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-   -   ESL 57 : how much weight on the jig ? (http://www.diyaudio.com/forums/planars-exotics/164490-esl-57-how-much-weight-jig.html)

Fabien Lefebvre 4th April 2010 08:30 PM

ESL 57 : how much weight on the jig ?
 
The ultimate secret in the universe after women : how much weight to put on a jig, more or less the same as the one used by factory ?

It seems to me that no-one really knows, that professional re-furbisher made their own minds themselves, that DIYers do it the way they feel it (and at the end this is not worse than old panels they had).
Of course I read some figures here and there. Most reliable ones seem to be 45 for treble and 60 for bass (applied to 40*80cm). But I can't believe this is kg. Pounds seem much more acceptable. But maybe I am wrong.

So, anyone has the answer to the second most protected secret in the universe ?

Fabien Lefebvre 7th April 2010 09:56 PM

Is there any info on this jig in the book "QUAD - The Closest Approach" (page 45) ?
Thank you !

arend-jan 8th April 2010 11:04 AM

However nice it is, there are no technical production details in that book that I can recall.

Fabien Lefebvre 8th April 2010 11:39 AM

Quote:

Originally Posted by arend-jan (Post 2146440)
However nice it is, there are no technical production details in that book that I can recall.

Thanks for this reply.
Meanwhile I found some similar conclusion here: Planar Speaker Asylum: The book... by Gary Jacobson
Yet there are some pictures of the jig in this book but maybe nothing more than these ones:
One Thing Audio/Manufacturers/Quad/Pictures

I am interested in photos because this could give information on the weights to apply. Certainly not directly the value itself but at least the relative values between a bass and a treble panel.
For example, on the 3rd photo, we can see the weights used for tensioning the bass panel. For me there is no way that it makes 60kg.
On the same photo or on the first one, in background, we see a similar jig but with (much ?) heavier weights: is it for treble panel ?

My intention is not to set up an international business. I just want to repair my ESL. My jig is ready, mylar was just received,... just have to find the right tension to apply now.

kavermei 14th April 2010 07:55 AM

Fabien,

"60" could be pounds or kilos, remember the mylar film has very high elastic modulus and can take a lot of tension with a minimum of strain.

I used to stretch my film by hand, using plastic tape, and I remember I had to apply a lot of force to get it nicely stretched taut.

if you don't find the exact values, you can increase the weights until the membrane has the desired resonant frequency. This can be tested by tapping it. The problem with this is that, if you heat-shrink the membrane afterwards, the resonant frequency will go up. So it is hard to estimate the final resonant frequency.

Kenneth, quad fan (but not owner :) )

Fabien Lefebvre 14th April 2010 12:09 PM

Quote:

Originally Posted by kavermei (Post 2152993)
Fabien,

"60" could be pounds or kilos, remember the mylar film has very high elastic modulus and can take a lot of tension with a minimum of strain.

I used to stretch my film by hand, using plastic tape, and I remember I had to apply a lot of force to get it nicely stretched taut.

if you don't find the exact values, you can increase the weights until the membrane has the desired resonant frequency. This can be tested by tapping it. The problem with this is that, if you heat-shrink the membrane afterwards, the resonant frequency will go up. So it is hard to estimate the final resonant frequency.

Kenneth, quad fan (but not owner :) )

Indeed I think now that the bass panel will not need a lot of weights contrary to the treble panel which will require very high tension.
Measuring the desired resonant frequency is a nice alternative. But what is the resonant frequency to be achieved with each panel ? In which conditions ? Un-bonded, bonded and charged, ...
If measuring is done once bonded then this can mean a lot of trials and a waste of mylar.
I will avoid heat-shrinking because this is not very predictable and repeatable.

kavermei 14th April 2010 12:37 PM

If you could stretch the mylar with one stator laying underneath, then I think a pretty good measurement can be made. I don't think gluing and charging will make a big difference. The main parameters will be the tension and the distance between the diaphragm support pieces.

Afterwards you can remove the stator from the work bench and re-tension the film for coating and gluing.

If you are refurbishing several old panels you can adjust by ear, by tapping another old panel's diaphragm for reference. Otherwise it's a little more difficult, maybe use microphone, soundcard and FFT program to measure it?

I don't know what the nominal res. freq. is for the Quads, maybe someone else here will know?

Kenneth

Fabien Lefebvre 14th April 2010 12:57 PM

Quote:

Originally Posted by kavermei (Post 2153168)
If you could stretch the mylar with one stator laying underneath, then I think a pretty good measurement can be made. I don't think gluing and charging will make a big difference. The main parameters will be the tension and the distance between the diaphragm support pieces.

Afterwards you can remove the stator from the work bench and re-tension the film for coating and gluing.

If you are refurbishing several old panels you can adjust by ear, by tapping another old panel's diaphragm for reference. Otherwise it's a little more difficult, maybe use microphone, soundcard and FFT program to measure it?

I don't know what the nominal res. freq. is for the Quads, maybe someone else here will know?

Kenneth

All right I will practise.

But knowing the right weights to apply would have been so simple !

Just one point: applying a charge makes a big difference. Because it corresponds to negative compliance (opposite in sign to the one due to mechanical tension) and this reduces significantly the resonance frequencies.
It is so important that a safety factor has to be respected (see papers from Baxandall if I remember well).

kavermei 14th April 2010 01:09 PM

Quote:

Originally Posted by Fabien Lefebvre (Post 2153184)
Just one point: applying a charge makes a big difference. Because it corresponds to negative compliance (opposite in sign to the one due to mechanical tension) and this reduces significantly the resonance frequencies.
It is so important that a safety factor has to be respected (see papers from Baxandall if I remember well).

Hmm, interesting, will check! I have a PDF of his book chapter here.

orjan 14th April 2010 01:19 PM

Hi,

From Baxendall's chapter in Loudspeaker and Headfone Handbook, the polarized resonance frequency is for bass panel 70 Hz and treble 260 Hz.

/örjan


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