Quiet Your Car The Cheap and Effective Way

If you’ve been on the Earth for a couple of decades or more, or have just grown up riding around in some older metal, you’d know that cars can be incredibly noisy. If you’re unfamiliar, buy yourself a nice car like a 2000 Honda Civic, strip out all the carpet and interior panels, and go for a drive. Huge amounts of research and development have gone into making modern cars as quiet and comfortable as possible. Through the correct use of sound deadening materials and techniques, a car can be made much quieter and audio quality from the sound system can be improved too. [camerajack21] decided to get to work on their Volkswagen to see what could be done.

The project in question pays special attention to the door panels. These are where the primary speakers are housed, and there were issues with rattles if the speakers were allowed to operate at frequencies below 100 Hz. Weather stripping, foam, and improved fasteners were pressed into service to reduce this issue.

Think of a musical bell. If you touch a small part of the bell with just your finger, it no longer can ring true. You don’t need to wrap your entire hand around a bell to keep it from ringing. Your finger is not absorbing sound, just preventing the bell from ringing.

Focus then moved to the body panels. Special sound deadening material (in this case, Silent Coat brand) was then applied to the insides of the doors and trunk to bring the sound level down. The key to effective application of such materials is not to waste money covering entire panels – the Reddit comments are particularly enlightening here. It only takes a small amount of material to stop a panel from vibrating, with most testing suggesting anymore than 30% coverage of a panel brings diminishing returns.

With your car’s sound environment tidily improved, you might be looking for ways to improve your sound system. There’s plenty of ways to go about it – you can even use guitar effects.

31 thoughts on “Quiet Your Car The Cheap and Effective Way

  1. Bitumen roof sealant strips replace the stuff with a pretty name and a higher price tag.
    Yes some of them are foirmulated to perform better, but price performance ratio doesn’t win out.
    You can alwasy double up on the cheap stuff.

    Also stuffing panel voids with “rockwool” aka fibreglass insulation helps a lot too and can regulate internal temps in say the trunk.
    Obviously not in door where windows need to move, but those voids in your trunk Stuff them and it’ll deaden sound and help keep it warm/cool. Also cured trunk consendation issues in some saloon/sedan cars I’ve had.

      1. “How well does the bitumen stand up to the temperatures on a hot summer day?”
        The same way it does on your roof I would image, except without the direct heating.
        Most roof products are also good down to -25C or so, before they become brittle.
        I would suggest it is quite a good choice and would work well to keep the rust out too.

      2. My thoughts instantly drift to failure mode, so a high speed car crash and fire. Bitumen may not be the best of things to surround your self with, but fibreglass sounds fine. If you have ever had even a single drop of molten tar land on your flesh, it stores and releases a lot of energy. And I’m not even talking about it being on fire, that is just too unimaginable to think about.

        1. There’s plenty of other things to ruin your day before that happens. If you’re in the cabin and bitumen is melting, you have already had very severe injuries inflicted to you and you probably aren’t worried much about a couple hot tar drips.

          Safety engineering is hard. Most people overweight very unlikely issues by a spectacular amount and ignore the most likely risks.

      1. Fords of that era rusted because Ford did nothing to corrosion-proof the metal. It took the Japanese to do the job right, then the US manufacturers followed. I used to squirt motorcycle chain lube into the bottoms of my doors to fill the seams and keep the salt water from rotting them out.

        IIRC, Ford used coconut fibre matting under the carpets — it trapped water.

        Never had a ’65 Mustang, but my mom had a ’63 Falcon. That thing was light and fairly quick, except when you mashed down on the gas and the engine roared while the auto transmission slowly tried to figure out how to shift all that power to the rear wheels! Once it got started, though it went pretty well. The Mustang was built on a Falcon chassis and drive train.

  2. Before the Mr-2 was mine I was asked to find the rattle in a bass voice in the speakers in it. Annoying, but hard to find. I brought my FM transmitter and a frequency generator out to the driveway. Tuned in, in a couple of seconds I had the interior panels rattling with a tone from my radio station. Hands on, easy to fix with glue. Nowadays with a plug in connection (no bluretooth) it’s a cinch to use a phone app to sweep out those booms and rattles. The key is real time, oh here it is. Not Oh’ I heard it, now what is it.

    Nit picking, what makes the finer life. Free of bugs.

