@three_easy_payments,
"Isolation below speakers works from my experience...but it greatly varies from speaker to speaker and from room to room."
Can’t argue with that.
In my experience, isolation makes considerably less difference with concrete floors.
The size, and especially weight, of the speakers must also be factors to be considered.
Perhaps most importantly, there’s also cabinet construction to take into account. As far as I’m aware, no manufacturer has given this issue as much thought as Harbeth have. As they admit, they are merely following the decades old BBC research into cabinet construction.
The BBCs conclusions were that low frequencies are better dealt with by pushing them below the threshold of hearing (some 20dB below if I remember correctly) than attempting to suppress by sheer mass and rigidity.
Hence Harbeths lossy cabinets are almost in direct opposition of everyone else’s.