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Discussion Starter · #1 ·
If anyone has further useful information please post it here. Please Do not bring arguments about which brand is best based on only you having used it once or twice. Only results showing db reductions, STC, or similar measured reductions of sound are wanted here.

Reason for this thread

I looked at soundproofing my truck because of the engine noise. I turned the radio off on almost a 2,000 mile trip because it was to loud in the cab for me to enjoy the music while driving down the road.

At idle my sound meter says I have 85 db sitting still. I am really only hearing the knock of the engine itself. Most often people spend a lot of time and money putting on the various sound deadeners over the entire inside of their trucks. After tearing out the interior they put the aluminum foil backed sticky stuff over almost every inch of the interior. Is that however the best approach?

Most of the information I found regarding soundproofing said brand A is better, no brand B is, then brand C is mentioned as being best... Then the arguments continue with nothing to back up any claims made. I still have seen very little to show that most automotive sound proofing material actually stops any sound. I keep hoping to find the scientific approach. This material has a STC of (insert number here) at 125 hz (diesels have low frequency sound) so I could compare and determine which material should work best for my use.

What frequencies do we need to be concerned with to quiet a diesel engine?
Low Frequency Noise Concerns
" The audible frequency range varies from about 20 Hz (hertz, or cycles per second) to about 20,000 Hz. An example of a low-frequency source is a large idling diesel engine, which can produce large amounts of low-frequency sound in the range from 20 Hz to 150 Hz. Low-frequency sounds (long wavelengths) tend to travel easily over long distances. Therefore, it is most efficient to control low-frequency noise at the source, although it may be difficult to obtain a satisfactory result."

This is why we have so much trouble quieting a diesel engine. It produces low frequency sounds. Because of their nature they are hard to block out. The same situations exists when you hear a car playing music way to loud. 1/2 mile away you only hear the bass because the higher frequency sounds naturally dissipate over that distance.

You will find that sound proofing materials get tested over several different frequencies. Some materials work best at those frequencies that will not affect the noise of our diesels enough to notice.

Why are the newer diesels quieter?

We have learned that the new diesels inject fuel 3 distinct times instead of once like our older trucks do. Those multiple injections produce lower emissions and less noise. There are other improvements we can add to our trucks to reduce the noise levels our trucks produce also.
<from Noise reduction effort update - Page 3 >

"The really quiet Mercedes diesels are the ones that intrigue me. I used to work for DaimlerChrylser before the 'Diamler Debacle' ended my career with them. I had the opportunity to speak with a couple of their engineers and ask how they made their diesel engines so quiet.

This is what I was told, I haven't been able to verify it all, but it makes sense:

Double wall valve covers, double wall exhaust manifold shields, and double wall exhaust pipes are used to a great extent. The injectors, injector lines, and injection pump is either buried or shielded wherever possible."

Look under the hood of the new trucks. There is a lot of soundproofing under the hoods today. You will even see soundproofing on the inner fenders. That has to be there to stop noise from getting into the cab instead of helping people outside of the truck who think it is to loud. If you can put enough soundproofing on, under, and around the engine and engine components including the turbo, injection pump, and exhaust pipe that will greatly reduce the noise coming into the cab from the engine.

Areas of our trucks producing or transmitting sound
A lot of sound comes through the windshield and other windows. Except for closing the windows and making sure the seals are intact there is nothing we can do to stop sound from these sources.
The back wall has nothing to block sound. If you have loud exhaust soundproofing the back wall is a good plan.
The floor will transmit sound especially from the exhaust sitting underneath it.
The firewall transmits engine sound quite nicely.
A lot of noise comes out of the valve cover.
The injection pump is just plain noisy.
A lot of sound comes through the doors.
The roof can be a culprit largely due to vibration when you have drone coming from stacks.
Tires can create a lot of noise depending on the tread pattern.
Wind and other road noise. This can be a result of worn out seals or mounts.
The exhaust can make a lot of noise especially when modified.
The oil pan on the cummins 5.9 in our trucks resonates like an empty 55 gallon oil drum.

