Sound Deadening - Share Your Experiences

[Panici]

Looking for experience from those who have spent some time & money improving their vehicle's NVH.
I'm planning for future improvements in my project cars.

Please include details such as material type (Butyl Rubber, Closed-Cell Foam, Mass Loaded Vinyl, etc), and coverage.




I'll go first.

Vehicle: 1987 325is
Material Type: HushMat 10500 Ultra Black (Butyl Rubber)
Coverage: Inside Firewall, Transmission Tunnel, Front Floorboards, Inside Rear Quarterpanels, Under Rear Seat (partial coverage), Trunk.
Other Details: Removed factory sound deadening on trunk floor many years ago for weight reduction.

Notes:
I chose the HushMat as it blocks both sound and heat. Applied carefully with a roller (see pictures).
Didn't have enough material for full interior coverage.
Not concerned with added weight now that car is turbocharged.
Factory carpet is in place over the Hushmat, with Lloyd Mats Ultimat Carpet Floor Mats front & rear.
Cloth interior/seats with CAtuned Black Headliner.

Impressions:
Unfortunately I can't provide a great back-to-back comparison here, as the car has a different powertrain & exhaust setup then when I last drove it without sound insulation a few years ago.
When you sit inside the parked car you get a hint of that void-of-sound sensation like when inside a walk-in-closet or surrounded by padded material.

I can say that the car feels more luxurious then ever, and I'm sure the sound & heat insulation helps with that. A quieter exhaust setup will be my next step.


At minimum I plan to revisit this project with more HushMat inside the car, as well as the door skins and trunk.

EDIT for 2024: Added additional sound deadening to the trunk, see post further in this thread for pics. Noticeable difference here as well, helped kill noise from the rear end poly bushings.









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Vehicle: 1990 NA6 Miata
Material Type: Kilmat 50mil (Butyl Rubber, foil backed). HushMat 10500 Ultra Black (Butyl Rubber)
Coverage: Hushmat on Driver's Side of Trans Tunnel & Firewall.
Kilmat 50mil on Transmission Tunnel, Front Floorboards, Rear Parcel Shelf, Rear Bulkhead, Trunk Floor (full coverage), Trunk Lid.
Other Details: Hardtop w/factory lining.

Notes:
I used HushMat in areas to block heat.
Weight was initially a concern so 50mil Kilmat was used. Now that it's turbocharged weight is less of an issue.

Impressions:
Night & day difference.
Car went from a rattly tin can to tolerable levels of noise.
Firewall and trans tunnel no longer cooks you while you drive.

The Butyl rubber products by themselves improved the daily driving experience so much, that I will be exploring further improvements in NVH reduction.
I've already bought a box of Kilmat 80mil so I have it ready the next time the interior is out of the car.

[jsta1109]

I went overboard with butyl on the entire floor pan and inside the front doors and rear quarters after some rust repair removing the factory sound deadening. I added closed cell foam to the doors and rear quarter area and behind speakers. Overall, I really didn't notice much difference over the stock and I definitely added too much to the floor. If I had my time over I would have place the butyl strategically and copied the factory placement as much as possible. I think I would have better results if I made my exhaust quieter, used different tyres and added insulation to the underside of the bonnet/hood. Worth noting I haven't touched the boot area, I think there's some gain here.

[varg]

Foam won't do anything in an automotive noise reduction application, its primary use is to reduce reflection, carpet and headliner does most of the job of reducing reflection in the cabin. You see it in anechoic chambers and studios for that purpose, the walls are full of vibration isolation and extra mass and that does the "blocking" of outside sound. In a car, your panels are vibrating. Your most effective strategies are to decouple to reduce vibration (soft bushings, engine mounts) and add a material such as Mass Loaded Vinyl, which damps panel vibrations. Thinner and flatter panels are the worst for noise; roof, doors, quarter panels, trunk. You usually don't even need to cover the whole panel to make a noticeable difference in noise. If you have a chance to look at a higher end car like an S class or 7 series which has been stripped out at the junkyard, take note of where they place the stuff and copy the experts.

[McGyver]

I covered the entire floor of my 91 coupe in Dynamat Extreme. I think the car sounded a little more solid, but I still had plenty of NVH due to suspension and exhaust. For some reason, that car always felt hotter inside than any other e30 I've owned.

If I did it again, I would probably be strategic about damping panels and focus more on blocking heat.

[Panici]

Foam won't do anything in an automotive noise reduction application, its primary use is to reduce reflection, carpet and headliner does most of the job of reducing reflection in the cabin.

I've read that closed-cell foam works well to decouple between a panel and mass-loaded vinyl. I don't have first-hand experience with either material though.

