Welcome to Sound Deadener Showdown

This site is about making vehicles quieter. That's a pretty big thing, but that's really all there is to it. If you're new to this, you are probably as confused and discouraged as I was in 2005 when the combination of buying a noisy car and the Internet promise of the cure, "sound Deadening" led me down a path that has apparently changed the course of my life :)

I found it confusing, at least. Unlike most people, I became obsessed with the idea. For years it was an all consuming hobby and then a business. I tried every recommended treatment on my car and every other vehicle I could get my hands on. I tested. I studied. I spoke to scientists, engineers and manufacturers.

You won't need to go that far. Reducing vehicle noise after manufacture is not a trivial task. Expect a full treatment to take between 2 and 4 full days. Even a couple of doors or a trunk aren't going to be done in an hour. You need to remove the interior of the vehicle. You need to treat it and put it back together. You don't want to do this twice and you don't want to be confused about what you are going to do once you remove the interior of your vehicle. Fortunately, the concepts and techniques are not complicated at all. It takes mostly time and patience but then you are done and enjoying the end result.

My goal is to take you from novice to confident installer and to find the straightest line between the two. Read through this page and the entries on the How To page and you'll understand the materials you'll need, which areas of the vehicle to treat and how to treat them. You'll also be able to build a materials list. There may even be a materials list I've built from measurements supplied by other customers. I'll explain why I use the materials I sell and why I think you should too.

Let me say it again: this is about making vehicles quieter inside the passenger compartment. I know that some car stereo enthusiasts come to this from a different perspective. I'd encourage them to jump to the Car Stereo Implications tab. I'll make the case that the single best thing one can do to improve musical fidelity in a moving vehicle is to make the vehicle quieter inside the passenger compartment. Everything is better with less noise. Conversation, music and thinking.

Noise Sources

Sometimes it's a single problem, like drone from an aftermarket exhaust. The more challenging projects are those vehicles for which NVH (noise, vibration, harshness) wasn't a priority, either for economy or to minimize weight for performance. In this case the vehicle's occupants are submerged in a cacophony of noises from multiple sources and directions.

Tires/Wheels

Tire noise is one of the most common problems we face and one of the most difficult to mitigate. Noise originates where the tire contacts the road and radiates out from there. That makes the entire underside of the vehicle a target.

It reflects off of adjacent vehicles and obstacles along the roadway and enters your vehicle through the doors and side panels. This is why your tire noise is so loud when you drive close to a wall.

The complexity of this noise sources requires treatment to most of the vehicle to be effective …

unless

… tire noise is the only noise you are concerned with. In that case, new tires might be the best option. Tire replacement may also be part of an overall treatment. Tires may get noisier with age and wear. Some tires are just much noisier than others, even when brand new. Tire Rack.com rates tire by noise levels. Not perfect, but pretty good. If you’re on the fence, see how the tires you’re running compare to other options.

Engine

Primarily enters through the lower firewall and front floor. Can also enter the vehicle through the front edges of the front doors and the center tunnel.

Exhaust

Another complex under vhicle noise that interacts with the environment.

Air Turbulence

Treating the roof and ouer door skins can help.

Traffic

Noise that originates from nearby vehicles or noise that orginates from your vehicle and reflects off of nearby vehcies.

Rain/Weather Impacts

I include this one because it's cool not to be startled by the sound of a sudden downpour hitting the roof. It's somehow really nice to have the loudest impact sound coming from the windshield.

How Quiet can we Make this Vehicle?

Hard to predict precisely. Far too many variables. It is generally true that the noisier a vehicle is and the less the manufacturer addressed noise issues, the bigger the improvement. Conversely, a luxury car will have very low noise levels to start with and most of the space we're counting on is already used.

I will guarantee that you your vehicle will not be silent. That's barely possible if you were designing the vehicle from scratch and there were no budgetary constraints. We have to work with the existing suspension, drive train and glass. Can't get to silence. It's a lot of steel, glass, rubber and composites rolling on a rough surface, propelled by exploding petroleum. You are going to put a lot of time and money into the project and somewhere along the line silence can become the target.

