Taking care of the floor to reduce rolling noise
One area that I never tackled in the 406 Coupé or the C6 was the car floor. Taking care of the doors makes a huge difference because they are right beside you, but deadening the floor takes care of rolling noise, engine noise and exhaust noise. It makes the biggest difference and has the most impact in noise reduction measurement, 2dB reduced at 80km/h in tire noise.
Before Brexit kicked in I ordered a door kit pack of Dynamat Extreme from the Sound Deadening Shop, as they are from the UK, rolled up my sleeves and started to take the interior apart.
Unfortunately not everything went according to plan, one of the bolts that holds the seat down either had too much red Loctite or was driven in crooked. Long story short, the head was stripped, I had to cut the head of the bolt with a manual metal saw and use a nut and washer to fix it in place. An entire day of work lost because of this.
Took me three days because of this, otherwise two days would be enough to deaden the entire floor.
Removing everything and checking what is underneath the carpet
It's not complicated to remove the carpet, just remove the lower side trim, center console and armrest, rear floor console and the seats. I was happy for once that the seats on the Ampera are manual, they are heavy! I can only image how much more would the seats on the 406 and C6 weigh as they are electric.
The carpet comes out as two entire pieces, left side and right side. I've seen cars where there are four pieces and they meet under the seats and some need to remove the dashboard. Not the case here.
After removing everything I could see there was a lot of horizontal space, easy to add deadening material to it.
So there is only an ECU on the passenger side, the cables for the seats (airbags and heating function) and the seat support structure. The rest is nice and open to get deadening material.
You can see on the pictures that there is a lot of liquid deadening material on the floor and center tunnel. I've read that this was formulated specifically to reduce the metal vibration frequency on the Ampera / Volt, and it might work great on that frequency and avoid resonance. But tapping on the metal makes a lot of noise, not deaden at all it seems. So, we are not getting resonance from the metal, but there is nothing there to really block the noise, only the carpet.
And for those of you curious, that big orange block is the main battery manual disconnect.
As the seats and the carpet where out of the car it was time for a good cleaning and adding Leatherique to the front seats. Temperature was not perfect as it was only 20ºC, but they would be at least 48 hours sitting so the results would be good.
So the plan for the floor would be to fill has much as possible with Dynamat Extreme, as well as the sides of the center tunnel, then add Dodo Super Liner on the floor for heat blocking and decoupling of the Dodo Barrier MLV that would be the top layer blocking most of the road noise.
The only issue I would have was in the passenger side, there is an opening on the carpet to show the VIN. This makes no sense to me, usually the VIN is visible on the windscreen and that's it, in this case on the annual inspection (MOT) they check this and it can't be covered with deadening material.
Dynamat Extreme was added to about 70% of the surface area. The idea was to make the metal sound as solid as possible to avoid resonance, block noise and heat from the engine and exhaust, as this is an E-REV.
The center tunnel doesn't have a transmission as the car is front wheel drive, and it doesn't have the exhaust there. In it's place sits the battery, it's quite dense so already blocks a lot of noise, but I still added Dynamat Extreme. The center tunnel metal sounds very thin and it could then start to vibrate as the floor is now solid and deaden.
Under the rear seats is the battery, as well, it has a T shape. I've already deaden under the rear seats to block rolling noise. So in this panel I would only add Dynamat.
Dodo Super Liner
The center tunnel is complete with only Dynamat. Now on the floor Dodo Super Liner was added to cover the entire area (except above the VIN) to block noise, heat and decouple the MLV from the metal to properly block noise instead of helping propagate it.
I added a bit more to the sides just in case if the MLV moves so it stays decoupled from the metal.
Just by adding the Dodo Super Liner the noise inside the car went from echoey to being baffled. It improved the overall sound quality inside the car even with the carpets out.
I then filled the seat frame support with polyethylene foam as it is light and blocks noise traveling inside it.
Final step, Dodo Barrier MLV
Now the only thing left is cut the MLV to size and put it on top of the Dodo Super Liner. Sounds easy, but not so fast. It took a few trials with the carpet back in place to make sure nothing would mess with the pedals. I like silence, but not the ultimate silence, so it's nice to be able to brake.
The only issue I had was with the accelerator pedal that was touching the carpet. There is, as you can see on the pictures, a small ridge in the middle of the floor that is raised even more with the Dodo Super Liner. Because of this the MLV was not flexing enough and pushing the carpet up by a few millimeters. The solution was to make a cut in the middle of the MLV and tape the edges with aluminum tape.
After this I added more Dodo Super Liner on the edges where the MLV was or could be touching the metal to decouple it.
After putting everything back in place it was time to go for a drive and do some noise measurements.
Before driving, as I did deaden the kick panel area and that might block noise from the engine compartment I took a measure of noise at idle. 27.6 dB, it was at 28.5 dB, almost 1dB less. I will round this number up to 28dB just to avoid decimal numbers. Why the noise at idle? There are water pumps to cool the battery and electric systems, no electric car is 0dB even at a standstill.
So when I started to drive, first thing I noticed was that I couldn't hear any suspension noise. Usually as I leave the garage I could always listen to the suspension working. Not anymore, even as I was driving towards the highway at low speeds I didn't get any rolling noise. The weight also helped to reduce vibrations felt from the foot well or the front seat, so the car feels more comfortable as well.
So I speed up to 80km/h and measured 54.1dB, a 2dB reduction. At this speed I measured lows of 48dB and highs of 60dB. I always get at least 30 seconds of noise at a certain speed to get an average, and the values measured where amazing.
At 120km/h it's a very strange feeling, you hear the wind rushing and little to no rolling noise. The difference is less noticeable because of the wind noise, but 1dB reduction, now at 58dB.
This means the car is now quieter at 120km/h than it was at 80km/h from factory.
Now, the weight, this was where I added the most weight to the car, 12,3 kg in total. 3.8 kg in Dynamat Extreme, 1.5 kg with Dodo Super Liner and 7 kg of MLV.
The car now as an extra 33.6 kg in deadening material alone, but rides like a luxury car in pure silence, with a 5dB reduction in noise inside the car from stock.
It is so good that I find myself driving without the radio on just to enjoy the silence and sometimes I notice that I'm going faster than usual. Deadening the floor really made a huge improvement.
Done in 23 of March, 2019