Dynamat

Yes. It works but remember this.

1. You don't need as much as you think
2. Measure twice, cut once. It ain't cheap
3. There's a strategy to placing it: Attach it to large areas that aren't really bolted to anything. These things vibrate the most.

The picture is overkill IMHO

4. Good tires help more than anything

As for brands, Noico on amazon is best bang for buck. It's pretty high quality for relatively cheap.

Its like 10 pounds for 35ft./sq. That's negligible.

>4 MB, 4032x3024
yeah no
resize your shit

Postan from phone

>no

>Anyone got experience with it?
Back in the early 90's, dynamat seemed to be a mealy asphalt-based substance that was a drier version of peel and seal sold at home depot and lowes. But over the years it became rubber based due to the EPA warnings about petrochemical exposure.

Dynamat Xtreme works in some cases and not in others. It is best against vibration noise transmitted thru the air to a large flat surface. It is weak against longitudinal vibration or standing waves transmitted through a beam. For that type of noise, the 3M product Damping Foil 2552 is the preferred choice. It's also similar to B-Quiet.

What got you to choose Dynamat Xtreme over more modern competitors such as BQuet or 3M Damping Foil? It's too bad Harbor Freight no longer has sound deadener. But long ago, they used to carry a "dynomat" foil-sided copycat made in china. It was super low-priced too. It was more of a thick heavy sheet of butyl rubber than anything else though.

Possible sound deadening choices:
Accumat scosche.com/accumat
B Quiet/Brown Bread b-quiet.com
Dynamat dynamat.com
edead edesignaudio.com/ep2/edead.htm
Noise Killer noisekiller.com
Quiet Coat quietcoat.com
RAAMmat raamaudio.com/
Second Skin secondskinaudio.com/
VBlok cascadeaudio.com
3M Damping Foil (2-inchwide): many online sellers
Dodomat: similar to dynamat but for UK market

>Dynamat is overpriced.
It certainly is overpriced for what it is. The concept of butyl rubber sheets with adhesive on one side and foil on the other is not a novel idea either as it is quite old. But Dynamat has a good hold on the market and profitable distributorships with various installers since the high price allows it to discount to the installer to boost their profit margin in return for using dynamat exclusively.

By keeping the available marketshare for competing products small, competitors don't find it profitable enough to enter the market and develop a set of dealers committing to use their product over dynamat. It's the classic story of many other products.

Does your computer make funny noises before you can browse Veeky Forums?

>Does your computer make funny noises before you can browse Veeky Forums?

My dashcam does. That cheap chinese thing is always making a low-pitched squealing. Since everyone in the car can hear it, it is a bit embarassing.

That's why you need dynamat or 3M Damping Foil. So everyone can hear the squealing noise even better!

i vote for second skin, has a black coating on the sheet metal.

I put it all over my Nissan Patrol, It keeps things quiet.

HOWEVER, it is more of a load dampener, ie you put a 6" square on the whole door panel which stop it vibrating and letting in noise as opposed to COVERING the whole door.

>pic related

>Any of the actual brands are overpriced as fuck.
My local only uses dynamat. They refuse to use other sound dampening items. So there's no choice unless I do it myself which is a bit scary.

Nah it's easy. Watch a video on how to disassemble your car's interior, then watch a few videos of deadening installs.

You literally clean the surface with alcohol or windex, then peel n stick like a sticker and mash the shit out of it to get it to stay.

Dude, its literally a sticker.
And it doesn't need to be perfect. Gaps/overlap doesn't matter. Hardest parts is the aluminum tears, but you'll figure that out on the first piece.
Just don't try to lay it over "peaks", the rubber stretches but not the aluminum- just cut and butt there.

I've never taken apart the plastic interiors before. I just hope I don't break something like one-way prongs or other things. Looking at the headliner, it goes into the pillars, so to get the headliner off, I have to take apart all of the front, middle, and rear pillars first.

There's no screw holes, so I guess I have to grab somewhere and pull the pillars off? Is that done with bare hands or a tool? I don't want to break anything in the new car. The chevy dealer likes to disqualify warranty items for any reason at all.

Get you some of these shits.

Most of the pieces click in with little attached clips like a lego set. Every once in a while there will be screws or a bolt. Especially on door panels.
Everything generally has an order that it has to be removed. I'd start in the trunk, It's hard to fuck up, everything is easy to to take apart, and everything is easily accessible. It's also a huge noise culprit. ESPECIALLY if you have an aftermarket exhaust.

good post

>Anyone got experience with it?