Just because it isn't silent doesn't mean it isn't drastically better. I consider a project a success if the vehicle is transformed from unpleasant to drive to pleasant to drive. That's a really big deal. If you can speak to a passenger without shouting, if your music sounds better and louder than ever before with the volume knob turned down from previous standard levels. If you can drive to work without getting a headache. All really big deals in my book.

The most interesting reactions by far are from people who parked their car and didn't drive it again until it was fully treated. It's harder to get the full impact when you've worked on the vehicle yourself since you adjust to the changing acoustics as you go. A really common reaction is for people to spend a lot of time listening to the sound of their own voices. They really can sound much different. It's also common to hear things that you couldn't hear before.

Reducing noise levels is always a good thing. What we are doing is re-engineering some luxury into the vehicle. There are all sorts of vehicles that have desirable characteristics - performance, economy, utility - but are just too noisy. Being able to influence noise levels with aftermarket treatments significantly lengthens the list of great vehicles.

 

Four Lines of Attack

  1. Control vehicle component - mostly panel - vibration and resonance.
  2. Block air borne sound.
  3. Decouple objects that would otherwise transmit vibration or make noise themselves by making intermittent contact (rattles).
  4. Absorb.

 

Control Vehicle Component - Mostly Panel - Vibration and Resonance

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We don't want things vibrating. Vibrating objects are broadcasting sound at their resonant frequency and rattling against other objects. Resonance provides free transport from one side of an obstacle to the other. We are concerned about the amplitude of the resonance, not it's frequency.

Picture a tuning fork. Tap it on something and it starts vibrating at its resonant frequency. Touch the times to the palm of your hand and it stops. We are trying to shorten the time it takes for the palm of your hand to damp the vibration, not trying to change the pitch of the tuning fork.

The difference between amplitude/decay and frequency is very important. Our only goal for this treatment step is resonance control.

Before

This is a 12 inch square of 22 gauge steel suspended by the top corner and struck in the center of the side facing away from the camera with a xylophone mallet. The piece on the left has no vibration damper applied and the piece on the right has a 6 inch square applied to the center (25% coverage). You can see the measurement microphone jutting in to the photos from the left. Play the two sound files and tell me there is any point in adding more vibration damper.

After

That's all you need.

The idea of using a limited quantity of vibration damper used to be controversial in the aftermarket. Actually, aftermarket automotive was the only place that ever embraced multiple layers of vibration damper over 100% of the area. You start to build a barrier when you pile up enough of anything. The problem is that even in multiple layers, vibration damper makes a poor barrier. It is directly coupled to the substrate  and isn't dense enough to add significant mass with a layer or two or four. Excessive use complicates body work. If a barrier made of vibration damper ever has to be removed from the vehicle, it will be destroyed in the process.

It's not vibration damper's fault that it is a poor barrier. It's our fault for trying to use it as one.

This gets back to the amplitude/decay versus resonant frequency question. Not only shouldn't we use vibration damper as a barrier, we shouldn't try to use it to add mass to drop the panel's resonant frequency below the audible range. This has been argued for years as justification for using roofing materials. The problem is that you really can't add enough mass to accomplish that frequency shift. You need to quadruple mass for every octave dropped. You'd end up with door panels that weighed hundreds of pounds.

It's not that these cheap alternatives won't work but in tests that I and others have done, it takes about 10 times as much material. More expensive, more work and more potential points of failure, before you consider the inferior adhesive characteristics.

This was the genesis of my CLD Tiles™. If we could study each vehicle panel we could probably control its resonance with enough vibration damper to cover 1/8 of the surface or less. Since we can't, we have to sort of scatter shot it. I use 24% coverage as my target. Sometimes I'll do a little more, some times less. My goal was to take maximum advantage of that 25%. The foil is thicker and the adhesive has been through OEM testing. Using the right amount of the highest quality vibration damper costs less than enough of a poorer quality product to approximate the same result. Why compromise? Put it in and forget about it for the life of the vehicle.