One person used a DB meter and said the oil pan is the noisiest place on the engine. It is about 110 decibels at one foot!! Years ago the government Dept Of Labor said 1/2 hour a day was all that was allowed for exposure to that level of sound.

Exhaust pipe modification for quieter running From Lsfarms
"What I did for my downpipe is to take a length of 4" straight pipe and slit it lengthwise and open it up like a big 'C' then slip it over the straight sections of the down pipe, then tack-weld it in place such that there was an 1/8" gap between the inner pipe and the new outer 'skin'. Then I wrapped the whole thing with the fiberglass header-wrap. It seemed to help."

There are some heavy duty trucks that come factory with double walled exhaust pipe. Maybe this is a good sound solution most of us miss.

One person had the dreaded drone with one exhaust setup and eliminated it by changed the preload and hanger locations to stop the pipe from resonating and droning.

Clamp a piece of angle iron onto the straight pipe to change its weight and resonance to reduce and eliminate drone. Putting different lengths and weights may be required to find the sweet spot.

(from) TheDieselStop.Com Forums: Can I dampen my drone? Please!
"Do a search on "flex kits" and you may find your answer. My truck had a significant drone/resonance starting in the 1700 RPM range. After reading a couple of positive posts about installing a section of flexible exhaust I obtained a pre-made kit that consists of a 6" section of flex exhaust complete with the couplers and U bolts. I installed the kit last night and I am very pleased with the results. I cannot hear/feel the drone." (and) "The flex pipe eliminates about one third of the normal noise this truck makes" That makes sense as putting in a flexible pipe would change the resonance frequency of the exhaust system.

Another person glued lead sheet using liquid nails panel adhesive onto their roof. This was done because of drone using stacks. That helped the drone a lot. The roof can be a cause for excess noise in at least some cases.

Stock trucks are around 92-98 Db under load at 70 mph. (88-90db is where most say hearing damage starts) and this is more than enough to cause hearing damage over time.

Those folks who have drone at 2000-2200 rpm are in the 96-98 Db range. If you have to turn your radio way up to hear it on the highway, then turn the radio way down at a stop light the truck needs some sound proofing.

(Tire and road noise)
Obviously this has 2 solutions.
1. Put on quieter tires.
2. Soundproof the cab.
3. Use earplugs while driving. This is not really a proper solution but will help to prevent hearing damage.

The tires chosen can make a vehicle a lot quieter or noisier.

Product types (not brand names) to consider using

There are 3 ways to reduce sound through sound proofing

1 absorb = foams
2 change resonance = any panel stiffener (my imperfect terminology)
3 block sound = lead or mass loaded vinyl (transfers sound wave into heat)

When it comes to sound deadening there are typically three types of products used, mass loaders, FLDs, and CLDs.

(from here) peel and seal as sound deadning - Page 3 - Product Reviews - Post a review on a product you have first hand, personal experience with. - SMD Forum

Mass loaders are exactly what they sound like, they add mass to lower the resonance frequency of the panel. Asphalt based products typically fall into this category because they lack the viscoelastic properties that the butyl products do.

Mass loading was a popular technique in years past, but mass loading is EXTREMELY ineffective. Why? You need to apply approximately four times the weight of the panel to drop the panels resonance just one octave. I don't know about you, but I don't want 100 pound doors just to listen to my music clearly.

The other two types of products are CLDs (constrained layer dampers) and FLDs (free-layer dampers).

CLDs include Dynamat, Damplifier, Audio Wrap, SDS Tiles, etc.
Simply put, CLDs convert the vibrational energy into low level negligible heat. The reason P&S ISN'T an effective or efficient CLD is the fact it doesn't have a thick enough constraining layer (foil) to do any good.

FLDs include products like Spectrum, LizardSkin, Cascade VB-1X, etc. There are FLDs that are not liquid, but these are the most common ones in our field.
The way FLDs work is that vibrational energy is dissipated as a result of extension and compression of the damping material, vs. a cld where the energy is lost through shear deformation of the material.

