Build A Microphone Sensitivity Measurement Box

lotion16

Member
2020-02-26 8:03 am
Hi Good Morning, every one

I have a plan to build something and I think this plan have been done by someone, Since I don't know what are a better ways that I can do to get a result as I expected,

So the plan is, I would like to build a box to test microphone sensitivity, I've already tried to find out the method and all things I found was using anechonic chamber room, that was such a large room and I think it will spends a huge cost. So I decide to build a smaller one like a box with the size 70x30x30 cm.

Then the questions that I want to ask are, Is that possible to make anechonic chamber box like that, will the result far from an exact result? and any suggestion/advice how do I build anechoic box (DIY)?


thankyou for you kind reply and suggestion
best regards
 

PRR

Member
Paid Member
2003-06-12 7:04 pm
Maine USA
www.diyaudio.com
> anechonic chamber .... size 70x30x30 cm.

Sorry for the antique units.

So a foot square. Say 4 inches open in the middle. 4 inches of fuzz to absorb sound.

Fuzz does not absorb sound waves if the wavelength is much longer than the thickness of the fuzz.

That's why real anechoic chambers have fuzz-wedges a yard (meter) deep.

4 inches 10cm will absorb above about 800 Hz, but below 200Hz it will be a small hard box.

What are you doing for a speaker? Most speakers are not flat (not like a good microphone). Nearly all speakers are sensitive to the acoustic load they work into, and a 60L box is very much smaller than the usual room.

Acoustic measurements by Beranek, Leo Leroy
https://www.abdi-ecommerce10.com/asa/images/product/medium/0-88318-5903.pdf
Acoustic measurements : Beranek, Leo Leroy : Free Download, Borrow, and Streaming : Internet Archive
Acoustic Measurements by Leo Beranek - AbeBooks
Acoustical Measurements by Leo Beranek - AbeBooks
 

lotion16

Member
2020-02-26 8:03 am
thank you all for your quick and kind reply

@rayma

Thanky for your advice @rayma, now I also currently look for an anechoic chamber room to be rent for our project,
For microhone, nope, I do not design it by myself, I just want to test some available microphone in the market

@PRR

thank for your suggestion and explanation,
I think, the large size will be 2100 cm2, and the availbale space inside according to plan is 60 cm length and 20 cm wide since I would like to use foam with 5 cm of thickness.

@PRR, FYI the microphone that I test, will be used for capturing sound around low frequency approximately 10Hz till 200 Hz,
I would like to use a bluetooth speakers for my testing since I still try to find out the high quality speaker for testing.
 

PRR

Member
Paid Member
2003-06-12 7:04 pm
Maine USA
www.diyaudio.com
....I would like to use a bluetooth speakers....

a Sound Level meter calibrator is smaller than the meter.

For that frequency range, a standard anechoic chamber will be useless (much too small).
Loudspeakers will not go that low, either


Microphone measurement tends to depend a LOT on what you need to measure.

As Speeskater says and thosuk's link documents, a small hard sealed space can work below some frequency. This <400Hz plan looks simple and cheap and reproducable. Full-range calibrations need much smaller space, minimal volume between driver and microphone. An SPL meter calibrator is just a hole made to fit the microphone.

BlueTooth is "wireless wire". I don't see how that applies. "Bluetooth speaker" is any kind of speaker with a $5 BT module added.

Only special microphones go into subsonics. A sensitive microphone "must" have a bass roll-off: barometric pressure change, or being slammed in a car trunk/boot, would burst the diaphragm if there was no bass leak. The real sub-sonic mikes must be sealed before measurement and un-sealed (leaked) before storage or shipping.

Are you looking at windmills?