From jchanes_at_er4.rutgers.edu Tue Sep 16 18:20:16 1997
Date: Tue, 16 Sep 1997 21:20:13 -0400 (EDT)
From: "John C. Hanes" <jchanes_at_eden.rutgers.edu>
To: Dale B <dale_at_unofficialbmw.com>
Subject: Re: <E30> Bazookas in the trunk

Dale,

Originally, it was wired up to the stock BMW Premium Sound System, but now it's hooked up to a Kenwood aftermarket tape deck head unit (also sourced from my long gone dead Camry).
The Bazooka 10" amplified subwoofer tube (The 10T-A80 if I remember correctly) has two sets of inputs - high gain for hooking it up in parallel to a set of speakers (the rears would be the easiest), or line level RCA for hooking into the line out jacks of any decent aftermarket head unit.
For the stock system, I ran two pairs of parallel wires (one pair per speaker) to the +/- high-gain leads on the Bazooka. The reason I did this was because the sub itself is mono, but I wanted it to boost the low bass frequencies of both stereo channels. So the left/right - went to the Bazooka's input -, and the left/right + went to the Bazooka's input +. This worked okay except for a few freak situations. If you are playing music where the bass is alternately coming out of both channels (Nine Inch Nails does this sometimes), the sub gets confused and the signals cancel out, resulting in no bass. This is not audible (unless you expect it and don't get it), or harmful.
In addition, the need for running a turn-on lead from the head unit can be eliminated by using the Bazooka's auto-on switch when installed in stock locations. This makes it extremely easy to install in BMW's - a couple sets of wires from the rear speakers (which are just overhead in the rear deck from the trunk), a power wire from the battery (which is just a few feet away), and a ground wire to the grounding bolt next to the battery, also just a few feet away. This enables a sub to be completely installed without running any wires anywhere except the trunk. One caveat - the auto-on switch causes an annoying amplifier thump when you turn the radio off. Also, at low volumes, the switch gets confused and constantly thumps the sub on and off. At higher volumes, it's always on.

When I installed the Kenwood head unit, I rewired the entire car to bypass the stock outboard amp, running new speaker wires through the car's wiring harness channels to all four speaker locations. While I was at it, I ran a stereo RCA cable from the back of the head unit along through the stock harness channels to the trunk, as well as a little turn-on lead. The RCA cable takes advantage of the line-level inputs, and the turn on lead eliminates the need for the auto-on switch, which can be bypassed by moving a little jumper. The lead is spliced into the power antenna wire on the head-unit end. All it does is provide a voltage to indicate the sub should turn on, and another one when the sub should turn off (at the same time the antenna goes up and down). No more thumps.

If more specific knowledge is required (how to rewire the stock stereo), I can also provide that without too much trouble. Hope this helps out!

-jch

John C. Hanes
AgBiotech Center
Foran Hall 135
Cook Campus, Rutgers University
New Brunswick, NJ 08903
email: jchanes_at_eden.rutgers.edu
phone: 908-249-2623
fax: 732-932-2972