sound transmission loss measurement

[dzhoucam]

I want to test the sound transmission loss of one new sandwich sheet material. I checked the ISO standard test (ISO 10534-2, ASTM C384-88, ASTM E1050-98)and almost all of them require special microphones (such as impedence tube or two microphone methods), which are quite expensive (perhaps 6000 Sterling pounds/per microphone?). Can anyone give me other idea which can measure the sound transmission loss easily with acceptable accurarcy? My background on acoustics is limited.

Thanks a lot.

 

[Highspeed]

All depends on what is "effective accuracy"
One method you can use for quick checks is use your computer sound card + download a sound analysis freeware/shareware and compare the two spectrums with and without your sandwich.
On top of that ASTM's & ISO are requiring a "room configuration" depending on your application (indoor outdoor, ....) and those are dealing with wall reflections/absorbtion ...
We are running our quick tests in our conference room (very quiet).
When going to the acoustic lab for official testing there is never more than 3dB's drift.
Good Luck

 

[dzhoucam]

Thanks a lot to Highspeed. The approach you said looks very interesting. Could you tell me more about this method?
I would like to know:

1. What kind of microphone or sensor do I need? Can I use the common microphone? I feel that the main cost in the measurement is microphone.

2. Could you tell me roughly the name of those analysis software? I only know Labview.

3. If possible, could you give me some related literature or web resource where I can find this approach. I checked a lot of books on sound transmission but most of them only mention the ISO or ASTM standard test method.

The intention of the experiment is to compare this sandwich sheet material with monolithic plate in order to show the advantage of this sandwich material in terms of sound transmission loss. So the accuracy in fact is not the most important thing.

Thanks a million!

 

[Highspeed]

If you use Labview, You can use it, but you need to develop your tool and that is time consuming (In Labview you have the vi's to run the sound card).In our lab that is our approach (16 bit DAC for free with the sound card)

CoolEdit was a software that used to have a limited trial version that you could use but now it's part of Adobe and I am not sure it's still available for download.
Another one named "spectrum analyser Pro" is available at

http://www.pas-product.com

Regarding mikes :
We have 2 (cheap) mikes: one is a classical good quality audio mike (30-50 €)
The other one is an electret mike with home made preamp
This one is made directive by beeing in the bottom of a thick aluminium tube (25cm long)

You can also find affordable sound level meters such as Roline RO-1350 (RadioSpares)
Good Luck