Sound deadening can be done with various techniques. It can be done cheaply, or expensively. I used a few different methods in sound deadening my 1st gen. There is a very noticeable decrease in road noise, and very minor gain in weight. There were 3 main methods I used for making the car quieter.

1. Noise reducing underspray.
2. Noise reducing mat
3. Various foams / fabrics

Any combination of these may be done. For best results, you need to find out where your noise is originating from. In my case, my 235/45 R17 tires made a lot of road noise, as well as my exhaust system. Other noise was due to the airflow over the car. As you are reducing noise in one area, you will hear more noise from another. The car is in fact getting quieter, but may now seem noisier than before. So improving one section may lead you to want to improve another.

1. Underspray:
For this, I used Dupli Color's Undercoat and Sound Eliminator, this is rubberized and dries to a deep black. I applied this to the fender wells and to the driveshaft tunnel between the firewall and first carrier bearing. For best results you need to thoroughly clean the surface. Then spray multiple light coats, letting each coat dry thoroughly. I used 1 can in each front fender, 1 can for both rear fenders, and almost 1 can in the tunnel. If you spray it on anything you don't want covered, a rag with break parks cleaner on it will easily wipe it away if it's still wet. This needs to be applied in a very well ventilated area, it's also a good idea to have eye protection while using this, as it creates a floating mist. To spray the surfaces properly, you should remove the wheels, and any other objects that would block your spray path. I did mine when I had already pulled the transmission out of the car, and also when I was swapping the break pads.

The next 2 methods are more tedious, and require various interior panels to be removed.

2. Noise Reducing mat

For this, I used Dynamat's Extreme sound deadener. There are various quality mats available, this is their higher rated sound deadening mat. This is fairly simple to work with, but can add weight. I ended up using 3 rolls in the car, with most of it being used on the rear fender wells. This is used on interior surfaces, and best results are achieved with complete surface to surface adhesion (no air pockets). Along with clean surface prep, this requires a few tools.

- A roller, I got a roller from Home Depot, used for laminate counter tops. The roller has a rubber wheel, and is ~ 3 inches wide.
- A sharp utility knife
- Scissors, grocery store bags, and a pen

Start by cutting the grocery store bags into flat sheets. Then overlay them over the area you'd like to cover, trace the edges, then cut out the sheet as a template. Next try fitting the template over the area and make sure it will relatively easily form to the surface (the dynamat has some give to this). Now transfer the template to the dynamat, and cut the mat with the utility knife. I found it easier to pull the dynamat through the knife, rather than trying to pull the knife through the dynamat.

Now form the dynamat over the surface to be covered. Pull the paper off the back and put it back on very lightly. The trick is using just a few contact points to ensure it is properly positioned. Once you're satisfied with it's location, use the roller and roll it out. It's best to start in the middle and work towards the edges.

3. Various foams / fabrics

I chose to use a thick cotton batting material. It is very light, cheap, and available at just about any fabric store. This can be made to be permanent, or removable. This is pretty simple to work with. I did 2 basic things with it.

I stuffed in between the body panels with it, just cutting small strips, and filling as needed. I didn't pack it in, I just used enough so that it would fill the volume, and not move around. I also cut full size strips to line the bottom of the trunk. I did 2 layers in that with one having a hole cut out for the hump. This was quite effective in making the exhaust quieter.

I also covered the main section of the floor. For this, I cut individual pieces that fit in between the cross supports. I then cleaned the body panel, and sprayed contact cement to both that panel, and the back of the fabric. I then set it in place. Note that if you go too thick, you will have a difficult time getting the carpet to fit properly.

Since I had all of the panels out, I went ahead and covered the backs of them. I did this the same way I put it on the floor. Note, if you have the Canadian seat belts to make sure to leave an open spot for the belts to retract easily (or they'll just go up very slowly).

I did all of this for ~ $100. It made a very noticeable improvement for me. I even covered the little panel that goes on the hatch. I decided against using a spray foam as it would have been difficult to remove if I chose to later on. If you do use a spray foam, make sure it's non-expanding (Dap makes one), so that it doesn't distort any body panels. The dynamat was probably the most time consuming out of the 3. I ended up using 3-4 yards of 12 oz cotton batting for all the areas. I didn't do any sound deadening on the doors, I may later on though. To finish this off, apply a dab of rtv sealer to every clip before attaching the panels back onto the car. This will help prevent any squeaks. I did almost everything at the same time, so I can't comment on the effectiveness of any 1 of these individually, but I have added a few more of them individually and have noticed instant improvements from each of those.