Unfortunately no direct measurements of the mesh, only inferences.
There is a track on one CD I have that was only playable at very low volumes - barely audible - without the mesh. The track included a bass note, probably close to the membrane resonance at 37 Hz, that caused the membrane to slap backwards and forwards between the stators. Once I glued the mesh to the rear stator, the track was playable at full volume - maybe a factor of 30 higher in voltage - perhaps 50-60 dB in SPL.
There is a track on one CD I have that was only playable at very low volumes - barely audible - without the mesh. The track included a bass note, probably close to the membrane resonance at 37 Hz, that caused the membrane to slap backwards and forwards between the stators. Once I glued the mesh to the rear stator, the track was playable at full volume - maybe a factor of 30 higher in voltage - perhaps 50-60 dB in SPL.
What mesh 'count' is most useful? My google inquiry reveals a wide variation in the tightness of the weave.
I don't know your speakers but having rebuilt the Quad 63s for a lot of folks the biggest bass killers in these is the resonance of the panels around 200 hz. Your panels have to be really rigidly secured so they don't flop around like stock 63s. It's so strong in the stock quads that it's like the mylar stays still and the and the stators move back and forth so the stators are moving the air and cancel out the movement of air from the diaphragm.
You have to secure the panels to reduce or lower the frequency of any resonance. I have a method of securing the panel structure to the frame that greatly reduces and damps the panels movements and thus the resonance. I used quads one year at the audio show and got comments like "I've never heard Quads sound so good." and "amazing bass". Bass drums you can feel in your chest.
The other result is that the imaging greatly improves and is much more stable.
Good luck.
You have to secure the panels to reduce or lower the frequency of any resonance. I have a method of securing the panel structure to the frame that greatly reduces and damps the panels movements and thus the resonance. I used quads one year at the audio show and got comments like "I've never heard Quads sound so good." and "amazing bass". Bass drums you can feel in your chest.
The other result is that the imaging greatly improves and is much more stable.
Good luck.
For detail on mesh recommendations see post #47 at Mechanical Sectioning .vs. Silicon dots for resonance control
Re mechanical resonances. I've no direct experience of managing mechanical resonances in the stators, but I have thought about it a bit. From a physics perspective, there are two types of mechanical resonance likely to occur.
The first is where the membrane moves backwards and forwards driving the air and the stators both move backwards and forward in the opposite direction - but the distance between the two stators stays the same. The movement comes about because of the force applied to the air by the membrane, since the membrane is driven by the stators, there must be an equal and opposite force on the stators. In this case, there is a slight loss in output, but no non-linearity to cause distortion.
The second case comes about because of attraction between the stators whenever the ac voltage peaks -because they have opposite voltages on them - so this happens at twice the frequency of the audio signal and causes the distance between the stators to change/oscillate. This introduces second harmonic distortion because the force between the stators increases as the voltage squared.
In general there are two solutions to these types of resonance problem - increase the stiffness of the stators, or increase the mass of the stators. Increasing the stiffness will reduce the amplitude of the resonance, but it will also push it to higher frequencies where it is more audible - so it's not that much of a benefit. Increasing the mass of the stators will lower the resonant frequency and reduce the amplitude of the movement above the resonant frequency. Adding ribs to the stators obviously has both effects. I have thought seriously about using steel ribs to get the mass and stiffness up without blocking the sound transmission through the stators.
Re mechanical resonances. I've no direct experience of managing mechanical resonances in the stators, but I have thought about it a bit. From a physics perspective, there are two types of mechanical resonance likely to occur.
The first is where the membrane moves backwards and forwards driving the air and the stators both move backwards and forward in the opposite direction - but the distance between the two stators stays the same. The movement comes about because of the force applied to the air by the membrane, since the membrane is driven by the stators, there must be an equal and opposite force on the stators. In this case, there is a slight loss in output, but no non-linearity to cause distortion.
The second case comes about because of attraction between the stators whenever the ac voltage peaks -because they have opposite voltages on them - so this happens at twice the frequency of the audio signal and causes the distance between the stators to change/oscillate. This introduces second harmonic distortion because the force between the stators increases as the voltage squared.
