Panel Resonance and Controlling Resonance via CLD (Constrained Layer Damper)

Personal Preface and Experience:
As this product probably has the highest saturation of any sound treatment product on the market, it is often highly contested and acutely discussed. This leads to several marketing claims pushing you one way or the other, it is easy to feel like you are buying a premium product when most of the time, you aren’t. More than half the CLD or CLD/Foam combo products are made out of the same build houses with the same sub par ingredients. Personally, I have used 4 different brands in my time so far: Killmat 80mil, Soundskins Pro, Dynamat Extreme and Resonix CLD. Having been able to peel the 3 former products off with my thumbs months after install and being able to tear them with my hands, I have a hard time to not recommend Resonix here. It sticks to ANYTHING (this is a compliment and a warning) and makes an immediate impact. In my build, the use of CLD in both front doors and the roof have has substantial impacts on my system.

CLD Key Notes:

• CLD is only for lowering structure-borne vibration, aka resonance.
• It does not block road noise. While it does help lower the overall noise floor by reducing structure-borne vibration, you should use a noise barrier for blocking outside noise, or a sound absorber for absorbing outside noise.
• Most likely will not lower panel-on-panel vibration if used alone. This is different than structure-borne vibration, aka resonance (see decoupling below).
• Using multiple layers is a waste of time and money. Just use one layer of the best product you can get your hands on.
• Many smaller pieces of CLD are not as effective as a single piece of CLD with a similar overall size. Our typical smallest size piece we bother with (for resonance damping purposes) is at least 8 square inches. Small pieces are only used by us to prevent small panels and clips from buzzing.
• Roofing products from big box stores are not a suitable solution and do not work at all.
• Using more of a cheaper product may cost more and takes more time and effort to achieve X results, and many times will still not yield the same result of a better product that is carefully and properly installed.
• Beware of products that come in rolls or as a folded mat. Bending the material compromises the viscoelastic properties of the butyl layer and lowers its performance.

What is a Constrained Layer Damper sound deadener? How does it work?

Constrained Layer Dampers, such as ResoNix CLD Squares, ResoNix Heavy Duty CLD Squares, and ResoNix Lite CLD Rectangles, which many technical hobbyists will refer to as “CLD,” and the general hobbyists and many ill-informed installers and salesmen refer to as “sound deadener,” is the most common product used to sound treat a vehicle. A CLD features two layers; a visco-elastic (fluid to a degree yet stretchy/snappy like elastic) butyl rubber layer and an aluminum constraining layer on top. Typical CLD’s use a backing paper and are peel-and-stick for their application.

How a Constrained Layer Damper works is for the most part, pretty simple. When the panel it is adhered to bends and flexes, and subsequently, so does the CLD. The aluminum constraining layer provides a stiff reference across the top surface of the visco-elastic butyl. The differences between the panel the CLD is adhered to and the top aluminum constraining layer causes the butyl to stretch, resist, and want to snap back into position. The shear forces generated by the viscoelastic butyl is what “Constrains” the panel to prevent flexing. This process converts the mechanical energy of the panel into minuscule amounts of heat. This conversation of energy is the reduction of resonance that we are looking for.

The stiffer the aluminum constraining layer, the more of a “hold” it has on the butyl. The better the butyl formula, the better it constrains the panel against the aluminum constraining layer. The goal when installing this product onto a panel is it will ideally go from sounding like a hollow drum when knocking on it to sounding something like a wooden table top.

Again, the point of a CLD is to lower the resonance of the panel or surface it is adhered to. It does this by using the natural shear resistance of the visco-elastic butyl stretching and wanting to snap back into place. Note how I said it “lowers resonance”, not “lowers the panels resonant frequency”. They are two different things, and a proper Constrained Layer Damper works by damping the resonance, not by lowering its resonance frequency, although the latter is usually a side effect of the added mass of the CLD on the panel. See Figure 1 below.

Here’s a very in-depth explanation of the Resonix CLD products that help give you some insight of the parts and pieces that go into CLD, some industry insights and will provide some good tips and tricks for usage and application.

When and where do we use Constrained Layer Dampers?

These products are typically the first to consider, and the first to apply before any other type of sound treatment product, and they are installed directly onto metal and plastic panels of a vehicle (and even in industrial, commercial, and residential applications). These panels typically include but are not limited to the doors, trunk lid, floor, quarter panels, floor, firewall, pillars, wheel wells, fender liners, rear deck, roof, various interior trim panels, etc.

Why do we use Constrained Layer Damper Sound Deadener?

Why is this product type an important and arguably the most essential step in the process? I’ll break it down in two ways. Car audio installations first, and regular driving installations after.

Constrained Layer Damper Use In Car Audio:

In car audio, we add larger, more powerful speakers with a lot of power being applied to them to the vehicle. With these more powerful speakers, there is a lot more acoustic energy being introduced into the cabin of the vehicle. Notable areas for this would be in the doors and the trunk area. The doors are usually the worst offender, so let’s focus on those for the example. When you have a speaker mounted to a door, the front wave of that speaker, when installed correctly, is only partially radiated directly forward through the door panel grille and into the cabin. The rest of that front wave doesn’t make it out of that door grille due to the speakers’ dispersion pattern, and that energy must go somewhere.

