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Old 19th July 2009, 03:22 AM   #1
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Default Vehicle Sound Dampening Opinions

Okay, I want to know what you think about sound dampening as a whole. What are your personal thoughts and experiences on the topic? What are some of the materials and tools you prefer to use when installing dampening? Are there any questions you have reguarding sound dampening or how its installed? This thread is designed for education in installation through installer information. All comments and replys are appricated.

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The level of performance in any mobile sound system is a direct result of the way it was installed. Passion, pride, perfection.
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Old 19th July 2009, 03:35 PM   #2
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In general, I think it should be considered carefully in terms of cost and time in relation to where else the money could be spent.

There's always a point of diminishing returns. That could be $1000 into the job, or that could be $10 into it, depending on the rest of the installation.
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Old 19th July 2009, 08:23 PM   #3
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I completely agree. I did an install back in 1999 on a dodge intrepid. The project was meant to be a SQ comp car. That eventually fell through, but we ended up spending about $650 in sound dampening materials.
The level of performance in any mobile sound system is a direct result of the way it was installed. Passion, pride, perfection.
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Old 19th July 2009, 08:37 PM   #4
Glowbug is offline Glowbug  United States
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Pretty decent article on it:

As far as materials, I'd prefer Second Skin products if money isn't limited, but I've also had good luck with 60-mil thick RAAMmat.

I'd want a heat gun during the colder the summer just leaving it in the sun for a little bit should do the trick. Rollers can be found at home improvement or craft stores.
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Old 20th July 2009, 10:20 PM   #5
mda185 is offline mda185  United States
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I just installed dampening material in my wife's Pathfinder driver's door over the weekend. I used a butyl/foil product called Brown Bread on the outer door skin and covered that with a 1/4" thick, mold resistant foam layer using material purchased from McMaster Carr. I used 3M 77 spray contact adhesive to attach the foam to the foil side of the Brown Bread. I also replaced the thin plastic vapor barrier with a sheet of 40 mil vinyl mass loaded noise barrier also purchased from McMaster Carr.

I did not tell my wife I only did her door and the next day she wanted to know why the driver's side door was so much quieter than the passenger door. Not very scientific.

I am still trying to figure out how to measure what she hears. I have a calibrated mic and Praxis software. I tried putting the mike in the nearfield of the mid woofer mounted low in each door and took measurements at a steady 65 mph. I had the mic surrounded by foam to shield it from any sound other than what was coming from the door. I thought the interior noise of the door would be detectable through the midbass speaker even if it was attenuated. (The stereo was off.) I expected to measure a difference between the two doors. The sound levels detected in the nearfield of the midwoofer were identical for left and right doors.

I plan to remove the midwoofers and measure the sound coming out of the opening with no obstructions next.
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Old 21st July 2009, 09:26 PM   #6
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I wanna thank everyone who replied to my post. And I encourage those of you who have experience in the topics at hand to please post. So that others may learn from you and advance in DIY mobile electronics. Thanks again.
The level of performance in any mobile sound system is a direct result of the way it was installed. Passion, pride, perfection.
J. Kim~I.A.S.T.
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Old 22nd July 2009, 01:55 AM   #7
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At one time, there was a site that compared various damping materials. It's now a commercial site that's only for sales (no real tech info). The old site information can be found on the WayBackMachine site. It's lost it's formatting and you have to look carefully for the menu but it may be useful to those who are completely new to this.
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Old 22nd July 2009, 09:12 AM   #8
dangus is offline dangus  Canada
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For measuring what's coming from a particular panel, an accelerometer might do the trick. It'll tell you how much the panel is vibrating. As for what kind of accelerometer and where to get one cheap, I'll let you google for that...

I suspect it would be worthwhile to tear apart the interior of an old Detroit sedan from the '70s or '80s and see what made them so quiet. They chose materials based on maximum effect for minimum cost.
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Old 22nd July 2009, 11:04 AM   #9
luka is offline luka  Slovenia
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I think you have best buy there: second skin...
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Old 22nd July 2009, 12:08 PM   #10
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Yes, the old had more info than the current (uncompleted???) one, although there is less info to wade trough now and some good tips.

As far as I've read and learned on the subject it comes down to some basic mass-related physics. There are different sound/noise related issues too, depending on your goals. Measuring things is also very difficult as the guy from SDS said himself on some occasions.
Driving a '94 VW Golf TDI Mk3, I have done some dampening myself, more to get a luxury feel while daily commuting and to get more from the sound system I installed when I dismantled the car. Like swatting 2 flies with one stroke. Now that I did the doors, I noticed more noise coming from the trunk so I'm looking into alternatives for that.

I would summarize things like this:
- you have noise being *generated* from the car itself by flexing panels or noisy tires. You add mass to the panels so they vibrate at lower freq. (The total energy stays about the same, so even if you hear less noise, it is just lower [Edit: in frequency] and an SPL meter will still indicate little effect.) If you add a rigid layer on the outside of the added mass - like an aluminium plate - it adds stiffness too so you lose less pressure from bass. The viscoelastic properties dampen the vibration so it doesn't last so long.
- you have noise *coming in* from outside the car. You can block that out with a barrier. A good start would be to fill the door seals with a foam tube (still have to do that) to increase the sealing. Then you can add a coat of liquid dampener to the inside of the doors to cover up as much metal as possible to block sound out. (you can do this on top of the weight-mat you already put in in the middle of the panel. No use in covering up the whole panel with the mat, it is more effective in the middle where the most flexing is and else it is a waste of mat). Once you have done this, you can add an extra layer of closed cell foam (3mm thick) on top of the moisture barrier in the doors. This is a part of next paragraph. On top of the foam layer you can put a rubberized barrier. This barrier will be decoupled from the car by the foam layer and thus doesn't transmit vibrations (=sound) to the interior cabin.
- the sound that does *get trough*, you can absorb with foam or fibres etc ...

Basically you put in heavy stuff so it doesn't vibrate that much - or at lower freq which is less intrusive - and you try to make everything as airtight as possible. At each layer you will have some sound that gets *reflected*, so more different layers are better than one thicker one, and also each layer will *absorb* some of the sound that gets trough, so the heavier and thicker each layer is, the better.

Just make sure you use materials that are up to the task, ie high temperatures from being parked in the sun. (you don't want glue that gets loose or bitumen roofing mats which get "liquid" and fall off.) A car is a closed enviroment, so toxic fumes are a no-no. (again, roofing is not recommended.) And you have rain and humidity that gets in, so open-celled foam must be placed at dry places or replaced by closed celled foam.

I used bitumen-based undercoating in the doors since it is made to stick to metal panels and I made sure my foam/moisture barriers were as air/water closed as possible! Lots of extra ducktape.
Then I put 2 layers of 3mm closed-cell carpet underlay in my trunk but it was not so effective for the noise now coming from the back instead of the doors. Currently I am looking into vinyl sheets or EPDM roofing sheets which should be a lot cheaper than MLV (Mass Loaded Vinyl) and still provide a large uninterrupted barrier for the road noise coming from below. If I put in 2 layers they should be the same mass as the MLV, while one layer of carpet underlay will decouple it from the metal floor.
I already tested it with a 4mm thick bitumen roofing sheet put under the carpet in the trunk, but due to the above, I will not use it permanently in the car in this summer, hence my EPDM alternative.

There are lots of cheap (housing)alternatives to the expensive materials sold for sound deadening in cars, as long as you stick to the physics and use different materials.
-- If in doubt: overdesign!
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