[SpHEAR-devel] latest musings (PCB, new Octathingy, calibrationand more)

[Marc Lavallée]

Hi Fernando,

>> Because building an ambisonics microphone is a lot of work (even the 
>> ones from the SpHEAR project),
>
> Yup, it is a LOT of work... almost not worth it, ha ha :-)

It's worth it, because you are documenting your project and methods, 
with a free license. To my knowledge you're the only one doing it for 
the benefits of the greater good. So please, don't let us down! ;-)

> Hmmm, I guess it would be possible and better than nothing, but I'm 
> not sure how practical. After all, if you can measuring the individual 
> capsules you might as well measure the finished microphone and be done 
> with it :-) And as you point out the acoustic shadows of the capsule 
> holder, other capsules, the mount, etc, all affect the response of the 
> microphone and would be difficult (but not impossible) to simulate. 
> Aaron (Heller) has some matlab/octave code to simulate arbitrary 
> capsule arrays, but the simulation of the Octathingy, for example, and 
> the real thing as fabricated are different...
>
> Senheisser does that (AFAIK) with their Ambeo microphone, they do not 
> provide individualized calibrations, I presume they have the resources 
> to match the capsules (and/or not having a perfect result is good 
> enough)...

Aren't 4 calibrated capsules the same than 4 matched capsules? So If a 
simulation is impossible, measurement of one microphone minus the 
calibration profiles of the capsules would provide a generic calibration 
profile for all similar microphones made with capsules calibrated with 
the same reference microphone. Does it make sense? Am I missing 
something? Thinking about it, that's probably how the Twirling720 Lire 
was produced, and I suspect that its internal ARM chip is processing 
calibration of the capsules, while its (proprietary) software(s) and SDK 
are using a generic calibration profile.

> For a tetrahedral design you can get away with 8 measurements equally 
> spaced around the microphone in the horizontal plane, which is not too 
> bad.

Mmhh... I think I read that before... I'd really like to learn more and 
try! :-)

>> The devil is in the details (n'est-ce pas?).
>
> Indeed! A big part of the calibration is getting good measurements, 
> and things are not as easy as you would think (but not impossible). 
> I'm slowly learning...

We're all learning! I don't want to read again, on any forum or mailing 
list, that calibrating an ambisonics microphone is too difficult for 
ordinary humans.

Marc