Attic Shaped Studio

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Soundman2020
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#61

Postby Soundman2020 » Mon, 2020-Mar-30, 01:34

Ahh, yes: welcome to my world! :) The juggling game of studio design, where you have to keep 197 balls in the air at all times... and they are all different sizes and different weights! :) :lol: And you have to do that while riding a unicycle, backwards, on ice.... blindfolded...
Sometimes, it really does feel like this:
crazy-juggler-11-ENH-BIG2.jpg
crazy-juggler-11-ENH-BIG2.jpg (60.91 KiB) Viewed 31747 times
crazy-juggler-11-ENH-BIG2.jpg
crazy-juggler-11-ENH-BIG2.jpg (60.91 KiB) Viewed 31747 times
:)

OK, a few more twists that you could take into account as you work through the process of coming up with the perfect room design: If you need more mass in a thinner package, then consider fiber-cement board. The density is a bit more than twice that of drywall, so you can have the same mass in a thinner panel. Drywall density is around 680 kg/m3, fiber-cement around 1550 kg/m3. MLV is around 1800 kg/m3, if you really want to spend a LOT of money to get mass in a thin package (MLV is really expensive: I rarely use it for isolation but I do use it in other parts of studios...). Other crazy things: Aluminium sheeting is around 2750 kg/m3 (so a sheet 3mm thick has the same mass (surface density) as 12mm drywall). Steel plate is around 7850 kg/m3 (thus, 2mm thick steel plate has the same mass as 23mm thick drywall... As you note, lead sheeting it about 12,000 kg/m3, so 1mm of lead is about the same as nearly 18mm of drywall. (And for the insanely extreme, exotic, and impossible end of the scale: gold is around 19,300 kg/m3, and platinum is around 21,500 kg/m3. So gold leaf just half a mm thick has the same mass as 14mm of drywall, and a sheet of platinum 1mm thick is the same as roughly 32mm of drywall.... :ahh: )

So, considering those, maybe you can come up with some combinations of materials that would allow you to get the right thickness for good symmetry while still retaining the right mass (surface density).

Next up: Why bother?

For all those folks following this thread (and there are lots of them! Your thread has nearly 4,000 views right now, Jennifer... :thu: ), what Jennifer is proposing might seem to be silly, crazy, overkill, since she already has a successful studio that is producing great mixes, and making money for her (click on the link in her signature or profile...), so you might be wondering why she would want to change that?

Answer: The better your room is, the better your mixes are, and the more effortless it is to mix well. She will be able to to produce even better mixes, will take less time to to do it, and will be less fatigued at the end of the day. That's the basic reason here. She has a good studio, and she wants to make it a great studio. In commercial terms, that means faster turn-around on jobs (thus, more jobs per month = more $$$ per month), as well as improved reputation: folks who use her studio will want to go back for more, and will also tell their friends and colleagues about this fantastic place where its just so easy to track, and the vibe is great, and the results are outstanding, etc. And they won't mind paying more for that. People do actually appreciate quality!

So, she's investing in making her place even better: better isolation between rooms, higher precision in the mix, more accurate acosutic response, flatter, better, smoother... easier to hear defects in the music, and fix it. Better mix translation. Etc.

Thus, her concern about a few mm of "asymmetry" in the room. Some people might think that a few mm here or there won't make any difference, but it will. If you take a look at the science of psycho-acoustics, you'll see why.

Psycho-acoustics deals with the way we humans perceive sound, rather than with the way the sound actually is, physically, in the air. Ears do not work the same way microphones do: a good mic captures the actual pressure changes in the air very accurately, and turns that into precise voltage fluctuations, but ears do not work like that. Our ears are amazing devices that do many things all at once to give your brain the perception of sound, but they do it in a manner that is very different from a mic... and some of that can cause your ears to "lie" to you: so you perceive sound differently than it really is.

For example, if your ear hears the direct sound from a speaker but there's also a reflection that sends a "copy" of that direct sound to your ears with a small delay (because it took a longer route), then that can fool your ears into hearing something that isn't really true. If the reflection is strong and the delay is short (less than about 30ms), your ears do not hear that reflection as a separate sound: rather, it hears a smeared interference pattern between the two sounds, and your ears/brain interpret that interference pattern to mean that the sound came from a different direction (neither from the speaker nor from the spot where the reflection occurred), and also that the frequency response was different from what it really was: this is because your ear itself creates similar interference patterns inside your ear canal, for the very purpose of trying to identify which direction the sound is coming from. That's the real purpose of all those ugly folds, wrinkles, and twists on your pinna (the fleshy thing that sticks out to the side of your head, that most people just call an "ear"). Those folds and wrinkles and bends and angles have a purpose: to create interference patterns inside your ear canal, which the rest of your ear and brain then use to figure out where the sound came from.

Thus, if you are standing out in the jungle and a lion roars, this system is pretty good at identifying where that came from and how close it was, so you can turn the exact opposite way and start running like crazy.. away from the lion! You want this to be accurate, because running the wrong way would not be a good thing... if your ear told you the lion was in behind you when it is really in front of you, then that would not be a good thing, as you'd end up running towards the lion... :shock: So your ear works very well out out in the open, where there are no reflections to mess things up, and you get to live for another day... But inside a room, there are reflective surfaces around, and those can send reflections back to your ears, that create other interference patterns inside your ears... so your ears can tell you the wrong thing! You can hear the sound as coming from a different direction. Your ear has no way of knowing if that interference pattern was produced by the ugly wrinkles in your ear lobe, or by a strong reflection that arrived after a delay: it just recognizes that particular interference pattern as meaning "the sound came from there, not here".

Fortunately, inside a studio, your life does not depend on this: there are no lions to eat you (at least, I hope you don't keep lions in your studio!). But it does mean that you can't pan and mix as well as you'd like, because you are not hearing the way things really are: the reflections are fooling your brain.

Worse still, because of the way this happens inside your ears, those interference patterns reduce the intensity of some frequencies and increase the intensity of others, so you are also not hearing the right frequency balance.

When you are out in the jungle and this happens for real, your brain "knows" about the different frequency response for each and every angle that a sound might arrive at your ears, and it compensates, telling you that the frequencies were actually at the right intensities even though they were not, because it "understands" that each angle has a different response. But when that happens in the room from a reflection, your brain has no way of determining that it was a reflection! It assumes that this is a direction clue coming from the folds of your pinna... Therefore, it tries to "compensate" for a frequency problem that does not really exist, and tells you that the levels of the frequencies were difference from what they really are.... Long story short: a strong reflection messes with your brain, and it thinks that it is hearing sound coming from another direction (not the real one) and with another frequency balance (not the real one).

