O.C. 703 Substitute?

[Ray Collins]

A friend of mine, who is a building contractor on the gulf coast, had lunch with me today. I asked if he would check with some of his HVAC subcontractors to see if they used OC 703 and if so could they give him the end pieces and/or scraps that they would other wise discard. He called me a few minutes ago and said that they don't use the OC 703 because of expense but did use a Johns Manville product called Linacoustic in the 1" thickness. I looked at it and have attached their web site. The subs brought him two large trash bags of it this afternoon. What do you think?

http://www.jm.com/insulation/performance_materials/products/AHS-329_linacoustic_rc.pdf

Ray

[ThomasW]

Sound absorption coefficient of that stuff is 0.08 @ 125 Hz for 1" material. OC 703 is 0.11 @ 125Hz for the same thickness.

So it appears all you'd need to do is use a little more of it to get the same effect.

[Ray Collins]

That is good news. The OC 703 is about $1.50 per square foot and the Johns Manville product is about 20 cents per square foot...of course free is ALWAYS better.
I assume one would remove the backing on one piece before combining it to double the thickness?

Ray

[Curt C]

I assume one would remove the backing on one piece before combining it to double the thickness?

Ray

Not necessarily. having the doubled backing sandwiched between would provide some visco-elastic damping at the expense of a slighly smaller effective enclosure volume. Depending on if the intent is absorption or damping, I'd think some experimentation would be in order...

Here's a link that lists absorption coeficients of both OC703 and The Linacoustic products, as well as numerous others. They look pretty similar in performance. Looks like a good product.

C

http://www.bobgolds.com/AbsorptionCoefficients.htm

[Dennis H]

In Bob Gold's absorption page, he says "Differences in coefficients of less than 0.15 are not significant." The low numbers look especially suspicious to me. I don't know why 705 would be so much worse than 703 and 701 at 125 unless it's a measurement glitch. Overall, the Linacoustic looks just as good as 703 to me. I think some of the pro theater builders over at AVS use it.

http://www.bobgolds.com/AbsorptionCoefficients.htm

Product thickness mounting density 125hz 250hz 500hz 1000hz 2000hz 4000hz NRC
701, plain 1" (25mm) on wall 1.5 pcf (24 kg/m3) 0.17 0.33 0.64 0.83 0.90 0.92 0.70
703, plain 1" (25mm) on wall 3.0 pcf (48 kg/m3) 0.11 0.28 0.68 0.90 0.93 0.96 0.70
705, plain 1" (25mm) on wall 6.0 pcf (96 kg/m3) 0.02 0.27 0.63 0.85 0.93 0.95 0.65
Linacoustic RC 1" (25mm)--------------------- 0.08 0.31 0.64 0.84 0.97 1.03 0.70

[gbegland]

Have you guys seen this stuff?

http://www.bondedlogic.com/ultratouch.htm

I just found out about it and can get a roll that is 16" wide for $71.00 plus shipping tax. The roll is just over 100sq. ft. Navigate to the tech specs menu and look at the brochure for the noise ratings.

It's a little thick @ 3.5, but very good noise reduction across the full measured spectrum.

Greg

[Dennis H]

That cotton stuff is almost as good as fiberglass. It's more expensive than the fluffy fiberglass (you need to contain loose fibers with cloth or whatever) but cheaper than the resin-coated stuff like 703 (no problem with loose fibers). Plain old fluffy fiberglass is still the best bang for the buck but it does have some installation problems.

[Ray Collins]

Curt C,
Refering to post #4: I intend to use Linacoustic to line my Statement CC build. Would sandwiching the backs together to get the needed 2" thickness reduce the volume to a discernable level? If it would the backing is easily removed.

Thanks,
Ray

The pieces I received are about two feet square so if this stuff performs well some of you may want to ask around for similar scraps. These pieces were pulled from the dumpster so it is not an imposition on the HVAC contractors.