Originally Posted by 3ll3d00d
apologies if I missed this earlier in the thread but how are you measuring velocity here?
(I may have mentioned, if so, it is buried in this or some other thread..)
I made a velocity measurement device out of a retired lf driver, I had some laying around, destroyed 2, and now I have 2 nice velocity probes.
This velocity probe works like a velocity microphone for low frequencies, the theory behind this is well described in any electroacoustics textbook.
Any electroacostic transducer which is not mounted in a box, so that the front and rear is acoustically shorted, will work more or less good. Size should be as large as possible and still very small compared to the wavelengths one wishes to measure.
Such a device will measure velocity in the direction perpendicular to the diaphragm, acoustic velocity has direction as well as magnitude.
So, find an old retired bass driver, 6"-10" will do, I used a 10", it will be good for up to several hundred hz.
Connect it to a microphone input, measure something, see what happens.
This will not measure sound intensity, which is the vector product of velocity and pressure.
There are measurement devices available that may be suitable, just need to make sure they are usable at low frequencies, and they will most likely cost quite a bit more than the usual USB measurement microphone.
Such devices are usually intended for noise measurements.