Audio Tuning? Yes!!!!

Posted on restoration of my 1976 BMW 2002

Ok I have all the pieces. A clean head unit that puts out a nice undistorted signal. An efficient and high power amplifier to handle that clean signal and send it to the speakers. And finally speakers capable of handling that signal and performing well at the task they were designed for. Flawless reproduction of the audio signal. Install of all these devices was done by me with attention to detail. Make sure the installation was top notch. With all the pieces finally in place. How did it sound. Well it was nice and loud. And at times was phenomenal but at times it was well….unbalanced. Bass heavy or treble heavy. Depending on the song playing. So I did more research bought a digital multimeter and began to tune.

First up…setting the gains.

I have installed lots of car stereos over the years and have never had to set the gains. So now on this amp it’s a must. The gain adjusts the input voltage for different levels of input. Some decks put out higher voltage signals than others. So the key is to set this properly so there is no distortion sent to the speakers. If the gain is too high you will get square waves that will blow the speakers. Too low and you get unwanted noise from having to over amplify the signal. Get it right and it’s bliss. This is done by using test tones at various frequencies and reading the voltage being put out at a certain volume level. It’s basic math. Multiply the wattage of the amp x the resistance and take the square root of the result. This is the voltage the amp will put out. I used the internet to generate test tones at 50 hz for the subwoofer and 1 kHz for the fronts. I then played the tones through the system with the speakers unplugged and adjusted the gain until I got the appropriate voltage. I my case it was 18.4 volts for the fronts and 26.4 volts for the sub.

Next Set the Low pass filter for the sub and the high pass filter for the fronts.

I did this by playing a 100Hz tone (that was my desired crossover frequency) and played the tone without the filter on it. Then adjusted the crossover frequency until the voltage was 1/2 of what it was at full. That represents the crossover point for my low pass and high pass filters with a 12db slope.


Once I connected my speakers the I could adjust bass, mids and treble eq as well as subwoofer level.

The Results?

Phenomenal. It was more technical than I thought but the results are truly phenomenal. The sound is clear, crisp, balanced and powerful! The low end is deep, tight, punchy and clear. The high end is crisp and clear. The imaging and soundstage is wide and in your face. It’s almost 3 dimensional. It’s the same at all volumes and it’s the same on all source material. It took about 30 minutes to tune but it was the most important part of the install by far.

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