Sound Deadener Door Treatment for Miata

[TimTim]

The motivation for this post was to document a comprehensive treatment of the miata door panels for improvements in NVH primarily, audio performance improvement was only a byproduct of the treatment. (But a welcomed one for sure)

When I purchased my roadster in October, I lived a mile from work and drove maybe 3 days a week so fun was a priority. My job is now 105 miles away and during the week I rent a place 28 miles away. Although the miata has been great as-is, I thought some sound deadening treatment might be helpful as I look to make the car a better commuter/tourer. I have been extremely curious about treating a vehicle for sound and the doors are a great place to start; they have the easiest access, the efforts of one door can be duplicated for the other (save for minor stamped interior door differences) and at any stage, the car is still drivable. The one drawback is the complexity of fitting around wiring, existing door card NVH treatment, locking mechanisms and windows. Additionally I had planned on replacing my window regulators so, per usual with me, there was an added measure of "while you're in there" syndrome thrown in the decision too. I placed an order with Don at Sound Deadener Showdown for some butyl rope, cld tiles, MLV, and CCF along with vinyl cement and Velcro.
So I started with removing the door card, window glass and regulator/motor assembly. For good adhesion it is vital that all the surfaces are clean and then finish with isopropyl alcohol so everything has the best condition to stick.

Next I molded the butyl rope into the space between the door reinforcement bar and the outer door skin.



I left the backing on to keep dirt out as the butyl will stay tacky indefinitely.

[TimTim]

Next, I places the CLD tiles against the outer door skin to dampen the vibration of the panel.
I chose to fit the MLV and CCF to the inner door skin and looking back, I would have preferred to attach it to the outer door panel as I feel there is more space for more coverage. Anyways, fitment started with the door panel and the CCF. I used the door panel screws to hold the foam in place as areas around panel clips and attachment point were trimmed. It is a tedious process of trim and fit and trial/error.
After getting a solid fitment, the pattern was traced to the MLV.
MLV is heavy, doesn't compress, and isn't as pliable as CCF, so this makes fitment more difficult still.

More trimming and fitting until clips start staying in place and the door lock mechanisms and handles work

Once everything was starting to get close to fitting I went ahead attached Velcro strips to the door panel and MLV. The CCF was cut to allow the MLV and door panel to sandwich the CCF and attach at the Velcro. Then I glued the MLV and CCF together. By creating a single piece, final fitment touches could be made

Here it's easy to see the additional sections that had to be cut away to fit the panel in place. There are a few foam pads on the plastic door panel seal and foam glued into the door panel that take up a good portion of the space.
Unfortunately a modification like this is completely subjective. At first I felt the change was rather small but having spent a few hundred miles driving the install, i have noticed less fatigue, generally lower stereo volume and I actually had to dial back bass from my head unit where before I had it maxed. Of course the lexus-like thus when the door shuts is a nice touch too! Relatively speaking, my wind noise is now much more noticeable. The process for door treatment here reflects the strategies described on sounddeadnershowdown.com so I do give credit where due and reference that source material for the project.

[— Malibu Q —]

Nice post. I have a question. What are CLD,MLV and CCF?

[Pfunk]

Closed Cell Foam, Mass Loaded Vinyl, and I've read that CLD is the generic name for Dynamat, but I've also seen that CLD is trademarked, so I'm not sure.

[— Agent☣Orange —]

CLD is just an engineering term for constrained-layer damping, i.e. typical Dynamat, Fatmat, Hushmat butyl or tar sheets.

Thanks for the writeup and photos!

[—atank—]

Very Good Write Up and Pictures TimTim!!!!!!!!

[— kung fu jesus —]

Awesome.

I need to do some of this to the e30.

[— kung fu jesus —]

Tim,

As an experiment on my NA, I sprayed undercoating on my rear parcel shelf cover...the flimsy tin cover held down with a number of 10mm bolts. The smell was bad, but if I were to do it again, I would use sheeting like you used. Just a heavy layer of coating on that reduced a noticeable amount of road noise from the trunk area.