So what happens when you have a whole bunch of less strong reflections, all arriving at slightly different times and levels? Since your brain can't make head nor tail of that mess, it just tells you that the sound is "broader", "wider", or more "spacious", coming from all around you, rather than from a specific direction. And since the frequency balance is also all messed up impossibly, your brain tells you that the sound is "warmer", more "mellow", and more "pleasant". (I guess that sort of calms you down a bit if there are dozens of lions roaring all around you, so you are more tranquil as you consider the inevitability of your impending demise... ).

So, this is where some studio designers go wrong (even professional ones), as they think it is a good idea to have a warmer, more pleasant, more enveloping "spacious" sound that feels nice, when you are mixing... so they try to create that, with many low-level early reflections... but that is actually very wrong! Because it "colors" the sound! That's fine for an audiophile listening room, or a home theater, or even for a concert hall: those early reflections give the music "depth" and "width" and "ambiance".... but you do NOT want that in a control room! Control rooms must sound "accurate", not sound "nice". This often gets confused in control room design: people think that the room should make the music sound good, but it most definitely should not! It should make the music sound exactly the way it really does sound. Control rooms need to be "clinical". Surgical. Pristine. They must NEVER change the sound in any way, because the entire purpose of a control room is so you can hear the ix accurately, precisely as it really is. If the control room acoustics change that, so that bad music already sounds good, then you have a problem. In a control room, bad music must sound bad: no covering it up to sound "nice" or "warm" or "spacious". The control room should just "tell it like it is", warts and all.

The entire purpose of a control room is so that you can hear the speakers, only the speakers, and nothing but the speakers... and that you can hear them cleanly, accurately, with raw surgical precision. You are suppose to hear exactly what is on the track, not a warm, fuzzy, nice, happy, spacious version of it: you WANT to hear reality, exactly as it is... because that's what you need to hear, in order to mix correctly! You create the warmth and the spaciousness in the mix, not in the room. That's your job as a mix engineer: to take those clinically sterilized individual tracks, and mix them all so they sound pleasant, good, broad, mellow, and happy. But you cannot do that if the room itself already sounds pleasant, good, broad, mellow, and happy!!!! Because you won't know which part of that is in the room, and which part you are creating in your mix.

Thus, modern control room design philosophies aim to totally eliminate those strong early reflections, and only allow diffuse, delayed, low level reflections that arrive at your ears with delays greater than about 20 ms, so they don't mess up your brains ability to clearly hear the sound.

The entire basic philosophy of a control room is that it must tell you the cold, ugly, harsh truth: it must allow you to hear your tracks exactly as they are, in all their ugly glory, "warts and all"..., So you can then start working to get rid of those warts, and make it sound good. If you mix sounds good in a room that tells the pristine truth, then it will also sound good in any other room that DOES add its own character to the sound. ie, your mixes will "translate". On the flip side of the coin, if you mix in a bad room to make the track sound good, then you have undoubtedly compensate for the deficiencies of the room, in the mix. So when you play it in another room, then those compensations will be acutely audible, and your mix will not translate. That's what I do when I'm designing a control room: endevour to make it as neutral, transparent, and accurate as it can be.

Getting back to Jennifer: she wants her mixes to translate better so she doesn't have to work as hard to make them sound good in OTHER rooms: she wants fewer trips out to the car, living room, bedroom, i-phone, etc. to check how it sounds elsewhere. Because with an accurate room, she already knows that if it sounds good in there, it will sound even better elsewhere.

(Sorry for hijacking your thread, Jennifer, to rant about why accuracy is so important in a control room, and why you are doing what you are doing! But I thought it was a good opportunity to bring that up, in case some of your followers were wondering about your sanity...)

Soooo.... yes, it is important to get the room as symmetrical as you possibly can, because your ears are symmetrical! Your left ear needs to be able to hear the same acosutic "signature" of the room as your right ear, so you can hear both the sound stage and the frequency balance equally accurately with both ears, and make good mix decisions to produce mixes that are not "skewed" to one side or the other.

But millimeters? Is it really necessary worry about a few mm here or there? Do you really need to have the speakers within a couple of mm of being symmetric?

YES!

Think of it this way: the wavelength for a sound wave with a frequency of 1 kHz is about 34 cm. At 10 kHz it is 34mm. At 20 kHz (the upper limit of human hearing), it is just 17mm. So if the sound arriving at one of your ears is offset by, say, 34mm, then that's a an entire two wavelengths! at the high end, and one complete wave at 10 KHz! In other words, the left speaker is 720° out of phase with the right speaker for the higher of those two, and 360! for the lower... And for all other frequencies, it will be out of phase by differing amounts that depend only on the frequency... which implies that, where the difference is 180°, you wont hear that frequency at all, since it will cancel itself out... Ooops!

So there's a phasing issue here, which affects different frequencies in different ways... and messes up your perception of sound.

There's also the issue of those darned early-reflections again: if your speakers are not symmetrically laid out, the early reflections won't be symmetrical either, so one ear will get a different set than the other ear.. thus skewing your perception in other ways...

Conclusion: symmetry is critical, and the better you can get it, the easier it will be to mix accurately, producing clean mixes that sound great everywhere, and translate well.

Quick real-life story: about a year ago, I was approached by a small studio owner in the UK who had built his studio with some help from an "acoustician" friend... but he found he could not produce decent mixes in there at all! He hired me to fix that. I got him to analyze the room using REW (like this: How to calibrate and use REW to test and tune your room acoustics), and the data he sent me was really really ugly! Symmetry was way off, frequency response was all over the place, terrible early reflections, etc. So I re-designed the front end of his studio for him: mostly just improving symmetry, clarity, "tightness", and eliminating the early reflections (plus some stuff that needed doing on the rear wall). He built that, and then we started some precision tuning of his room, but that got sidelined after a while and we didn't complete it back then (mostly my fault... :( ) ... however, recently he send me a message that I'd like to quote, but removing identifying information: "I have just finished an album for a nine piece [genre] band, recorded live with just a few overdubs. I tentatively sent the first mixes out to all having mixed them unattended by the band. All nine have come back with "sounds awesome" and not a single change to be made. This is unheard of in my world!! ... What's changed ? ... It's down to the control room that you designed for me last year. Thank you so much Stuart I couldn't be happier.". That's a partial quote of what he wrote, selecting the pertinent bits. This is a very clear demonstration of why this stuff matters. Before, he could not mix at all in that room. Now he can produce mixes that translate perfectly and come back from his clients with zero edit requests! He did not change any gear in his studio: same mics, same speakers, same effects boxes, same DAW, same plugins. The ONLY thing that he changed, was the room acoustics. He's a member of the forum, and we are currently working on even higher precision tuning for his room, but I'm not going to identify him or his studio (unless he wants to pop in and tell his story.... that's up to him). The point I'm trying to make, is that this stuff IS important! It can very literally make or break a studio, as in this case. Just getting the front end symmetry precise, reducing early reflections, and cleaning up the overall acoustic response, can make a world of difference. (This is not an isolated case: it happens all the time. I just chose this one since it happened a few weeks ago, and is very relevant to what Jennifer is doing).

