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

Hey all,

I'd like to add sound deadening material to my car. I'm going to be using Spectrum (paint like substance). I was told the dry weight is about 70 lbs for the whole inside of the car with the floor only being covered. If it's a significant decrease in MPG, I'll probably only do the trunk.

My question to you all is, how badly will this hurt MPG? I already have about 40 lbs of audio equipment. Most of that is just a sub, and an amp. Is 70 lbs really that much more?

I have a Honda Civic VX.

Depends on driving conditions. When you are driving at a constant speed on the freeway, weight is not very important. Now if you are constantly accelerating and decelerating (e.g. city driving), weight becomes more of a factor.

I live in a city, so there's a lot of stop and go. It's not like NYC, but it's similar.

I might start with the trunk first to see how the car sounds before doing the front.

adding weight in a lot of stop and go is definitely the last thing you want to do, but there is going to be a small difference. Compensating how you drive with the weight is easy to balance it out and make your number drop insignificantly.

BTW: If you haven't sound deadened before, note that chances are, the difference will be miniscule for actual road noise (if that's your goal). I don't remember where, but I read how you can actually use 1/4 the amount of total deadener for the same resonance deadening effect. If you are looking for road noise reduction, there are a lot of more effective ways (but you'd likely be adding more weight). If you are after rattle reduction, it'll help to a degree, but rattle hunting every hurtz is your best bet (long process).

(Used to be a huge stereo guy, ran a stereo shop for a while. Do a lot more home audio now)

A lot of noise gets into the car thru tiny openings such as around doors and windows, or is generated by mirrors, wipers, and antennae. One way to find these leaks is to get a 3 or 4 foot rubber tube to use as a listening device and listen all around the passenger cabin while someone else drives. There are also sheets of sound absorber that one sticks on the inside of the door between the window and the outside skin. I'd try the rubber hose thing first to see how much noise is leaking in and where, as it works and the price is right.

I'm not really having issues with rattles. The hatch glass does rattle a little, but that's only when I'm on poorly paved roads. My main problem is the drone of the road coming up through the back. I don't really notice any serious noises from the front of the car.

I've seen examples and I do know that by adding sound deadening material to the trunk and wheel wells, it'll eliminate a lot of road noise. That's really all I want to do. I just can't stand the drone when I'm on a highway.

By the way, if I only do the trunk it'll be around 30 pounds.

If your car is like mine, and I assume it is since it is basically the same car, just one generation older, most of the noise will come from the tires.

Generally speaking, the wider and sportier a tire is, the noisier it will be.
A set of quiet LRR tires in the original size will do wonders for noise and fuel economy. :)

Also, I've noticed that removing the parcel shelf noticeably increases cabin noise. If you have it off, try reinstating it.

Sorry for the somewhat off-topic nature of this post, I'm just trying to think of things you can do without adding weight. :)

If I drive on a freshly paved highway, the car is pretty much quiet. I can enjoy it. It's very rare that you find new pavement in my state :D.

What is parcel shelf?

The tires that are currently on the car are Falken tires. Haven't checked what size, but they look stock.

Yep, that's tire noise.
Also, I forgot: as tires get old, they get noisier.

By parcel shelf I mean the piece that sits between the rear seat and window, covering the trunk area. Probably a British term, sorry.

Do you mean the cloth fabric that lays over the back of the trunk?

I have that up at the moment. It's incredibly thin, so I can't see that dampening any noise at all.

*EDIT* The shelf is missing. We call that a cargo cover. The mounting points are somewhat broken. I tried mounting an aftermarket cover, but it didn't fit. That could have been the cover itself.

The spare tire lid was missing, but I ordered an OEM one from eBay.

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.

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.

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!:o

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.

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.

http://mbworld.org/forums/attachment...el-removal.jpg

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!

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.

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

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.

On a recent highway trip we picked up two passengers, total weight about 300 pounds. Mileage was unchanged.

regards
mech

Thank you for the advice! So far, I've added about 50 lbs with the current sound deadening material. To finish the car I'll need about another 18 lbs. I was hesitant to order the last bit, but I checked this forum again to re-read the information everyone has posted here. Looks like I'll be ordering it after all.

I should have a total of about 85 lbs including my audio equipment.

I hope that being my car is a VX, it doesn't struggle more from the lack of HP it has. I'm already getting roughly 30 MPG and I can't figure out why it's not better than that.

I'm beginning to have doubts... Some people are saying 80 lbs is a lot for a car that only has 95 HP. Can anyone shed some light on this?

Let's go back to the rattle of the hatch. In general, if something rattles, it is loose somewhere. If the back hatch is loose, road noise will enter; lots of it. So, why not fix the hatch so it doesn't rattle. Low cost. Then, do the rubber hose noise listening thing to see where the noise is really coming from. Low cost. Then you will KNOW where to put your attention.

And if it is rattling because it is loose, then something is wearing away. And this means it will fail sooner than it should.

If sound, abundant power & fuel economy are important to you, you may want to consider a quieter car if in your budget. The older Hondas & Acuras I have owned were not nearly as quiet on the road as my 11 year old Corolla. It easily averages mid 40's with a big sub box in the back & only mild hypermiling. No EOC & rarely P&G.

Steely Dan never sounded better!!

I don't have rattles in my Honda. I wanted to eliminate road noise while maintaining as much MPG as possible.

