MGB V8 - Sound Proofing

My intention for this car is to make it just as quiet as any modern car when cruising (with perhaps just a little extra engine and exhaust noise). I've followed a pretty standard procedure of sealing, panel damping, then sound proofing on this car.

Wind noise is a another big source of noise when cruising, and I've addressed this with my side window modifications. Without the wind noise improvements there might not have been a lot of point in carrying out all of the modifications on this page.

Body Sealing

The first and most important thing to do is to seal all holes between the cabin and the exterior. Air-borne noise leaks into the cabin are generally the major cause of interior noise Poor sealing is particularly noticeable as a large change of tone and noise levels when going from a tarmac road surface to a concrete road surface.

There tends to be a lot of noise inside the body structure as there is no acoustic treatment in there. I've sealed all holes into the body sides using thick sheets of polythene. This should reduce high frequency noise. The trim panels should sort out the low frequency noise.

Panel Damping

Damping pads are useful for reducing mid range noise - not the booms, just the general loudness of the interior noise.

I went around the car tapping the panels adjoining the interior and applied damping pads to all the panels that 'rang'. The floorpan needs a good coverage - the original factory damping pads are next to useless. I used unbroken sheets of the same material to cover the floor. The roof and side panels will also ring, but there is no point in treating the roof as very little road noise will be transmitted so high in the structure. Whether to treat the side panels and doors is up to personal preference. I did on this car.

Sound Proofing

The material in the photograph is a rubber layer weighing 5kg/m2. This is isolated from the metal panels by 1/2 inch thick open cell foam. The idea is that the body panels can vibrate away, but the rubber layer is isolated from the panels so will not vibrate so much - and hence will not transmit the noise into the cabin.

It's pretty effective stuff, but is relatively heavy.

I've used a lot of sound proofing in this car. Probably the total extra weight is about 30kg. My installation is known as an overkill pack. It's the sort of level of soundproofing that Rolls Royce or Aston Martin might start off with before weight saving.

In a modern car this would be optimised - the manufacturer would do lots of noise measurements, and each piece of sound proofing would be thinned down or replaced with something lighter if it doesn't give much benefit. Unfortunately I don't have the equipment (or time) to optimise the acoustic pack, so I'll have to bear the weight penalties.

The result is excellent. I can listen to talk radio at motorway speeds, and the car feels isolated from the outside.