Typically speaking CLDs have the upper hand over FLDs because of their ability to maintain a higher loss factor across a wider range of frequencies, temperatures, and thicknesses of the substrate. Basically they are more efficient at controlling vibrations. This is especially true when applications require a light weight solution. For instance on a substrate of say 1/8", a cld mat of only 1/16" may be required to control the vibrations. The FLD on the other hand may require three or four times the thickness, so 3/16 to 1/4", to achieve the same loss factor.

P&S simply lacks the properties that would make in an effective vibration control product. It's not heavy enough to make a difference (unless you slap on 50+ pounds of the stuff). It doesn't have a thick enough constraining layer to withstand the shear strain of panel flex. It has a poor adhesive (typically consisting of asphalt, bitumen, petroleum distillates, and/or low grade rubber).

I've said it once and I'll say it again, DO NOT USE PEEL AND SEAL!

(from here) :: View topic - Sound deadening comparison video: Read this thread. It has a lot of useful information beyond what is quoted below.

"There are three categories of sound deadening/vibration control products out there, and unfortunately most people don't know the difference.

First you have mass loaders. This is old technology and is fairly ineffective at reducing vibrational energy and resonance.

These products are typically constructed from asphalt or asphalt and rubberized compounds and weigh a significant amount.

They work by adding mass to the panel to lower the panels resonance frequency. Only issue is that you have to quadruple the weight of the panel to drop one octave. A skin of a door weighing three pounds would need nine pounds of material added to it to see a reduction of only one octave. So by the time you achieve a noticeable reduction in sound, you would have 70-80 pound doors.

Then you have CLD (constrained layer dampers). These products are lighter weight and sport a butyl based adhesive, no asphalt. They should have a fairly thick constraint layer (typically an aluminum one) as the correlation between the thickness of the aluminum layer and the effectiveness of the product go hand in hand. These products work by converting the vibrational energy into low level negligible heat.

And finally you have FLDs (free-layer dampers), or extensional dampers. These would include most liquid vibration products and a few self sticking mat products. The way they work is that vibrational energy is dissipated as a result of extension and compression of the damping material, vs. a cld where the energy is lost through shear deformation of the material.

Typically speaking CLDs have the upper hand over FLDs because of their ability to maintain a higher loss factor across a wider range of frequencies, temperatures, and thicknesses of the substrate. Basically they are more efficient at controlling vibrations. This is especially true when applications require a light weight solution. For instance on a substrate of say 1/8", a cld mat of only 1/16" may be required to control the vibrations. The FLD on the other hand may require three or four times the thickness, so 3/16 to 1/4", to achieve the same loss factor.

Once a panel is sufficiently 'dead' by using a CLD or FLD product, other means of blocking and absorbing sounds are needed.

CCF (closed cell foam) rarely, if ever, adds much of anything to providing a quieter ride. It's best used as a decoupler to 'float' a MLV layer above the surface or as a gasketing material to prevent rattles and squeaks. So anyone who suggests you use CCF to increase your sound deadening results is just trying to get more $$$ from you."

Peel and stick dampers are designed to control and reduce vibrations, not block sound. These products are just too thin and lightweight to block sound.

MLV (and thin lead) on the other is designed to block sound because of it's thickness and mass. Average noise loss when using a 1 pound per square foot MLV is around 25 dBs (across a wide range of frequencies). So the addition of a MLV over a vibration mat would just further decrease the noise level inside the vehicle, creating a much more pleasant listening environment. And remember, MLV has been used in the building industry for years as a barrier without a foam decoupler. Sandwiched between the 2x4s and sheetrock MLV creates an amazing sound barrier between rooms, great for isolating media/theater rooms and even apartments.

As stated several times in the industry, 25% coverage is pretty much all that is needed to sufficiently control vibrations. Upping that to 50% coverage may only increase the results a decibel or two, probably not enough for most anyone to notice.