In general there are two solutions to these types of resonance problem - increase the stiffness of the stators, or increase the mass of the stators. Increasing the stiffness will reduce the amplitude of the resonance, but it will also push it to higher frequencies where it is more audible - so it's not that much of a benefit. Increasing the mass of the stators will lower the resonant frequency and reduce the amplitude of the movement above the resonant frequency. Adding ribs to the stators obviously has both effects. I have thought seriously about using steel ribs to get the mass and stiffness up without blocking the sound transmission through the stators.
As I mentioned mine are Acoustat panels, the louvred structure once mounted to the frame is very rigid so resonance is confined to the membrane. The wire stators are glued/embedded in the styrene louvres. I did find the thread you mention with great info just now. However there remains the question of optimal resistence. A matter of experimentation it seems. It might be possible to provide for adjustment by doubling the mesh and sliding them apart to close/open the passage
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Has anyone tried making an ESL bass only panel by just enclosing/sandwiching the membrane between two others to eliminate resonance? I recall seeing a pair of massive ESL Stax subwoofers somewhere in a pic
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It sounds like you are describing the Quad ESLs (all of them). The dust cover is a tensioned membrane on each side.
bolserst also worked on using undriven membranes next to driven ones to modify resonance.
bolserst also worked on using undriven membranes next to driven ones to modify resonance.
I am aware of the Quads but I thought they were just dust covers/protection and too far away from the membrane to serve as dampeners. I'm quite often wrong though; just ask my wife 🙂
If the thread count and thread size is not available to use the chart golfnut created from Saarti mesh data, you can also get a first order estimate of the acoustic resistance of a mesh if the pore size is specified. Thinking about a segmented wire stator ESL
I posted some measurements of the LF and HF effect of the Acoustat felt pads here: Acoustat Answer Man is here: Post#1529
Unlike using mesh, you can see that the thick pads adds some mass which lowers the resonance a bit. Perhaps this was desired. Strickland couldn’t lower the resonance any more by reducing tension as Acoustats are already running out of stability margin for keeping the diaphragm from collapsing to a stator.
The effect on HF response from the thick felt pads is much less than I had anticipated (+/-1.5dB), but much more than using mesh which still acts like a pure acoustic resistance at higher frequencies. Compare with the mesh measurements here: Mechanical Sectioning .vs. Silicon dots for resonance control
For those interested, here is a link to a post showing the measurements for using an adjacent undriven membrane to damp the resonance of a driven membrane.
Optimizing my DIY full range esl
A summary pic is shown, but more extensive measurements sets and details are contained in the Passive_Damp_v2.pdf file.
Looks like DEA Electrostatics is still showing some of their models using this technique.
They call it “environmental resonators”
Electrostatic loudspeakers model Magic Music - DEA Electrostatics | Audio systems design and production
So How does membrane tension tune FR and freq. extension? Just tapping on the frames with no power on exhibits the resonance. Would this be a good test for measuring subjectively how well the silk screen is performing?
The membrane resonance frequency decreases if tension is reduced, and the response rolls off sharply below resonance so it defines the LF extension. You can get a subjective impression whether mesh or felt is providing any damping by tapping the frame and listening to the resonance. But, once damping gets Q below about 5, I think it will be very difficult to tell differences between damping levels just by listening; you would probably need to measure.
Is there a positive effect if you can prevent resonance from traveling into the frame? For example if you built a structure so rigid it swamps the membrane's ability. Is the frame a factor?
Hi Discopete
I think you misunderstand the nature of the resonance.
The resonance is determined by two things - the tension in the membrane and the air mass in front of the membrane - which is determined by the area of the panel (crudely). Almost nothing else matters.
The movement in the frame is similar to a gun recoil - the membrane pushes the airmass, the charge on the stators push the membrane, and the stators are bonded to the frame - so it is recoil from pushing the air - the frame moves in the opposite direction to the air. The only thing that really reduces the effect is increasing the mass of the frame and stators - but there is no point in getting carried away. You'll be able to feel the frame recoil if you put your hand on the frame when music is playing - you will feel all frequencies, not just the resonance. The movement falls in proportion to frequency, so you'll not feel the high frequencies.
I think you misunderstand the nature of the resonance.
The resonance is determined by two things - the tension in the membrane and the air mass in front of the membrane - which is determined by the area of the panel (crudely). Almost nothing else matters.