This acoustic energy will end up between the door panel and the inner door skin, and that acoustic energy will transfer into both the door panel and inner skin and be converted into mechanical energy. That mechanical energy does two things. First, it will rattle the hell out of your door. I don’t think I need to tell you why this is undesirable. And second, it will cause resonance. Resonance will be heard as distortion and will cause the system to sound muddy and lack dynamics and impact. Applying a constrained layer damper to the door panel and inner door skin will constrain those panels, and the mechanical energy of the panels moving will then be absorbed and converted into minuscule amounts of heat by the CLD. It’s a pretty simple concept. Another reminder, while they do add mass, which will help lower the resonant frequency of the panel, mass-loading is NOT the main reason why or how a CLD works. Constraining the panel and converting mechanical energy into heat, therefore lowering resonance is how they work.

Constrained Layer Damper Use To Lower Noise While Driving:

Now, how will a Constrained Layer Damper help with lowering the noise heard inside of a vehicle in everyday driving? Simple. It’s the same concept. When driving, wind/turbulence, and mechanical energy transferred from the tires/suspension will cause the same panels mentioned before to move, vibrate, and resonate. This will be heard as resonance, drone, and general automotive “noise.” Think of the panel acting like it’s a speaker cone, moving in and out to convert mechanical energy (movement) into acoustical energy. Applying a Constrained Layer Damper to these resonating panels will prevent that resonance and lower the overall noise floor that is being generated by the cars body itself while driving.

How Much CLD Should I Use?

Now, something to note. Every vehicle is different, and every vehicle will behave differently. Each vehicle and each individuals end goal will require a different amount of CLD and sometimes a different approach to the overall game plan of applying a CLD. This can come down to the locations it’s placed, how much is needed in certain areas, etc. I find that economy cars benefit more from these products than rugged premium and luxury cars. When we work on something like a Toyota or Honda, there is a more noticeable difference when applying a CLD vs. applying CLD to, say, a Mercedes. This is because these higher-end vehicles have much more robust and sturdier parts. That said, I have yet to find a vehicle that I have worked on that wouldn’t benefit from having CLD applied, even considering diminishing returns and time spent on the project. This goes from 80’s Toyotas, all the way up to modern Rolls Royce models. Every vehicle can benefit from a Constrained Layer Damper.

Instructions and Examples for Using Constrained Layer Dampers:

Constrained Layer Dampers can be applied to metal, plastic, wood, etc. Please make sure the substrate you are applying it to is clean and free of dirt, oil, and grease. I prefer to use isopropyl alcohol to clean panels before application.

Do not heat the Constrained Layer Damper. Too much heat can damage the butyl layer and cause performance and reliability loss. My rule of thumb to customers with this is if it is too cold to work with, it’s too cold for you to work on your car. Go inside and make yourself some hot chocolate, preferably with marshmallows.

Another thing to note is that a single, continuous large piece of CLD will be much more effective than multiple smaller pieces that take up the same size. My personal rule of thumb is if the piece of CLD is going to be less than, say, 6 square inches, don’t bother unless you are using it to help with something such as a smaller rattle of an attached mechanism, trim, etc. Applying a smaller piece to a much larger panel wastes time, effort, and product.

One more thing about Constrained Layer Dampers, they do NOT block noise. That is right. Nearly EVERY other sound deadener company will claim this about their CLD product, and many hobbyist forms will say this, but it is just not true. A good Constrained Layer Damper Sound Deadener can most definitely lower the noise floor of a vehicle since it will reduce the amount of noise generated by the resonance of panels, but it will NOT block outside noise from entering the vehicle. Any company claiming this about their product is lying to you. Why it doesn’t block noise is simple. Noise from the outside of the car is transferred through the body of the car, and again radiated out as the same sound. All it is is energy transfer through molecules. The CLD being coupled to these panels will just transfer the energy as well. While it will technically lower the transfer, it won’t be by anything measurable. This is a totally separate behavior that has nothing to do with the CLD constraining the panel it is adhered to in order to reduce mechanical resonance.

When applying, make sure you roll it down after sticking it on. You do not need, nor want to press down very hard. Just enough to ensure the whole piece has contact with the panel on a relatively microscopic level is fine. Using too much force can deform the butyl and stretch/weaken the aluminum which will cause performance loss. That brings me to another point: flat pieces that haven’t been rolled, creased, deformed, etc., will have noticeably better performance than their deformed, beaten, and mangled counterparts. This performance drop also goes for products that already come in rolls. CLD products are manufactured in flat sheets. Rolling them up reduces their performance through the deformation, therefore degradation, of the butyl and aluminum layers before their product even leaves their warehouse. The very same goes for products that come in stamped patterns. These patterns act as a relief cut of sorts which allows the product to flex with the panel more freely. ResoNix CLD Squares is our original CLD product, and to date, they have not only tested independently as the highest performing product on the market, but the overall best value available as well. *That was until our ResoNix Heavy Duty CLD Squares came out.

Watch this video (0:00 through 13:40) to watch a detailed explanation and installation of door mounted CLD into the Porsche 911 GT3:

and here on the door card (4:00 to 7:00):

If you want to read to even MORE detail about CLD and see more installation examples, read more here:
ResoNix Reference Information & Guide - CLD

Independent testing results (performed by Chris Purdue of The Deadending) for CLD can be found here:
Sound Deadener Independent Testing

 

Decoupling – Preventing Panel on Panel Vibration

Personal Preface and Experience:

Rattles are system killers. I don’t care how you spend on your system or install, if there is any annoying buzzing or rattle from a loose clip or panel, it will overshadow your entire investment. This area is cheap material and labor wise but can save you tons of headaches down the road. If your door is off, grab some Tessa/good quality cloth tape and treat your body clips, add CCF to plastic panel joints, etc. This is often one of the best compliments I get about my truck is how silent it is, even under 110-120+ db demoes. One sheet of CCF and a few extra minutes while you have a panel off will save you tons of heartache as your new (or old) car ages.