How to apply sound deadening products for best results

Read this thread. It appears to cover almost everything you wish to know about applying soundproofing. Sound Deadening 101 - Diesel Place : Chevrolet and GMC Diesel Truck Forums

Firewall and sound deadening material - Page 2 - Ford Powerstroke Diesel Forum
" I am an acoustical engineer (certified) B.S.E.E. San Diego State, and MECP (Mobile electronics certification Program) Master installation technician. And many of you have it all wrong?!?! Dyna mat and such (asphalt base dampening materials) are not for blocking sound from entering the cab although they will "if there is 100% coverage" it is too cost prohibitive considering the much better and much less costly alternatives! the dyno-mat and such was designed to be used as a material to stop the "RINGING AFFECT" of the metal sheet itself (Known as resonant frequency dampening) and should be used in center of flatter areas at or larger than a square ft or so in patches of around 4" ( Must be applied to clean dry surface and heated to get good adhesion) Test application, example thump the area of sheet metal firewall etc w/finger nail and you will hear a tink then again after application and you will hear a thud!!! patches should be placed evenly on inside and motor side of firewall to cover and eliminate higher pitched "Noise" then a shredded treated automotive insulation should be used to dampen lower frequencies usually in 1/2 in thick (looks like a carpet pad made of shredded multiple colored string "available usually at HOME DEPOT 5 ft wide and by the linear ft! C H E A P ! " attach pad w/spray glue "3M heavy duty or equiv." use this inside cab only as it will absorb and retain moisture as high and as full of coverage as you can on firewall and I also recommend another layer under the whole cab carpet "If you have a floor shift insulate with this here too as well as possible this treatment will make your truck sound like a lexus on hwy!!!!!!! OK not, but you should be able to reduce internal noise w/windows closed by at least 10 - 25 decibels = MAJOR IMPROVEMENT!!! "

Is there a big difference from dynomat to something like peel n' seal? - Page 3 - Car Audio Classifieds
there are a few tutorials out there for proper placement of sound deadening but it's really not all that necessary if you follow two simple rules.
1. Only 25% of a panel needs to be treated. So a door that measures 6 sq. ft. should theoretically need no more than 1.5 sq. ft. of actual sound deadener (not Peel & Seal).
2. Placement of the material should be in the center most of the panel. No need to treat reinforced or welded areas, just the flattest areas of panels need it. Now why only 25% coverage you may ask? That tends to be the best bang for your buck in terms of achieving great results.

For instance, 50% panel coverage will typically increase the sound lose 2-3 decibels over 25% coverage. And 100% coverage will net another 2-3 decibels over 50% coverage. So the overall sound loss difference between 25% coverage and 100% coverage is typically 4-6 decibels. Quite often it's less than that.

Also when you just go all out and go 100% coverage, you (the typical person) tend to cover up and treat areas that do not need it, thus wasting product, time, and most importantly... money.

(That means there is some benefit to complete coverage but may not be worth spending that much more money.)


Once I read that someone put something over the engine oil pan and valve covers with the result of greatly reduced the engine noise it made sense to me. I talked to a diesel injection pump rebuilder. I was told just the p-7100 injection pump alone sounds like a diesel truck running when it is being tested on the bench. To me that means put sound insulation around the injection pump also. If the injection pump is so loud other parts of the engine could also be noisy and need quieting down.

This is one website showing a product they sell that they claim kills off a lot of engine noise. It is a very expensive approach. I am sure something similar could be made at home.

Here is a report by a person who bought and installed that kit.
Installed ATP Wap Noise reduction kit - Dodge Diesel - Diesel Truck Resource Forums
"Tim used a db meter to check the sound, with the kit intalled he said it read 59db at idle." Although I am not sure where the db meter was placed that is a huge reduction in sound from what I have now at 85db in the cab.

These 2 threads are long. Look at the sound reduction from making a lead liner around the oil pan. Also, notice that the first pan cover fell off while driving down the interstate. A better mounting system was needed and used the second time.

