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Old 29th May 2014, 02:10 PM   #1
SyBorg is offline SyBorg  United States
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Default Full Range Electrostatic Question

In the various threads here on making ESL panels one common theme is that the panel resonance defines a low end cutoff for the usable frequency response of the speaker. (That and the saturation of the transformers, the d/s etc.) In making several panels myself, the lowest I could get the resonance and have the panel work reasonably well was in the 60-65 Hz range.

How is it that Martin Logan, Acoustat and others can produce a full range panel? I have a pair of ML CLSII that have a fairly smooth response down to about 30Hz. Nowhere in the electronics do I see a notch filter for the resonant frequency of the panel. Is it Judicious spacing of the damping tape, the curve of the panel, or something else?
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Old 29th May 2014, 03:55 PM   #2
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I don't know anything about ESL panels, but the idea that Fs limits useable bandwidth is common with cone speakers also, but it's not true. A voltage source amplifier doesn't care about speaker resonance, but tube amps might have trouble. The impedance spike would mess up crossover filter, but you are full range.

Quad uses 4-6 smaller panels rather than single large panel like Martin Logan, so Quad's panel Fs should be higher. But they play <40Hz without any problem.
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Old 29th May 2014, 09:52 PM   #3
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Quote:
Originally Posted by SyBorg View Post
In the various threads here on making ESL panels one common theme is that the panel resonance defines a low end cutoff for the usable frequency response of the speaker….In making several panels myself, the lowest I could get the resonance and have the panel work reasonably well was in the 60-65 Hz range. How is it that Martin Logan, Acoustat and others can produce a full range panel?
You are correct that the fundamental resonance of an ESL panel defines its useful low frequency limit. Near field acoustic output will fall -12dB/oct below resonance with frequency independent voltage source driving the stators. This is similar to the behavior of dynamic woofer in sealed enclosure. Far field response will most likely have an additional -6dB/oct roll off increment from dipole cancellation, again similar to a dynamic dipole.

With dynamic drivers, you adjust resonance by varying moving mass and suspension stiffness. With ESL diaphragms being so light, the moving mass is defined by the airload which is roughly proportional to area. For ESL diaphragms of a given area, you can adjust resonance by varying tension and unsupported width. If you are after resonance ~ 30hz, I would suggest using minimal mechanical tension(or heat shrink tension) and unsupported widths of 6” to 10”. Be aware that if you want to have useful(+95dB) output down at 30hz you will need large area as your excursion is generally limited to 1/16” – 1/8”.

One other option is to use a large unsupported width which results in extremely low resonance and perhaps diaphragm instability and sticking to the stators. Then, start adding silicone or foam tape "dots" spaced down the middle of the panel until you achieve the resonance you are after.

Acoustat and QUAD apply acoustic damping to keep the LF response around resonance from being too peaky. Acoustat used thick felt pads spaced down the center of the panel. QUAD used/uses silk screen mesh attached to the inside of the stators. Martin Logan did not use any damping on their CLS that I am aware of. See the attached published response curves comparing the LF behavior between CLS(undamped) and QUAD ESL63(damped).

I posted measurements showing damping effectiveness of felt and silk screen mesh here:
Mechanical Sectioning .vs. Silicon dots for resonance control

Also, be aware that with low tension, resonance frequency will decrease noticeably as bias voltage is increased.
Details here:
Diaphragm Resonance change with HV bias
Current vs voltage drive ESL?
Attached Images
File Type: png CLS_LF_resonance2.png (214.9 KB, 436 views)

Last edited by bolserst; 29th May 2014 at 09:57 PM.
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Old 29th May 2014, 11:24 PM   #4
sreten is offline sreten  United Kingdom
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Hi,

Open electrostatics like the Quad use a high Q panel resonance
to obviate the baffle loss of an open baffle and the end result
is inevitably pretty poor low bass power handling.

The manipulation is all acoustic / mechanical, and you won't
see it in the circuitry. But it is still there and has serious
consequences to the nature of the bass capabilities.

e.g. a ELS57 can't do bass louder than an a LS3/5A.

All FR electrostatics have relatively very restricted bass SPL,
but can go low, unfortunately not very loud in any sense.

rgds, sreten.
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Last edited by sreten; 29th May 2014 at 11:34 PM.
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Old 9th June 2014, 10:36 PM   #5
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Also, we are always talking open baffles - that alone limits the bottom end.

Having said that (and with all the cautionary thoughts in previous posts), the Dayton-Wrights achieve pretty good bass to maybe 50 Hz - which sounds a whole lot better to your ears than you'd imagine from hearing people talking about systems that go to infrasonics.

But these speakers are very large, can eat tremendous power, are filled with welding gas (which has a whole bunch of good consequences for bass), and have 39 lb transformers. And some models need augmentation in the tweeter end.

As a fan of ESLs, I wonder if ESL concept can take a better shot at being full-range output (and dispersed, etc.) than trying to make a single cone driver do it. Of course, headphones manage the trick pretty well with single cone-like drivers (albeit in a more benign acoustic setting).

