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Clarification of terms on Quad ESL-63s and their progeny

24.154.216.28

George S. Roland

I keep seeing references in articles, ads and even reviews, where, one assumes, authors know what they are talking about, to "bass panels" in the Quad ESL-63 and following series of speakers--989s, etc.
I see this in reviews, where the company, it is claimed, "added two bass panels" to the four-panel ESL-63. I see people selling ESL-63 "bass panels" on the net and so on.
As I understand it, the original ESL, or ESL-57 as it is sometimes called, actually did have a treble panel and two bass panels that were structurally different from each other, and that received different parts of the audio signal. I am not entirely clear whether a crossover network was used in this speaker to divide the audio signal up between these two panels, but it would seem likely. Perhaps someone who knows could elucidate this point for us.
As I understand it, the ESL-63 and its followers had no crossover network and that the entire audio signal was fed to every panel. There were delay lines used to determine exactly when sound was propagated (from the center of the speaker to the outer edges), but that, it seems to me, is very different from a crossover network as that term is generally understood. Aren't peoples' references to "bass panels" in the later Quads simply incorrectly informed? Or am I?

Edits: 03/05/17

Follow Ups:

RE: Clarification of terms on Quad ESL-63s and their progeny - kentaja 06:26:10 03/06/17 (2)
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.
- RE: Clarification of terms on Quad ESL-63s and their progeny - George S. Roland 13:47:21 03/06/17 (1)
  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!
  - RE: Clarification of terms on Quad ESL-63s and their progeny - kentaja 16:54:26 03/06/17 (0)
    Yes the ESL-63 is designed to emulate the wave front coming from a theoretical point source 30cm behind the plane of the speaker.
RE: Clarification of terms on Quad ESL-63s and their progeny - Artoa 15:58:47 03/05/17 (0)
Quad ESL63 and more recent iterations have
- 2 panels with delay lines (full range).
- 2/4 bass panels, no delay lines, but added filter.

The low pass filter for the bass is a RC filter (360k resistor, panel makes the capacitance).
RE: Clarification of terms on Quad ESL-63s and their progeny - cawson@onetel.com 12:32:44 03/05/17 (1)
> Aren't peoples' references to "bass panels" in the later Quads simply incorrectly informed? Or am I?

As I understand it (and I'm not a Quad expert), the newer big Quads (2905 and 2912) have 2 centre panels that are dedicated to mid and high frequencies and 4 bass panels - 2 above and 2 below the centre ones - that are dedicated to low frequencies. The newer smaller Quads (2805 and 2812) have just 2 bass panels. As far as I understand it, there are no crossover circuits, but how the panels know what to do remains a mystery to me!

No doubt there are Quad experts here who can offer chapter and verse. All I can say, after buying a pair of used 2905s last week is that the bass is a lot better and fuller than I was expecting. They really do offer serious wellie when called upon to do so. The twin 10" drivers in the subs of my Avantgarde horns give more grunt still but not with more delicacy.
- RE: Clarification of terms on Quad ESL-63s and their progeny - George S. Roland 20:30:59 03/06/17 (0)
  I agree wholeheartedly with you on the bass of Quads. They go deeper than many good dynamic speakers I have heard and they are so clean-sounding, so revealing of the timbre of the instruments that you can identify the instrument not just generalized bass sound.

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