Amp Riser Effectiveness

[endorka]

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";

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

[Soundman2020]

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!


- Stuart -

[endorka]

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...

Cheers,
Jennifer

[Soundman2020]

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

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.... )



- Stuart -

[endorka]

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

[Soundman2020]

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... ).


- Stuart -

[endorka]

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

[Soundman2020]

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!


- Stuart -

[endorka]

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

[Purelythemusic]

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...

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

Good to document your findings here, helps everyone!

[endorka]

A crate of green glue has arrived, time to get serious

I'll be building several risers based on Glenn Stanton's design: 2 layers of 18mm MDF topped with 1 layer of 18mm plywood.

- one 1800x1200mm (6x4') for general day to day use. Big enough to stand or sit on with an instrument e.g. double bass, cello, amps, thumpy foot musicians and singers. Small enough to stand on edge to make a gobo, or to move to another room if necessary.

- two 1200x600mm (4x2') for amp risers.

This sandwich sits on top of a layer of 50mm thick Knauf RS45 earthwool insulation, also now arrived.

I'll be putting 2 layers of green glue between the plywood and MDF. Here's a quote from Ted White on gearslutz, one of the original founders of Green Glue;

It's worthwhile to note that all things being equal, having three mass layers + 2 thin damping layers (1 tube per sheet) will be more damped than a system with two layers of mass and one thicker damping layer (2 tubes per sheet). Again, assuming same overall system mass and quantity of damping compound.

So that's good news. I wonder if having two "thicker" layers of green glue (actually the standard amount) would offer even more damping than two thin layers (each half the standard amount), or if it would be a diminishing return? Especially as reducing impact and structural noise transmission is the goal of the riser, there will of course be no effect on airborne noise transmission.

Cheers,
Jennifer

[Adhoc]

... snip ...

It's worthwhile to note that all things being equal, having three mass layers + 2 thin damping layers (1 tube per sheet) will be more damped than a system with two layers of mass and one thicker damping layer (2 tubes per sheet). Again, assuming same overall system mass and quantity of damping compound.

So that's good news. I wonder if having two "thicker" layers of green glue (actually the standard amount) would offer even more damping than two thin layers (each half the standard amount), or if it would be a diminishing return? Especially as reducing impact and structural noise transmission is the goal of the riser, there will of course be no effect on airborne noise transmission.

Cheers,
Jennifer

If you are going to make a CLD (Constrained Layer Damping) with 1 stiff sheet - 1 damping layer -1 stiff sheet; don't follow the good pizza recepie of "extra everything". You should be better off with a thin damping layer. As it is when the layer under strain and bending (shear) that it will work as intended. There will be less stain with a thick damping layer. If it is 1 stiff sheet + 1 layer of damping (like bitumen), then it is better with a thick damping layer, roughly the same as the stiff sheet.

I hope Stuart don't mind if I point to a post I made at another forum where CLDs have been discussed. It doesn't matter if it is loudspeaker boxes or walls/ floors, the principle would be the same in this case. Green Glue is softer than the DG-A2 as it is not a construction "goo" (not useable in fact for that purpose) and more meant for very low frequncies and large sheets like drywall sheets. https://www.diyaudio.com/forums/multi-w ... 60064.html

[Soundman2020]

I hope Stuart don't mind if I point to a post I made at another forum where CLDs have been discussed.

No problem!

And welcome to the forum too! It's good to have you here.

- Stuart -

[endorka]

If you are going to make a CLD (Constrained Layer Damping) with 1 stiff sheet - 1 damping layer -1 stiff sheet; don't follow the good pizza recepie of "extra everything". You should be better off with a thin damping layer. As it is when the layer under strain and bending (shear) that it will work as intended. There will be less stain with a thick damping layer. If it is 1 stiff sheet + 1 layer of damping (like bitumen), then it is better with a thick damping layer, roughly the same as the stiff sheet.

I hope Stuart don't mind if I point to a post I made at another forum where CLDs have been discussed. It doesn't matter if it is loudspeaker boxes or walls/ floors, the principle would be the same in this case. Green Glue is softer than the DG-A2 as it is not a construction "goo" (not useable in fact for that purpose) and more meant for very low frequncies and large sheets like drywall sheets. https://www.diyaudio.com/forums/multi-w ... 60064.html

Thanks for the info, that's good news, the Green Glue is expensive so needing less is a bonus

Thanks also for the link, a very interesting read.

Cheers,
Jennifer

[endorka]

To recap, here are details of the riser construction. Top layer is 18mm plywood, middle and bottom layers are 18mm MDF. Insulation layer is 50mm Knauf RS45 Earthwool. It's the same as Glenn's design, but with 2 thin green glue layers applied as per Ted's quote. The layers will be glued together with wood screws spaced 400mm apart from centres. This is the 1800x1200mm riser;

Height of edge trims will depend on deflection of riser when loaded;

Exploded view;

3mmx15mm trim of PVC solid bar or similar added around edge of top layer to ensure the edge trim does not come into contact with the layers below. If done in a contrasting colour to the plywood it will also make a nice "edge warning" strip near the perimeter.

Cloth added to cover the insulation, stapled to bottom layer.

Edge trims added.