Decoupling Key Notes:

• It has two primary purposes; to prevent panels from vibrating against each other and to provide an air gap for a noise barrier (more on this in the following post).
• Closed Cell Foam based decouplers will not reduce road noise by any amount, period, and should not be used to attempt to block outside noise from entering the cabin. Fiber Mat style decouplers on the other hand, will absorb noise that tries to pass through. More on this below.
• The ideal decoupler is very compressible but still has a firmness that can still provide some stability between panels.
• If a closed cell foam is being advertised as a sound absorber, they are lying to you. If a foam is being advertised to block noise, they are lying to you.

Summary:

Decouplers are the second product that will get installed in almost every traditional automotive sound treatment application. A decoupler, typically a closed-cell foam or a fibrous mat material, is used to accomplish two different goals. First, it acts as a cushion between two panels that could otherwise vibrate together and cause annoying buzzes and rattle sounds. Second, to act as an air gap and isolator for a Noise Barrier, but we will touch on that second part later, in the Noise Barrier section.

As mentioned, Decouplers are almost always a Closed Cell Foam, aka a “CCF,” but are sometimes, as in our case with our Fiber Mat products, a fibrous, non-woven mat material. As mentioned above, a Decouplers typical use case is to provide a cushion between two panels to prevent them from rattling against each other. What makes one decoupler more ideal than another? Well, in my experience, being thick enough to touch as much of both panels as possible, yet still have enough compliance and is soft enough to compress down and not cause issues when re-installing these panels. Having a specific Compression Set specification (spec that tells you how well it holds its shape once compressed) can also help provide a Decoupler that can compress a lot of itself down but still provide some resistance for the panel instead of acting like a soft sponge.

Open Cell Foam and DIY Solution Decouplers, What to Avoid:

Speaking of sponges, we do not want to use open-cell foam as a Decoupler. Generic open-cell foam products will hold and retain moisture and cause mold and mildew to grow in your car. I see some people who try using polyurethane foam (ordinary acoustic foam) for this in an effort to “beat the system” and save money. This generic acoustic foam, shredded denim, jute, etc., will all hold moisture and cause issues.

Another popular product among those that want to save money is using gym and yoga mats. The problem here is that the foams that these are made of defeat the purpose of a decoupler. They are too hard and stiff to decouple properly, will not effectively reduce panel vibration, and will certainly not provide correct isolation and an air gap for a Noise Barrier. A popular choice in these products that budget-conscious hobbyists use has the specifications for the foam that it’s comprised of listed on the website. It has a Compression Deflection (stiffness) spec of 18-26psi. This means it takes between at least 18 and up to 26 pounds per square inch to compress the foam by 25%. That is exceptionally stiff for our uses. The CCF decoupler 7, for comparison, has a Compression Deflection spec of 1psi maximum, so it is 18+ times less stiff than a popular DIY option.

How to install a Decoupler:

Most of these products, ours included, feature a peel-and-stick adhesive; you can cut it to shape and stick it where needed. Our CCF Decoupler 7 and CCF Decoupler 3 will typically be used on plastic trim, or on the metal where plastic trim will touch. Anywhere a trim panel can vibrate against another panel, this is where you want to apply a decoupler. On larger panel decoupler installations, I usually prefer to adhere the decoupler directly to the trim panel that is getting installed into the car instead of directly on the vehicle itself. I find this works better and also has much better serviceability and longevity.

Here’s a brief example of a great use of the CCF as a panel decoupler (3:30 to 4:00):

Misconceptions of CCF and Sound/Thermal Absorption:

What closed-cell foam decouplers do not do, even though many other companies claim this, is reduce, absorb, and/or block noise. It does NONE of those in any meaningful way, shape, or form. Beware of companies that advertise their CCF products as being able to do this. They are lying and preying on the ignorant. A quick summary of why they do not block or absorb noise is that you need a lot of mass to block noise, and you need open cells or a fibrous mat to absorb sound. A lightweight closed-cell product has no chance of blocking noise or absorbing noise. Also, beware of products from companies that claim that their decouplers block heat or are excellent thermal insulators. While many thermal insulation products are comprised of a closed-cell foam construction, it is usually a VERY different type of closed-cell foam that is used for decoupling. The foams that are used for decoupling are generally not great thermal insulators.

As hinted above, we offer a few options for Decoupling. Our most obvious one is our CCF Decoupler 7, a closed-cell foam product that is 6.5mm thick. This is best to use for smaller panels and tight spaces. Our newly released CCF Decoupler 3S and 3F, 3mm thick foams, are even thinner and for even more fine detail work. Small clips, switches, wires, etc., that might rattle can be handled with CCF3S or CCF3F.

Here find a detailed video explanation of CCF:

That said, our Fiber Mat 25 and Fiber Mat 45 by far much better, so long as it is not a very small or tight tolerance area. Think of door panels, rear deck trim, quarter panels, pillars, etc. The Fiber Mat products are much better at decoupling and offer an added benefit: Absorption. I will include more details about this in the next post.