Ben
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Last edited by bentoronto; 9th June 2014 at 10:42 PM.
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Old 17th June 2014, 08:09 PM   #6
EStat is offline EStat  United States
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Quote:
Originally Posted by bentoronto View Post
Having said that (and with all the cautionary thoughts in previous posts), the Dayton-Wrights achieve pretty good bass to maybe 50 Hz...
Ah, Dayton-Wrights! It was a pair of XG-8s an audio reviewer friend had in the 70s that turned me into a stat freak. The Hi Fi Shop I worked at during college picked up line selling the MKIII at the time.

Quote:
Originally Posted by bentoronto View Post
But these speakers are very large, can eat tremendous power, are filled with welding gas (which has a whole bunch of good consequences for bass), and have 39 lb transformers. And some models need augmentation in the tweeter end.
Inhaling SF6 can be fun as it has the opposite effect of helium on your voice.

Quote:
Originally Posted by bentoronto View Post
As a fan of ESLs, I wonder if ESL concept can take a better shot at being full-range output (and dispersed, etc.) than trying to make a single cone driver do it.
Ever heard a big Sound Lab stat? My U-1s measure flat to 30 hz in my room and don't suffer the top end limitation of the Daytons as they use two overlapping toroidal transformers. They also make double diaphragm electrostatic subwoofers.

They take a different approach on dispersion. While the D-Ws arrayed the 8-10 panels in somewhat of an arc, The SL has a single diaphragm with a lattice that controls directivity. There are lots of flat facets varying in height across an arc. There are 22 degree, 45 degree and 90 degree models. The only exception is the subwoofer which is flat across. Some like mine have metal frames.

With controlled dispersion, they are designed to be used in arrays for more output and coverage. Google "Soundlab Ray Kimber" to see the two and three set arrays he used to take to shows. Yes, those really are nine feet tall.
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Old 17th June 2014, 09:17 PM   #7
tyu is offline tyu  United States
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WOW Estat Has got it going on....
My U-1s measure flat to 30 hz in my room and don't suffer the top end limitation.

I just put the New toroidal transformers...... SoundLab M1 for a guy i do tube work for....I myself have had the older SL A1.......like driveing a dead short!
M1s top end is still not even as good as my old moded Acoustats M3s....M1s Bass great 25-30hz ezey....but the top sounds like 15k at best.....SL M1 are out of the guys setup less the trany change with a littel time...........
King sound ESL are so ezey to drive an the topend is the best of any ESL.......there twoways with tweeter an bass.........
An the SL M1s have to be driven with $50k in amps an frontend.....these M1 are in a room 25'X30'.....
Sounds like your SL are some real keepers....
good luck
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Old 17th June 2014, 10:03 PM   #8
EStat is offline EStat  United States
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Quote:
Originally Posted by tyu View Post
WOW Estat Has got it going on....
My U-1s measure flat to 30 hz in my room and don't suffer the top end limitation.
Understand that Dayton-Wrights from the XG-8 MKII forward used a piezo tweeter to extend HF response. My friend's MKIs were a bit polite on top. I can't say that the SLs are flat to 20 khz, but they don't need a supplemental driver either - especially with the Toroid II trannies. I find there's precious little musical content up in the belfry. My 1+1s don't sound quite as pure on top, although they're now getting updated by Roy Esposito and I suspect they will return better in that respect. I opted for the "air" mod.

Quote:
Originally Posted by tyu View Post
An the SL M1s have to be driven with $50k in amps an frontend...
Somehow I manage with 2001 VTL MB-450s that ran only $10k (call it 12 with aftermarket cords) in a 15'x26' room.

Measured in room response curve showing third octave smoothing:

Click the image to open in full size.
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Old 18th June 2014, 07:11 PM   #9
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Quote:
Originally Posted by sreten View Post
Open electrostatics like the Quad use a high Q panel resonance
to obviate the baffle loss of an open baffle and the end result is inevitably pretty poor low bass power handling. The manipulation is all acoustic / mechanical, and you won't see it in the circuitry. But it is still there and has serious consequences to the nature of the bass capabilities.
Most ESLs which do not use resistive damping have diaphragm resonances with Q of 10 – 20. By comparison, Quad damped their resonance to the point where it could effectively be used to equalize the bass response flat. The attachments show the ESL-63 LF modeling based on parameters provided by Baxandall and comparison with measurements published by P. Walker in his AES paper.

The bass capability (SPL at a given frequency) is defined purely by the volume displacement (area x excursion capability). It doesn’t matter whether the motion of the diaphragm comes purely from the electrostatic driving force, or partially from Q “amplification” of that driving force. For comparison with dynamic drivers simply compare volume displacement capability. With D/S spacings of only 1.5mm – 2.5mm, typical ELSs need to have roughly 10x to 20x the area of a dynamic driver to have the same LF output capability. For example, a single 10” woofer would have similar bass capability to the ESL-63 when mounted on the same sized dipole baffle. A modern 10" woofer in a sealed enclosure would easily outperform the ESL-63 in bass output capability.

@bentoronto,
Any idea on the total area and excursion capability of your Dayton-Wright ESLs?
Attached Images
File Type: png Quad_ESL63_LF_01.png (49.6 KB, 256 views)
File Type: png Quad_ESL63_LF_03.png (76.5 KB, 254 views)
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Old 18th June 2014, 11:06 PM   #10
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Minor note: I am puzzled why the later DW need the tweeters. Earlier models had a fine treble, I believe.

Ben
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