Since there will be a decent amount of bass coming out of the boot, there will also be a decent amount of vibration. This vibration will love to bounce around off large thin metal panels and distort the sound. The idea is that adding dynamat (or similar sound deadening product), the panels will vibrate less and provide a more punchier bass response.
The generally accepted theory is the 35% rule. That is you get the best value for money benefit from well placed dynamat with around 35% coverage. If you put more than this, the value for money decreases for smaller margin of gains. For example, let’s use an arbitrary sound deadening value. At 0% coverage (no dynamat) you have a deadening factor of 10. At 20% it raises to 20 (twice as much) and at 35% it raises to 30. Now if you go to 100% coverage, it will only raise to 35. Therefore, spending three times the money on an extra 5 points isn’t value for money.
However, if you have lots of money or care about the extra 5 points, do it! But I’m working on the 35% coverage rule and trying to save some money, but still make a difference to the sound. To do this, you need to try and find the parts that most need help (the more hollow sounding places) and not put any on the solid parts (that have a high sounding note when tapped). This is also a time versus money factor since it takes a lot longer to find the right spots, but it saves you money.
The following will show how to apply dynamat in this fashion. Others may put more or less in different spots, but this is how I did it. Firstly, cut the dynamat into strips – either with a stanley knife or scissors.
Then take the strips and cut it into the right little pieces to go in the places it needs to go….
For larger panels, you can get a lot more coverage as it will probably need it. For the large cavity (the inside of the outer panel) I think it’s better to give more coverage as this one is going to be the main surface to vibrate. Since we have to do the same on both sides, I just cut a sheet in half diagonally.
I’ll use one half to cover the passenger side and the other for the drivers side. I can then make up the gaps with strips from another sheet.
The following two photos show how I did it. There is no right or wrong in this process, just preference. When you think you’ve done enough then you’re finished.
Okay, when you’re done, reverse the previous instructions and put the top and rear panels back on, but leave the middle panel off because next comes the wiring.
In the mean time, turn around and have a look at the pile of interior stuff and chuckle a little….