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Post by highanddry on Mar 27, 2021 20:05:21 GMT
someone posted on another forum that 703 had changed and was no longer the best bass absorber. Is this true?
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Post by rock on Mar 28, 2021 19:56:15 GMT
I did not know it was changed but there are quite a few alternatives with varying but similar properties. Here is a list that was compiled some time ago but still seems to be quite useful when comparing insulation used for acoustics. www.bobgolds.com/AbsorptionCoefficients.htm
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Post by Hexspa on Mar 29, 2021 17:28:36 GMT
4" 703 is basically fully absorptive at 125Hz. Testing below this frequency is uncommon. However, the logic is that when you double the thickness, you double the octave effectiveness. Therefore, 8" 703 is an ideal absorber down to 62.5Hz. Absorption coefficients within 0.15 are basically the same so 0.85 is essentially 1.00 which is total absorption for the most part.
Ethan's tests have shown that the ideal deployment of absorption is in coverage in ft2. A fully-covered room with 4" will have shorter decay than half the room at 8". Even so, a fully-covered room with 8" will be better still; just more expensive. Aim for at least 15% coverage for the first critical point. You may need to add more coverage for additional points like theater seating, surround sound, or recording zones, etc.
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Deleted
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Posts: 0
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Post by Deleted on Mar 30, 2021 12:27:24 GMT
4" 703 is basically fully absorptive at 125Hz. Testing below this frequency is uncommon. However, the logic is that when you double the thickness, you double the octave effectiveness. Therefore, 8" 703 is an ideal absorber down to 62.5Hz. Absorption coefficients within 0.15 are basically the same so 0.85 is essentially 1.00 which is total absorption for the most part. Ethan's tests have shown that the ideal deployment of absorption is in coverage in ft2. A fully-covered room with 4" will have shorter decay than half the room at 8". Even so, a fully-covered room with 8" will be better still; just more expensive. Aim for at least 15% coverage for the first critical point. You may need to add more coverage for additional points like theater seating, surround sound, or recording zones, etc. No material (porous absorber) is "fully absorptive" at 125hz in thickness of 4inch...
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Post by Hexspa on Mar 30, 2021 22:24:34 GMT
703 plain, 4", On Wall: 0.84 absorption coefficient @ 125Hz. Per the link:
"1.00 = 100% absorbtion." [sic] "Differences in coefficients of less than 0.15 are not significant."
All I know is what they tell me.
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Post by highanddry on Apr 6, 2021 16:40:46 GMT
thanks for the input everyone. I am going to dismiss the idea that 703 is no longer good
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ths61
New Member
Posts: 22
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Post by ths61 on Jun 24, 2021 17:40:33 GMT
thanks for the input everyone. I am going to dismiss the idea that 703 is no longer good
FWIW, OC's new spec sheets shows 4" of 703 is now 0.51 (not 0.84) at 125Hz (new 705 is 0.60 @ 125Hz).
0.51 + 0.15 (variance) is still considerably less than what it used to be ([0.51 - 0.66] is well under 1.0). I believe the BobGold's numbers (0.84) are based on the original OC 70X formulations, not the current product offerings, thus obsolete for new material purchases.
The Rockwool Safe 'n' Sound Spec Sheet shows 6" of SNS is 1.11 @ 125Hz (which has a lower GFR than 703). According to BobGold's original 703 numbers, this would put 6" of SNS at the same performance of 6" of the original 703 @ 1.19 (applying the 0.15 variance logic).
I have heard test result values over 1.0 (i.e. over 100%) come from the way measurements are done. The absorption from the exposed sides are included into the face's surface area. (e.g. 4" thick panels would have an extra 8" when adding the sides to the face's surface area, 6" panels would have an extra 12" added to the face's surface area. Same goes for top and bottom edges). In short, total exposed surface area (face + 4 sides) is calculated as the face's surface area absorption which can create values over 1.0 or 100%.
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Post by Hexspa on Jun 25, 2021 21:30:45 GMT
Looks like only 703 unfaced changed. The rest are the same or within 0.15 difference. Bob still has the correct data for safe n' sound at 3" but doesn't list 6".
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