Single vs Multiple driver loudspeakers...

Twl: By the way, Nelson's comments about this being "the best sounding speaker he's ever heard" has a LOT to do with the linearity of it. After he was done combining equalization and amplifier loading characteristics, that speaker was VERY close to being "flat". While he did comment on the lack of bass, he's taking care of that in his next article. That is, he's going to bring in "El Pipe-O", which is a HUGE vertical pipe housing a sub that he built a while back. Sean
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I readily subscribe to El's opinion,

It just isn't fair to force an excellent midrange driver to perform woofer and tweeter duty

and would add, it's not necessary, either.
The average Lowther, Supravox, Diatone, AER, etc will get you through the dangerous 150-8kHz region famously, even without a wizzer. Sensitivity is usually well over 95db and many of these drive units allow 30+W rms, offering a prodigious dynamic range, comparatively speaking.
Cut the low Xmax FR at ~150, and leave it alone n the highs. One can easily add low frequency energy to a FR using a pair of (active) subwoofs, either a W horn or open baffle.
A super tweet, while difficult to place (wave lengths at 8-12kHz are VERY small), will do the job once you calculate its position precisely (there's always some elbow grease & maths when it comes to spkrs!).

And, you're set! Lowther PM5 & EX4 (that I'm familiar with) have no trouble anymore reproducing the complexity of a full-scale orchestra -- add a chorus too, while you're at it.
The dynamics are incomparable, of course!

Well we have some Lowther fans here. I bought mine to just fool around with. I stuck them in an empty room, with a receiver--for breakin.Every couple of hours I'd sneak in for a listen.It wasn't long till I moved the Montanas to make room. That was the week before Thanksgiving. I haven't changed the Montanas back yet. To me the simple description would be--These speakers emit a set-sound even when driven by a ss amp.----In my case a Marantz receiver. No matter what the numbers say it's the music and does it sound good?? Way simple,huh?

Gregm: According to the chart that Nelson Pass had published in that article, the Lowther DX55 showed a gradually dropping slope below appr 700 Hz. As compared to the average output levels in the upper midrange & treble regions, output was down appr -4 dB's at 500 Hz and appr -13 db's at 200 Hz. As such, without some type of equalization circuit, the usable bandwidth of this specific driver is much narrower than what you've described.

For those of you that are "into" the full-range driver approach, AudioXpress recently had an article about modifying a small Tang Band driver. After modifications, it was FAR more linear than any Lowther i've ever seen and even had greater bass extension and linearity. The fact that it is only a 3" driver severely handicaps the ability to achieve the spl's and / or dynamics of the much larger Lowther drivers. Once again, we come back to the fact that there are trade-offs with ANY loudspeaker design and they become even more complicated as one reduces the number of drivers used.

It's too bad we can't find some way to make a plasma driver both more efficient and wider bandwidth. This would solve all of our problems. Well, that and getting rid of the excess ozone that they generate : ) Sean
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I just read Nelson Pass's writeup on his "Kleinhorn". Surely this was intended for the April issue of some magazine.