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Old 17th October 2006, 05:51 AM   #11
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on the size of the panel. This idea was used by Roger Sanders. Roger used a single pipe that he called a "beam splitter". I have used multiple (smaller usually three) pipes of the plumbing variety as they are cheap and easy to get in various sizes (can be loaded with sand) and one large and two small will break up the rear wave off of the panel making the wave diffuse rather than being identical to the front wave. This helps make placement easier to do and also helps keep direct reflections form making their way back to the panel too. Regards Moray James.
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Old 22nd October 2006, 12:21 AM   #12
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I've played a bit with curved panels, and I keep coming back to flat ones. With curved panels, you get a bit more dispersion, but nothing like a monkey box speaker. And when you curve the panel, the insanely great dynamics go away. My solution is to have a set of competent bookshelf speakers to use when not seriously listening.

Sheldon
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Old 22nd October 2006, 08:31 AM   #13
Calvin is offline Calvin  Germany
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Hi,

I´ve played a bit with flat panels, and I keep coming back to curved ones or flat segmented ones. With flat panels You have to fix Your listening position to a tiny little spot. Those are al- or-nothing machines. The hardly noticeable advantage regarding high-freq-dynamics -and only there! and there are other factors with which You can influence the dynamic character far more!- costs in ease of handling and flexibility of listening position and so on.
My solution is to spare the money for additional bookshelf speakers but have a panel with some dispersion first hand.

jauu
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Old 22nd October 2006, 04:52 PM   #14
Few is offline Few  United States
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The dynamics of flat panels, as mentioned by Sheldon, are of particular interest to me. I think they were the first thing that struck me when I got my first pair of big flat panels working. I've long wondered what the origin of the effect is---they sound almost horn-like in that respect. That had me wondering whether the acoustic impedance match between the air and diaphragm, or perhaps the small diaphragm displacement, might somehow be responsible (since horns and large ESL panels share those characteristics).

As I design a new pair of ESLs, and consider using wire stators so that I can make the directivity less frequency dependent, I worry that I might lose some of those dynamics that I've gotten so used to. They're not something I want to give up. Sheldon, you've clearly heard more than your share of the original Quads, with their segmented panels. Do they give up some of the "snap" or dynamics that you hear in your single-wide-panel design? If so, might there be a cause other than the panel segmentation?

Sorry, I just realized this is a bit off the stator material thread, but it follows from the most recent posts.
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Old 22nd October 2006, 05:09 PM   #15
Calvin is offline Calvin  Germany
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Hi,

if You do things well, the difference between a segmented wire stator and a completely driven stator -wether curved or flat doesn´t make a noticeable difference- is marginal and could just be heard by direct comparison. Differences in frequency linearity, HV-supply and other parameters affect the sound of the panel far more.

jauu
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Old 23rd October 2006, 02:32 AM   #16
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The quads have a midrange naturalness that is the equal of any ESL I've heard. However, they do not have the dynamic impact of larger panels, segmented or not. They also lack the frequency extension that makes them lack weight, and actually in the case of the 57 actually makes midrange stand out even more. They are very polite speakers, and very gentle speakers, which make poorly recorded material listen-able. I don't feel that the quads are as good as my simple perf-metal one piece ESL speakers, but they are good enough that I would not hesitate on living with them if I didn't have my DIY speakers. There's a very short list of "livable" speakers that are not DIY for me.

I think Calvin is onto something with his mention of the segmented stators. I strongly suspect that if the segments are crossed over just short of beaming, then the dynamic impact you seek and the better dispersion can be had. I need to build some wire stators.

I built perf-metal stators due to the ease of construction and likelihood of success. But I do think that a well-done set of wire stators will make a better sounding and more versatile speaker that would allow segmentation and segmentation changes. I did try to build a long narrow ESL panel with perf metal, and a slightly wider one. The resonances within the strip were insanely bad. Segmentation can really only be done with wire stators, or with some method to hold the perf metal that doesn't create a cavity, and electrically separates the two stator sections.