So: Jennifer is on the right track here, for sure! The case above was making a bad room good, and Jennifer is making a good room better. After she is done, I reckon we'll see similar messages from here! :)


[THREAD HIJACK MODE = "OFF"]


This created a problem for soffit design demonstrated by a draft design below. The first reflection point of the listening positing hits the door. Of course the soffit face on the left will be wider than the right, creating an asymmetrical response.
You can deal with the first-reflection point to a certain extent with treatment, but of course eliminating it would be better. But the asymmetric baffles on the soffits is a different thing: that's big: they do need to be symmetrical, or the frequency response won't be the same. Try to get them as symmetric as you can.

With the Genie clips and furring channel installed with just the original 12.5mm plasterboard layer, this is pretty much corrected. The door has been beefed up with ~41mm of MDF, almost doubling its mass and keeping it flush with the moved plasterboard. This means that first reflection point and soffit symmetry is within 4mm, not bad at all;
That's fine! 4mm is pretty darn good.

for when we add another layer of 16mm plasterboard to the left wall the soffit asymmetry returns, now a 12mm difference.
Use two layers of 6mm fiber-cement board: total thickness only 12mm, for the same mass as about 27mm of drywall...

If this asymmetry is significant,
Probably not too much of a deal for the first reflection points, but for the soffits, I would try to keep it tighter. A good goal would be to have the actual faces of the two soffits identical (in mirror image, of course), and also have them set up symmetrically i the room (speaker axes equidistant from side walls, mirror-imaged around the room center line), and to compensate for any gaps with miniature "wings" between each soffit and its associated side wall, where the "wing" is basically just a thin gap stuffed with insulation and a fabric front face: so "soft wing, not hard". It won't be entirely symmetric, but it's one of those many juggle balls: sometimes you have t compromise, and a "skinny soft wing" would be the least serious compromise.

Once again, sorry for the slightly off-topic rants that were not really pertinent at all to your questions, and which I'm pretty sure you already knew about anyway! That was mostly for the folks following your thread.. but maybe a little too much! :jammin: I do get carried way, occasionally :oops: :!: Sorry!

- Stuart -



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#62

Postby endorka » Tue, 2020-Mar-31, 08:13

Thank you Stuart, you are totally correct about my motivations, and please feel free to rant away to your heart's content!

Soundman2020 wrote:Source of the postOK, a few more twists that you could take into account as you work through the process of coming up with the perfect room design: If you need more mass in a thinner package, then consider fiber-cement board. The density is a bit more than twice that of drywall, so you can have the same mass in a thinner panel. Drywall density is around 680 kg/m3, fiber-cement around 1550 kg/m3.... Use two layers of 6mm fiber-cement board: total thickness only 12mm, for the same mass as about 27mm of drywall...


The fiber cement board seems very useful, I see Tom has used it in his build. It is commonly used for interiors as a tile backing, is porous, non combustible and can be installed direct on studs or existing plasterboard. It is available in smaller sheets e.g. 1200x600mm so the extra density is not such an impediment to lifting. Here's a few more twists concerning its use though - from the Green Glue website;

(1) "The Compound is used between two layers of building materials – typically drywall, OSB, MDF, cement board, or plywood, each at least 1/2 inch (12 mm) thick. One of the layers of which must allow moisture to pass through."

So it officially works with Green Glue, as long as 12mm or thicker is used. I could use the existing 12.5mm plasterboard layer with an additional 12mm layer of fibre cement on top of it, with Green Glue in between. Mass a little bit less than 12.5+16+16mm of plasterboard, but gives only 8mm difference in the left and right small wall widths. Somewhat better than 28mm with two extra layers of plasterboard.

(2) It's more than twice as dense, so presumably the backer rod & coloured caulk method used to seal edges of drywall installs will not be dense enough? Specialised cement is commonly used for typical installs, and presumably would be fine between sheets, as long as it penetrated to the full depth. But where a flexible join is required e.g. floor, corner or ceiling edges, or silencer sleeves, it surely wouldn't be appropriate?

(3) Gypsum plasterboard walls have something of a "bass trapping" effect. Is this also present with the cement fibre board? If not, more in room bass traps may be required.

....asymmetric baffles on the soffits is a different thing: that's big: they do need to be symmetrical, or the frequency response won't be the same. Try to get them as symmetric as you can... A good goal would be to have the actual faces of the two soffits identical (in mirror image, of course), and also have them set up symmetrically i the room (speaker axes equidistant from side walls, mirror-imaged around the room center line), and to compensate for any gaps with miniature "wings" between each soffit and its associated side wall, where the "wing" is basically just a thin gap stuffed with insulation and a fabric front face: so "soft wing, not hard". It won't be entirely symmetric, but it's one of those many juggle balls: sometimes you have t compromise, and a "skinny soft wing" would be the least serious compromise.


I think I understand, here are some simplified draft soffit cross sections. These are not the exact measurements but will hopefully serve to illustrate the concepts. On the soffits, hard surfaces are represented by wood texture, soft insulation by green. The acoustic axis of the speakers is the line coming out the front wooden baffle.

(1) If the short walls at the front are the same length we have the ideal scenario. Both soffit faces identical, both acoustic axes the same distance from side walls, both acoustic axes same distance from the room centre line;
Soffit Symmetry.png


(2) Now the right wall is 30mm longer than the left but we keep the soffit faces identical. Here's one of my interpretations of your solution Stuart. Put a 30mm soft wing between the soffit and side wall. Right acoustic axis is now 30mm away further from the right side wall, and the acoustic centre of both speakers no longer lines up with the room centre line;
Soffit Asymmetry - s2.png


(3) Another interpretation. Extend the insulation at the other side of the soffit to make up the 30mm difference. This way all the hard soffit surfaces remain symmetrical, the acoustic axis of both speakers are the same distance from their respective side walls and the acoustic centre of both speakers lines up with the room centre line. The right soffit will be visually larger by 30mm, but it's only the soft parts that are larger;
Soffit Asymmetry - s1.png


(3) Seems best, but with all that juggling who knows what I haven't thought of!

