Sound proofing experiment on the 370Z

Originally Posted by 370bluez

So I figured since I didn't have much going on this long weekend I'd do a sound proofing project on the Z to see if it makes a difference.

My goal was to get the most gains without going crazy and tearing the entire interior out or using 30+lbs of sound insulation.
I went with my left over Dynamat and Frost king which you can source at the local home depot (2 of which didn't have it, FML) at 18.99 a roll.

A few comments to those that are thinking about frost king.

1. It isn't all that cheap. 18.99 gets you ~15 sq feet so about 1/2 the price of dynamat but given the way the material feels etc it may not be worth while.
2. It is very light 1/4 of the weight of dynamat, and I am not sure the sound insulation properties of this material by itself are good because they lack mass/density etc, but since I bought it I decided to use it.
3. It does have a slight smell on the glue layer, once you apply it it goes away (since it isn't exposed) but ... it could come back, I wouldn't use rolls of this **** in the car since it will likely smell. Dynamat is pretty much odor free.

I pulled apart the trunk of my Z which was surprisingly easy/quick. My first try took me about 30 min, if I was to pull it apart again, I can likely do it in 15 min or less. No broken clips or anything.

My strategy was to supplement factory sound deadening and add to flimsy/high noise areas. I put dynamat down as a baselayer, and put frost king on top since dynamat is the heavier more dense product.

I used about 10sq feet of dynamat ~4lbs. And I used about 10sq feet of Frost king ~1-2lbs. Total of 5lbs.

Overall the results were somewhat disappointing same as my golf where I did my entire trunk with dynamat. The car does seem a bit quieter but bad roads are still really shitty.

I took 3 separate measurements all at around 65-70mph on the same stretches of road.

Bad pavement
82-83 after 80-81
ok pavement
75-76 after 73-74
Good pavement
72-73 after 70-71

Overall I'd say it cut about 2-3 db out at best. Is it noticeable, yes... slightly. I was hoping for a reduction of 5-6db which would have been good. I do not think adding any more sound insulation makes any sense. I addressed all the key areas and anything incremental would be simply chasing a 10% improvement by adding 90% more weight.

I believe the next best thing to do would be to use thicker carpet type insulation as most OEMs. But that presents a lot of other challenges that I wasn't willing to tackle.

Here are some pics

Trunk plastics pulled (not the factory sound deadening was really thin and comparable to dynamat)

Originally Posted by mishuko

as Ark said you need to get the towers both sides and the centre piece as well. i'd also try and get into the wheel well as deep as you can get it. also the inner side of the trunk is nice and flat but has a big hollow noise.

i think you will get closer to the 5db reduction mark if you did a single layer over the entire thing and a double layer over the wheel wells but i can't back that up with tests.

the one thing to remember though is the dynamat/hushmat will not sound proof, it will only reduce the noise levels a little bit. my biggest notice is the road noise from the tires + the rock 'pings' from the underside. if you want to really reduce the noise you need to go the whole 9 yards.

Originally Posted by 370bluez

The shock towers were solid metal and not paper thin 1/16" of an inch like the wheel wells and the bottom of the trunk. I got the wheel wells with two layers on the front and the back. On top of the factory material as well as some surrounding areas...

I'd like to see if someone actually got measurements of sound reductions. It is easy enough to go back and add more, but I don't want to waste time and add unnecessary weight. Covering the entire trunk etc is not wise just for the sake of covering it doesn't make sense.

Originally Posted by mishuko

to be fair you should have hit every piece of metal in your rear hatch so you didn't have to go back. all the metal parts will vibrate and send out the sound.

the dampening material adds mass to reduce vibrations and dampens the sound a bit. i think you would have hit your 5-db target if you did the entire hatch instead of portions but that's me speculating.

i'd suggest searching the audio section... tons of good material there to kill some time reading and learning

Originally Posted by 370bluez

I did... I looked at at least 10 threads. Most don't have any measurements behind their claims. And from what I could tell most seem disappointed even after covering the entire trunk etc.

The proper way to apply material like dynamat isn't to cover every single space of metal but only a portion preferably in the middle of a panel i went a bit overboard since these cars don't even have wheel well liners?! WTF is up with that. Which explains the whole pebble issue.

Unless you're looking for mass damping through the sheer weight of the material. But that would require 2-3 layers of dynamat which would weigh 50lbs and is completely insane.

Originally Posted by mishuko

i agree with that statement about 2-3 full layers being insane but i did double up on the wheel well since there was no insulation as you have pointed out.

one of the things to remember is this is a pure-bred sports car. it's not a luxury sports coupe or anything close to a 'luxury' branded car so you won't be getting the same conveniences that come with the luxury badge.

i tried just the wheel wells and the spare wheel section, went back and did the entire trunk and noticed an improvement. also going from the stock tires to re-11's made a big improvement in road noise.

the road noise is fine minus hearining the pebble pings and long drives (more than a few hours). I did a few 4 hour drives before and after the install and it definitely helped relieve the road noise stress.