Also, on my NB, I had removed a portion of fluff mat Mazda puts on the rear bulkhead. The portion I removed was behind the passenger seat. That actually increased the noise in the cabin considerably. I think if I were trying to reduce noise like you are without adding a LOT of weight, the front and rear bulkheads would be a priority to me. The 'tunnels' on the sides of the car that run from behind the seats to the trunk could also be stuffed without detriment. I would think something simple like throw pillows would do a lot to cut the noise in the cabin that is channeled into the cabin through those.

Also, a hardtop with a liner would be a lot quieter than a softtop.

[— kung fu jesus —]

Forgot to add...

Pfunk had also done some extensive sound deadening to his NB. I don't know if he posted pictures of it on here or not. Maybe reach out to him and see.

[— Phatmiata —]

Nice write up? What size Butyl Tape is that? looks like 1/4" x 1/2" from the photo?

I used some Tremco 440 double sided Butyl Tape when I did something similar to adhere some 6 mil Visqueen polyethylene plastic sheeting to help waterproof the doors of my last Miata.

[Bohman731]

Tim,

I think if I were trying to reduce noise like you are without adding a LOT of weight, the front and rear bulkheads would be a priority to me. The 'tunnels' on the sides of the car that run from behind the seats to the trunk could also be stuffed without detriment. I would think something simple like throw pillows would do a lot to cut the noise in the cabin that is channeled into the cabin through those.

I actually did this. I did rubberized undercoating throughout the trunk and then dynamat. Followed up with pillows in the rear parcel shelf tunnel area. I got some $2 pillows from walmart and I got 4 to fit back there. My concern was that if moisture got back there and soaked the pillows I could have a problem with smell/rust. So I check it once a month just to be safe. I have to say it removed a TON of cabin noise. Very happy with the results.

[TimTim]

Nice write up? What size Butyl Tape is that? looks like 1/4" x 1/2" from the photo?

I used some Tremco 440 double sided Butyl Tape when I did something similar to adhere some 6 mil Visqueen polyethylene plastic sheeting to help waterproof the doors of my last Miata.

It's 3/8" wide and 15' long. It is fantastic stuff and I only used 5-6' to do one "stipe" along the door bar. My personal choice was to reserve some of the rope for other areas. I retained the plastic weatherproof as well, but cut some of the foam attached to it to make room for the layers I added

[TimTim]

Tim,

As an experiment on my NA, I sprayed undercoating on my rear parcel shelf cover...the flimsy tin cover held down with a number of 10mm bolts. The smell was bad, but if I were to do it again, I would use sheeting like you used. Just a heavy layer of coating on that reduced a noticeable amount of road noise from the trunk area.

Also, on my NB, I had removed a portion of fluff mat Mazda puts on the rear bulkhead. The portion I removed was behind the passenger seat. That actually increased the noise in the cabin considerably. I think if I were trying to reduce noise like you are without adding a LOT of weight, the front and rear bulkheads would be a priority to me. The 'tunnels' on the sides of the car that run from behind the seats to the trunk could also be stuffed without detriment. I would think something simple like throw pillows would do a lot to cut the noise in the cabin that is channeled into the cabin through those.

Also, a hardtop with a liner would be a lot quieter than a softtop.

I plan to completely treat the rear bulkhead and behind the seats. Covering the large rear section of the car will require much more material and time, working with more complex curves requiring laminating separate layers because MLV only bends in one direction at a time. With that said, I agree that it will be the greatest benefit there. Alternatively treating the trunk and tunnels is easily accessible and could provide major benefits. For "stuffing" 3M has a product called thinsulate acoustic that does not retain moisture and can be pulled apart like a fabric but has a strong backing that can be glued anywhere/ packed into anywhere.

[— Agent☣Orange —]

Blocking the tunnels is a great idea but a lot of noise actually comes from the rear wheel wells like a speaker box. As long as you're stuffing the tunnels, try to get some material inside the wheel wells. You can access them from the trunk and by removing the seatbelt recoilers and reaching up from there.