Class D and High Efficiency Speakers?

High Efficiency speakers in general prefer an amplifier with a relatively high source impedance, due to the reactive nature of high efficiency drivers.

The use of low output impedance amplifiers with high efficiency drivers is the reason why horns have a reputation for being strident.

If you really are intent on this, add an 8-ohm resistor in series with the speaker load. True, you will dissipate likely up to 50% of your power in the resistor, but it will simulate (somewhat) a higher source impedance.

Or- you could get a tube amp. You won't need a lot of power. In the case of a high efficiency speaker, a good tube amp will clean the clock of any class D amplifier made.

09-18-08: Audiofeil
I can't think of a good reason to use class d amps with horns unless you're the adventorous type.

IMO you'd lose much of the "warmth" without the tubes.

Borrow some digital amps and give a listen. It may be your cup of tea.

But don't form your opinion until you give a listen to the ridiculously affordable Onkyo A-9555. Onkyo's design has some patented circuits to specifically address the problem of switching noise in class D amps.

Robert Deutsch reviewed the A-9555 for Stereophile into a pair of very high sensitivity Avantgarde Acoustics Uno horn speakers. He makes special mention of how he often has to chase down hum and buzzes when reviewing upstream electronics because of the Avantgarde's sensitivity. When he hooked up the Onkyo, however, he asked himself, "Is it on?" It was. So unlike most, it can be a good match for horns. And its power rating should be a good match as well.

Unlike pretty much any other class D on the planet, *once it's broken in,* the Onkyo is known for a relaxed presentation and a smooth, engaging treble. Even the little summary blurb in S'phile's Recommended Components section compares the Onkyo's *resolution of low level detail* to tube amps.

I have one and have to agree. It reminds me of the high priced class A/AB amps (Ayre, earlier Rowland) more than anything, and replaced two highly regarded vintage amps--the Amber Series 70 and VSP Labs Trans Mos 150.

Another thing: Class D amps require the best, cleanest power you can feed them. Some reviews I've read say it's like listening to two different amps, depending on the power cord used, and which, if any, power conditioner it's plugged into.

In the case of the Onkyo, after it broke in, it sounded smooth, but also dead and lifeless with blunted transients and a lack of bloom and fade, similar to when you have too much damping fluid in a tonearm. It turns out it was the power cord, a 12-yr-old Synergistic Research AC Master Coupler. Playing a hunch, I swapped out the SR AC MC for a late model PS Audio XStream Prelude, and voila! All the tubelike nuance, low level detail, instrument resonance and room ambience returned to the musical presentation. I got a second boost in transparency when I bypassed a filtering power strip for a direct connection to the wall.

Thanks for the replies guys. I already have 300B mono blocs, I'm just interested if anyone has implemented a class D amp with high efficiency.

Anyone tried the Bel Canto Ref1000, with high efficiecny?

Low powered tubed amplifiers are a better match for horns than class d amplifiers.

Onkyo, Pioneer, Sansui, and Kenwood notwithstanding.

That's my formed opinion based on experience.