Quad ESL 57 panels?
I am having a pair repaired and when the treble and one bass panel were refurbished in one speaker due to arching the efficiency and the bass response was changed considerably. This means that there is now a mismatch and I must get the other side fixed doubling the cost. So a couple of newbie questions:
1. Is this normal (logical)?
2. Should I have been informed of this by the store?
IMHO,it is novel too keep those things going !
The cost of repairing them is trivial and you could easily build a set of ESL's probably much much less than the cost of one repair job !
There is much to be learned here in these threads.
And, In doing so you could maybe repair them in your own shop (just a suggestion but not to be taken lightly).
The fact that the repair job that was once did, made for a mismatched pair.
I always wanted an old set of Quad's and still do ( for a standard of ) , But the technology of today has surpassed that of way back then.
Do a search of the threads in this forum and you will find much (alot) of info on the Quad's, and other ESL systems.
You did not state of which store you went too and what area you are from.
Good Luck on your project !!!
Actually I am relatively familiar with the ESL-57 and repairing them is pretty common. They still perform rather well generally speaking, and I have yet to hear any diy ESLs that run anywhere close to full range and sound nearly as good.
Some run in time may be required to determine whether or not the newly repaired panels will change character.
I'm not an expert when it comes to repairing the panels in these, but I suspect that differing membrane tensions, and material differences between the old and new may account for some of the differences. If after some more time has passed and the repaired unit sounds better than the other one, and you are sure there are no problems with the cross-over, transformer and energizer supply in your other 57 then you might want to get those panels redone so that they match.
Disclaimer: I'm a professional Quad loudspeaker refurbisher.
Yes it's normal that sensitivities differ. And yes the supplier should have informed you of this fact (I always advise to send at least both treble panels and will make sure a matched set is returned, but it is the customers choice).
The problem with the Quad ESL 57 (which by the way is not easy to repair due to amongst other things a d/s of 0.5mm) is that the tolerances of the treble panels were not tight enough in production. They need to be tightened during refurbishment. Bass panels are far less critical and show less variance from one piece to another. Aging of old unrefurbished panels results in 99% of the bass panels being out of specifications. As a result a refurbished bass panel will play a bit louder and will have more low frequency output.
So randomly replacing a couple of panels will likely result in less than optimal performance.
Also a proper repair of the panels requires the use of proper materials (film, coating) and more importantly manufacturing procedures. Workmanship matters! I've seen plenty of 'repairs' that made me feel sad indeed.
arend-jan is right. There's actually two confounding factors that he alluded to. First is that even if you are the owner of the last pair of Original Quad ESL's off the line, the panels are now over 30 years old. And I'd argue that their performance has changed significantly over time. Secondly, there's are several different materials commonly used in Bass panel rebuilding. I use a saran material nearly identical to the original diaphragm. However carefully tensioned mylar can also be used assuming that the tension is adjusted such that the resonant peak is at the same frequency. The mylar diaphragms will have a slightly higher "Q" though.
The one thing mentioned earlier is that like any new mechanical device, some break-in is required. Depending on the build method, it can take a month for a new panel to settle in.
An important point also mentioned is that the precision of the original ESL panels is horrible, as was the quality control. It is very hard to match ESL panels to the level of the much more precise ESL63 panels. So depending on your speakers, and their treatment over time, as well as how well they were matched to begin with, you may have a built-in imbalance.
Here's some plots of rebuilt ESL63's and a pair of Braun LE-1's. The Braun measurements are typical of randomly selected treble panels rebuilt carefully, but stators that were made at different times.
it could be as simple as the other power supply is lower in voltage,
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