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

https://www.dropbox.com/s/t04zi26c84...38.42.jpg?dl=0

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

On 28/03/2021 10:49, Tricky Dicky wrote:
I am doing the finishing touches to our kitchen and have framed
around the ceiling extractor and the duct leading from it to
outside.

https://www.dropbox.com/s/t04zi26c84...38.42.jpg?dl=0

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.

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.

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?

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.


--
Regards,
Martin Brown

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

--

This newsgroup posting comes to you directly from...
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"Martin Brown" wrote in message
...
On 28/03/2021 10:49, Tricky Dicky wrote:
I am doing the finishing touches to our kitchen and have framed
around the ceiling extractor and the duct leading from it to
outside.

https://www.dropbox.com/s/t04zi26c84...38.42.jpg?dl=0

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.

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.

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?

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.


--
Regards,
Martin Brown