I got to thinking the other day... is it possible to do your own STC measurements of a wall? There are many published ratings done by certified labs for specific wall assemblies and those do a fantastic job of giving you an idea of what kind of performance to expect. But lab measurements only go so far. Those are ideal settings for one wall. When you build it on-site and then add doors and such and connect it to slabs and other walls and ceilings and on and on, then you'll have different performance. By how much?
I have been unable to find anything online that describes how to actually perform an STC measurement of your own wall or theater at home. This seems to be the exclusive domain of labs. Indeed, the STC curves may well be proprietary.
When did a little obstacle like that ever stop me!
The Theory
ASTM E413 lists a 1/3 octave range of 125Hz to 4000Hz as being important for sound transmission and concentrates on testing in that range. A test tone spanning those frequencies (pink noise, perhaps) is played at a specific noise level and the frequency response is captured on one side of the tested partition. I believe that the dB value at 16 specific frequencies is captured. The microphone is then placed on the other side of the tested partition and the noise band replayed.
The dB values at each measured frequency range are compared and the difference is extracted. The differences are graphed into a curve. The curve is then compared against a set of published STC curves. Whatever curve matches the closest to the actual tested results is considered the STC value of that partition.
DIY Style
Given that, how can I do the testing myself on my own theater? Here's my thoughts:
1. Setup a pink noise generator in the theater to play at a consistent level. It doesn't matter what that level is.
2. Place an omnidirectional microphone 1 meter from the wall and 1 meter high. I'll use a calibrated Dayton Audio UMM-6 microphone
3. Play the pink noise and capture the result using an RTA measurement in Room EQ Wizard. Export the results into tab-delimited text file.
4. Move the microphone to the other side of the wall and place it 1 meter on the opposite side and 1 meter high.
5. Replay the same pink noise and capture it using an RTA measurement. Export the results
6. Insert the results into a spreadsheet and get the difference between them
7. Enter the deltas in the following online STC calculator: http://www.diracdelta.co.uk/science/source/s/o/sound transmission class/source.html
I don't believe that I can get the actual STC curves since they are hidden behind a firewall. If those are freely available (legally), then let me know.
Reality Check
What do you'all think? Is this a valid test to do? Or am I missing something very fundamental that makes it utterly pointless and invalidates any results I do get?
I have been unable to find anything online that describes how to actually perform an STC measurement of your own wall or theater at home. This seems to be the exclusive domain of labs. Indeed, the STC curves may well be proprietary.
When did a little obstacle like that ever stop me!
The Theory
ASTM E413 lists a 1/3 octave range of 125Hz to 4000Hz as being important for sound transmission and concentrates on testing in that range. A test tone spanning those frequencies (pink noise, perhaps) is played at a specific noise level and the frequency response is captured on one side of the tested partition. I believe that the dB value at 16 specific frequencies is captured. The microphone is then placed on the other side of the tested partition and the noise band replayed.
The dB values at each measured frequency range are compared and the difference is extracted. The differences are graphed into a curve. The curve is then compared against a set of published STC curves. Whatever curve matches the closest to the actual tested results is considered the STC value of that partition.
DIY Style
Given that, how can I do the testing myself on my own theater? Here's my thoughts:
1. Setup a pink noise generator in the theater to play at a consistent level. It doesn't matter what that level is.
2. Place an omnidirectional microphone 1 meter from the wall and 1 meter high. I'll use a calibrated Dayton Audio UMM-6 microphone
3. Play the pink noise and capture the result using an RTA measurement in Room EQ Wizard. Export the results into tab-delimited text file.
4. Move the microphone to the other side of the wall and place it 1 meter on the opposite side and 1 meter high.
5. Replay the same pink noise and capture it using an RTA measurement. Export the results
6. Insert the results into a spreadsheet and get the difference between them
7. Enter the deltas in the following online STC calculator: http://www.diracdelta.co.uk/science/source/s/o/sound transmission class/source.html
I don't believe that I can get the actual STC curves since they are hidden behind a firewall. If those are freely available (legally), then let me know.
Reality Check
What do you'all think? Is this a valid test to do? Or am I missing something very fundamental that makes it utterly pointless and invalidates any results I do get?