Hi a.wayne,
no, the plot belongs to the Element 160, which is the smallest fullrange.
But the CSD behaviour is similar to all my models. There is a principle difference for the larger models X2 and E2.5 because of the additional ESL woofer panel. The additional esl panel interferes in a frequency range between 250 and 400 Hz at close nearfield (about 1 meter). As a result CSD show negative impact at 250 to 400 Hz at close nearfield. Since larger models are optimized for listening distances between 2,5 and 4 meter (X2) and 2,5 up to 6 meter (E2.5) its not an issue. At those distances interferences are minimized to a non-measurable level.
Capaciti
no, the plot belongs to the Element 160, which is the smallest fullrange.
But the CSD behaviour is similar to all my models. There is a principle difference for the larger models X2 and E2.5 because of the additional ESL woofer panel. The additional esl panel interferes in a frequency range between 250 and 400 Hz at close nearfield (about 1 meter). As a result CSD show negative impact at 250 to 400 Hz at close nearfield. Since larger models are optimized for listening distances between 2,5 and 4 meter (X2) and 2,5 up to 6 meter (E2.5) its not an issue. At those distances interferences are minimized to a non-measurable level.
Capaciti
As long as you keep the impulse response windowed to remove reflections, I found the far field CSD will correlate with the near field CSD for the odd diaphragm modes.
Capaciti brings up a good point though, many ESLs have poor CSDs because of resonances in the panels unrelated to diaphragm modal resonance.
Honestly, there are very few ESLs that I have measured that are not "embarrassed" by a slow sine wave sweep like Capaciti suggests.
I was somewhat successful with damping certain modes with strategic placement of silicone dots. But as you can imagine, it is alot like playing a game of "whack a mole" where certain placements damp particular modes but enhance others...a rather frustrating game I must say. After successful experiments using extremely thin monofilament silk screen mesh for damping I abandoned the silicone dot game.
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Glad to hear I'm not the only one to find spurious ugly sounding resonances in a DIY ESL panel! I've long been troubled by a buzz in my perforated steel non-segmented ESLs. I haven't tried scanning a sine wave frequency to isolate it, but once you hear it it's hard to ignore it. What I hear isn't a buzz like you'd hear with a loose wire touching a speaker cone, it's something more inherent in the construction. I'd spend time tracking it down but I'd rather just finish the new panels in the hope they'll not have the same problem. Based on this thread, though, it sounds like I'll have to anticipate finding such resonances in the new panels as well; I hope I can do a better job fixing them.
The whack-a-mole problem is exactly what I'd feared. It sure would be nice to find a formulaic way to solve the diaphragm resonance problem. I dread having to tear panels apart a couple hundred times to gradually track down problems. I'd certainly appreciate hearing about successful strategies others have developed to make that process less painful.
Bolserst, your fine mesh approach seems to do a great job for frequencies below 300 Hz or so. Since my panels will cross over at around 300-400 Hz I'm really looking for a way to achieve clean response at higher frequencies. Looking back at your near field measurements, though, it looks like the most obvious resonances you measured were at or below about 300 Hz.
Few
The whack-a-mole problem is exactly what I'd feared. It sure would be nice to find a formulaic way to solve the diaphragm resonance problem. I dread having to tear panels apart a couple hundred times to gradually track down problems. I'd certainly appreciate hearing about successful strategies others have developed to make that process less painful.
Bolserst, your fine mesh approach seems to do a great job for frequencies below 300 Hz or so. Since my panels will cross over at around 300-400 Hz I'm really looking for a way to achieve clean response at higher frequencies. Looking back at your near field measurements, though, it looks like the most obvious resonances you measured were at or below about 300 Hz.
Few
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Hi,
there are two basic root causes for ESL noises when sine sweeping:
1. The inner edge of the surrounding membrane frame. Some people use scotch tape or something similar. After a certain time the movement of the membrane will result in briddled attachment of the membrane at the border tape-free moving membrane, cauing noises.
