From: Matt Pobursky <piclist@mps-design.com>
To: Microcontroller discussion list - Public. <piclist@mit.edu>
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Date: Thu, 19 Mar 2020 07:06:23 -0700
Subject: Re: [EE] Measuring speaker impedance
Thread-Topic: [EE] Measuring speaker impedance
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Hi Neil,

I've been designing loudspeakers since the mid 80's and can hopefully
provide some advice from the experience I've had over the years.

Using a known frequency sweep and "doing the math" is how it's been done
pretty much since the beginning. It's how I started since professional
audio analyzers used to cost many $1000's 30 years ago.

Using a dynamic signal is problematic for a lot of reasons, many have tried
and few if any achieve results that are as accurate as a known sweep.

Depending what your friend's goals and objectives are would shape my advice
to you guys.

If you are wanting to accurately measure speaker drivers of known or
unknown specifications for speaker building, i.e. some number of drivers,
driver sorting/matching, parameter verification, etc. then I would highly
recommend a commercial device like:

https://www.parts-express.com/dayton-audio-dats-v3-computer-based-speaker-a=
udio-component-test-system--390-807#!

I have one, have used it extensively and it's fast, relatively cheap and
accurate. It's also very versatile and can measure a lot more than just a
single speaker driver. You'd be hard pressed to roll your own anything that
comes close for anywhere near the same money and especially time.

If you are mostly doing this as a learning experience then I'd recommend a
couple reference books:

I've been using this one since the 2nd or 3rd edition back in the 80's and
a great all around tutorial on how loudspeakers, drivers and crossovers
work.

https://www.parts-express.com/loudspeaker-design-cookbook-7th-edition-book-=
-500-035

Also a great technical reference, probably not for a beginner but written
by one of the industry giants (Joe D'Appolito) and full of great
information:

https://www.parts-express.com/testing-loudspeakers-book--500-030

Good luck. It's a deep rabbit hole once you go down it, I've done dozens of
designs and learn something new with each design! I've been working on the
design of some new speakers to add to my collection and have recently been
updating my design tools, technical information and component sources.
There's so much cool new stuff available I'm really impressed.

Matt Pobursky
Maximum Performance Systems

On Thu, 19 Mar 2020 01:02:18 -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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