Chapter 12
Subsonic Filtering
The Need for Filtering
The problem of wobbling bass-cones seems to be worse than it’s ever been, and I surmise that many users changed from infinite baffle speakers to reflex (ported) designs with extended bass when it became clear that CDs gave clean LF with no subsonic rubbish. Going back to vinyl and retaining the same speakers sets the cones flapping, promising severe intermodulation distortion, not to mention Doppler effects. Intermodulation in a good solid-state amplifier should be negligible, but dreadful things can happen in valve amplifiers.
Rumble is actually not a very accurate description of the problem. The subsonic signals are not audible in themselves, but the intermodulation they cause in bass units ...
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