Thanks again!
Jennifer



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#63

Postby Soundman2020 » Tue, 2020-Mar-31, 13:07

It is commonly used for interiors as a tile backing, is porous, non combustible and can be installed direct on studs or existing plasterboard.
Right! It can also be used as exterior sheathing. I did that on my own house many years ago: we had a balcony on the second floor that we hardly every used, so I enclosed it and converted it into a home office, bathroom, storage, and mini lobby. I used fiber-cement board on the exterior, then added a thin layer of a special type of "graveled plaster-paint" finish, to math the rest of the house. Worked very well, and still holding up to the elements, years later.

So it officially works with Green Glue, as long as 12mm or thicker is used. I could use the existing 12.5mm plasterboard layer with an additional 12mm layer of fibre cement on top of it, with Green Glue in between.
You could, but I would recommend doing it the other way around: take off the drywall, put the fiber-cement board on the studs, then put the drywall back over that. It would be better to have the " layer which must allow moisture to pass through" facing towards the room, rather than towards the interior cavity of the wall. I presume that GG wants one porous layer to allow the moisture in the GG compound itself a way to get out, and if that's the case then you would not want to load up the wall cavity with moisture: better to have it "leaking" into the room air, where it can dissipate or be removed by the HVAC system... :)

(2) It's more than twice as dense, so presumably the backer rod & coloured caulk method used to seal edges of drywall installs will not be dense enough?
Caulk is more than twice the density of drywall, or a little bit higher than fiber-cement board. To be more exact, drywall is around 680 kg/m3, fiber-cement is around 1,500k g/m3, and caulk is around 1,600 kg/m3. So you are still good with "backer rod plus caulk", as long as you keep the backer rod thin, and over-fill with caulk. Or just use caulk, with no backer rod. Now, if you were going to do 12mm fiber-cement board (which is WAY heavy! Probably over-kill), I would suggest building up the caulk as two beads each 6mm (allowing the first bead to cure mostly before doing the second one), or maybe even 3 beads of 4mm. If you tried to do all 12mm at once, it would take forever to cure, and with some types of caulk, it could shrink, tear, or crack as it cures.

In similar vein, any time you are doing multiple layers of sheathing, only caulk one layer at a time, as soon as it is up, and before you put the next layer on. Don't try to do them all at once at the end! One layer at a time.

(3) Gypsum plasterboard walls have something of a "bass trapping" effect. Is this also present with the cement fibre board? If not, more in room bass traps may be required.
Ahh yes... Andre's famous "invisible alpha"... :) I'm sure Andre won't mid if I re-quote his original post on what that is all about:

Invisible Alpha© is an adjective I coined to make the use of sound absorption of walls and other partitions as integral part of the room acoustics design sound more fancy, mysterious, high tech and a great marketing/sales tool.

In its basic form Invisible Alpha© refers to the low frequency absorption component of a an apparent wall or other hidden absorber. To a layman, a wall is a wall. The layman does not recognize the acoustic effects of the surface. As an example, 100 mm of 703 or equivalent material against a wall with a ~80 Hz mam resonance would have great absorption down to ~63 Hz. The low end absorption is invisible to the lay person.

Another example of partion absorption not being visible is the panel absorbers pioneered by Hidley and championed by Newell. A quote from Newell in Recordng Studio Design is in post #42 in this thread. Even with panel absorbers 1 m deep membrane (Invisible Alpha©) absorbers are used the behind the panels for lowest frequency absorption.

Post #127 in this thread, is the first time I used Invisible Alpha©.
The Alpha comes from Greek letter used to denote some forms absorption of materials.

Some time after the I first used Invisible Alpha©, some discussions came about regarding getting even lower (frequency) absorption. I brought up the concept of using a triple leaf partition tuned to cover a wider deeper range of frequencies. Because the partition would use 2 air gaps (and I was having lots of with Invisible Alpha©), I decided to call that design strategy Invisible Alpha²©. In addition to appearing even more techy, fancy (dare I write it) sexy (well at least to acoustic geeks), and market savvy, it also challenges people to use character map even more. The dollar/euro/pound value is obvious if a cost analysis is done.

Invisible, sexy and cheap,
Andre
( That comes from his 2011 post on GS about that: https://www.gearslutz.com/board/studio- ... alpha.html )
Yes, it is a real thing: yes, you can use walls as part of your bass trapping strategy.... Yes, it should probably also work with fiber-cement board, but I'm not sure how you would figure that out. Hopefully Andre will see this post, and maybe chime in with more info on how that might work. Yes, Andre is the proud father of "Invisible Alpha", and the world's leading expert on the issue...

On the soffits, hard surfaces are represented by wood texture, soft insulation by green. The acoustic axis of the speakers is the line coming out the front wooden baffle.
OK. Is that to scale? Your speaker angles look a little steep to me. What toe-in are you using there? I'm sure you've seen the article I wrote about the "equilateral triangle" myth, so you know that it's fine to have angles that are not 30°... but your angles seem to be excessively steep, which has the effect of squishing up your sweet spot...

(1) If the short walls at the front are the same length we have the ideal scenario. Both soffit faces identical, both acoustic axes the same distance from side walls, both acoustic axes same distance from the room centre line;
That would, indeed, be ideal, if you can figure out a way to pull that off by varying the thickness of your wall sheathing.

(3) Another interpretation. Extend the insulation at the other side of the soffit to make up the 30mm difference. This way all the hard soffit surfaces remain symmetrical, the acoustic axis of both speakers are the same distance from their respective side walls and the acoustic centre of both speakers lines up with the room centre line. The right soffit will be visually larger by 30mm, but it's only the soft parts that are larger;
Exactly! That's the "lesser of two evils". Keeping the speaker axes and side walls symmetrical is more important that keeping the inner sides of the soffit symmetrical.

That said, I would put a lot more absorption in the sides of your soffits: make it thick. Better still, leave some of the side area open to the soffit interior, mostly above and below the actual speaker soffit region itself. You could also "rake back" the side panel of the actual speaker area (so it is perpendicular to the soffit face), leaving a wedge-shaped area for your absorption there, deeper at the back than the front. I often do that in a different way when the CR is small and there's a window at the front, to maximize visibility and minimize unwanted artifacts from the discontinuity in the front wall.

