Amp Riser Effectiveness

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endorka
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Amp Riser Effectiveness

Postby endorka » Wed, 2019-Sep-25, 08:58

I was doing some sound transmission measurements around my studio yesterday, and as a small aside decided to measure the effectiveness of this "amp riser in progress";

amp riser - small.jpg


It's 1200 x 600 mm, and is a reduced version of Glenn Stanton's drum riser design. Top layer is 18mm plywood, bottom two layers are each 18mm MDF. I've not screwed them together yet. They are currently "floating" on two offcuts of 100mm thick Rockwool RW5. The design calls for a uniform 1200 x 600 mm layer of OC703 or similar, which I'll get next time I put in a big order for mineral wool.

The riser has been stunningly effective in reducing the vibration & rumble from a floor fan to the room below - putting the fan on a chair predictably achieved nothing - so I thought it would be interesting to see how it performed on a bass amp. For the actual test I had the amp & riser in the middle of the room. Decibel meter in the room below at seated ear height, 120cm from floor.

Pink noise was put through the bass amp reading 105 dB (C weighted slow) just over a meter from the speaker. It was excruciating in there, I tell you.

With the amp directly on the floor, noise in the room below was 76 dB.
With the amp on the riser, noise in the room below was 73 dB.

A reduction of 3 dB, not bad at all for a few bits of wood and some offcuts. It will be interesting to see if any improvements are made by screwing the panels together and having it on the proper sized absorbent pad.

Cheers,
Jennifer
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Re: Amp Riser Effectiveness

Postby Soundman2020 » Wed, 2019-Sep-25, 13:49

That's great! It's always good when practical implementations work like theory says they should.... :)

If you have other types of insulation, other than RW5, it would be interesting to see what effect they have. If you feel like experimenting, you could even try some of the "myths, legends, and old-wives-tales", such as carpet, towels, blankets, and tennis balls (!) You might be able to lay to rest some of those... or perhaps even surprisingly show that they do work!


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Re: Amp Riser Effectiveness

Postby endorka » Wed, 2019-Sep-25, 20:51

For sure, I'll try some other things out when I get the proper insulation for it. I'll start saving the egg cartons now, and how about that giant bubblewrap over there I was going to throw in the bin... :D

Cheers,
Jennifer

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Re: Amp Riser Effectiveness

Postby Soundman2020 » Wed, 2019-Sep-25, 23:34

Oh yeah! Egg cartons... Darn it! ... I completely forgot about those... :) :shot:

Of course, what will REALLY make a big difference, is using some of that special US$ 10,000 per meter cable, to hook up your speakers.... That stuff is incredible! (... said no sane person, ever.... :) )

:D

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Re: Amp Riser Effectiveness

Postby endorka » Fri, 2019-Sep-27, 05:10

:-)

The more I think about it, the better the 3 dB reduction from the riser seems. Presumably the only sound transmission the riser can affect is that done via direct coupling to the solid structure and components of the house. It will have no effect on sound transmission through other means - such as air, flanking and so on.

So if these other ways are staying the same, and the overall reduction was 3 dB, it means there was a greater than 3 dB reduction in the structural transmission, right?

This would explain why it reduced the sound transmission from the floor standing fan to the room below more than 3 dB. A far greater proportion of the sound transmission in that case was due to direct vibration.

No doubt obvious to an experienced acoustician, but it took a moment for the light bulb to light up in my brain :-)

Cheers!
Jennifer

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Re: Amp Riser Effectiveness

Postby Soundman2020 » Sat, 2019-Sep-28, 22:26

That sounds about right to me, Jennifer. Also, the fan might have been noisy mostly at higher frequencies, where your make-shift riser was more effective than just 3 dB, while the amp was putting out more energy down low, where the riser wasn't so effective. Using a lighter insulation might have a greater effect on the amp as well. (OR tennis balls... :) ).


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Re: Amp Riser Effectiveness

Postby endorka » Thu, 2019-Oct-10, 07:57

In his drum riser design, Glenn Stanton mentions gluing and screwing the layers together. He didn't specify a type of glue though, so I'm wondering if something with viscoelastic properties like Green Glue is required? Apparently its effects give more isolation than normal glue (or caulk?), which just combines everything into a single mass.

Green glue certainly seems beneficial on multiple layers of plasterboard.

Cheers,
Jennifer

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Re: Amp Riser Effectiveness

Postby Soundman2020 » Thu, 2019-Oct-10, 17:54

I think Glenn was just referring to ordinary construction glue, or wood glue, basically just to keep the layers firmly together, but to my way of thinking, it makes sense to do it with Green Glue. It's certainly worth a try! It can't do any harm, so I say: Go for it!


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Re: Amp Riser Effectiveness

Postby endorka » Fri, 2019-Oct-11, 05:20

Good stuff, when the time comes I'll test it compared with just having them screwed together, and the comedy options too :-) Cheers, Jennifer

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Re: Amp Riser Effectiveness

Postby Purelythemusic » Sun, 2019-Oct-13, 18:01

endorka wrote:For sure, I'll try some other things out when I get the proper insulation for it. I'll start saving the egg cartons now, and how about that giant bubblewrap over there I was going to throw in the bin... :D

Cheers,
Jennifer


I literally had a conversation the other week with one of the grab wagon guys about his mate using egg cartons all over his music room :shock:

Good to document your findings here, helps everyone!


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