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In Reply to: RE: Clarification of terms on Quad ESL-63s and their progeny posted by George S. Roland on March 05, 2017 at 10:04:14
There are two different panels is the ESL-63 type speaker. The two center panels have a concentric ring panels and the two outer panels do not. The outer panels are called 'bass' panels to identify them from the concentric ring panels. I call the concentric ring panels 'tweeters'.
Calling the outer, non-concentric ring panels bass panels is a good description since they only play below 300Hz or so. Calling the concentric ring panels tweeters is lazy but a quick way to identify them from the non-concentric ring panels.
Ross Walker said that when the speaker was in development they called it the dart board. Given the concentric ring pattern one can see why. If you look at the speakers you will note a circle in the middle about 5" in diameter. And then there are the concentric rings that surround the circle. With the exception of the outer ring all the rings are the same area.
The circle in the middle sees the entire frequency range no filter or delay coil of any kind. As the signal moves out from the central area each successive ring is feed with its own signal from the delay line assembly. Each successive ring is delayed in time, rolls over more high frequency and reduces output. The outer ring is only playing about 300Hz and below and is significantly down in output versus the central area.
If you look closely at the two center panels you will notice the outer ring pattern is truncated. The outer edge of the two central panels and the two bass panels make up the last ring. With the larger speakers, 989/2905/2912, two additional bass panels have been added making a larger outer ring. Electrically the (4) panels, or (6) in the larger speakers, act as one panel but they were mechanically divided into smaller panels to make the speaker easier to build.
The original Quad is a more traditional approach. There are two panels and we call them tweeters and bass although this is also not actually correct.
The central strip of the tweeter panel runs full range. A strip that is 1" wide and 24" tall is not going to produce any low end so it is reinforced with the outer strips of the tweeter panel and the two bass panels flanking the tweeter panel. There is no crossover network. Instead there is a filter network that rolls of high frequency of the tweeter panel outer strips and the bass panels. The transition point between the tweeter and bass panel is around 1.2kHz blending the two panels.
Hope this is helpful.
Follow Ups:
Thanks Kent,
This is a very thorough, yet comprehensible to the layman, description of what's going on in the speaker.
I understand the idea was to produce a likeness to a spherical wave of sound. If I understand you correctly, the diminishment of the volume as sound is launched from the outermost panels might form the outer edges of that sphere.
Fascinating stuff!
Yes the ESL-63 is designed to emulate the wave front coming from a theoretical point source 30cm behind the plane of the speaker.
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