Mechanical Sectioning .vs. Silicon dots for resonance control

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Microphone was placed 1 meter in front of the midpoint of the diaphragm

1) Effect of 1/16” felt place on the front stator, or the rear stator
2) Effect of 110 count mesh, on the front stator, or rear stator
3) Effect of 160 count mesh, on the front stator, or rear stator

Felt on the front stator progressively filters out more with increasing frequency.
Felt on the rear stator is interesting in that it filters out the midrange but actually boosts the highs.(reflections from the felt? Or cavity resonance effect?)

Both of the silk screen meshes had essentially no effect on the response.

Thanks again to Atom666 for suggesting the silk screen. The results are much better than any other woven cloth I had tried, providing significant LF damping without affecting the HF response.


The panel sounded like it measured. Adding LF damping with the 160 count silk screen(or felt) tightened up the LF response. Drums had noticeably more impact with the damping in place. When the felt was added to the rear stator you can notice slight loss of detail and "sparkle" in the midrange. I could not tell any difference in the midrange when the silk screen mesh was added.


Dear Bolserst,

I was wondering if you are still of the opinion that silk screen mesh has no audible influence in the midrange? And how about high frequency range?
Are you still using mesh on your panels? If so, is it only on the back stator?
I was just wondering about this damping screen as I still experience colouration in the bass range of my full range esl's and I want to give it another try... I tried it only once and that time it had a negative impact on midrange sound - resulting in a clearly less transparant sound.
 
Hi,

after 3 years since my last experiment with 160 count silk screen mesh and no noticable results, I tried to mount the same silk screen again at the back of one esl. This time I used double sided tape on the back stator and horizontal stator bars. I managed to get it reasonably thight - but not very tight.

I did measurements, unfortunately at low sound level, at 15 cm in front of stator, with and without damping screen:

freqency response:

fq.jpg


THD:

thd.jpg


I did listening tests and in my opinion there is a small difference in sound when comparing the esl with and without screen: it seems voices are a little bit duller, but this is a rather small difference. When testing some o experimental jazz music that has low frequency content, there is a big difference to be heard: the esl without screen starts to resonate and there is heavy distortion (rattling sound), whereas the esl with damping screen sounds much better, only subtle resonance sounds.

The screen is about 2 cm seperated from the membrane.
 
Are you still using mesh on your panels? If so, is it only on the back stator?.
Yes, I still use mesh on my panels. The 160 count silk screen I had been using was only about 18 Rayl, but I found a small supply of 40 Rayl mesh at a local supplier. I did purchase some of the T120 mesh mentioned here(Planar Question), but have not had the opportunity to test it yet. If it comes close to the predicted acoustic resistance, it would be an excellent choice for ESL damping mesh. I will be sure to post the results.

I use the mesh on both front and rear stators to achieve the damping in the bass that I desire. It also helps keep dust and pet hair out of the air gap. I have one ESL pair still in operation with felt on the rear stator. As mentioned earlier in this thread, midrange quality was changed by the felt. But I found if I use EQ to match the response(1.5m anechoic using windowed impulse) before the felt was added, the midrange difference in quality I was hearing went away. So, I think that the majority of the change in “clarity” that you are hearing may just come down to small changes in frequency response.

… it seems voices are a little bit duller, but this is a rather small difference. When testing some o experimental jazz music that has low frequency content, there is a big difference to be heard: the esl without screen starts to resonate and there is heavy distortion (rattling sound), whereas the esl with damping screen sounds much better, only subtle resonance sounds.
The screen is about 2 cm seperated from the membrane.
Sounds like you are achieving some of the improvements in bass damping that you are after with the improved mesh mounting technique. For even better damping (to remove all the resonance sounds), you would need to use mesh with increased acoustic resistance, use mesh on both front and rear, or mount mesh closer to the diaphragm.

Concerning effect of mesh on midrange response: the further your damping mesh is from the diaphragm the lower in frequency the reflection effect from the mesh will be seen. With 2cm separation, the largest effect will be seen in the 1kHz – 2kHz range. I usually mount mine within 5mm of the diaphragm so the effect is limited to a minor roll-off change in the top octave which is easily compensated from with small change in transformer primary damping resistor value. Quad mounts theirs on the diaphragm side of the stator...can't get any closer than that.
 
Bolserst, this is interesting as I am refurbishing a pair of Audiostatic ESH 100. As you probably know this esl is an hybrid with a crossover of 100hz. So the esl part is getting a considerable portion of bass. I’ve also read reports of nasty resonances in the Audiostatic.
Perhaps I can clamp the mesh to the horizontal aluminium bars or use double sided tape to get the mesh as close as possible to the diaphragms.
 
