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Since fitting a bulkhead in front of the fuel tank, the cockpit has got quite noisy from the rear with a resonance setting in at 70 +

The aluminium bulkhead had butyl type vibration absorbing pads stuck to the rear of the new bulkhead but I am now thinking of lining out the rear of the cockpit and the floor with acoustic sheet of some description

There is already a layer of sound absorbing felt underlay under the carpet but any suggestions for reducing the noise level or experience of the materials available? 
 

Phil

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Ed is correct. If the panel is resonating (drumming), the 2-3 mm thick mastic glue-on pads, as originally installed on the floor pans, is enough.

Waldi

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23 hours ago, PhilipB said:

 with a resonance setting in at 70 +

 

Surely you wouldn't break the speed limit Phil...

I spent ages trying to track down a resonance after doing some work on the car which turned out to be a couple of loose bolts on a propshaft U/J, nowhere near where I'd been working.

Pete

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I kitted out my TR4 over the Christmas break. Fitted equivalent to Dynamat to the floor and inside the doors too. It doesn't have to cover the entire surface it just needs to change the mass of the panel which then changes the resonant frequency too so stops panels vibrating etc. As an acoustic engineer I've got access to meausurement kit and it reduced the decibel level by 4 dB when driving at 80kmh (50mph), which is a perceptible difference when driving - stops the low frequency road noise too. I fitted a couple of squares of material to the fuel tank too. Trick is to make sure sure there is an even contact with the surface and no voids. I then fitted foam carpet underlay and sealed all the edges with aluminium tape. Bit over the top IMO.

My priority would be door inners, floor pans, including the space behind the seats, fuel tanks and bulk head, plus gearbox cover as shown in the photo.

if you are getting a resonance on one area I would check to see if the panel itself is loose or is drumming. Get your passenger to apply some pressure to the panel and see if that stops it. I fixed foam along the edges of my rear trim panel to isolate from the bodywork. I've probably got one of the quietest TRs now. Can hear the induction and exhaust sounds perfecty now!

 

IMG_4066.JPG

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I have used a similar product as Ed above, which was also the original type used. 
Relatively cheap too, which appeals to us, Dutch:)

Waldi

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The cost of the CLD damping mats is related to both materials and thickness.  Cheaper mats are thinner and/or use bituminous compounds.  Thinner pads are less effective, and the bitumens have an odor. Some less expensive pads are not CLD (Constrained Layer Damping) at all, but just resinous mats, like the originals.

Ed

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1 hour ago, Cameron said:

Thanks Stuart, how many sqm required for a 6?

 

I usually use 2/3 boxes (10 in a box) as I fit them in the doors and either side of the tank and behind and in front of the rear firewall.

Stuart.

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If you install a pad of the bitumen like material, and knock the panel, you get a dull sound. Area’s without any pads resonate more. There is a distinct difference.

Waldi

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