Speakers specially the tall and narrower ones are not too stable due to their high center of gravity. A little nudge sets the unit vibrating.
I once had a Vandersteen 1C spiked upon a wooden floor and no matter what I did, could not ameliorate a wooly bass problem until I made a support that I either read about or invented (this happened 15 years ago in a far away land!). It worked.
The method is strikingly simple and a snap to build. I just braced the speaker cabinet against the wall of my living room using a wooden pole. This stops tendency for the front-to-back teeter-totter. Do a short test, grab a pole of the right length, sharply bump the top front of a speaker with and without a pole brace and you will know what I mean.
The brace will also tame the resonance of the back panel of speaker cabinets.
I am not presently using this method because my speakers are spiked upon a granite floor and the stand has a large footprint. Now that I remember the tweak, I will make a pair of wall braces for them. It is too easy a tweak to pass up.
Try it, you'll possibly like it
Mandym