Soundproof car DIY to reduce noise

Apr 26, 2014
Soundproof car DIY to reduce noise
  • Adding soundproofing to your car

    This article will show you how to add soundproofing to your car, give some basic soundproofing theory, and list some good brands of soundproofing for cars like dynamat, brownbread, bquiet, or raammat.

    Introduction

    Every car can benefit from additional soundproofing, even luxury cars. I have found that VW diesels have more soundproofing in selective areas, but are as lacking in soundproofing as gas VW cars. One of the biggest factors distinguishing cheaper car's sound level from luxury cars is the amount of soundproofing. You can add as little or as much soundproofing as you want but like other modifications to your car, you should have a goal. And don't be surprised if the radio sounds bad after you install soundproofing. When you change speaker setups, it will sound funny to your ear until you get used to it. It could just be that the speakers are more accurate. (Soundproofing should not touch the speaker cones and prevent them from moving).

    A basic soundproofing job at your local audio store will add some sound proofing around the speakers and the back of the door panel. Most people would barely notice the difference if at all. Results also vary by car since it requires very exact placement and will only dampen some resonance. Well designed speakers already have pretty good speaker enclosures, so a small square of sticky mat will make little difference. These are the speaker kits that are sold at "big box" electronic stores with a 300% markup.

    Basic-advanced levels of soundproofing

    First identify what's causing the noise. Is it wind noise, road/tire noise, engine noise, or general noise? You can address wind noise by checking for loose trim or door skins - these can cause errant wind noise. If your tires are worn or out of alignment, they'll be more noisy than new tires. Different tire brands/types also have different noise levels. You can't do too much about noise from the road but you can help stop it from entering the cabin.

    Most people would benefit from a moderate soundproofing. This address both road noise and general noise. Soundproofing the area around the wheel wells and in the doors would make a small but noticeable difference in how quiet the car is. Adding closed cell foam to the doors and undercoating material to the plastic wheel well liners are probably the best value in addition to sound deadening mats. This is the easiest in labor because almost most should be able to do this themselves and the materials cost should be about $200-$300.

    Below is an example of what I did to the front plastic wheel wells, lower engine side covers, and timing belt cover. I sprayed black rubberized undercoating to address road and engine noise. This significantly reduced tire and road noise from the front wheels. I wouldn't put undercoating on the inside of the timing belt cover because of belt clearance and if it flakes off, it could damage the engine. I would also avoid additional undercoating behind the car's wheel wells since it could cover up important drainage passages. I've tried 3M and Duplicolor spray on rubberized undercoating and found that it works well. Rustoleum undercoating doesn't seem as thick or foam up as much as 3M and Duplicolor.
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    If you would like an even quieter interior, you could also add material to the floor and the firewall (the area behind the dashboard). This is more difficult because you would have to remove the seats and carpeting and possibly the dashboard, but it adds the most dramatic benefit because it quiets the engine and entire cabin. Coating the wheel wells with liquid undercarriage coating and putting closed cell padding in the door is highly recommended at this stage because it has a lower effort-benefit ratio. You will also require about 50-100 square feet of mat soundproofing for this job and will spend about $300-500 in materials. Labor costs vary according to how easily the interior can be removed.

    If you want an extreme quiet then get an electric car. Unless you never open the windows, never rev the engine, and have a very high quality sound system, then you are going past the point of diminishing returns. To get extreme level results, just doing the doors with a high level of soundproofing will be pointless unless you also do the floor, dashboard, and roof since at this level, any area that you do not do an extreme level job on will create noticeable noise. Even still, you can't address the windows or other misc. sources of noise. Closed cell mats are also necessary here to achieve an extreme quiet. Liquid soundproofing to the inside and outside of the wheel well liners is absolutely necessary here because no one solution will be enough to dampen the interior without breaking up the sound at its source before it reaches the metal. To get extreme quiet, you must do extreme soundproofing! The cost of this will exceed $800 in materials and definitely over $1,000 in labor. Most people would not notice the additional benefits of this level of work.

