How to control road noise in your LH sedan (or most any other vehicle).
When I purchased my new Chrysler Concorde (2000 model), I was very impressed with the car in most every respect. The only real concern was an abundance of road noise on rough surface roads. On smooth pavement, it is whisper quiet, but on roads that are worn and have a rough gravel-like texture or rural roads that are surfaced with oiled gravel (like where I live) there is considerable noise inside the car.
At first, I put full blame on the tires (Goodyear Eagle GA), but after spending a few weeks driving the car and paying close attention to the noise, its volume, and source, I concluded that regardless of its point of origin (tires), it was being amplified by the floorpan of the car. I could actually feel the floor of the car vibrating like a big sheet-metal speaker. Part of the appeal of the LH sedans is their long wheelbase and generous legroom, however this creates a large continuous floorpan that can behave like the aforementioned speaker and will amplify any vibrations introduced to it.
I briefly considered having the car undercoated (which is what the dealer recommended) but most vehicles made in the last 20 years are designed to NOT be undercoated, at least as far as corrosion & rust protection is concerned. Undercoating can plug up drain holes and cause water and dirt to be trapped in corners and crevasses rather than letting it drain away freely. That only left placing some sort of material on the floorpan under the carpet.
There are several products available which are designed specifically for this purpose, though most installations are for deadening in cars that have high-power stereos so that the vehicle itself does not "color" the sound. A quick search on the web will turn up well known products like "Dynamat" and "Brown Bread" and these (and others) are respected products that do a fine job. However, I am always looking for something better - or should I say - cheaper. I found what I was looking for at a web site called www.b-quiet.com and ordered a roll.
This is the "stuff". It is an asphalt-based material with a vinyl face and paper backing that peels off to expose a VERY sticky surface that will adhere to most anything. It is not all that thick - only about 1/16" (0.060") with the paper backing but is effective and can be applied in multiple layers if needed.
Before we start applying this stuff, the car needs to have a few things moved out of the way, like the seats and carpeting. The primary tool I used was a flat pry bar. If you don't have one, GET ONE. They are inexpensive and indispensable for so many different projects. Here's a pic of the prybar while using it to remove the plastic retainers on the edge of the carpet.
I started with the rear seat cushion. It pulls up on the front edge then lifts out. Pop off the trim pieces at the base of the door openings, but be gentle! This stuff is just plastic and you have to reuse it all. Next remove the 4 bolts at the base of each seat. Move the seat full forward to access the rear bolts, then vice-versa. After the seats are out, you need to remove the front seat belt anchor bolts at the base of the body center post. Slide up the plastic cover and use a T-50 Torx bit to remove the bolts as shown.
I left the center console in. Messing with the shifter, wiring and ventilation ducts in the console did not appeal to me. The less disturbed, the better. The front kick panels as well as the center post trims can be left in place but will make it harder to re-lay the carpet.. I pulled up one side of the carpet and held it out of the way (mostly) with a piece of wire as shown.
This gave me access to the floorpan on each side of the center hump which is all I wanted to cover with the material anyway. I wiped the exposed floorpan with a damp rag to remove dust and cut my first strip of "stuff". It comes on a roll 36" wide and the floorpan is only about 20" wide on each side so the 36" dimension became the length of each strip. Reading of other people's experience with this material, they recommend cutting small manageable pieces. I ended up cutting a 10" strip the full width of the roll (36"). I peeled back about 2" of backing from one end and placed it at my starting point below the brake pedal and along the outside edge of the floorpan. Then with that top edge stuck down I began pulling back the paper backing and pressing down the material, working my way back, stopping to cut out around the bolt hole for the seat and running it under the wiring harness.
Another strip behind it and 2 more placed alongside and I've covered the entire driver's side. I can see that I'm going to have plenty of this stuff and it is a bit thin, so I place 2 more strips down the center of it all.
The other side is duplicated in mirror image fashion and then a couple of strips laid across the area directly under the rear seat. DONE!
I replaced everything and took the car for a drive. My initial impression was that the damping material only made a 10% - 15% reduction in road noise. Not what I had hoped for. Sound, however, is a complex animal.
After a few days of driving, I made a couple of interesting and gratifying observations. On those stretches of road that produced the most noise, I previously felt myself become tense from the din that encompassed me. NO MORE! I also noted that I could hear my stereo better and at much lower volume settings as well.
It would seem that the damping material made a much bigger improvement than it first seemed. Obviously, the frequencies that it reduced were greater than the overall impression of volume reduction. The lower sound frequencies, which are hardest to control, were only slightly reduced, yet the higher frequencies, which were the most bothersome, were significantly cut. Simply put - this stuff works!
The final improvement would be to replace the harsh Goodyear tires with something quieter (likely Michelins). That will have to wait for another day and some "extra" money.