I haven't used it, but I have an observation. When there is an accident, autobody work to remove dents requires access to the metal on the other side of the dent. If there is dynamat there, don't they have to remove it before they can really pound the dents as smooth as they can before applying any body cement? That would mean a lot of that dynamat would get pounded pretty flat if they didn't remove it. I wonder if the body shop charges extra if dynamat gets in their way? Anyone know how dynamat affects a bodyshop?

Works great, but I use the knock-off fat mat stuff because it's 1/3 the price for the same thing.

The one repair I've seen on a door I put the stuff on, the body shop peeled it off and stuck it back on after, but the adhesive failed after a while and interfered with the window.

No big deal, I had a couple of rolls handy. I threw it away and put a new piece in.

Is it better to get the red set with that big wide tool? I have to remove pillars so isn't that big wide tool the one to use for prying pillars off?

Red Set of 5 tools:
amazon.com/Panel-Removal-Tool-pcs-Upholstery/dp/B00LUPOSD4

Yellow Set of 4 tools:
amazon.com/dp/B01DJXF7D4?psc=1

Or I can go to the Autozone and look there, but usually amazon would be cheaper. I think I will go to Harbor Freight. I got a 25% off coupon for the Independence Day weekend which is better than their usual 20%. Time to try some cheap chinese plastic. Checking Harbor Freight website now. Here are the various auto trim removal tool sets at HF:

harborfreight.com/catalogsearch/result?q=car interior trim tool

Hmm, now those darn light fixtures on the ceiling. I see how that Chevy dealer is going to do things. You broke one fixture. That means your engine and powertrain warranty is now void. While exaggerating, I had a minor scuff of one rim on the curb (not a crunch, just a rubbing while parallel parking) and that Good Chevrolet said no more warranty on alignment or rim for the new car. They are quick to invalidate parts of the 3 year bumper to bumper warranty of a new car. They just want to do the same work out of warranty so they can keep all the money as well as inflate the charges which they cannot do for in-warranty work. So this is very much why I am so chicken to work on the car.

The dealer is a real ass for trying to invalidate the warranty with any minuscule reason knowing full well going to court is expensive and won't typically be done. So Good Chevrolet service writers are abusing things.

Their reward system is promoting corrupt behaviour just like Jiffylube upselling air filters by rubbing a dirty rag across it to make it look dirty. It's quite frustrating. Good Chevrolet takes all the "magic" out of owning a new car and turns it into FEAR instead.

I've used Dynamats xtreme and Stinger Roadkill, and in my opinion the Stinger is just as good for a lot less. depending on how crazy you want to go, a fully dampened 4dr Accord would easily eat up about 100 sq ft. of material.

If you're looking to reduce road noise however, "Dynamat" IS NOT THE SOLUTION HERE. This type of material is mainly use to reduce resonance to improve audio sound quality. To reduce road noise, you should go with Mass Loaded Vinyl (MLV).

you can do both if you want. my only advice is to get a roller, and take your time to do it right. It took me 3 days (about 5 hours per day) to fully deadened/dampened my car, and i couldnt be more happy with the result.

Bigger pieces typically you can use a screwdriver with tape on it.

As for warranties, I doubt you'll void your warranty removing panels. I've seen more idiotic things though.

Bump to save from alphonse

>To reduce road noise, you should go with Mass Loaded Vinyl (MLV).

That's also where 3M Sound Dampening Tape works well too. It's thick yet flexible aluminum strips that are 2 inch or 1 inch wide and have a very very VERY strong AND stiff adhesive. The adhesive is the key item here more so than the aluminum. Because when it bonds the aluminum (metal is about 2x the thickness of duct tape), the stiff adhesive is able to couple the vibrations to the aluminum and get it damped out. If the adhesive was all soft and wiggly, it would not hardly couple the energy to the aluminum. Because it also forms an offset beam with the surface, it works well on removing some of the road noise coupled through metal beams. Just use enough of it on all sides. I've noticed the difference but you have to cover a long run.

Even walmart.com sells the 3M product but only in one-inch wide strips. This product is pretty thin so it would even fit under dynamat althought I don't know if that would be counterproductive. But if you thought dynamat was high priced, well, this stuff is higher. But it certainly works better than dynamat especially if you need both low profile and a smooth metal surface (no folds, bends, crevices, creases) that doesn't hold mold or dust.

