Objective analysis of cabin noise solutions

[SeattleLion]

There is general agreement that the 370Z is noisy. The sport package versions appear to be the loudest. There also is agreement that reducing the road noise would be a good thing.

Several solutions have been tried by members. Members report different results applying the same solution. Since "loud" is subjective, I suggest that members preparing to perform cabin sound reduction provide some objective data.

If you have an iphone, a droid, or a Windows phone, you can download an app (99 cents I think) for measuring sound levels. Since we are interested in "before" and "after" numbers, we are not really concerned with how accurate the absolute values are; just the difference between before and after.

How to do the measurements
Download the app and familiarize yourself with how to use it.
Before you install the material:
Find a road you can easily reach that you consider noisy. Measure the sound level between two points you can find again. Drive at a constant speed. Note that level. It should be in db (decibels).

After the material is installed:
Return to the exact spot you measured the first time. Take a sound reading at the same speed you drove before the installation. Note the sound level.

Post the readings as well as what you did to reduce noise in this thread.

Some notes on sound readings
The decibel scale is logarithmic. That means that changes are not linear...for example if you measured 85db before and 75db later, you didn't reduce noise by 12% (the difference 10 divided by the original 85). You actually reduced the sound level by 1/2. A 10db change down is 50% of the original.

So if you reduce the noise by 10db, you have cut it in half. However, that does not mean the sound is half as loud to you. The human ear is not linear either; so reductions in sound level do not necessarily sound quieter to the ear. This is one reason why subjective reports are hard to understand.

If you can help with this, we can compile some objective expectations for various noise reduction solutions.