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Old 17th March 2013, 11:53 PM   #41
Bazukaz is offline Bazukaz  Lithuania
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Quote:
Originally Posted by Kindhornman View Post
Bakukas,
I would think that a higher tension on the diaphragm would change the transfer of energy as the losses into the membrane would be lessened due to damping and the elastic properties of the membrane would also have to be considered. I know you wouldn't have any but a material such as Kapton would have a very high Young's modulus of elasticity. Thickness is also going to have an effect on transference of energy, the thinner the material is the more transparent it would be for the same material. It is an interesting experiment but what is your end goal? What exactly are you trying to accomplish with the experiment, is it only to look at the transparency of the material to sound passing through the membranes?
Hi,

I have done in fact two experiments with different goals:

1) The effect of wire ESL structure on sound coming from external sources.Like what you could expect if such an ESL was used as a mic.
I do not intend to so but it was interesting to me.
2) Try to observe partial diaphragm modes in mid range and treble and what effect the membrane tension has on this. Some people have mentioned that effects of partial modes can show up to midrange.So I wanted to collect some evidence for or against that.

Regards,
Lukas.
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Old 18th March 2013, 12:11 AM   #42
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Bazukas,
I have been involved in a flat panel speaker development in the past and one issue that did crop up was the bending modes and resonances of a square or rectangular diaphragm. Some not very nice things were happening in that situation and though I know it is not the same as an ESL type drive with distributed drive over the membrane I would suspect that these same problems would rear their ugly heads. I often wonder why the frames have been rectangular on ESL speakers with no consideration to this phenomena, why there wasn't some large radius at least in the corners to alleviate some of the poor bending modes the diaphragm is forced to endure and the poor damping properties of the edge mounting of the diaphragm. It is not an easy problem to resolve or easy to understand some of the bending modes that are created across the frequency band.
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Old 18th March 2013, 01:15 AM   #43
Bazukaz is offline Bazukaz  Lithuania
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Quote:
Originally Posted by Kindhornman View Post
Bazukas,
I have been involved in a flat panel speaker development in the past and one issue that did crop up was the bending modes and resonances of a square or rectangular diaphragm. Some not very nice things were happening in that situation and though I know it is not the same as an ESL type drive with distributed drive over the membrane I would suspect that these same problems would rear their ugly heads. I often wonder why the frames have been rectangular on ESL speakers with no consideration to this phenomena, why there wasn't some large radius at least in the corners to alleviate some of the poor bending modes the diaphragm is forced to endure and the poor damping properties of the edge mounting of the diaphragm. It is not an easy problem to resolve or easy to understand some of the bending modes that are created across the frequency band.
Hi,

It is interesting. I have done a lot of experiments with my ESLs and currently the only identifiable modes seem to be at 75Hz(fundamental) and 140Hz(very reduced in level) as these do respond to external damping.
My impression is that very thin and light diaphragm can be quite effectively damped with things like low open area(<30%). Put a silk screen mesh with light cover cloth and the fundamental is just a few db above the level.
The measurements I posted before with bare membrane do not suggest resonance resonance modes in mid range and up. However to see a proper picture I would need to make the membrane same sized as a typical ESL and cover the frame with some felt to remove high frequency reflections.

Regards,
Lukas.

Last edited by Bazukaz; 18th March 2013 at 01:18 AM.
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Old 25th March 2013, 10:33 PM   #44
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Quote:
Originally Posted by Bazukaz View Post
Your observation about HF roll off seem to be correct.
Below are two diagrams, with and without membrane, zoomed in and smoothed to 1/3.
I recently performed a similar test to compare HF roll off for different diaphragm thicknesses.
Attachement shows experimental results match very well with theoretical roll off calculated based on radiation resistance(2*rho0*c) and diaphragm mass.

