Semi-Rigid V's Polyester

cowanaudio · Post by **cowanaudio** » Thu Apr 22, 2004 10:58 am

G'day all

I just posted on the building materials forum about the high pricing of Semi-Rigid board in Australia. I'd like to know if polyester is a viable alternative? At 35Kg/M^3, it is around half the price. The NRC is around 1 for both products, and at 125Hz, both are around 0.45 I don't have any data lower than this freq for the polyester.

Thanks for any help you can offer.

William Cowan

AVare · Post by **AVare** » Thu Apr 22, 2004 1:47 pm

I'd like to know if polyester is a viable alternative? At 35Kg/M^3, it is around half the price. The NRC is around 1 for both products, and at 125Hz, both are around 0.45 I don't have any data lower than this freq for the polyester.

Can you give us some links to the polyester material so that we can look at the absorption coefficeints in detail?

BTW I just gave you a reply in the other forum.

cowanaudio · Post by **cowanaudio** » Thu Apr 22, 2004 4:19 pm

G'day again

The company in question, Nashco, doesn't appear to have a web page, but they faxed me some absorption info a while back.

The 50mm 35Kg/M^3 batts have the following figures:

125Hz..... 0.45
250Hz..... 0.85
500Hz..... 1.00
1KHz....... 0.95
2KHz....... 0.95
4KHz....... 1.00

NRC....... 0.94

Their acoustic polyester batts range from 25mm to 75mm thick and from 10Kg/M^3 to 70Kg/M^3, but not in all sizes. The 35Kg batts appear to offer the best absorbtion for the money.

I'd love to obtain some comparative figures for fiberglass and polyester for below 100Hz. Absorbtion above this frequency isn't too hard to achieve. I was very surprised to discover that the polyester is much cheaper than the glass fiber batts. I expected the opposite to be true. Polyester is certainly nicer to work with.

Application is a purpose built music room / HT.

Cheers

AVare · Post by **AVare** » Thu Apr 22, 2004 6:02 pm

What thickness is the material?! That affects absorption, especially at the low end significantly. My guess is 2" If it is, you can use that material like fiberglass of mineral wool at the same density. OC 703 is 3 pcf which is 48 kg/m^3.

I have some numbers below 125 Hz. You can find them in

http://www.musicplayer.com/ubb/ultimate ... 6;t=000146

Eric has posted a great analysis of thickness and density at

http://johnlsayers.com/phpBB2/viewtopic ... highlight=

The prices of various material types vary wildly from area to area. That is why most people say check the prices in your area.

I will try and get some info on the polyester material.

cowanaudio · Post by **cowanaudio** » Fri Apr 23, 2004 12:09 pm

G'day again

You are right, 2"/50mm is the thickness I am investigating.

You have put together a wealth of information in the first liked page.

That is a must keep!

I saw Eric's post the other day. What struck me as most interesting is the ability of an absorbant material to absorb significant amounts of sound even though it is significantly less that WL/4 thick.

I found out a little more info on the polyester batts. They are actually made by a NZ based company called Autex, who also have manufacturing plant here in Australia. They have some info here: http://www.autex.co.nz/insulation/aab.html
It appears 100mm thicknesses are available.

Cheers

AVare · Post by **AVare** » Fri Apr 23, 2004 9:49 pm

You have put together a wealth of information in the first liked page. That is a must keep!

Glad you found it of value. Most, if not all, of the information in that post is known by people involved in acoustics, but I had never seen one document to bring it all together. Especialy for people getting into acoustics.

Thanks for the link.