Car = 1991 MR2 Turbo, T-Tops, White w/blue interior. Original options = everything except AT, leather seats, and stock alarm. Had premium system, but only had single DIN AM/FM w/cassette.

At the time that I designed the stereo for my MR2 (1994), it was my only car. It was my only transportation to work, and it unfortunately found itself parked in a lot of places where cars were broken into on a regular basis. I also love to drive around with the T-tops off, which was a big reason why I was drawn to this car in the first place. Therefore, the stereo I installed had to be as absolutely stealth and hidden as possible, and take up as little space as possible. Also, since it was my daily driver, the system had to be as convenient as possible, so that I didn't have to waste time fidgeting on the stereo as I got in and out of the car (for example, taking face-plates on/off, covering things up, etc.).

First, a CD changer was paramount. I had found that either in town, or on long trips, a single CD player was cumbersome, and the CDs themselves could easily be damaged as they are changed while driving. I've also found that the ability to change magazines from the driver's seat to be invaluable on long trips. So, a CD changer small enough to fit inside the glove-box was the best solution. In a stealth system, a head unit is the most visible item. While removable face-plate radios were abundant at the time, I had read and heard about situations where thieves would break into a car with a face-plateless radio. Once they saw that there was such a radio, they'd break in anyway because odds were, there would be other equipment in the car to steal. Upon leaving, they would damage the radio beyond repair out of spite. A lot of people found themselves gaining nothing with a radio with a removable face-plate. I decided to keep the stock head unit. It was sufficient for the very few times I listen to tapes or the radio, I could interface it with available CD changer controllers on the market, and it would not attract any thieves who were looking for expensive stereo equipment. The only thieves it would attract were crack-heads and other addicts who were looking for ANY radio to give them their next fix. But, if you have a decent alarm, that same element would rather go break into the un-alarmed Taurus parked next to you for it's radio instead (call me selfish).

I was able to find an Alpine 6 CD changer and external controller (with a separate pre-amp input for the existing head unit) that would fit nicely in the glove-box. After I designed the mount and installed it, I found that I still had room in the glovebox for the manual, gloves, a map or two, air-pressure gauge, etc. The CD changer skips on the average of once a year, even after five years of service. The only option missing from the controller is the ability to program, but I have never needed that function anyway. My second car came with a 12 disk changer, but I've personally found that a 6 disc magazine is much more convenient than the 12 disk.

I didn't even bother with rear speakers. First, I felt that the rear of the car itself is close enough to the driver that rear fill is unnecessary, especially since the portion at ear level is glass. This already produces a lot of the same effect that rear fill speakers try to emulate in the first place. Additionally, the stock location of the speakers is so close to ear level, that it would have a terrible effect on imaging. The left and right channels have to be the same distance from the ears for the best imaging effect. In the front of the car, you make the best of the situation, and you come out with a difference of appox. 4 ft to the left channel vs. 6 ft to the right. The reason why kick-panel locations are desirable is because even in the MR2, the difference changes to appox. 6 ft on the left vs. 7 ft on the right. For the rear stock locations, the difference is a HUGE appox. 1 ft vs. 4 ft. This extremely detrimental to imaging, so I left them out. Additionally, it has been proven by studies that distorted sound at a particular sound level is more damaging to your hearing as clean sound at the same levels. Since the rear locations would have had to have been filled with smaller, and most likely lower quality speakers, I would be putting sound that was slightly dangerous within a foot of my ear. I wanted to avoid that possibility completely, so the rear speakers were out.

I kept the stock tweeter locations. Again, I wanted to keep it stealth, so I didn't need tweeters hanging out in the open. Even though the imaging of the stock tweeter location would be slightly worse than the mid-bass location, I felt that the sound quality would suffer in the midbass location. Since the higher frequencies are very sensitive to obstructions between it and the listener, I wanted to locate them where they wouldn't be blocked by any knees. Therefore, I sacrificed some imaging quality for sound quality.

Before choosing the main speakers, I choose the subs. I only had appox. 0.6 cu. ft available, but I wanted to avoid using a ported box. Even though they have better output at a particular frequency range, that range is pretty limited, and response drops off very quickly towards the bottom end. I wanted a system with as much low end response as possible, and ported boxes cannot deliver that. Additionally, I was going to build these boxes myself, and sealed boxes are much more forgiving than ported boxes. After a long search, I found the Kicker Solobarics. Without going into it, these subs were built to mimic the response of an Isobaric setup. The result is that the solobarics are built twice as heavy as their conventional subs, with magnets and baskets designed to compliment them. A good side effect of this design is that the subs require a box that is NO MORE THAN 0.33 CU. FT. while producing some very low frequencies for an 8" sub! The drawbacks are that the boxes have to be built very sturdily, and the subs require a little more amplifier power to achieve the same sound level as a standard sub on a much larger box. I could live with these compromises!

