Sound Proofing a Renault 4

Noise Absorption

Noise reflects backwards and forwards against hard surfaces. A bit of foam will help absorb higher frequency noise as it bounces around. It won't reduce booming or engine noise but will make the car feel less open and make talk radio easier to make out.

The Renault 4 originally had three strips of hessian on the inside of the roof behind the headlining. There seemed to be room for soft material across the whole roof. I've used a sheet of 12mm open cell foam. In hindsight I would have used 8mm hessian material as the headlining rails were difficult to slide against the foam and it was difficult to equalise the tension in the headlining sections.

This will only be effective in cars with the fabric headlining. The later moulded headlining might benefit from some thin headlining foam on the sabin side. I have found it impossible to remove the pre-'82 headlinings (with the cardboard section around the edges) without ripping them. The later headlinings in French models are easier to remove as they are edged with a thinner plastic section.

A bit of 12mm foam has gone behind the rear quarter trim. There is space so I may as well, and also it helps the panel achieve the correct shape especially after it has been sitting in a damp car for 40 years.

It'll not make a huge difference. The noise from the rear is mostly from lower down (it gets much worse with the rear seat folded). But every little helps.

Noise barrier

Noise from the suspension or radiated from tyres will make the metal panels vibrate, and there radiate the noise into the cabin. The Renault 4 has thick rubber matting on most surfaces directly attached to the panels. These will vibrate with the panel and transmit noise. Spacing off the rubber from the panel will isolate the rubber. It'll vibrate less and transmit less noise.

This will be effective for all noise frequencies including booms and engine tones.

The back of the R4 tends to sound quite hollow and the rear wheelarches get noisy when it rains.

I've fitted an 8mm layer of hessian behind the rubber wheelarch cover. It will make the wheelarch cover stand off the panel a little so it won't reach all the way around, but working in combination with the cover it should be quite effective.

Open cell foam would be more effective than hessian as it's less stiff so would better isolate the rubber from the panel.

Sealing

I've not covered sealing yet. This probably the most important part of sound proofing. Imagine someone being really noisy outside and you decide to close the door. It's only when the door is nearly completely shut that noise starts to reduce. That's sealing for you. Tiny gaps in grommets or door seals can let through a lot of noise.

I'm using GTL plastic side window frames on this car as the earlier steel ones have a habit of rusting and leaving rusty streaks down the bodywork. I've seen some cars with a thin foam behind the side window to help seal it to the door frame, but other cars have not been sealed. I suspect any sealing I have found has been aftermarket.

I've used 1mm thick double sided foam tape on the flange to help seal the joint between the side window and the door. Thin draft excluding foam would also work. The side window is very close to the driver's ear, and a little soft foam can reduce windnoise at lower speeds.

Door Seals

What a hassle the door seals have been. I bought an "original style" replacement set from a supplier in France, and while the style was near original the shape, and more importantly the material was not.

The original seal was of a solid expanded foam type which adjusts itself to the shape of the door over time. That's not ideal in itself as the seals aren't very flexible, and the slightest movement in the door frame will lead to gaps and wind noise.

The replacement seals appeared to be made from the wrong material and didn't adjust to shape. I gave them a month to settle with the door forced shut, but I think it would have been several years before I was able to shut the door.

Angel on the forum helped me. He has a supply of seals of the correct size and shape that are hollow. The hollow seals should spring as the door frames move outwards at speed, and hopefully reduce wind noise.

The hollow seals fit very easily and neatly. I used good quality contact adhesive (Evostick) which worked very well. I had started with a DIY store brand adhesive on the other seals at first and that didn't work at all.

You can see the difference between the hollow seals and the solid seals as they are compressed against eachother. The hollow seal compresses almost flat before the solid seal even starts to compress. Don't buy the reproduction solid seals. Or if you do contact me first - I have a set going cheap.

What a simple pleasure to be able to close the doors!