SET amps and speaker sensitivity.

Ok, thanks guys. So the higher the the dB rating on a speaker, the more sensative it is? 93dB is more sensative than 90 dB and so on?

peter

That's right Peter. And dB is a logarithmic scale, so a 10 dB increase is twice as loud! Also FYI, 3 dB is perceptible as an increase in loudness (less than that is often perceived as better but not necessarily louder). So you need to double the power output of an amp to get a significant increase in volume. FYI, sensitivity is generally in units of dB/1 watt/1 meter; 1 watt (or 2.8 volts) of output, producing X dB of sound pressure measured at 1 m from the speaker.

You also have to consider the actual impedence of the speaker. Assuming a benign impedence, then 60 tube push pull watts for a 95db sensitive speaker. 30 watts for a 98db push pull amp and 15 watt SET amp for a 101db speaker. If I had a pair of Lamm ML2 I would be looking at a speaker of at least 100db sensitivity.

If I told you that I could carve a turkey with my $30k pocket knife I would not be lying. Just as SET amp maker will say that their 18 watt SET can drive a 95db speaker. Sure it might play loud, but the question is would it sound better with more power?

In SET amps as with many others, all watts are not created equal. Other aspects than simple output figures determine abilty to drive real speakers. In particular, the size and quality of output transformers is a factor. Now they are heavy and expensive, so in simplistic terms, the more you pay for an amp, the better it will drive speakers for a given output.
AS Ultrakaz says speaker impedence is very important for SET's, the speaker may be quoted at 8ohm impedence, but have nasty dips to 2ohms in the frequency range. A SET won't respond well to that.
The answer, try your speaker and SET together preferably in your own rooml, see how they match.

This, Maria, can be a proverbial can of worms, but here goes...

Regarding speakers, 'high-sensitivity' MIGHT be defined as anything at or above 93dB, but there's NO concensus here. As the 'typical' or 'average' speaker is rated around 90, I figure a system requiring half the power for the same output is high in sensitivity. 'High-sensitivity' goes WAY beyond that, however; speaker systems intended for home use with sensitivities approaching 110dB are not uncommon.

The higher the sensitivity, the less power the system needs for a given acoustical output. IF, and it's a BIG 'IF', an average system uses 90dB speakers and 100 Watts per channel and fills a room to satisfying levels, then with 93dB speakers one would need only 50 Watts, and with 96dB speakers only 25 Watts, and with 99dB speakers 13 Watts, etc.

An individual's need for loudness and dynamic 'liveness', and the room volume, are important factors in this complex issue. I'm using 97dB-sensitive speakers with 2.5WPC SETs on the midrange and am getting highly satisfying loudness and dynamics in a largish (3200CF) room while playing large-scale orchestral music. Yet some dideebopper may determine that my system doesn't get NEARLY loud enough since his ears aren't yet bleeding.

Perhaps a rule of thumb might be that if you want to use single-digit-power SETs, you'll need speaker sensitivity at least approaching 100dB.

I expect others will add more to this discussion.
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