Thanks guys much appreciated
One thing I did forget about mentioning on here is the sound treatments I’ve ended up using to get the van quieter than a Mercedes S-Class (it’s been very accurately measured)
Some photos are missing because I can’t find them but I’ll add them in shortly.
So, the steps are many and everyone has their opinions on what works how where and why. I decided to test everything I could and measure the effects using an RTA and microphone.
Here’s what I did, the product used, and in the order of first to last.
Butyl rope, aka headlight sealer, aka butyl sealant tape.
Everything was stripped from the interior and all panel gaps, brace bars, etc, were very tightly stuffed with the rope. Warm it first with a heat gun so it’s softer and pushes into the seams. The most noticeable difference was the brace bars across the roof and the side panels inner to outer panels especially when driving in rain or a heavy headwind. The brace bar in the doors front doors made a small difference and I also used it on the joints between the outer rear wings and inner arches but it yielded no noticeable results.
The only purpose of this is to make the joints as rigid as possible and reduce any chance of resonance between panels.
Deadening. Aka sound deadening, aka constrained layer damping.
Firstly, 100% coverage is pointless. The only thing deadening mat does is add density to flat metal surfaces. It won’t make any significant difference in reducing anything that isn’t caused by panel resonance.
Use the biggest pieces of mat you possibly can as that’s how CLD is designed to work. Cardboard templates make it a lot easier and cut oversized to cover any lips and joints.
I used single layer 2.5mm CLD sheets ONLY on the flat panels of the roof sections, rear side windows, side outer arches, inner wheel arches, outer door skins, front floor, under the seats, front inner arches, and bulkhead.
I also removed the arch liners and added a layer on the inner wing and the arch liners with an additional layer of 10mm closed cell foam.
Lightly score the surface with 80 grit, thoroughly wipe down with isopropyl alcohol, warm the sheet and the surface and apply with light pressure using a smooth solid roller. Seal all edges with aluminium foil tape.
Closed Cell Foam. CCF.
CCF greatly reduces noise. It’s lightweight, easy to work with and it yields excellent results. I used adhesive backed foil coated ccf of different thickness depending upon the location of application. Roof and sides got 50mm, front floor and bulkhead got 10mm, and outer door skins got 25mm. Again, template makes life easy, use the largest pieces possible and aluminium tape all joints. Only use products suitable for vehicles or boats (hydroponic) due to water and moisture repellent properties especially in the doors.
Mass Loaded Vinyl. MLV.
MLV blocks noise. It’s heavy, it’s a bastard to work with, nothing sticks to it and frankly, if it wasn’t so effective I’d burn it all. I’ve used 1.5mm against the rear outer arches, front floor and bulkhead.
Soundproofing.
I tested over a dozen products and the best results were from Knauf Acoustic Roll. Fill every possible void with the stuff.
The method here is not to pack it overly dense as the material needs a certain degree of space to work. The Knauf product is suitable for vehicles, it’s an earthwool so it’s not hazardous or harmful in any way, and it tears like soft bread which is great. Literally fill every space you find including all the way down the A-Pillars.
Where you’re filling against MLV you can pack it a little tighter to keep the MLV stable.
Also use behind trim panels with a light coat of spray glue on the panel
Aluminium foil tape.
This is one of those little difference that makes a big difference things. Tape everything!
My testing was done at 30mph, 60mph and 75mph on certain roads I travel often. So the M25 between Cobham Services and the A3, the M26 & A2, normal roads in central London and the countryside lanes of Surrey and Kent.
I won’t post all the measurements and results because it’s mind numbing but here’s the before and after from the Knauf Insulation Roll.
On the M26, my van as a base model with no modifications on a dry day at 75mph produced 109.6db, now it’s 71.1db and it cost less than £250
tbh I wish I’d kept my R seats lol
