Acoustical Cotton Pad Source/Price?

[tbryanh]

I am interested in using some Acoustical Cotton Pads around my isolation cabinet.

The price for a 2'x4' piece from American Micro Industries is about $60.00 - $65.00. http://order.americanmicroinc.com/cg...c/EA124C6.html

Since I need about 10 pieces, this is way too expensive.

Does anybody know of a better source?

[tbryanh]

Maybe carpet padding is an alternative. Anybody got any ideas on this also?

[tbryanh]

What about this stuff? http://www.greenbuildingsupply.com/u.../?objectID=406

[tbryanh]

It appears NRC ratings need to be evaluated.

The acoustical cotton is about 0.8, and the carpet pad can be as much as 0.25.

http://www.polyurethane.org/s_api/bi...5&DOC=FILE.PDF

[tbryanh]

Acoutical cotton is 6lb 2'x4' for $60.00.
This is about $7.50 per sq ft

Polyurethane carpet pad is 8lb 1'x9' for $3.30.
This is about $0.37 per sq ft

Cotton NRC is 0.80
Polyurethane NRC is about 0.25

0.75^5 = 0.24

This means that about 5 times as much polyurethane is needed to replace cotton.

$0.37 x 5 = $1.85

$1.85 is still much cheaper than $7.50.

It appears polyurethane beats cotton on price about 4 times over.


The remaining question is performance.

The low frequencies appear to be the big issue.

The question is what are the NRC ratings at a 100 hz?


I have not used cotton or polyurethane yet, but I have heard the cotten is really good at suppressing the lows. I wonder if polyurethane is as good?

[tbryanh]

I have heard that brick works the best, but I am thinking this might be a little difficult to mount to my IsoBox. Also, it tends to make the box hard to move.

[tbryanh]

Flat Polyurethane Foam

It looks like FLAT POLYURETHANE FOAM is good.
http://www.acousticalsolutions.com/d...tfoam_poly.asp

What about price?

[tbryanh]

Actually it appears that the FLAT POLYURETHANE FOAM does not do so well with the bass.

[tbryanh]

Here is some noise reduction info. Maybe brick isn't so good.

http://citysoundproofing.com/producttypes.html

[tbryanh]

How about fiberglass. I think it might be as good as cotton, but it is pretty nasty stuff. Its hard to get ratings at the bass frequencies, so it is hard to know in advance.

[Steve Conner]

Did you look at that acoustic damping material they sell to high-end car audio guys for soundproofing their cars? I believe it goes under the trade name "Dynamat" or "Brown Bread" or something similar. I think if you lined the walls of your cabinet with this stuff, and put fiberglass inside, it would soundproof pretty well.

If you think it's too expensive, there's always the ghetto version, a sandwich of sheetrock and carpet.

If you want to attenuate bass you should also consider sitting the cabinet on a big square of thick foam rubber. Bass is often transmitted by conduction through floors and walls, rather than through the air, so if you can break the join between the cabinet and the floor, it can help a lot.

[Earl Norton]

If this is for guitar (starts at 80 Hz) why consider bass?

[tbryanh]

Well, I got a referral from another group. It looks like cotton is the way to go. The place that sells it claims an NRC of 0.97 at 125hz. Thats almost total absorption. The prices seem reasona ble too.

http://sensiblesoundsolutions.com/pr...products_id=49
http://sensiblesoundsolutions.com/pr...products_id=32

[tbryanh]

NCR is the measure of absorption or reflection and is measured by lining the wall with the material and measuring the amount of reflection.

NRC = 0 means complete reflection
NRC = 1 means complete absorption

Since the cotton has NRC = 0.97, I was thinking a single thickness would isolate my cabinet, but it appears I need double thickness.

It appears that when measuring reflection, the sound travels through the cotten twice. It travels through the cotton, reflects off the wall and travels through the cotten a second time in the opposite direction.

In my situation, I am trying to isolate my cabinet. The sound needs to travel through two thicknesses to be reduced to 3%.

[Steve Conner]

You do know that a reduction to 3% is only 15dB of attenuation, right?