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Old 21st November 2005, 06:16 AM   #1
Bazukaz is offline Bazukaz  Lithuania
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Default Sealed box and ESL

I would like to ask if somebody experienced placing ESL into a sealed box ? Wouldn't that give better bass response ?
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Old 22nd November 2005, 03:21 AM   #2
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Well, it depends on what you mean by "better". There is no guarantee about it being better, as there are so many variables at play. Certainly dipole cancellation is eliminated from the bass frequencies, and that’s a start. The potential for "better" bass exists, but also the potential to get an under-damped bass bump. Careful design and adjustment of driver and enclosure parameters could make the difference. I believe that more work needs to be done in general with ESLs in enclosures, or better yet, what I've been toiling on, ESLs covering all faces of a closed cylinder.
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Old 23rd November 2005, 10:25 PM   #3
Bazukaz is offline Bazukaz  Lithuania
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A closed cylinder would act as a closed anclosure , wouldn't it ?
I think it would be hard to build.
I will try both bipole and sealed enclosures, if i succeed making plates from wire net.
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Old 23rd November 2005, 10:53 PM   #4
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Sure, it acts like a closed box, but instead of side walls which flex and resonate, the whole cylinder expands and contracts ("breathes"). Absorptive damping material must fill the inside, of course. There are many advantages to this kind of approach. Peter Walker of Quad fame built experimental cylindrical ESLs many years before introducing the well-known planar models to the market. Let us know how the two models work out for you.
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Old 24th November 2005, 01:08 AM   #5
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Default Christmas is comming

Brian: a whole bunch of years ago I built up an ESL which was to be conical. I built the long triangular panels out of perf steel with a nylon powder coat dielectric. Due to other concerns I had to stop panel construction with only half of the necessary panels built. Since I had the frames all ready built I set them up with just half of the panels each. The resulting effect was much like that of the big MBL radial speaker. There was excellent stage width and depth with the interesting effect that as you walked toward the speaker the image stayed the same but moved forward an equal distance to that you had moved closer. The other nice effect was that as you walked back and forth across the back end of the listening room the image stayed solid but your perspective shifted as it would if you were to move across the front of a stage. In other words the players did not move from thier aparent positions but the balance of the presentation shifted as you would expect to have it do in a live situation.
I never got the time or chance to finish the project. I had thought that the conical shape would have less problems with internal back wave cancelation (as compared to a cylinder) as the presure wave front would have the natural tendency to vent out of the open bottom of the cone shaped frame. I did not get the chance to prove or disprove this theory as I only got the half cone versions up and running. Thought that this might be of some interest. Best regards Moray James.
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Old 24th November 2005, 07:44 AM   #6
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I did place a large sewer pvc pipe behind the esl (cut the pipe half). I kept the upper and bottem open. I expected more extended and powerful bass which was not the case. Maybe I got other results with a larger enclosure but I didn't try.
Even the hudge beveridge are compromised in bass extension so I stick to dynamic woofers for bass.
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Old 24th November 2005, 12:29 PM   #7
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Moray,

Interesting project. Do you have any pictures? Relative to your open-end venting comment, I would tend to think of it as depending on wavelength. At low frequencies the open cone end is a large vent, so below some frequency, you have "dipole cancellation" just as if it were a regular planar design. (This is also why MJ Dijkstra didn't achieve deeper bass.) At mid and high frequencies, the wavelengths "see" the other side of the cone as a reflecting boundary, and this distance would vary up and down the cone, distributing the comb filtering effect of the reflections. In my experiments, the configuration is a closed (top and bottom sealed) cylindrical drum with absorptive material inside to swallow the reflections. If the cylinder is tall, from floor to ceiling, you get an ideal line source, with a radiation pattern independent of frequency, and with the potential for pretty deep bass, although the last part is tricky as my efforts have shown me. I will report on this if/when I have something to show and tell.
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Old 24th November 2005, 08:18 PM   #8
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Default no pics

Sorry Brian: no pictures, don't think digital cameras were around back then. You are right about the cone spreading out the reflections that was part of the intent. The fact that the diaphragm was also shifting from wide at the bottom and narrow at the top was also intended to sperad panel resonances. The panels were about a hand span wide at the base and 1.25 inches at the top and about 40 inches long. Even with only half of the intended panels there was lots of surface area and they were quite dynamic. Stator to diaphragm was just under 1/16 inch. I used an Acoustat interface to drive them.
I must say that I have held doubts all these years about a mono pole design wondering if one could possibly absorb backwave over anywhere near a wide enough bandwidth with uniform absorption. I feel that dipole structures are the way to go. Letting a dynamic driver do what it can do best for the bottom end. I think that if recordings are made with directional microphones then playback ought to be directional as well. No proof about that it's just my impression. Good luck with the experiments. Regards Moray James.
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Old 25th November 2005, 05:55 AM   #9
el`Ol is offline el`Ol  Germany
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Here are some ESLs from the professional sector. Recommendations are 80l to 210l, but in this setting a 150 to 200 Hz crossover is needed, so the use of an enclosure is just to make placement easier. http://www.sonus.de/download/pdf/dat...d1211v2_de.pdf
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Old 25th November 2005, 09:18 AM   #10
Calvin is offline Calvin  Germany
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Hi,

imo a cylindrical ESL won´t work well. The reason is, that the soundwaves emitted from the inner side of the diaphragm interfere with the ones outside. They are not(!) reflected and kept inside the cylinder, even not at high frequencies. Think of the sealing membrane of Quad. The very thin diaphragm is acoustically nearly transparent! Filling the tube with fiber doesn´t solve the prob, but just reduces it slightly -and only at higher frequencies.
Putting the ESL into a CB can be a solution, but is imo far from optimum. Indeed does it help in reducing phase cancellation, but it should be constructed such way, that the sound from inside is absorbed completely, because every reflected sound will pass through the membrane to the outside -with accompanying interference probs.
So a classical box won´t be best. As Mr. Walker described, a very deep and heavily dampened compartement should be fine. But beeing closed, this box will still suffer from the problem, that almost all panels exhibit a very high Q-resonance with a long decay (group delay). This Q is even raised in a CB. A solution could be to reduce the input signal to the panel with a notch-filter. A measurement that´s used by many designers anyway. Another one is to use an open box design instead of CB. A BR-design for i.e. could be tuned such that the resonance frequency is dampened mechanically. By appearance this design will probabely look more like a tapered TML.
You have still to keep in mind, that with any box the problem of acoustic coupling is enhanced in hybrid-designs.
Too the compartement will always be quite voluminous.
I´d prefer to use a panel with a greater width in a hybrid design, without sealing the panel. Wether driven passively or actively its very easy to equalize the resonance and to correct for the phase cancellation. Depending on the build geometry of the panel the correction can be quite subtle. As I pointed out in an earlier thread ("Please rec. step-up transformers for ESL"), a combination of a dampened second-order-HP, together with a Notch-filter can equalize many panels perfectly.

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