OC705 vs. OC703

[BoomieMCT]

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?

[bpape]

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

[Ethan Winer]

BoomieMCT wrote:

What am I missing here?

See this:

www.ethanwiner.com/density.html

--Ethan

[grn1969c10]

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?

[bpape]

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