I thought it was about time I chipped in with some help for others...
I have been looking at options to reduce the noise levels inside my Defender. Let's be honest - it's about reduction not sound proofing. If you want a quiet vehicle buy a Nissan Leaf.
Now there is a lot of info about noise reduction on this an other forums. Some of it is really helpful but some is, well, a bit weak to put it politely.
There is a lot said about how the only way to reduce noise is to add mass. Bigger, heavier rubber etc is a common stock solution. From my engineering days I know it is more complicated. There are also people out there who think that something like dynomat is basically an over priced bitumen roofing produced. It's not.
I used to work for the (then) largest butyl rubber manufacturer in the world. Butyl is really hard to make and so it is expensive but it also has some remarkable properties. One is that it absorbs vibration in a way that is way beyond the ability of most other rubbers. We used to demonstrate this by dropping two balls - one made from natural rubber and one made from butyl. The natural one would bounce back into the air, the butyl one would almost stop dead in its tracks. In not very sciency terms, the natural rubber one released the vibration energy back out again while the butyl one absorbs it even though they were basically the same weight.
Noise is vibration. Vibrating panels transfer noise by vibrating the air. More vibration, more noise. By fitting a vibration absorbing material to a panel, it vibrates less and so vibrates the air less, and so becomes quieter. This can be achieved by adding lots of mass but it can also be achieved by adding less mass of a better absorbing material. Sticking with the natural rubber vs butyl example, I don't have any scientific test data but it is common sense that 2mm of butyl will absorb a lot more vibration than 2mm of natural rubber. Purely guessing, it wouldn't be surprising if you needed 4mm of natural rubber to get the same reduction but that would weigh twice as much. So it's not simply a question of adding more mass, what that mass does with the sound energy is important.
Of course 'soft furnishings' are great at absorbing vibration (and therefore sound) but if your defender leaks then it has to be closed cell material or you will be driving a rotting sponge in no time.
As for the bitumen roofing material, it is not made from butyl, it's closer to road tar than any rubber material. Those smells that people comment on, they are the volatile bits of the tar evaporating and I wouldn't expect them to be good for you. Lots of aromatic oils are carcinogenic and so I would be amazed if the roofing materials are designed for use in a confined space such as inside a defender, even if it does by design and default allow a lot of air flow through the vehicle. Just on health grounds I would give them a wide berth.
So what I'm I going for? I've already got some camping mats under my head lining. Next step is some 2mm butyl based material for the entire floor pan. I'd prefer that it didn't have an aluminium coating as that will reduce the effectiveness a bit but it's not readily available. I'll see what that does before I do anything else.
Hope this helps.
I have been looking at options to reduce the noise levels inside my Defender. Let's be honest - it's about reduction not sound proofing. If you want a quiet vehicle buy a Nissan Leaf.
Now there is a lot of info about noise reduction on this an other forums. Some of it is really helpful but some is, well, a bit weak to put it politely.
There is a lot said about how the only way to reduce noise is to add mass. Bigger, heavier rubber etc is a common stock solution. From my engineering days I know it is more complicated. There are also people out there who think that something like dynomat is basically an over priced bitumen roofing produced. It's not.
I used to work for the (then) largest butyl rubber manufacturer in the world. Butyl is really hard to make and so it is expensive but it also has some remarkable properties. One is that it absorbs vibration in a way that is way beyond the ability of most other rubbers. We used to demonstrate this by dropping two balls - one made from natural rubber and one made from butyl. The natural one would bounce back into the air, the butyl one would almost stop dead in its tracks. In not very sciency terms, the natural rubber one released the vibration energy back out again while the butyl one absorbs it even though they were basically the same weight.
Noise is vibration. Vibrating panels transfer noise by vibrating the air. More vibration, more noise. By fitting a vibration absorbing material to a panel, it vibrates less and so vibrates the air less, and so becomes quieter. This can be achieved by adding lots of mass but it can also be achieved by adding less mass of a better absorbing material. Sticking with the natural rubber vs butyl example, I don't have any scientific test data but it is common sense that 2mm of butyl will absorb a lot more vibration than 2mm of natural rubber. Purely guessing, it wouldn't be surprising if you needed 4mm of natural rubber to get the same reduction but that would weigh twice as much. So it's not simply a question of adding more mass, what that mass does with the sound energy is important.
Of course 'soft furnishings' are great at absorbing vibration (and therefore sound) but if your defender leaks then it has to be closed cell material or you will be driving a rotting sponge in no time.
As for the bitumen roofing material, it is not made from butyl, it's closer to road tar than any rubber material. Those smells that people comment on, they are the volatile bits of the tar evaporating and I wouldn't expect them to be good for you. Lots of aromatic oils are carcinogenic and so I would be amazed if the roofing materials are designed for use in a confined space such as inside a defender, even if it does by design and default allow a lot of air flow through the vehicle. Just on health grounds I would give them a wide berth.
So what I'm I going for? I've already got some camping mats under my head lining. Next step is some 2mm butyl based material for the entire floor pan. I'd prefer that it didn't have an aluminium coating as that will reduce the effectiveness a bit but it's not readily available. I'll see what that does before I do anything else.
Hope this helps.
