Using PA Speakers In A Home "Audiophile" Application!

@ditusa Its worth noting that my drivers use a beryllium diaphragm (as you probably already surmised); the driver is also modified to run a field coil. As far as I'm concerned, JBL knows what they are doing with their horn structures- I've seen no reason to replace mine. The diaphragm uses a Kapton surround so doesn't act weird when you get near the cutoff frequency. As a result its fine with a 6dB/octave crossover.

@ditusa Its similar to this one. The horn was installed in 1998 FWIW.

That’s not much of a basis for qualified comparison here. Which JBL’s are those, and how are they (or the Altec’s) representative of a whole segment of speakers?

Look, I believe we’ve been here before, but there’s nothing to support the narrative inkling towards modern pro drivers, or even a range of older dittos, being in particular marred by breakup modes. There’s tons of great pro drivers and horns out there with solid R&D behind them, and they don’t suddenly turn harsh when pushed - believe me. If they did they’d be out of business. Of course you could find cheaper "weaklings" among them with sub optimum horn profiles, flimsy material choice, less than stellar drivers and overall execution, and they would be the easy and even convenient target for field coil-, beryllium diaphragm-fitted and lovely hardwood housed speakers like your no doubt great Classic Audio Loudspeakers to make a case against them.

@phusis You make a really good case- most of my experience with the speakers I mentioned didn't include any investigation of what was actually causing the harshness. I assumed a breakup because I got to compare a beryllium diaphragm made for the old Altec horn against the stock aluminum unit; I have to assume that difference really was on account of the differences in the diaphragms.

The JBL to which I referred is the JRX115. Seems to me we had an expanded version of that speaker in the studio that used the same horn driver. A lower (not rock concert) levels it was pretty convincing in the mids and highs.  It uses a Titanium diaphragm in the midrange.

My CARs use a JBL tractrix horn which seems to work really well. He has since replaced this horn with a machined maple horn; but as I understand it his maple horns correct an error that was in the TAD maple horns he used to use.

Modern pro drivers (and even ones decades old) are extremely well designed, and used within their design parameters - not least actively - will yield no effective problems with breakup modes. 

@phusis I've run into breakups in older designs (like Altec, with their aluminum diaphragms) and also in newer designs, like the JBL speakers I use for my keyboard setup. If I get over a certain volume, the speaker doesn't handle it that well (gets harsh) so it does seem like I'm setting off a breakup in the horn. 

My speakers at home use beryllium diaphragms; the first breakup is at 35kHz. 

@deep_333 You will need a low noise amp for that and also one that has low gain, otherwise the noise floor of the amp won't be much help. The Benchmark, while excellent, as over 30dB which means you'll notice noise from your front end.

Our class D amp is quiet (but not that quiet) but it only has 22dB of gain.

I think you'll have to try things out and see what works. High efficiency speakers are often a challenge that way.

SET amps often have only 15 dB of gain, sometime even less. But their noise floors are not as good as our amp but that doesn't mean they won't work. But you would be looking for low noise tubes...

I don't think an SET is a good idea with this speaker since its designed with the idea that the amp can behave as a voltage source. SETs can't do that so you'd have a tonal coloration due to frequency response errors.

@deep_333 My concern would be breakups in the drivers, which cause distortion and harshness. PA stuff mostly does not care about that sort of thing since sound pressure is the main goal. But its a big deal with home audio speakers, where such things can shoot the product down.