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 5 kHz. The felt should be positioned as close to the panel as possible.
