Richard Clark $10,000 Amplifier Challenge - Why Couldn't Anyone Pass this Test??

I don't understand the comment re Melcher.  He is a neuropharmacologist.  Can you provide a citation to which of his publications you are thinking of??

Ampilfers need to have a low output impedance preferably far less than < 1ohm, otherwise they start to act like a tone control instead of being flat.

If an amplifier with high output impedance (>1ohm) were to drive these speakers there would be very little bass!! All you would get is upper-mids and highs that would fry your ears.
http://www.stereophile.com/images/1213Walexfig01.jpg

Cheers George

@georgehifi , that's correct! As I pointed out in the article, any time you mix equipment from the two technologies, the result is likely to have a tonal aberration.

The example you give is a good one, although 'fry your ears' is likely not what would happen on account of the higher impedance would result in low distortion from the amplifier. It just would not make the bass energy since designer is expecting 3 db more power output out of the amp in the bass region.

Another example is solid state driving an ESL- with the reduced impedance at high frequencies and the tendency for the load impedance to vary about 10:1 (IOW, if 10ohms at 50Hz, could be about 1 ohm at 20KHz) over its range, the result will also be too bright with not enough bass. The reason is that the impedance curve of the speaker is based on a capacitor and not a driver in a box, so the impedance curve is not also an efficiency curve.  This is quite unlike a driver in a box, where the resonance of the driver is represented by a peak in the impedance curve (IOW the impedance and efficiency curves are the same thing).

This is why the equipment matching conversation is still very much with us 5 decades on! Its also why of two amps on the bench that might measure perfectly flat to 100KHz, one might sound bright while the other does not. 

Its worth pointing out that if the designer of the speaker is expecting the amp to have a higher output impedance that the crossover will be designed differently as well. The fact that the source impedance of the amp can affect how the crossover works means that drivers might be operating outside of the area for which the designer intended! This is one of the reasons that horns got the reputation for being 'honky'.

Yes speakers manufactured back in the the old days that were "voiced" by manufacturers using tube amps with little to zero or very low damping factor amps should be used with the same with the same amps to get the frequency right as the manufacturer wanted you to hear.

But I know of no speakers for the last four to five decades that are voiced using low damping factor amps, maybe some horns or single driver Lowthers or similar.

For those that don’t know what amplifier output impedance or damping factor is
Low damping factor is high output impedance EG: more than .5ohm
High damping factor is low output impedance EG: Less than .5ohm

EG: for an amp to have a damping factor of 8 into a theoretical flat 8ohm speaker, the amp would have an output impedance of 1ohm,
If it had a damping factor of 16 the output impedance would be .5ohm
If it had a damping factor of 20 " " " " " " " .4ohm
If it had a damping factor of 100 " " " " " " " .08ohm
and so on.


Cheers George

Then to just complicate what I said above, the current output of an amp comes into as well, to keep the said control over the speaker.

Cheers George