CLD Tile™ Specifications

Size 6" X 10" (152mm X 254mm)
Adhesive Butyl
Gross Thickness 2 mm (80 mils +- a few)
Foil Thickness 8 mils
Heat Tolerance 400°F+ for 8 hours+
Adhesion Immediate (1 in², 5 lbs. @ 90°) 34.36 seconds
Adhesion after 96 hours (1 in², 5 lbs. @ 90°) 153.02 seconds

Block Air Borne Sound

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You'd be forgiven for thinking that vibration damper was the most important treatment. It certainly gets most of the attention. Doesn't matter. It's the barrier layer that makes the most difference. I use mass loaded vinyl (MLV) for this. MLV is the answer to the question: "How inexpensively can we create a substitute for lead sheeting that will accomplish the same thing"?

Mass loaded vinyl is dense and limp - the ideal characteristics for a barrier. A material's resonant frequency is determined by its mass, stiffness and geometric. Low mass/high stiffness mean high resonant frequency. High mass and low stiffness mean a low resonant frequency. MLV and lead sheeting have resonant frequencies below the the audible range. Makes it an excellent barrier..

 

Build the Bubble

Single most important concept and the most important tool we have. Barriers work best when they form an unbroken shield between the noise sources and your ears. CLD Tiles are designed to work best with just 25% coverage. That isn't true for a barrier. For best results, you will want to completely line the floor, doors, quarter panels and trunk or cargo area for a hatchback, station wagon or van.

That's everything below the glass line. The glass will always be the weak link. That's why there's very little point in installing a barrier on the roof. It would only be effective for sound coming from directly overhead and there isn't much of that. Fortunately, most of the noise hitting a vehcile is coming at it from below.

Probably be better to think ofit as building the bottom 2/3 of a bubble. To the extent possible, you want a layer of mass loaded vinyl all over the that bottom 2/3

Now that you've got the image of the protective bubble in your mind, you need to decouple it from the vehicle. That usually means putting a layer of 1/8" cloased cell foam (CCF) between the MLV and athe vehicle, trim panel or other hard surface. May sometimes be a lyer of 3M Thinsulate™ Acoustic.

Build the bubble.

Sound Transmission Loss for 1 lb/ft² MLV

Frequency (Hz) 125 250 500 1000 2000 4000
Sound Transmission Loss 15 19 21 28 33 37

MLV Specifications

mass/area 1 lb/ft²
STC 27
Nominal Thickness .107 inch (2.7mm)
Tensile Strength (PSI) 762
Elongation 200%

MLV Comes in Many Grades

Any 1 lb/ft² flexible material is going to have similar performance as a barrier. Tensile strength and flexibility are worth considering but odor is the biggest concern. I've been trying to figure out why some MLV is very inconsistent between batches and why the only MLV that is consistent costs me more by the ton than most online sellers charge per square foot. I guess I've been doing this for long enough and am selling enough MLV to be considered "on the inside" by my manufacturer. Finally got an explanation that makes sense.

Most MLV is called "regrind". The vinyl component is made from recycled material. That may be a good thing for the environment but it makes it very difficult to control the exact characteristics of the finished MLV. A persistent odor, less flexibility and lower tensile strength apparently aren't deal breakers when the MLV is sealed inside the walls of a building. They are for me in a vehicle. The MLV I sell is made from virgin materials for consistency and quality.

At 1 lb/ft² it is heavy to ship. I'm on the East Cost. It crrently costs more than $100 dollars to ship a 135 ft² roll to California. It can be worth looking for a local source. Just be sure you can handle and smell the material before you buy it. Three customers have removed the MLV they bought somewhere else from their vehicles because of the smell.

 

Decouple Objects that Would Otherwise Transmit Vibration or Make Noise Themselves by Making Intermittent Contact (Rattles).

This is 1/8" vinyl nitrile closed cell foam. It's the best general purpose decoupler there is. Because it has vinyl content it can be tacked to the MLV using HH-66 Vinyl Contact Cement. Vinyl is difficult to bond to anything and this takes care of the problem.

