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Thanks for the offer :) One of these days I'll have to attack that project.Quote:
Originally Posted by Farrar
On another note, I sort of feel like we should start our own forum called 'Jon and Farrar talk to each other all day.com' as we seem to run into each other in a lot of threads.. :lol:
If you're lucky, you will be able to find a good noise dampener to adhere to the back of the plywood panels. After looking back there I think I have decided that I can probably get away with 1/2" of foam, assuming it is soft enough to compress where the tolerance isn't quite so large.Quote:
Originally Posted by jawn101
I have questions, you have answers... Seems reasonable enough, right?Quote:
Originally Posted by jawn101
Farrar
Update: McMaster sells an adhesive-backed foam rubber which reduces noise by 75% and is one inch thick. It is soft, so it is compressible -- I wonder if I could get away with it behind the wood panels.
The thing that would concern me about putting it behind is that you've then got two adhesive bonds, one from the wood to the foam, and one from the foam to the fiberglass. The foam will probably disintegrate or rip and the wood may come loose as a result. Why not just dynamat over the front of the replacement wood panels?
Dynamat is good for increasing the density of a panel to move its resonant frequency down to a point where it's no longer annoying. I was looking for something which actually absorbs sound. The reasons I would adhere it to the back of the panel would be because I need the material to face the direction the sound is coming from.Quote:
Originally Posted by jawn101
The foam is a combination of open-cell and closed-cell polyurethane. Polyurethane has a very long lifespan (as you can tell from our facias) so I am not worried about it disintegrating.
Adhesive "from the foam to the fiberglass"? I don't get your meaning there, I'm afraid. I plan to "line" the wood with the foam, and then adhere the wood to the fiberglass like stock.
I was envisioning a 'sandwich' of materials like this (the fiberglass is the body tub):Quote:
Originally Posted by Farrar
http://dmctalk.org/attachment.php?at...7&d=1331220881
Please forgive the crudity of this model, I didn't have time to make it to scale or to paint it.
If that's not what you meant then I stand corrected. I do get what you're saying about sound absorption vs mitigation. I am just not sure how you'll be able to do it without compromising the integrity of those wood panels. Are you just planning to tuck the foam around the edges? Or make a "sandwich" that has fiberglass, wood, foam, wood?
I now see that we are talking of different installations. Here's a (crude) diagram of what I am talking about. This is a side-view -- the empty space to the left holds the battery.
Attachment 8840
Insulation would go only on the wood panel behind the seat. I have not got around to the floor yet as my carpets are toast, but I imagine something akin to Dynamat would work to lower the resonant frequency of the body tub in those areas.
I see what you're getting at and I think we're talking about the same thing - but the wood isn't just glued to the floor of the tub, it's adhered to the whole back structure as well. So in your diagram, the 'red' adhesive should be under the blue foam where it bonds to the body - unless you're planning to change that. But without that adhesive there, I would think the panel would rattle around.Quote:
Originally Posted by Farrar
It IS?! Holy crap -- my car is worse off than I thought. In my car, those panels are only stuck to the floor and nothing else. I had no idea they were supposed to be adhered elsewhere. *sigh* More work for me, then...Quote:
Originally Posted by jawn101
I was afraid that was going to be your answer... maybe that's why you think you need foam behind them :)Quote:
Originally Posted by Farrar
Of course I will caveat this whole conversation by saying that they are adhered *in my car* and maybe my installer was just overzealous. But I believe they are like that in most cars.
Both you guys are way over thinking in a spot you really dont need to.
The wood panel behind the seats, which closes off the battery bay and storage compartment doesn't need all the soundproofing your thinking about. A layer of dynamat extreme over the wood would be plenty. Due to the thickness of the wood and all of the epoxy (supposedly, perhaps not in Farrar's case) those panels do not pass much sound or resonate themselves. What you really need to take care of in the back, is the bottom of the shelf (between the two electrical bays) and the rear wall below the rear window (both fiberglass and OEM wooden closing panel). THOSE are the most crucial areas of soundproofing behind the seats. (and the "OEM" body tub holes if you have an early VIN).
Much of the sound being passed into a car is in lower frequencies. These are very difficult to "absorb", as the foam must be very very thick. The alternative is blocking the sound, which can be accomplished with minimal space, at the expense of weight. A "Loaded Mass Damper" is what your looking for here. It is best to be sandwiched between two pieces of acoustic foam to decouple it from the solid surfaces. McMaster sells both acoustic foam and 1lbs/sqft vinyl mass dampers which I will be using for just this purpose in the next month or two. This type of soundproofing will be very effective in the rear shelf/wall area. Be sure to get some dynamat on the fiberglass first though before adding the foam sandwich!