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In Reply to: RE: Try Kent's panels :) (nt) posted by kentaja on October 11, 2020 at 16:33:31
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.
Follow Ups:
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.
Excellent, thanks.
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