2. An inapproriate coating will allow charge to flow on the outer surface of the coating altough the coating appears to be high resistive. This depends on final surface roughness of the coating. imo any coating which feels rough when wipping with a finger over it, will cause charge flow noises.
Its not proven, but i think that an ESL which makes a certain level of noises will never "disappear" when playing music. Sound sticks to the speaker.
There has been a study years ago, where one showed that even the first move of a dome tweeter makes the ear to detect the speaker, since the move of the dome tweeter is at frequency and timing close to the situation where evolution made us sensible (in level and direction) for dangerous noises
Capaciti
there are two basic root causes for ESL noises when sine sweeping:
1. The inner edge of the surrounding membrane frame. Some people use scotch tape or something similar. After a certain time the movement of the membrane will result in briddled attachment of the membrane at the border tape-free moving membrane, cauing noises.
2. An inapproriate coating will allow charge to flow on the outer surface of the coating altough the coating appears to be high resistive. This depends on final surface roughness of the coating. imo any coating which feels rough when wipping with a finger over it, will cause charge flow noises.
Its not proven, but i think that an ESL which makes a certain level of noises will never "disappear" when playing music. Sound sticks to the speaker.
There has been a study years ago, where one showed that even the first move of a dome tweeter makes the ear to detect the speaker, since the move of the dome tweeter is at frequency and timing close to the situation where evolution made us sensible (in level and direction) for dangerous noises
Capaciti
In the past I have experimented with PEDOT coatings in combination with n-Butanol. According to a patent, pretreating the PET-foil with this alcohol should improve the adhesion of the coating.
Apart from the fact that I couldn't derive a benefit from doing this, one disadvantage was the resulting roughness of the coating. It felt like very fine sandpaper when wiping with the finger over it. Compared to a panel without n-Butanol treating, the sound was 'hashy'. But I could never nail down the reason for this. Because this rough coating is also more sensitive to dust accumulation, I stopped further experiments.
Will take a look if I have saved the impulse data for recreating the CSD.
Harry
Harry,
if you would have sine sweeped this panel having the rough coating, possibly some questionable noises would have been audible. As you describe the hashy sound it schould correlate to CSD as well.
Capaciti
if you would have sine sweeped this panel having the rough coating, possibly some questionable noises would have been audible. As you describe the hashy sound it schould correlate to CSD as well.
Capaciti
"Polyester foils (PET) are surface-hydrolysed in industry, usually via chemical treatment with, for example, trichloroacetic acid or potassium hydroxide, as disclosed in WO2005/111606 A1. Wettability and surface tension are stable in these methods even after storage."
In my experience, nylon coating, if not melted, is slightly rough, somewhat like polished marble or limestone. Approximately the same happens if one utilize phenol based coating. Surface activated PET film (capacitor grade) has one surface less shiny then the other.
Alex
Capaciti,
I've been following this thread and been playing around with various loose Acoustat panels, and the tone sweeps I've done have revealed these little noise "gremlins". Out right buzzing from obvious mechanical defects such as loose wires and bad glue joints at the frame edges are all understandable. Also arcing from charge migration is something that has occurred to me. A "soft" gentle arcing not a sparking "SNAP" type which would indicate a major breach of insulation somewhere. The 30 to 300 Hz range is especially brutally revealing of shortcomings.
Would you please expound upon the "sound sticking to" the rough coating surface idea? Acoustat has a rough coating which faces front. Would there be a better sound if some noise masking that might occur if the rough surface was turned to the back? Should coating be applied front and back to a diaphragm? I also wonder if a diaphragm might be designed such that the resistive conductive layer is captured between a laminate of ultra thin PET or other film on each side to net a total thickness inline with acceptable standards of total diaphragm thickness? Adhesive would be ruled out I think. Would have to be a high heat melting process to create a totally fused bond of the layers I would think. What say all of you?