Another curve ball: If you don't need access to all of that glass, then you could even extend the soffit front baffles a bit: more area there is a good thing, if you can pull it off...

Not sure if I'm explaining any of that clearly!

(3) Seems best, but with all that juggling who knows what I haven't thought of!
:thu: Careful with that juggling! It can get nasty....
crazy-juggler-3-ENH-SML.jpg



- Stuart -



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#64

Postby endorka » Wed, 2020-Apr-01, 14:41

All understood, thank you. I'd have never thought of that for the reason for green glue requiring at least one porous exit, but it makes total sense right enough. If I can get away with the existing 12.5mm plasterboard and 6mm of cement board it'll be happy days for sure, as it brings the short front walls within 2mm of each other. My only concern is the green glue document stating a minimum of 12mm thickness for each board.

Ahh yes... Andre's famous "invisible alpha"... :) I'm sure Andre won't mid if I re-quote his original post on what that is all about:
...
Yes, it is a real thing: yes, you can use walls as part of your bass trapping strategy.... Yes, it should probably also work with fiber-cement board, but I'm not sure how you would figure that out. Hopefully Andre will see this post, and maybe chime in with more info on how that might work. Yes, Andre is the proud father of "Invisible Alpha", and the world's leading expert on the issue...

Fascinating! I hope he does. According to Gregwor's mass air mass transmission loss calculator these stud wall partitions have resonances around modal frequencies that smallish rooms are very prone to.

OK. Is that to scale? Your speaker angles look a little steep to me. What toe-in are you using there? I'm sure you've seen the article I wrote about the "equilateral triangle" myth, so you know that it's fine to have angles that are not 30°... but your angles seem to be excessively steep, which has the effect of squishing up your sweet spot...

Pretty close to scale, the toe-in is 45 degrees, it was another one of these compromises. If I keep the location of inside face of the soffits constant, the closer the toe in gets to 30 degrees, the further the listening position goes back into the room and out of the modal sweet spot, the soffit faces get smaller. At 45 degrees they are about 825mm across. My old monitor position was pretty close to this and I liked it, I don't mind the small sweet spot, and love the "widescreen presentation" but I know it's not ideal. My plan is to do your walking mic test in those positions and work with it for a bit before going with the design. Perhaps some improvements will be possible.

That said, I would put a lot more absorption in the sides of your soffits: make it thick. Better still, leave some of the side area open to the soffit interior, mostly above and below the actual speaker soffit region itself. You could also "rake back" the side panel of the actual speaker area (so it is perpendicular to the soffit face), leaving a wedge-shaped area for your absorption there, deeper at the back than the front. I often do that in a different way when the CR is small and there's a window at the front, to maximize visibility and minimize unwanted artifacts from the discontinuity in the front wall.

Makes total sense thank you. My only concern is that having a 90 degree angle there with the hard face will be turbulence, for want of a better word, or some sort of discontinuity. I think in my mind I had the notion of the ideal infinite baffle as being flat, and attempting to keep as close to that as possible. Very happy to have these doubts put to rest if unfounded, however!

The HVAC design has the silencer sleeves entering the room through the small wall at the rear of the soffits, so a 90 degree rake may not be possible, but I'm sure a smaller angle could be incorporated. That glass area definitely has some funky resonances in need taming.

The draft soffit design has some of the side and front area open to the inside that will be filled with insulation and covered in fabric. Front face is about 825mm across, and believe it or not, the proportions and vast majority of properties comply with your soffit design guidelines; quite a feat of juggling it was :-) You mentioned in a previous post that the studwork will have to be far chunkier, and various other revisions.
Studio Room 1 and 2 - soffits - ventilation v3.png


Another curve ball: If you don't need access to all of that glass, then you could even extend the soffit front baffles a bit: more area there is a good thing, if you can pull it off. Not sure if I'm explaining any of that clearly!

I know what you mean, and it would certainly ease the design constraints considerably. Access to the glass is required, the rightmost diagonal and vertical windows are doors to the balcony, required by building code for fire exit. There's that, and also, that large glass area with view is inspiring to musicians, and myself :oops: I think impinging on it might be, ah, visually sub optimal. I have a feeling I'm going to find a place in your "deaf architects" file with that statement :D

Cheers,
Jennifer



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#65

Postby endorka » Thu, 2020-May-07, 07:31

Just a small update. Due to the virus lockdown, I've had to put the HVAC plans on hold for the moment. Most of the tasks I'll be able to do myself, but there are a couple of parts that require professionals. I have some mixing and post production work to do in the meantime. When I've made a dent in that I'll finish the HVAC design so it's ready for implementation once lockdown restrictions are reduced.

Recent observations of note concern the transmission of sound from double bass. It's a surprising instrument in that regard, not particularly loud in the room it is in, yet the sound can carry to other rooms like anything! In all seriousness, I've recorded amplified lead guitarists here at ear bleeding volumes, and most of them are not audible in room 5, two floors below. Yet my plucked double bass was, to the point of distraction. Thankfully the acoustic isolation improvements have made a big improvement to this, and it's now possible to do quiet work and read in room 5 with double bass played in the studio.

I suspect the problem was twofold. Presumably the metal endpin on the instrument acts as a very effective transmitter of sound to the solid floor and therefore the structure of the building. I now perch myself and instrument on one of the 6x4' risers to reduce this.

Also note the sound transmission levels from the studio to the adjacent landing and stairwell are particularly poor at the fundamental frequencies of the low notes on a double bass, starting at 41Hz. There's a dip around double those frequencies too, right in the octaves / overtones of these notes. The double bass puts out a lot of energy there;
Landing before - after.png


The improvements made those areas a bit better, and that in combination with the riser has made a significant difference. Beefing up the studio / landing wall as discussed earlier should help a lot too.

Cheers!
Jennifer



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#66

Postby endorka » Tue, 2020-Jun-09, 19:17

It's time to address the matter of ventilation in room 1. Actually way over time - with all that south facing glass, it sometimes gets hot in there, even in a Scottish 'summer'. We've had a few days so far a little above 21°C outdoors. Inside room 1 it was 35°C. That's with the heat reflecting blinds fully closed, and no-one in the room.

