High value, high efficiency speakers for SET amps

The Classic Audio Loudspeakers have efficiencies that are what you want for a 300b SET (which only makes about 7 watts). The best suited in their line is the Hartsfield reproduction.

Sorry to pop some bubbles here:

The problem you are up against is that with almost any SET, if you really want to hear what the amp really does (the magic) you really **don't** want to push it past about 20% of its full output. If you do, the higher ordered harmonics come into play and there is an interesting interaction that occurs with the human physiology when that happens!

(The interaction is that the higher ordered harmonics will be showing up on transients, and the ear/brain system will interpret that as loudness. As you increase the volume, the loudness cues are thus initially only occurring on transients. Thus the amp will *seem* to be much more dynamic than it has any business being for its output power! This is a common comment about SETs- and one that indicates that the amp is not set up properly. The speaker used needs to be more efficient to avoid this problem. BTW, now that you have read this I may have ruined it for you: knowing that the dynamic quality is really caused by distortion makes it easier to hear the distortion itself.)

(A further note: about 90% of the time when audiophiles are talking about 'dynamics' they are really talking about distortion. The word is so heavily charged that if I really do mean dynamics I often use other words such as 'impact'.)

So with only 2 watts or so to really play with your speaker must be over 102 db or so- otherwise you simply are not hearing what the amp can really do. SETs have the property of distortion that becomes unmeasurable as power is decreased; this is the source of their 'inner detail magic'.

The bottom line is if you have a 300b SET, unless your room is very small you will need a horn system of some sort; single driver speakers like the Zu or Lowther simply lack the efficiency in an average room.

Well, I do have single driver Zigmahornets but also run Coincident Conquest & Mini Triumphs. The Eclipse is out of your budget.

Atmasphere,

I think you are assuming that the speaker is full or near full range with your numbers.

Smaller speakers with less low end extension MUST require less power to achieve a certain level, all else the same.

The lower the frequencies attempted, the more power is needed, all else held constant. I think that is basic physics.

So I think my argument is sound that one way to coax more out of a few good watts is to defer on or even filter out the lowest frequencies if needed one way or another at some point. That allows your watts to go further.

The sacrifice is the lowest octave or so to some extent but the fact is that may not matter much for most recordings, especially in a smaller room.

But you are correct that the only way to get flat response full range sound out of a few watts is very high efficiency speakers. I have only heard it achieved well with very expensive and very large horns, along the lines of Avantgarde or similar custom horns.

Rebbi,
I will email you regarding my personal experience with 300b SET, OTL and speakers with sensitivities of 92-95 db. Believe me you have a fine amp with many good options. Trust me.
Charles,

04-22-15: Mapman
Atmasphere,
I think you are assuming that the speaker is full or near full range with your numbers. Smaller speakers with less low end extension MUST require less power to achieve a certain level, all else the same. The lower the frequencies attempted, the more power is needed, all else held constant. I think that is basic physics. So I think my argument is sound that one way to coax more out of a few good watts is to defer on or even filter out the lowest frequencies if needed one way or another at some point. That allows your watts to go further.

I would put it that deep bass extension, efficiency, and compactness of cabinet size trade off against one another in the design of a speaker. Sacrificing deep bass extension and/or making the cabinet larger (not smaller) will work in the direction of enabling the speaker to have greater efficiency.

So I agree that in choosing a speaker having significantly greater efficiency than the De Capo, that also meets Rebbi's stated price point and size preferences, much or all of the bottom two octaves or so will probably have to be sacrificed.

However, the efficiency of a given speaker is what it is. (Although that is not to say that it is what the specs say it is :-)) And provided that the efficiency number is defined in a way that is representative of the speaker's performance across the range of frequencies it is capable of reproducing with reasonably flat frequency response, a speaker having an efficiency of 102 db/1W/1m, to use Ralph's example, will produce within that frequency range an SPL of 102 db (+/- frequency response variation) at a distance of 1 meter when provided with 1 watt (neglecting room effects), regardless of what the speaker's deep bass extension is.

Regarding filtering out the deep bass at a point upstream of the amplifier, yes, that of course would make a given number of watts go further, but of course implementing that filter without compromising the SET magic is another matter, especially at a modest price point.

On the other hand, though, how far the 2 watt figure Ralph mentioned will go in conjunction with a given speaker efficiency will of course vary considerably depending on the volume preferences, listening distance, and room size of the listener, and perhaps even more so on the dynamic range of the music that is being listened to. And it seems clear in this case that Rebbi is generally quite happy with the performance of his SET amplifier with the 86.7 db/2.83 volt/1 meter De Capos. My guess, therefore, is that a speaker which honestly gets into the mid-90's/1 watt/1 meter, while also not compromising anything about the De Capo's sonics which he finds appealing, would make for an excellent upgrade. I have no specific suggestions to offer, though, in the stated price range.

A probably unnecessary reminder, also, that efficiency and intrinsic sonic quality are not all that have to be considered. Ideally impedance should be high, and should not dip down to low values at any frequency, and should not have severely capacitive phase angles (especially in the lower part of the spectrum where lots of energy is typically required, and especially at frequencies coinciding with impedance minima). And the less variation of impedance as a function of frequency the better. Speakers not meeting those criteria would not only entail increased risk of unsatisfactory results, but would tend to give results that are not even consistent among different SETs, due to differences in impedance interactions.

Just my $0.02. Best regards,
-- Al