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I did sound isolation in my 5 door 8th civic. instead of dynamat I used two layers of bitumen (which is the same as dynamat), and instead of 3M Thinsulation material I used carpet foam (mentoined here). both materials you can find in you home depot for very low price (instead of dynamat or 3M Thinsulation).
I covered whole back of the car with bitumen and with carpet foam. I covered doors with bitumen and front floor and engine firewall with carpet foam. I put polyuretan foam on rear wheel arches inside the car.
bitumen costs 17euro for 1.5m2 and carpet foam costs 7euro for 1m2. I used 4 m2 of both. It's a work for whole 3 days. The most effective was to cover the back of the car.
I measured sound level after sound isolation, and it is now 78dB at 80mph and 80dB at 90mph. I don't need to increase the voice, when talking with other person, even when they are sitting at the rear seats.
Conclusion: civic is now quiet as middle class car (volkswagen passat, honda accord), it's worth the money and time spend. To make civic quiet as lexus, the active noise control is needed (all luxury classes cars used it), which is impossible to DIY.

some photos and vids:

http://imageshack.us/a/img705/579/20130509201401.jpg
































 

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Has anyone tried out some laminate floor underlay, the ones designed to reduce noise from foot steps.

FloorMuffler ::

These can often be found in low quantities for cheap on craigslist, would this be suitable also? I feel the carpet padding is just too thick

floormuffler wouldnt work in car. it doesn't absorb the sound. it just prevent transiting direct knock sounds between two solid materials: the wooden floor and the concrete floor.
 

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Bitumen and Butyl don't act the same way.

Bitumen is asphalt, which works to mass load, but is a very poor viscoelastic compound. It works mainly as you said, by adding mass, and slightly stiffening the panel.

Butyl on the other hand, depending on the mixture, is a very good viscoelastic compound. It works by converting vibrational energy into heat as the compound tries to shear from the aluminum layer, as well as by adding weight, and slightly stiffening the panel.

I've tested 15 compounds so far.

The only asphalt that has tested well is STP-Atlantic's Bomb. Every other asphalt for example, is at or near the bottom of the list, in every objective reguard.

For instance, STP-Atlantic Bomb, reduces impulse vibration amplitude by 16.11db. From impulse, to 150 milliseconds, it reduces the amplitude of vibration another 44.87db. Like I said, Bomb is a special case, as its 1.5lbs per square foot, and 165mil thick/4.2mm thick.

The next best bitumen product I've tested so far, GTMat 110mil, reduces impulse vibration amplitude by 8.89db. From impulse, to 150 milliseconds, it reduces the amplitude of vibration by another 23.99db.

While this product works better than some butyl products (Stinger Roadkill Expert, Raamat BXT2, GTMat Onyx), lets look at Dynamat Xtreme, which performs better.

Dynamat, a butyl product, reduces impulse vibration amplitude by 11.35db. From impulse to 150 milliseconds later, it reduces vibration another 31.95db.

STP-Atlantic Gold, a butyl product, reduces impulse vibration amplitude by 12.99db. From impulse to 150 milliseconds, it reduces vibration amplitude another 35.19db.


As for sound absorption, you need a material at least 1/4 as thick as the wavelength your trying to absorb, to be effective at absorbing it. There is just no way that carpet padding is absorbing 98% of the sound going through it at 2000hz, or even 4000hz. That's not to say its not absorbing some sound, its just not absorbing 98% of it. To be an effective absorber at 2000hz, you'd need something about 1.7" thick.


For barriers, its not exactly thickness that matters, its density. For instance, if you use a mass loaded vinyl about 0.125" thick, it would work as well a lead sheet layer 0.015" thick. For more info, check out the product specifications for Cascade VB-3 and VB-4. One is a lead septum barrier, with closed cell foam on both sides, the other is a mass loaded vinyl with closed cell foam on one side. The lead layer is 0.015" thick, while the MLV is about 0.125" thick. Both weigh 1lbs per square foot, but the lead performs slightly better, especially in the low frequencies.


That said, aside from the glass, you can definitely get lexus quiet. It costs money, around $5-750 if you do it yourself, but it can be done. I'll be starting on my wife's civic at the end of this year after deadening testing wraps up, and phase two of testing begins.
 

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I just got back from Home hardware. I bought 2 cans of 3M Spray adhesive for foam ($10 each), Two Rolls of Aluminum Tape ($5 each) and 9 square meters of Foam Carpet insulator (identical to above for $25). I also bought 5 cans of rubberized spray coating (for sound insulation and rust prevention) from Canadian Tire for $3 each (on sale hehe). I am going to Rempve all the interior, then Cover all of the Critical Areas where I want sound dampened with Carpet insulator attached with 3m adhesive, and then coat any suspicious areas or areas that are possible exposed with moisture with the rubberized coating, this includes removing all the plastics from wheel wells and coating them in 2 layers of this good suff (weather proof, does not crack = good stuff) As I do this I will talke lots of pics and make a pretty simle (lenghty DIY)

Thanks for the idea, I have been looking for ideas for a project like this.
Awesome tip on what and where to buy. Just now upgraded from my EG civic to the 06 coupe and was thinking how loud it is in comparison.
 

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Good DIY, will probably look into this in the summer, can't be bothered to pay for dynamat and all the other overpriced stuff
 

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Well, I bought a big sheet of carpet padding and put it in: all 4 door panels, above head liner in-between roof braces, under rear floor carpet, on drivers side firewall, trunk/wheel wells and under the rear speaker deck.

The whole interior is already out of the car since the quarter panel is being replaced after an accident. I bought the car already smashed so I will not know how loud it was before the carpet padding but hopefully it's quiet now! :)

Here is a pic of one of the rear door panels. I stuffed as much padding as I could in there! 20150321_134650.jpg

20141126_200212.jpg
 

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Hey me too i did my doors with a product call peel and seal, took care of the door rattles gonna tackle the trunk , floor board then the last pain would be the roof , i must be getting old but damn those road noise are starting to get to me
 

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I can hear my stock exhaust during highway speed of 80mph + plus the road noise, but the left side of the trunk toward the left rear tail light under the carpet theres a vent to keep your trunk from moist is also brining in noise from the rear end of the car
 

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Doing this mod with Rammat eliminated all rattle in my car with my JL10W7 AE. All I did was the trunk area. I also foam insulated the trunk lid with expanding foam.
 
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