 

Closed Cell Foam Specifications

Polymer Vinyl/Nitrile
Color Light Gray
ASTM-D-1056-67 & 68 Grade # SBE41
ASTM-D-1056-91 & 07 SAE J18-R7/92 2C1
Density (PCF Approx) 4
Compression Deflection @ 25% 2-5 PSI
Water absorb by Weight Max ASTM Method 5%
Elongation % Min 100
30 30
Tensile Strength Minimum 50 PSI
FMVSS No. 302 Flammability PASS
 
 

Tight, Fully Closed Cell Structure - Electron Microscope Image

We use closed cell foam as a decoupler because we don't want it to absorb moisture and odors and because we want resistance to compression. For these features to be active, each cell needs to be completely closed or sealed. It's like a bunch of grapes. If this is true, the CCF will be impervious to moisture beyond the surface layer. 

A Competitor's Closed Cell Foam

This would more accurately be called partially closed/partially open. Moisture can migrate deeper than the surface. Not saying this is a disaster, just that there is a difference and it's cool to have these images.

Closed Cell Foam Does Not Absorb or Block Sound

I know people say it does, but it doesn't. It's too light to block anything meaningful. It doesn't absorb sound well for the same reason it doesn't absorb moisture. Combine that with the thickness consideration in the next section and it just doesn't. CCF is a mechanical not an acoustical material. It's a gasket.

Absorb

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A material has to be 1/4 as thick as the wavelength of the frequency you want to absorb. Even if CCF were a good absorber, a 1/8"-1/4" layer would only absorb frequencies at or above the audible range. There are really 3 things preventing our using absorbers as the primary noise mitigation strategy:

  1. Insufficient space to install a layer of material thick enough to absorb lower frequencies.
  2. Absorbent materials usually need protection from the elements.
  3. Related to insufficient space, the absorber won't function well if compressed.

There are a few areas where an absorber can be used effectively. Between the roof and headliner, inside hollow trim panels and to fill voids, like empty quarter panels. I use 3M Thinsulate™ Acoustic for absorption. It's a very high quality absorbent material that won't hold moisture. 25mm (1 inch) thick and 30 inches wide. It has a charcoal colored fabric scrim on one side for protection. The fibers are hydrophobic. Moisture can pass through the space between the fibers but the fibers themselves won't absorb moisture, mildew or deteriorate.

3M Thinsulate™ Acoustic is an outstanding decoupler and an excellent thermal insulator. It's a great product that's finding increasing use in new vehicles.

Supporting Tools of Note

This is a coordinated system of products. A few of the pieces are determined by our use of a vinyl based barrier layer.

HH-66 Vinyl Contact Cement

HH-66 Vinyl Contact Cement connects CCF to MLV, MLV to MLV (critical), CCF to CCF – any two surfaces of materials with vinyl content. That’s why I have the CCF manufactured with vinyl as one of the polymer components. It’s also why the adhesive on the Velcro Strips I sell is optimized for adhesion to vinyl. When you get right down to it, we’re trying to line our vehicles with vinyl – a material to which very few things will stick :)

HH-66 is a contact adhesive that will only bond materials with vinyl content. That means MLV to MLV, CCF (like the material I sell with vinyl content) to CCF and MLV to CCF. You need to coat both surfaces and let them dry until just tacky, 3-5 minutes. Press the two parts together. The bond is more than strong enough to work with immediately. It will achieve its full strength after a few hours.In most cases you won't need to coat the entire surface - tacking in a few spots is usually sufficient.

 

Velcro® Strips

I'm really proud of this product. It is the result of rethinking the way we mount foam and barriers in our cars. It is my firm belief that the fewer permanent changes we make, short of compromising the project itself, the better off we are. Developing the CLD Tiles to produce optimal results with 25% coverage went a long way toward achieving this goal. These Velcro® Strips take the concept the rest of the way. Instead of gluing foam and barrier material directly to the sheet metal and making future maintenance much more difficult, you now have a strong and removable alternative that will even let you reuse the products you mount in your next car.

These aren't the same strips you can buy at a hardware store - they are a very special item that I've never seen anywhere else. The adhesive is much stronger and more heat resistant and is optimized for adhesion to vinyl and steel.

We sell two configurations. The first has adhesive on both sides and is ideal for mounting vinyl to steel. The second has adhesive on one side only. The PSA on one side only version are for very unusual applications.