Hi,
as mentioned before i cannot proove that undesired noises make the speaker detectable for the ears (brain) regarding position, but i am quit sure that imaging and depth of listened music increased proportional to progress regarding "noise free" ESL design.
Even this might be a subjective argument, there is nothing to accept about a speaker creating unintended noises as we talk about music with dynamic ranges up to 90dB. The scale of sensitivity which is provided by our ears owns a factor of 1000000. Easy to conclude that an unintended noise of lets say even -30dB lower than music level will be detected, analyzed and as a result judged to be disturbing.
It doesn't matter where noises come from (coating, spacer, loose wires, .....), such a transducer will be compromised and can never be claimed good, perfect, excellent or something else.
You might think why i treat this somekind like a philosophy ? i listended to much people, i read a lot of threads and mostly those discussions are about whether a fullrange is better than a hybrid, or which radiation pattern is better for an ESL and bla bla bla..... To me such discussions are worthless until one is able to make an ESL which fullfills basic principles. And a rattling, singing, whistling..... ESL is far away
Capaciti
as mentioned before i cannot proove that undesired noises make the speaker detectable for the ears (brain) regarding position, but i am quit sure that imaging and depth of listened music increased proportional to progress regarding "noise free" ESL design.
Even this might be a subjective argument, there is nothing to accept about a speaker creating unintended noises as we talk about music with dynamic ranges up to 90dB. The scale of sensitivity which is provided by our ears owns a factor of 1000000. Easy to conclude that an unintended noise of lets say even -30dB lower than music level will be detected, analyzed and as a result judged to be disturbing.
It doesn't matter where noises come from (coating, spacer, loose wires, .....), such a transducer will be compromised and can never be claimed good, perfect, excellent or something else.
You might think why i treat this somekind like a philosophy ? i listended to much people, i read a lot of threads and mostly those discussions are about whether a fullrange is better than a hybrid, or which radiation pattern is better for an ESL and bla bla bla..... To me such discussions are worthless until one is able to make an ESL which fullfills basic principles. And a rattling, singing, whistling..... ESL is far away
Capaciti
I’ve been following this thread with a great deal of interest and appreciation for those who share their knowledge. I only wish I had something to contribute. For the benefit of those like me who haven’t the experience and aptitude and equipment for such fine tuning, it would be great if someone would pen a list of general guidelines for minimizing resonances in the diaphragms and stators. Thanks for your efforts!
For folks that had missed it, Charlie provided a nice solution for stiffening up large perforated sheet metal stators which are prone to vibration when the stators are flat and have large unsupported widths. Check it out 🙂
http://www.diyaudio.com/forums/planars-exotics/166280-jazzmans-new-stat-panels.html#post2174940
A few things I have found that reduce the potential for buzzes and rattles in your DIY ESL.
1) Avoid diaphragm material thicker than 1/4mil(6µm).
2) Avoid high diaphragm tension. I prefer using the minimum tension needed to avoid wrinkles when gluing to frame followed by heat shrinking.
1) & 2) both lead to less pronounced diaphragm resonance modes and less vibrational energy induced into the stators.
3) As Capaciti already mentioned, avoid brittle glues or tapes when attaching the diaphragm.
4) For hybrids, suppress the fundamental diaphragm resonance. This is the most prominent source of stator buzzes and vibrations. Remember that the woofer will also be acoustically exciting this vibration mode, even if you cross over the ESL well above resonance. To check it out, disconnect the speaker wires feeding the ESL panel and play some music with the woofer alone. Place your ear near the ESL panel and you will hear the diaphragm humming along with one note. If you have test equipment, a slow sine wave sweep fed to the woofer will highlight acoustic excitation of the ESL diaphragm resonance also.
My preferred damping method is the application of thin woven mesh to the rear stator. Acoustat used felt which works well, but affects the midrange response some. A row of silicone dots in the middle of the panel helps to some extent. Capaciti has obviously perfected the art of silicone dot damping through the use of many precisely placed dots, but I'd say this is beyond the capability of most DIY builders. Crossovers with notch filters at resonance help also, but they do not avoid the ESL diaphragm humming along to the woofers tune the way physically or acoustically damping the diaphragm does.
