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tade 22nd July 2005 03:00 AM

quad esl's delay lines
does that particular model of quad esl, 989 i think, use massive lengths of wire to delay the audio signal, or some other method? if this wire were coiled wouldnt it act as a grand inductor?


Brian Beck 22nd July 2005 03:45 AM

Yes the Quad ESL-63, 988 and 989 all use several high-turns-count air core inductors as series elements in a ladder arrangement, with cross-coupled shunt caps to form a tapped delay line, also called a lumped element delay line. The ESL stator rings are tapped along the way, each concentric ring farther out getting a more delayed signal. Hard to describe without a picture. There are websites that show it. Try Googling the Quad ESL-63.

I_Forgot 22nd July 2005 09:01 PM

Re: quad esl's delay lines

Originally posted by tade
does that particular model of quad esl, 989 i think, use massive lengths of wire to delay the audio signal, or some other method? if this wire were coiled wouldnt it act as a grand inductor?


The length of the wire is not what causes the delay! The delay is created by the interaction of the inductance of the coils and the capacitance in the delay lines/capacitance of the speaker segments.

Quad started putting delay lines in the ESL-63 and continues with the 988 and 989. The delay line serves three purposes. It delays the start of the waveform to successive segments of the drivers in order to simulate a "pulsating sphere". I think it also "equalizes" (i.e. flattens the frequency response) of the speaker by reducing high frequency output relative to low frequencies. Essentially, the highest frequencies are applied only to the center segment of the speaker. Reducing the radiation area reduces the output level and increases high frequency dispersion in the listening room.


tade 22nd July 2005 10:52 PM

makes sense.

i found a thread on this site about this very subject by google searching. i didnt search very well...

bret 26th July 2005 08:00 AM

Cylindrical wavefront?
Presumably this same technique could be applied to vertical segments rather than circular ones to create a cylindrical wavefront a la Beveridge.

Brian Beck 26th July 2005 11:44 AM

Absolutely! I've been working on a design for just such an approach.

bret 26th July 2005 12:04 PM

I assume your stators are made of segments of vertical wires. How are you implementing the delays - resistors or inductors? Do you have any results yet? I would be interested in trying something similar in the future.

Brian Beck 26th July 2005 12:36 PM

No, most recently I've been toying with plastic grating with stainless woven material for the stators. I've built tall narrow drivers, but the delay elements have been only paper and very limited "breadboard" tinkering so far. I have simulated using both resistive and inductive elements combined (you really have no other choice in the real world when using inductors). The resistive approach is not new of course; the variable-width Acoustat designs of Jim Strickland come to mind. Even Quad incorporated a resistance element (shorted turn) in its inductors. I haven't decided on where Iím going with delays yet. One advantage is the potential to improve the impedance presented to the driving source when using R-L delays elements.

bret 26th July 2005 01:02 PM

If I understand you correctly, you have multiple adjacent panels. I have considered doing the same thing, but doesn't this approach severely limit your low frequency response? I would think that the resonant frequency of each panel will be quite high. Also, maximum excursion will presumably by a bit lower than a larger panel(?). The total surface area may be large enough but does it translate to any meaningful mid/bass frequencies?

phase_accurate 26th July 2005 01:19 PM

There is one commercial design using vertical aluminium rods as stator. Lowpass/delay is achieved by driving them via resistors that act as first-order LPF together with the intrinsic capacity between the opposing stators.



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