Cookerhood sound reduction

Hi All,

I'm continuing to make improvements to my horrible 'Luxair' cooker hood. I have already moved the fan unit outside along with hopefully most of the noise and vibration. Now I want to reduce the structural vibrations of the oil-drum-of-a-hood. You can see it in the pics below:-

I was thinking of gluing some 3/16" plywood in to the insides to stiffen up the large surfaces. But I also like to try to absorb some of the higher frequencies coming through the airstream from the external fan. I suppose I could try drilling a million holes in the plywood but if I can buy some stick-on material that has a proven effectiveness I think I'd prefer to go this route to save time. (I'm already being warned that this job is taking too long )

So, does any one have any experience of a stick-on material that will stop panel vibration, acoustically absorb and is obtainable in a 'domestic' quantity please ? mmmm ...as I write I'm thinking such a thing might quickly get clogged with grease....

Just stick on some hefty metal disks, they should drop the resonance enough to stop the drumming.

Neil

Maybe something like this Ebay

You can get similar from motor factors too

Adrian

Edited By AdrianR on 16/05/2020 16:51:28

Edited By AdrianR on 16/05/2020 16:52:15

You could use anti drum stick on panels like the ones found inside car doors not foam, but that would depend on how they withstand the heat.

If it's too quiet there's a good chance you might forget to turn it off and in the winter suck all your heat out

Stop the noise at source? Get a decejnt slow-speed extractor fan?

Thanks for your comments chaps ! I have some lead sheet so I will place some of this in the centre of each panel and will cover over with some Adrian's acoustic sheeting. Perfect !

Dave it could never be too quiet, but sucking all the heat out of the house is a possibility! Initial tests show that on full speed any room door not properly closed is pulled open by 5 inches ! Its a good job my boiler is in the attic !

Gerry

Once you have it silent you will probably start forgetting to turn it off.

;O(

Martin

Unless I have missed the point, what I think you need is to isolate the 'drum of a hood' from the source of vibrations (or the other way round really).

No matter how resonant or tinny the hood metalwork is, if its just sat there it cannot produce any noise by itself. I suspect that the vibrations from the motor are being mechanically coupled through the duct.

Can you interpose a flexible rubber coupling between the hood and the fan motor? You could make something out of sheet rubber or possibly an tyre inner tube. Maybe mount the motor on rubber suspension too .

Ian P

That has worked well for my family for years. Fit a larger fan and run it on reduced voltage.

George B.

Hi Gerry. Where are the vibrations coming from if you have isolated the fan from the hood ?.   I have a fairly large S/S cooker hood with the fan remote via ducting with a flexible joint and have no issues with vibration whatsoever.

Maybe you could hang the hood on flex mounts. If the hood is to be completely built in and hidden you can add sound proofing to the top of it. If it is on show anything you stick to the inside is not going be good when it comes to cleaning the oils & greases given of by the cooking process. I would steer well clear of any combustible materials inside the hood.

regards

Edited By Oldiron on 17/05/2020 12:20:55

There shouldn't be much direct vibration coming into the hood as the fan unit is now reasonably isolated on the outside wall. But the hood is a shockingly flimsy thing and it wouldn't take much to set it off, so the lumps of lead should take care of that. At the very least the lead will stop it sounding so 'cheap and narsty' when you press the buttons to switch it on, set the speed or turn the lights on.

But there is plenty of airborne white noise coming down the pipe and when that gets into the hood it will just bounce around and be focussed down to the cooker methinks. I'm hoping that the acoustic layer will take care of some of that. I probably need a to put a horizontal baffle in front of the exhaust port too, thinking about it.

This project is very much suck-it-and-see and with hindsight I should have perhaps gone for an even bigger fan but as they say, experience is all about mistakes. I could still come back to that later when I run out of things to do!

Adrians acoustic sheeting is 'said' to be suitable for engine bays so hopefully it will have sufficient temperature resistance and the aluminised coating will make it cleanable to a degree. If not, I can rip it all out and think of something else.

In vehicles extensive use is made of self adhesive pads of a bitumen type material, they may be effective in this application.

Mike

We had a horrendously noisy cooker hood that IKEA replaced with another one that was also noisy. Finally fitted a different one but I think a large factor in the noise was the corrugated plastic pipe. I found several comments saying that smooth bore pipe was a much better idea and didn't set up resonance in the tube to the same extent. Might be worth a try . Sandy

Hi Sandy, yes most cooker hoods are a complete disaster as far as noise goes. That why I started to build my own. With the top notch ones costing around £2000 I didn't think I could go too far wrong. But as its pointed out to me regularly " this has been going on for 3 years now. When will it be finished?".

….. and yes I have a smooth pipe ! Only issue was I drilled a hole with a 150mm core drill only to find that the standard "150mm" tube wouldn't fit through it. I had to use a 150mm sleeving which brought my bore down to 146mm ! Why do these plans always go wrong in the wrong direction instead in the right one ???!!!

Gerry

You won't forget that TUBE is measured by the O/D and PIPE by the I/D in future though!

Neil

Neil, thanks for clarifying that It reminds me of my ex-colleagues in Denmark that used to tell me that tube was flexible and pipe was rigid !!! All we need to do is get builders supplies catalogues on side and we'll all know what we are doing

Gerry, you may find that adding more localised mass isn't particularly effective with sheet metal, the best construction is to sandwich a dampening material between two sheets, though you may well find that dampening material on its own is adequate for your needs.

The mastic used for sticking car body kits on, such as sikaflex, spread over a panel at 1-2mm thickness is a low cost and resilient method of reducing sheet metal noise.