Diaphragm heat treatment

I read somewhere that Quad performs a heat treatment after tensioning the diaphragm to 'set' the film.
I am curious if anybody has a clue or good guess as to what perpose this serves. I mean what are the effects on the performance of a panel? Does the tension hold longer? I'm also wondering how one would deduce the obvious parameters like temperature and duration of the heating.

Thanks for any insight into this process!

Arend-Jan
 
Hi,

the heat treatment is very commonly used with ESLs.
First : it is very easy to do with a heatgun e.g. and without the need to build a extra tensioning frame
second: the mechanical tension is relatively low, but within small tolerances. So its good for serial production (and You need a series of two at least ;-))
third: the tempering releases internal material stress. The panel works like ´played´ (broken in(?)). So the usual 50-100hours break-in time -where parameters and sound change a bit- reduces considerably.
fourth: If the membrane looses tension over time it can be retensioned by heating again -which is impossible with mechanically tensioned membranes.

The important parameter is temperature. As soon as You reach the needed degrees (~150°C) the material shrinks. It won´t shrink further by longer heating or hgher temperature, but it dosen´t harm to go over the membrane twice either ;-)

jauu
Calvin
 
Hi Calvin,

thanks for the reply Calvin, but I think we might not be talking about the same thing here. Perhaps I was not very clear stating my question, because I don't mean heat shrinking. I am talking about an after-tensioning heat treatement, maybe (probably?) at modest temperatures for longer time. At least that is the process as I understand it.
But perhaps a number of the advantages that you talk about are also a factor here, I don't know. Thanks anyway.

Arend-Jan
 
Quad diaphragms

Hello,

I believe that Quad diaphragms have always been Mylar. Mylar is a polyester film, and most grades don't heatshrink much at all: 1 - 3%, just before the melting point. Also the amount of shrinkage varies with direction.

Mylar is cast on very large machines, and the master roll is sliced into still large, but managable rolls. These tend to be consistent through the roll. I also find it astonishing how well the manufacturers can control parameters from one batch run to another.

As the yield is huge on each roll (I have one next to me now with 2,200 metres of film on it), most panel manufacturers find one roll lasts quite a long time, so variation between rolls isn't much of a problem!

Quad used to use elaborate stretching jigs to mechanically tension the film. I have seen a photo of one, but I can't remember where. I don't know if they still do this - it was an old photo.

However, the dust covers (material unknown to me) that are applied over the stators may well be heatshrunk. I certainly believe that a heat gun is a standard way of re-tensioning them if they develop wrinkles over time.

Hope that helps.

Paul
 
Some 20 years ago I ordered replacement tweeter panels from the factory for my Quad ESLs (the ESL-57, although The Acoustical Manufacturing Co. Ltd. themselves never used this type number). They included a mounting instruction in the kit, and the dust cover had to be tensioned with a hair dryer after having mounted the unit in place. Important was the continuous movement of the hair dryer so that no hole be burned. I applied this method also for the bass panels. There I used polypropylene foil that needed more heat in order to shrink. The goal of the whole process is to tension the dust cover up to the point where the wrinkles disappear and it won't rattle any more. You don't have to do any heat treatment on the diaphragm itself.
 
Diaphragm Heat Treatment ...

Interesting links:

Sheldon Stokes Website: Quad Stretcher - With Oven in background ?
http://www.quadesl.com/photo/quad_stretcher.jpg

Wikipedia Article on PET Films:
http://en.wikipedia.org/wiki/PET_film_(biaxially_oriented)

This photo was supplied by Quad in England a long time ago, while I have seen the machinery, including the "Mystery Box" at the end of the stretching jig, with it's door open, at the German http://www.quad-musik.com/html/english.html site, but can't find it there now...

The "Mystery Box" has never been described on any of the Quad Refurb sites - Stokes, Jacobsen, or King - and discussions of tension are pretty thin as well...
 
Re: Diaphragm Heat Treatment ...

torroid88 said:
... while I have seen the machinery, including the "Mystery Box" at the end of the stretching jig...
The "Mystery Box" has never been described on any of the Quad Refurb sites - Stokes, Jacobsen, or King - and discussions of tension are pretty thin as well...

I suspect that it is indeed an oven. My guess is that the process must have been something like this: The film is mounted to the stator on one end of the line and is laying on some sort of sled that is then moved into the oven. The second sled is larger so one can move over the other. While one is in the oven the other is created. At least, that is how it looks to me.
What is not clear to me is if the heat setting is/was done only for the 63 or also for the original ESL..

The oven looks like the type used on package shrinking assembly lines or pizza heaters.

Thanks for the wiki, perhaps I should ask Dupont about the right temperature and duration. They must have some info on this.
 
Unless I'm mistaken, those pictures show the stretcher for the original Quads ("57s"), which the German company might be using for panel rebuilds for all Quad models now.

