Before You Begin

Goals

Research & Options

Solutions

• Front & Rear Speakers
• Head Unit
• Amplifier
• Subwoofer
• Cost

Additional Thoughts

Wiring Chart

Images

• Crossover install
• RCA jacks
• Amplifier setup
• Subwoofer

1. Clean sound & solid bass at high volumes
2. No visual modifications to the car (this influences the next goal)
3. Keep the stock head unit (Business CD unit) - I wanted to keep the stock look of the head unit as well as the speed sensitive volume feature
4. No loss of trunk space
5. Reasonable price tag (<$1000)

Phase II: Research & Options

There's good news and bad news. BMW's execution & implementation of the stereo system may have been horrible, but they did do an excellent job with the design & layout. The good news is that the 2000 Z3 has factory locations for 5 1/4" component front speakers, 4" rear fill speakers, has a subwoofer between the seats, and uses a separate amplifier in the trunk rather than one integrated into the head unit. The one negative with the layout is that the front midbass speaker is located pretty far down in the foot well, not the greatest location for stereo imaging, but all in all it's a good setup. The bad news is that the speakers, amplifier, and subwoofer are total crap, and there's no obvious space in the trunk for a decent amp. The subwoofer (non-HK) enclosure uses a single 5 1/4" driver and a passive radiator, both of which are of low quality. The foam surround on the passive radiator in my Z3 had come loose from the box and was responsible for the rattling/buzzing I heard at anything past low volume. Repeated efforts to glue it failed.

I did some extensive online research but couldn't find anything that anyone had done that fit all my goals. I saw some folks use a small aftermarket amp in the factory location (wouldn't give me enough power to do what I wanted to do) and various other styles of mounting amps in the trunk (all of which took up some degree of trunk space). To address the bass issue, options I saw included simply using 6 1/2" mid-woofers in the foot well location (not nearly enough bass volume or bass extension), putting new drivers in the HK subwoofer (not an option for me as I didn't have the HK system, and not an ideal solution for a number of reasons), or putting an 8" sub in a custom enclosure in the passenger foot well (too expensive and violates the heck out of goal #2). There is (or used to be) a BMW factory subwoofer upgrade made by Bob Carver/Sunfire for Z3's made after 10/2000 with the HK stereo (the 2 amp setup). I think this was probably a solid option, but unfortunately fit only a limited number of Z3's, cost $695.00, and doesn't appear to be for sale anymore. Another option was a 8", 10", or 12" sub in an enclosure in the trunk. This violates goal #4, but I had a 10" JL Audio sub in an enclosure originally made for a Miata's trunk, so I tested it out. The results weren't good. The Z3 has a trunk that's difficult to get sound out of. There's so much metal and insulation between the cabin and the trunk that bass in the cabin was less than 25% (measured with an SPL meter) of what it was in the trunk. The problem was that driving the sub at the level required to get reasonable bass in the cabin really vibrated the rest of the car, causing so much rattling and unwanted noise as to make the overall sound both unbearable and embarassing.

Some parts of the upgrade are pretty straight-forward. There are dozens of speakers from all price/quality ranges that will drop right into the factory front and rear speaker locations, and you can fit 6 1/2 (instead of 5 1/4) woofers in the front midbass location with some slight modifications. The problems were how to keep the factory head unit and use an aftermarket amplifier, where the heck to put the amplifier, how to get a decent subwoofer, and how to do all that without breaking any of my goals.

Phase III: The Solutions

• Front Speakers - 5.25" Component MBQuart PSD213 - Price $219.95 (SoundDomain)+ $70 Installation (Best Buy)
• Rear Speakers - 4" Coaxial MBQuart DKD110 - Price $64.99 (etronics) + self-installed

  These were easy upgrades, and I highly recommend buying online - I saved $500 over the local price just on these two sets of speakers. The front components are the next-to-top-of-the-line Premiums, beautifully musical speakers. I went with the entry level Discus line for the rear fills - since they are located behind the seats you're not likely to notice the difference in quality. It's good to match speaker brands front/rear for mids and highs to avoid any timbre differences. In this car it's not that big of a deal because the rear fill speakers just don't get a chance to contribute that much to overall sound, but better safe than sorry. If you are looking to save money in your upgrade save the rear speakers for last or don't do them at all, they are the least important component. Also, the factory system has both a midrange and a tweeter in the upper door panel location. To get the best stereo imaging put the new tweeters in the factory midrange spot, which is the one closest to the front of the car. This further forward location helps to equalize the distance between your ears and each tweeter. It won't make a huge difference, but it's the same amount of work either way so why not?