5) If silicone dots are used for damping or stabilizing the diaphragm make sure they are smooth and round dots with no trails or whiskers of silicone leading away from the dots out on to the diaphragm. Also, remember that the silicone dots will be feeding vibration from the diaphragm right into the stators and frames so stiffen them up accordingly.
Thanks Bolserat!
That's exactly the kind of information I and others sorely need-- especially considering that this hobby takes so much effort and money that a first time builder might never muster the energy for a second attempt if their first speakers don't sound at least decent. Thanks again!
My next project will be to rebuild my old stat panels (the ones I just replaced) and this time I will reduce the diaphragm tension, as the logic of doing so is now apparent.
Charlie
That's exactly the kind of information I and others sorely need-- especially considering that this hobby takes so much effort and money that a first time builder might never muster the energy for a second attempt if their first speakers don't sound at least decent. Thanks again!
My next project will be to rebuild my old stat panels (the ones I just replaced) and this time I will reduce the diaphragm tension, as the logic of doing so is now apparent.
Charlie
The suggestion that lower diaphragm tension yields better control of buzzes and resonances raises a conflict with the admonition to go for the highest tension possible in order to allow small diaphragm-stator spacing and highest sensitivity (Calvin comes to mind here). Of course it may very well be true that low diaphragm is better in one way and worse in another, but it leaves us with a dilemma, doesn't it?
Few
Few
Imagine that, an engineering design problem that requires compromise. 😀
Seriously though, I think the idea behind the statement higher tension = higher sensitivity goes something like this. Suppose you have a panel where the diaphragm collapses to one stator or the other as the bias voltage is increased. If you rebuilt the panel with higher tension, you could increase the bias voltage before collapse, thus increasing efficiency. Or, as Calvin has shown, for a given step-up transformer, your efficiency increases as the D/S is reduced. But, for the same unsupported width of diaphragm, you will need greater tension with the reduced spacing to avoid diaphragm collapse when the bias voltage is applied.
There are two other solutions to the problem besides increasing tension.
1) Use silicone dots as Audiostatic taught in their patent:
Electrostatic loudspeaker having ... - Google Patent Search
2) Add spacers to reduce the unsupported width. CharlieM used this technique to good effect in his wide hybrid panels.
http://www.diyaudio.com/forums/planars-exotics/166280-jazzmans-new-stat-panels.html#post2174940
Hi Bolserst,
I agree with your summary of the reasoning that leads to the conclusion that higher tension can yield greater sensitivity (probably at the cost of decreased low frequency extension). That's what I had in mind when I posted, although I may not have made that very clear.
I also agree that compromises are nothing new in this game. They're clearly the norm not the exception. My main point was that I hadn't previously been aware of the compromise that is associated with diaphragm tension. Most previous discussions seemed to emphasize the sensitivity issue and ignore the buzz/rattle issue. I appreciate the efforts you and others have made to highlight the latter.
Thanks for the Audiostatic patent link. I hadn't seen that. My current (now many years old) ESLs use the same double-stick foam spacer technique Charlie shows. I am going to try to reduce stray capacitance in my new panels by going with the dots.
Few
I agree with your summary of the reasoning that leads to the conclusion that higher tension can yield greater sensitivity (probably at the cost of decreased low frequency extension). That's what I had in mind when I posted, although I may not have made that very clear.
I also agree that compromises are nothing new in this game. They're clearly the norm not the exception. My main point was that I hadn't previously been aware of the compromise that is associated with diaphragm tension. Most previous discussions seemed to emphasize the sensitivity issue and ignore the buzz/rattle issue. I appreciate the efforts you and others have made to highlight the latter.
Thanks for the Audiostatic patent link. I hadn't seen that. My current (now many years old) ESLs use the same double-stick foam spacer technique Charlie shows. I am going to try to reduce stray capacitance in my new panels by going with the dots.
