Speaker Impedance Variation-A question

[Gandalph]

In looking at a number of designs of amplifier, I am surprised that there is no mention (as far as I can find) of the variation of impedance of the load to which it will be connected, i.e. the speaker.
When looking at commercial speakers I find that reviews give some information on the variation of ‘input’ impedance, usually the minimum impedance value, but usually with no reference to the frequency at which this occurs, nor to the type (inductive or capacitive).

The input devices used for audio are, in contrast, well characterized, the load impedance being specified, and the frequency characteristic being given; this normally being smooth over the audio range.

It would be interesting to ascertain the typical impedance characteristics for various speakers, and the conditions under which the deviations from the nominal value occur.
There was a thread back in 2003 in the Multi-Way Forum entitled "Speaker impedance not what it seems? " originated by annex666 which came some way to addressing this question, but did not go far enough to be of practical use.

Of interest would also be frequency / 'volume' characteristics of various types of music; this could influence the effect which impedance change causes - both theoretically and as perceived by the ear.



Gandalph.

[nigelwright7557]

I have a couple of bass speakers and the impedance varies wildly over the frequency spectrum.

There appears to be a high impedance at resonance which I would expect.

The quoted impedance seems to come around 150Hz then rises with frequency.

[Ola]

When The Audio Magazine was alive, there was a story about the influence of speakers' reactive impedance on amps' sound. It was a new thing then, magazines did not measure amp's output at various load reactive impedances.

Speaker influences amp through it's feedback cirquit and there were mesurements of some welding class power amps' (like Levinson and Threshold) output frequency response at various reactive loads. Result was not a straight line from 20 - 20 000 Hz and and fluctuation was surely big enough to be hearable for sound comparison at such a level of machinery.

Time ago I measured drivers' impedance at various signal levels. It may differ a lot from that standard input level, that's why many speakers change sound when input level changes.

[tiefbassuebertr]

Originally Posted by Gandalph

In looking at a number of designs of amplifier, I am surprised that there is no mention (as far as I can find) of the variation of impedance of the load to which it will be connected, i.e. the speaker.
When looking at commercial speakers I find that reviews give some information on the variation of ‘input’ impedance, usually the minimum impedance value, but usually with no reference to the frequency at which this occurs, nor to the type (inductive or capacitive).

The input devices used for audio are, in contrast, well characterized, the load impedance being specified, and the frequency characteristic being given; this normally being smooth over the audio range.

It would be interesting to ascertain the typical impedance characteristics for various speakers, and the conditions under which the deviations from the nominal value occur.
There was a thread back in 2003 in the Multi-Way Forum entitled "Speaker impedance not what it seems? " originated by annex666 which came some way to addressing this question, but did not go far enough to be of practical use.

Of interest would also be frequency / 'volume' characteristics of various types of music; this could influence the effect which impedance change causes - both theoretically and as perceived by the ear.
Gandalph.

Read this in "Electronics World:
The Audio power interface: Part 1 Douglas Sellf Sep 1997 p717
The Audio power interface: Part 2: cables Douglas Self Oct 1997
The Audio power interface: Part 3: speakers Douglas Self Nov 1997
I have found this titles about
Amplifier Articles in Electronics World & Elektor
also the topic "Output Stage Stability"
about
Elliott Sound Products - Audio Power Amplifier Design Guidelines

also helpful the Otala article "Intermodulation at the amplifier-loudspeaker interface"
are in the wireles world Nov 1980 - see attachement and ebay Item number: 220483311502 about
http://cgi.ebay.co.uk/Wireless-World...23141003r12585

by the thread
Bob Cordell Interview: Negative Feedback
you will find also some informations