    The one advantage about doing an extreme job is that it isn't that much more in labor than a moderate soundproofing job it's really just a matter of more money on higher quality and more materials. Instead of applying just one or two layers of soundproofing, you will cover all holes, apply liquid soundproofing to all the areas that you couldn't reach with the mat, and add a moisture barrier closed cell foam like ensolite foam on top of it.

    Even for "extreme jobs", you can break it down into areas. You can do each door or the trunk on separate days if you are doing it yourself. The only area that requires at least a full day to do is the dashboard and the floor since you have to remove the seats and carpeting. This would be a good time to clean the carpet.

    Soundproofing brands - what to choose?

    First, you need to buy the soundproofing. There are lots of brands out there, so here are some tips that I have learned on soundproofing brands.

    Avoid buying retail soundproofing at the local "big box" store. The "Dynamat" brand is decent quality stuff, but the worst value by far. There are better brands at much lower prices from ebay or direct from the manufacturer. I have also found the same exact basic "Dynamat" sound deadener at mcmaster. Do a search on the internet for dynamat mcmaster and their poly mastic self adhesive sound deadening sheets. This is the same exact thing as "Dynamat" and is rated for automotive use/temperatures. Their catalog changes from time to time, last I checked they were out of stock and switched to an EVA foam sound deadening sheet with a lower temperature rating that is not appropriate for auto use.

    The "edead" found on ebay works well, but I would use at least two layers of the stuff to equal better soundproofing. In critical sound areas such as the doors and wheel wells, you should be prepared to use 3-4 layers. Even their premium level soundproofing is not as good as other premium brand soundproofing but it's reflected in their lower price. Raammat from raamaudio is recommended by many as a good value. Unlike many makers who sell cheap, better, best grade materials, he only sells premium stuff. It's also a good value because you will find yourself using less layers as a basic cover where you would use two layers of the lower quality stuff. Of course, if you are like me you will end up using two layers anyways, but it's high quality stuff. It is twice the price as the cheapest ebay brand, but also twice as good. Since labor is the same, I would just buy the better stuff, especially since this job only has to be done once and the difference in price for a whole project is minimal. Brownbread, B-quiet, Damplifier are also all good brands and can be found without huge markups.

    If you insist on saving a little bit of money, I would buy a small roll of rammat and a small roll of ebay "edead" brand. The ebay "e" brand can be used on less critical areas such as the roof and trunk or as additional cover. However, after using ebay "e" brand I would buy raammat in the future. The raammat has real aluminum and is hard to cut through. The ebay "e" brand can be cut like butter with a regular pair of scissors and has a plastic back layer. Less scissor resistance equals less sound resistance. And the amount of money saved in the end would only be 1-2 fill ups at the gas station, so I recommend just buying the better stuff.

    Lastly, do NOT buy asphalt based sound proofing mats or lowes/home depot "peel and seal" type roofing products for interior auto use. They will melt off in the summer heat and stink your car up with a tar smell. Once they come unglued, they are basically useless since they aren't absorbing vibrations and if placed in the door, could leave a black tar streak on your windows every time you lower them. For the same amount of labor, just buy something that was designed for auto temperatures and use.

    This independent test breaks down various brands by price, quality, etc. Note that some of the brands, such as edead have since switched to butyl instead of asphalt and others have changed their prices. It also includes other brands so you can educate yourself about what products are out there. It can be found here: http://www.sounddeadenershowdown.com/ although it's dated. The listing on this (myturbodiesel) page is current.

    For liquid soundproofing, there are products available for the interior but these can be very messy and require multiple coats. For soundproofing on the wheel wells, you can use spray on undercarriage undercoating, etc., to break up the sound before it reaches the metal. 3M and Duplicolor spray on coating work well. Rustoleum seems to not foam as much as 3M and Duplicolor. A product called GraviTex or truck bed liner can also act as soundproofing.

