Plasterboard and noise insulation

Very much so. The biggest problem with PB is resonance, it can act as an acoustic transformer at resonant frequency, effectively amplifying the volume.. What's needed is damping. Rockwool works, so do carpet offcuts fwiw.

Your problem's going to be getting something in there without trashing the plaster.

NT

I don't mind drilling a few holes - would expanding foam of some kind do the trick?

Ah... as a cavity filling damping material its very badly behaved. The big issue is its tendency to expand with massivce force after its solidified, destroyng whatever tries to contain it. If you can get the type that doesnt do this (some do, some dont), then I guess it should just about work. You'd need quite a lot of foam & holes, but they should be fairly trivial to fill afterwards. Think I'd be more tempted to try and rig up a homemade blowing device and blow losefill in.

NT

I don't know if you're right about the 'resonance' thing (my own gut reaction was reading the OP was "no way, he's imagining it"; however if the PG is indeed resonating then wouldn't it help to inject small squirts of expanding foam through holes at intervals; in effect creating a 'dot'n dab' support for the PB? Surely that would dampen things down?

David

If this was a problem, tapping it would reveal the frequency. But I've never known plasterboard produce a 'note'. It produces a thud suggesting multiple frequencies. And each part of it a slightly different thud due to the supporting method.

Think it is your imagination - or you've invented an amplifier that uses no power. ;-)

Was the old wall damaged or altered when erecting this stud work? For example was some or all of the old plaster removed?

yes, but as said it can also do a lot of damage as it expands. I found this out the hard way.

Re resonance and acoustic transformer effect, theyre not new concepts. If you doubt it, try attaching a noise making thing to a panel of undamped PB, it will become much louder. Try it with a hand held blender, power tool etc. Compare this with damped PB, very different result.

(PB resonance is low Q compared to musical instruments etc)

NT

What, you weren't the guy with the canoe, were you? ;-)

I know what you mean, but I was thinking in terms of a small drilled hole for each 'dab' and not more than a quick squirt of foam down each hole. There'd be ample space for the stuff to expand freely in 2 dimensions, plus even back out of the drill hole, without risk of bowing the PB.

(Assuming you're right about the resonance thing anyway...)

David

David

The usual recipe for sound insulation is two layers of plasterboard on batten with rockwool filling. BUT you must keep the battens separated from the wall (anchored top and bottom only) so there is no direct conduction of sound fro mall to batten. In addition you need to increase the mass of the panel to lower its resopnant frequency and damp it) so you use two layers of plasterboard. The cavity is filled with rockwool. it's important to 'caulk' - fill all the little gaps.

Robert

Lol, I'm very grateful I'm not :)

ah... optimism :)

NT

There are several things one can do that reduce noise from PB walls, and the above is a fine method. But I assume the OP doesnt want to replaster, having just done it once.

If Sean is happy to redo the job, I'd remove the PB and fill the space with mineral wool, and use 2 layers of PB.

If major noise reduction is wanted, to far below original levels, then go the whole hog and remove the frame, refix it an inch away from the wall, fixing it top & bottom, and add concrete weights onto the noggings. Then mineral wool & 1" of PB.

... there are always other options.

NT

please tell me more about concrete weights - how and where, is it to stop the frame vibrating?

/snip>

Isn't a sounding board just that? Tuning fork in free air is relativly quiet but the same tuning fork held against a sounding board is much louder.

Archie

I wonder if filling the gap with sand would help. Sand is dead accoustically.

Archie

The main thing to control sound is mass Hence I agree wiith the suggestion of sand but have my doubts that the plasterboard will be stong enough over time

~So I suggest very dry sand in holes in the top and cross the fingers

absent any bulging of the plaster board and its failure you have "won"

If the plasterboard does go then that is the time to set to and do the job properly isolated as described by others! Chris

Thanks for the advice folks.I may give a few squirts of expanding foam a go - not much to lose if I'm cautious. I never though to ask about additional insulation when it was put up, I just didn't consider that another layer with a gap could possibly make things any louder (and I realise the juries out on that and it could just be I'm listening a bit more carefully for it).

if the foam doesnt explode the plasterboard then it will add support and maybe you can put some sand in there...

there are different types of foam with different expansionisms- dont get the canoe stuff which expands a hundredfold (allegedly)

There is - it could actually increase the coupling between the walls and make things worse.

It can't if the two are separated. Are you certain the original wall wasn't damage in some way when the new partition was built - old plaster removed producing holes through it etc?

It should have produced a noticeable reduction.

In my similar project, ok i can build a new timber frame and put 2 layers of plasterboard on it but how much better would it be to use sand rather than rockwool in between (maybe with some plywood so it doesnt bulge out)

Will the sand absorb a lot more sound than the rockwool, or just a little more?

ps o yes foam could connect the wall to the plasterboard and conduct more noise...