The Harbor Freight site has a printable coupon, so I'll go pick up the trim tool set (blue) from them. It looks like they copied the USA tools but used a cheaper (not glass filled) polymer nylon mix. That type of mix sounds like they just mixed both nylon and recycled plastic bottles together to make the tools.

thank you user, you're the hero we deserve

>adding weight in the worst possible place to stop a small amount of heat getting though your roof
idiocy

>Thinking 5lbs of weight matters

Although you're right, that is the least useful place

>Is it better to get the red set with that big wide tool?
Looks like Harbor Freight has the knock-off duplicate of that name brand Bojo trim & panel tool set.

>Although you're right, that is the least useful place

The doors and firewall are the places where vibration noise comes in from those metal panels. I am thinking about being aggressive on getting as much decibel reduction as possible, so I have to decide on which methods have the greatest reduction and which don't get in the way of wires and existing looms that are fastened to the metal walls.

Think about attacking the wheel wells to begin with. That's where the most sound is coming through and then work your way back from there.

>Think about attacking the wheel wells to begin with.

That sounds like a smart approach. I hadn't thought of the problem that way. Do you mean put sound deadener such as 3M metal tape there onto the wheel well under the hood? Dynamat is too ostentatious and thick. In a lot of places, stuff is already mounted against the wheel well too. So I have to remove those things to install and sound deadener. I wonder if I can carefully paint the metal tape after I install it so it doesn't stick out too much.

Make sure if anything goes in the engine bay if is heat resistant to pretty high temps. If not directly on the wheel wells, go for the front foot well and remove the rear seats to get to the side rear wheel well facing the occupants.

Sound deadening can only reduce so much noise though. It will be very noticeable but not super crazy so don't set your expectation amongst the stars.

>the road noise is pretty obnoxious.

One significant way to reduce road noise is to get quieter tires. That doesn't mean you have to give up your nice grippy tires. But consider that your tires come in a variety of speed ratings. The higher the speed rating, the stiffer the treadblocks will be and the stiffer the sidewalls are too. All that increases the amount of road noise transmitted up into your suspension.

So if you were simply buying the highest speed rated tires you could find, note that "more" is not necessarily better. In this case, replace them with tires rated for a lower speed under the assumption that you're not going to drive that speed anyways.

Picture from the TV documentary show "Modern Marvels: Tires" on the History Channel. There's various automobile-related shows in that series about modern technological advances and how things work.

>Adding weight.

It's not like we're adding unsprung weight. And this type of weight is for the good reason of reducing interior cabin noise because we're the drivers that like a quiet environment. It probably isn't a good car mod for those who install noise-making devices for their cars such as droning or other types of loud exhausts though.

They're all tin cans faggot

I have a performance exhaust system but I also do a lot of highway driving. I use a resonator and sound deadening to keep the drone and road noise in check while cruising. Actually works pretty well if you want the best of both worlds

>I live on 500KBps

>3M product Damping Foil 2552
It's also waterproof and but its operating environment heat resistance only goes up to 80 degrees celsius.(176 degrees fahrenheit). That seems within the range of being used under the hood on the wheel well. That's plenty far from both the engine and any radiator fluid reservoir.

I just like how it is thin and scratch/friction resistant. It cannot tear or rip like dynamat.

>176F

I don't know if that is high enough for engine bay, usually approaching max operating temp like that that often will eventually break down the adhesive. I guess if it is far away from the engine it wouldn't matter but it would still be sketchy.

Then there isn't anything really available. 3M is a USA company that is reasonable with its numbers. I'm sure there would be a Chinese company copying the same patented product but it would have a higher temp rating.

For example, chinese LiON batteries are often advertised having higher power ratings than USA or japanese batteries. Consequently, many such companies went out of business and had to ironically sell their assets to chinese companies. As an example of chinese ethics:

candlepowerforums.com/vb/showthread.php?400136-Disassembly-of-some-UltraFire-batteries

LiON are required to have certain safety features under USA law. So they are not just a simple container of energetic substances in the same way that NiMH and NiCads are constructed.

That is fair. I would still go with something rated to be used in the engine bay. I THINK dynamat has a under hood product but I don't know the rated heat levels.

One thing that can be said for most of the aluminum + Butyl Rubber products is that they are very flame retardant. They don't really catch fire, they just lose adhesion and become gooey.

I bet dynamat buys their foamed butyl rubber raw material from china. As long as they apply the adhesive or foil, they can claim "made in the usa" due to bush's trade law changes that made it easier for usa companies to get cheaper materials in order to have a "made in usa" label.

