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Discussion Starter · #1 ·
I just received a sample booklet for GOM FR701 fabric and noticed that the NRC rating is 0.00 to 0.05. Presumably the 0.05 is at high frequencies at which point 5% of the sound hitting it will be absorbed. Absorption coefficients typically span the frequency range of 125 Hz to 4 kHz. If the NRC is 0.05 at 4 kHz, I can only imagine that it will be worse at even higher frequencies. I am trying to design my home theater so that it has a fairly even RT60 over the audible frequency range and was not planning on having to take the fabric into consideration. This has me questioning whether or not I want this fabric covering my walls and especially my speakers. The samples I received are too small to cover a speaker for checking its effect on high frequencies. Has anybody noticed any negative effect on the sound of their speakers after placing them behind this fabric?
 

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I tried my speakers both with and without fabric in front of them. I could tell no difference in sound by my own ear. I have a pretty good ear for detail...as Steve Bruzonsky will attest to. :D


I did remove the standard grill covers, before covering in FR701 fabric.
 

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I am also considering using the Guilford of Maine FR701 fabric for speaker grill cloth. I received a sample of the fabric and became concerned about using it for speaker grill cloth because of the relative thickness of the fabric. I called Guilford of Maine and they sent me their acoustic test results for this fabric. Listed below are the results where TL represents sound transmission loss in decibels (db) at various frequencies.


Frequency (Hz)____TL (db)

50______________0.5

63______________1.0

80______________0

100_____________0

125_____________0

160_____________0.5

200_____________0

250_____________0

315_____________0.5

400_____________0.5

500_____________0.5

630_____________0.5

800_____________0.5

1000____________0.5

1250____________0.5

1600____________0.5

2000____________0.5

2500____________1.0

3150____________1.0

4000____________1.0

5000____________1.0

6300____________1.0

8000____________1.0

10000___________1.5

12000___________1.5

16000___________2.0

20000___________2.0


I would have no concern using this fabric to cover acoustic panels but I am not so sure about using it for speaker grill cloth. We all spend good sums of money to optimize audio performance and I am not sure that covering speakers with a material that loses 1 to 1.5 decibels in the 2500 to 12000 Hz frequency range is an ideal solution. It appears by the data that this fabric is not 100% acoustically transparent. I lack knowledge about the noise decibel scale but I do know that it is a logarithmic scale and therefore a sound transmission loss of 1 to 1.5 decibels could possibly be significant. Hopefully someone else with more knowledge can chime in.
 

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Discussion Starter · #7 ·
Actually those sound transmission loss numbers look better than I would have suspected. In a typical room, I think that you could expect frequency response to easily vary by plus or minus 10 db. The transmission loss problem can be corrected through equalization. My mind is set, GOM here I come.


Scott
 

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I am building my HT based 90% on the fantastic advice present on this forum. I have not much to offer as a rookie...However...I am an audiologist, and hearing is my profession. The ability of an individual to hear a change of 1.0 dB is highly unusual and typically only seen in persons with quite significant hearing loss. Reading the stats on transmission loss of the 701 material leads me to believe that it is absolutely transparent relative to the ability of the human ear to perceive it.


Larry
 

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In ASTM testing, 1-2 dbSPL is statistically insignificant, considered outside the range of audibility, and, in several of their testing protocols, an acceptable error between tests of the same material.


In your own room, if you can hear (or measure) that difference, then you'd also have the equipment to EQ it out AND it is very likely that other peaks and dips exist within the room that are greater and not at all related to the fabric.


Again, get your favorite speaker manufacturer to provide you with the INDEPENDENT ASTM TL results of their own speaker grills. I think you'd be surprised (or shocked).
 

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Quote:
I would rather not bother silentsource since I have found a local source with a better price.
Scott, who is your local source? I'm in the Toronto Area and I would like to purchase my GOM North of the Border.


TIA!
 
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