Soundproofing ventilation duct

[Tricky Dicky]

I am doing the finishing touches to our kitchen and have framed around the ceiling extractor and the duct leading from it to outside.

When in operation the extractor is quite noisy with a damper just behind the outside grill and also I suspect as the air flows down the duct in particular the short flexible corrugated length between the extractor and the 150mm rigid ducting.

Is there anyway I can temper the noise, I was thinking of packing the space around the ducting with something like rock wool before covering the framework with plasterboard. Any other suggestions welcome, or am I wasting my time?

Richard

[Martin Brown]

I think you will find that most of the noise is coming from the fan motor rather than the ducting. Though it may be acting as a sound box.

The most effective sound insulation is a dense closed cell foam with a layer of rubber in the middle and then a second layer of foam. Sold mainly for acoustic insulation in performance spaces but also available in smaller sheets for making PCs quieter too. Often just remounting the fan motor on silcone washers will make a big difference to noise levels.

[Brian Gaff (Sofa]

Yes if you are hearing air noise its going to be harder to stop, since the sound you hear is the air turbulence over the blades and duct surfaces. Moving more air with a larger fan running slower can be good but otherwise its really hard to stop air Bourne noise. Maybe some kind of filter in the duct, but that might impede the airflow and the system would be rather useless. I noted the other day running a vacuum with all its filters removed made less of the air noise, but moor of the compressor noise, not that I'd want or suggest anyone tried this unless there was no intention of using it!

Brian