  3. You know what else is loud? All the plastic panels in my 2014 camry. They creak when you turn a corner, or press near the touch screen! Any way to make then stop?

    1. You probably just need some new plastic retainers in the door panels. If they’ve ever been taken apart they can especially be worn out, broken, or not fastened correctly.

    2. Good ol’ weatherstriping/teflon tape. Plastic doesn’t really creak on its own (unless it’s being bent out of shape), it’s usually plastic rubbing against other plastic that makes squeaking noises.

    1. That was a superb little video. I’m glad I took the time to watch that, thank you.

      Hmmmm… I have a spare 50wx50w bluetooth amp lying around, might get some transducers and start building some panel speakers. I also have a fabulous 100wx100w power amp that I haven’t even tested yet, I’d like to see how it fares. Time to get some scrap wood and warm up the table saw. I wonder how odd angles would help to dampen the resonant peaks, such as to make an irregular trapezoid or some other polygon instead of rectangles. Perhaps use a voronoi algorithm to place the transducer and counterweights.

  4. I have used Peal & Seal to deaden car doors for two audio installs now and it works great! Wayyyy cheaper the the real stuff so you can put a bunch on. I load it up everywhere you can stick it in the doors. The tar smell only lasts a day and never comes back, I’ve had it on my car for 3 years now. Did this on my friends car recently and it got rid of the cheap echoey sound the doors had when you closed them.

    1. There’s some neat stuff called “body seam sealer”. I got a box of it (looks like black licorice strips, but tastes much worse) from a body shop supply place round the back of an industrial building in a dodgy part of town. Comes in sheets of round strips, separated by parchment paper. It’s like BluTac on steroids. Wonderful stuff for stopping leaks and filling gaps. Stays where you put it.. I’ve hardy used a quarter of the box over 15 years, and it’s still good. I

  5. As an acoustic engineer, I’m pretty familiar with a couple of different types of “sound deadening” panel material. Anything long and flat will radiate sound. Some things don’t resonate sound when they vibrate. Strings are a good example. If you take a string by itself and whack it, it doesn’t produce a lot of sound. However, if you take that same string and make it vibrate a solid piece of wood (sound board), then it will make a sound like a guitar, piano, violin, etc. Car panels do exactly the same thing. Your car will vibrate due to all sorts of sources (the string in the last example), and the flat panels will turn that vibration into sound inside the cab. Driving on those road strips (cuts in the side of the road) is a good example of that. When you drive on them, it sounds like the noise is coming from everywhere, not just the tires.

    So, one goal of these materials is to move the resonances down. There’s the kind that just adds mass. The goal is to move the resonant frequencies down by increasing the mass [2*pi*f = sqrt(k/m)]. This does two things. (1) Your hearing is best at 1000Hz, and is really bad at low frequencies. Make the resonant frequency lower, and the same sound pressure won’t feel as “loud.” (2) It takes a lot of energy to create low frequency noise. That’s why tweeters don’t require a lot of energy, but bass speakers are massive and sometimes need their own power. The same amount of energy at high frequency will have a “louder” sound than at low frequencies. When using this type of material, put the weight where the panel deflection is the most. It will have the biggest bang for the buck. Not edges, but middle of the panel.

    Some materials add damping. This is meant to remove vibrational energy from the system and turn it into heat. Usually, the material is multi-layer. There’s an outer material that adds mass, and a middle material that is flexible (panel middle material mass outer material) When “well” bonded, the vibration will cause the middle material shear back and forth as the panel waves like the ocean. Normally, this material is placed where the velocity is the most (not the deflection) if it is just adding damping. Or sometimes placed where velocity and deflection are the most, if the material also adds significant mass.

    Overall, put it where stuff moves. Push on the panels with your hand. Where it is stiff, leave it blank. Where it feels “soft,” add material. Make sure to clean the surfaces, because the bond maters A LOT. If it isn’t sticking, it isn’t working like it’s supposed to.

    1. This reply almost deserves its own article. perhaps you could collaborate with some of the authors to post something with more insight than the result of trial and error like the article posted here. Not saying i dislike the aritcle, contrary, I like to read some more.

  6. Not to be a scary creature living under a bridge, but canceling noises your car makes, and from the outside world, is not a good idea. Thats why driving with headphones is against the law. Modern cars are so comfortable, drivers fall asleep at the wheel. The car is more comfortable than the lazy boy.

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