From: Neil <picdude3@narwani.org>
To: Microcontroller discussion list - Public. <piclist@mit.edu>
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Date: Thu, 19 Mar 2020 06:59:34 -0700
Subject: Re: [EE] Measuring speaker impedance
Thread-Topic: [EE] Measuring speaker impedance
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On 3/19/2020 1:16 AM, James Cameron wrote:
> Problem foreseen is that the impedance you measure will then depend on
> a set of simultaneous frequencies rather than a signal of just one
> frequency, so using the impedance meaningfully is limited.

This I expected.  I was thinking I'd do a test with 2 frequencies and=20
compare impedances of each with impedance of both together.



> The other thing is that the starting position of the cone would
> matter; a low frequency signal within the mix of signals could cause
> the cone to be in a position that may beat with the sampling.  So
> despite doing it rapidly you could have the low frequency signal
> imposed on the results.

I think I partially understand this.  Is there a way to calculate/cancel=20
this out, given the audio signal measured from the output of the=20
amplifier vs. the same audio signal measured with a microphone?  Though=20
with a microphone, we'd have to ensure there's no other external noise=20
being picked up.



>
> On Thu, Mar 19, 2020 at 01:02:18AM -0400, Neil wrote:
>> Hi,
>>
>> I'm working on a project for a friend, which will measure speaker
>> impedance over a given frequency range.  I'm thinking I'd use a function
>> generator sweeping across frequency range, then measure current (prob
>> with a clamp sensor) and voltage across the speaker and do the math from
>> there.  No prob so far.
>>
>> But can how about doing this dynamically?  IE: play music and
>> dynamically figure out speaker impedance from there.  He believes
>> commercial devices do this.  So far, all I can think of is measuring the
>> voltage and current as before, but dynamically FFT-ing both and
>> (rapidly) doing the math from there.  Does this seem workable?
>>
>> Cheers,
>> -Neil.
>>
>>
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