Adding weight can reduce unwanted vibration. The vibration is a side effect of the speakers vibrating to make music. It is harder to move something heavier. So make your speakers heavier by weighing them down. If you can't bolt them to matched stands then also weigh down the speaker itself by putting a bag of silica sand on top of it. (Do not ever breathe in the dust of the sand while filling the bag. Make sure the bag is sealed tight!)

Personally, I used lead shot of various sizes with silica sand to fill in the gaps.

  • Do not use playground sand as it retains moisture.

see also spikes