Earlier in the thread, I noted that opening a couple of windows for a short time in those situations equalized the ambient outside and inside temperature. Even peak daytime temperature rarely gets above 21°C in Scotland, so simply exchanging inside air with outside will offer sufficient temperature reduction for the vast majority of days. An average temperature chart tells an even colder tale, LOL!
Capture.PNG


Of course studio windows cannot be open, so here is my best effort design for getting sufficient outside to inside air exchange with ventilation. If it offers sufficient temperature reduction that's great, but I'll design the the system to allow for additional fitting of a mini split system if it does not.

Requirements for highest demand heat and air exchange

The goal is to get 6 changes of air per hour from outdoors to indoors to bring the inside temperature close to outside ambient.

- Studio Room 1 volume is 31 cubic metres (1094 cubic feet)

- 6 air changes per hour gives 6564 ft3/hr or 109.4 cfm or 186 m3/h or 51.6667 l/s. From Rod Gervais' book, this is considerably more than enough for five active people to breathe.

- So the minimum cross sectional area of registers into Room 1 to maintain a velocity of less than 300 ft/m must be no less than 339 cm2 (CSA = CFM/300 or 109.4 divided by 300 = 0.365 ft2)

- According to Rod Gervais' book, the inlets from outside to the silencer should be no less than half this i.e. 170 cm2. 150 mm (6") diameter duct gives 177 cm2 which will work well.

Requirements for lowest demand heat and air exchange
If it's just me in the room in the middle of winter, then sufficient air exchange to breathe is all that is required. That amount is 15 cfm. The less heat taken outside, the better. So ideally the fan could be run at a slower speed to give this amount of flow. So fan will be running at 15/109.4 = 0.14 of maximum flow.

Silencer Design
In a post somewhere a while back Stuart said;
the design of those silencer boxes depends on the overall isolation design. You need to know how many decibels of isolation you need, which in HVAC terms is called "insertion loss", so you can build those boxes correctly. You also need that number to determine how many silencer boxes you need: for low to moderate isolation, you can get away with just one silencer in each duct, but for high levels of isolation you need two: one on each leaf penetration.


From room 1 to the roof eaves, for equivalent reduction of sound transmission to the rooms below the isolation should be similar to that of the eventual short Room 1 wall i.e. two layers of 15mm drywall.

The isolation to match from inside room 1 to the outside is the large double glazed window bay, which Velux claim is either "35 or 37 dB". With unfiltered pink noise in room 1 I measured a reduction of 32dB through the window to the balcony. Hopefully a single silencer box per duct system will approach this.

- Radius of duct = 7.5cm, duct cross section area is therefore 177 cm2
- Minimum cross section of silencer path should be at least double this, i.e. 354 cm2

- Two silencer boxes in eaves on either side of front of studio. Made of 36mm (2 x 18mm) layers of OSB3 (rated for potentially damp spaces), lined with 25mm of duct liner. The inner leaf of the walls at this point will be 2 layers of 15mm plasterboard.

From Gregwor's silencer design for 3 baffles, with X=20 cm, Z=18 (gives 360 cm2 cross section), 25mm duct lining, 36mm walls, silencer outer dimensions are;

Y = 597mm
X' = 1126mm
Z' = 302mm


Static pressure calculations

Silencer box flow calculations using the equivalent duct length method

Cross section area of silencer is 18cm*20cm = 360cm2
Equivalent diameter is 21.41cm = 8.43"

Equation for converting a sharp 90 degree bend into an equivalent length of straight duct is: Duct Diameter x 60

8.43” x 60 = 506” or 42’ for each 90 degree turn

x 8 for each silencer = 336 feet of straight duct

Using the engineeringtoolbox.com friction or head loss calculator this results in;

Friction Loss (inH2O): 0.0618
Friction Loss (inH2O/100 ft): 0.0184
Air velocity (ft/min): 282
Air velocity (ft/sec): 4.7


Giving a combined loss for all 2 silencers of .1236 (inH2O) or 30.8 pascals and apparently achieving an air velocity of 282 ft/min at the point it enters the inner plasterboard leaf.


Other frictional losses;

External louvres with insect screens - running at 60 l/s each loses 12.33 Pa. The system runs at 51.6 l/s so ~10 Pa each for a total of 20 Pa.

Provisional duct routing - minor loss coefficients:
3 x 90 degree smooth turns 0.25 = 0.75
4 x 45 degree smooth turns 0.05 = 0.2
total = 0.95

Speed of air in 150mm duct is 9.56 f/s or 2.91 m/s
Δpminor_loss = ( 0.95) (1.2 kg/m3) (2.91 m/s)^2 / 2
= .95*1.2*8.47 / 2
= 5 Pa

Estimate eventual 7m of round duct. Assume flex duct for all of at least initial system, so will be more than this depending on how stretched out I can make duct;
= 6 Pa

Total of 63Pa so far.

Friction loss for supply and return grilles and plenum boxes will have to be added to this too, but I am not 100% sure of the final implementation of this yet. I hope to determine a reasonable approximation for this and specify the fan accordingly.

More diagrams and details to follow...



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#67

Postby Starlight » Wed, 2020-Jun-10, 17:38

Hang on a minute, Jennifer. You mentioned using the ventilation to cool Room 1. That rang an alarm in my head.

I think there is a bit of confusion as to what piece of equipment normally does what job. Cooling is one of the four jobs (conditionings) of the AC - heating, cooling, dehumidifying and simply blowing otherwise unconditioned air. I say I think as I am by no means a master of HVAC and need Stuart to put us both on the right track (or just confirm that you are spot on, as you normally are). I got a bit bogged down by Chapter 7 in Rod's book as his example uses a ducted AC, so all the air jobs are handled by the one device.

Can I remind you of Stuart's topic Myth: "My studio does not need HVAC"? The finishing points in the conclusion are where it really gets interesting.

Calculate the volume of air in the room (multiply length x width x height), and assume you need to circulate that volume 6 times per hour (minimum, preferably 8 )

You went with 6/hr, as per Rod's advice. The circulation that is talked about is what the AC (AKA air handling unit) does, blowing that air around the room. I used to think it was the amount of fresh air the room needs pumped in every hour. Not so, it seems.

Of that circulating volume, you need to exhaust somewhere between 20% and 40% to the outside world, and replace it with the same volume of fresh air. The actual amount depends mostly on how many people are in the room, and the size of the room.

So we see that of the 186 cu.m/hr that you are looking to circulate in order to get 6 air changes per hour, only 20-40% needs to be fresh air. That will reduce the required volume and speed of air coming on through the ventilation system to 20-40% of your figures.