    You should also use closed cell foam. If your car already has a layer of closed cell foam in the door, go to a junkyard or buy a new one from the dealer - it will already be perfectly preformed! If not, ensolite is a very good closed cell foam. The inside of the door gets wet from rain and condensation so a closed cell foam is required to act as a moisture barrier and not get moldy.

    Soundproofing theory

    To help you decide where and how much soundproofing to apply, here is some basic theory.

    The first is mass loading. This is what your basic soundproofing mats do. The idea is to add weight to whatever it is you're trying to dampen. By doing this, you change it's resonant frequency and decrease it's likelihood to vibrate. It also absorbs some vibrations and converts it to low level heat. Don't worry, it won't heat up your car, the process of absorbing energy creates heat. Sound = energy, when absorbed, it is converted to heat. This is good for vibration damping but blocks only little sound. This is where the ebay brands are most effective. This is also what the liquid soundproofing materials' best purpose is.

    The second type of damping is called barrier loading. Unlike mass loading, barrier loading does block a significant amount of sound. Usually what these have is a sandwich of materials, some neoprene rubber or foam, and some acoustic lead or other metal powder. These also turn vibrations into heat and absorb the acoustical energy of sound waves. This is where the raammat is a huge improvement over the ebay "e" brand. The raammat uses a thicker butyl layer and an aluminum backing where the ebay brand uses a thinner butyl layer with a plastic backing. You can add two layers of the cheaper stuff to get a thicker layer, but you still don't have that aluminum layer to turn sound into heat.

    Absorbing is the final layer where air vibrations are absorbed. Ensolite is an excellent product for this and the only one that I would recommend for auto use. Do not use open celled foams because they will absorb water, rot, and fall apart. In fact, the Mk3 passat already had one layer of closed celled foam in the door, the Mk4 jetta does not. If you have a car that already has a closed cell foam layer, search an auto recycler (junkyard) for an extra sheet of closed cell foam - the advantage is that it will be cheaper and be perfectly pre-formed! The door has water pass through it, so it is extremely important to use only closed cell foam and seal all of the edges as a moisture barrier.

    To reduce the amount of sound these have to absorb you want to reflect it before it's absorbed. Use spray on truck bed liner or undercoating to coat the inside of the wheel wells. Try to put tape over any screws or access holes so that they aren't covered up and avoid blocking any drainage passages. This will make a big difference in road noise levels because you can't otherwise do much about tire noise or road noise. As pictured above and here again, I put it on the plastic wheel well liners. This turns the almost useless plastic wheel well liners into a significant sound absorber/reflector. You might not notice too much difference until it's raining and the sound of water hitting the wheel well is different.
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    Lastly, mat soundproofing is best for dampening low frequency noises, but road noises have a lot of mid and high frequency components. A well engineered soundproofing job would also use minimal materials by placing the soundproofing in select spots to dampen the metal resonance. The engineers who made your car have probably already placed some select soundproofing but it could always be improved.

    Procedure
    First remove the trim where you want to work. There are DIY door panel removal articles in the FAQ, search to find the one specific to yoru car.

    Then clean the interior where mat is to be applied. This is extremely important! Clean it until you wipe with a clean paper towel and it comes back perfectly clean. If there is dust, oil, or dirt on the surface, the sound deadener will not stick properly. Not only will it not do its job of absorbing sound, but if it is applied to an area like the inside of the door panel, it may smear all over the window if it falls off, causing black tar streaks on the window each time you raise the glass.

    Test fit a panel and cut it as necessary. Use smaller strips rather than larger strips, especially on curved surfaces because it will help lessen the chance of bubbles and wrinkles. Add another layer as necessary. The bottom layer is what sticks directly to the surface, so make sure it is as smooth and bubble free as possible! Small pieces can be more easily applied smoothly. Areas such as the wheel wells, firewall, and the doors need more than one layer of soundproofing, I would add at least two layers. If you are using lower quality soundproofing, I would use at least four layers in heavy areas for best results.

