After hearing some improvement by others following their installs, I went ahead applying a sound deadener material into the trunk to see if that would quiet down the exhaust noise in the cabin. I also took some noise level measurements using a decibel meter to try and verify the effectiveness.
I purchased the
Noico 80 mil sound deadener mat and the
170 mil sound insulation foam materials. I went with these because I wasn't totally convinced of what the results would be and didn't want to drop the money for something more expensive like Dynamat. Plus, others have done a similar install with reported success.
The install went relatively smoothly, but took a lot more time measuring, adjusting, and rolling than I had anticipated. This was my first time doing any type of sound deadener, but this product was really easy to work with and forgiving if you had to peel it up and reapply into any creases/surfaces. I did manage to tear the foil backing a few times, but it was easily patched up with foil flashing tape. The diamond pattern on the back was helpful in telling the progress areas where you had rolled. All together I would estimate that the total time spent on the install was around 10 hours. I ordered the 18 square foot package of the 80 mil mat and used all but one full sheet and a few remnants. I did not end up using the Noico Green 170 mil sound insulation foam because I wanted to see how the mat itself performed.
Prior to the install of the mat, I took a noise reading using a decibel meter that I rigged up in the front passenger
seat about where someone's head would rest. My measurement run consisted of driving down the local surface streets using a "normal for me" right foot and then going one exit down the highway (~1.5 miles) trying to get the revs up. I started out (surface -> hwy) in comfort mode, then exited, turned around and backtracked the same route (hwy -> surface) in sport mode. The car was empty aside from the meter and myself - no radio, minimal AC. The contents of the trunk consisted of the battery, spare tire, jack kit, tire cover, stock carpet pad, cargo tray, and cargo net.
Test before deadener:
- Comfort mode, surface streets (~45 mph @ 2k RPM) to Hwy (~90 mph @ 4.5k RPM) = 84 dB max
- Sport mode, Hwy to surface streets (similar speeds) = 82.3 dB max
Interesting reading, but it did confirm my suspicion that comfort mode seemed louder. My guess is that the car's desire to keep the RPMs relatively low (1.5-2.5k) create more of a resonating rumble when pulling off.
Test after 80 mil deadener:
- Comfort mode, surface streets to Hwy = 81.3 dB max
- Sport mode, Hwy to surface streets = 82 dB max
Conclusion: The mat installation definitely reduced the loudness of the in-cabin noise from the exhaust. The decibel meter recorded an overall drop of around 3 dB in comfort mode. Not sure about the frequency difference, but resonance of the exhaust system in the cabin of the car is definitely improved over not having the mat installed. In my opinion the noise is definitely reduced, but you can absolutely still hear the Borla exhaust. On a recent road trip, a highway "drone" was present when cruising (~2k RPM) but negligible; normal conversation wasn't an issue and the radio would have easily drowned it out. Following these results, I may try installing the foam insulation mat around the trunk areas and on the underside of the stock carpet pad. Overall, I would say that I am happy with the results.
Check out the images below for more details on my install and setup:
The decibel meter set up on a tripod inside the cabin near the passenger headrest.
Post install images:
Also, for kicks, I set up my GoPro to record a time-lapse of the install:
