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

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

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 

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.

This is a common myth.

An amplifier can have a very low output impedance without having much ’current’.

Ralph you jumped the gun mate, read again, I never tied output impedance and current output together in the same sentence.

Cheers George

Also to add, an amplifier "with low output impedance", but with not much "current ability" like otl's, have no chance driving a pair of Wilson Alexia's and like, which drop to an EPDR of  .9ohm around 100hz (the power region) without serious problems.

Cheers George      

I was told by out 80+ year old Sydney Quad speaker restorer Otto Major
http://www.stereo.net.au/forums/uploads/monthly_12_2014/post-106213-0-29462600-1419899180.jpg
who was good friends with Peter Walker, that yes original Quad 57’s were voiced with early Quad prototype tube amps and also maybe Williamson’s?, with not much current ability or wattage and high’ish output impedance’s (low damping factor)

From what Otto told me the Quad 63’s was eventually released for sale in 1981 and were voiced around transistor amp/s of the time, and that the Quad 303 and later 405 amp was developed around it, much lower output impedance’s and higher damping factor and current drive than the tube amps were for the 57’s, I think they may have been Williamson’s.
http://www.oestex.com/tubes/WW12-1943-BPT.jpg
Cheers George