Noise reduction effort update (and)
Noise Reduction
Pay attention to Lsfarm's replies.
"I got 2 sheets of lead put in and the cab is back in order.
The sound test came in at +- 2-1/2 db less than before on the low end and hardly any change at the top end of the frequency scale. The tester said that is a 75% drop in noise and according to him most of the noise drop is in the lower levels area."

"I covered the oil pan, and changed the sound of a screwdriver tapping on the side of the pan from a "ting, ting" sound to a "thunk, thunk" sound.

The unprotected pan radiated sound at 102dB!! With the layer of lead, it radiated at 92-93dB. then I put my pan blanket back on and the pan now reads 90dB. All these readings in my shop on a concrete floor.

Wheelwell readings went from 96-98 db down to 87-89dB."

"Open your hood, and look between the fender and the hood hinge down inside just ahead of the door hinges. There is a thin 1/4" foam 'seal' just ahead of the door hinges. I added a layer of the 'superfoam' from GSI over the top of the factory piece. There is a lot of noise coming into the cab from this area."

"I had chimed in earlier when I had covered the firewall and cowl area. At that point, I had a baseline noise reading of 84 to 86 dbA on the center console between seats. The firewall work brought noise down to 81 or so at my baseline freeway speed of 82 mph. I completed seat removal and followed Greg's experience and covered all the areas outlined in his threads. The results are too amazing to have not done this a long time ago. I now have readings of 74 to 75 dbA which is more than 10 points lower than at the start. My main culprit was reflected engine and road noise. I now hear the engine sound as it should be but no overwhelming other noises. The truck is now much more pleasant to drive and I'm sure will result in less fatigue on the long hauls."

"I found the area around the steering column to be a big transmitter of noise. There is an aluminum casting supporting the steering column on the inside of the cab, and bare metal on the engine side of the casting, so there is nothing insulating this area so it picks up and radiates all the noise from the engine right into your lap.

I just cut pieces of foam to fit around the braces and brackets, cut slots in the foam to go around wiring. A bit of trim adhesive will hold the foam in place.

Use some foam around the floor shift if you have one. The floor of the cab radiates a lot of road and exhaust pipe noise.

Some panel deadener on the floor was effective in my truck"

One person laid some lead sheet across the entire firewall and across the top piece that the top of the dash screws into. Doing the firewall made a big difference even with the rest of the truck already done.

If after putting some sound barriers over the oil pan, valve covers, and injection pump there is still more noise than you want I would put soundproofing material on both sides of the firewall and on the inner fenders. Look at your under hood firewall insulation. Some later trucks have a panel that comes all the way up to the hood. Also, later trucks had an insulator that more or less covers the bell housing and transmission. Go to a dealership. Look under the hood of the new trucks. There is a lot of soundproofing under the hoods today. Add the same kind of sound proofing to an old truck and you should get some sound reduction.

It may be true that soundproofing the cab is mostly a waste of time for most who do not have drone. Maybe soundproofing the engine is where the effort and money should be concentrated. After all, most of us are not looking at a super expensive sound system trying to eliminate panel rattle. We are not trying to kill off most of the road and wind noise. We are trying to silence the mighty cummins engine noise for a more comfortable ride.
The noise reduction measurement of Lizard Skin applied to valve covers looks like a 1-2 dB difference.

A comparison video
Here is a long video showing several different brands of soundproofing subjected to heat. If whatever you buy slides down and then off the panel it is not what you want in your vehicles.

9,320 Posts
Discussion Starter · #2 ·
Noise invades an automobile passenger cabin through one of two paths (from

"The physics of sound and vibration inside a vehicle isn’t that hard to understand. The two main components of cab noise are airborne, noise or vehicle-structure noise.

Airborne noise is noise from wheel vibrations on the road surface, wind noise, engine noise, transmission noise or exhaust system noise that makes its way through panel joints in the passenger cabin to the driver’s ears. Sealing any gaps, and installing or adding another layer insulation, is much like adding a double pane window to your home, it’s quieter.

Structure borne noise is produce by direct vibration of an unsupported, thin metal panel due to engine, transmission, or wheel movement. Both types of noise can be lessened with aftermarket sound-dampening materials."

