Deadening the boot

The boot is the noisiest place inside a car. Unlike the interior of the car the boot is just an empty space with nothing to absorb sound and you get noise from the exhaust and the rear tires. That's why so much deadening material is installed there by car manufacturers.

My idea was to not only reduce noise but block sound from leaving the boot to the outside. There are two woofers on the parcel shelf (I won't call them subwoofers) that give the biggest bass output of the entire sound system, so this would be good to increase the Sound Quality of the sound system.

I also wanted to block heat from the exhaust but there isn't much space available, so I used Dynaliner 1/8" instead of 1/4" to avoid loosing space in the boot because the carpet would be raised as well as the spare wheel.

The boot lid has almost no space available for Dynamat and is already quite heavy because the speed sensitive spoiler mechanism is there. So, I will not add Dynamat there.

Sound proofing already in place

Faurecia was the company responsible to ensure the sound deadening on the Citroën C6. They also produced most of the trim in the car. I never took the trim out of the boot so I didn't know what was there, apart from what I could see on the battery access door and on the boot floor.

In the boot there was some special attention to reduce noise. A mix of MLV and high density foam was used on top of the rear wheel wells, each must weight almost 3kg.

Mix of MLV and high density foam on the wheel wells for sound proofing
Mix of MLV and high density foam on the wheel wells for sound proofing

At the back there's some closed cell foam sound proofing and the hollow spaces are filled with a lighter foam. I tried to remove it, but it was glued in place and started to come apart, so I left it as is.

Foam near the boot air puller vents
Foam near the boot air puller vents
Lighter foam filling the hollow areas
Lighter foam filling the hollow areas

I was disappointed with the deadening material applied on the boot floor. It's quite thick and looks heavy, yet when knocking on the metal in the boor floor the noise was the same as surface without nothing.

Deadening on the boot floor
Deadening on the boot floor

The boot floor mat has a thick foam on the underside as well, feels like rubber, helping to further reduce the noise.

Boot floor mat underside
Boot floor mat underside

Rear wheel wells and surrounding area

First I applied Dynamat on the wheel wells and the surrounding area on the boot floor were the side trim would be. This would allow me to put things back in place to avoid having at least the battery and fuses exposed on the left side while I was working. Since Dynamat Extreme has aluminium I didn't want to run the risk of touching a battery terminal with Dynamat.

On the wheel wells Dynaliner was only applied on the area that the mix of MLV and foam didn't cover, the rest was just Dynamat Extreme.

Dynamat Extreme on the wheel well
Dynamat Extreme on the wheel well
Dynamat Extreme on the floor were the side trim sits
Dynamat Extreme on the floor were the side trim sits

I forgot to took pictures of the Dynaliner application on the wheel wells and the quarter panel on the right side of the boot.

On the left side sits the battery and some fuses. I was going to remove the battery, but the fusebox on the right side uses a lot of space and the battery itself is a tight fit. Also there was already foam applied in the quarter panel, glued to the metal so I couldn't add Dynamat or Dynaliner there.

Dynamat Extreme on the wheel well
Dynamat Extreme on the wheel well

One issue I had was that there was no protection from the metal on top of the battery. If someone was going to remove the negative cable they could easily touch the metal on top, were the rear lights are. So I added Dynamat Extreme and on top two layers of Dynaliner 1/8" to avoid any contact with metal parts

Dynamat Dynaliner
Dynamat Dynaliner

Boot floor and spare tire well

After finishing the sides I applied Dynamat Extreme on the boot floor and the spare tire well.

A sea of Dynamat Extreme
A sea of Dynamat Extreme

While I was applying Dynamat in sections the sound when I knocked on the metal was changing quite rapidly to a more deadened sound. A much better result and probably with less weight then the deadening material used by Citroën/Faurecia.

Under the rear trunk lining I applied Dynamat Extreme and Dynaliner on top so I could put it back together. On the top only Dynamat Extreme was applied, I thought there was not enough space but after putting everything back there was space for Dynaliner. Maybe next time I will fix that.

Dynamat Extreme and Dynaliner under the rear trunk lining
Dynamat Extreme and Dynaliner under the rear trunk lining

Now, the worst part of the job, and I thought it would be the easy bit. Applying Dynaliner to the boot floor and spare tire well. Dynamat Extreme molds itself quite easy to the curves of the spare tire well. Dynaliner doesn't work that way, it won't stretch and won't give when applying both on a straight and round surface.

Pieces that were cut straight would be out of shape leaving small gaps. I was tired of this so, as the Internet says, I just went full retard and started to overlap Dynaliner like crazy to make things faster and easier

Dynaliner on the wheel well, looks terrible
Dynaliner on the wheel well, looks terrible

Of course, with all this overlapping the boot floor mat was raised by a bit. Imagine if I was using Dynaliner 1/4", that would have been even worse!

It looks terrible. I was never worried how the application of Dynamat Extreme or Dynaliner would look because it is going to be hidden from view, but I'm not happy with how Dynaliner is in the boot

Dynaliner on the boot floor and wheel well
Dynaliner on the boot floor and wheel well

The results

It took me one and day and a half to finish the boot and I added more then 5kg of weight there, but it was worth it. Almost 6 sheets of Dynamat Extreme were applied.

As amazing as it seems with the engine idling now the meter oscillates between 43 and 44dB, staying most of the time on 44dB. This didn't happen when I deadened the front doors, so maybe it's related with the noise from the exhaust. At speed I got another 1dB reduction, now 62dB at 120km/h.

Regarding the sound system I was expecting a bit more gain on the bass. It has improved, but I think I had higher expectations.

Now what really matters is what I hear and feel and now the car feels even better. The rolling noise from the rear is heavily reduced, I can't hear the rear suspension working on bumps and the heat from the exhaust on the boot floor is gone, it's cool to the touch.

Citroën C6
Done in 13 of August, 2014 at 13:00
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