the energy doesn't just disappear: a modal null is a phase problem, and a position problem, so the energy you pour into that "hole" would appear at another point in the room, that is NOT in the modal null at the mix position, and it would appear with a phase shift.... So you would make matters worse, not better. Even though you were just trying to "fix" a lousy speaker by eq'ing it, if the room is not treated properly then that is doomed to failure, because it will always have unwanted consequences for the room itself, even though it was intended just for the speaker.

Gosh!!! This is from another world!!! You definitely nailed it there, Stuart!!! Well done!!
Thanks! That's an example of what can be done with very careful precision tuning in a well-treated room. It took a LOT of time to get that right, and Rod and I worked late into many, many nights, tweaking here and tweaking there. But once again, it would not have been possible to get those results just from the digital tuning alone: the room first had to be treated to the point that made it possible. You would not believe the truck loads of treatment that went into the ceiling of that room, to damp the low end....

Ok, so next I will track down that nasty first reflaction to see where it comes from and post again
:thu: Great!


- Stuart -




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