T3/T25 Cab Door Sound Deadening

Been tinkering in the garage again? Post it here.
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spikeemikey
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T3/T25 Cab Door Sound Deadening

Post by spikeemikey » Mon May 31, 2010 11:18 am

Hi Guys

Have started on a bit of a sound deadening. Apparently practically all the commercial-derived vehicles are pretty much devoid of sound deadening. A swift tap on a panel or two confirms this, consumer-orientated Caravelles etc have some installed.

I want(ed) to Waxoyl all the door/slider/tailgate sections and check out how they are coping after almost 30 years, so this was the ideal time to kill two birds with one stone by installing the sound deadening at the same time (though I have now realised combining two jobs quadruples rather than cuts the time taken!).

Dynamat sheet (expensive) or bitumen or butyl flashing tape seem to be the way to damp the doors so they dont resonate. All the products are similar - a dense and heavy membrane covered by a very thin layer of Aluminium sheet. Adding mass to the resonant panel drops the resonant frequency, stoping it ringing, or shifting the resonance to a lower less noticable range. There is a really good thread on it at The Brick Yard:

http://www.brick-yard.co.uk/forum/dynam ... 23411.html

25-50% coverage is enough to get a good effect, so there is (as usual) a law of diminishing returns, its not worth going mad.

There was a fair amount of Waxoyl still in the doors so it became a protracted job to get this out (heat gun and some sort of solvent) before appying the sound deadening matering. I used bitumen roof flashing tape, then added a smaller quantity of the butyl stuff over it. Both from B&Q.

When warmed with a heat gun both soften up. The bitumen type 'Evo-Stick Flashband' is very easy to apply. The butyl one 'Corotherm' has a thicker Alu skin and isnt as easy to apply, so not wanting to create air moisture pockets against the metal door skins, I just applied the butyl over the bitumen. A small decorating type roller is used to firmly affix each to the surface. The Dynamat website has lots of details about installation.

Toolstation has much cheaper bitumen flashing but its thinner also, so wont be as effective at adding mass. I may double it up and use some in the bigger sliding doors. I havent done a full-test yet (its too damp to install the Waxoyl today) then I need to let it dry a bit before finally re-installing the speakers, but there is a huge difference in giving a tap on the outside of the now-damped cab doors compared to the undamped sliding doors. A short 'thunk' compared a very drummy sustained high-pitched ring. Slamming the door sounds more solid too.

The next area for attention is the storage boxes under the cab seats. Apparently these are terrible resonators (mentioned in the Brick-Yard thread as one of the wost offenders).

Cheers

Mike
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Sound-deadening (i.e. flashing tape) installed in the cab door.
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Close-up of the area behind the speaker cut-out. Larger bitumen 'Flashband' overlaid with butyl 'Corotherm' flashing tape.
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Dubmatix
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Re: T3/T25 Cab Door Sound Deadening

Post by Dubmatix » Mon May 31, 2010 6:17 pm

Good info there Mike, I must say it's something i am considering doing too as the cab road noise is excessive! The Bays also have boxes under the seats which i'm sure are great (rubbish) for resonant noise.
Have you used any of that stuff you got at Stanford Hall?
A thought that crossed my mind whilst looking at your pics was that stiffening (or deadening) the surfaces of your door should improve the bass response of the 'door box' for your speakers. :) You mentioned that you could hear the sound from your new speakers outside before, i wonder if it is noticeably reduced now?

Keep us posted with any more you do!

Cheers

John

spikeemikey
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Re: T3/T25 Cab Door Sound Deadening

Post by spikeemikey » Mon May 31, 2010 10:43 pm

Hi John

Yeah this should improve the front speaker sound, by damping the rear wave which otherwise resonates and bounces back thru the speaker cone. Eww! I am guessing it will deaden the sound leak to the outside, actually that one doesnt bother me too much ;)

This afternoon I finally cut up some of the stuff from the Stanford Hall show. I cut two of the three sheets I bought to cover the rear loading area above the T3/T25 engine hatch, each was big enough to make a rectangle to cover about 90-95% of the area. Its weird stuff, almost like a super dense scrubbing/scouring pad that has been impregnated with plastic. Its heavy and very stiff. I was thinking I might have to take a jigsaw to it, but actually it cuts fine with a decent stanley knife blade.

So I put the two sheets in and placed the carpet that came with the van on top, which has some thickish (and slightly decaying underlay). So three layers in total.

I went for a spin (just a couple of miles with the lower tinware off) and there was a definite difference, the engine noise was rather muted, and I was hitting 80km pretty darn quickly with less notice of the general noise. So far its treating the cab doors and adding two layers of this deadening over the loading bay/engine cover. Quite impressed, and this is with the door cards off still, which cant help.

The danger here is that as you remove dominant noises you uncover others, so the creak I have in the right front suspension (caused by monster potholes in North Wales) becomes more obvious, and loud resonances you cure get replaced with rattles between interior trim and the vehicle body, etc.

I cut some pieces of approx. 3/4 inch fibre board to fit the boxes under the seats, and to those I will glue the rigid sound damping material with contact adhesive, then bolt these in to the trays. That should add loads of mass to damp the boxes, this will give me a convenient platform to screw the amps I have for the front speakers.

Its funny when you start tapping things you realise how resonant the vans are. The whole underseat box/battery box/cover making up the wheel arch is a drum waiting to beat! I may try some of the butyl flashing tape to calm things down where it cant be seen. I am little cautious on using the bitumen in the cab in case it gets smelly on a hot day.

I am trying to decide what to use on the sloping bulkhead in front of the engine. Its either gonna be the flashing material (as mentioned in the Brick-Yard post) of this weird impregnated scouring pad material, which was what the guy from Stanford Hall suggested, and the guy from www.noisekiller.co.uk who (I think) wanted 250 pounds for a whole noise killing kit for a VW Van (chatted to him at VolksWorld).

I'll try and find the sticker/flyer the guy from Stanford Hall gave me who was selling the sound deadening offcuts as he mentioned he could offer more. Its definitely good stuff.

Cheers

Mike

spikeemikey
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Re: T3/T25 Cab Door Sound Deadening

Post by spikeemikey » Tue Jun 01, 2010 10:24 pm

Ok Guys

Just a shot of what the 'scouring pad' sound deadening material looks like, so its some sort of fibrous material bonded/impregnated with a plasticy (guessing here!) resin.

I wouldnt glue it inside any doors but it seems to work well over the engine cover.

Cheers

Mike
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