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Acoustic and Electrical Impedance Relationship?

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KaphaSound View Drop Down
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    Posted: 27 August 2021 at 10:44pm
Posted in Newbie discussion for probably obvious reasons but is there a direct relationship between the acoustic and electrical load? For example if the acoustic impedance goes up does this get reflected somehow by the electrical impedance? A quick glance at some hornresp charts didn't seem to point out any obvious relationship. If there's any good reading on the subject I'm all ears!
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AndyWave View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote AndyWave Quote  Post ReplyReply Direct Link To This Post Posted: 29 August 2021 at 9:58pm
This is a tough one (at least for me), only complicated answers to this simple question.

In general, if acoustic load goes up, the electric impedance will rise also.

All the honours to Mr D.B. Keele.

As I'm not certain should I insert a direct link here, look for Keele Aes paper 1991-10 - Max Efficiency of Speakers.

Heavy maths and electrical vs mechanical circuit analogies involved. Norton/Thevenin circuit analysis needs to be familiar also.

This may help with one view about the subject.

-Andy




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Post Options Post Options   Thanks (0) Thanks(0)   Quote APC321 Quote  Post ReplyReply Direct Link To This Post Posted: 30 August 2021 at 3:52pm
I have copied a link below to a couple of pages from an old book that I have called "An Introduction to Loudspeakers and Enclosure Design" by V. Capel.

It says that there is a relationship between the physical excursion of the cone (acoustic impedence) and the back emf generated by the movement of the coil (electrical impedence).

The speaker driver and the box it is loaded into need to be considered together as a system (as in above for sealed / reflex boxes) to get meaningful results.

I agree that this is a very complicated topic.



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toastyghost View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote toastyghost Quote  Post ReplyReply Direct Link To This Post Posted: 30 August 2021 at 8:47pm
It’s a little hard to define without referring to a specific enclosure type, but for simplicity’s sake it’s easier to consider the sealed cabinet first.

The electrical load impedance curve reflects reactive components of the coupled dynamic transducer. In a sealed box, you’ll see a peak in the electrical impedance at the resonant frequency of the enclosure combined with the mass and compliance of the driver suspension.

Below this resonance, the electrical impedance is dominated by the reactance contribution from the stiffness of the combined driver and air load. Above the resonant peak, you see the inductive contribution of the moving mass component of the driver. Continuing up in frequency, the curve will trend toward the DC resistance of the driver, as the load becomes purely resistive. Going further, the curve will continue to rise due to the inductance of the voice coil, and some resistive loss from the suspension and motor assembly.

For other cabinet types, that add forms of resonator - Helmholtz for reflex loading, for example - you’ll see the contribution of these components appear in the electrical impedance too, giving the familiar second peak. Horn systems or bandpass systems tend to add a third peak. These are all caused by the same fundamental effects as for the sealed cabinet, although the component contributing the reactance, resistance, inductance or compliance will vary.

Unfortunately this is an area where there’s no ‘cheating’. It might suck to go back for electronics 101 - it certainly did for me last year - but it’ll put you in far better stead to read some books
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KaphaSound View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote KaphaSound Quote  Post ReplyReply Direct Link To This Post Posted: 31 August 2021 at 1:06am
Wow yea sounds like it’s time to get back to basics and do some more reading but thanks for pointing me in the right direction!
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