Sound Insulation

montaillou

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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.
 

montaillou

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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.
 
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Jeepsinker

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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.
 

montaillou

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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.
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.
 

Special T

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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

Sent from my SAMSUNG-SM-G930A using Tapatalk
 

montaillou

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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!
 
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montaillou

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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.
That could be a consideration. I do have plans on a custom paint job down the road...dazzle camo.
 

montaillou

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Just an update. I started putting dynamat in the cab.

I also did a frequency measurement in the cab with the engine running. The two highest peaks were at 38Hz and 75Hz with a lesser peak at 115Hz. The more I look into sound insulation, there's really a great deal out there (especially when you get off Amazon) and I'd like to find something in my budget range ($300) that caters to the low engine noises of the deuce. For instance, most sound insulation I'm looking at list how well they do at different frequencies, but most charts start at 125Hz.

After further research, pretty much the only thing that blocks low frequency with any efficiency is something like 4 inches of rock wool, or a 2 inch thick fiberglass blanket. Neither of which is particularly practical in a truck cab. I have found a foam with fairly high density of 1lb sq/ft at 15/16" thick. I will probably go with this as the density should help.

If anyone's interested, there is new ground breaking research on lightweight material specifically to work with low frequency sounds. This article is from 2016.

Manufactured panels are not quite there yet, however.
 
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Floridianson

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Just a thought if insulation under the hood would redirect more heat back on the cab? Firewall inside or out I can see.
 
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rustystud

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Just an update. I started putting dynamat in the cab.

I also did a frequency measurement in the cab with the engine running. The two highest peaks were at 38Hz and 75Hz with a lesser peak at 115Hz. The more I look into sound insulation, there's really a great deal out there (especially when you get off Amazon) and I'd like to find something in my budget range ($300) that caters to the low engine noises of the deuce. For instance, most sound insulation I'm looking at list how well they do at different frequencies, but most charts start at 125Hz.

After further research, pretty much the only thing that blocks low frequency with any efficiency is something like 4 inches of rock wool, or a 2 inch thick fiberglass blanket. Neither of which is particularly practical in a truck cab. I have found a foam with fairly high density of 1lb sq/ft at 15/16" thick. I will probably go with this as the density should help.

If anyone's interested, there is new ground breaking research on lightweight material specifically to work with low frequency sounds. This article is from 2016.

Manufactured panels are not quite there yet, however.
Here's how mine turned out using the "DynaMat" liner. The DynaMat I installed under the hood is still working great too ! Nothing falling off. One thing I ended up doing was plugging "every" single hole on the firewall no matter how small. If it was just a 1/4" hole I put a bolt and nut in it. Plus I did the inside of the doors with the DynaMat. Really made a big difference. Here's the post. https://www.steelsoldiers.com/showthread.php?158593-Noise-levels-in-cab-after-installing-DynaMat
 

montaillou

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Yeah, I'm doing dynamat everywhere in the cab. inside the lower part of the doors and on the rest of virtually every inside surface except the dash console (I'll remove and do the wall behind it) and the windows. Though I did read that acrylic is better at sound insulation than glass and I'm still planning on going that route. I'm putting dynamat under plates (like the PTO one) and the seats (which I'm replacing as well). Past that I'm planning on something on top of the dynamat, then probably a horse stall mat for the floor on top of that. I'll have to cut wells out for the pedals & my feet and will probably make plugs for some of the hatches on the floor.

I need to figure out where I'm going to mount some stuff in the cab before layer #2 because it'll go over the dynamat, but the next layer will wrap around them and I don't want to rip anything out.

I did read a thread about someone that went around his truck and used silicone washers everywhere a bolt touched metal, I'm not sure I want to go that far - maybe on some of the worst offenders (they know who they are!)

I'm still looking into what to get for the second layer of soundproofing, but I'm leaning towards something with a high STC rating using the logic that most NRC stuff has their best ratings with relatively high Hz readings and our engines are pretty low on that scale. I'm thinking something dense, like 2 lbs sq/ft. All told, I'll probably end up adding about 150 lbs to the cab for the soundproofing - I'll have the final numbers in a few weeks.

So, I've been reading up on sound insulation for the last several days and came across this thread in another forum that is a good summary of many things I've found out - a must read if you want to save hours on the internet and get some good info.

One thing to keep in mind, the person that wrote it makes some conclusions that make sense for their '97 Dodge Ram but don't necessarily matter as much to a deuce owner. For instance, adding weight isn't as big an issue also, the person on the thread is starting out at 85db, not 105db or more. While he makes the point that 25% coverage is your biggest bang for the buck, when you start much louder reducing an extra 10db by going to 100% coverage might be worth it to some.
 
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