RussB

Car: 1988 5000CSTQ

I'm in the middle of a sound-deadening orgy. At the moment I've removed all factory trunk liner and carpet and have been applying Dynamat Xtreme (with excellent road test results so far).

The car's spare wheel well is a single molded plastic (polystyrene?) piece, above which a carpeted and sound-deadened (with foam) fiberboard "floor" fits. I think that this is a fairly standard Audi sedan layout.

Question: What material is sensible for quieting this plastic molding? I'm thinking of gluing 1/4" closed-cell foam sheet to its inside surface (rather than Dynamat Xtreme). Any BTDT or suggestions?

TIA.

boxerfan

I figure the road noise stops me from hearing all the pesky squeaks and rattles of an older car. Since the cover and trunk will be treated then wouldn't just securing the spare and extras in there be enough?

qpower

now i hear more sh*t than ever

mcorrow

(qpower)..What did you do to the wheel bearing?

RussB

I didn't think that deadening ANYthing in the trunk would make much of a difference (since the rear seat upholstery must dramatically attenuate noise from there), but I was wrong.

I was amazed by how much cabin noise was reduced just by filling the bare trunklid panel sections with Dynamat Xtreme and filling the lid's channels with expanding foam (Great Stuff, $5 / can from Home Depot). Tapping on the lid now returns just a dull thud. This alone (after the doorskins) made a tremendous difference. That encouraged me to proceed with the remainder of the trunk. I figure that I'll stop when I no longer can hear any improvement.

I regret not having used a dB sound meter at the start, to establish a baseline.

From what I've read, it seems that in general applying sheet foam to plastic panels is more effective than applying elastomeric deadening mats; hence my question.

If you're looking for a (cheap in terms of parts, expensive in terms of labor) project that will dramatically improve your ride experience, I recommend this exercise. I'm amazed by how much more enjoyable the car is to drive now. Of course, it doesn't improve the bling factor one iota.

qpower

from the rest of the car , just being sarcastic about my car

RussB

What part of the vehicle should I do first?

A: We recommend applying Dynamat to any surface you can easily reach. In general, we recommend treating your vehicle in the following order: Doors, Trunk, Rear Deck, Floors, Roof, Hood, then Fenders.


So far, I've found this to be true. I added Dynamat Xtreme to the forward and aft firewalls when I had the heater box out of the car recently. I expected this to reduce engine noise, but it also reduced road noise.

Oh -- I also added a couple small pieces of pre-cut flexible closed cell foam sheets beneath the car's shift boot. I'd noticed that some gear whine and assorted noises were coming up from that area. Now the noises are gone.<ul><li><a href="http://www.dynamat.com/faqs_faqs.html#text3088anc">http://www.dynamat.com/faqs_faqs.html#text3088anc</a</li></ul>

Will Ng

Perhaps that should serve as a better more rigid material instead of closed cell foam. Unless you have some of that dense neoprene foam (like a thick mouse pad), most of the adhesive cell foam sheet I've run across is pretty skimpy. If you can adhere some non resonating, yet light weight materials, you may be able to lessen the vibrations of the plastic without lining it with lead.
Maybe a styrofoam or neoprene and balsa wood sandwich. Or gluing 1/4" thick sheets of thick rubber.
Must say, it's a cool project and endeavor. I think I'm going to dynamat the doors and trunk lid of my daily driver when the weather gets warmer.

RussB

I like your sandwich idea. I guess that I'll finish the rest of the trunk first before tackling the spare wheel well. Others have pointed out that the fiberboard trunk floor will help isolate the spare wheel well and that I should first apply foam to the floor's underside.

I've seen that throughout the car Audi took care to strategically apply sound-deadening material, but they weren't extravagant.

Working on (in) the trunk is taking longer than I'd estimated. There's lots of measuring / template making / cutting required, and much of it must be done in situ - which means crawling inside the trunk and working there. That's not so hard, and once I'm in, it's okay, but getting out is a bear!

There's an insulation seller (Bigham) in town who stocks a wide variety of foam and fiberglas products. I've bought a foam sheet (very Neoprene-like) from them and am using a spray-on 3M adhesive to fasten it. I think that open-cell foam and loose fiberglas battes would be great sound absorbers, but would make a mess if they became wet, so I've stayed away from those materials on this project.

I think that you'll be pleased with the results of sound-deadening. I bought my first box of Dynamat Xtreme from www.ikesound.com,whose price was the lowest, but have since found a less expensive vendor (Sounds Great) on eBay. Its gross weight for 9 sheets totalling 36 sqft is 22 lbs. Delivered cost was $111 per box.

Until recently, Dynamat Xtreme was the best mat. Now it has serious competition. See www.sounddeadenershowdown.com. Also, www.secondskinaudio.com has a forum dedicated to quieting vehicles. You'll see there that some guys go nuts on this stuff. I'm intrigued by the liquid dampeners (there's a thick glop called Sludge) but doubt if I'll use any on this project.

Let us know when you start your project.<ul><li><a href="http://www.sounddeadenershowdown.com">http://www.sounddeadenershowdown.com</a</li></ul>