Thanks for your reply Bolserst. A few days ago I ordered 80T/200 mesh for testing and comparison to my current 72T/180 mesh. But after reading your post in which you advice for 100T or 120T fabric I'm wondering if I should order another mesh (100T / 120T) as well for testing and comparison.

In a previous post in this topic (#25, link here) you wrote about the 200 count mesh:

"As you can see, down to 80Hz, the 160 count mesh damps as well as the felt.
The 200 count mesh should be even better."

But in another post (#46, link here) you wrote:

"The 80T fabric you linked to has Ra not that much higher than tightly stretched grill cloth. I would suggest using the 100T or 120T fabric instead."

This sounds a bit contradictory to me. If I'm interpreting your table about showing the estimated acoustic resistance in Rayle correctly, 80T/200 count mesh has still a much higher acoustic resistance (16.0 Rayle) than let's say your previously mentioned 64T/160 count mesh (9.4 Rayle)?
 
As I said I'm really interested in this damping technique. At first I tried to use double sided tape to attach the mesh to the aluminium cross bars in my Audiostatics. This was not very successful. A sticky business, a lot of work and almost impossible to rearrange or correct your mistakes. Then I found a plastic u-profile that had a tight fit on the cross bar and in the same time could clamp and stretch the mesh. The folds at the edge of the panel will be straightened out when joining the two stator halves.
 

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Hi All

There is a company called Saarti that sells acoustic mesh with specified values for the acoustic resistance. Using their specifications I assembled the following chart - hope it helps. It should work for any mono-filament mesh like screen printing mesh, filter cloth (eg for flour ), etc. The equation I used to assemble the chart gave the saarti numbers within about plus or minus 20%.

The damping required depends on the size of panel and the resonant frequency of the membrane, but it should be between 20 and 100 rayl, probably close to 40 or 50 is a good starting guess.

As Bolserst advises, the cloth should be as close as practical to the stators to minimise the effects of reflections on the frequency response. Quad glue their cloth to the inside surface of stators. Of course this blocks >50% of the holes in the cloth, so the resistance goes up by > 2 X.

The cheapest source of mesh I have found so far is aliexpress - wide range of thread counts, suppliers and sheet sizes.
 

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Bolserst, this is interesting as I am refurbishing a pair of Audiostatic ESH 100... I’ve also read reports of nasty resonances in the Audiostatic.
Perhaps I can clamp the mesh to the horizontal aluminium bars or use double sided tape to get the mesh as close as possible to the diaphragms.
Yes, mesh stretched tightly between aluminum bars should provide useful damping of the ESH100 diaphragm resonance if you can pull it off. Your solution with the U-profile clamps looks easy enough to try and see if the resonance is damped enough for your hybrid use.

Alternatively, you can improve the HP filter portion of the crossover by adding a shunt resistor. This will reduce excitation of the resonance.
See posts #8, #10, & #12 here for more details. Audiostatic esh50 renovation project
 
@ silvershadelynx,

Regarding the apparent contradictory statements concerning the mesh damping ability…note that there was 8 years between the statements you linked to in which time I learned a lot about testing the mesh and theory behind what parameters of the mesh affect the acoustic resistance. For example, two different 200 count mesh samples may use different thread size resulting in different pore sizes and mesh thickness and thus different acoustic resistance. I did not fully understand this back in 2009. Follow-up information on the original 200 count mesh I had tested was posted here: Another segmented ESL

Even the best theoretical formulas available only give an indication as to what the actual acoustic resistance of a mesh might be. The trend plot golfnut posted based on least squares fit to published measurements of Saarti mesh will give a good estimate of what to expect. But, the only way to know for sure is to measure it. I will let you know what I find out for the 120T mesh. I’m expecting it to be somewhere in the 30-40 Rayl range.

I know it has been mentioned that the mesh needs to be mounted tightly to achieve full damping effectiveness. The reason for this is that the mesh acts like a porous diaphragm that will have its own resonance frequency. Above and below resonance, the diaphragm is essentially stationary and the air particles must flow through the resistive mesh openings providing damping. At resonance the diaphragm will move with the air particles and thus not require the air particles to make their way through the resistive openings, resulting in little damping. Attached is an example measurement taken in an impedance tube compared to Uno Ingard's model of the behavior for 4 different tensions. You can see that even though the mesh has 34 Rayle resistance, at resonance it doesn’t provide much resistance to damp the diaphragm at all. Increasing the mesh tension moves the resonance up in frequency so that effective damping is provided at lower frequencies where it is needed.

As golfnut mentioned mounting mesh directly to stators like Quad does will increase the acoustic resistance of the mesh by the reciprocal of the open air fraction. It also is an effective way to avoid the mesh resonance problem.
 

