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Discussion Starter #41 (Edited)
On Sounddeadenershowroom, did you view the build-log of the 5-door Mazda3? I am not sure what you mean re the Mazda6, above... i.e. hanging the MLV between the plastic ("door-cards") and the inner-sheet metal of the doors? Please confirm that that is what you mean. In SoundDeadenerShowroom the owner of the Company shows how velcro is used to hang the MLV onto the inner sheet metal part of the doors... with the isolating CCF having "windows" cut in it so the velcro patches show-through and allow the MLV to hang with adhesive velcro onto that sheet metal. Yes, where the velcro is located, the MLV is not totally isolated from the sheet metal... but the male/female halves of velcro - industrial velcro - do have some "isolating / insulating" properties.

Mazda3 Build log: Mazda 3 4 door Hatchback 2014- Build Log | Sound Deadener Showdown

I think the photos of behind the door-card are from Archerfish... Useful, so you can see what you are dealing with...
 

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Not the doors. Underneath the car there are plastic covers - I'm talking about stuffing some MLV between those and the underside of the floor pan. You'd essentially be putting the isolation outside the car, which stops the noise before it can get inside and bounce around. Manufacturers do this with various materials, but I haven't seen MLV mounted outside the car before, so it seems like a good use if you can pull it off.

As far as the doors go - modern doors are pretty tough to put MLV into. I had the driver's side door card off the 6 a few days back and decided it wouldn't be worth the effort. The shape is pretty complex, and my goal isn't total sound isolation, I'm primarily concerned with the road noise reduction. And I know some road noise can come from the sides, but the majority is from the floor and firewall.
 

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Discussion Starter #43
The idea about MLV outside the floorpan: I don't think that would work well... because the sound from the road is (I suspect) only in a minor way due to the road surface rushing-by under the car. Rather, the road texture and tires over top of said road "telegraph" that noise and vibration through the suspension members onto that "drum-skin" of a surface AKA the floorpan. The MLV, continuously (i.e. in a contiguous, un-broken manner) interposed between the floor pan and your ears (de-coupled from the floor pan using closed-cell foam - CCF) solves this issue. EXCEPT, placing this MLV / CCF layer is a right-PITA. Whole interior has to come out to do this. BTW, judicious use of small sections of Constrained Layer Damping (CLD) self-adhesive asphaltic tiles (inside car, onto floor pan) to prevent/reduce floorpan resonances at the natural frequencies we care about is also appropriate to do...
 

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I think the photos of behind the door-card are from Archerfish...
I thought the funny looking reflected face looked familiar that I have to confirm it. Yes indeed! That face is mine.
?

It seems that applying this sound deadening material is a real pain DIY project. Perhaps I'll just pay a professional than do it myself. This will surely save me a lot of agony once I realize that I messed up the job.

Then again, I might not do it as my wallet is broke.
?

I got used to the noise that somehow, it doesn't bother me anymore. The suggestion in using a cheap insulator for the door is a good alternative. I just hope that @OCTOGONPC can provide an actual picture where he placed it.
 

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The idea about MLV outside the floorpan: I don't think that would work well... because the sound from the road is (I suspect) only in a minor way due to the road surface rushing-by under the car. Rather, the road texture and tires over top of said road "telegraph" that noise and vibration through the suspension members onto that "drum-skin" of a surface AKA the floorpan. The MLV, continuously (i.e. in a contiguous, un-broken manner) interposed between the floor pan and your ears (de-coupled from the floor pan using closed-cell foam - CCF) solves this issue. EXCEPT, placing this MLV / CCF layer is a right-PITA. Whole interior has to come out to do this. BTW, judicious use of small sections of Constrained Layer Damping (CLD) self-adhesive asphaltic tiles (inside car, onto floor pan) to prevent/reduce floorpan resonances at the natural frequencies we care about is also appropriate to do...
I'm going to respectfully disagree. Some noises can transmit through a unibody, but a modern car makes for a pretty lousy drum (the factory slaps on damping materials specifically and strategically to muffle the instrument). I'm not an acoustics engineer, but as I understand it, the vast majority of "road noise" is from the impact of the tires on the pavement - the sounds radiate out fairly uniformly from the points of impact and bounce around under the car and inside the wheel wells. The engine can also make quite a racket.

Picture this: a big truck thunders by you at high speed, does the noise come from the truck's body? How about the change in sound as you transition from an asphalt road to a concrete one, does the body of your car hum along differently? It's the tires impacting the roadway - it's the steel-belted slab of rubber slapping the ground.

There is good reason every single major manufacturer today puts insulating materials on the underside of their cars. The only reasons you don't see MLV on the bottom of cars is because 1. it's expensive, 2. it's heavy, and 3. it's flexible. A manufacturer wants cheap, light, and rigid under the car even though expensive, heavy, floppy things are better at soaking up sound.
 
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