By Wilde Becker. Speaker Stands. At Monday, July 22nd 2019, 18:15:39 PM.
One way to improve the situation is to add mass by means of a platform fixed to the top surface of the foam. Primacoustic do this in their Recoil Stabilizer by using a very thick steel slab with rubber matting on top, while Auralex and other companies use MDF topped with dense rubber on their more up–market platforms. IsoAcoustics take yet a different approach, by using a frame made from rigid components joined by resilient isolators.
That’s where you need to put the sub. If your sub has a phase adjustment knob, or a polarity–invert switch, adjust this until you hear the loudest result from frequencies around the crossover point, typically 80 to 120 Hz.
We tend to think of a loudspeaker as a fixed box that produces sound directly from the moving cones of the speakers (and, where the speaker is ported, from the port as well). Although that is certainly where most of the sound comes from, the reality is that no matter how rigid the cabinet is there will also be some vibration of the cabinet walls.