So, I've been wanting to make my car quieter inside for a while. We use the car regularly for roadtrips and while I only have an axleback right now, I'll be installing a CBE shortly and that, combined with louder tires (Nitto Neo Gens) at higher tire pressures with a stiff suspension setup, leads to a fair bit of noise. Definitely not bad but our cars could stand to be a bit quieter - not quite luxury rides from a sound perspective. I did a lot of research and it all pointed towards using mass loaded vinyl as a barrier material to really cut down on the noise.
Mass loaded vinyl is a limp heavy material that is a modern day substitute for lead. Lead is what they used to use for a sound barrier but due to the toxicity, you don't see it used much anymore. The density of the product is the key and standard 1/8" MLV is usually about 1 lb/sq ft. It's not light. If you are a weight weenie and trying to keep your car light, it's not for you. On the other hand, if you want to cut the road noise, this is the stuff. You can get 1/4" MLV as well at 2lb/sq ft but it's apparently a lot harder to work with and you're probably looking at diminishing returns in any case.
Note that the MLV is only part of a soundproofing solution. The other components are the sound deadeners, (Dynamat, Raamat, eDead, B-Quiet etc), which reduce the resonance in the sheet metal and an isolation layer (normally foam) to decouple the panel from the barrier material, the MLV. I wanted to do the job myself and keep it as cheap as possible - cost was a primary factor.
There are lots of options for deadeners, some more costly than others, but general consensus is that you want to stay away from asphalt based products, like 'peel and seal' as found at home depot etc, and stay with a butyl based product. Contrary to popular belief, you DO NOT need to cover everything with this stuff. There's a great post on diymobileaudio.com where the OP was sorely disappointed in how little a difference in noise reduction resulted after covering everything with deadener: http://www.diymobileaudio.com/forum/...oad-noise.html
I chose to use B-Quiet Ultimate as I found a decent deal on it (50 sq ft on ebay) and applied as much as I could as simply as possible (plus they're a canadian company to boot).
The next layer is the decoupler - to isolate the barrier from the sheet metal. Lots of options here with closed cell foam generally regarded as the best. As well, if cost isn't as much of a factor, there are composite products available that have the foam and the MLV bonded together already... one of the most popular is second skin's Luxury Liner and LL Pro. One has open cell foam, the other closed cell (pro). This is probably a great solution for many but as I was working with a tight budget and as well having concerns about the greater ~3/8" thickness, I chose to source my own decoupler. I ended up going with a 3/32" closed cell foam underlay used for flooring from one of the local home improvement big box stores. It may not be the best, but this was the one area I figured I could cut costs. I got a big roll for about $20, more than enough for the car. One of the important considerations about this layer is that it doesn't retain water so jute and other cheaper open celled alternatives may not be the best if there's any chance of exposure to moisture.
The MLV I purchased in bulk as well, splitting a 130 sq ft roll with a buddy to save money. I was able to find a roll on ebay from seller auburndarter for US$120. The catch is the shipping - this stuff is HEAVY - the ship weight on the roll was 142 lbs. If you're shopping around for it, make sure to include shipping costs
. Those that can pick up the product in person stand to save the most. My roll cost $88.50 to ship, so total cost was US$208.50 for 130 sq feet. I ended up with ~67.5 sq feet which is more than enough for the car.
So, on to the installation
I pulled the door panel and the vapor barrier off and applied as much deadener to the door as I could easily and simply. There are a number of folks out there that say judicious application of this layer is more important than covering everything. I think this is the smart call. Just rap the metal with your knuckles and if it sounds tinny, add deadener. Make sure you do the outer door skin as well. I applied more material to the outer door skin than the inner. I also applied deadener to the inside of the door liner as well.
I used the vapor barrier as a stencil and cut the foam and MLV using it. I wasn't sure whether or not to retain the vapor barrier initially but decided in the end that I was basically replacing it with what I was about to install. As you can see from my pics, I don't think it's needed at all. Not only that, but it's messy and a bit of a hassle to work with. That said, I did leave the adhesive goop that was left on the door as I felt it would assist in holding the foam and MLV on to a degree.
So, I then applied the foam, taping it down at the edges and then layered the MLV on top as well. Again taping it down well. I made sure to really rub down the tape to make sure it was adhered properly. One of the MLV suppliers recommended the red Tuck tape as it's what they use to seal the stuff in construction soundproofing applications, the primary usage of MLV as far as I can tell. (Other folks have glued down the MLV or used industrial strength velcro to hang it, but you need to be very careful as most adhesives won't bond well to the vinyl.) The key with the barrier material is to keep any holes/gaps to a minimum as the sound will make it's way through any holes. Basically, by using a single piece, in the shape of the factory vapor barrier, I think I've been able to realize that goal to a large degree. Of course, you have to have the access holes for the latch cables, the handle and the wiring etc but for the most part its a continuous barrier.
I have to say I'm very
pleased with the results. There is a significant reduction in road noise
through the doors and my stereo sounds way better. (On a side note, I reinstalled my factory tweeters that I had originally removed when installing my JL coaxes. I think that may have been a mistake and I'll likely remove them next time I have the door skins off.)
This was the first step in a two part project. I'll be doing the floor pan next but not for a few weeks. I'll take a full weekend to do that, likely in early May, as I plan to pull most of the interior out and lay down as complete a layer of the MLV on the floor as I can. That should really complete the soundproofing as I can tell now that the road noise is now coming through the floor with the bulk of it coming from the rear of the wagon.
Here's the pics.
This one's a bit dark, but shows the deadener on both the outer and inner sheet metal. I put rope caulking around the lower plastic cover as well deadener on the backside of the plastic panel as well.
Here's the 3/32" closed cell foam underlay on the entire door.
There's the finished product - the MLV taped on over the foam.
Here's the door panel (took photo upside down) with the deadener applied to help reduce any resonance in the door panel itself.
Passenger side front door complete.
Driver's side rear door complete.