The balance in my car seems off. Can I use a cheap digital SPL meter ($20) centered in my car along with test tones/pink/white noise to see if each channel is outputting equally? Will cabin acoustics affect the results? I need to know if somethings off or of I'm going deaf. Having someone with good ears to listen to it would help, but it's hard to trust random stereo store people. An actual SPL test seems the most trust worthy.