Noise Reduction

[Tony]

Been a few threads on here lately about this which set me wondering. A while ago I removed the bitumen on the floor which was in pretty poor condition, this increased the noise level but not hugely. So after reading the threads I thought I'd get some Dynamat or Silent Coat to replace the bitumen - then got to thinking a 964RS has no bitumen coating, just a very dense rubbery foam under the front carpets (over an inch thick). The Dynamat approach as I understand is about vibration damping, I presume the foam like that in the engine bay is for sound supression, so which is going to reduce the overall noise level most in an early 911 on a results per kilo basis?

Tony

[sladey]

I'd be interested to know more about this as well. At some stage I'm looking to make mine quieter on the inside- more wife-friendly

[TheEasyLife]

I've had a southbound carpet set fitted in the last few months. That has made the interior quieter and more family friendly which is where I need it to be at this point in time. I have a toddler who had to wear ear defenders on the way to and from Classics at the Castle last september when she was 2.5.

I haven't a clue about results per kilo basis though.

HTH

James

[inaglasshouse]

Damping the resonant frequency of relevant panels, vs blocking external sound, are different things.
http://sounddeadenershowdown.com has a nice overview.

[Gary71]

Best move I made with my car was a doubled up thick acoustic foam and heavy layer barrier for the engine bay. Other than windnoise this is the most dominant noise source.

[neilmcd]

So, I'm a bit rusty on this stuff, but it was my day job years ago......

The heavy layer is indeed to stop panel resonances that transmit acoustic energy into the cabin. Because they're heavy, they also reduce direct noise transmission into the cabin. Basically if you double the panel mass per unit area you halve the sound transmission (reducing it by 6dB). That's why heavy layer is sometimes used on bulkheads. It's also why wind noise is transmitted more easily through Perspex windows.

The foam reduces high frequency noise, much like your soft furnishings do in your house - the problem is that foam can absorb oil and become a fire hazard in an engine bay - so I'd not recommend that! It's most commonly used in the cabin under the carpet.

I think the answer is you need a mixture of both. Don't be afraid to lash something up with duct tape to try it out. NVH is just common sense really - give it a go!

Or buy two small bits of yellow memory foam and stick them in your ears!

Neil

[TheEasyLife]

Ah, yes, windnoise. I was in an SC recently that had either a 964 screen rubber or a 964 screen and rubber and there was much less wind noise from the front screen than on mine as the 964 rubbers don't have the ally trim in them and are therefore more aerodynamic.

hth

James

[Gary71]

Some of the later cars (not sure when it was introduced) also have an additional door seal running up the A pillar around the window frame. I replicated this on my car and it made a massive difference. It's since fallen off (quality work on my part!) but I must get round to fixing it.

[Northy]

I believe you can buy a RUF part that goes in-front of the lip on the a-pillar that is meant to reduce wind noise a lot.

I used a lot of second skin in my car, which took a lot of the ring out of the panels and isn't that heavy. I've been planning on backing that up with a load of foam inside the car to try and remove some of the high pitched whine from my ailing gearbox. Woolies sell a lot of this stuff: Sound deadening felt - I was thinking a layer of the sound deadening felt would work on the rear bulk head, rear seat area and maybe the floors.

[squirdan]

Agree re wind noise.. By far the worst noise in my hotrod

The stuff Tuthills used is good .. Goes on hot for a nice neat fit.. See my resto thread

Leaving A pillar passenger side the main culprit at m way speeds

Might look into that RUF part - sounds good

[Tony]

Some of the later cars (not sure when it was introduced) also have an additional door seal running up the A pillar around the window frame. I replicated this on my car and it made a massive difference. It's since fallen off (quality work on my part!) but I must get round to fixing it.

Pretty sure this started on the 964.

There's soe good stuff here, I think the wind noise thing is useful, Ruf's A pillar add-on probably helps a lot in overcoming the turbulence from the rain gutters. Still not sure there's an answer for the best result per kilo of added weight, it's alright if you've 250bhp+

Squirdan - what did Tutiils use? Looks good, almost be happy with that as a final finish but must have missed any reference to a product.

Northy, Second skin appears to cover a whole raft of products - which did you use?

[sladey]

I ve got those door seals on mine which is an 87

[Northy]

Northy, Second skin appears to cover a whole raft of products - which did you use?

I used the paint on stuff - I think it's called second skin spectrum sludge.

[Northy]

Might look into that RUF part - sounds good

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