Hi,

I compared my 1974 pair of ESL57s against a pair of newish TDL speakers
using a test CD with stepped tones and measured the output with a sound
level meter. The high-frequency roll-off of the ESL57s was very noticable.
The higher tones (10kHz up) were there but the volume dropped off rapidly. I
was using a late (mid-eighties) Quad 34/303 combination for the test.

What is the most likely cause of this? Is it most likely to be the treble
panels or could there be a loss of voltage to the panels. I believe they
were overhauled by Quad around 1995 but that was before I owned them so I
don't know what was done.

The panels certainly hold a charge well. I switch off the mains to them
while I swapped connections about and when I reconnected them 20-30 minutes
later they still worked for a short time even though I had forgotten to
switch the mains back on.

Regards,

John.