I picked the VX because it was on the Governments website for one of the best fuel efficient economy cars. I haven't been able to achieve anywhere over 40 MPG. So, I'm taking the steps to replace components that may have an impact on the MPG.

I'd say it's a little too late to switch out cars. I've already invested a lot into it and I really have no way to get my money back to switch cars. It would be a huge waste at this point.

Hondas, until perhaps recently, I've always found insufferably noisy, especially so in the lower end of the frequency range. Low frequencies, once created, basically can only be killed off by adding mass, though panels trying to resonate in sympathy can be dampened. I think Honda's big fail must lie with their design of suspension bushings which play a big role in transmission of road noise into body structures. My 1999 Toyota Solara was tomb quiet compared to the same year Accord and I doubt if the difference was due to "sound proofing".

Others are much better at isolation; I noticed fairly recently that my Chevy Volt even uses composite, rather than steel, sway bar end links for that purpose.

So far I've found Second Skin Damplifier covered with Dynamat's Dynaliner foam to be both effective and easy to work with. (The tar-based stuff is messy, smelly, and heavy.)

I've also found, especially for stereo purposes, doing the inside of the front door skins is the single most effective location, followed by underside of the roof, rear doors, trunk rear surface, trunk upper surface, trunk floor, then lastly, passenger compartment floor.

Seldom-mentioned, I also consider damping material on door beams and cross braces between the rear seat and trunk to be a good idea - they will ring like tuning forks without much provocation.

Also, stay away from tires restricted to rolling only in one direction. Rolling in a single direction often causes the individual blocks of rubber on the tread to cup, creating a racket that increases with age.

Can anyone comment on the MPG a 95 HP motor will suffer from the extra weight I've added?

The EPA states a 1% reduction in mpg per 100 lb increase in weight for a ~3200 lb car.

Based on this study: http://www.drivealuminum.org/researc...ardo-Study.pdf

Which is an awesome read btw. See page 24 for your answers.

That's a very good read! Thanks for the link.

The MPG difference should be minuscule, but you might find that you notice the extra weight in accelerating and braking. My car has weighs less than yours, but I really feel it when I have a passenger.

My vote would be replacing your tires, even if it's only the rears. Not all tires are created equal when it comes to noise transmission, and my (uneducated) guess is that you're not hearing noise being transmitted through panels, but rather, it's coming from the suspension up into the frame. Dampening your floors will probably do little to help.

A quick google search returned this:

DIY solution to deadening tire noise

You might also be interested in this:

Lexus LS Wheels Have Sound-Deadening Hollow Spokes » AutoGuide.com News

I actually have LRR tires that are pretty new. I'm just under 6k miles on them. I can stand the noise. I'm just a tad concerned about the low MPG I'm currently getting with my VX.

Might want to start another thread on that.

It could be your driving style - my father-in-law gets low 40's to high 50's when he drives my car, and for the life of me I can't figure out how he does it. On the same trips I average 70+ doing nothing but driving at a constant speed (~the speed limit, even), and have pulled 100+ when I'm actively trying.

It could be a mechanical problem - bad compression? Clogged EGR? Brakes rubbing? Tires out of alignment?

It could simply be your driving conditions. Even the best drivers will get horrible economy in stop and go traffic, because any time you need to use your brakes, you're very effectively converting gasoline into brake dust. Compound that with the engine idling while you're not moving, and you're got a recipe for poor fuel economy.

I'll start another thread :).

Update:

I've been consistently getting 40 MPG all day every day pretty much. I've been pretty happy.

I added sound deadening material to the floors and realize that when it was done, the entire floor was covered. I did the math and I can save about 30 lbs if I remove 75% of it. Is it worth the aggravation of removing the carpet to save 30 lbs?

That going to be a personal preference, but I would say no. 30 lbs is not going to be noticed at all.

you would be better off dropping 15 lbs yourself! :thumbup:;)

Of course, I don't know you, and you could be skinny as a rail!

BUT. :eek: ..most of us could lose 15-30lbs before starting to worry about 30lbs of material on a car.

I am a tad on the skinnier side. So, I must account for something :-D.

Okay, I appreciate that. I wish I knew how much my car weighs now with all the sound deadening material I added, but I think it can't be more than say 80-100 lbs.

The last thing I can do to my car is to clean the injectors and I've done everything I can do mechanically to boost the MPG.

Depends. 30lbs on a 1500lb car is a lot of weight (2%)! But 30lbs on a 4000lb car is very little (0.75%). This is especially true for your 0-60 times (or just daily driving acceleration).

For MPG sake, it depends on your routes and how you drive. The more you use your brakes, the more weight effects you. Hence, why weight makes little/no difference on the highway. But, the above applies and you really need to look at it in percentages.

Could you tell a good difference in sound when you added it? I'm guessing it was subtle difference. That's been my experience, at least, mostly dulling the noise, but not ridding of it (a lot of drone/low-mid frequency still about as loud). As mentioned in a prior post, 2-leaf system using foam and MLV is far more effective, but also, adds a lot of weight.

I can't say if it improved the acoustics in the car because my car still isn't completely put back together.

I don't have speakers or door panels in the car right now.

I have to make this decision within the next week if I want to remove some of the material. The rest of the dash is going back in.

Something is just bothering me about having too much sound deadening coverage on the floor.. Only 25% should have been covered, but the installer put down 100% coverage. It's been on my mind for a while now.

I'm trying to get the best MPG out of my car. I just can't see 40 MPG city mixed with highway is the best I can get...