If you want to read to even MORE detail about Decoupling and see installation examples, read more here:
ResoNix Reference Information & Guide - Decoupling

 

Absorption – Absorbing Outside Noise and Energy from Speakers

Personal Preface and Experience:

This area to me, is the up and comer in the sound treatment community. It’s undervalued and underutilized at the shop and hobbyist level but has been huge ROI to me. I know some folks have some homemade solutions to this (bags of Roxul, spray foam, etc) but I urge you to consider a proper automotive product from 3M or Resonix. The Resonix will always win for me because of the adhesive backing and always remains in place during service. The Fiber Mat I have stuffed in my doors and headliner make giant gains in reducing outside road noise and less decay in my speaker response. I spent a day adding Fiber Mat in small locations (B/C Pillars, Front Wheel Wells, Frame Rails) and you’d be surprised what the sum of the small treatments yield as a whole. I wish Guardian existed when I was building my truck but Blackhole Tiles have been a big help in the interim.

Absorption Key Notes:

• Using any old acoustic foam in your doors is not a good idea. It will grow mold and smell once it holds water for some time.
• Due to the constraints of a vehicle, we cannot use very thick/dense absorbers; therefore, typical acoustic absorbers are only good for reducing high-frequency noise. ResoNix Fiber Mat 25 and ResoNix Fiber Mat 45, and ResoNix Guardian all help overcome this.
• Most absorption products will only be effective for mid to high frequencies. It can help lower overall noise floor, but will not take care of road noise like a noise barrier will. ResoNix Fiber Mat 45 is able to absorb effectively below 200hz, and ResoNix Guardian is also great at lower frequencies thanks to its built-in noise barrier.
• Stuffing empty cavities in the vehicle can help lower overall noise floor even further. Areas such as quarter panels, B-Pillars, etc. Just make sure it will not interfere with moving parts or prevent moisture from draining.

Summary:

Absorption is next and third on the list of sound treatment products to be installed into a vehicle. Absorption is pretty simple for the most part. Acoustic absorption converts airborne noise into another form of energy, therefore reducing the overall noise level in the vehicle. An open-cell or fibrous materials are two typical types of acoustical absorption products. The thickness, density, size of the fibers or open cells, and more contribute to what frequencies are absorbed and how much they are absorbed. Higher frequencies are easier to absorb than low frequencies. However, some products can effectively absorb relatively low frequencies in a vehicle, such as ResoNix Fiber Mat 25 & 45, and our ResoNix Guardian. Both have two different areas and reasons for application, so we will break them down individually.

ResoNix Fiber Mat:

ResoNix Fiber Mat 25 & 45, as mentioned earlier, are an acoustic absorption and a decoupling product. ResoNix Fiber Mat products are made out of microscopic synthetic melt-blown fibers that are formed into a mat, have a peel-and-stick adhesive on the back, are 100% okay with being installed in the harshest automotive environments and will not grow mold or mildew, and are naturally hydrophobic. They handle water, heat, cold, and anything else just fine, so ResoNix Fiber Mat can be installed practically anywhere without worry. They are typically used on door panels, quarter panels, rear decks, roofs, wheel wells, fender liners, pillars, sometimes even floors, trunk floors, and anywhere else you can think of.

A detailed overview of the Fibermat product:

The general rule of thumb with ResoNix Fiber Mat 25 & 45 is any application is always increasingly beneficial. Any time you add more of an absorption product, you will theoretically absorb more noise. There is one caveat, though. Stuffing it to the point of compression will alter the product’s behavior and shift and change the acoustic absorption properties, usually in a way that is negative to our requirements in the automotive environment. For larger voids such as roofs, quarter panels, etc., only fill them until they are full, but do not add extra to the point that the Fiber Mat compresses. Fiber Mat should remain “lofty” for the best performance. The only time compressing is okay and even preferred is when you are using Fiber Mat as a decoupler as well. Light compression of ResoNix Fiber Mat will drastically increase decoupling performance and panel stabilization without having enough adverse effects on absorption to be concerned. Door panels and rear decks come to mind here since these are areas that we are typically very concerned about with panel-on-panel vibration.

Fiber Mat Thickness Selection:

Regarding picking Fiber Mat 25 or Fiber Mat 45, that’s hard to say. While we have done many vehicles, we still haven’t done most. While we can help guide you based on our experience, it is ultimately up to you to determine which version best suits your application. Remember, fill, but do not compress. So far, in my experience Fiber Mat 45 will be better suited for larger tolerance door panels, rear decks, rear hatch trim panels, quarter panels, roofs, fender liners, etc. Fiber Mat 25 is typically suited for smaller tolerance door panels, pillars, floors, trunk floors, tire wells, etc.

Installing it is very simple. Just cut to shape with heavy-duty scissors (I use 10″ and 12″ Wiss scissors), peel the backing paper, and apply it to the desired surface. As with anything, ensure the surface is clean and clear of dirt, oil, and grease. I prefer to clean the panels with isopropyl alcohol beforehand. You can stick this anywhere you want, so long as it is clear of any moving parts. I do not recommend installing these inside door cavities as an absorber as I worry that window mechanisms can snag the material and cause issues. Same with seat belt areas. But everywhere else, free game.

Here’s a great video example (7:00 to End) of Fiber Mat installation and things to watch out when installing on high service areas of a vehicle:

ResoNix Guardian – 3 in 1 Solution (Absorption, Noise Barrier, Insulator)

This new product from ResoNix Sound Solutions is a familiar concept to some that has been further improved. It is a composite-style material that consists of ¼” Hydrophobic Melamine foam, 1/8″ thick 1lb Mass Loaded Vinyl (aka MLV), another layer of 1″ Hydrophobic Melamine, and an Acoustic Polyester Facing. It features a peel-and-stick adhesive for easy installation. This product is multi-faceted, so we will give a general breakdown of each.