The -3dB point for Mylar diaphragms can be estimated by:

F(-3dB) = 93,400/t

where t = diaphragm thickness in m.
Attached Images
File Type: gif Test_mass_diaphragm.gif (24.2 KB, 171 views)
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Old 27th March 2013, 04:35 PM   #45
oshifis is offline oshifis  Hungary
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bolserst, I saved your graph for reference Do you know if the material of the diaphragm (soft, rigid) does matter? Same question for the dust covers. Also, how do you take into account the diaphragm and dust covers with different thickness together, that is three vibrating surfaces acoustically in series? Could they be modeled as one diaphragm having the combined thickness, i.e. sum of the three?
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Old 29th March 2013, 04:13 PM   #46
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Quote:
Originally Posted by oshifis View Post
Do you know if the material of the diaphragm (soft, rigid) does matter?
I'm not sure I understand your question. Do you mean high or low diaphragm tension? If so, then no, the tension does not affect the HF response and roll off. I guess you also migh be talking about the material strength of the diaphragm. The only property that determines the HF roll off is the mass. However, stronger/stiffer materials will have more pronounced higher order diaphragm resonance modes which could show up in the midrange if not properly damped.

Quote:
how do you take into account the diaphragm and dust covers with different thickness together, that is three vibrating surfaces acoustically in series? Could they be modeled as one diaphragm having the combined thickness, i.e. sum of the three?
If multiple diaphragms are driven together, as in a 3-stator 2-diaphragm arrangement like the woofer panels on the ML CLX, then combining the thicknesses for calculation of HF roll if will give you a good approximation. If only one of the diaphragms is driven, then things get more complicated as the air volume between the diaphragm and a dust cover acts like a compliance. Depending on the relative masses of the diaphragm/dust cover and the air volume compliance you can get different behaviors ranging from smooth roll off to resonance peaks of +3dB or more.
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Old 30th March 2013, 07:49 PM   #47
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Hi!
This thread is a very interesting subject and also entertaining. Using glass make me remember an advertisement of about 45 years ago. I saw there a driver that you could use without any box or whatever! The best mounting for it was a glass panel the larger the better brick and concrete was useless . as it is acoustically dead I wonder did some of you had any experience or knowledge of them? It was apparently very good for background music. How it worked I do not know as they were too expensive for an apprentice to purchase just for inquisitiveness sake . I never heard or have seen any of them since. The same go for the poly planar speakers I read about in this thread. I did obtain one but I did go back to paper cones quickly as the sound was not that fantastic and they were brittle to handle. It did come cheap and I discovered soon why! For the glass microphone it seems to me as if this driver that worked on any stiff area would be just the thing. In the ad the other surfaces being metal etc.preferably
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Old 26th June 2013, 10:58 AM   #48
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Quote:
Originally Posted by bolserst View Post
I recently performed a similar test to compare HF roll off for different diaphragm thicknesses.
Attachement shows experimental results match very well with theoretical roll off calculated based on radiation resistance(2*rho0*c) and diaphragm mass.

The -3dB point for Mylar diaphragms can be estimated by:

F(-3dB) = 93,400/t

where t = diaphragm thickness in m.

Hi bolserst. Interesting measurements. I've currently made a 12 micron ESL and used the ESL_UI software (which you know well) to calculate segmentation resistors for a flat frequency response. Judging from your measurements, I need to equalize the high frequencies up to almost 9 dB with my diafragm thickness. Am I right? If so, I'd rather use different resistors to compensate for the diafragm roll off.

Thanks.
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Old 26th June 2013, 04:47 PM   #49
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Quote:
Originally Posted by jeronimo83 View Post
Hi bolserst. Interesting measurements. I've currently made a 12 micron ESL and used the ESL_UI software (which you know well) to calculate segmentation resistors for a flat frequency response. Judging from your measurements, I need to equalize the high frequencies up to almost 9 dB with my diafragm thickness. Am I right? If so, I'd rather use different resistors to compensate for the diafragm roll off.
Response to this question was moved to the segmented wire stator thread.
Segmented Wire Stator ESL simulator (esl_seg_ui)
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Old 27th June 2013, 04:09 PM   #50
Marik is offline Marik  United States
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Quote:
Originally Posted by bolserst View Post
I'm not sure I understand your question. Do you mean high or low diaphragm tension? If so, then no, the tension does not affect the HF response and roll off. I guess you also migh be talking about the material strength of the diaphragm. The only property that determines the HF roll off is the mass. However, stronger/stiffer materials will have more pronounced higher order diaphragm resonance modes which could show up in the midrange if not properly damped.
This however, is not the case for microphones, where response mostly depends on tension, esp. in true pressure transducers.

Best, M
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