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Professor smith 25th July 2010 12:21 AM

speaker and amp distortion
A good speaker typically distorts up to 1% on average but can be much higher at lower frequencies and depending on the room. We might have >10% distortion under certain circumstances. Yet many amp designers speak about distortion profiles and so on at <0.1%. Arguably, in a hifi system the speaker makes the most audible difference to the listener, which is justifiable on the basis that the magnitude of distortion is higher and that frequency response can vary by a similarly large magnitude. Naturally we might ask what the significance is of 0.1% distortion in an amplifier if it's being distorted again by a factor of >10 by the speaker?

jcx 25th July 2010 02:14 AM

the order of the nonlinearity is of importance in determining the proliferation and level of InterModulation Distortion - higher order distortion is generally considered much more objectionable than just 2nd and 3rd

while there is no excuse today for such poor design there is a historical worry about zero crossing distortion in amplifiers - particularly low bias "Class B" outputs - where the amplifier's distortion may actually rise with decreasing signal level

Professor smith 25th July 2010 04:11 AM

One argument is that speakers don't produce significant levels of higher order harmonics. I would like to see some evidence of that.

It's interesting that we measure the distortion of an amplifier at its output and not via the output of a speaker. Why is that?

lineup 25th July 2010 05:03 AM

I agree with the Professor.
When today power amplifiers are dealing with THD 0.001 % levels
it is more a question of Loudspeaker distortion
if we want to improve sound quality. Substancially.

Jan Dupont 25th July 2010 05:29 AM

What about the fact that the music allready has been through 100 or 1000 circuits (recorcing, mixing and editing) before it even gets into your amplifier. All those circuits also adds distortion, that's passed on to the next circuits in line...........

jcx 25th July 2010 06:24 AM

yes to improve audio reproduction we should concentrate on speakers
look at Dr Geddes posts - having explored distortion audibility he considers speaker-room interaction, directivity control, frequency response, minimizing diffraction and high order propagation modes primary - and speaker driver distortion secondary

he doesn't worry about amps at all below a easily achieved threshold of "inaudibility"

he rates amp distortion unimportant as long as its low, and decreases as level decreases - demoing his (US$ 9K/pair) speakers with a Pioneer integrated amp

AndrewT 25th July 2010 04:35 PM

is speaker distortion dependent on level or frequency or temperature or even the room?

If it is level dependent then at what level is 1% or 0.1% distortion measured?
At what level would it reproduce with better than 0.01% distortion?

Professor smith 25th July 2010 04:37 PM

You're a clever man, you can find that out. The answer is here: View the 800 Diamond specifications at Bowers & Wilkins - The World's leading Hi Fi and Home Theatre Brand

jcx 25th July 2010 05:15 PM

Klippel GmbH: Introduction - app notes, technical papers and measurements on speaker distortion

5th element 25th July 2010 07:07 PM

One thing to bear in mind also, is that an amplifier will typically perform far worse into a real speaker load, then into the purely resistive load that most are tested under.

Granted this is also an aspect of design and an amplifier that's applicable to a given system should never clip, or it's distortion should always remain inaudible over the entire frequency range and under any dynamic situation it will ever be presented with.

This is one area that quite a lot of systems probably fall down under, but then you can always crank it up one step further, no matter how much power you've got. It might be hazardous to your hearing and the loudspeakers, but most people will turn it up beyond unreasonable at least a few times. Is clipping acceptable here? I'd prefer it not to be, but that isn't always possible.

As to Geddes comments on the importance of distortion, lets not forget that he is dealing with drive units and systems that have inherently low non linear distortion. He considers a driver that produces high distortion to be defective and one that should never be used. This doesn't mean that distortion isn't important, rather it is, but it's a factor that is easily controlled, within acceptable limits, on the performance of todays higher quality transducers.

This also doesn't have to cost a fortune, it just requires knowledge in the area and a good idea on how to maximise the performance of a given design.

I agree with him that the interaction of the loudspeakers within the room is the dominating factor with regards to sound quality and it is good to see that a few people are attempting to address this issue.

One thing perhaps to ask is, should an amplifier and loudspeaker really be considered a system as a whole? Or rather should we use a DSP before the amplifier to control the distortion profile of the music played through the loudspeakers?

Going to absolute limits you could design a system that actively introduces distortion within the electronic side of things that attempts to cancel out the distortion produced by the loudspeakers. Doing this would be no small task though.

I do remember planet10 once mentioning that the total distortion of a friends system was in fact lower with the high distortion SET driving the system, then with a low distortion amp. The SETs distortion was cancelling out the distortion produced by the loudspeaker.

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