Noise reduction. Washers/gaskets and sound deadening

[mepbowles]

The plastic dash components of my cavalier and be quite noisy, especially at engine speeds that produce a kind of harmonic resonance. 

 

I wondered if anyone has tried used foam gaskets or washers between parts to reduce the buzzing and vibration noise.

Also, I'd welcome any experience on sound deadening mats versus sprays. My gut is saying the mats would be a potential moisture trap and the spray would be easier to apply to the whole of the inside. I'm not sure on the cost/performance of each method.

[cam.in.head]

im with you on this one .

its usually the lower section and rattles / creaks can come from many areas. mine seemed most from the fusebox lid and ashtray so i have put some self adhesive foam on the back which seems to help a little.

also the wiring up behind the ashtray for the radio and clock can vibrate too .later vauxhalls had a lot of the wiring covered in a type of foam sleeve so i used some of the self adhesivefoam there too.

its realy a case of finding the areas on yours that may not be the same as on mine .maybee the plastic panel that houses the heated window and fan also ? 

in theory if you wanted a full solution you could remove the lower section.and rubber insulate all the contact areas and tape all the wires back too.

[Trooker]

I guess it would be worth trying neoprene covered washers from the building industry to isolate the dash panels. 
 

No experience in cars but if you want to reduce sound then you need a material that converts sound waves into heat. Spray on stuff won’t be great. You need something with a little mass for absorption. Dynamat is probably the best known & seems expensive but doesn’t absorb water. You could go totally old school & burn on some thick felt with tar like the inside of doors 😆

[cam.in.head]

as regards soundproofing. i did most of my undercarpet floor area ,boot and inside doors with rubber sheet type deadening panels and then a foam sheet on top. its an expensive exersise and a very hard to get right and i dont notice THAT much difference .theyre not a particularly noisy car to begin with realy 

another issue which i have noticed with mine.over the years as i have added more underseal you end up thickening the actual metal (in theory) which tends to lower the resonant frequency and can actually make a car noisier.or more boomy in lower sounds .hard to explain but ive known it before on other cars than seemed quieter BEFORE i wayoyled them !

 

[Trooker]

24 minutes ago, cam.in.head said:

 

another issue which i have noticed with mine.over the years as i have added more underseal you end up thickening the actual metal (in theory) which tends to lower the resonant frequency and can actually make a car noisier.or more boomy in lower sounds .hard to explain but ive known it before on other cars than seemed quieter BEFORE i wayoyled them !

 

That’s the issue with uniform thickness & no real absorption. It just alters the frequency. 
 

I’ve been in diy ‘recording studios’ with either thin foam or the bizzare egg boxes glued on the walls & thin carpets. They sound worse than no treatment as it takes out a bit of the high frequencies but does zilch for the bass so it sounds more boomy. 

Edited May 24, 2022 by Trooker