The GSL-SE Stereo System

Mazda's 3-component electronic-tuner/tape/equalizer system, made by Clarion

This page last updated 8/11/01.

I came up with a great sounding stereo for my RX-7 without spending megabucks. No audiophile with half a brain and at least one good ear would deny that upgrading to top quality speakers is the absolute most important thing that one can do to improve the sound of any system.

The stock electronics of this system feed into two 25 watt per channel stereo amplifiers located under the storage compartments behind the seats. Mazda doesn't give any distortion specs for these amps, but if they can put out 10 "clean" watts per channel (and maybe 25 watts, peak) then that should be more than enough for most person's listening habits. With reasonably efficient speakers, that should be enough for a clean 100 decibels on average -- maybe about lawnmower volume. There's a few tricks that can be done to clean up the sound a little more.

If you have any questions that I haven't already covered here, feel free to e-mail me.

Speakers:

The stock speakers are "full-range," single-driver Panasonics -- 4" inches in the front, mounted in the kick panels, 6 1/2" in the rear, mounted aft of the strut towers. The first thing I did was replace these with Infinity Reference Series two-way speakers of the same sizes in the stock locations. (There are plenty of other good brands. Polk Audio and Boston Acoustics come to mind.) The new speakers were a perfect fit, requiring no cutting or drilling, and they resulted in an immediate improvement in mid- and high-frequency response.

I prefer to have the sound-stage in front of me. But the 6 1/2" rears were just overpowering the 4" fronts. I could use the console-mounted fader to compensate, but the 4" speakers couldn't put out enough bass. The equalizer could help add bass, but the system just didn't seem to "come alive" until I turned the volume knob way up. (And it still wasn't very loud. 4" full range speakers will always be very inefficient.) I blew two sets of those little 4" Infinities before I gave up on trying to get reasonable volume and bass out of them. The kick panel location of the original system didn't help much, either. All of the mid and high frequencies were firing into my ankles. It was time to move to door mounted speakers.

After taking the interior door panels off, I found a location that could accept 6 1/2" speakers without interfering with the power window mechanism. 6 1/2" speakers at all four corners should result in good imaging and frequency response, even into the mid-bass range. I decided to get a little better speaker for the doors, so I moved up to Infinity's Kappa Series of two-way speakers.

Mounting the Front Speakers:

I'll save you the trouble of determining how and where to make your speakers fit in these doors: measure 3.75" up from the top edge of the map pocket, and 7.75" back from the front edge of the door panel. That's where the center of my speakers are on the door. Drill a pin hole through the door panel at that point.

Then take the door panel off, and use the mounting template that (probably) came with your speakers to cut a circular hole in the door panel. Tip: Cut an undersized hole, and check and double check clearances frequently throughout the process. You can always cut away more material to make the hole bigger, but it's really difficult to put material back if the hole's too large.

When you're done cutting, mount the door panel back on the door, mark off the sheet metal on the door, and cut away the little bit of metal that you'll probably need to remove. (Use sheet metal sheers, not a hack saw like I did during my first such speaker installation. The saw will create metal shavings that will get stuck in the bottom of the door and clog up the drainage holes, eventually causing the bottoms of the doors to rust.) Note that speakers all have different sized magnets, and that will be the biggest factor in determining how much metal you'll need to remove, and where. (Or, for that matter, whether or not you can even use this location without coming into contact with the window regulator as the window raises and lowers. This location proved to work well with both the Infinity Kappa 6.5" speakers that I used in my old '84 GSL-SE, as well as the Boston Acoustics RX-series speakers that are in my '85.)

If you've never installed speakers before, you can see that it's obviously not a highly technical job -- it's more of an art, and you'll get better at it with experience. It requires a little cutting of the door panels and sheet metal, but if you're smart about it and don't rush into things, even a novice can do it. The rule is "measure everything, then double-check, triple-check and then measure yet again." Or hire someone!

Standard Disclaimer: If you screw up your own speaker installation, too bad. I didn't measure your speakers, or the clearances where you intended to mount them, or do your cutting for you, or anything else. It's your car, and if you can't do this job right and you refuse to hire a professional who can, then you're the one who has to live with it. End of sermon.

Once the front speakers were mounted, the result was outstanding -- clean, bright sound at any volume; much more efficient, giving some relief to the stock amplifiers; and excellent stereo imaging, with the sound stage right in front of you where you want it.

