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

Interesting conversation at the Part Time Audiophile's The Occasional Podcast.
There, tube amp maker Justin Weber of Amps And Sound makes these comments:

At about 24:03 in, they have an interesting conversation about power in tube amps and speakers' needs.

Justin makes an interesting comment about power and speaker efficiency. He's careful to caveat that room size might be an important differentiating factor, but for many (most?) audiophiles (with small-medium size rooms), there is just not that much to worry about regarding amplifier power and speaker matching. He is not touching on "synergy" in some larger sense -- he's just addressing the "power needed to drive speakers" question.

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 whole interview is interesting, but here's the interesting bit -- I did my best to transcribe it, but go listen for yourself!

"Almost always, you need vastly less power than you realize....I've seen 1 watt power whole rooms and big rooms with moderately efficient speakers....What's a practical standard? 30 watts should do 99% of everything for everyone, and 15 watts should do 95% of everything for 99.9% of everyone....

Most audiophiles have small listening rooms.... [A more powerful tube amp may sound better, but] I think that’s a matter of it having a better output transformer and [that] output's transformer's core actually having a flatter frequency response and going lower.

So [in those cases where a more powerful amplifier is used] I don't know that it's a question of producing more power -- that you need more power -- as much as the transformer [in] the more powerful amplifier is [instead just] a better transformer."

Not sure what folks here think about these claims. Perhaps they seem so obvious as to almost not need repeating. But there are so many conversations about speaker sensitivity and watts that do not mention the quality of the transformers or which seem to overstate the importance of how powerful an amp is.

If Justin is right, then many, many pieces of advice related to "how many watts do you need" are basically wrong.


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He's making two, separate, claims:

1) About 15W amp power should suffice for most home systems

2) (IF) High powered tube amps sound better than the lower powered ones, it's probably because their output transformers are better -- i.e. transformer quality and not power is what makes the difference (if there is one).

I understand where he's coming from, but would add another parameter: current. It's not only the strength (watt) that makes a difference, it's also the "quantity" of energy provided that matters.


Otherwise, 15watts should be ample for speakers 91dB / 8ohms or better. At peak power you get over 100dB -- not bad!



This has been visited any times. My opinion,for what it's worth is that to adequately power your speakers headroom is essential. Instantaneous power needed to avoid clipping is a huge factor as to providing dynamic range. Don't want my amps clipping, or to even come close. Hasn't everyone here at one time or another had their system uncomfortably loud past a certain point?

If you can afford headroom that is a huge advantage in many factors related to musical satisfaction. Yes, if you listen at lower levels this doesn't become a problem. 


There is a caveat here.  Originally, the magic of tube amps was produced by SETs that made up to about 6 wpc.  Thus, the need for moderately sensitive speakers, say 94 dB and up.  

Then people who had already invested lots in less sensitive speakers wanted the tube magic, so much more powerful push pull amps were made.  Some of them are very very good (I have one) but many of us agree that the paragon of tube amp performance happens with just a couple of watts produced by a direct heated triode SET.  

So yes, you can power an 89 dB speaker with a Primaluna, but I'm aiming higher.