Quick question

p with classic pole-splitting compensation.

frequencies) have impedance fluctuations that will hurt the sound, but hurt it less if the amplifier output Z is the same as speaker impedance (i.e. m aximum power transfer).

nce to be low, so that any variations in the impedance the loud-speaker hav e minimal influence on the current through it. There's an argument - not a good one - for making the output impedance of the amplifier negative, and n umerically equal to the resistive part of the loudspeaker's input impedance .

wer transfer" argument doesn't make sense for audio frequencies.

amplifier than a fully voltage-feedback'ed op amp. Six ohms is typical.

especially since pretty much every speaker and crossover made has been desi gned for voltage drive

-Lasse

Wrong. It's exactly as I said.

Correct. That's called "damping".

Sounds like an invitation for stability problems.

Nonsense. Classic power transfer error. When you can vary the _source_ impedance, the best source impedance is ZERO. When you're given a source impedance, the best _load_ impedance is equal to the source impedance.

Ding-dong ;-)

"Perhaps not" is the correct answer. ...Jim Thompson

No!

That idea was firmly knocked on the head by Voigt in the late 1920s, again by Alfie Collins (of STC) in the 1950s, again by various contributors to Wireless World in the 1960s and again many times since.

Why does nonsense like this keep cropping up?

So you're saying that if had an ideal opamp with two speakers in series, it would be a perfect audio amplifier. Nonsense.

"Maximum power transfer" only has meaning when one is trying to get the most power out of a non-ideal (non-zero output impedance) amplifier. ...and then you only deliver half the power to the load. If you have a known load, the maximum power is transferred when the driver has zero output impedance (100%).

In fact, a (slightly) negative output impedance amplifier sounds much better than zero, even.

I have also wondered about this too.

Some projects in the 1870s and 1880s dynamos (DC generators) were built with source resistance equal to the load resistance. Quite soon, it became clear that this does not make any sense and early commercial (Edison) dynamos had a low source resistance

The audiophool mentality... why do you think Monster Cable is such a success? ...Jim Thompson

How can you create a name for yourself if you agree with the facts? Slowman has made a career out of this. Well, until the last employer figured it out.

The current goes up, but negative Z's inspire chaos. ...Jim Thompson

HA! We've just seen four answers,

(1) low output impedance (2) match the speaker (3) high output impedance (current source) (4) complex conjugate of speaker impedance

For most of its range, a speaker is resistive in impedance (that 'resistance' is the energy-lost-to-sound-output component). Trust me, I've looked. So, (2) and (4) are about the same, until you hit a resonance (and one doesn't know the speaker's resonance character when designing the amplifier). I'm sticking with (2), because that keeps the power output (the resistive power output) nearly constant through frequency-dependent variance in Z_speaker. The 'maximum power transferred' implies d/dF (V_out * I_out) = 0 for that choice.

Thiele and Small made yet a fifth answer, that the drive impedance be negative, in order to undo the wiring resistance of the speakers for enhanced low frequency drive. There actually were motion-feedback amplified speakers made, that did that.

pAmp with classic pole-splitting compensation.

edance fluctuations that will hurt the sound, but hurt it less >>if the amp lifier output Z is the same as speaker impedance (i.e. maximum power transf er).

edance to be low, so that any variations in the impedance the >loud-speaker have minimal influence on the current through it.

of the amplifier negative, and numerically equal to the >resistive part of the loudspeaker's input impedance.

power transfer" argument doesn't make sense for audio frequencies.

nce' is the

and

he speaker's

power output)

'maximum power

ative,

frequency

did that.

which is really just variation (1) removing wire resistance to make it even lower impedance

good luck finding a speaker/cross-over designed for anything but (1)

-Lasse

Some people like the sound of a nice class-A, zero feedback, $3000 per channel,

I once (around age 15) built a transformerless class-A amplifier using FIVE 2A3's in parallel ;-) ...Jim Thompson

Given the parasitics, you probably wiped out TV reception on the whole block. Plus the plate impedance of one of those is about 600 ohms, it looks like, so your open-loop output resistance would have been about

Cheers

Phil Hobbs

Why would you think that? It's just a _great_big_ triode.

I don't remember what plate load I used. I do remember that I capacitively coupled to the speaker.

...Jim Thompson

If you include yourself.

(5) Zero ohms real - negative (of the speaker) imaginary

Wrong, as has been explained by several here.

Not only the wires.

As long as you can control (for) the load, it works just fine.

I've toyed with the idea to have the amplifier mounted to the speaker, thus short wiring and best damping factor.

Distribute speakers all over a wall and send differential signals via twisted pairs... maybe even current loop as the signal.

Negates Monster Cable >:-} ...Jim Thompson

;-)

Get with the 21st century. Go digital.

So does zip cord. ;-)