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Measuring speaker element parameters

It's possible to get most of the Thiele-Small parameters from a loudspeaker by just accurately measuring the impedance versus frequency. If this is done twice, one with the driver in open air and one with an added (known) mass it should be fairly easy to calculate the fs, Vas and Qt.

What you need is a sine wave generator with reasonably low distortion (<1%), as flat frequency response as possible, and good, stable frequency. You'll need an AC voltmeter that is also flat over the indented range and has the needed sensitivity. A frequency counter is also useful, since the frequency calibration of most oscillators is pretty awful. You'll need an accurate means of measuring DC resistance as well. Add to that a precision 8-10 ohm resistor for calibration purposes, and a 1 kOhm resistor to turn your frequency generator into a virtual current source.

Here's how to proceed:

So, you have derived Fs, Res, Qms, Qes, Qts for the driver. You now have Fs, Re, Qms, Qes, Qts and Vas.

Information sources

The information in this article is mainly based on news articles from Dick Pierce posted to rec.audio.pro newsgroup at 1998.