Here is what I believe Quad used for the ESL-63:

Quad ESL-63 stretcher

Note that the fingers that contact the film resemble piano key actions, rather than the clamps, pulleys and weights of the older stretcher rig. A stator can be seen attached to a pivoting assembly on the upper left that can be brought down onto the stretched film. Exactly how all this works is open to conjecture. I hope that anyone with insight into how Quad "did it" will contribute.
 
Method re-tensioning mylar in finished panels

The important parameter is temperature. As soon as You reach the needed degrees (~150°C) the material shrinks. It won´t shrink further by longer heating or hgher temperature, but it dosen´t harm to go over the membrane twice either ;-)

jauu
Calvin [/B][/QUOTE]

Hi Calvin,

Your system looks awesome!!! Truly beautiful.

I've got a hybrid ESL system and a question about the heat treatment. Before I ask it, I want to share what my system contains:

Previously I used Martin-Logan CLS's from 325 Hz on up and then corner placed (!) dual Tact Audio W210 subwoofers, a Tact Millennium digital amp (so no tubes) on the panels and a M2150 on the bass. The x-over is done via Tact's 2.2x room correction amp. It sounded great, albeit a bit polite, due to the curved CLS's, and their spacer spec. So I wanted flat ESL panels tailored for mid range on up.

I had Russ Knotts of Just Real Music in Ohio make the panels. He required pre payment in full or else would not start his work. Once I'd paid, it took him and unbelievable 18 months after we had finalised the specs and sizes of the panels to even start putting the panels together. It also took me an estimated 50 phone calls during those 18 months to try to make him remember his commitment. Finally it went to the extreme. He actually told me that the reason I kept being last on his priority list was I lived far away. So in the end, after considerable agony, I had someone pay him a visit in person before he actually shipped my panels. Needless to say, I got them.

Once I had the panels I had frames made to hold them. Monday last week I hooked up one channel. And then on Tuesday the other. The second set of panels had significantly lower output than the first set. I tried switching the electronics to rule them out as the source of the problem. Then, on the first set, which originally had worked fine, the output started dropping significantly after about one hour of listening. I believe it's the mylar that has lost its tension, although I'm not sure why it would happen from playing on the panels (any ideas?).

Anyway, back to my question. I've got Roger Sanders ESL cookbook and he recommends using two heat guns, one on the front and one on the back. You are the first person who have actually specified the temperature for the heat guns (150 degrees C). I went out and bought a pair of cheap guns. Their lowest output is 375 degrees celsius - putting out some 400 liters of air/minute. I thought I could just increase the distance, use a thermometer and try to get the temp right. Heat guns with actual control over heat output are 6-7 times more, so I'd rather avoid buying them as I'm not planning to use them more than for this. Could you give me some more detail on the heat guns you've used, and some feedback whether you think my cheapo solution is the wrong choice or whether you think it can work?

Thank you!!
 
Hi,

My hairdryer (my wife's of course, I've little hair myself) wasn't able to heat shrink the Mylar enough. Probably not hot enough.
A heat gun (for removing old paint) worked, but...... I couldn't reach the very high tension required in some esls. It could burn a hole in the Mylar so it went hot enough. If your heatgun/dryer can burn a hole in the Mylar you're sure its getting hot enough and you just have to vary the distance to get the best results.

If your membranes have too low tension they will suck to the stator after switching the high voltage on. You may hear some tickling sounds when this happens.
Other possible problems which you could check out:
- thickness spacers the same? (original foam?)
-dust/dirt?
- chemically instable coating system?
-tears in mylar?
 
Hi,

thanks for the praise dbrotzen

too bad that You experince such troubles ith the panels.
I´m afraid to tell You that after Your description I don´t think, that lower mechanical tension is the reason for the output problems of Your panels. It rather sounds like contacting probs from input cabling over membrane contact strips to the coating of the membrane itself.
Another source of the problem could be heavy leakage. In this case a flashlight circuit could give You a clue

jauu
Calvin
 
One important practical guide with the heatgun: use a flat put-on nozzle that spreads the hot air. Start with a distance of about 1 ft and then move gradually closer and closer. Imagine it as a paint spray and try to paint the whole surface evenly. Most important: never stop moving the heat gun, otherwise it will burn a hole. BTW I stretched the mylar with a hair gun, and I could increase the heat by partially blocking the inlet by hand (just before the overheat switch triggered).
 
Heat Treatment ?

A thought just occured to me as I read this thread...

We have seen the original Quad Stretching Jig and "Mystery Box" photo, and are assuming that the box is an oven for heat treating
the Mylar diaphragm. What if the box was to heat set the adhesive instead?

Any ideas, anyone ?
 
Mylar Postscript ...

There are some Industrial Films from the '50s from DuPont about Mylar Film at the Internet Archive. Just Google Internet Archive, and then Search on Mylar. There are two film segments to download ...

The films mention Mylar applications in Electronics, but not ESLs though !