cfair

So I was in the boneyard today, first time in at least a year and half. Saw maybe 5 60's cars in 3 yardes. Except for GM Sport Salvage in San Jose, CA., which is _all_ the 60's and 70's iron we like...

Anyway I was observing how GM made their later models (80's and 90's) quieter. My 66's have metal doors, lined with tar paper, then the put the door panel on top of that.

In the 80's/90's the basic scoop is GM put foam, either open or closed cell in the doors and glued down that blue jeans colored cotton-ish insulation all over the place.

The conclusion I draw about my 66 big cars is as follows:

1) Closed cell foam on the doors as Phase I experiment. Stuff is cheap and it's an easy project. If that doesn't make much difference

2) Put Butyl rubber based dynamat extreme or equivalent on the wheel wells, floors, firewall and see what that does.

3) Maybe put butyl based mat on the doors too.

The goal is a quiet car, but I'm also trying to avoid adding 150 lbs of sound deadening stuff. First, it's expensive. Second, it's heavy. If the closed cell (cheap $50 for a roll) will get me most of the way there and that what GM did, well then maybe that's the right next move.

cf

csstrux

http://www.edesignaudio.com/index.php?cPath=1_24

I ran across this on the net, but have not tried the stuff. My project has been stalled for about a year now so cant tell you how it works, but it sounds like it might warrant a closer look.

jslabotsky

I think the cotton-ish stuff you refer to is called jute.

I've read a lot about sound reduction on car audio forums. The guy who runs www.sounddeadenershowdown.com seems to know what he's talking about. His site looks very commercial now, but it was not always that way. Don't be put off by the looks. If you read the articles you'll see that he's not just trying to separate you from your money. He doesn't recommend piling on numerous layers of material because it's a waste.

What I took away from all my research is the following:

To keep the body panels themselves from resonating, you can use a small amount of butyl constrained layer damper (CLD for short, such as Dynamat) on all the large metal panels. Contrary to what a lot of car audio guys do, SDS has shown there's no significant benefit to going buck wild covering everything with CLD. Covering about 25% of each flat panel is plenty.

Note that butyl rubber without the aluminum backing doesn't make a very good deadener. A lot of guys have tried this as a less expensive substitute for CLD with disappointing results. Also, not all butyl is created equal and not all is suitable for sound deadening.

To block ambient noise, you can use a layer of foam coupled with a layer of dense material between the door panel and the inner door shell. Lead sheets are used in home theater setups. For automotive use SDS recommends mass loaded vinyl (abbreviated MLV). MLV by definition is heavy because that's what makes it a good acoustic barrier. But you can always add MLV in increments and see what nets the best weight-vs-noise trade-off.

The only reason to use CLD on the door panels is if the panels themselves are resonating. I'd try CLD on the outer door skins combined with foam/MLV behind the door panels first. And of course these same treatments can be applied to floors and trunk as well. Word on the street is deadening the roof makes very little improvement.

SDS has good information on why he thinks this is the best combination. He recommends using no more material than is really needed, because it's a waste of money and weighs down your car. Good site.