Probably should send suggestions to Harbor Freight to sell butyl rubber products with adhesive on one side and foil on the other. They'd clean up the market and a lot more people than now would be able to afford sound dampening products. If enough different people asked Harbor Freight, then they'd probably start getting interested.

>One thing that can be said for most of the aluminum + Butyl Rubber products is that they are very flame retardant.
Hopefully the aluminum protects the butyl rubber. The gov't categorizes butyl rubber as a flammable substance.

>The gov't categorizes butyl rubber as a flammable substance.

Not really sure why, butyl rubber's flash point is like almost 500 degrees if I remember correctly.

I've always considered sending suggestions like that to Harbor Freight. Their slogan should be like "Here's pretty much the same thing. It's pretty cheap"

Spotted the benchracer

>I've always considered sending suggestions like that to Harbor Freight. Their slogan should be like "Here's pretty much the same thing. It's pretty cheap"

Their local shop sometimes has some odd things that appear once and are gone. They had a box of back scratchers a year ago. Two years ago they had a stiff plastic mat about 1.5 feet square with vertical walls about 3 inches high and tie down slots where straps could be passed through. That was for those plastic car battery cases in case you put a spare battery in the trunk. This kept the plastic case from falling over when you did sharp turns. Naturally, if the 12 volt car battery in the case tipped over, the acid would leak out. Only recently did I want to buy one, but they have never restocked those one-time items.

Since Harbor Freight doesn't always put these "one shot" items on their display table at the front of the store, to find them you basically have to browse all the aisles in a time-wasting "treasure hunt" that has low chance of payback of finding a new non-regular item. I wonder if these things are the results of customer suggestions? Or because the buyers in china found a supply of something cheap and bought it up. I still am wary of HF plastics though since cheap plastics from china can contain lead and other processing aids. That's because items for an industrial setting are exempt or have relaxed product safety rules than items sold in a normal consumer store.

I've noticed that. I used to work retail and we'd have random items come and go that I never saw again. That stuff was usually from a vendor for a good deal though. I'd be willing to bet it is the same deal at HF. They likely have regular companies they buy from regularly that they get bulk stuff from and get a good deal on a random item.

>There's a strategy to placing it: Attach it to large areas that aren't really bolted to anything. These things vibrate the most.

Is it important to apply it to the firewall behind the dash? I'm about to give up on the firewall other than the bottom part behind the carpet.

In my car, the dash is next to impossible to remove. And even though the dash front can eventually be removed. Then all those devices in front also have to be removed before the firewall itself can be exposed. There is so much "stuff" behind the front cover of the dash that it's actually kind of scary. I can already see from trying to peer underneath that there's a billion things clipped or fastened without much play on wires. That means those things have to be unfastened too and then re-fastened when putting the entire assembly behind the dash cover back together.

The bottom area of the dash has a crossbar with a "leg airbag" so that has to be the first thing removed at the bottom before I can access more bolts to unbolt the bottom parts of the dash in order to remove the front cover.

>Probably should send suggestions to Harbor Freight to sell butyl rubber products with adhesive on one side and foil on the other. They'd clean up the market and a lot more people than now would be able to afford sound dampening products. If enough different people asked Harbor Freight, then they'd probably start getting interested.

Harbor Freight's suggestion box:
harborfreight.com/customer-service-contact.html

I can see the typo-filled suggestions now.
"Please sell dynomite. I use it to sondpruff my car."
"Dynomite is popular and will sell with your other car products for shops, mechanics, and car-audio DIY people. The example URL is"

Foot wells behind the carpet should be plenty enough. Taking the dash apart on most modern cars is hell on earth.

Now if you wanted to attach some to some of the dash pieces, like in the back side of them if you popped them off, I guess that couldn't hurt? But the entire idea of your project here is:

>How do I make my car ride like a luxury car but not spend 70000 dollars

If you are smart where you put it and do it efficiently, only putting just enough to get the job done, you'll get tons of results.

I would say:
>inside the door
>trunk pretty much everywhere you can get to bare metal
>under the carpet in the cabin

Don't forget obscure places like under the rear deck of your trunk area like in my pic. That's also a pretty good demonstration of how much you need.

Lol I would love to be the one getting those.

>Taking the dash apart on most modern cars is hell on earth.
There's also those "pine tree" type plastic nails. Some are long and some are short. But when you pull them out, a lot of the prongs are bend and no longer have the same firm grip they used to have. So you have to buy packages of them ahead of time to replace the ones you break. Depending on the make, some fasteners are meant to self destruct so you will have to buy some of those too depending on your car model. Look that up in your hayne/chilton/alldata. Your library might subscribe to their online versions.