[varg]

There are adhesive MLV applications and mats which you would decouple. How much mass do someone wants to add and how much do they want to reduce noise is what that would come down to. You could put some butyl product like dynamat on the panel itself to damp vibration, then add a layer of decoupling, then a layer of MLV mat, then your carpet or interior panel. An E30's carpet is probably a little over 4' wide by a little under 6' long, so you'd be adding 50lbs or more with 2lb MLV under an E30's carpet by the time you cover the driveline tunnel as well. There you will damp with the butyl and block sound with the decoupled MLV mat. It's dense and not very rigid so it does not tend to vibrate sympathetically well when it is decoupled, so sound is "blocked" by it in this type of application. You typically see this kind of application in structures, where there's a wall, some decoupling, a layer of MLV, another wall or exterior wall. There is the caveat that you want your MLV sheet to be as close to continuous as possible in this case because otherwise sound will propagate around it or through gaps.You could stick a sheet of MLV to the back of the door panel then decouple the door panel from the door with foam, that is part of the function the foam backed plastic sheet you see on the inside of a factory door. You can stick adhesive MLV directly to a panel and use it to damp through its considerable mass as well. Foam on its own does almost nothing. The right type of soft small closed cell foam might be better than an open air space between the quarter panel of a coupe and the interior panel, but not by much. Stiffer foams will directly couple to the door panel and transmit more vibration. There isn't much reflection going on inside the car that isn't from the glass, that's one of the banes of audiophiles setting up a car sound system.

[DEV0 E30]

I'll add more to this soon(ish) but there is a lot of good info out there. Too much multi-tasking this afternoon.

I believe the combos of dynomat and vinyl / mass loaded vinyl / is the way to go, but it's about strategic application, not covering every inch as suggested.

Good stuff and information from this company, https://www.secondskinaudio.com/

Awhile back I went down a rabbit hole on this stuff, and started reading customer reviews and installs via Amazon, and other sites.


I wanted to go a bit overboard on my 100 series land cruiser, and probably add a decent amount to the E30 - but that won't be for awhile.

This topic definitely pertains to my interests.

[Panici]

Updating this thread RE: E30 Sound Deadening.

I added some to the trunk last year to replace the OEM material which I had removed many years ago.

Definitely took the edge off the extra noise from going poly bushings on the rear subframe and trailing arms, along with the 2nd diff mount.
(Wouldn't have used poly, but needed them to control axle movement and wheel hop.)

Also have a Lloyd Mats Ultimat trunk mat which adds some mass onto the trunk floor.

[Panici]

Vehicle: 1998 328i
Material Type: Kilmat 80mil (Butyl Rubber, foil backed)
Coverage: Trunk only.
Other Details: All OEM sound deadening, padding, and carpet reinstalled into trunk.


Notes:
12" Subwoofer in ported box installed.
Near-straight exhaust system.
Did switch to an OEM front section with cats and resonators before even adding sound deadening.


Impressions:
There is a difference.
Subwoofer doesn't rattle the car like a tin can anymore.
Exhaust sound is slightly better, but you can only do so much with pipes putting out significant volume. I still wear earplugs on the highway.

It is worth the effort on anything you drive regularly, and the Kilmat 80mil product isn't too expensive.
If I ever have the interior apart again I will add some there as well.

[strickland]

I’ve also dabbled in sound deadening. Applied to the doors, rear quarter panels, & behind the back seats. Haven’t touched the trunk.

It does make a difference… I honestly miss hearing the exhaust note in the cabin.

Things i wish I had done differently:

Start with the floor / under carpet.

On the door - Put the butyl in place of the plastic vapor barrier, so it sits against the door card. Some modern cars have this. Has anyone tried it? I wonder if the door cards would still fit okay.

[808ETA]

Found this facebook group https://www.facebook.com/groups/651457188787366

[Panici]

On the door - Put the butyl in place of the plastic vapor barrier, so it sits against the door card. Some modern cars have this. Has anyone tried it? I wonder if the door cards would still fit okay.

Seems like this would be MESSY to remove servicing components inside the door?

[McGyver]

It's so funny to see an old post of mine saying EXACTLY what I would have posted today.

I really want to do some sound deadening for my 89 sedan. I've added a skid plate and x-brace that transfers significant NVH, even for a stock drivetrain with OEM bushings. This car is only going to get louder so any reduction in NVH will make it more enjoyable for my wife on longer rides. Plus, I plan to get the AC working and don't want to feel like I'm in a reverberating tin can with the windows up.

Heat and NVH reduction would be my main goals. Panici, would you use HushMat again?

[Panici]

Heat and NVH reduction would be my main goals. Panici, would you use HushMat again?

For an application where heat reduction is needed, I would definitely use HushMat again.
(Or in the case of the E30 I wasn't concerned with cost, so used it everywhere even if it wasn't strictly required.)

My Miata went from cooking my feet (almost painful temperature) to comfortable by adding HushMat inside and DEI Reflect-A-Cool on the bottom near the exhaust.
Small cost for a huge reduction in suffering on a non-AC car.