Whether you can do all the desired HVAC functions with only a ventilator, I suspect not.

Maybe I commented out of turn - if so, sorry, Jennifer - as I have not mastered this but if my understanding is right you won't have half the challenge you have set yourself. I am following your topic with interest and hope that Stuart can set the record straight.



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#68

Postby endorka » Wed, 2020-Jun-10, 18:26

No worries at all Starlight, thanks for posting, I am interested in hearing all comments.

You are correct, the plan is a bit of a mashup based on one simple observation: ambient outdoor temperature in Scotland very rarely gets above 21°C. So the requirement to make indoors air cooler than outdoors air is very unusual, and one of the reasons domestic AC is hardly ever installed in Scotland. On 99% of "hot" Scottish days all you need to get comfortable indoors is sufficient air exchange between the inside and outside.

Opening windows does the job, even in a room with south facing windows like this one, but of course that can't be done for studios. Instead the plan is to exchange inside/outside air via the usual studio ventilation methods with ducts, silencers and a fan. I uprated the air flow from "enough for people to breathe" to 6 room changes per hour to bring more colder air in and hotter air out, if that makes sense! I figured if 6x is good for AC, hopefully the effect will be similar. The goal is to equalize indoors and outdoors temperature as much as possible.

Most times of year cooling of indoors air isn't required, it's heating, and there are already radiators here. At these times it would be ideal to run the ventilation fan slower, at the 20-40% type rates you mention to allow breathing and keep as much heat as possible inside! A fan with variable speed control will be necessary.

My hope is that this system will cover all the ventilation and majority of temperature control situations. It won't directly control humidity like a proper AC unit does though. With variable airflow control though, I hope to avoid sudden swings in temperature and the condensation this causes. In a way it's like a very scaled up version of the fan based ventilation systems we have in kitchens and bathrooms here, and if these are designed and installed properly they are effective at controlling humidity.

It's a bit of a gamble, but the way I see it is this: it will definitely do the V in HVAC, and that is required anyway. I've designed the system so if the AC part is found wanting it will be possible to install a mini split at a later date to provide it. We had a bit of discussion about much earlier in this thread; viewtopic.php?p=37#p37

Cheers, and thanks again :-)
Jennifer



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#69

Postby endorka » Wed, 2020-Jun-17, 14:17

The design is nearly finished, I'm currently looking for a dust filter for the ventilation intake. Space is pretty tight so an inline box type looks useful.

There are various filter grades available, from G3 (for garages & factories) up to H13 for clean rooms etc. Are there any recommended types for a studio? The surrounding area has a lot of woodland and pretty clean air quality.

Thanks again!
Jennifer



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#70

Postby Starlight » Wed, 2020-Jun-17, 15:02

In my previous studio the big investment was the AC and the ventilator I just looked in the owner's manual and I see it came supplied with an EU-G3 filter and an EU-F7 is available as an option.

Here is a table, probably similar to whatever you found to learn about the different filter types, jennifer. The descriptions give me the impression that the purpose is more to do with what you are likely to have in the air outside that you do not want getting in, eg. pollen, car or paint fumes, evaporated chemicals, bacteria, smoke. The description by F7 would be a close-fit for a recording studio.



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#71

Postby endorka » Wed, 2020-Jun-17, 15:27

Thanks Lester, that table is exactly the one I found, LOL! Agreed about F7 looking ideal.

Cheers,
Jennifer



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#72

Postby endorka » Mon, 2020-Jun-22, 07:18

Interface to the great outdoors

Vents to the outside will be though the roof soffit, very useful as it avoids breaching the walls or the actual roof. The latter are serious undertakings with many potential complications and way beyond my capabilities. Soffit fitting is far simpler and cheaper.

I got the idea from an existing bathroom fan that vents to the roof soffit. A potential downside of this is damp air exiting the bathroom vent then going up into the roof cavity via the roof vents (the long narrow cutouts). There have been no adverse effects though and it's been this way for 15 years so I think the plan is sound. The area around the vent is very open, so I reckon any expelled air is carried away swiftly. The actual roof ventilation is also very effective, so any damp air getting in is presumably expelled in short order. Room 1 of the studio leads to the balcony, so is well placed to make use of this soffit.
Vent in roof soffit.jpg


The supply vent is on the left of the picture, going to an F7 rated inline filter box. Access for fitting replacement filter elements will be through the ceiling of room 4 below, so I'll have to install a small access panel. On the right is the return vent connected to an inline fan. After this supply and return go into silencers, then sleeves through the knee wall into the room proper.
Outside view - 1.png


Local building code mandates a gap of at least 50mm above objects in the eaves for roof ventilation, so the silencers will have to fit within that. The existing roof soffit vents must also be a certain size and/or percentage of the soffit area, so my plan is to leave them exactly as they are when fitting the room vents.
Outside view - 2.png


There's already a hatch from the landing area to the eaves, so fitting the return vent, ducting, motor and silencer will be relatively simply. The supply side will be a bit more of a squeeze, and the access panel from the ceiling below much needed;
Outside view - 3.png


Silencer Design

An imaginary Socratic Dialogue between Stuart and myself;

Q. Stuart from an earlier post - "the design of those silencer boxes depends on the overall isolation design. You need to know how many decibels of isolation you need, which in HVAC terms is called "insertion loss", so you can build those boxes correctly. You also need that number to determine how many silencer boxes you need: for low to moderate isolation, you can get away with just one silencer in each duct, but for high levels of isolation you need two: one on each leaf penetration."

So that's the general concept. And the decision of "one box or two", depends mainly on "The Number One Big Question": How much isolation do you need? If you are looking for 40-something dB of isolation then you'll likely be fine with just a single box. But if you are shooting for the rather high goal of 60- or even 70-something dB of isolation, then you really do need boxes on every penetration.


A. From studio to eaves, the isolation should be similar to that of the short wall i.e. two layers of 15mm drywall. So the silencer box walls should match this. Once in the eaves, the open soffit vents imply a ventilated deck, meaning not amazing isolation from there to outside. In number terms, the outside isolation to match is the large windowed expanse, which Velux claim is either 35 or 37 dB. Again, a single set of silencer boxes should do this. The inside isolation to match is 36 dB to the room below, and again a single set of silencers should suffice.

