Avantgarde Trios, SETs, and Impedance Curves

The Trio is tricky to set up because the impedance curve is very unusual for a horn- high in the bass and low in the highs, due to the design of the crossover, which is mostly capacitors. A lot of SETs have difficulty with the speaker as a result.

FWIW It is very easy to set up the M-60 to work with the speaker, by using the same technique that the designer used: negative feedback. The speaker is so sensitive that about 6 db of feedback can be employed in the M-60, solving any rolloff issues. This is easy to set up with an external jumper arrangement.

We don't regard the arrangement as ideal, but since the designer's amps used feedback, that's what you have to use. Neither the Duo or the Uno seem to have this requirement.

The problem is that really low output impedance amplifiers don't sound right on highly reactive/high efficiency speakers (like most horns). There are interactions that result in shrillness. So a tube amp is indicated...

A friend of mine was using the 45-based Kondo, which realistically makes about .75-1 watt. This ought to be enough on the Trio, but he was unable to run the amp so there was not a high frequency rolloff.

The problem is that the midrange unit is not rolled out when the tweeter rolls in. This is because there are only caps in the crossover- no chokes to kill the highs to the midrange. The result is that the midrange is in parallel with the tweeter. The big horn OTOH is 19 ohms, but with the midrange and tweeter in parallel with it, you have a low impedance at high frequencies.

To make this work you have to play with the taps on your output transformer. The issue is that if you have a zero feedback amp (really about the only thing that otherwise sounds right on a speaker like this), you will not get the proper loading of the output transformer at frequencies less than that for the tweeter. The result is ringing (harmonic distortion) which obscures detail.

The end result is while you get the speaker and amp to work, neither is presenting the best of what its capable of. If, OTOH, the crossover were dealt with, this would not be the case. I would be very interested to see what that speaker could do then!! Given the cost of really good tube amplifiers, it seems that correcting the crossover would be a relatively inexpensive way to create a transformation.

I have a friend with the ART PX-25- its not bad on the Trio at all. There are no 45-based SETs that can drive the speaker- try as you like, 0.75 watts is not enough...

Most people I know that are driving the speaker successfully use surprisingly large amplifiers given the efficiency of the speaker. This is probably due to the impedance curve, which is tricky for a lot of zero-feedback amps (which otherwise will be the best sounding on a speaker like this).