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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2 Comments »

  1. […] I also measured a tiny 8Ω loudspeaker that I had bought to experiment with ultrasonics (see Redoing impedance test for tiny loudspeaker): […]

    Pingback by Loudspeaker impedance with Analog Discovery 2 | Gas station without pumps — 2016 December 13 @ 23:12 | Reply

  2. […] 1cm one that I have posted about before (Ultrasonic rangefinder tests with tiny loudspeaker and Redoing impedance test for tiny loudspeaker) and an 8Ω oval loudspeaker that we used to use in the class until Parts Express sold out of them […]

    Pingback by Changing the loudspeaker lab | Gas station without pumps — 2017 June 28 @ 21:38 | Reply


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