Matching Power and Speakers -- Much Ado about Not-that-Much? (Tube amps and speakers)

I have his Nautilus. It drives both my Devore O/93's and Spendor D7.2's very well. I do have a small listening room. And after about six months of using it to drive the loudspeakers it has been relegated to headphone use.

The Nautilus is a beast of an amp build-wise. It weighs about as much as my 10x higher wattage ARC Ref 80S. I think what Justin is saying is that speaker driving power is much more complicated than watts. 

Does the Nautilus sound the same or similar to my more powerful tube amps (also have an ARC Ref 150 SE)? No. And the differences go beyond mere sonic signature. I will concede the low-end grunt of even moderately low bass goes up as I go from the Nautilus to the Ref 80S to the Ref 150 SE. The Nautilus on the other hand has a sonic purity thing going on that is not there with the higher wattage amps. 

If I'm understanding the upshot of what he's saying, it's that lower-power tube amps made with quality transformers (and well made generally) have a very good shot at doing an excellent job for a much wider range of speakers than is typically assumed in conversations audiophiles have.

The issue is deciBels. The ear hears on a logarithmic curve; deciBels are a logarithmic unit of volume. 3dB is barely perceptible to the ear in terms of volume increase but requires double the amplifier power. So the difference between 30 Watts and 300 Watts is only a doubling in the perceived sound pressure.

This is why if you need more than 100 Watts to make your speakers work, you'll probably need 600-800 Watts or more to get the sound pressure you're looking for without clipping the amp. If you need more power than that the speaker is really impractical or your room is really large.

OTOH we have SETs which are a unique phenomena. Because they use no feedback (and so are 10% distortion before clipping), if you want to get the most out of them, your speaker has to be so efficient that the amp is never asked to do more than about 20-25% of full power. At power levels above that the amp will make more higher ordered harmonics on transients, causing the amp to sound 'dynamic', since the ear uses those harmonic to sense sound pressure.

That makes SETs impractical on most loudspeakers and is why horns made a comeback in the 1990s. SET users get by with so little power because the amp can sound 'loud' when pushed, so the user tends to think its plenty of power. When using a cleaner amplifier the volume tends to go up... but if such a user goes from a 7 Watt SET to a 30 Watt PP amplifier, they may find themselves running the 30 Watt amp out of gas because they are trying to get the same 'loudness' as they got before, if they don't understand that the perception of 'loudness' was caused by distortion.

Mr. Weber is ignoring a significant swath of high end speakers that have low sensitivity and a difficult impedance curve. Wilsons and Thiels are two prime examples. In the more extreme cases the speakers also have phase issues which makes them even more difficult to drive. Anyone who reads Stereophile and pays attention to the sensitivity, impedance, and phase measurements is aware that many speakers require a robust amplifier to operate at their best.

In my case I have a pair of Thiel CS6 speakers driven by a Krell KSA 300S (2400 watts into 1 ohm) and it takes everything that amp can produce to drive my speakers to concert levels. Because of the punishing impedance curve (around 2 ohms for part of the audio band) a tube amp will act as an unintended tone control on these speakers.

It's interesting that high end speaker companies are still designing speakers that have low sensitivity and a low, variable, impedance curve. This apparently is a tradeoff that some speaker designers are willing to make to get the sound they are after. These speakers need a solid state amplifier that can double it's output as the impedance drops by half.

Mr. Weber designs tube amps that cannot run speakers like mine. Sure, they will sort of work but they will sound anemic and the frequency response of the speakers will not resemble what the designer intended. His statements are uninformed and obviously intended for people with little experience in matching amplifiers and speakers. As this subject comes up over and over again I am disappointed that people like Weber, who should know better, espouse this drivel.

@8th- note I suggest you listen to a bit more of the interview before judging him so harshly.

I do think audiophiles are taught to chase big amps far too much and you can get amazing results with some sweet small amps and a half-decent speaker.

There’s also cases of speakers rated for 4 ohms which are 2 ohm speakers and they don’t need power so much as current. You tend to get higher current with bigger amps (not universally true).

I’m thinking of models from older Legacy and the KEF Reference1 which I’ve recently seen measurements for and going "wow."  The current requirements of those speakers is just far above what a lightweight amp which otherwise would sound fabulous.

Take a CJ Classic 60.  Pair it with a Fritz speaker and it's going to sound fabulous.