Here’s a video breakdown of the product if you don’t want to read the narrative below:

First, it is used inside doors, subwoofer enclosures, or anywhere behind speakers that produce a lot of energy. The point here is to absorb the acoustic energy inside the door or enclosure BEFORE that acoustic energy makes it to the door skin or enclosure wall. Since ResoNix Guardian’s Hydrophobic Melamine layer absorbs noise, and the Mass Loaded Vinyl layer deflects noise, all before said noise reaches the door skin or enclosure wall, the amount of acoustic energy that even reaches those boundaries is significantly lessened, therefore reducing the overall amount of resonance and vibration that is created.

The second use for ResoNix Guardian is to make use of the floating layer of 1/8″ thick, 1 pound per square foot Mass Loaded Vinyl Layer. We didn’t cover noise barriers yet, but this is the first product that makes it extremely easy to install a noise barrier to the roof and sides of your vehicle. Previously, installing a noise barrier on vertical, or god forbid overhanging surfaces, was difficult, tedious, and not consistently effective. Mechanical fasteners, specific Velcro (that we still offer), or other hoops must be jumped through to install noise barriers, such as Mass Loaded Vinyl or ResoNix Barrier, onto these surfaces. Now, it’s just peel, stick, done. And all with the added benefit of being fully decoupled and isolated, and with the help of acoustic absorption of the Hydrophobic Melamine.

The third use for ResoNix Guardian is for its thermal insulation properties. While Hydrophobic Melamine is an excellent acoustic absorber, it is also a top-tier thermal insulator, so much so that it is even used on the tips of rockets to protect them from heat. ResoNix Guardian is the ultimate solution for treating a camper van or RV since you get not only the acoustic benefits but also the thermal insulation benefits as well. It will help keep heat in when it’s cold and help prevent heat transfer into the vehicle when it is hot outside.

How it is installed is simple. Just cut it to size carefully with a sharp box cutter, peel the backing paper, apply it to the panel, and apply pressure. Again, ensure the surface is clean and clear of dirt, oil, and grease. I prefer to clean the panels with isopropyl alcohol beforehand. ResoNix Guardian is most commonly installed on top of CLD on the outer skin of doors inside of the door cavity, inside of subwoofer enclosures and speaker cabinets lining the walls, on roofs, and covering van/RV interiors after CLD application. This product is thick and not very compliant, so this is not to be used directly behind typical interior panels, in wheel wells, etc., unless there is plenty of room and there is not too much curvature.

Here's an example of installation (13:36 to End) of Guardian in the Porsche 911 GT3 doors:

Plus a Guardian specific cutting tips and trick video:

If you are planning on making use of ResoNix Guardian as a noise barrier, make sure you have FULL coverage, and make sure you butt up the edges of each piece as closely and perfectly as you possibly can, as even small flanking paths can ruin the perceived performance of a noise barrier, which brings us to our fourth category…

If you want to read to even MORE detail about Absorption and see installation examples, read more here:
ResoNix Reference Information & Guide - Absorption

 

Noise Barriers – Blocking Outside Noise

Personal Preface and Experience:

Can’t offer a ton of personal experience with this besides having molded and held the Barrier product in my hands. I know it is super easy to work with and mold to nearly any shape. Based on what I understand about traditional MLV, the time savings alone when using Barrier are enough to justify the premium price point.

Noise Barrier Key Notes:

• Do the entire vehicle with as close to 100% coverage with no gaps to the best of your ability if you want to lower the perceived volume of road noise. The headliner will not be possible in most cars due to the weight of a noise barrier, so stay tuned for our future product to handle that.
• Attempting to reduce road noise by only doing a few areas (like just the doors) is usually a waste of time, effort, and money. The significant gains come the closer you get to 100% coverage. Sound will take the path of least resistance and enter through flanking paths.
• Having an air gap between the noise barrier and the panel of your vehicle is important. It is not suggested to use a noise barrier without a decoupling layer between the car and said barrier. That air gap is typically closed-cell foam, which ResoNix Barrier already features.
• When using ResoNix Barrier, it is not 100% needed to use more foam, but it is never a bad idea to have more cushion for decoupling if there is still plenty of room.
• ResoNix Barrier can also be used to seal large holes.

Summary:

The fourth and final official step and category of sound treatment application is noise barriers. While they can be hugely beneficial and arguably the most effective wide-band sound treatment you can apply when installed correctly, they are almost always difficult to install, very picky about the installation, and can be costly. The point of a noise barrier and how they work is simple. A noise barrier is made from a material to act as a limp and decoupled mass, and said mass is used to block, reflect, deflect, whatever you prefer to call it, acoustic energy away from the area you are shielding with it. The only driving factors in the performance of a noise barrier product are its weight, and how non-resonant it is. The heavier the noise barrier is and the less inert it is, the more noise it will block. What makes them very picky is the fact that a noise barrier ideally needs FULL coverage to be effective. While not having full coverage can still yield some improvement, it will be minuscule compared to full coverage. When you do not have full coverage, sound acoustic energy will travel around and take the path of least resistance right past the noise barrier. Written in our more detailed section, I use this analogy…

Say your annoying and inconsiderate next-door neighbor decides to cut his grass with his obnoxiously loud mower at 7 am on a Sunday while you’re trying to sleep in on your only day off. It just so happens that it was a warm night, and you slept with your window open. The second he fires up that old John Deer of his, it wakes you up. You think to yourself, “Ugh, here we go again. Better close my window and try to get back to sleep”. What happens to your perceived volume of his mower when you close your window halfway? Nothing, right? What about when you close it 90% of the way? Still pretty much no different than with it fully open. What about when you close it pretty much all the way but don’t lock it and have a good seal? Yeah, perceived volume is lower, but not by as much as you had hoped. Your perceived volume of his mower only becomes significantly lower and tolerable when you fully seal that window shut. It’s no different when trying to sound-proof your vehicle.