Rock auto is also good for parts matching by parts number

Does anyone recommend any specific youtube videos on removing pillars and headliners (especially from a GM car)?


>Rock auto is also good for parts matching by parts number
Got back from Harbor Freight. They have both the yellow and blue trim tools, so I bought the blue set as that was closest to the Bojo name branded trim tools. The plastic sure looks a bit cheap and smells like "smoky burned plastic" so it is probably a mixture of nylon and recycled melted plastic. China does buy a lot of USA recycled paper and plastics, so there is the possible chance I might be using a tool that has one or two high-quality molecules donated from either Taylor Swift's or Britney Spear's douche plastic bottles getting recycled. A few molecules closer to heaven.

I should try to find out the parts numbers first before I start taking apart the door panels, headliner, and some of the pieces in the footwell area. From probing around, it seems that some of the larger trim pieces have those plastic pine trees built-into the actual trim. So instead of having a separate "pine tree bolt" that goes through a hole in the trip (which looks bad) the trim itself has a short pine tree sticking out of it. I hope I don't break too many pine needles off which would make the trim loose.

Well, baby has to take first steps sooner or later. I am just having "first time" nervous jitters about breaking car trim.

>Does anyone recommend any specific youtube videos on removing pillars and headliners (especially from a GM car)?

I will search up some vids and study some of them first before trying to pry those pine trees. I don't want a "learn by error" method when I could have a "learn by success" method instead.

Gah, one of those "how to remove a headliner" vids was nothing more than someone talking about buying a new headliner.

Try to find diagrams of the parts so you can see where the fasteners are. It's always going to be tough pulling an interior apart the first time on a modern car, if you really care about it going back together perfectly and your car isn't too uncommon try going to a pick and pull, finding the same model as your car, and pulling the interior out (salvage any clips and hardware you think you could break on yours).

>Try to find diagrams of the parts so you can see where the fasteners are
It's a 2016 and the Haynes and Chilton sites don't even have manuals for it yet. Otherwise I would buy one.

I heard of "factory service manuals" being available for sale and those have superb detail. Is there some sort of clearinghouse that sells such a thing? I had always thought only GM would sell those, but I haven't found a place at their website that sells ones for Chevy. Do you happen to know of any sellers?

I've been to my dealer's parts dept and they have super detailed pictures listing where all the parts go relative to each other and exploded views of assemblies with parts listed. But they always refuse to make a printout or even parts list (no pictures) for me. It's proprietary info they say.

Look for dash parts on eBay, sometimes they take pictures of the the back.

>I want everyone to hear my shitty exhaust except me
mp3 engine sounds did nothing wrong

>adding "mass" type sound deadening on rigid stuctures
top wew

youre allowed to browse and post from your phone but dont make it shitty for the rest of us trying to retain any semblance of collective image quality

>56k warning

Just how poor r u

>shitty
Not everyone on here is poor user. Some of us can afford actual performance parts.

It's not really rigid. It's a 2 layer metal piece that bolts to the frame of the car.

>Just how poor r u
There's actually still quite a few people using 56Kbit dialup modems out there. Many people can't afford comcast cable on their own, but may share it with neighbors. I know of quite a few people who use a wireless router to share their comcast internet and they split the bill to make it affordable.

>Rock auto is also good for parts matching by parts number

I'd better buy a bag of clips and fasteners ahead of time. I was reading how one guy broke 100% of his fasteners the first time. Then when get better he only broke 70% of them. He wasn't able ever get to zero loss, so some of these newer fasteners must be truly one-way one-use consumable items.

That is a good idea. I broke 3 like immediately.

>Get better tires first
How do you know which tires are quieter? Tire descriptions always say they are quiet. Some people even say Michelin Pilots are quiet.

What are typical installation prices of dynamat from the car audio shops? I would like to have some ideas of what are "reasonable" prices so that I don't get ripped off by fast talking "sounds good" salesmen in the front office.

Call the dealer up while recording phone call, ask if setting up dynamat yourself would void any warranty, if they say no then you've got evidence to show if they ever try to give you shit in the future. If they say yes then you know you gotta be real careful.

All sound waves are longitudinal waves.

I use roof repair tape because I am a cheap fuck.

Your point?

Called fy Chevy Dealer's service writer who said it is an unapproved car modification that can violate the new car warranty if improperly applied. He would not clarify so I think it is their generic safe statement to make for anything their dealership doesn't itself do the work.

