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)