Another part that makes noise barriers picky and selective is that they need full coverage and a decoupling layer, ideally on both sides, to isolate them from the vehicle. Noise barriers need to be decoupled from the body of the vehicle and the panels that cover them. Otherwise, the resonance of the body panels will be transferred directly to the noise barrier, which will also resonate and radiate its own noise, rendering the noise barrier mostly ineffective.

Mass Loaded Vinyl (MLV):

The most popular type of noise barrier is Mass Loaded Vinyl, aka MLV. It is popular because it is heavy, limp, and, most importantly, cheap. The downsides are how thick it needs to be to achieve the desired weight and its poor flexibility and moldability. Most MLV is 1/8″ thick and weighs 1 pound per square foot. Couple that with a decoupling layer on both sides, and you have an extremely thick product that is not moldable to complex contours. In short, you end up with a product that will be extremely difficult to work with and fit behind the panels of almost all newer and even many older vehicles.

Resonix Barrier:

ResoNix’s solution to this is our ResoNix Barrier, which is comprised of 1/32″ sheet lead encapsulated in our 3mm thick CCF Decoupler 3. This gives us a noise barrier that is much thinner yet twice as heavy per square foot as the standard 1/8″ thick MLV, is much more flexible, and is moldable to complex contours. Long story short, ResoNix Barrier is a much higher-performing noise barrier and is much easier to work with. The downside, it is admittedly not nearly as inexpensive as MLV.

Here's a video overview of the Barrier product:

Installation:

ResoNix Barrier is very easy to install. For floors, just remove the carpet, roll it out, contour it to dips, peaks, bends, etc., as tightly as you can, overlap layers and even fold them once over to lock them together to prevent sound from leaking through, and let gravity hold them in place.

For vertical surfaces, I prefer to use riv-nuts and stainless steel machine screws with fender washers to hold them into place. I do not suggest using Velcro to hold up ResoNix Barrier. The foam will not be able to bear the weight and will rip. The adhesive will also tear the foam apart if you try to remove it. For roofs, this isn’t easy. You can again use mechanical fasteners into the roof braces or can somehow install it directly onto the headliner, but I am not sure how that will hold up as it may be too heavy for a headliner to support. This is where ResoNix Guardian or ResoNix Fiber Mat comes in, making treating the roof much more manageable.

ResoNix Barrier can also be used to seal access holes on inner door skins to turn the door into a quasi-sealed enclosure. Typically, sturdy plastic is used for this, but in many new cars, these inner door skins are more than just a flat opening. They are 3-dimensional and have complex curves and contours that can make it difficult to mold a plastic sheet to do this job, especially with the tighter tolerances of many newer vehicle door panels.

If you want to read to even MORE detail about Noise Barriers and see installation examples, read more here:
ResoNix Reference Information & Guide - Blocking Noise

 

Misc Tips, Tricks and Detailed Sound Treatment Install Examples

Personal Preface: There are several other products in the sectors outlined below, obviously the Resonix stuff is excellent but making sure you address the problems they are solving is most important.

ResoNix Strips

ResoNix CCF Strips are a product that is used to couple your car speakers to the panel and grille that reside in front of them. The purpose is to direct all acoustic energy created by the speaker through the grille into the listening space instead of losing acoustic energy to the open areas behind your door panels and dash panels. This has two main benefits. First, we gain more output since we can force all acoustic energy into the listening space. The second is less resonance and distortion created by the panels themselves since the acoustic energy is no longer getting trapped behind and exciting the panel. They also provide minor stability for the panel they are coupling to. Long story short, install these around your speakers, especially midbass speakers for a free lunch of more volume, lower distortion, and fewer rattles and resonance.

ResoNix Butyl Rope

ResoNix Butyl Rope is precisely what it sounds like. It is a 3/8″ diameter butyl rope used for various sound treatments in your vehicle. Two popular uses include stuffing it between the crash bar and outer door skin to help further stabilize the outer skin, and using it in small areas where two layers of a panel may overlap and introduce the possibility of them rattling together. It can also be used on the base of clips to prevent them from rattling. See the product page for installation examples.

Here's a great example of the buytl rope being used on the doors the of 911 GT3 (2:23 to 3:30):

OEM Audi/VW Interior Non-Woven Tape

This “cloth tape” is commonly used in installations for various reasons. But for sound treatment purposes, you can use it to bundle wire harnesses that reside behind panels to prevent them from rattling and buzzing, or you can use them on clips and/or clip openings to help reduce their vibrations. The difference between the tape we sell and the popular option, ours will not turn sticky and gooey over time. See the product page for installation examples.

Detailed Guides:

Complete Door Treatment: ResoNix Reference Information & Guide

Complete Wheel Well Treatment: ResoNix Reference Information & Guide

Vehicle Database w/ Sound Treatment Examples: Vehicle Database


Conclusion:

Resonix:

I hope this covers all relevant types of automotive sound treatment products and does so with enough information to understand the basic concepts of how these products work, how to use and install them effectively, and sheds light on false advertisements of other products in their categories. I also hope you continue reading the rest of our original Reference & Information Guide, which will cover the same topics and may even repeat much of the information above but will provide even more detailed information unlike anything seen on any other website.

