Derived Physics Model of a Planer ESL - Page 2 - diyAudio
 Derived Physics Model of a Planer ESL
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diyAudio Member

Join Date: Nov 2004
Location: close to Basel
Hi,

change the word ´SPL´ in the following quote of post#7by ´maximum SPL´
Quote:
 In part 1 the assumption is that the membrane stays centred between the stator plates which it doesn´t in praxi. While by the principle of superposition this doesn´t affect the alternating signal forces on the membrane it does decrease the SPL limits seriously by introducing a mechanical Offset.
.
Which means that by the principle of superposition you can analyse the forces working upon the membrane independantely -signal forces and attraction by bias voltage. But the higher the bias voltage the more offset the membrane shows, the less free excursion is possible -> hence reduced SPL max. So if You want to calculate the possible SPL levels and its max limit, You have to put the bias voltage and its effects into the calculations.

It is a very common failure of ESL-beginners to use low diaphragm tension in the strive to get a low Fs. This results in a large offset, hence a smaller ´airgap´, hence lower SPL limit. In the extreme sloppy membranes might be pulled into the stator even without any signal voltage at all, thereby reducing the airgap to 0!
To correct for the large offset you might suply a lower bias voltage, or a larger stator-stator distance, but both measures reduce efficiency. That´s the reason why you should always use as much mechanical tension as possible for your application.

jauu
Calvin

 14th October 2008, 05:32 AM #12 diyAudio Member   Join Date: Aug 2003 Location: Calgary on the Bow just in case... you might have missed this one. http://cat.inist.fr/?aModele=afficheN&cpsidt=3622310 __________________ moray james
 15th October 2008, 03:43 AM #13 diyAudio Member   Join Date: Aug 2008 Hi Moray, No didn't see that one. From the abstract looks like a very realistic model. If you have could you send it to me? If not I can buy and if its no copyright infringement provide the forum with it. thanks bryan
 1st November 2008, 11:40 AM #14 diyAudio Member   Join Date: Mar 2005 Location: Stockholm Hi, there is an aricle in JAES: JAES Volume 43 Issue 7/8 pp. 563-572; July 1995 A model is being developed for the electrostatic loudspeaker, which incorporates simultaneously the mechanical, acoustical, and electrical behavior of the diaphragm. The nonlinear model can be solved fairly accurately in the steady state and is used for calculating the frequency- and level-dependent sensitivity and distortion for an infinite-strip push-pull electrostatic loudspeaker. The results are compared with previously published and new iproved small-signal approximations. and Marchal Leach book Intro to electroacoustics and audio amp design there is a spice model. The math in the Streng article is a bit hard... /örjan
 1st November 2008, 11:58 AM #15 diyAudio Member   Join Date: Mar 2005 Location: Stockholm Hi again, when I started to think there a few other articles by Streng, found a link http://www.quadesl.nl/documents/Streng.tar.gz /örjan
 1st November 2008, 07:38 PM #16 diyAudio Member   Join Date: Aug 2008 Hi Orjan, Thanks for the information. Right now I am getting myself ready to develope a numerical routine to handle the acoustic model. After this we should have nice simulations to all look at. Thanks Bryan
 2nd November 2008, 06:12 PM #17 diyAudio Member   Join Date: Mar 2005 Location: Stockholm re your post #5 The only damping you get is from the air. The membrane has no bending stiffness or damping ( or rather small enough not to be important ). This of course if you don't add damping with thin felt or so. /örjan
 2nd November 2008, 08:12 PM #18 diyAudio Member   Join Date: Aug 2008 Orjan, That is true the damping the membrane feels is from the air, in fact it is like having some kind of membrane effective mass, since the layer of air next to the membrane has more mass then a typical membrane's mass. bry

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