Sheldon
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Old 23rd October 2006, 03:59 PM   #17
Few is offline Few  United States
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Thanks for the responses Calvin and Sheldon. By the way Sheldon, when you wrote "The resonances within the strip were insanely bad" does this refer to diaphragm resonances because of the way it was clamped (a long narrow strip) or to cavity resonances set up by the structure surrounding the diaphragm? I assume insanely bad means lots of peaks and suck-outs in the frequency response plot.
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Old 23rd October 2006, 06:43 PM   #18
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Quote:
Originally posted by Few
Thanks for the responses Calvin and Sheldon. By the way Sheldon, when you wrote "The resonances within the strip were insanely bad" does this refer to diaphragm resonances because of the way it was clamped (a long narrow strip) or to cavity resonances set up by the structure surrounding the diaphragm? I assume insanely bad means lots of peaks and suck-outs in the frequency response plot.
I think the problem was cavity related, rather than film resonances, but I'm not 100% sure. Neither the cavity resonance calculation or the film tension resonance calculation exactly matched what I measured. It was really honky and not good sounding at all.

It was bad enough that I bailed on trying to EQ it. And I realized that even if I could EQ it, I've still got diffraction and other problems with segmenting using perf metal. I had a frame built that held each section which meant that there was nearly 2" of dead space between the mid panel and the tweeter strip. That would hose up radiation pattern way more than the laser beam of sound was a problem (if that makes sense).


The way to segment in my mind is to use wire stators and one big piece of diaphragm that is driven differently in different parts be differing signals on the wires. I just don't see a reasonable way to use perf metal and not have big gaps between driven parts (it's possible, but kludgy). Quad 63's use fiberglass circuit board material and etch away portions to establish different driven regions. The 57's used conductive paint on plastic.

The way DIY ESL's shake out in my mind is:

perf metal: Easiest, most likely chance of success. Cheap, and quick, particularly if you aren't too worried about insulation. All one driven area which produces laser beams of sound. Hope you like to sit still. Tremendous dynamics.

Wire Stators: Hard, labor intensive, and may not be as flat or precise as perf metal. Chance of success is more closely tied to skill of fabricator. Less potential issues with cavity resonance. Flexible, can be segmented, or not, segments can be varied as part of the voicing process. Can be more ugly, but doesn’t have to be (see audiostatic for beautiful wire stators). Typically more bulky panels, requiring a larger frame structure to mount.

Exotic Methods: Circuit board material: Easy to build (like perf), free from shock hazards, can be segmented, can have wild segmentation (concentric circles, etc). Expensive! Mesh screening: like wire stators, but often harder to get flat and rattle free.

Anything I forgot?


Sheldon
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Old 23rd October 2006, 11:23 PM   #19
Few is offline Few  United States
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Quote:
Anything I forgot? -Sheldon
That's quite a bit already. Thanks very much. I too tried the segmented perforated metal approach, albeit just in prototype mode. I didn't have any more success than you did coming up with a way to avoid the gaps or cavities that you mentioned. I eventually bailed and just went with large laser-beaming panels. They sound great when you're in the hot seat, but I find that I log more hours out of the hot seat than in it, especially since the speakers are used for home theater applications as well as music.

The potential for easier segmentation is what has been causing me to lean toward wire stators, even though they're clearly trickier to put together than perf metal. I agree that they really provide the most practical way to provide segmentation without some sort of awkward resonance-supporting framework keeping the segments in position. I've been planning on using the same approach you described---segmented wire stators with the diaphragm treated as one large piece. If others have alternative approaches, I'd love to hear about them.

Few
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Old 24th October 2006, 07:55 AM   #20
Calvin is offline Calvin  Germany
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Hi,

imo one of the reasons for heavy resonances of a panel is due to lacking damping. You will certainly experience standing waves that depend on the physical dimensions of the panel. These can be minimized if the horizontal and vertical dimensions of a segment (or a complete panel) are chosen appropriately. Most panels don´t account for damping of the standing waves, since the diaphragm is pulled taut and fixed on hard spacer-material. The absence of damping at the edges and the big difference in mechanical impedance leads to heavy resonances. Using foam tapes helps a bit, as well does some damping material at the segment´s circumference. If You add some spots to account for the 1:70-1:100 rule (regarding the d/s) use some soft material (Audiostatic uses silicione-drops along the middle line of the membrane, ML did it with horizontally orientated foam-strips). My finding is that curved panels exhibit a bit less standing wave related resonances. Maybe because of the inherent higher stability of the metal sheets, maybe the bent membrane is less prone to this effect, I´m not sure. But I can´t measure the often to find resonance around 1kHz (~ 17cm wide panels) in my panels.
So I´d suggest to build curved panels in case You want a fullsize-diaphragm panel, or a segmented wire stator in case You want some dispersion.

jauu
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