The reason the heavier sub requires less air is simple, once you understand the basics. Let's use a car's suspension spring as an example. Say we have two springs with the same spring rate: One is one foot tall, and the other is only 6 inches tall. If we put 100 lbs on each of them, the one foot spring will compress twice as far as the 6 inch spring. But if we put 50 lbs on the one foot spring, it will compress as far as the 100 lbs on the 6 inch spring (if you don't understand why, ask someone before reading on). Just like those of us with shorter springs in our cars can tell you, shorter springs are stiffer. Air works in the same way, a 2 cubic foot box is not as stiff as a 1 cubic foot box, while a 0.33 cubic foot box is even stiffer yet. Subwoofers rely on the air inside a sub box to help support them, just like a suspension supports a car. Therefore, subwoofers are designed to the size of the box it's intended to go into. Due to the fact that the Solobaric's cone is twice as heavy as a regular sub, it needs a "stiffer spring", or in this case, a smaller box that's stiff enough to support it. Another draw-back from a subwoofer utilizing a heavy cone is that it's frequency range is limited. While a regular subwoofer will have a frequency range of 20-400 Hz, the Solobaric only has a range of 20-200 Hz. This means that the cross-over frequency can be no higher than 100, preferably 80 for good performance. This in turn means that the mid-bass speakers must have a frequency range that goes down to 50 or 40. For best results, this normally means that you need a 6 1/2 inch mid-bass (as opposed to a 5 1/4 inch midbass). Since I've always had my eye on Boston Acoustics, I purchased a 6.2 Pro Series component set. The frequency range was rated all the way down to 40, and the tweeters were small enough to easily fit in the stock tweeter locations.

My selection of amps was limited by the fact that I decided to mount the amp under the passenger seat. I was also limited by the fact that I required an amp with on-board crossovers due to the limited space. I was able to locate the Alpine V-12 F304. It is a four-channel amp with two continuously variable crossovers. It offered what I needed to install it now, and enough flexibility to add to the system in the future. It is rated very conservatively at 30 watts per each of the four channels. By the time that everything is taken into consideration (voltage, etc.), the amp actually puts out 50 watts/channel. Due to the small size of the car, the subwoofers are very close to the listener, so 50 watts provides for good clean sound in the MR2. Channels 1 and 2 are crossed over at appox. 90 and sent to the BA component speakers, while channels 3 and 4 are crossed over at appox. 80, and sent to each of the subs. In cars, due to the small space, there is normally a natural peak in the bass around that point. I did the settings by ear, and I'm constantly changing it ;) Since the low frequencies reproduced by subwoofers are hard to locate by ear, and because most engineers record low bass in mono, most car systems set up subwoofers in a mono configuration. But, since the location of the subs in a MR2 is practically under the listener's seat, the listener can actually feel the imaging in the low frequencies that were recorded in stereo. Since more and more high-end stereos are becoming popular more and more engineers record bass in stereo. This adds another dimension to a stereo installed in a MR2.

To install the amp, I cut out piece of carpet under the passenger seat to give the amp a flush look, and to give it enough room to clear the seat. The power and speaker connections are up front, while the pre-amp connections are to the rear. The crossover controls and levels are in the rear, and are accessible with the seat moved forward. The CD Controller has 4 channels of output, 2 for the front, and 2 for the rear. I use the front two channels for the BA components, while I use the rear 2 for the subwoofers. That way, I can adjust the subwoofer level by adjusting the fader on the CD Controller.

I did not include an EQ in the system. First, there was little room to install one. Second, due to the MR2's size, the acoustic environment changes drastically when a window is opened, or the sunshades are removed, or the T-tops are removed altogether. Because of that, I felt that EQ tuning would only be beneficial if I were to tune to a specific song for the purpose of competition, so I left it out. The passive crossovers for the BA components allow some adjustment for the level of the tweeters. Since there is so much glass in close proximity to the metal tweeters (which tend to be brighter than cloth or composite tweeters), I found it necessary to bring the level of the tweeters down slightly.

