I think this outlines some of the problems in using an RTA inside a car - it isn't really a great idea. (its only really useful at low frequencies in a car)
A 3dB gain is certainly not quadruple the voltage. A 6dB gain is double the voltage, a 3dB gain is ~1.414 times the voltage.
Boosting on an EQ is not as bad as people make it out to be. It can be useful, provided you understand what you are actually doing. If you boost a particular frequency range, by 3dB, the effect you will get is actually lowering all of the other frequency ranges bar that one by 3dB - since you'd also lower the gain by 3dB to avoid clipping. These days when you have with massive amounts of headroom - using 300w+ amplifiers on speakers that will play loudly with 50w, they can actually afford to do a bit of boosting.
However, this assumes that you actually have a legitimate dip in the response to boost - not all of the response problems in a car can be solved with an EQ and tuning solely with an RTA might look flatter on the RTA but that doesn't mean that the actual frequency response will be flatter - it may be even more messed up even though it looks flatter on the RTA....
Also, some of those peaks/troughs are not down to the filters used at all -
QUOTE
Hhhhhhhhhhhhhmmmmmmmmmmmm didn't know that phase anomalies of filters preserve as high after one decade. Interesting........... wonder what "feel" effects it has on so many other systems out there..........
Uhhh, no....