My sound deadening project (1 Viewer)

[accasbel]

I layered my floorpan (front to back), doors, and many interior pieces with Second Skin's Damplifier and replaced all the jut with Second Skin's Heat Wave. The truck doors now close with a thunk, and most of the high pitched clangy sounds are gone. For that I am most pleased. However, the measured noise levels have hardly changed.

Measurements taken with Radio Shack SPL at 55 MPH, asphalt road, windows up, radio & heater/AC off.
Before SPL: A weighting 77 dB: C weighting 94 db
After SPL: A weighting 74 dB: C weighting 94 dB

A weighting was 3 dB lower, C weighting was the same. The differences of different measurement standards. But I gotta say the truck felt quieter. As I mentioned, many of the high pitched sounds were gone. While I didn't see the measured differences I expected, I am happy with the results.

 

[Carpe Discus]

Well, if you think about if this is about what you'd expect. dB(C) is more sensitive to lower frequencies as dB(A), and the latter is said to most closely approximate human perception. So your measurements show that the sound reduction weighted to human perceptual curves is roughly equivalent to halving the input power of the source (your 3 dB(A) reduction.

They also show that on the weighting that favors lower frequencies comparatively more (dB(C)), there wasn't any/much of a reduction. Seeing that lower frequencies are generally harder to attenuate than higher ones, this makes a lot of sense.

 

[Benjaman]

I think 3db is a 50% reduction.