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In Reply to: RE: Try Kent's panels :) (nt) posted by 13th Duke of Wymbourne on October 08, 2020 at 11:58:05
I will if I need to. Mine are as new and even have a few spares.
NOS orignal Quad panels? My understanding is that the diaphragms age and even unused NOS panels will not behave as they would when new. Rebuilds are a different story (no pun intended). Also, Kent claims his diaphragms are thinner than the originals and sound better. I have a late model pair and after the ESS refurb they sound a lot better.
I have serviced my 57's many times and the thought of touching them without good reason now since they are working perfectly does not appeal. There is never enough time to accomplish what we all want.
My treble panels from QS&D I know were much better than the originals, but the originals were shot - no mystery there. I have the low end crossed over to save them from those frequencies and hand them off to the subs.
And since they sound sublime and put me off of this sick planet every time I listen I am in orbit to take me away to journey's known and unknown. I usually don't mess with things until a problem arises and they have been spot on for many years now.
Unfortunately no matter how well maintained none of them are working close to spec. any longer Given the materials that were used at the time especially the film in the bass panels it just isn't possible. Even if one was lucky enough to find a NOS pair, never opened or used, they would be way out of spec.
That doesn't mean one should rebuild them. I work with people all the time that aren't having issues and hesitate to rebuild them. If the speakers don't have any problems and one is happy with them I say leave them alone!
They are however a far cry from what they once were, what they can be. All of them are very old at this point. My personal pair was produced in 1959, never been touched since they left the factory, still work nicely. But they are way out of spec. I don't plan on rebuilding them since I always have rebuilt speakers around and I like the fact they are factory original and never been touched.
Kent, could you elaborate on in what regard QUADS (in my case the original "57" model) go "out of spec"? In frequency response linearity, bass extension, sensitivity, etc? Thanks---Eric.
Hey Eric happy to elaborate.
They degrade in three ways.
The conductive coating looses its mojo over the decades. Too long of a discussion to go into detail but basically this mean is does loose some efficiency over time. In extreme cases about 3dB.
The carbon composition resistors in the filter network go high in value over the decades this is typical with carbon comp resistors. The resistors in series with the bass panels are there to attenuate the bass panels relative to the tweeter panel. As they go higher in value this upsets the balance between the bass panels and the tweeter with bass panels loosing some output. The result is a slight leaning out of the sound overall.
These two areas are no too bad its the third area that is the major problem.
Quad did not use Mylar for the bass panels just the tweeter. I imagine Mylar was quite expensive when production first began so Quad looked for an alternative. What they used was polyolefin, stretch film, Saran wrap if you will.
Polyolefin has lots of plasticizers which leach out over time whether the speakers are in use or not. The film gets stiff and brittle. This results in the bass panels increasing the tension on the film, raising the panel's resonance, as much as an octave, loss of bottom end and dynamics. This is easily measured. System resonance should be in the 50-60Hz range. Old speakers will be as high as 120Hz!!
It doesn't matter how well one maintains the speakers the degradation will occur. And this all has a major impact on performance most dramatically in the bass. The bass is essentially gone.
Mylar work hardens as well but it's time scale is much longer and not nearly as dramatic. Early ESL-63 are approaching 40 years in age and we can measure the panel resonance and see the shift. But even after 40 years it's minimal, perhaps 10Hz, and if all else is well with the panels I usually recommend it be left alone. Not so with any of the original Quads.
Most original Quads are 50 years old it's amazing they still work at all let alone how well they perform it's a testament to the overall correct and robust design. But working as they should? Nope not possible.
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