Sound deadening

[72Mountaineer]

I've installed sound deadening/heat shield everwhere within my '53 cab, just have to do the doors now. Where is the best place for this stuff? Inside the doors, on the outer skin, or the inside, I guess on the interior side?

[mongocanfly]

on the inner side of the outer door skin....

[joedoh]

there are two types of sound deadening, mass adders and absorptive. most likely you are using a mass adder like dynomat or fatmat or any kind of asphalt based sound deadener. I use peel and seal from home depot, its about 16 bucks a roll.

asphalt based sound deadener adds mass and lowers the resonant frequency of the panel. thats fancy talk, so how about we talk in laymans terms?

when you hear road noise in your cabin, even when you have sealed the air leaks and rolled up the windows, you are hearing all the panels vibrating. sound doesnt travel through the panel, the sound vibrates the panel from the outside and the panel sympathetically vibrates on the inside. there is a point where the vibrations are strongest, stronger than any other point. this is called the resonant frequency, where the panel naturally wants to vibrate.

reproducing frequencies is easier the higher they are, reproducing lower frequencies takes a lot of energy. if you have ever looked at a sound system, the tweeters are very small (high frequencies) and the bass speakers are very large (low frequencies). the same is true for the amplifiers, the high frequency amplifier (mid/high) can be smaller and will run cooler, the low frequency amplifier (woofer/subwoofer) is very large and works very hard.

with no sound deadening, the resonant frequency of a panel is also comparatively very high. when you add mass, you lower that sympathetic vibration frequency. now it takes more energy to vibrate the panel (you have lowered the resonant frequency and its now acting like a woofer/subwoofer). since you havent increased the size of the panel it is also less efficient at the lower frequency.

there is a point of diminishing returns when adding mass. you get to a point where the resonant frequency is so low that adding more mass doesnt lower it any further. therefore, any application of mass to a panel is effective, and you dont need to cover the whole panel to see the best result. put it in the middle of large panels, and it will be fine.

absorptive sound deadening works by absorbing reflected sound. cloth, any soft surface, and products like lizard skin are absorptive. these coatings work best in complete, gapless, covering because any bare steel will reflect sound.

sorry for the book. now you know though!

[svr]

Joedoh, i was looking at the Home Depot stuff the other day, does it emitt an asphalt smell when hot? Did you cover the complete inner firewall with it? Did it slow or stop the heat from the motor compartment? Sorry for all the questions just wanted to pic your experience.

[mongocanfly]

svr ,,,that's "professor joedoh" to us now...hahahaha

[svr]

I bow to the professor, LOL

[joedoh]

Originally Posted by svr

Joedoh, i was looking at the Home Depot stuff the other day, does it emitt an asphalt smell when hot? Did you cover the complete inner firewall with it? Did it slow or stop the heat from the motor compartment? Sorry for all the questions just wanted to pic your experience.

no smell from my installs. I did cover the firewall, I didnt notice a lot of engine heat beforehand though so I cant speak for heat rejection. the foil is on the non sticky side so I dont imagine it would do a lot for keeping heat out. there is a foil bubble wrap made that would work for that.

the only problem I encountered was the sticky side did not tolerate anything less than a clean surface. I wire brushed the firewall and floor where I installed it. it worked great.

[svr]

Thanks Joe, i would think it would stick to a good clean dry primered surface, true?

[joedoh]

absolutely. instead of sanding every nook and cranny to bare metal, I primed some.

[Black_Sheep]

Since the truck will have full interior door panels, I put a layer of Fatmat on the interior sheetmetal of the doors. After reading joedoh's post, my plan for sound deadening should be pretty effective. There's fatmat rattletrap throughout the whole interior with a layer of fatmat floor liner from the top of the firewall to the back of the cab. It will be topped off with 40oz jute carpet padding and loop pile carpet. The door and kick panels are covered with high density foam so they should help dampen sound as well.

[72Mountaineer]

Thanks for the replies. Two different suggestions here, and an explanation of how it works. Any other suggestions of where (maybe a tiebreaker)? Putting it on the inside of the outer doorskin seems right, though will be a ***** to do.

[joedoh]

doing the doors helps, and definitely want it on the inside of the outside skin (and some on the inside of the inside skin too!) but road noise comes mainly from the wheels so the floor and firewall and back wall are where you should really focus.

I love love love jute padding under the carpet, hands down that is one of the best absorptive products you can use.

[mongocanfly]

this door im working on now has a undercoat like material on it on the inside of the outer skin...its only about 18x18 square sprayed in the middle of the door..has about 8" or so all the way around it that's not coated...if you look close on the far right you can see where the edge is....

[_Ogre]

i suggest a piece of sheet metal under the carpet where your heel will sit on the go pedal
ogre has 2 layers of rammat and 2 layers of insolite foam on the floor of truk
i have worn a considerable divot under the heel position, it's covered by floor mat but still there