Thread: Sound insulation in Defender

In the interests of sharing knowledge I will set out my insulation install with some noise metering experiments so people can ascertain the benefits and materials required to do the job.

Material - Jaycar (product AX-3689) 3mm closed cell foam with aluminium foil and butyl. retails for about $29 per roll and discounted in larger volume. I paid $23 a roll.

quantity - 10 rolls used

area covered - seat boxes, transmission tunnel and bulkhead on drivers side and 1/3 bulkhead on passenger side (air con in the way). I had planned on doing the rear seat floor. I'll get some more and do it another weekend. Likewise with the bonnet.

pic attached of finished product before the reconstruction of the cabin. _MG_5924 | Flickr - Photo Sharing!

Comments: found 55 cents, swiftly repatriated by the minister of finance. Good to pull it all apart to give her a good clean and remove the build up of dirt.

10 rolls were used with no excess thus no room for error. I had to use off cuts to make it stretch. If you prefer a neat one sheet application (as opposed to a mosaic of off cuts) buy another roll or 2.

The material is generally easy to work with. Once the paper backing is removed the butyl likes to bond. So long as you don't apply pressure you can pull it off again. You can buy a wooden roller to smooth and press it down or use your hand to massage it. Cut it with a stanley knife.

I tried to fill gaps ie the battery box lid and surrounds to eliminate airborne noise as well as reverberation.

Tapping a surface with the insulation and a surface without it there is a distinct thud to its sound. The 10 rolls were not heavy, say 12 kg (for those conscious of adding too much weight to the car).

Took a solid 8 hrs of work by the time you pull the cabin out, clean all the surfaces, scratch head and make the decisive move to apply the product, then rebuild the cabin.

To do the job properly you would need access to the bulkhead therefore a job for a restoration or from the factory.

Noise insulation experiment.

All db readings were done with windows up, stereo off. Measured with a iPhone App. Not very accurate but it was used throughout therefore take the results as a before and after not necessarily accurate of actual db levels in the truck. The phone was mounted in the window cradle. Each result was measured for about 30 sec, the result being the average recorded. When driving i was driving a suburban street in the same manner I would every other day of the week. Trying to create the usual experience of driving. I'll record the db levels the next time i'm on the freeway.

Idle vents open, no insulation 65 db
Idle vents closed, no insulation 63 db
driving vents open, no insulation 82-83 db
driving vents closed, no insulation 79 db

Idle vents open, insulation 63 db
Idle vents closed, insulation 62 db
driving vents open, insulation 78 db
driving vents closed, insulation 73 db

Surprising the idle db without and with insulation wasn't significantly different. I recorded a 6 db reduction in noise with vents closed and insulation. Not being a sound tech I don't know the multiple between 73 db and 79 db.

My perception: the raw noise of the engine was removed. The low rumble permeated the cabin which I expect could only be eliminated with high density material that is almost inert. I found the tyre noise (mud tyres) at the test speed was evident. Previously I couldn't hear them at 50/60 km/h with the windows up. I previously could hear them at 80 km/h when the engine is in its harmonic balance but otherwise the tyre noise was drained out by the engine.

While I was in the noise reduction mode I replaced the bulkhead vent seals and placed 3mm thick foam strips on the seal contact point of each door to improve the seal. I have a few doors that are out of whack and i could see day light. While no individual measurements were taken after the door seals were fitted I expect that have had a positive effect even if minor. For $25 for a 14 m roll of self adhesive foam, money well spent.

The OEM bulkhead vent seals are 12 mm thick, 15 mm wide. I bought 12 mm thick, 18 mm wide from Clarke rubber. The arc of the vent movement causes the seal on the high side of the vent to catch the lip on the bulkhead therefore not creating a proper seal on the outside of the vent on the high side. The seal sits inside the lip with no foam on the outside of the lip. When i removed the old seals it was evident that they had been pushed down by the lip in the same way the new seals were affected.

This would be a problem with the OEM seal as well as the Clarke foam because of the thickness of the seal. I will try a 10 mm thick seal on the high side to see if that resolves the issue. If not I'll give the next size down a try. At some point the seal will not be thick enough to fill the void. Trial and error.

For those thinking of replacing the vent seals, the easiest way to get access is to undo the 2 bolts that connects the mechanism to the vent flap. I stuffed around with removing it from inside out until I saw the error in my ways.

Overall for $250 in materials and 2 days of tinkering I think there is a perceptible difference worthy of the effort. It's not lexus quiet and the engine still dominates the driving experience. I'm curious if the highway cruising noise is improved, after all that's what prompted the installation.

cheers MLD

Just wondering if anyone has tried FatMat looks similar to dynamat 100sq ft of fatmat extreme delivered for $282 aus . supplied ex qld . they also have floor mat which is a compound layer that will be available soon . found it on fleabay