Poor man microphone calibration/measurement cabinet

[PureBasic]

Hello folks,

So, I'm designing a measurement microphone that will be corrected digitally on a receiver board.

From what I've read, I believe I can forget about finding a one size fit all measurement electret capsule, as the good panasonic stuff is no longer produced. My biggest problem right now is to find a way to test and compare different electrets cap and driver circuits.

I could get in touch with an acoustic laboratory and send them prototypes to be measured, but I guess it would be less expensive to send them one commercial measurement mic and one calibrator, and ask them to measure those. I then would have a nice reference.

The thing I miss now is how the actual measurement would have to be made at home. I don't really need that cabinet to have a flat response as the prototype mic signal will always be compared to the calibrated mic. I still think that the flatter will be the better, just to put aside as much problems as possible from the start.

How would a good measurement chamber look? A CTP wood box lined with fiber wool and a speaker attached to the outside and a hole transmitting pressure to the inside? What kind of dimensions should this have? What kind of driver should be used? etc... I'm slowly finding some elements here and there but still don't have a strong idea about how this could be done. So if anyone already did such a thing I'm all hear.

 

[kingkorg]

I am not sure i get all the details regarding your project, but one advice i believe i can contribute with is not to mix different pattern capsule types in process off calibration or measurement.

So if you work in cardioid mode, make sure all the capsules involved are cardioid. Same goes for omni, etc.

I've been chasing my tail for years using calibrated omni mic to calibrate the system in order to measure cardioid, or f8 mic. You get all sorts of phasing issues even with ideal measuring environment.

Needles to say, make sure latency introduced by dsp does not interfere with phase, compared to reference setup.

 

[PureBasic]

Hi kinkorg,

Okay thanks. Yeah I'll only be working with magnitude after correction. So phase and latency are not that important.
Good point about the directivity. I guess I'll have other problems such as reflections and overall shape of the microphone also...

 

[doqmemory]

You will find some useful information at Henry Spragens' site http://www.audioimprov.com/AudioImprov/Welcome.html

 

[PureBasic]

Oh yeah that's some good information; thanks.
The results are quite decent given the kind of drivers he's using and the fact that so few of the environment parameters are controlled.

 

[abbey road d enfer]

You may want to check the micbuilders website. This has been discussed there. Check Leslie Watts and Ricardo (Richard Lee) posts.