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Thread: Sound Insulation

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    Colonel montaillou's Avatar
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    Default Sound Insulation

    This is gonna be an ongoing thread as I want to include both the hood and the cab.

    My general plan is a thin underlay followed by something thicker.

    For the hood, I also plan on doing the firewall, at least with the thinner layer. Then a thicker hood liner

    I did a bit of searching on the web and did not find any actual studies where someone compared one brand to the other using any sort of instrumentation , every review I found was based on the reviewer's ear. I decided to go with Dynamat because every review said it was the best. Every review also said it was the most expensive.

    I didn't do a starting decibel because I didn't think of it, but even if I did it would be tainted because I've made other sound improvements beyond stock.

    So, before any sound insulation I have a D turbo, an 18" Donaldson muffler and my stack is 11' high.

    20190527_195100.jpg
    Probably the cleanest the underside of the hood has been since it rolled off the assembly line

    20190602_205823.jpg

    So, I used just under 6 sheets of Dynamat Extreme. Each sheet is 4 sq/ft and .067" thick. I used a good pair of 10" heavy duty scissors and a framing square to make rough cut outs. I also had a rolling tool (they're cheap). I would guess that the under side of the hood is really close to 22 sq/ft. I overlapped a little bit here and there. A bulk box of Dynamat is 36 sq/ft, I'll probably use most of the rest on the firewall.

    This stuff is also .45 lbs per sq. ft., so, I added over 10 lbs to the hood and it is noticeably heavier. I will be adding a handle to the hood, not totally necessary, but I just think it's a good idea. The hood liner is about half the weight of the thinner stuff.

    I did do a decibel test after the above pic. It's 102 decibels from about 10 feet in front of the engine, and 104 decibels in the cab. I'm using a freeware decibel meter app on my phone, so I can't say how accurate it is, but hopefully it'll at least be consistent. It did seem to me that some of the high notes were mellowed out - more deep rumble, which is one thing sound protection is known for.

    Next step is the hood liner. I'll try to get to that in the next week.
    Not so much a signature as a cry for help.

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    Sergeant Major Fatalid's Avatar
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    Default

    Interested. Love the pics. Good looking truck!


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    4 Star General Jeepsinker's Avatar
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    I did my firewall with M939 hood insulation pieces.
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    I sink Jeeps... That is all
    1969 Kaiser Jeep M35a2 w/winch (Daily driver, no joke)
    Now a hot rod deuce: 6BT swap in progress, Waterloo overdrive, 2 micron fuel filtration installed, riding on 11.00r20s
    1971 M151A2 w/ ROPS
    3: 87' M35a2c Air Force trucks
    1991 BMY M936a2 wrecker
    2: M1061 flat trailers
    1: Fresh rebuilt and load tested good Mep003a genset
    I do Fort Polk and other recoveries in my state. I can be reached at 337-401-2470

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    Colonel montaillou's Avatar
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    Quote Originally Posted by Jeepsinker View Post
    I did my firewall with M939 hood insulation pieces.
    I thought I'd apply the .067" sound insulation to both sides of the firewall. I know I won't be able to get complete coverage on the engine side but I figure it might help. Part of the purpose of the insulation in the engine bay is to redirect (bounce) the sound and this is what I'm hoping to achieve.

    I found a site that sells sound insulation for heavy construction machinery and after I know how much I'll need, I'll probably get something like what they sell for the second layer in the cab. I'll probably then finish up the cab with something like a horse stall pad for the floor.

    Just a note on hood liner. The stuff I'm using (and probably most brands) is 12 sq ft, so you'll have to buy 2 for our hoods.
    Last edited by montaillou; 06-03-2019 at 16:31.
    Not so much a signature as a cry for help.

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    4 Star General Jeepsinker's Avatar
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    Ok, so I had no intention of applying a hood liner to my truck, but I'm curious what method of attachment you are going to use since most foam friendly glues don't stay fast in a perpetually hot environment.

    I used permatex sprayable trim adhesive on my firewall but I'm expecting it to start falling off in a few years just because of the heat.
    I sink Jeeps... That is all
    1969 Kaiser Jeep M35a2 w/winch (Daily driver, no joke)
    Now a hot rod deuce: 6BT swap in progress, Waterloo overdrive, 2 micron fuel filtration installed, riding on 11.00r20s
    1971 M151A2 w/ ROPS
    3: 87' M35a2c Air Force trucks
    1991 BMY M936a2 wrecker
    2: M1061 flat trailers
    1: Fresh rebuilt and load tested good Mep003a genset
    I do Fort Polk and other recoveries in my state. I can be reached at 337-401-2470

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    Colonel montaillou's Avatar
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    Quote Originally Posted by Jeepsinker View Post
    Ok, so I had no intention of applying a hood liner to my truck, but I'm curious what method of attachment you are going to use since most foam friendly glues don't stay fast in a perpetually hot environment.
    The material I'm using has a self-adhesive backing. If it comes off, well, I'll just worry about that when it happens. I'm sure it will over time, but I open the hood enough that I'll probably notice if it starts to come loose.
    Not so much a signature as a cry for help.

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    General Special T's Avatar
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    I used Frost King pipe and duct insulation. It is a closed cell foil backed self adhesive. It works well in the interior and is used in many hotrod builds. Fairly cheap at least than $1 a square found at Lowes or Home Depot

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    Colonel montaillou's Avatar
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    So, I got the actual hood liner material up:
    20190606_190401.jpg

    As you can see, I got pretty good coverage and after doing the same decibel test I get 101 outside, 10 feet in front of the engine and 105 decibels from inside the cab, at idle...

    So, a little disappointing.

    In a way, it's not surprising. After all, I'm only blocking/absorbing sound on one side and there is plenty of sound to go around. It still does seem if the high notes are being knocked down, but these aen't exactly screaming engines even at highway speeds.

    Based on these results I certainly can't recommend the hood liner at all. Maybe the undercoat of the butyl sound insulation is doing a little something, but I don't know that I would say it's doing enough to justify the cost/time involved on the hood.

    I have to pick up some lumber on Monday and will be on the freeway for a short period, maybe the effect will be more noticeable at highway speeds, but I have my doubts.

    I do think when I insulate the cab that I'll most likely see the greatest effect and most likely because the idea there is to insulate as much around you as possible. I'll get started on that this weekend. And I'll also post any results after insulating the firewall on the engine side.

    Silver lining time: At least I won't have to incur further costs replacing the hood liner when it peels off over time!
    Last edited by montaillou; 06-06-2019 at 22:43.
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    4 Star General Jeepsinker's Avatar
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    The real silver lining is that it will stave of the fading of the hood paint from the engine heat. That's the main reason I'd insulate the hood.
    I sink Jeeps... That is all
    1969 Kaiser Jeep M35a2 w/winch (Daily driver, no joke)
    Now a hot rod deuce: 6BT swap in progress, Waterloo overdrive, 2 micron fuel filtration installed, riding on 11.00r20s
    1971 M151A2 w/ ROPS
    3: 87' M35a2c Air Force trucks
    1991 BMY M936a2 wrecker
    2: M1061 flat trailers
    1: Fresh rebuilt and load tested good Mep003a genset
    I do Fort Polk and other recoveries in my state. I can be reached at 337-401-2470

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    Colonel montaillou's Avatar
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    Quote Originally Posted by Jeepsinker View Post
    The real silver lining is that it will stave of the fading of the hood paint from the engine heat. That's the main reason I'd insulate the hood.
    That could be a consideration. I do have plans on a custom paint job down the road...dazzle camo.
    Not so much a signature as a cry for help.

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