I would've though that would be obvious.

>It is weak against longitudinal vibration or standing waves transmitted through a beam.
>All sound waves are longitudinal waves.

From wikipedia:
"Sound is transmitted through gases, plasma, and liquids as longitudinal waves, also called compression waves.

"Through solids, however, it can be transmitted as both longitudinal waves and transverse waves."

Seems the first poster was too terse in not using enough words. Dynamat would reduce sound radiating into the air from that beam, but it is apparently less effective at preventing the coupling of sound from that beam to other solid structures.

When doing the floor in the cabin, the area above the exhaust line can get hot. Does anything special need to be done about heat buildup? Or are all types of sound insulation going to be okay?

I would say "most" would be okay as long as they're butyl + aluminum based sound deadening. The plates above my exhaust in the picture take most of the heat here though.

>want to silence road noise
>doesnt want to listen to engine purr or transmission shift or how his car sounds handled on the road
some people really hate cars

Road noise is very different from engine sounds.

I want to get rid of wheel noise and drone, but I love hearing my engine and exhaust.

Anyone have any experience or opinions on lizard skin?

right. but in doing so you also lose the sound of your engine and exhaust

Not necessarily. Depends on where you put it. I didn't use a whole lot, only enough to remove vibration but not block noise. Whereas in the wheel well areas, I loaded it the fuck up fully intending to block all noise. I'm even debating taking the wheel wells out and loading up the back of them with truckbed liner.

The whole idea for my sound reduction in my car is to make it perfect for cruising and hammering back roads. Similar to a luxury car.

1. Reduce road noise
2. Reduce drone and resonance
3. Keep the sound of the engine and exhaust
4. Improve the performance of the sound system

I like the idea of it, but I have 0 experience with it.

>The plates above my exhaust in the picture take most of the heat here though.

Any guess as to how hot the in_cabin side of the floor metal got? I am thinking of going overboard and laying down strips of the 3M Damping Foil 2552 at all locations near the edges of some major flat pieces. By "major flat piece" I mean the whole flat section. After the 3M 2552 is laid down in hopes of reducing the amount of vibrations coupled to adjacent big metal pieces, I will cover the whole thing up with dynamat.

That butyl rubber has a thermal insulator effect, so who knows what the heat rating of its adhesive is like? The 3M 2552 adhesive is rated to 80c continuous and it's made in the USA. But that dynamat material and its container of adhesive might be from china for all I know so is the temp rating of the adhesive for dynamat reliable? Also, butyl rubber made by ExxonChemical has a melting point around 80~90 celsius. So it seems the 3M product is able to go higher than dynamat because the adhesive is able to go to 80 and remain serviceable whereas butyl rubber has a more extreme reaction of melting away.

apparently spectrum is better if you want the spray on stuff

Is it possible to apply sound deadening on the exterior parts of the vehicle? Such as underneath the car? It seems that deadening both sides of a piece of steel would reduce the sound even more.

But what types of sound dampening material can go on the outside?

Not too sure. But it couldn't be too hot, probably warm to the touch. I say that because look at whats touching it right now: trim pieces, rubber, plastic connectors for wiring, and carpeting.

You know, I'm not sure. I dunno what sort of longevity it would have. I think this is an application for undercoating though. That's design for external use. That's not to say sound deadening wouldn't stay though.

oh damn that sounds great

I need to do that

>I dunno what sort of longevity it would have.
It would have to be applied before any rust or corrosion began to occur on the undercarriage. SO that means a new car is the most likely candidate. Low profile, non-hygroscopic, cannot be torn by debris, brush, and pebbles. It must not be ripped by flying glass particles and sand, and should not grow mold or absorb salt water or other corrosives.

That leaves out things like foamed butyl rubber, porous spray coatings, and stuff that scratches away easily. Rips and tears can serve as places for corrosive liquid to gather and eventually form a pocket between the spray coating and the metal. That would accelerate corrosion. It would seem that B-Quiet and 3M Dampening Foil 2552 are the primary candidates able to withstand partial exposure to an external environment without causing future problems for the under carriage.

Actually talk with someone who knows about it.

It doesn't 'block' the sound, it adds damping mass to a panel to stop it vibrating. You don't need to slather that shit on like it's a nutella sandwich when your mother is away for the day.

Good question.
My Direzza's sound like they're running over rumble strips just going over a centreline.
A small brass band when it's going over a wet centreline.