On 12/11/2010 7:56 PM, Home Guy wrote:
Don Phillipson wrote:

Even if you suspend the speakers from the ceiling, the low
frequencies coming from the speakers will still couple with
the room acoustics and your floor and walls will still
probably vibrate almost as much as if the speakers were
in contact with the floor.

This suggests a non-standard physics.

No it doesn't.

The basic complaint is that the floor vibrates,

No - the basic complaint is that low frequency sound is heard either
above or below the room with the speakers. The theory is that this can
be reduced if the speakers are removed from direct contact with the
floor.

and we know the speaker cases are in direct contact with the
floor. HG now suggests that if the cases were separated from
the floor by a foot or two of (compressible) air the "floor
and walls will still probably vibrate almost as much."
We should be interested to learn how this could possibly occur.

Car speakers are not directly connected to the exterior surfaces of a
car, yet low-frequencies are easily transmitted by those surfaces to a
listener dozens or even hundreds of yards away.

A different and rather complex environment. The car is of smaller
dimensions and the bass wavelength are much larger than the car
dimension. In addition, there is little damping from the sheet metal.
And as previously mentioned, a 15" or larger woofer is more like to be
heard at a distance that an 8", this is roughly analogous to power
factor in house current. The "power factor" changes with distance from
the speaker. Just a "trick" to get more sound outside.


If the room's walls, floors and ceiling is made from compliant materials
(ie wood, sheetrock, etc) then it's quite likely that low frequency
sound from a suspended speaker will create standing waves that will
cause the walls, floors to resonate.

Unlikely to be significant. Such resonances that do occur seldom couple
out. Once more it is conductance that is of concern. A diffuse wave
bouncing off or being somewhat absorbed is not even coupling in phase.
Do the math or look at the geometry. The bass wavelengths are more on
the order of the room size.

In this case, if indeed we are talking about a poured cement structure
(ie - modern multi-story apartment building) then that will be far less
likely.

But I still can't believe that a speaker sitting directly on a concrete
floor that is presumably 3 or more inches thick can possibly experience
enough of a vibration amplitude to be transmitted through the floor.

Believe what you will. The theory and practice are against you.

A quick search for (better) floor speakers.

http://www.google.com/products/catal...d=0CDcQ8wIwAg#

http://www.bestbuy.com/site/Polk+Aud...=1207352527510

Note the feet. What do you think they are for?

isolation cones, note the minimal contact area:

http://compare.ebay.com/like/2606668...=263602_304692

Beats the hell out of me why you keep pursuing these theories of yours.
The physics is more than you think.

You can just wait for Andy to report back.

Jeff
Who at one time spent a lot of time listening to room acoustics and has
friends with commercial recording studios.