What sound proofing will not do
"Before any acoustic treatment can have a major impact on the passenger environment, the vehicle’s body panels must be aligned and sealed and suspension mechanics must be in tip-top-shape. A noise leak is a hole (or gap between body panels) which offers little or no resistance to the flow of air-borne noise from entering the passenger cabin. Air gaps can be found in such places as:

Excessive holes in the body structure.
Poor or incomplete welds where body and floor panels come together.
Inadequate sealing of metal joints such as mechanical access panels.
Misalignment of doors, vent panels, the hood and trunk.
Poor fitting grommets and boots for bringing cables, pedals, steering column and shift levers into the vehicle’s interior.
Inadequate sealing of weather strips around doors, windows and the hood and truck."

Just remove the shifter boot to see how much louder any stickshift gets. Then try adding some foam inside the boot. It may even get quieter. The same principle applies to all gaps allowing extra noise into the cab. An even easier method to show how easy noise can come though an opening is to open the door with that cummins running. That will bring more noise into the cab.

Using lead for soundproofing
24 pages in this free download show how to use lead for sound control. Read this even if you will use other materials. It shows a lot about sound transmission.
Lead blocks sound 2 ways. Leads inherent limpness clips the bottom from low frequency noises. That is the most important one for diesel owners. Read the file to see what the other way is.

Avoid rigid fastening of lead to stiffer panels (like the back wall) to maximize leads limpness. Use visco-elastic adhesives when bonding lead. 2 single sheets of lead separated are more effective for soundproofing than one sheet double the thickness is. Using the wrong adhesive can reduce sound dampening.
The quietest engine I've ever heard run was a big Cummins in a semi truck. Don't remember all the details but the truck was what Spicer used to test and evaluate transmissions. It had several mufflers and ran the exhaust out the very back, but the most impressive thing was the entire engine was wrapped, more like plastered, in lead sheet. Even the rear axle was wrapped up in lead sheet, and I think the mufflers too. It was at the Auburn ATHS show a few years ago just sitting there idling, and until someone said it was running you wouldn't have guessed it. Lead sheet all over the engine would be heavy, a nightmare to service, and probably adversely affect cooling, but sure makes for a quiet engine.

Other thoughts
A few pinholes in a wall can allow 30% of the sound to pass. Seal those gaps, leaks, and holes!

The 1st gen trucks have a second layer of metal on the inside of the oil pan. That is for vibration dampening and sound reduction. The SAE paper from the Cummins/Dodge development team mentions it. It's also about an inch shallower than a 2nd gen pan. Apparently dodge got cheap in 1994 and provided us with much louder engine oil pans. I saw where one person put a thick heavy piece of steel on the bottom of their oil pan. They claimed it cut down on the noise. Unfortunately I can not find that link.

Address voids, Get an extra set of seals from the front cowl/hood and use it to block sound from engine compartment.

Maybe you were thinking about using peel and seal for some cheap soundproofing for your truck. Depending on who you listen to either is a great or horrible stuff. Some say it is smelly and leaks goo while others say it does not. Ignoring that point lets look to see just how well it works as a sound deadener. A real scientific test was done in the link below. This also included other name brand soundproofing products that are used to deaden a panel.
Another Peel & Seal thread... but not what you think - Second Skin Sound Deadening and Automotive Insulation! - SMD Forum

If you were interested in using lizard skin for sound deadening but the price seemed to expensive read this thread. It shows a much cheaper possibility.
alternative to Lizard Skin - Hot Rod Forum : Hotrodders Bulletin Board

And consider this advice. "Most significant differences would be the ones that are thermal blocking products. These typically have ceramics or glass beads added instead to them. This increases their ability to withstand higher temps, absorb, block and dissipate the heat, but reduces their ability to control vibrations." That means make sure the suggestion above uses the right additive.