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I just finished my Audiostatic ESH100 refurbishing project. Member Bolserst (knowledgeable and very helpful) inspired me to attach some mesh to these speakers so I ordered 64T 160 mesh from Ali. Problem was how to attach it as close as possible to the diaphragms. As you can see in the pictures the ESH stators are made of pertinax strengthened by aluminium crossbars.
In de 63 series and later Quad applied a mesh just behind the diaphragms. I decided that the most feasible solution here was to apply the mesh just over the stator wires.
So the mesh had to be tightly stretched in length and width and then firmly attached to the stators. For stretching in the length and fixing the mesh to the stators I found a plastic u-profile with a tight fit on the aluminium bars. For stretching in the width I could kill two birds with one stone. To join the two stator halves I used spring clips that people use to bind loose papers together.
To prevent HV leakage I put some tape under the clips. At the same time I use tape and clips to fix and tension the mesh. A lot of words but I think the pictures will clear it up.
One problem though. Although it was a nice finishing touch to my refurbished speakers which btw are sounding very nice I have no way to tell if I improved something as I have no measurement gear. Furthermore it's the first time in my life I've heard Audiostatics. Mmmm time to buy a measurement microphone ??
 

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Good morning,

nice to see you managed to attach the mesh screen. I guess you listened to these stats before attaching the mesh screens to the panels? I would just add one screen to one panel and leave the other as is in order to be able to compare them? This is what I did to get an impression about different options and their results: measure and listen to modified and unmodified panels.

I find this an very interesing topic as I'm in the process of building my fourth pair of electrostatic loudspeaker panels: this pair will be the first pair where damping screen is intagrated in the design: I will attach it as close as possible to the membrane @ 1.9 mm distance, just between the membrane and stator wires.

I did listening tests on both my current big panels and an older pair of smaller panels. The mid / high frequency quality improved on the small panels after attaching a mesh on the inside of the back of the wire stator, but showed a slight deterioration at mid / high frequencies on the big panels. (slightly duller / less spacious sound) So it is unclear to me / hard to predict how the final result will be. But it certainly helped to improve resonance problems I'm currently facing.


I just finished my Audiostatic ESH100 refurbishing project. Member Bolserst (knowledgeable and very helpful) inspired me to attach some mesh to these speakers so I ordered 64T 160 mesh from Ali. Problem was how to attach it as close as possible to the diaphragms. As you can see in the pictures the ESH stators are made of pertinax strengthened by aluminium crossbars.
In de 63 series and later Quad applied a mesh just behind the diaphragms. I decided that the most feasible solution here was to apply the mesh just over the stator wires.
So the mesh had to be tightly stretched in length and width and then firmly attached to the stators. For stretching in the length and fixing the mesh to the stators I found a plastic u-profile with a tight fit on the aluminium bars. For stretching in the width I could kill two birds with one stone. To join the two stator halves I used spring clips that people use to bind loose papers together.
To prevent HV leakage I put some tape under the clips. At the same time I use tape and clips to fix and tension the mesh. A lot of words but I think the pictures will clear it up.
One problem though. Although it was a nice finishing touch to my refurbished speakers which btw are sounding very nice I have no way to tell if I improved something as I have no measurement gear. Furthermore it's the first time in my life I've heard Audiostatics. Mmmm time to buy a measurement microphone ??
 
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I just finished my Audiostatic ESH100 refurbishing project. Member Bolserst (knowledgeable and very helpful) inspired me to attach some mesh to these speakers so I ordered 64T 160 mesh…One problem though. Although it was a nice finishing touch to my refurbished speakers which btw are sounding very nice I have no way to tell if I improved something as I have no measurement gear. Furthermore it's the first time in my life I've heard Audiostatics. Mmmm time to buy a measurement microphone ??
Congrats on completion of your refurbishing project! :)
Unfortunately, without having a side-by-side comparison with one speaking having the damping mesh, and one without, it is tough to quantify how effective your mounting method is without measurement equipment. Do you happen to have an android smart phone or iPhone? There are several free measurement apps that could be used for this and considering the low frequencies involved you should be able to just use the built in microphone. There are also signal generator apps that you can use to do a low frequency sine wave sweep in bass range so you can listen and hear how peaky the resonance might be as you sweep across it.
 
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Bolserst, after I got some problems with my Quad esl's I was able to fix it with help from you, Sheldon and others. I fact I liked working on esl's so much that I bought a pair of old and worn out Audiostatics. Now they are finished I realize that I need some measuring equipment before starting a new esl adventure. Your idea to start with free measurement apps on my Ipad really got me thinking. I've seen that there are several useful apps for this purpose. I also looked at buying a measuring microphone (Umik?) that is working with the Ipad and these apps.
 
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