Been meaning to post this article for a while.

With a 2011 G37 Coupe Journey and the 19" Enkei sport wheels, I find the car rather loud. I use Michelin AS3s as my tire and they are one of the quieter tires out there. But I wanted to take it a step further.

Material:

• 3M Sound Dampening Material
  3M Sound Dampening Material
  - Approximately $15 per can. I used 5 cans to cover the 4 wheel wells.
• BoomMat Spray
  BoomMat Spray
  - Similar price, wanted to give this brand a try. I used 4 cans to spray underneath the car.

BASELINE dB Readings:

• Local Road @ 55MPH - Range = 64dB - 67dB
• Local Street @ 25MPH - Range = 66dB - 67dB
• Highway @ 70MPH - Range = 68dB - 74dB

Procedure - Wheel Wells :

1. Jack up car, remove all wheel well material
2. Cover up all suspension parts
3. Liberally spray the sound dampening - avoid key areas (brake lines, suspension,...)
4. Allow to dry for a few hours, put everything back together

Before and After Pictures :



Wheel well, no insulation shown



Bare metal - nice noise chamber






First coat looks a little wet...



Coat is now dry



Showing off the Koni Adjustables

dB Readings - AFTER Wheel Well Sound Dampening Applied:

• Local Road @ 55MPH - Range = 64dB - 66dB (~1dB gain)
• Local Street @ 25MPH - Range = 62dB - 65dB (~2-4dB gain)
• Highway @ 70MPH - Range = 66dB - 71dB (~2-3dB gain)

Procedure - Under-Carriage :

1. Put car up on Ramps - front wheels first
2. Lay down a tarp under the car, lay old towels over the exhaust system
3. Wear on old long sleeve shirt - its gonna get trashed!
4. Put a mask on and wear an old hat b/c you may end up throwing it out too
5. Wherever you see bare metal, spray it.
6. Don't get the spray on the drive axle or any exhaust components

Before and After Pictures :



Driver side looking in





The frame is a good source to have sprayed



Another shot of the frame, but don't mess with the drive shaft - best to cover it.



Wet looking frame



Who cares what it looks like - you just want results!

dB Readings - AFTER Under-Carriage Sound Dampening Applied:

• Local Road @ 55MPH - Range = 61dB - 62dB (Overall gain ~3-5dB)
• Local Street @ 25MPH - Range = 61dB - 64dB (Overall gain ~3-5dB)
• Highway @ 70MPH - Range = 64dB - 68dB (Overall gain ~4-6dB)

Bottom line: : well worth the 4-5 hours it takes to do all of the maneuvering to prep get yourself into position to be able to apply this material. Wished I put on more than I did, but I'm very happy with the results:

Summary:

• Total Cost: ~$135
• Total Hours: ~5
• Skill Level Required (1-5 where 5=hardest): 1
• Satisfaction Level (1-5 where 5=most): 3

 

Interesting project, going after this from the exterior. Glad it worked out for you, 3 out of 5 notwithstanding. Have you ever considered Dynamat behind the rear seat?

 

Not yet. The spray on is quite easy. May consider lifting up the rear seat and trying either the mat or another round of the spray. But great idea. If I do I'll be sure to measure the additional gains I pick up.

But based on what I see/hear/read, most of the noise could be traveling up through the suspension components and steering and into the cabin.

It's a gradual process (but fun none the less).

 

Welp, subbed here for whatever you do next. Dynamat isn't cheap, so I suspect you could burn through another $150 in materials covering the sheet metal behind the rear seats.

Here's a related story... two summers ago I installed a short throw shifter, and there were a couple of days where I was driving around with my center console & armrest removed, along with the inner rubber shift boot. I could actually see the pavement while driving... and Holy Hell what a racket! It was crazy loud.

So maybe under the shifter console is a good target for sound deadening, too.

 

Thanks for taking the time to detail this so well and record your findings along the way, well done! I'm moving this to the DIY folder and making it a "sticky" to keep it fresh!

 

Which one do would you say is better, the 3M or BoomMat spray? I'm thinking I might do this sometime soon.

 

Well the biggest improvement came from spraying UNDER the car frame as opposed to the wheel well. It surprised me (i thought the wheel well would have made the biggest difference).

But in terms of the product, one was not better than the other. I'd go with what is the cheapest.

I may buy another can or two and hit a few spots again and cover some spots I missed.

 

Thanks for the answer. I'm planning to get maybe 12 or 15 cans to make sure I get good coverage.

 

I wish I found this sooner,

 

 

Hi, petemo94. Thanks for posting this useful guide/review! I am also running A/S3+ on 19" wheels and this sounds like just what I'm looking for. Would you mind elaborating on your satisfaction level of 3? While I appreciate your method of measuring the noise magnitude in dB, I want to know what you feel has notably improved since the installation (music listening, conversation, etc) as that also depends on the timbre/pitch of the deadened noise.

 

So in terms of satisfaction, I rated it a 3 mainly because even though it improved the road noise and tire noise, I wanted the car even more quiet. The A/S3+ is what I had when I tested the dB levels. I now own Conti-DWS. I still feel there is room to improve underneath the car to make it a level 4 or so. Mainly near the back of the engine bay as well as under the tunnel of the shifter (as one reader noted there was a lot of road noise coming from there).

With summer coming, I may try to spray another 2 cans under the drive shaft area (I left it alone due to the drive shaft). Hoping this will get me to a level 4 in terms of satisfaction.

Again, I was mainly interested in road noise reduction and not so much with stereo improvements. It is easier for conversations to take place now. I seriously considered downsizing to an 18" 5-spoke 350Z anniversary wheel but held off b/c the look of the 19" is too nice.

Hope this helps.

 

wowwed: Did you ever do this to your car? Any new findings?

 

I'm currently away and I plan on doing this when I get back towards the end of summer. I'm going to take my time to wrap up all the parts that need to remain dry. While the boom mat is drying I may go in and do the shifter area with some Dynamat.

 

If you have a sedan im finding one of the biggest culprits of noise/ resonance is the spare tire well. That would be a great candidate for this. I currently have dynamat inside its still not enough. The rear seats are next and it looks like ill use this spray to do the underside of the spare tire well.

thanks OP