Hi all,

My questions all relate to using Denim in place of Rigid Fiberglass for both mid/high frequency absorption and especially for corner bass traps. I really like the non-skin-irritating factor of the Denim option. Any thoughts or considerations would be appreciated!

A handful of starting questions for this thread:

1. How effective is Fluffy Cotton/Denim Insulation for Sound Absorption?

2. How does it compare to rigid fiberglass in terms of mass needed for the same effect?

3. Specifically, is 6inches of the fluffy cotton/denim as effective as 6inches of thick Rigid fiberglass for bass traps?

4. One of the main considerations I have in building the enclosure is going to be how to contain the fluffy cotton/denim. I'm thinking that a frame with some kind of trellis or grill might work well & fabric could go either over or under the "trellis".

1. Cotton products that are designed for use as acoustic absorbers work similarly to rigid fiberglass. I can't speak for a pile of shredded blue jeans, but that's probably okay too.

2. Similarly. The way to know for sure is to compare product specs, which are readily available.

3. Again yes, or at least close.

4. I can help with the theory, but I leave the DIY type details to you. I do know that cotton absorbers are very floppy, so you'll need some sort of frame.

--Ethan

Here are specs for a commercial cotton-based product called Quiet Batt.
This would be similar in form to traditional fiberglass batt insulation, but made from cotton fibers.
Product Data Sheet: http://www.soundprooffoam.com/pdf/Quiet-Batt-Insulation.pdf

Specs:
RANDOM SOUND ABSORPTION / NOISE REDUCTION
Freq. Hz 125 250 500 1000 2000 4000 NRC
R 13 0.39 0.86 0.99 0.92 0.96 1.01 0.95
R 19 0.60 1.08 1.02 0.96 1.02 1.01 1.00

Here's another similar product. Specs seem better, but are they realistic?
http://www.bondedlogic.com/documents/UltraTouch_broch.pdf
Sound Absorption was tested in accordance with ASTM E90-02, ASTM C423 (Type A mounting per ASTM E 795)
ABSORPTION COEFFICIENTS @ OCTAVE BAND FREQUENCIES (Hz)
R-VALUE THICKNESS (MM) 125 250 500 1,000 2,000 4,000 NRC
R-13 3.5” 89 0.95 1.3 1.19 1.08 1.02 1.0 1.15 NRC
R-19 5.5” 140 0.97 1.37 1.23 1.05 1.0 1.01 1.15 NRC

I have a similar question as I'm preparing to buy my treatment material. Are these numbers realistic? These are for 4" recycled cotton bass absorber panels.


Comparing to numbers from Ethan's page:

If I'm interpreting correctly and higher is better, these cotton products would perform better, at all frequencies, than OC 703, which seems to be the standard. I'd prefer to go with cotton in my small room than fiberglass, naturally (pun intended?) but I'm skeptical since all the pros seem to use OC 703 as the standard.

What am I missing? Are these numbers not realistic? Is there an issue with too much absorption in the mids? Is cotton just way more expensive than OC 703?

I found these here:

http://www.cascadeaudio.com/commercial_residential/cotton_bass_absorber.htm
SS-ACLF-424C
Acoustic Cotton Bass Absorber
SS-ACLF-424C cotton bass absorption panels are the absolute highest performing low frequency absorption available. Made from 100% Class A nonflammable material, SS-ACLF is at home behind screens, in pillars and in corners. They are also used behind triangle corner traps to increase low frequency absorption.

The SS-ACLF-424C panels work well because of the random thread length, diameter and orientation.

Size: 2' x 4'
Thickness: 4"
Density: 2 lbs ft²
Color: Charcoal

thanks,
..ant

Understand that the data from my site is for panels only two inches thick, while the cotton data you show is four inches thick. I doubt cotton absorbs appreciably more than rigid fiberglass, if it even absorbs more at all. Bottom line, all such materials are similar, especially once you get to four inches thick.

--Ethan

I think I will seriously consider cotton for superchunks-like corner bass traps and then rigid FG for mid/hi panels.

There's minimal handling and no cutting for the mid/hi panels, so not mso much concern for the fiberglass dust and splinters.

There's a lot more of that work with the corner traps and cotton would make handling much less of a concern. Cost is also pretty reasonable for cotton.

Thank you Ethan.

..ant