Gas station without pumps

2016 August 19

Redoing impedance test for tiny loudspeaker

Filed under: Data acquisition,freshman design seminar — gasstationwithoutpumps @ 18:21
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In Ultrasonic rangefinder tests with tiny loudspeaker, I tested the 10mm CDM-10008 loudspeaker and found it ringing around 9.4kHz, but I reported

I don’t see any resonance around 9.4kHz in the impedance plot, though I admit not looking for narrow resonance peaks in that range.

Today I redid the impedance tests using a 10Ω sense resistor, so that I could use the same range for all voltage measurements, resulting in more correct impedance measurements.  I could definitely hear a resonance around 9.5kHz (and given my deafness at high frequencies, it must have been very loud indeed for me to hear it so clearly), so I looked for another peak in that neighborhood.  It is there and measurable, but not very prominent in the plot:

Because the second peak is on the sloping part of the plot and quite small, I had to model the loudspeaker with a j ω^α L semi-inductor to get a good fit.

Because the second peak is on the sloping part of the plot and quite small, I had to model the loudspeaker with a j ωα L semi-inductor to get a good fit.

I have not attempted to fit the data points past 200kHz, because I don’t believe that the multimeter I was using is really good at those frequencies.  The “corner frequency” I’m reporting around 100kHz is where the DC resistance is equal in magnitude to the impedance of the semi-inductor.

Given how small the peak is on the |Z| graph, but how loud the sound is around 9.5kHz, I probably need a different way of looking for resonances beyond the main one. I can’t rely on my ears for loudness at high frequencies, but perhaps I could use a microphone and record the amplitude it sees as a function of frequency.

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