My only remaining complaint: the Infinity Reference Speakers in the rear are very slightly more efficient than the Kappas up front, so I still have to compensate slightly with the fader. The Kappas sound a little cleaner throughout their range, though. In retrospect, I should have gone with Kappas all around. It's easy to fix, though -- replace the rear speakers. (I've since sold the car that this page was written about, and I've installed four identical Boston Acoustics RX-67 speakers in my newer '85 GSL-SE. The Bostons have somewhat smoother response than the Infinity speakers in the old car, and using four identical speakers at all four corners took care of the front-to-rear balance problem.)

The above speaker replacements will probably be as much as most music-lovers would ever wish for. But I wanted more....

Adding a Subwoofer:

A subwoofer is a speaker designed to handle very low bass, such as the notes from a bass guitar or some orchestral instruments, or even the low notes of a pipe organ. There are many types available. (Try Crutchfield for an overview.) I ended up getting a Kenwood powered tube-style subwoofer. It fit's nicely in the RX-7 hatchback, and it comes with a 60 watt amplifier and a continuously variable crossover. I hooked it up to the rear amp hookup coming out of the electronic tuner. (See shop manual diagram, below.) Pins 1, 3, 4 and 5 should be obvious enough -- they're for the audio signal. Pin 2 is an accessory power lead, to turn the subwoofer amplifier on and off with the rest of the system. The sub also requires a full-time power lead, which I took from the stock amplifiers under the storage bins. (Any full-time source will do. Most folks run a line from the fuse-box -- I just found the mid-car location of the amps to be more convenient.)

What all this does for me is that it allows me to continue to use the OEM joystick fader in the RX-7's center console, and the fader on the tuner can be used to fade out the subwoofer, if you ever want to demonstrate why you have that "thing" in the back of your car.

I was able to purchase the 6-pin DIN connector from a local electronics store. (To my recollection, Radio Shack had either the 6-pin male connectors or the 8-pin connectors, but not both. One of these days I'll check, and then I'll update this page.)

The same wiring could have just as easily fed a separate subwoofer amp -- they make amplifiers with built-in low-pass crossovers, just for use with a subwoofer -- and subwoofer drivers mounted where the storage compartments once were. But that's a future project.

Crossovers and Filters:

I added line-level high-pass filters to the signal lines coming out of the tuner, and before the joystick fader in the console. (Again, pins 1, 3, 4 and 5.) This has the dual benefit of limiting the amount of deep bass that would go to the main speakers (I don't feel like buying any more speakers) and also saving some of the main amplifier power for the mid- and high-frequencies. This makes it much less likely that I'll overdrive the main amps into clipping, so that it's equally unlikely that I'll fry any more tweeters. The whole system can get louder, while still having very clean sound.

Crutchfield sells a very inexpensive line of filters called F-Mods by Harrison. For all of $30, these connect via male & female phono-plugs, require no power supply wiring (unlike a component-type crossover) and fit very easily in the console behind the stereo. There are various frequencies available, but I chose 100hz high-pass filters as a mid-bass cutoff that I could match nicely with the continuously variable low-pass cutoff frequency of the subwoofer.

The Results:

After purchasing a test CD ($12) and a sound level meter ($30 at Radio Shack), I was able to adjust the subwoofer crossover frequency to produce a frequency response that is flat (+/- 1 db!) from 42hz to about 200hz. I was unable to get reliable measurements above that frequency due to standing waves within the car interior but, trust me, it sounds very clear and uncolored. At the maximum volume at which the system still sounds clear to me, I measured peak volumes of over 120db at normal listening positions!

With the rock, jazz and blues that I usually listen to, the system has plenty of punch and sounds almost as clear as my home system. It's equally capable with any classical music, including Bach organ fugues that would tax any aftermarket system. Cathedral sound in a two seater -- this is cool. :)

The point of all this is that you don't need to trash the original stereo that fits so well in the console. The electronics have reasonable frequency response, comparable to many contemporary tuner/amps. The original amps put out a healthy 100 watts total, plus the 60 or so supplied by the aftermarket subwoofer. With the exception of the door mounted speakers, the interior retains it's original appearance. Best of all, there's enough clean sound available to make for a great tailgate party!