Amps don't sound. Speakers do. In my opinion, an amplifier's performance is intertwined with the speaker or driver it is used with. An amp may be very linear with one speaker and be all over the place with another. If linearity is the goal find an amp that allows the speaker to behave linearly. It really is no biggie. It may or may not be easy but really, if that's the goal, that's all there is to it. Whether you actually like the result given that linearity is only a small part of qualitative assessment, is another matter altogether.
Which should be easily demonstrable and...well, I'm a bit shocked, frankly, that some of you guys just seem to just accept this as if it is no biggie. It strikes me as extremely problematic. Manufacturers have worked for decades to reduce distortion, drop noise floors, etc., knowing that once you actually hook their amps up to speakers all bets are off? I would think the best amp builders would be busting their patooties to solve this problem and tooting their horns, complete with charts and graphs and paragraphs on the back explaining each (forgive the 60s hippie reference) every time they made an improvement. One thing is for sure -- if it's frequency response and distortion spectrum, at least, and it's audible? It's measurable. Why would the better magazines not be doing these measurements when they review amps, across a range of speakers representing a range of loads, so they could make informed recommendations regarding how to best use the amps they rave about? If the XYZ Extraordinaire is clean, quiet and linear driving Magicos but struggles with the upper midrange, generating a fatiguing harshness when wired up to Revels, wouldn't that be critical information that would be part and parcel of reviewing? And wouldn't measuring, at least the basics of noise, FR, distortion spectra, across multiple loads be the very heart of creating system synergy?
I'm not sure I believe it. I know I don't want to. Something is terribly wrong with this picture.
Tim
If I can step in here, first, anyone interested in this subject should read this article:
http://www.atma-sphere.com/Resources/Paradigms_in_Amplifier_Design.php
In a nutshell, we have the issue of making the amp or speaker look good on paper as opposed to (or somewhat opposed to) sounding good. The two are not the same IOW. If you want the amp to follow human hearing rules, and do the things the ear is looking for in a good way, it does not follow that it will measure well as the things we measure don't have a lot to do with that.
I'll give you a great example. The ear hears harmonic distortion as tonality. In fact it may well favor distortion over actual frequency response. In that regard there is a tipping point. This is why one amp can sound bright and another won't and yet both measure flat on the bench. The bright one will have slightly more odd ordered harmonic distortion.
Taken to a more base level some audiophiles found that they prefer tubes. Over the decades, this resulted in tubes not going away. Since tubes can't double power as impedance is halved, some designers make speakers that don't demand that of the amp. Sometimes they make other demands. I'll give you two examples:
ESLs. Not so happy with transistors- with such they tend to make too much highs and not enough bass. This is because transistors double power as impedance is halved (which can work really well with a box speaker, where impedance peaks often represent resonance). ESLs have an impedance curve that is based on a capacitance rather than box resonance. So they really want
constant power rather than
constant voltage. They have a high impedance in the bass and a low impedance in the treble region. This makes it hard for a transistor amp to make power and at the same time makes it hard to not sound bright. OTOH a tube amp can make, in many cases, constant power over the impedance range. In the case of the Sound Lab this means that a 200 watt tube amp can easily keep up with a 600 watt transistor amp.
Box speaker. In this case the speaker is designed on Voltage rules. The crossover is supposed to keep highs out of the woofer by causing an increase in impedance at the out-of-band frequencies. However, a tube amp with a high output impedance is being used. The crossover is found to be ineffective- it is somehow passing information to the woofer that the woofer should not see. The result: colorations and extra energy in the midrange. This is caused by the fact that the voltage ruies for designing a crossover don't work with such amplifiers.
It is the conflict of these two design, test and measurement paradigms that we have the tubes/transistor debate and also the objectivist/subjectivist debate, and the topic of this thread, why some amps will have variable response on some speakers. You have to match amps and speakers of the same technology or you get colorations as I gave in the examples above. It would be nice if we could rely on one method to insure uniform response (that was the purpose of the Voltage Paradigm BTW) but the fact is that to get that uniform response a price is often paid, a sonic price. That is why the Power Paradigm is still around.
There is also a current drive model, but it never developed into a set of rules although people such as Nelson Pass do experiement with it. And for those who think I made some of this up, that is not the case. I simply created the outline of what is already there. If you want proof, take a look at this:
http://www.google.com/search?client=ubuntu&channel=fs&q=fisher+A-80+amplifier&ie=utf-8&oe=utf-8
Its a Google search, look at the third hit. Its a video of a Fisher A-80 amplifier, a veiw of the 'Z-Matic' knob, labeled 'Constant Voltage' at 7 o'clock, 'Constant Power' at noon and 'Constant Current' at 5 o'clock. IOW this has been going on for about 55 years. Its an inconvenient truth that the industry does not like to talk about (one which also costs audiophiles money over mis-matched components); the specs on paper are there to make the equipment look good, but our ears hear something else. This problem would go away if the market insisted on specs having something to do with human perceptual rules. Don't hold your breath.
