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

" They need about 15 Watts of the best amplification you can get your hands on."

" The Quads will play up to about 100 dB, which is much louder than I play music even when playing loudly. "

" The second downside is that they are a difficult load for the amplifier to drive. They are highly reactive loads (primarily capacitive). Their impedance drops as the frequency increases. This makes the Quad ESL a bad choice for single ended tube (SET) amplifiers. "

I think I can figure out why this guy isn't an authority, desperate or not.

All ESL panels I know of follow this descending impedance curve, which is a problem for a lot of amplifiers since most amplifier’s have rising impedance at the upper end of the frequency spectrum, resulting in an overall significant net loss of output.

This is in addition to current limiting, which thanks to music being bass heavy, is less of a concern.

Tube amplifiers rarely have the low output impedance (anywhere) that solid state amps do so they start at a disadvantage.

However this is all basic electrical / and voltage dividing theorems. The final choices about matching any given amp to any given speaker has to include the speaker’s acoustic output and room.

Given the impedance curves of the amps and speakers you can predict reliably that amp X’s electrical output will drop 6 dB at 20 kHz with a given speaker, but I can’t tell you if you’ll like it. :)

Best,


E

So this brings me full circle. I've seen speakers that are hard to drive at the top end, at the bottom and all across the spectrum.

The ESL speakers come by their low impedance and difficulties as do the full-range planar-magnetics (Apogee) via legitimate reasons. That is, the speaker technology itself poses challenges which the designers accept in exchange for other benefits. ESL's are essentially giant capacitors, no way to get around that.  The sacrifice is made to submit the amplifiers to brutal loads in exchange for having a large single driver driven across it's surface (how well ESL's actually do this is arguable, but not for here).

I think that with the worst of these panels, a lot of OK amps are going to perform quite a bit differently, which with "nice" speakers could perform nearly identically.

And  as I mentioned, some speakers are deliberately hard to drive in the bass, or use smaller-dual woofers which put a strain on amplifiers.  When I look at the impedance curves and read about reviewers talking about how "discerning" this speaker is, how easily it could tell the difference between a Boulder XYZ amp and their Onkyo receiver, well, duh. It was made that way.

But this discernment does not make either the amplifier or the speaker more musical. It's just more demanding.

Best,


E

And as I mentioned, some speakers are deliberately hard to drive in the bass, or use smaller-dual woofers which put a strain on amplifiers. When I look at the impedance curves and read about reviewers talking about how "discerning" this speaker is, how easily it could tell the difference between a Boulder XYZ amp and their Onkyo receiver, well, duh. It was made that way.

But this discernment does not make either the amplifier or the speaker more musical. It’s just more demanding.

Yes, I am very much in agreement, Erik. As I and some others (including Shadorne) have said in other threads here, the musical resolution of a component or system, and its ability to resolve differences between components, cables, or tweaks, are two different things. And generally speaking the correlation between the two, while certainly not zero, will be a loose one.

My perception has been that many audiophiles fail to recognize that point, as evidenced by how quick some are to allege lack of resolution (referring to musical resolution) as being the reason others may not hear differences when performing comparisons between various hardware.

Regards,
-- Al

They need about 15 Watts of the best amplification

The above quote is taken from the link Erik provided.

I've serviced the 15-watt tube amps that Quad made to go with the '57s; in a nutshell driving a 'difficult load' is something they can't/don't do. But they drive the Quads just fine.

When 15 watts is all that's needed, its not a hard load and no mistake :)

As Erik points out, the impedance curve is very typical of an ESL.

I suspect that what Shadorne calls 'difficult' (and for that matter the author at the link Erik provided) is the simple fact that solid state amps (even ones known for driving difficult loads) can't make as much power into the relatively high impedance that the Quad presents at low frequencies. So you might need a 60-watt solid state amp to make the sound pressure on the Quad that a 15-watt tube amp can. But it will still play it, and if one puts one's hand on the heatsinks of said solid state amp, it will be found that the heatsinks won't get all that warm, despite hours of operation (unless the amp is class A)!

IOW, the solid state amp isn't working that hard. Why? Its not a difficult load; the amp is never asked to make anywhere near the power of which its capable. The 'difficulty' might be that the Quad will easily reveal the shortcomings of any amp which is asked to play it; so to get the best out of this speaker, you need a good amp. But that amp does not need a lot of current capability, which is traditionally associated with driving 'difficult' loads. We have lots of customers with Quads and they usually use our smaller amps. Folks, 'small OTL' and 'the ability to drive difficult loads' are two concepts not normally found together :)

The simple fact is, this speaker can be driven by a variety of amps (including SETs) that are not known for being able to drive 'difficult' loads. I would not use an SET in this case simply because I don't know of 15-watt SETs  that can make the bandwidth that the Quads can, but if you have one, it will work fine.

This is an excellent example of how not all amps are the solution for all speakers!