I'd like to add sound deadening material to my car. How adversely will it affect MPG?

[RPM]

That's it: you call it cargo cover in the US. It is pretty thick. I was surprised by how much of a difference it makes.

[GearHead]

I'd love to use the cargo cover, but the mounting points are broken on the sides of the interior wall . Maybe I can try it again with an OEM version and see how it fits.

[Xist]

My Forester had a trunk cover that rolled out like some window coverings, but a tab was broken. I periodically wonder about trying to copy the good one with some Q Bond and reverse it.

Of course, I mostly just want to sell the car...

I should put the engine back together, shouldn't I?

[Edit] I put the engine back together and it worked! I sold the car with the tonneau cover, but neither tab!

[oldtamiyaphile]

An 1100lbs trailer costs me less than 2l/100km in 100% city use. That works out to 0.0018L per 100 km per pound (without factoring in the aero drag and CRR from an extra axle).

[GearHead]

Originally Posted by oldtamiyaphile

An 1100lbs trailer costs me less than 2l/100km in 100% city use. That works out to 0.0018L per 100 km per pound (without factoring in the aero drag and CRR from an extra axle).

That doesn't sound bad, does it? I wonder if the results are not worse for you because of how much HP your vehicle has.

[Vman455]

I'm actually in the process of deadening my car right now, too, and upgrading the audio (Precision Power 3-ways up front, stock rears for fill, Stereo Integrity BMI MkIV 12" sub in the spare tire well). I figured, if I'm planning on keeping this car for the next 15-20 years, which I am, I might as well make it comfortable, and part of that is making it quiet.

This will be the 4th vehicle I've deadened, and one thing I've learned from that and others' experiences is the end result is completely dependent on how OCD you are on the installation. Spectrum is a vibration damper, designed to turn the energy of vibrating metal panels into heat. It's also very light, about 1/4 lb per square foot. It will lower the resonating frequency of the panels you apply it to, but I don't think it will do much to quiet the car by itself. All the marketing blather on Second Skin's website about this single product creating "tomb-like silence" is just that--blather (nothing against Second Skin; I just ordered a pack of Damplifier from them, in fact). There's a reason they and other vendors sell a variety of products; to make any noticeable difference in noise levels in the car you have to go with a layered approach, add as much mass as you can in the space available, and cover as much area as possible leaving as few holes as possible. There's a reason very quiet cars, like the Lexus LS or Mercedes S-class, are heavy and have solid doors.



In my Prius, I've started by putting vibration damping mat on the outside door skins, sealing up the access holes with acrylic panels with Damplifier on them, then a layer of acoustical foam to decouple a layer of mass-loaded vinyl, both of which cover the entire door with holes only for the speaker, lock switch cables, and window wiring harness. From there, I'll move on to the floor and hatch with the same layering approach. The car will end up weighing about as much as a Plug-in Prius when I'm done.

[NoD~]

Originally Posted by Vman455

In my Prius, I've started by putting vibration damping mat on the outside door skins, sealing up the access holes with acrylic panels with Damplifier on them, then a layer of acoustical foam to decouple a layer of mass-loaded vinyl, both of which cover the entire door with holes only for the speaker, lock switch cables, and window wiring harness. From there, I'll move on to the floor and hatch with the same layering approach. The car will end up weighing about as much as a Plug-in Prius when I'm done.

There's the key! Decoupling and getting a 2-leaf system going is a HUGE difference in ridding of noise. Adding mass (a part of what sound dampening materials will do) can only do so much.

In my studio, we have a 2-leaf system. It can be 110db inside the live room through the entire frequency spectrum and, on the outside, a whisper at most.

By getting that "air spring" (foam) between the two layers (car's metal body/chassis and your MLV layer), it's going to absolutely kill a majority of the noise. Down side is, it adds weight, installation complexity, and cost.

If I ever get a car that I care a lot about again, I'll probably have to really put the time and money into it. After going active 4-way in my house with MiniDSP, there's a small part of me that would love to do it in a vehicle!

[cosmick]

I'm always removing all my heavy sound deadening and insulation, for performance, not MPG, and I can't say I ever did before and after MPG tracking, but in V8 ponycars, it's not a dramatic difference. I like hearing my rumbly exhaust and whiny fuel pump.

[oldtamiyaphile]

Originally Posted by GearHead

That doesn't sound bad, does it? I wonder if the results are not worse for you because of how much HP your vehicle has.

1.6L NA with 77kW. Total weight up to 4400lbs. City commute speeds as low as 10mph avg.

[GearHead]

I just got my aftermarket OEM style carpet with a rubber backing for sound deadening. It's for the front of the car. I'm going to install that first to determine how much sound is really coming through the back. If I can, I'd rather just put a thick cargo carpet in the trunk if I have to.