2005: Cleaning up the Tunes

The car was originally equipped with an AM monaural radio and an 8-track unit. For many years I toyed with the idea of restoring the car to original format, and even came very close to installing a vintage factory 8-track player. I figured anything would be better than the badly cross-wired (out of phase, etc.) aftermarket LearJet tape deck that was sitting in the car since God knows when. Besides being out of phase, the sound was pretty crispy and rattly out of the rear shelf speakers (6x9 units, installed by cutting out the holes in the rear shelf, a popular approach in the late 1970s). With digital tuning and clock, I figured this unit might have been from the early 80s. The speakers began intermittently cutting out, so a plan was hatched. A properly sized Kenwood MP3 full-gizmo player was purchased, and the install began immediately.

The very first snag was the worst to deal with: while attempting to remove the unit by starting with the knobs, it became apparent this was a false face plate. Removing this face plate showed me that this car had NOT been cut up to accept the aftermarket radio! How rare is that? Most installations of aftermarket equipment involved hacking out the textured faceplate shown here, which most likely hadn't seen the light of day since the early 80s! Once cut, there's no going back. After much deliberation, a decision was made to address the speakers first and worry about the deck later. Everything was put back together.

The speakers were "AudioDek" brand, and after looking closely I became certain that they were most likely NOT tan coloured at the time of their original installation! These puppies were pretty dried out! Indeed, removal of the units proved that they were rattly because they were practically seized internally, and the cones were brittle. To the trash they went...

Luckily the car's structure was already set up for 6x9 speakers as factory options. I reused the package tray holes to install the new 6x9 units, a pair of 6x9 3-way Cerwin-Vega speakers that were rated for decent power but most importantly seemed to have a very deep bass frequency response.

Of course they fit right in. I took advantage of the situation to correct the cross-wiring and out-of-phase condition (whoever installed the system decades ago was really NOT familiar with the basics of wiring at the very minimum! I'm surprised it even played any music at all!).

While I was down there, I noticed that the original large 10-ohm mono in-dash speaker was still present and the wiring accessible. I took advantage of this in order to try something I had always wanted to try in a car: a simulated surround-sound setup pioneered by David Hafler in the 60s to generate 3d sound out of conventional 2d signals (Left and Right).

The Hafler technique

As described in U.S. Pat. No. 3 697 692, the Hafler technique generates rear channel information out of conventional 2 channel signals by extracting difference signals. In simple terms, that means adding two speakers in the rear to reproduce the difference signals between the left and right original signals in different order (ie. L-R to one rear channel and R-L to another rear channel). The technique is accomplished by wiring two speakers in the rear of the listener with the "-" terminals tied together, and the "+" terminals wired to the "+" terminals of the amplifier. A conventional system is wired this way:

The Hafler technique is applied as follows to a home sound system:

A typical car stereo deck with front/rear channels (both front and rear playing the same information, controlled by a front/rear fader) is wired as follows:

Given that I had a dash-mounted mono speaker, I used that speaker to reproduce the difference signal... sort of combining the two rear speakers in the traditional Hafler technique, and inverted because the "real" stereo sound is coming from the rear. I modulate the amount of sound coming from the "center" channel by controlling the front/rear fader. The result is a new "mix" coming from the center channel in front of me, sometimes it's vocals and other times it's some other instrument that might be otherwise buried in the mix.

Eventually, I removed the old original dried out center speaker and replaced it with a plate of 2 small aftermarket speakers wired in series to reproduce the center channel. They were too small and too close together to be used in the real L/R Hafler method, so they now act as one single center speaker.

Access to the center speaker area is via the glove box, which must be dismantled.

There's the old speaker, and the attaching bracket.

This is what an original GM 10-ohm mono center speaker looks like.

It took a lot of work to get the new speaker plate up there, such that it would properly bolt up to support everything properly. The effort is worth it: you cannot tell from the outside that the speakers are aftermarket. The results were so good that for now I'm keeping the old deck in service until I decide what to do.