Few
I thought about using tape dots on my panels but I figured dots wouldn't provide enough surface area to hold the perf stators properly gapped. The problem with all 3 sets of perf metal panels I've built so far is that not one piece of metal was straight and flat when it arrived. Every piece was at least concave on the smooth-hole side (that faces the diaphragm) and most had some creases, dents and/or bent corners-- and if you try to get them truly flat they end up "oil canning"-- it's maddening. Anyway, that's one reason I went with two full length vertical supports on 12'" wide panels -- to keep the stators stuck together gapped and to keep the diaphragm centered across the deviations in the stators. My first panels had the diaphragms stretched to 1% elongation and I never heard them bottom out to a stator so I know I can go at least as low as 1% with the d/s spacing, bias voltage and support spans that I used.
I've seen the wire stators on Capaciti's website and also saw some photos of Few's wire stators and they were beautifully built-- and I bet they are flatter than my perf panels. It seems to me a nice feature of wire stators is that they are aligned and stiffened externally by the framework and don't have to rely on dots or supports to keep the stators properly aligned and gapped.
I'm looking forward to seeing Few's wire stators completed.
I've seen the wire stators on Capaciti's website and also saw some photos of Few's wire stators and they were beautifully built-- and I bet they are flatter than my perf panels. It seems to me a nice feature of wire stators is that they are aligned and stiffened externally by the framework and don't have to rely on dots or supports to keep the stators properly aligned and gapped.
I'm looking forward to seeing Few's wire stators completed.
Charlie,
I know what you mean about the creases etc. in perforated metal. Once it gets non-flat, it's a real bear to try to flatten it again without some heavy duty equipment.
I'm looking to seeing Few's stators completed also!🙂 Unfortunately, life/work has been getting in the way big time, and my limited time has been spent on the open baffle woofer array that's going to complement the ESL panels. I am making (glacially slow) progress, though, so perhaps I'll have something worth posted before too long. I do appreciate your patience and interest.
My implementation of "stretched" wires hasn't created an array of wires that's as flat as I would like. There are a few kinks and poorly tensioned areas that nag me. The good news is that it'll be easier to straighten the kinks, or at least ensure that they bend away from the diaphragm instead of toward it, than would be the case with perforated metal. I can't help thinking that copper clad fiberglass boards such as those used to make printed circuit boards would be almost guaranteed flat and kink-proof. Nonetheless, I'm trying hard not to start planning the next project until I'm at least halfway done with this one. This diy speaker stuff is a strange sickness.
Few
I know what you mean about the creases etc. in perforated metal. Once it gets non-flat, it's a real bear to try to flatten it again without some heavy duty equipment.
I'm looking to seeing Few's stators completed also!🙂 Unfortunately, life/work has been getting in the way big time, and my limited time has been spent on the open baffle woofer array that's going to complement the ESL panels. I am making (glacially slow) progress, though, so perhaps I'll have something worth posted before too long. I do appreciate your patience and interest.
My implementation of "stretched" wires hasn't created an array of wires that's as flat as I would like. There are a few kinks and poorly tensioned areas that nag me. The good news is that it'll be easier to straighten the kinks, or at least ensure that they bend away from the diaphragm instead of toward it, than would be the case with perforated metal. I can't help thinking that copper clad fiberglass boards such as those used to make printed circuit boards would be almost guaranteed flat and kink-proof. Nonetheless, I'm trying hard not to start planning the next project until I'm at least halfway done with this one. This diy speaker stuff is a strange sickness.
Few
Mike Wright used rigid girder-like plastic frames in his ESL units. The stators have to be as strong as the sound force rise.
Shouldn't it be pretty straightforward to identify bits that ring by striking them or singing to them (like long welding-rod stators and sheets of perforated aluminum)?
Shouldn't it be pretty straightforward to identify bits that ring by striking them or singing to them (like long welding-rod stators and sheets of perforated aluminum)?