David Smart said:
There's not enough of it. In addition to the floor there is glass all round the room: too many reflective surfaces suck the lower freq and magnify the mids and highs. So trying to what little I can to improve the situation. I guess another question - do I want to couple or isolate the speakers from the floor?
David,
The argument goes that when the cone is pushing outward against a column of air, an equal and opposite force pushes the enclosure backward. This force results in a small backward movement of the enclosure which in turn reduces the effect of the forward cone motion, reducing bass performance. There are holes in this argument, but as a general rule, speakers want to be firmly supported and the stand should be coupled to the floor to provide a solid support.
The only time you may want to go against this advice is if you have a suspended floor which could be 'excited' by vibrations coming down the speaker stand - in which case isolating the stand may make sense.
I take it from your note you are still wrestling with your conservatory. My guess is that poor bass is caused by standing wave room effects, which no amount of fiddling with the stand will improve. Try moving the speakers or your listening position - that may help. Also try opening all the conservatory windows, that will reduce boundary reflections - if this makes a big difference then it is definitely reflections causing your problems.
I think it has been suggested in the past to try room equalisation of one type or another. That can certainly tighten up bass in a reflective room.