# OC705 vs. OC703



## BoomieMCT (Dec 11, 2006)

I often hear that OC705 is better for building bass traps. However every time I see a comparison of absorption characteristics OC703 seems to absorb more @ 125 Hz. 

Here is an example, ATS comparo

What am I missing here?


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## bpape (Sep 14, 2006)

125Hz performance doesn't map directly to making a good bass trap. Unfortunately, you can't really do standardized tests at 40-50Hz.

The other thing that nobody addresses is thickness. If you're limited to 4", then 705 is a better choice. If you can go 6", then 703 will work just as well and will cost you less.

Bryan


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## Ethan Winer (Jul 21, 2006)

BoomieMCT said:


> What am I missing here?


See this:

www.ethanwiner.com/density.html

--Ethan


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## grn1969c10 (Sep 18, 2008)

Is it OK to resurrect a really old thread? There may be updated information available somewhere, but I'm chasing rabbit trails with the search feature right now.

http://www.ethanwiner.com/density.html

Ethan touts reducing the Q as a positive benefit. This spreads an effect across a wider frequency range. Wouldn't increasing the Q (giving a peak narrower bandwidth with steeper slope instead) make it easier to accurately target with a narrower parametric EQ filter?


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## bpape (Sep 14, 2006)

If you want to do that, you have to start adding a membrane, calculating the specific resistance and flexibility of the membrane and a specific thickness of the 703/705, etc. 

As an example:

Coefficients at 125, 250, 400, 1k, 2k, and 4k for various thicknesses and densities.

1" 
703 FSK
0.18 *0.75* 0.58 *0.72* 0.62 0.35 

705 FSK
0.27 *0.66* 0.33 *0.66* 0.51 0.41 

2"
703 FSK
0.63 0.56 *0.95* 0.79 0.60 0.35

705 FSK
0.60 0.50 0.63 * 0.82* 0.45 0.34

3" 
703 FSK
*0.84 0.88 0.86* 0.71 0.52 0.26

705 FSK
*0.66* 0.46 0.47 0.40 0.52 0.31

Standard R-19 wall insulation ( around 1lb/cu ft density), paper faced. Paper facing the room
0.94 *1.33 * 1.02 0.71 0.56 0.39

Some of those will actually show humps below the standardized 125hz band.

Bryan


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