    If you are doing a higher end job, cover all the holes with soundproofing and put a layer of ensolite or other closed cell foam between the door and door panel. Avoid putting the foam on the exterior door panel since it acts like a moisture barrier, could interfere with the power window, and is not the most economical use of the foam since it's expensive.. Make sure that all wires are protected from chafing and that all door handles and windows, etc, can move freely. Make sure to avoid areas around the edge of trim panels/securing clips/screws and close to the window track, and other areas where clearance is needed for the trim and door panel to fit back properly.

    Use a roller to make sure it is stuck well. No stick = no absorption of energy. If you didn't read the earlier section on why you shouldn't use roofing peel and stick products in your car, go back and read it now - they don't work well and they smell bad, so don't use them!

    That's about it! Again, if you are doing a basic job, you can use less material and just stick with mat. If you want a high end job, use more layers of sticky mat and use a layer of ensolite on top of everything. For the hard to reach areas, apply liquid soundproofing as necessary.

    Here is a before picture. Note that the rear quarter panel comes stock with only 1 small square of sound absorbing material. My guess is that the VW engineers decided that this was the most efficient spot to put soundproofing. The reason they don't use more is because saving even a little soundproofing can save a lot of money. Unfortunately, it blocks only the most obvious vibration.

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    Here is an after picture - I used too large of a piece on the wheel well so I had to make relief cuts to relieve the tension and get it to conform. This is what it should not look like on the wheel wells! The flat areas look better.

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    Note the green vacuum line for the power door locks - try to avoid covering lines and electrical wires. Remember, the dampening material works by absorbing vibration, if you are doing a more extreme job, you can cover those spots with foam so the lines will still be accessible later. This time I used more manageable pieces to avoid having to make sloppy relief cuts. Remember, adding undercoating to the tire side of the wheel wells can reduce road noise by preventing it from reaching the metal in the first place.

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    The seating and cabin area is very important. I would like to add more soundproofing to the area under the carpeting later.

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    The large spare tire panel is not covered but this can be done later without pulling the interior plastic panels. It also already has foam padding on the underside.

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    This is an ensolite like closed cell foam that comes stock on the passat and not on the same year of jetta. It's one of the reasons why a passat is quieter. It's also a water repelling moisture barrier because the inside of the door gets wet! If it gets torn it should be taped up again to prevent water leaks. If you already have a closed cell foam layer, I suggest going to a junkyard or buying another layer from a dealer (expensive). It'll be already formed perfectly and will make a big difference in speaker quality and sound levels. If not, you can add a layer of closed cell foam here. It's not recommended to put the foam on the exterior door sheet metal, only between the interior door metal and the door panel. This is because it can fall off onto the window if it's not stuck on well.
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    Below is a picture of a same generation jetta - there is no sound absorbing foam, only a thin plastic moisture barrier. Later jetta used a thicker board with a few foam blocks. The yellow foam is all the dampening the speakers get.
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    The outside panel is important. Clean it, clean it, then clean it again or else the soundproofing will not stick!

    Unless you are doing a high level job, just cover as much as you can. There's so much engine and noise that comes through the window and roof that it's difficult to get it super quiet unless you tear apart the dashboard and floor too. Remember, the purpose of the sticky mat is to change the resonance - it's not a foam layer! Sticky mat is best on metal. Be careful that the mats don't interfere with the edges of the door panel and handle screw points, etc.
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    The door panel can benefit a little from soundproofing too, but adding dampening material to the metal and adding a foam layer are the most important things you can do for a basic-medium level job. I had some left over and I doubt it made much difference. A foam layer for the door card should be more effective than sticky mat.
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    Overall, I did notice a difference. After adding the sound deadener there was a small improvement in sound quality from the stock sound system. Highway noise was also reduced. The sound of the tires and water splashing during a rain storm was reduced. Tapping on the outside metal skin of the door produced a dull sound instead of a tingy sound. Shutting the door also sounded very solid. Again, don't expect magic if you only add a few pieces of mat to the doors and trunk because a medium level job means medium level results! But if you are already removing the door panels to do other maintenance work, adding soundproofing while you are in there is a great idea.