Applying Sound Deadening to Car Doors...

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miked

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#293135 31-Dec-2021 20:06

I'm planning to install some Dynamat sound deadening in my Mazda Premacy, as these seven-seaters are great to drive, but are pretty noisy inside.

Was going to start by doing the sound deadening on the rear doors as I have them opened up anyway for another job (and those door-skins are super clangy!). Then maybe I'll follow-up later with some cheap closed-cell foam on the inside of the door cards.

Has anyone else done this? (or anything similar?) Was it worth bothering with?

Not wanting to spend a fortune... Or add heaps of extra weight for that matter! But seems sensible to do something whilst I have the rear doors open anyway.

So my understanding (based on a quick read but no actual experience treating a car yet) is that there are two main types of noise.

Self-resonance, where a big panel rings as it vibrates.
And road / tyre noise and wind noise passing through from outside the car.

Most of the car panels on the Premacy resonate when knocking on them.... so are probably self-resonating to create sounds when driving. I understand that that will probably be helped by the dynamat extreme foil-rubber stuff, which can be used to add weight and vibration absorption to make panel sound dull when knocked (and that 25% - 40% coverage is enough apparently - as more than that apparently gives dimishing returns). So if I do 25% - 40% coverage (for cheaper cost), does it matter how I lay that out? Some sort of checkerboard pattern? Or something else?

My understanding is that the tyre/road and wind noise is better dealt with by covering the whole panel with closed-cell foam, which is lighter. So I'm assuming that is where I want 100% coverage (or as close as possible?). Thinking I'll put this on the inside of the door cards.

Any help or opinions appreciated. Anything I mis-understood?

Batman

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#2841031 31-Dec-2021 22:06

I've done this. Works for outside noise but doesn't work for road noise. Zero effect on road noise.

Involuntary autocorrect in operation on mobile device. Apologies in advance.

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Sred

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#2841224 1-Jan-2022 10:08

In my opinion don’t bother Very rarely any benefit

Batman

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#2841229 1-Jan-2022 10:18

it was late last night so i'll explain a bit more

have a subaru legacy wagon that sounds like a resonating chamber. on chipseal roads i cannot hear myself speak let alone hear other passengers. i do run 40-45 profile tyres michelin pilot sport 4. the wider the tyre the higher the speed the louder the road noise. basically very fatiguing.

so i applied dynamat on all the doors at 100% coverage, the entire boot, all over the rear wheel well and under the rear sears inc the transmission tunnel.

the only bits missing is the front firewall and the floor and the front wheel well. this is where the road noise is coming from as when i sit at the back it's actually relatively quiet but since i'm always the driver i've not managed to test the back seats to compare the front back and forth.

but it does insulate non road noise sound. i can have my sound system blast at over 100dB with a sub and when i shut the door and stand outside you cannot hear the sound system.

Involuntary autocorrect in operation on mobile device. Apologies in advance.

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#2841232 1-Jan-2022 10:20

and no i did not add foam, I did all these during lockdown and i've given up. it's made no difference. cost was about $50 and a lot of sweat and blood. (though i did buy the foam for another $30 lol). foam is sitting in the store room. if i wanted to do anymore it'll be removing the front seats and doing the floor but i looked at the front firewall and it's not easy to get to. there are a lot of stuff - basically the entire dashboard needs to come out to insulate the firewall and the half front wheelwell area. the other half of the front wheelwell is in the engine bay.

Involuntary autocorrect in operation on mobile device. Apologies in advance.

miked

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#2841433 1-Jan-2022 13:58

Thanks for the detailed reply.

Out of interest, what did you buy that was so cheap for the mass loaded rubber and for the foam? $50 and $30 seems very cheap for bot parts!

For simplicity I got the Dynamat Extreme door kit, which has four sheets of the mass loaded rubber. Far from cheapest, but was able to pick it up local so I could fit it in the next few days, which was crucial whilst doors were already open. The kit is designed for complete coverage of two doors, but hoping to spread it over the four doors at about 40% coverage. It should vastly reduce the ring in those panels. I will probably buy some more for other locations too, but hopefully have more time for that, so find something cheaper next time rather than Dynamat itself!

Planning to buy a big sheet of the closed cell foam from foam.co.nz or similar. Either 5mm or 10mm, or maybe one of each. I can buy and fit that later, as the door cards come off very easily. If it is cheap enough, as well as the 100% of each door, I might do under the boot carpet and under floor carpets etc with that too. I expect that to be the most sound reducing element for road and wind noise aspect. (Will do minimal dampening too, but nearer the 25% range for other under floor panels.)

Most of that is future plans, but hoping to fit the dynamat I already have in the next couple of days. But uncertain of pattern to achieve 40% ish. Guessing squares or rectangles in a checkerboard pattern will be as effective as any other layout? Probably will go diagonal so I can reach towards edges and middle. Guessing maybe 20cm x 20cm squares, or 30cm x15cm rectangles would be a compromise between too small and fiddly... and too large to handle (and leaving too big gaps). Any thoughts on pattern? All online videos seems to focus on 100% coverage not 25%-40%.