911 Stereo – Tuning It Up

One of the reasons the 911 I bought appealed to me was the upgraded audio system (I knew I would be unhappy with the stock Bose system). A critically important element of a car – for me – is the way the stereo sounds. I took a bit of a calculated risk since I didn’t know exactly what I was getting, but I’m pleased to report it paid off.

The only thing actually advertised was the upgraded head unit. There was also a picture of two JL amps (but no mention of them in the sale text). The stock Bose system is fiber optic and I surmised that if someone went to the trouble of replacing the head unit they probably replaced the speakers as well.

When I first turned the car on the sound was pretty muddy and there was a distinct lack of clarity and detail. The sub was much too loud in relation to the mids and it was suffering from some pretty bad distortion. The staging was all wrong too. The worst part though was a ground loop buzz in both rear speakers. Not too impressed. The first step was to figure out what I was working with.

The head unit was a Kenwood DNX8120. Back in the day (say 2008) this was top of the line stereo. Lots of features (DVD, Navigation, Bluetooth, etc) and plenty of audio adjustments. I did think about replacing the head unit, but decided this one would be fine for the time being.

The amplifiers were, as I suspected from the picture, a JL Audio HD 600/4 and an HD 750/1 (both top of the JL Audio products and the same amps that I just put into my Corvette).

Poking around further (actually pulling a few things apart) I was able to determine that Focal 165 VR3 3-Way Component Speakers had been installed into the front of the car. The back speakers were also Focals,  but I wasn’t able to determine exactly what kind. The sub seemed to be stock.

The install and wiring seemed to be excellent. It was clear that someone had dropped a good chunk of change this setup.There was lots of potential- I just had to coax it out.


I played with the adjustments on the head unit first. Aside from knocking down the volume of the sub, nothing I did seemed to make much difference. I removed the amps and had a look at their settings. That was the problem. The gain on the sub was way too high and much too low on the mids. And the filters were set backwards (cutting off highs from the mids and tweeters). I changed the settings on the amps (and the crossovers too) and it was like night and day.


I turned the gain down on the rear channel to eliminate the ground loop noise (I’m not sure if it’s ground loop issue, but the rear channel picks up noise from something). Then  I boosted the decibel level of the rear speakers on the Kenwood head unit to compensate for the lost volume. Problem solved!  With the amps adjusted the audio effectively responded to changes and I tweaked staging and EQ levels with some help from Jim, my audiophile pal.

Sometimes the vocals can be a little ear piercing (it’s not sibilance), but overall I’m extremely impressed by the stereo. The sound is now clear and full; I really like the 3 way component set in the front. The “stock sub” (powered by the overqualified HD 750/1) sounds good to me, but is definitely the setup’s weak link (I may replace it at some point in the future). Overall  the whole system seems to blend really well. I’d venture to say the stereo is nearly on par with the Camaro and Vette now. Driving around in the 911 just got way more fun!