Comb Filtering is both audible and measurable. See below:😎
@aewarren , there certainly are absolutes but there are issues that may only pertain to certain situations. A good example is you do not want to place a turntable on anything that sits on a bouncy floor unless it's chassis design is well isolated.
Amplifiers should always be placed as close to the speaker as possible. This is more important for lower impedance loudspeakers but it does pertain to all loudspeakers.
Turntables are always a touchy issue because they are vibration measuring devices and they do not care where the vibration comes from. The more isolated they are the better. The volume of point source speaker drops off at the cube of the distance so keeping the turntable as far away from the speakers as possible is a good idea. The caveated is that there are locations where the bass can be amplified do to acoustic considerations and you certainly do not want to place the turntable in one of these locations.
Everything else could care less.