there's loads of info on what to use where, but the principles are fairly straightforward...all sound emanates from vibrations in free air...thin metal panels are flexible and have little mass, so they'll vibrate...the free air is provided by the space behind your trim panels, and the interior of the van itself...all sound deadening pads do is add mass and lower the frequency at which the panel vibrates...preventing those vibrations from being transferred is where sound insulation comes in. If you tap one of the bulkheads behind the cab seats, you'll hear a sound...if you place your flat hand in the middle of it and tap it again, you'll hear a different (lower) sound...it'll sound duller (and quieter) because you've reduced the resonance along with some of the higher frequencies...now if you put ear defenders on and repeat the process, you'll hardly hear anything, because you've prevented the sound from reaching your ears...pretty obvious stuff, but from a practical point of view, you're limited by what can be achieved. Treating all your panels with Silent coat will reduce 'drumming' (you don't need to cover the entire panel...about 40% of each panel will work fine...doors, floors, arches tailgate etc). Sealing the large side panels, doors and tailgate with closed cell foam sheet , before replacing trim panels, will reduce the transfer. Reducing engine noise is more involved as you need to remove the engine and bulkhead to treat the fuel tank compartment (a big metal resonator, inside another resonator!)...a job for next time your motor's out. You can also replace the useless stock sound insulation above the engine with something more extreme like lead sandwich (literally a sheet of code 4 lead sandwiched between two sheets of closed cell foam)...all your soft furnishings help to reduce resonance and high frequencies. It's a big job, but will pay dividends in the long run...if your bus is empty at the moment! filling your floor with concrete would work fantastically well but is not really an option... ;D
You could try a product called pyrosorb ,its used in sound proofing , it does work , its used in sound studios etc. They use it to make ventilation silencers /cross talk too.its not dirt cheap but easy to cut and i would think 6mm would work fine !! Has insulating properties too.
I used Autoleads stuff and VW's original padding. The Autoleads stuff along with new wood trim on the roof of the engine bay with no holes has done a great job. The quietness is quite outstanding and I only fitted the Autoleads stuff to the top part of the engine bay and firewall. If I'd had enough I'd have done the firewall too. However I'm glad I didn't. I now struggle to hear the engine. It's changed the sound dynamics inside quite a bit and how I drive.
Thank you all for all your info. I'm now in a right predicament... am now looking into dynamat xtreme instead of bitumen pads. from one extreme to the other
arghhh, still haven't ordered anything... i'm getting all tied up in the expensive stuff and forgetting why i need it in the first place! I'm not fussed about the noise from my stereo (cheap stereo & speakers), just want it not rattly and not loud in the back for the little 'un when travelling. and possibly some insulation. so nearly ordered dynamat but the amount i'd need it's cost a fortune (even only doing 40% of surface area).
You need it to stop the panels resonating. This is your first step in reducing the racket, as Bays, being delivery vans, didn't have any of this stuff. Dynamat's fine, but is hideously expensive. Bitumen, in my experience, does the job just as well and, as above, this is the stuff car manufactuers slather the panels with.
Go with the bitumen pads ermintrude they will make a noticiable differance hun Ive heard of people using flashing tape from diy stores before as a budget option
Just found this website - two 1000mm x 750mm sheets for £30 delivered. http://www.soundcontrolservices.co.uk/index.php?main_page=product_info&products_id=88 Type soundproofing bitumen into google and there are a lot of discussion results from other retro car enthusiasts to trawl through.
