Building question - Panel Matching

[jeffshort2000]

Still researching before starting a ESL project. Have a question that I have not found yet.

How do you go about matching the panels? I can set the tension the same on both and adjust the voltage for the same db output.

Is that all there is to it besides making sure all of the components are the same?

Thanks for all the great input on this board!

Jeff

[Few]

That's pretty much it, Jeff. The reproducibility and predictability of ESL performance are two of their nicest features (in addition to the excellent sound reproduction, of course).

[Calvin]

Hi,

measuring freq-response of course.

jauu
Calvin

[jeffshort2000]

I can do a freq sweep of the panel and graph the response at key points. How would I adjust for discrepancies (besides eq'ing the panel)

Is there another way to check and adjust the response of the panels besides building like 10 of them and then hard matching?

Thanks,
Jeff

[torroid88]

Short of some construction that allows diaphragm tension to be adjusted after assembly, no, there is no way ...

Most panels are assembled as a sandwich with glue and clamps, with the diaphragm already tensioned. Once set, the only way to "re-tune" the diaphragm is to rebuild it ! ...

You may have seen photos of condenser microphone capsules with a
ring full of adjustment screws which allows just such diaphragm tuning on the capsule, but they are small enough to handle. An ESL
panel would be to large and cumbersome to do the same. But it is food for though and if you come up with a solution, do let us know !

Good luck !

[jeffshort2000]

I wonder if a jig could be made so that the Mylar is wrapped around the spacer in such a fashion that the tension could be modified before the assembly is glued up. Then when the system is certified, and glued, the panel is removed from the jig.

This would probably look like the condenser mike adjustment jig, in fact I have an idea from pictures of ESL 57 jigs that i have seen.

I have to figure that the bigger manufacturers do not hand match the panels and have some sort of test Jig that they use to setup the parameters of the panels. Probably is some sort of an open table with mikes on at least 4 places on the top and bottom that they can use to adjust the response with.

I have a bunch of servo motors laying around, I wonder if I can get those to work instead of changing tension at certain parts of the panel, and letting it cool down (hi-voltage) then adjusting again.

[gvy]

Hi,

I have always tensioned and glued, the membrane of two matching ESL's together out of 1 sheet of mylar.

first I have used a mechanical stretching table, where 2 panels could be placed next to each other.

Now I have made myself a pneumatic stretching table (with bicycletires), where also 2 panels can be placed next to each other.

My panels have identical tension and resonance frequency.

greets
Geert

[Calvin]

Hi,

its always positive to use as much mechanical tension as possible.
When using a mechanical stretcher very high values of tension can be reached. When You start tensioning You´ll notice that at first the resonance frequency rises app. linearly with growing tension. From a certain point (depending on the film You use and often found around 1%-2% elongation) the resonance frequency keeps nearly constant with further rising tension. Tensioning up to this point (simple measurement of elongation) You will reach a good enough consistency.
Using thermal tensioning the film settles always at the same value of tension. So consistency isn´t really a problem with this method. Rather the relatively low value of tension could present a problem. But that depends on the concept and design of Your panel.

jauu
Calvin

[Capaciti]

Hi Folks,

i disagree that ESL are consistent in performance when comparing two to each other. Most constructions i have seen from DIYers suffer from constructional aspects.

especially when perforated stell is used on large ESL the eveness of the plates is the critical point. a stator-membrane spacing of e.g. 2mm makes deviations of the stators, which can be up to 1mm easily, very significant.

I do not want to put good speach on my owm work, but my panels are one of the most precise regarding construction. Nevertheless deviations in frequnecy response between two panels are at least 1dB. Lower than 1dB is a lucky case.

There is a second issue, which most builders ignore. I never listended to an ESL, which showed its final performance before 3 month break in time. Mechanical tensioned membranes even take longer. So what you measure or listening directly after building is not comparable to the situation after break in.

The right tensioning method considers the time based relaxing properties of mylar and those are strongly related to the bidirectional tensioning you apply. This bidirectional tensioning must be optimized in relation to the width-height-ration of the membrane area.

Capaciti

[Few]

Capaciti: By bidirectional tensioning do you mean to say that you recommend different tensions along the long and short dimensions of the panel? Is this assuming a particular style of stator-diaphragm spacers (arrays of dots, or perhaps several parallel horizontal or parallel vertical linear spacers)?