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View Full Version : Suspended floors and acoustic insulation



AlexM
05-07-2011, 14:32
Hi All,

I am approaching the end of a seemingly never-ending basement conversion project. I am very keen to ensure that sound transmission between the ground floor (where my living room is) and the self-contained basement flat is minimised as much possible.

To that end, below the floor joists I have used acoustic plasterboard and fireproof plasterboard, secured to resilient bars rather than the joists (they look like a folded metal strip in a 'z' profile), acoustic mineral wool between the joists, foam joist caps (to minimise impact noise), a high-strength tonge and groove chipboard, and a fioating wood floor.

The existing suspended floor where my rack is located was quite 'soft' in the bay window, to the extent that footfall is a major issue. I am relocating my rack to a corner in the room, and am wondering how best to support that section of the floor. I could

a) leave the floating floor/joist caps etc as per the rest of the room with possibility of footfall being amplified by the foam layer compressing when the floor is loaded by footsteps etc. The joists will be short in this location, and the rack positioned close to the wall where they are tied in.

b) take advantage of the steel RSJ under that corner of the to support the rack rigidly - builder has suggested that a steel plate could be welded to the RSJ, and capped with chipboard to level the floor surface. This would be effectively immovable. I wouldn't be concerned about impact noise as this small 0.75m sq area would be underneath the rack, so probably wouldn't compromise the sound insulation too much. I could even cast a concrete pad in this section if this would work better,

c) optionally tie the joists together in the bay window with noggins made from surplus joists and joist hangers - my speaker will remain here and the floorboards will be removed so easy enough for me to do at little or no additional cost

Anyone got any experience in this area or got any suggestions?.

Best Regards,
Alex

Effem
06-07-2011, 08:58
Unfortunately there is no cheap and easy fix for suspended wooden floors transmitting sound or footfalls. Even more expensive than that is sound insulation.

I have suspended floors and a large void underneath my listening room and it is fortunately not occupied. I could install "soldier" brick pillars, wooden posts, or steel beams to stop the floor bouncing up and down but as nobody lives beneath all it would give me is the loss of bounce walking across the room and maybe a slightly less room interaction with the speakers.

If it were me I would take the option "C" path.

AlexM
06-07-2011, 11:00
Frank,

Thanks for that. Brick Pillars or similar aren't an option, so I think that I will reinforce the floor joists as best I can in the bay window area, and mount the stand at the other end on a platform connected to the RSJ that runs underneath that corner, so options B&C i think...

Regards,
Alex

hifinutt
17-07-2011, 06:17
c sounds good. i have spent many hours and days under my floors with woodworm, insulation , wiring , installing earth rods for hi fi etc