So I finally did something to reduce the noise inside the car. It now feels like noise is reduced by more than half.
Here is what I did, what is needed, and how to do it:
Note: It certainly makes sense to do this systematically!
There is no point in doing just a bit this week, and then next week having to take the same stuff apart again to continue.
You need to be inside a protected room or garage, need basic tools, a few containers/jars or whatever for putting little bits and pieces into.
Btw, if you haven't sprayed the seams yet for rust-protection, this would seem a good opportunity.
This car had been corrosion-protected in its cavities some time before. The seams had been treated with wax-spray, but not the flat surfaces, eg. in the doors. Remember you can't glue anything on top of wax. The doors and trunk lid had already received something similar to bitumen tiles, and this was completely sufficient. Therefore there is no further mention of the doors and trunk lid here, although it is essentially the same as with the other parts.
A) One pack of sixty self-adhesive bitumen tiles, size 10 x 25cm, 3mm thick.
This is the actual product, but anything similar would be good enough:
This comes to a total of 1.5 square meters. Weight is 5kg per square meter. These are for getting rid of resonances. Roughly about 20% of surface-coverage on the sheet metal is usually fine.
B) A limp/heavy pvc material, a bit like felt, the stuff used under floor-tiles. It weighs about 5kg per square meter. I needed about 4.5 square meters. I got the stuff from a local carpet store. It is put on top of concrete ceilings, in essence und the floor tiles of the floor above. It stops the persons below hearing the folks above walking on their floor tiles.
In lack of it, you could simply use some heavy carpet. That should be good enough.
C) Contact cement, one spray can for attaching the above material so it stays in place and doesn't move about.
Taking it apart:
Firstly the inside needed to be taken apart! There is no getting around this, if you do not want to waste a lot of time.
I started by disconnecting the starter battery, because there are air-bags in this car and you don't want them to go off while working.
I took out the middle console first. It is fastened by two clips in front, and by two 10mm screws, one in the middle, one at the rear.
Then the plastic piece around the bottom of the steering-column in the foot area.
Then out with the horizontal plastic stuff near the bottom of all 4 doors, pulling upwards and being very careful not to rip off the clips.
Then off with all the lower grey panels, front, middle and back.
Then the upper beige panels, six in total, but be sure to thoroughly wash your hands before, in order not to make marks on the roofing.
Unclip the connections under the front seats, and remove the front seats. There are two nuts size 12, two size 14.
Then off with the roof lining, a second person for helping is needed. Do not forget to thoroughly wash your hands before touching the roof lining!
Remove the rear seat cushion. The rear seat-backs remained in the car.
Later everything has to come back in the same order. Be sure to take notes of how to put the stuff back, and keep the clips in one container each, one for each piece coming off.
Note: Looking at what needs to come out helps preventing accidental damage. Be careful not to rip out covers, but to do it carefully and gently.
With everything out, I started by applying the bitumen tiles. These needed to come on those part of the surfaces that rung like a bell when lightly tapped. I started in the very front, halfway up the firewall, then continued with the front floor. Then further to the area under the front seats, rear foot-wells, vertical surfaces to the seat-bench area, under the rear bench, then in the trunk.
Next the side panels inside the trunk. The outside metal of the rear side panels were tiled from the inside, there are holes in the metal panels where the side panel covers were, and they can be accessed from there. The roof area in the front and in the back also received bitumen tiles. Then it was time for the second step, putting in the limp/heavy silencing material.
The limp/heavy silencing-material was put on the floor, front and back, and over most of the area where the console belongs. You could use heavy carpet instead. I did not put much in the trunk, except for the vertical side panel area. Then in two sheets it was put over the front and back area of the roof from inside. I used contact-cement spray to fix it all in position. Just enough spray to keep it there. Then the roof lining was put back on.
The holes in the upper section of where the rear panels belong, was also covered with the heavy felt material in order to block the noise coming out.
The inside of the grey middle panel between the doors received a vertical strip about the width of a hand, and the length of a lower arm. Look inside that Panel, and it is self explanitory.
Then the carpet came back in place, including the little black plastic piece around the bottom of the steering column.
All the cladding parts were put back in place. The upper beige panels comes on first! Match the top of the beige panels with the roof lining first, before snapping them on. Then and only then the lower darker ones come back in place.
Don't forget to attach the wiring when putting the seats back.
When everything is in place and finished, it is time to reconnect the battery.
Five kg for the bitumen tiles, 22kg for the limp/heavy material = 27kg total.
I could have use less of the limp material, or used none of it, but the effect would have been less.
Light weight variation: For those wanting to scimp on extra weight, I would use the same amount of tiles, plus some limp material only in the front footwells from the firewall to where the front seats start. That would come to 5kg tiles + roughly 7kg limp material = 12kg total additional weight. That should be good enough to make a reasonable difference.
Congratulations! Its been at least one full day's work, if you've been quick.
PS: Sorry, I didn't take any photos. There would have been too many. However the text should explain it sufficiently for folks having the experience needed to do things like this...
DISADVANTAGE of the dampening: Although driving noises can still be heard, it is more difficult to hear the engine revving. It can happen you think it is in fifth, and you actually have it in third. Especially so if your stripped-naked model is just like mine and has no rev-meter.