Originally Posted by montr
In the mean time I measured the audio frequency response of my car. See attached response. To measure the response, I created a CD with a filtered flat white noise (200Hz to 20KHz). I used the sound card (16 bit @ 96KHz) of my laptop to capture the output of the radio. I did a Power Spectral Density of the data using Matlab.
Note: With Bass=0 and Treble=-4, the frequency response is within -1dB and +2dB.
I just noted your initial measurements were taken from the rear speaker terminals of the base audio output. I didn't expect such an ugly EQ curve but believe it is quite different from the front, full-range channels.
Unless I am missing something, would you mind running this exercise again with data for the front channel outputs of the BMW base audio head unit, with one graph detailing the electrical response before the Alpine amp is fitted and again with the outputs of the Alpine amp? I'd like to see what sort of normalization it provides as the HiFi Upgrade Kit only interfaces with the front channels.