Since the eaves are a potentially damp place, the silencers will be made from OSB 3. The walls will be 36mm thick, and be built from two 18mm layers.
Silencer - exterior.png


As determined in one of the posts above, the radius of ducts in the studio is 7.5cm, cross section area 177 cm2. The minimum cross sectional area of the silencer path should be at least twice that i.e. 354 cm2

Gregwor's silencer design for 3 baffles with X=20 cm, Z=18 gives a 360 cm2 cross section. Accounting for 25mm duct lining, 36mm walls, the silencer outer dimensions are;

Y = 597mm
X' = 1126mm
Z' = 302mm

Duct lining not showing in picture;
Silencer - interior 1.png


The sleeve for penetrating the room inner leaf has inside dimensions of 200x200mm giving 400 cm2 cross section. Caulk and backer rod will decouple the sleeve from the room inner leaf.
Silencer - interior 2.png


The silencer will be located in the eaves, mounted on and partially between the joists.
Side elevation.png


I am concerned that having the bottom of the silencer in such close proximity to the ceiling below would lead to more sound getting into the room below. Does this fear have any foundation?

Since the silencer is doing the isolation work usually done by the knee wall, and the knee wall is decoupled from the floor joists, I also wondered if it would be useful to decouple the silencer from these joists? Perhaps this could be done with Genie Clips or similar?

Here's how the silencers go through the knee walls into room 1. Backer rod and caulk to isolate the sleeves from the walls. The low mounting is very useful here as these will eventually be concealed behind speaker soffits. It will allow mains cable runs below the sleeves, and above it signal cable runs to other rooms. High performance intumescent grilles will be fitted to preserve the fire resistant qualities of the knee walls. Unfortunately these reduce the free area of the sleeve from 400cm2 to 225cm2. The datasheet is thorough though, and they are at least reassuringly quiet and have a very low static pressure at the air flow rates in use.
Silencer sleeve into room - 1.png


Silencer sleeve into room - 2.png
Silencer sleeve into room - 3.png


I see this as the completion of phase 1. Due to the intumescent grilles the air velocity with 6 changes per hour at the registers is higher than the specified maximum of 300 ft/m. At lower rates this will be possible though. But nothing to worry about, it's hopefully a useful arrangement to build on, and if the room ever stops being a studio will make a fabulous domestic ventilation & cooling system. The room was way too hot even before it was a studio!

Phase 2 to follow...



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#73

Postby endorka » Mon, 2020-Jun-22, 08:11

Phase 2

This will be soon after phase 1 is finished and working properly. It's a simple method of getting better air circulation and distribution by extending the supply vent closer to the rear of the room. If ever a mini split is required, around this area would be a good place for it I think.

An MDF panel covers the face of the supply register. 150mm diameter acoustic flex duct is attached to a spigot on this panel. The 150mm flext duct eventually joins to a section of 200mm diameter flex about a metre long. From this supply air goes to the rear of the room. Cross sectional area of the 200mm duct is 314cm2, close to the ideal of 360cm2;
Phase 2 - ducting.png


I chose acoustic flex duct not for any isolation properties, but to stop it becoming a voice pipe for carrying sound from the rear of the room directly to the silencer. Drums are usually recorded near the rear of the room!

It all gets concealed behind bass traps, the current arrangement.
Phase 2 - bass traps.png


The theory is that cold supply air will drop down from the supply pipe to the floor, mixing nicely along the way, and be drawn across the room to the return register in the opposite corner. My hope is that on cold days, when the radiator is on, some cold air will end up close to the radiator where it can be heated and then convected around the room.

Phase 3 to follow...



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#74

Postby endorka » Mon, 2020-Jun-22, 08:34

Phase 3

This part will eventually be integrated into the "as yet to be finished" soffit design that will be something like this;
soffits 7.png


The idea is to attach larger registers to the existing silencer sleeves to slow air speed and also give another impedance change. Connection will be with backer rod and caulk to decouple them from the sleeves. Might as well make use of a bit of attenuation from them if it's there.
Phase 3 - rear view.png


Attachment to silencer sleeve with backer rod & caulk;
Phase 3 - inside box view.png


This is the return register, inner dimensions of 25x25cm giving 625cm2, air velocity of 163 f/m. The face will be behind fabric of the soffit.
Phase 3 - left view.png


The supply sleeve has a box of the same dimensions attached to it, then the 150mm flex hose as before to the rear of the room. I'll eventually design a better bass trap system at the rear of the room so have left this area open for development. If the 200mm diameter hose exit isn't quiet & slow enough I'll attach a wider diameter hose in the meantime.
Phase 3 - right view.png


Precise component list, facts and figures to follow...



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#75

Postby endorka » Mon, 2020-Jun-22, 09:15

Static Pressure Calculation

For the whole system, including phase 3;
BOM.PNG


Total static pressure at 186 m3/h (6 changes per hour) is 147 Pa.

The best inline fan I've come across was suggested by (I think!) John Steel on this forum. It's a TD-Silent 500/150, and is one of the few that provide properly measured acoustic data. I've attached the datasheet, and here's the performance graph from it. If my static pressure estimate is accurate the fan will be suitable at the low speed (LS) setting. If I've underestimated static pressure there is some headroom there at the high speed setting.
TD Silent 150 - pressure curves.PNG


Running the ventilation at 186 m3/h for 6 changes per hour is only really for when there are lots of people in there, and/or when the room is really hot. For lesser duties such as mixing with just myself in the room during winter, it will be sufficient to run it with just enough ventilation for one person to breathe. So a variable speed fan controller is required, and apparently a variac type is required. Lesser types will apparently cause electomagnetic and acoustic interference.

This one, the Sentera STR-1 at 1.5A, seems highly recommended;
https://www.amazon.co.uk/FANTRONIX-Vari ... B0055YOPT8

The soffit vents should have flyscreens. The amount of space in the soffits is limited though, so the maximum size I can fit is for 150mm duct, which of course has a lower free area. These are the ones I've found;

https://www.i-sells.co.uk/150mm-louvred ... reen-round

Free area is 115cm2 instead of 177cm2. Static pressure drop 12Pa, not bad at all. But of course air velocity & turbelence will be higher there than nominal. Do you think any sound from this will have been sufficiently attenuated by the time it's been through the filter, motor and silencers?

Something else that has occurred to me: Should I have a backdraft damper somewhere in this system, to prevent gusts of wind from outside blowing dust into the room? Presumably the filter on the supply side has this covered, but on return would it be required between the fan and return vent?

What a marathon, I think that's everything I can think of for the moment. Looking forward to hearing comments!

Thanks again, and cheers!

Jennifer
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