Quote:
Originally posted by Tom Short
Alan,
I went through the same process that you did - dynomatted the entire back wall leaving the vents open, and noticed very little improvement. I would like to know your source for the 1/2" noise insulating aerospace foam. I have removed the rear seat semi-permanently, and will probably build an inslulated panel that covers the entire back wall including the vents.
What are you thoughts on the importance of those vents for re-circulating air? I always run the A/C on the position that allows bringing outside air in instead of re-circulating the same old air. I have installed Ventivisors and crack the window when a little fresh air is needed.
In summary, I find the noise level from those two *&@*%! vents so loud, I think I will block them up.
Tom
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Dynomatting isn't enough. You'll need absorbing foam too. Not so much to stop sound from going through the wall as to catch the sound that is bouncing back and forth from the seat as it comes out the vent. (unless of couse, you've got a low frequency rumble, like an exhaust - that's a LOT of energy to absorb). That's why it can rattle glass, a trunk lid, etc. It's a lot of sound energy. That's why it takes 300 watts or more to drive a subwoofer. Works the other way too - you have to absorb 300 watts of the same low frequency sound to make it quiet.
Since you're pulling the seat, you'll need to put foam inside your box as well as on the wall.
I's say the IDEAL material to use would be sound absorbing accoustic cones (foam that looks like egg crate material). Put one layer on the wall around the vents, then put some on the inside of your box. That would kill the sound, but let the air pass. A second thought would be to use the 1 inch foam that akie6 used on both the wall and the inside of your box. But I think accoustic baffles would work better and a box 4 inches thick (thinner than the back seat now) would be fine.
DON'T close those vents. It would be dangerous. Not that it would ever happen, but if you got an exhaust leak and it leaked into the cabin, you'd be killing the "natural" exit for the gas (you're getting fresh air whether or not the fan is on). Very, very very remote; but you could kill yourself that way. Too, you'd really screw up the ventilation unless you'd open the window all the time. I don't like that idea much. Too, you'd have even more ambient noise coming through the window than ever came through that vent.
If I was going to put a box there, I'd put fans on those rear vents to increase the air flow. I find that with my sun roof sucking air I don't even really need to turn my fan on except to turn on the air conditioning electrically and even then it's only on 1 (unless it's cooking hot, then the air conditioning is not very good even on high unless you recirc). It's a lot better ventilation that way and you don't have any fan noise (well, not much it's being dampened too) coming from the dash since you won't have to turn the fan up high to get a good air flow.
That's on my to do list and is a little "bit of work". Close down those vents and put a fan driven exhaust system so that the air would be pulled out rather than pushed from the dash. It's a LOT quieter that way. Too, I can enclose those vents a lot more with sound dampening material.
My problem is that I can't put too much material thickness there as I want to put amplifiers there too.
Alan