Effect of the damping felt on the Quad ESL treble panel
The image below shows the effect of leaving a cavity between the treble panel and the felt lining that's on the back (the grey laps of damping material). Often the felt is left at a varying distance of the panel (red) instead of being fixed tightly against it (blue). This creates an audible cavity and typical coloration around 5kHz. The felt should be positioned as close to the panel as possible.