Where Ford added sound insulation.
I know, we all have dodges. But consider that ford also wanted to quiet down their diesels. They obviously placed sound barriers in places that would also work in our trucks. We can follow their pattern of soundproofing placement in our dodge trucks. The ford pieces probably would not fit our trucks.
A few "off the shelf" sound insulation barriers can be purchased from the local Ford dealer. These parts were initially developed for the Excursion (circa 2000 or so) when it was introduced, but are now standard equipment in all diesel equipped F-Superduties, except for the wheel well shielding. They are as follows:
Driver's Side Firewall insulator
Upper Cowl insulator (usually missed by most who soundproof their trucks)
Wheel Well shield
Transmission Tunnel insulator

Ford owners came up with an interesting quieting method. They fix their door seals cheaply. It does not require new seals to be purchased. The ford guys put tubing inside their door seals. I read this would not work on the extended cabs because they had solid pieces in the inner channel. It did work for the regular cab trucks. This may or may not work on a dodge truck or your other vehicles.

Here is a write up on the idea.
Here is a video showing how it is done.

Minor Flanking Paths (of sound around where it should be stopped)
"How many times have you been able to listen to a conversation going on in another room by sticking your ear by the air vent? Standard ductwork is metal, and therefore very conductive. Ductwork can therefore accommodate airborne sound as well as conduct vibration through the duct itself.
Some things you can do to help reduce the effect of the ducts. (This refers to houses, but wait, the ideas can apply to our trucks with some minor modification.)
"Line the rigid ducts with a 1″ compressed duct liner. Generally available through any Heating & Air Conditioning (HVAC) distributor. Duct liner is available in sheets and rolls. Add as much as you can install by reaching in. If possible, replace the rigid ducts with flex duct. This round, flexible duct is soft and absorptive, and therefore not conductive at all. Introduce bends and s-shapes with the flex duct. Don’t simply make a straight line. The curves encourage the airborne sound wave to bounce up against the absorptive lining of the flex duct, thereby reducing the noise."

Here is how I would make that work for our trucks. Inside the cowl we have a plenum that diverts air into the cab. The windshield wiper assembly sits inside. It also can allow more sound into the cab especially if you use the airbox mod that puts an intake hose into that area. We could look for a waterproof material to put inside that chamber. Maybe mass loaded vinyl would work, maybe not. I am sure lead would go in that area. Being perhaps a bit nervous I would paint the top of the lead to encapsulate it. It would also be possible to make some bends in the lead (maybe a second piece glued in) to make acoustic chambers to catch more sound waves. Just be sure that no water will be held causing rust. That means make a smooth bottom without wrinkles and no gaps especially on the top or sides. This may require some soldering.

Useful links explaining more about loud sound.
STC ratings and what they mean.
As common as this measurement is, it is quite limited and should not be totally relied upon for real world soundproofing expectations.

This is a big paper on environmental noise.
NPC Resources: Environmental Noise Booklet from Bruer & Kjaer

This talks about protecting your hearing and how important that is.
Safety and Health Topics | Occupational Noise Exposure

Decibel (Loudness) Comparison Chart
Decibel (Loudness) Comparison Chart

This is a link to download a free EPA manual showing how to reduce noise in the home. It is only 117 pages long.

This link talks about concrete floors and how they transmit noise. There are also explanations and pictures showing how sound travels where it is not wanted and how to stop it. That information can apply to our trucks as well as homes.
Soundproofing Articles and Library Archive

This link talks about cutting sound levels down on big trucks.
E-A-R Specialty Composites

This is a link to a website selling really expensive soundproofing for aircraft. This page offers a free aircraft insulating guide.

If you want to get really technical read this. I got lost before I finished it.
Engineering Acoustics/Sound Absorbing Structures and Materials - Wikibooks, open books for an open world

Useful links about soundproofing.

The Definitive Sound-Deadening Thread!!! - Maxima Forums

This may or may not be of value. It has some options to consider.
(All Years) Sound Deadening Alternatives - Subaru Forester Owners Forum

This shows how soundproofing around your steering column can make a big difference.
Super Duty Sound Deadening - Colorado Diesel Truck Club

Sound Deadener install w/pics in a Diesel - Wow!!

