That "tube sound" and power ratings

How things distort is one aspect that varies with different amplifiers but is only one aspect of performance of sound.

How much power is needed to drive any particular pair of speakers is mostly a function of recording quality and SPLs (how loud you listen).

For optimal performance, it is almost always a good idea to have more power than needed rather than less.

Clipping is always public enemy #1 when it comes to amps and speakers. you want to avoid clipping at all costs in that it will only compromise the sound quality to various degrees.

The only way to avoid clipping is to have more than enough power than will ever be needed to drive the speakers OPTIMALLY.

Having said that, optimal performance is a good first goal but alone does not assure "sound quality". Personal preferences come into play when talking about what sounds "good" . Optimal performance is always a good thing but alone does not assure you will like what you hear, though the chances are best that you will for sure.

So always strive toavoid clipping no matter what first. Then decide on your favorite flavor of sound from there.

Clipping is the most common and pervasive form of distortion in most cases.

Unless you only listen at very low volumes, there is a very good chance that clipping and related forms of distortion will come into play and degrade sound quality in ways that might not be very apparent.

Its not that hard to avoid clipping. Just do not use an amp that is underpowered to drive the speakers. Use more power not less as an insurance policy. Most speaker manufacturers understate the power needed to drive their speakers optimally in order to keep markets open.

If your speakers are even moderately efficient, that helps a lot in terms of choosing an amp that is up to the task.

If you will only listening at low volumes, then none of this matters all that much. The world is your oyster and almost any amp/speaker combo might do.

Once teh amp is up to the task of driving the speakers OPTIMALLY, then you are in a position to determine what other remaining forms of distortion to choose among based on what you hear.

Public Enemys (of good sound):

1) room acoustics
2) amp clipping
3) choose your poison

Note that most tube amps (and some SS amps) soft clip which is why fewer watts seem to go further. But the clipping still occurs, though it will take more volume before the results become clearly unpleasant. But any clipping is distortion. You loose dynamics whic is what adds the excitement to a lot of music. If you don't care about that and only listen to small ensemble chamber music, you might be fine, but eventually you may realize what you are missing and look elsewhere.

The tube amps that have the most unique sound compared to the norm are probably those made well and with little or no Negative feedback applied, like Atmaspheres.

Hazy,

I don't understand why you are tying this question to optimal power levels. I don't think it has anything to do with that.

If it is the purest tube sound that you seek, that's probably the best tube amp design with the fewest tubes, like some very expensive sets. The best tube amp design is the one with the most linear gain, lowest associated distortion levels, and lowest noise floor. The more tubes involved, most likely the harder it will be to achieve the absolute best performance in this regard. Decide how you will determine those things, then after that, factor in how it will perform with given pair of speakers, which does have everything to do with power levels, and I think that's about it.

" I'm not sure the purest or cleanest sound does it for everyone"

Nop doubt about that. Top notch technical performance and what people like best are not always the same thing.

The difference is the first is objective and performance claims can be substantiated by measurements.

The second is completely subjective.

The domain of tube amps and SS amps are different, with some overlap but significantly different paradigms at work. But performance is performance.

For me, I have found the best sounding tube amps I have heard sound mostly like the best performing SS ones. What they both share is very high performance well matched into the system as a whole yielding similarly good results, though each different in design operating within distinct paradigms.

"Probably... A lot of what people like is the compression and fatness that occurs when an underpowered tube amp is over driven"

That's a very good point and a great example of how the best technical performance in terms of accuracy does not always win.

Atmasphere, who out there today is making good quality 16 ohm speakers? With no impedance dips much below that I mean.

A google search on 16 ohm speakers turns up little at least on teh fist page.

WHat are some good ones at various price points? Which ones are full range?

Most SS based systems I have heard over the years were underpowered in terms of achieving optimal performance not on purpose but for not knowing any better and/or not having many practical and cost effective options available, or people just being satisfied and it just not mattering much.

Same true I suspect with tube amps. It's not that tube amp lovers seek distortion, but rather that it similarly may be even less of a real issue for some due to the more benign sound of soft clipping.