Boot and floor under the rear seats
This was the largest area to deaden in the car. Much like with the 406 Coupé a lot of large parts had to be dismantled just to be able to remove the rear quarter trim panel from the boot (or trunk, since this is an American car). So the idea was to deaden the entire boot floor, sides, rear area and under the rear seats as these had to be removed too.
Took me two full days to do everything and, apart from the boot floor, I didn't know what space was available to add Dynamat or MLV.
The dismantling process
I had to remove the rear seats, rear floor console, C pillars, rear end trim panel, and so on. It was so much stuff that the rear suspension went up 2cm. Cool weight savings, bro.
After everything was removed it was time to assess what space was available in each area.
One thing GM did great, as I have mentioned before, is that every hole is plugged. This means that the hollow spaces between different metal layers cannot work as echo chambers.
With that said, you can see the last picture has two huge openings. These are there for the vents that allow air to escape when closing a door. In both the Peugeot and the Citroën the vents are visible when removing the trim, in here GM decided to hide them behind that metal piece. Sure, it's in the rear end of the car and has some deadening material on top from the factory, but it's one area where noise enters the cabin and it's a echo chamber.
The liquid deadening used is also not very effective in some panels, not sure if the sheet metal is thinner in some areas to save weight, but tapping on it makes the same sound as if it didn't have any deadening.
First I put Dynamat Extreme on the lower area of the boot floor. I used the silver one that I still had. I went for full coverage under the subwoofer just to improve sound quality and other bits and pieces to make the metal deadened.
Below the subwoofer I used Dynaliner 1/8" instead of DodoSuper Liner as it's thinner and I wasn't going to add MLV on top of it. On the top parts there was no Dynamat so only Dodo Super Liner was added.
You can also see a piece of MLV in the picture as I was testing how to tackle those thin areas on the sides.
After that I was time to do the same at the side areas. I applied a bit more Dynamat on the left to block any exhaust heat and noise. Let's not forget the Ampera has a range extender, so it has an exhaust.
The next picture is out of sequence and shows the end result with the MLV on top and a lot of trim pieces back in place.
When removing the trim pieces the last pieces that were removed were the rear end trim and the rear quarters side trim. So it made sense to first deaden those areas, put the trim back in place and see what space was left available to apply (or in that case remove) Super Liner or MLV. Fortunately as you can see by the picture there where no issues and I was quite pleased with the end result..
Space is at a premium almost everywhere in the Ampera. The rear quarters are filled with electronic boxes, cables, fuses, etc. Both the C6 and 406 had clear access to the rear wheel wells, the C6 even had a large piece of MLV with foam on top of each to reduce noise.
In the Ampera / Volt that is not the case, deadening is almost non existing. Join that with the Michelin Energy tires that come from factory that make a lot of noise and you understand why Volt and Ampera owners complain about rolling noise from the rear.
Since there where so many cables and electronic boxes around there was no way to add MLV, and in some parts there was not enough clearance to even add Dodo Super Liner. So only Dynamat Extreme was added as some Dodo Super Liner were possible for decoupling the plastic trim and block some noise.
At the rear it was not possible to add MLV so only Dynamat Extreme was added to avoid panel ressonance and some Dodo Super Liner where possible to decouple the trim. This area has a lot of soundproofing from factory under the trim and at the bottom end of the panel.
Rear seats floor
Under the rear seats was almost no deadening at all and the metal resonated a lot when tapped. Because of this I had to go to almost full coverage with Dynamat Extreme.
As I was planning to completely cover this area with MLV a lot of Dodo Super Liner was added to decouple it from the metal bellow. I would also use the already present material under the carpet for decoupling.
After a few test fits, and the bottom part of the seats really needed some persuasion to get back in place, this was the final result. I used aluminum tape to keep everything in place, really just as a precaution as I did with the front doors.
Everything back in place
As is custom, here are the pictures after the deadening. Unlike with the 406 or the C6 the boot floor was not raised because of the sound deadening, stayed exactly the same. It's a good thing because the boot is small on the Ampera.
Results, weight added and sound level measurements
I really wanted to deaden the boot before changing my rear tires. They are still the Michelin Energy that came with the car, and are really noisy. By keeping them it allowed me to properly hear and measure if there were any significant differences in noise reduction.
When driving the car it is indeed a lot quieter from the back, there is less rolling noise but also it was the main entry point for noise, beside the glass, as it was not deaden. Not in traffic I cannot hear the cars behind me and rolling noise is almost non-existent up to 100km/h.
The subwoofer also has a bit more punch. I tested the subwoofer with Giorgio Moroder - 74 Is the New 24 because there is a nice bass drop that, as the frequency gets lower, you can feel the bass shift from the front doors to the boot where the subwoofer is. Funny thing, now that the boot is deaden the boot lift gate now vibrates a little, so it probably will be the next step in deadening the car.
In total I've added 10.1 kg of deadening material. 5.4 kg in MLV, 3.4 kg in Dynamat Extreme and around 1.3 kg in Dodo Super Liner and Dynaliner.
The measurements are a bit tricky because I do the measurements at the front of the car, on the drivers seat, and although I can pinpoint with my ears that there is almost no noise coming from behind, the overall sound level doesn't go down as it is already very quiet.
At idle there are no differences, as expected since it's an electric car. At 80km/h I got a 1 dB reduction, makes a lot of sense since at these speeds tire noise is the most predominant. At 120km/h it was oscillating between 59 and 60dB, depending on the wind. This would mean between 1 to 2dB reduction.
Here is the tricky part, although the meter shows a big reduction in noise, to me it doesn't fell that big of a improvement because my perception is that the wind is still the most predominant noise.
There are only three areas left to deaden: the boot / trunk lid, the roof and the floor and kick panels.
Probably because of the vibration and since it's a small area I will deaden the boot lid first and then the roof as these areas will only use Dynamat Extreme and Dodo Super Liner.
The floor will be the last step and will probably mostly use Dodo Super Liner and MLV.
After that there isn't much more that can be done, the glass will still be the weakest point as I have yet to find sound deadening film that can be applied to existing glass and not only usable as laminated glass. The C6 had laminated glass all around with an acoustic film from the factory and there was a huge difference to the Ampera regarding the amount of noise that enters the cabin thru the glass.
Done in 24 of November, 2018