The movement in the frame is similar to a gun recoil - the membrane pushes the airmass, the charge on the stators push the membrane, and the stators are bonded to the frame - so it is recoil from pushing the air - the frame moves in the opposite direction to the air. The only thing that really reduces the effect is increasing the mass of the frame and stators - but there is no point in getting carried away. You'll be able to feel the frame recoil if you put your hand on the frame when music is playing - you will feel all frequencies, not just the resonance. The movement falls in proportion to frequency, so you'll not feel the high frequencies.
I get all you are saying. You are addressing the issue I brought up. So my question remains.. is there a positive effect if you stop the recoil? A massive enough substrait will do so. I mean this hypothetically.
Discopete - Yes. The frame holds the stator, so called because it is ideally stationary. The membrane, sandwiched between the stator panels, is what is ideally moves the air. When the stators are not held stationary (are floppy) and can vibrate they move air too. The stators are perforated panels but about 50% of it is solid area, not holes and that is the part that can move air.
Now when the whole assembly resonates the charged membrane pushes the air in one direction and the unperforated part of the stator is pushing air in the opposite direction. The air pressure from the stator is subtracted from the air pressure of the membrane and reduces the output of the speaker.
By making the speaker panel both rigid and rigidly held the subtractive effect of the stator surface area becomes much smaller because the stator is stationary. It's actually more complicated because in involves the phase of the membrane and stators and their resonant points. It can be so great that the stators are the only thing moving and the membrane stands still. Uncontrolled resonance.
What you will hear is much more impactful bass and more precise imaging and a cleaner presentation because only the membrane which is the only thing that ideally moves the air IS moving the air.
I've modified a lot of Quad speakers and that's the result I get. People have gladly paid me mucho $$ to get that kind of performance out of the Quads.
Now when the whole assembly resonates the charged membrane pushes the air in one direction and the unperforated part of the stator is pushing air in the opposite direction. The air pressure from the stator is subtracted from the air pressure of the membrane and reduces the output of the speaker.
By making the speaker panel both rigid and rigidly held the subtractive effect of the stator surface area becomes much smaller because the stator is stationary. It's actually more complicated because in involves the phase of the membrane and stators and their resonant points. It can be so great that the stators are the only thing moving and the membrane stands still. Uncontrolled resonance.
What you will hear is much more impactful bass and more precise imaging and a cleaner presentation because only the membrane which is the only thing that ideally moves the air IS moving the air.
I've modified a lot of Quad speakers and that's the result I get. People have gladly paid me mucho $$ to get that kind of performance out of the Quads.
Thanks. It's all intuitive logic applicable to any speaker topology. But what I want to know is how much would the general resonance issue be mitigated by rendering the stator inert. My reference is the Acoustat panels, namely Monitor 3. The main thrust in discussion about it refers to stopping the membrane from ringing with silk screen mesh. I just want to know if a solid substrate is worthwhile or if the ringing swamps any additional dampening of the stator.
You could make the frame and stators out of concrete posts and the resonance will still be there because it's nothing to do with the frame - its the membrane and the air.
Apparently I disagree. But my experience is with Quad ESL 63s in which the membranes are very low mass. In addition the the polarizing voltage will keep the membrane equidistant from the stators. Sound in the air that the speaker picks up will turn it into a microphone feeding a voltage back to the amplifier which will damp it according to it's damping factor. Short out the input transformer (if you have them) and see if that doesn't damp your membrane.
If the stators are vibrating at all then securing them is in order. You may find out the membranes aren't the problem. Let me put it this way: You need to clean the window for a clear view. Then you can address the membranes.
Bottom line- -You have to try it to decide since your ears are the only test equipment that counts.
I can say that with the Quads the difference is huge.
Good luck.
If the stators are vibrating at all then securing them is in order. You may find out the membranes aren't the problem. Let me put it this way: You need to clean the window for a clear view. Then you can address the membranes.
Bottom line- -You have to try it to decide since your ears are the only test equipment that counts.
I can say that with the Quads the difference is huge.
Good luck.
So aside from the fact the wire stators on the Acoustats are not a factor in the way misbehavior in the Quads may exist, how is resonance alone dealt with in the Quads? Is it the protective non-driven membrane on either side of the assembly after all? Or the perforated stator? It seems the stator would inhibit sensitivity by a large margin, much more than is the case, if it was part of the design of the stator.
I just went over to the Quad thread and indeed there is woven screen on one stator
I just went over to the Quad thread and indeed there is woven screen on one stator
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