Sound Deadening 101 - Diesel Place : Chevrolet and GMC Diesel Truck Forums

I saw EZ Cool Automotive Insulation heat barrier and noise reduction\ had a different kind of sound insulation compared to most. That is just low-e (brand) insulation. You may find a low-e dealer closer to you and get a better deal. This shows an install with results. citroen cx insulation The product works fantastic as a heat blocker. However, after covering everything possible with 2 layers they only had a 4db reduction. That is an improvement but perhaps not as much as could be hoped for.

This shows using actual lead being used for sound reduction if you read several pages
Noise Reduction

Make your own lead foam sandwich.
TheDieselStop.Com Forums: Sound proofing and Sound Barriers
a) I made 108 ft^2 of soundproofing mat by sandwiching:
- "8 pound" carpet underlay,
- 1 pound per ft^2 lead sheet,
- "8 pound" carpet underlay and
- 3 mil vapour barrier.
I used contact cement to hold everything together. (1 US Gallon will make more than 108 ft^2.) The soundproofing mat is about 5/8" thick, which is about the maximum you can have and still get everything together." (continue reading on the link above for more installation details)

Sound Deadening 101 - Diesel Place : Chevrolet and GMC Diesel Truck Forums

I am searching like many others trying to find the best and most cost effective solutions to quiet my truck down. I have posted what I found after a lot of searching. Some ideas above may be imperfect. I purposefully tried to avoid getting into a brand discussion. I figure once you know what to look for you can compare products on your own in a much more informed way.

A lot of the links above are not even related to diesel engines. Of those that are are almost all articles are about a different brand of diesel. However, the general ideas of truck and automotive soundproofing apply regardless of the make and model involved.

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If you google there is a company that makes sound proofing that snaps on various parts of the engine for sound reduction.
They say the most important place to insulate is the injection pump, I believe them.

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Discussion Starter · #4 ·
I found this The ‘Quiet Kit’ for the Dodge Ram with Cummins Turbo Diesel and included a link to it above. ATP makes this engine "quiet kit". They do not have an injection pump cover although it covers almost everything else. The entire kit is expensive. It is around the cost of a rebuilt injection pump.

However, they claim (and a thread shown above agrees) that this can cut the sound from 95 db down to 60db. Without buying the oil pan cover it could be 70 db.
There is a review here from a 2001 dodge truck.

There may be another company making another quieting kit for our cummins engines, I did not find it. I am sure a homemade approach could come up with good sound reduction results even if not quite as good as the professionally made and designed kit does.

Art (on this site) was nice enough to mention he had seen medium duty applications of the 6BT with a noise damper installed over the oil pan. "The original application was a medium duty Ford cab-over-engine truck. I don't know if the damper was Ford or Cummins. Those trucks used a front-sump pan that has a slightly different profile. Maybe a helpful Cummins parts guy could help. Try CPL 1527 as well as 1550." Perhaps a big truck junkyard could help find a cheaper alternative. The question remains as to whether or not those noise dampers would fit our dodge trucks.

The reason I started this thread was most threads just talk about what brand of sound deadener is best. Those threads did not cover which type to use, where to use it, or why it should be applied where it was installed. Trying to find out what actually works to sound proof our trucks is very difficult.

Most threads also just talk about quieting the cab and not the engine. I thought if I put all of this together it could help those who wanted to approach sound reduction in a more informed way. Besides, now I can find all of this easily when I need it. I do not claim to have all of the answers. I spent a lot of hours searching for information and this was the best information I could find. Hopefully it will help others to understand how to approach this silencing job in a smarter way.

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Sound deadener is my best spent money in the truck. I need to still do the doors. Good little write up. :thumbsup:

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Im gona do the inside of the cab on my truck, headliner, doors, floor, firewall and back wall. But i love the sound of my rattlin 12v on the outside!

Now on to read the book you have published above!

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Thanks for putting in the time it took to put that post together! That's a lot of research and reading all in one spot.

I've been thinking about putting some type of sound deadener in my truck and this helps a bunch!
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