In article
,
Andy Dingley wrote:
On May 18, 7:34 pm, sm_jamieson wrote:

However, I want to put in some proper acoustic stuff inside the boxing
around the PVC soil pipe to minimise the flushing sounds.

You need some mass in there. Layers of high-mass material, flexibly
mounted, with layers of wool between them. Chipboard is one of the
cheapest, Cement board is best, MDF isn't bad. If the location fits,
hanging boards on wire from above is a good way to install it.

Plasterboard is pretty good as regards density/cost.

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Dave Plowman London SW
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