Personal:

I always attribute the success of sound treatment (and most anything car audio) to be centered around 3 things: quality products in the correct application, attention to detail and understanding sound treatment works as a SYSTEM – no single component of the system makes the big difference, it’s the sum of many parts.

If you made it this far and read everything we (well mostly Nick over the past couple years) put together, leave a like and a comment. We hope this guide helps provide you a more clear path to properly building a solid foundation to your next audio system.



Updated 10/2023.

 

Saved for Change Log and Future Updates

@ Mods - any chance for a sticky?

 

 

Thanks for posting. That red B-pillar with the cloth tape looks extremely familiar. Looks exactly like mine.

 

Holy information dump, Batman!! Well done, I love the preface you wrote to this thread- it gives people the map to the information contained within, and to provide a baseline of understanding the products and application.
Thank you for taking the time and effort to create a go-to information guide to sound treatments.

I vote for a sticky.
Cheers!

 

Chris Purdue dispelling the myth that Resonix's support for his testing influenced the testing results

Sound deadner

What’s some good sound deadner thats around 4 ml thick that’s budget friendly?

www.diymobileaudio.com

Testing by Chris Purdue showing that Resnoix CLD can out perform larger amounts of lower-performing product

Sound deadner

What’s some good sound deadner thats around 4 ml thick that’s budget friendly?

www.diymobileaudio.com

Chris Purdue on buy once, cry once

Sound deadner

What’s some good sound deadner thats around 4 ml thick that’s budget friendly?

www.diymobileaudio.com

 

To all, please note that this thread's objective is certainly not to create a Resonix or bust mentality. It's about sharing the challenges, theory and using correct solutions to said challenges.

 

Resonix Sound Solutions – Glossary - Sound Treatment Terminology & Glossary - learn the sound treatment vocabulary

This page is everything I didn't know that I needed. Looks like I had more than a few things mixed up

 

Thx Rick, great write up. I did the best I can, mixed a few products from different vendors. I did splurge on the Fibermat 45, great product for rear quarters!

 

I"m interested in wheel wells right now. Kind of surprised to see Resonix recommend CLD all over the fender liner. I've always been skeptical of CLD on non-metal surfaces though. Fibermat is a solid suggestion though, I tried to build my own insulators out of plastic sheeting and Rock Wool but it was a joke on such a compound surface and tight area (I'd successfully created these insulation bags for the inside of doors before). He also lightly recommends a barrier liner as well if you can fit it, but again I'm a bit skeptical considering how many pathways the sound is able to take around any barrier.

Any thoughts on wheel well sound deadening ? Rick I think you were happy with your treatment what all did you use ?

 

I"m interested in wheel wells right now. Kind of surprised to see Resonix recommend CLD all over the fender liner. I've always been skeptical of CLD on non-metal surfaces though. Fibermat is a solid suggestion though, I tried to build my own insulators out of plastic sheeting and Rock Wool but it was a joke on such a compound surface and tight area (I'd successfully created these insulation bags for the inside of doors before). He also lightly recommends a barrier liner as well if you can fit it, but again I'm a bit skeptical considering how many pathways the sound is able to take around any barrier.

Any thoughts on wheel well sound deadening ? Rick I think you were happy with your treatment what all did you use ?

I can chime in on this. I looked at doing my wheel liners and thought there just wasn’t enough coverage to make it worth my while. What I did do was do the wheel wells from the inside when I had all the carpet out. There was quite a bit of component disassembly and bother around pedals etc. I think(hope ) I cut down road noise a bit but it is really the tire choice that makes the biggest difference IMHO.

 

Yeah I have the whole firewall and rear wheel well covered in CLD, CCF, and Vinyl Mat or Lead. Just trying to go that extra mile - Its hard to believe it would make much difference in my truck but tire/road noise is the loudest thing in my car on the freeway. I see 68-70 dB on the freeway which I think is pretty good but it still seems about 1-2 dB louder than my truck believe it or not. But dB isnt' enough to qualify sound, where that sound is on the spectrum makes a big difference. Always meant to take a REW recording but too lazy to get around to it. In fact I always "wanted" to do an REW recording (on the same section of road) in a car on the journey from stock to totally stripped interior and make a recording after each sound proofing step. Would really be educational I think. Maybe when I'm retired and bored !

 

As we all know, there has been dozens and dozens of threads made on this subject with lots of contrasting information but I wanted to take a shot at providing a comprehensive thread to provide objective knowledge and guidance through the sound treatment of your vehicle. This is hopefully intended to made a sticky article for folks to reference often.

Preface:

Most of the information here is going to provided via Resonix Sound Solutions via their website graphics and narratives as well as their ever growing Youtube page. I urge you to absorb this information with an open mind and recognize that while Nick may promote his products in his own videos - the knowledge, applications and installation demos on the subject he shares publicly for free is objectively excellent. There are paths to achieve good results exclusive of using Resonix products and many of the members here get very creative in doing so. I have chosen to use the Resonix suite of products as a reference because no other company has a such complete model line up of products that can address most, if not all, automotive sound treatment problems AND provides deductive reasoning and support for each of their products. I feel it is much easier to convey and teach with real world products and examples and hope you feel the same way.