  I'd installed dozens of car speakers, but shied away from doing the front components due to the need to remove the door panels to install the tweeters. Having seen the installers at Best Buy do it I would do it myself if I had to do it again. The door panels, contrary to message-board myth, are nothing to be afraid of. The panels attach around the perimeter with plastic clips, the door handle slides right through, and you only have the wires for the midrange and tweeter to deal with. There are no side-airbag issues to contend with as I had feared. For me it was worth the $70 to not have to deal with the hassle though. Best Buy warranties the install, and will even reinstall the factory speakers for free if you sell the car. It took them about 1 hour to do the install. Note that I wouldn't trust the installers at your average Best Buy without talking to them first to be sure they have a clue, and I wouldn't trust them with anything much more complicated than this.

  The rear speakers I installed myself in about 30 minutes. The speaker grilles come off relatively easily. Take a thin flat blade screwdriver, start at the bottom middle, press the screwdriver in, up, and then pull or pry out. Repeat the process around the grille until it is out. Then just unscrew the existing speakers, solder or otherwise connect the wires to the new speakers, install, and snap the grills back on. Make sure that the tweeter on whatever speakers you buy doesn't protrude more than about 1/4" from flush for the speaker or you may not be able to get the grille back on. The MBQuart DKD110's just barely fit.

MBQuart's have a well-deserved reputation for being bright (sharp in the highs), but excellent, speakers. The component MB's all have external crossovers that have adjustable settings for the tweeters. The MB's brightness coupled with the midbass speakers being so far down in the foot well necessitated setting the tweeters at -6.0dB (down) to get flat response at the listeners ear (Note: I like to hear the music uncolored and as it was recorded, i.e. with the bass/treble controls flat. I leave the head unit flat and adjust the amp gain/ crossovers/ etc. to get flat response at the listeners ear with an SPL meter and a frequency sweep). In a blind test my taste prefers the more mellow Boston Acoustics that many Z3ers have installed, but comparable BA's were more than double the price of the MBQuart's, so MB's it was. To give you an idea of the level of quality of the speakers, the MBQuart PSD213's were $600/pair from two local stereo shops.

• Keeping the Stock Business CD Head Unit - Price $FREE!!

  The good news here was that the factory system used a separate amplifier - meaning that the factory head unit had to have low-level outputs of some kind. The bad news is that the low-level outputs were a part of the large bundle of unlabeled wires that fed into the factory amplifier in the trunk. I am adamantly opposed to using high-level inputs (using an already amplified [crappy] signal as input to another amplifier) so finding those low-level inputs was a must, plus I had plans for the space where the factory amp was sitting, so it had to go. With a multi-meter and some patience I was able to diagnose all the wires - low-level inputs, speaker leads, amp power and ground (I didn't reuse these) and the amp remote turn on lead (see wiring chart). All that's left after that is to solder on some RCA jacks so that you can input the low-level signal into an aftermarket amplifier.

NOTE: The BMW CD head unit is manufactured by Nakamichi, and is of good quality. If you have the BMW tape head unit, you'll want to replace it as it is very crappy.

