Do amps have a sweet spot?

06-15-13: David12
To change the subject, do you think different amp technologies, or circuits, have a sweet spot in terms of rated output?

I'd be hesitant to generalize, David, at least without having a very large empirical database, that would most likely be impractical to compile. There are simply too many variables involved in the performance of different designs to allow meaningful generalizations to be inferred from a limited set of experiences, IMO. And if any general tendencies were identified, there would undoubtedly be many exceptions to the rule.

Best regards,
-- Al

The increase in SPL by increasing the voltage by 3 dB will always be less than 3 dB due to the speaker not being 100% efficient (it has losses).

If the speaker is being operated at volume levels that are not high enough to cause it to behave in a significantly non-linear manner (e.g., for "thermal compression" to become significant), then 3 db more in will result in very close to 3 db more out, as the % efficiency will be the same at both power levels.

On the other hand, see this post by Duke of Audiokinesis, about thermal compression.

Regarding Bombaywalla's comment about 50W vs. 100W, I believe he is simply referring to the fact that different 100W amps may differ from each other, both subjectively and objectively, in terms of their maximum volume capability with a given speaker load. Same goes for two different 50W amps. Obviously there are many possible reasons for that, including the ones he mentioned as well as the distortion characteristics of the particular amps at various power levels, differences in dynamic headroom, etc.

As far as the OP's question is concerned, yes amplifiers can have "sweet spots," but as others have mentioned there are a lot of other variables that may be involved, including the behavior of the speakers at different volume levels, the Fletcher-Munson effect, amplifier-speaker interactions, and acoustical differences between your listening room and the shop at which you listened to the speakers. Or perhaps the problem is simply that capacitors in the Aragon have degraded over time, and need to be replaced. I don't see a path forward at this point that wouldn't be somewhat hit or miss.

Regards,
-- Al

06-16-13: Csontos
"So... is it usual for an amp not to open up until you start pushing it?"

I don't know how "usual" it may be, Peter, but I certainly wouldn't be surprised if is an effect that is present to an audibly significant degree with many amplifiers. Albeit without a great deal of predictability.

For one thing, as Ralph (Atmasphere) has said in past threads certain odd order harmonics can, even in trace amounts, significantly affect our perception of loudness. Therefore variations of an amplifier's distortion characteristics that may occur as a function of signal level can significantly affect perceived dynamics.

For instance, if those particular odd harmonics are present to a greater degree, relative to signal level, on musical peaks than during soft passages, there will be a perceived increase in dynamics. And if the volume control is set lower the differences in distortion between musical peaks and soft passages may become smaller, resulting in a perception of lessened dynamics.

Also, of course, the operating temperatures of transistors and other circuit devices will be affected by the volume level, with all kinds of subtle sonic consequences being conceivable.

As I and others said earlier, though, in any given situation lots of factors unrelated to the amplifier could conceivably come into play, perhaps to a much greater degree, including the Fletcher-Munson effect and the behavior of the speakers .

Best regards,
-- Al

While curves like those can provide some insight into the characteristics of a particular amplifier that is being reviewed, I'm not sure that they help to answer David's question.

As I interpreted it he was asking if optimal power RATINGS could be defined for different basic categories of amplifier design. Things like tube vs. solid state, the type and quantity of output tube in the case of tube amplifiers, push-pull vs. single-ended, class of operation (A, AB, D), balanced vs. unbalanced, amount of feedback, and other differences in circuit topology.

The first problem is that curves depicting distortion or distortion + noise as a function of power level are not much help in trying to choose an optimal power RATING for a given application. Unless the user listens almost exclusively to very over-compressed recordings, the amplifier will be operating at points pretty much all over those curves, as a function of the music.

And in comparing performance at different power levels, a given increase or decrease in THD or THD+N may be subjectively either better or worse, depending on how the THD is distributed among different harmonics, on the relative amounts of THD vs. noise, and on the spectral characteristics of the noise.

Also, with many amplifiers, especially those using significant amounts of feedback, the THD numbers will be negligible even on the higher parts of the curve (well away from the bottom of the "U"). While TIM (transient intermodulation distortion), which is worsened by feedback and which is not normally specified or measured, may be a much more significant contributor to subjective sound quality (depending in part on how much propagation delay there is through the amplifier, that being another variable that is generally unknown).

So I don't see any reason to expect the amplifier to necessarily sound best when operated at the bottom part of the curve, and even if it does that would say little or nothing about what power RATING would be optimal.

Best regards,
-- Al