Again, this is not a paid advertisement for Resonix whatsoever - I use his information because it is comprehensive and presented in multiple, concise formats. He has given me permission to copy information here. I will inject my personal experiences at the beginning of each sub-section.

With that said, here we go.

Resources and References:
Facebook Group – The Deadening - https://www.facebook.com/groups/651457188787366 - a pubic group dedicated to car audio sound treatment. Please review the independent testing Chris offers on CLD products. He has conducted recent testing for CLD effectiveness and will be sharing results for CLD effectiveness and durability relative to heat in the near future.

Resonix Sound Solutions – Sound Deadening Reference Information - ResoNix Reference Information & Guide - EXTREMELY undervalued guide to understanding to theory, products and proper application of sound treatment products.

Resonix Sound Solutions – Glossary - Sound Treatment Terminology & Glossary - learn the sound treatment vocabulary

Resonix Sound Solutions – Buyer’s Guide - ResoNix Sound Deadener Buyers Guide - this page is relatively new and helps folks make value based decisions, based on their own vehicle, system objectives and location they are attempting to deaden. Also provides multiple, tiered buying options depending on your budget. Helps prevent the paralysis by analysis.

For starters, there are four main categories for sound treatment for your vehicle. The first one is to control structure-borne vibration, also known as resonance. Constrained Layer Dampers, commonly referred to as CLD, are the most common types of product to handle this job. The second category is to decouple panels and prevent them from vibrating against each other. A typical product for this is Closed Cell Foam (aka CCF) or Fiber Mat. The next category of sound treatment for your car is blocking outside noise. For this, you need something with mass. ResoNix Barrier is a modern solution to a variety of problems when trying to block outside noise. Lastly, sound absorption. This is something relatively less spoken about, but still can yield significant improvements to your vehicle. ResoNix Fiber Mat excels at this. Keep reading to learn all about how these types of products are used and the science behind how they reduce the overall noise floor of your vehicle.

Here’s a recent video series Nick started about a sound treatment focused project he is doing in a 2023 Porsche 911 GT3. Yes the car is exotic, but the theory and methodology can be applied to most other audio application. This video provides a good introduction on his intent of what he plans to do and why:

This series is on going at the time of writing this post but you will see the plan outlined in this video put into real time examples throughout the following (and future) posts.

The full, in-depth written sound treatment guide on the Porsche cited in this guide can be found here:
Make your Porsche 911 more comfortable to drive.

Table of Contents:

• Controlled Layer Damping – Reducing Panel Resonance
• Decoupling – Preventing Panel on Panel Vibration
• Absorption – Absorbing Outside Noise and Energy from Speakers
• Noise Barriers – Blocking Outside Noise
• Misc Tips, Tricks and Detailed Sound Treatment Install Examples

I'm buying resonix for my build

 

This needs to be stickied. Great writeup @RickWilson

 

This is the best content I've found all in one place. +1 definitely needs to be stickied! Well done @RickWilson !

 

Thank you all for the kind comments. I'm mostly just the messenger here but wanted to put this info in a consolidated location.

 

Can you speak on the ResoNix Guardian a bit (basically CAE VB-TSM)? My understanding of MLV/barriers is that it's not that effective unless it's very close to 100% seamless coverage, and it seems like anywhere you would be using Guardian wouldn't be close to that.

Why not use just the melamine foam or Fiber Mat 45 to save weight and cost?

Would a similar thickness of just melamine be more or less effective than Fiber Mat for absorbing (road) noise?

I have doors and a firewall that I could use either Guardian or Barrier, and I'm not sure where the tradeoffs are...

 

Can you speak on the ResoNix Guardian a bit (basically CAE VB-TSM)? My understanding of MLV/barriers is that it's not that effective unless it's very close to 100% seamless coverage, and it seems like anywhere you would be using Guardian wouldn't be close to that.

Why not use just the melamine foam or Fiber Mat 45 to save weight and cost?

Would a similar thickness of just melamine be more or less effective than Fiber Mat for absorbing (road) noise?

I have doors and a firewall that I could use either Guardian or Barrier, and I'm not sure where the tradeoffs are...

You are correct about MLV when used as a sound barrier. Guardian is not meant for this purpose. It is used in doors or enclosures where you want to absorb or effect the back wave of drivers. Similar to Blackhole Tiles. ResiNix's sound barrier product is ResoNix Barrier. It uses lead instead of MLV, Barrier is more effective than MLV and much easier for to form to vehicle contours. Any noise barrier must cover as much as 100% as possible, whether that is MLV or ResoNix Barrier. Fibermat on the other hand in an absorber and does not require 100% coverage, but it isn't as effective as Barrier and blocking noise, but it will quiet things down if used properly.

 

To add, the mlv also helps act as a barrier and force decoupler WITHIN the melamine itself. Melamine is a great noise absorbtion foam but it is fairly stiff and doesn't offer much rebound control, like ccf. By having the mlv layer, any poke or vibration in either layer gets distributed equally across the entire surface of the opposite layer. The little bit of noise blocking is just an added benefit.

 

Great information here and a lot of good material to read.

 

Has anyone used well nuts instead of rivnuts for securing Resonix Barrier when used as a door access cover?

 

I don't see any reason why they wouldn't work- rivnuts are heavier duty, better suited for more structural applications.

 

I suppose my main motivation to use well nuts is that they have a rubber coating which should insulate from further vibrations.

 

Yes a very good idea. Well nuts could hold a piece the size of the entire door without issue