Another benefit of locating the CD changer in the glove box and the amp under the seat, is that there is no need for any long wire runs, and that ground wires can easily be routed directly to the battery terminals. The benefit of running ground wires directly to the battery terminals is that it naturally eliminates ground loop noise, and any other resistance related noise that exists in the car's chassis. This accounts for 95% of the noise found in a car stereo system. All battery and ground wires for the amp, CD changer, CD controller, and stock head unit are run directly back to the battery. Additionally, when the power and ground wires are run parallel, they tend to cancel out RF interference, which is the other 5% of noise in a car stereo. At the same time, the pre-amp cables cross the power cables only when absolutely necessary, and when they cross, they cross as close to 90 degrees as they can. While these precautions may sound like voodoo, there is no discernable noise in the system, so at least some of it worked. Again, due to the fact that the power runs for the amp are less than 7 ft., I was able to use 8 ga. wiring without any compromise. The preamp cables are only 8 ft long, and the wiring between the changer and controller is only 1 ft. long. The subs are fed with 12 ga. wire, and the Boston Acoustics are fed with 16 ga. wire (2 pair of 12 ga speaker wiring would have been near impossible to feed through the door-grommet of the driver's side).

Finally, the CD controller is meant for remote mounting, and includes a small, wired display. The only buttons on the display are power, skip back, skip forward, and display color. All of the other controls (volume, fading, disk, pause, etc, etc.) are located on the included credit card remote. I immediately found it annoying to remove and hide the display every time I used the car, and I was worried that the little credit card remote would get lost or damaged when it was loose in the car (especially the way I drive ;). So, I looked for a solution. I remembered an article where somebody wired up a power mirror switch (which in effect controls 4 motors, two on each mirror) to control four motors that turned the four knobs on a parametric equalizer mounted in the trunk. Since the power mirror controls are conveniently located in the MR2, I decided to expand on the idea, and designed a system that would allow me to control the stereo with the power mirror switch.

First, I decided which buttons to include. I only had eight selections on the pm switch, but I really needed nine. So, I decided to add a separate button below right of the pm switch for the "mode" button (which steps through controlling volume, treble, bass, balance, and fade). With the pm switch set for the right-hand mirror, up and down controls the volume (bass, treble, etc.), while left and right control the skip track actions. With the pm switch set for the left-hand mirror, up controls disc advance, down controls pause, left controls random mode, and right controls repeat functions. The remaining three buttons that were omitted were for functions that I never use. In fact, I've forgotten what they're for, but in the case I do need to use them, the original remote is still fully functional.

I installed a set of relays so that I can change the pm control between the mirrors and the stereo. The relays are controlled by a button to the lower left of the pm switch. I also added an LED indicator, located above the pm switch, which glows red when it is in mirror adjustment mode. The leads from the pm switch are routed to a small black box, currently located in the glove box. Inside the black box is the PC board from a second credit card remote, and a PC board that contains the electronics that decodes the signals coming from the pm switch. The pm switch basically reverses polarity on two of three leads to control each mirror motor. I had to build a board that decoded the polarity of the incoming signals with diodes and transistors, and then activated the appropriate button on the second credit card remote PC board. The infrared transmitter LED was removed from the PC board, and extended with a couple of feet of headphone wire. The wire is wrapped up with the CD controller display wire, and semi-permanently mounted in front of the IR receiver window. That way, the display can stay in the glove box during short drives, and can be removed and set in the ash tray for viewing if desired. While the display is sitting in the ashtray, the original remote can be used as it was originally designed. A 1.5 volt battery eliminator was also designed into the interface board to power both the interface board and the remote PC board.

All in all, the system has been very maintenance free, and has performed above my expectations. The fact that the system is still running strong after more than five years is a testament to the quality of the equipment that I chose. In previous cars, with previous systems, I was replacing low and medium quality equipment within two years. If I had installed medium quality equipment initially, I would have spent just as much replacing it over the years, and I would not have enjoyed it as much.

Now, the MR2 is a weekend car. I don't have to worry as much about stealth, and I now have replaced my tapes with MDs. In the future, I intend to install a MD/CD combination head unit that will control a glove box mounted CD changer. The stock grills and cutouts for the tweeters and mid-basses were kept stock in the interest of stealth. These stock grills noticeably degrade the sound quality. I plan on replacing the tweeter grills with an acoustically transparent cloth, and I plan on getting custom mounts made for the midbasses that will angle the speakers towards the listener, and include acoustically transparent cloth grills. I also intend on adding an amp rated at 75 watts per channel under the driver's seat, which will drive the Boston Acoustics. I will then bridge the existing amp to appox. 125x2 for the subs. At full speed, with the T-tops off, the stereo isn't quite powerful enough for my tastes, and this setup should give me the headroom and flexibility that I need. I also intend on replacing the existing Solobarics with Kicker's new L7 line, which will put even more base into the stock boxes. Additionally, the existing alarm (which is pretty basic) will be replaced with a new, highly integrated system. But that's another article.