• The Amplifier - Kenwood 5 ch KAC-959 - Price $234.99 (etronics) + self-installed

  The KAC-959 is a solid 5 channel (40 watts X 4 + 120 watts X 1) amp with built-in high and low pass filters. I had originally wanted to try to use a two-amp setup and put one amp where the factory amp was, but an extensive research session yielded no feasible options. In the end a single, relatively compact mutli-channel amp took up less space than any comparable two amp combo. The problem is, the thing is still 11 7/16 x 2 3/16 x 12 5/8. Where the heck is that going to go? I decided that I would remove the spare-tire tool tray from under the carpet in the trunk and mount the amp there. To do this I needed to cut the carpet/board that covers the battery and tool tray to allow the top of the amp to vent. The amp itself is flush with the carpet, so no trunk space is lost. In the end this looks very, very cool and the modifications are relatively minor. I wrapped the tools and jack up into a cloth holder similar to most other vehicles I've owned, and they easily fit in the well beside the battery. The amp is mounted with velcro (no holes or screws!). If I were ever to sell the car AND keep the amp (not likely) I can always put the tool tray back and either make or buy a new cover for the bottom of the trunk.

• The Subwoofer - Custom enclosure with JL Audio 6w0- Price $79.95 for the speaker + the materials and LOTS of time to make and test the box

  This was by far the hardest part, but in the end certainly the most rewarding. I ended up learning far more about the physics of sound and subwoofer design than I had initially deemed necessary. I'll try summarize what I learned without getting too technical or detailed.

  Bass has two components that were of importance - frequency and volume. Most decent 5.25" or 6.5" full-range speakers have usable frequency response down to about 80Hz or so and the bottom threshold of human hearing is 20 Hz, so 20-80Hz is the frequency range we're interested in for the subwoofer. Theorectically any size speaker can reproduce sounds in that frequency range, but to do it loudly requires moving lots of air. This is why most subwoofers are large speakers - the large surface area of the speaker cone just makes the physics easier. The best subwoofers (high volume, flat frequency response, tight uncolored bass, and extension down to 15 Hz and below) are usually 15" or 18" woofers in large sealed cabinets.
  Another way to approximate the same results and get a smaller enclosure is to move air with a smaller speaker and use an enclosure with a port or a passive radiator. The air in the port (or the passive radiator) is vibrated by the speaker and the moving air in the port (or the air moved by the passive radiator) creates soundwaves and adds to the output of the speaker itself, giving you greater volume then the speaker is capable of alone. In addition, a ported box has a something called a "tuning frequency". The air in the port acts as an additional speaker, and the natural resonance frequency of this "speaker" is the tuning frequency. The tuning frequency is a function of the internal volume of the box and the size of the port (the cross-sectional area times its length). By tuning the enclosure to a low frequency, you can extend the usable frequency response to below what the speaker could achieve in a sealed enclosure. My home speakers (Definitive Technology) work on this principle, hitting cleanly down to 18 Hz with only two 6.5" speakers in each enclosure.

  The JL 6w0 is a substantial speaker and getting it to fit in an enclosure that fits in the factory location took a minor feat of engineering. The only modification needed was cutting a small ridge of plastic from the back of the factory subwoofer location area. Collectively the whole subwoofer (including research and education) took me about 100 hours. The end result was well-worth the time spent - clean, back-thumping bass with good extension at any reasonable volume. I won't win any SPL contests (I wouldn't want to and if I did it would be silly to try with a Z3), but my neighbors can hear me coming if I leave the volume up. Pictures and more details can be found here. The frequency response isn't perfect, but it never is inside the poor and noisy acousitic chamber a car makes - true audiophiles would want to add an equilizer (in the trunk) and use a frequency sweep and an SPL or other measuring device to tune the car for flat sub response. A cheaper but less effective option would be to buy an amplifier with a flexible bass eq feature.

• Cost

  My actual cost was about $840 plus about 100 hours of my time, most of that for the subwoofer. I only ended up using about $690 of components and materials, with the extra $150 being two Rockford Fosgate subwoofers that I tested and materials wasted in the trial and error process for the enclosure. I've decided to sell the completed subwoofer enclosure sans speaker here if anyone is interested. I'm hoping to recoup my investment in time and money at worst, maybe make a little cash at best.

  This write-up is titled the $1000 upgrade, and I calculated that price based on a prospective upgrader both buying a completed subwoofer enclosure from me and taking all the components to a local stereo shop to install everything! Obviously you could save money in various areas if need be. [Note that this installation is from early 2003, and prices and and availability of some of the components may no longer be valid. If you would like to duplicate this installation, look for the current versions of the products below]

• Front components - MBQuart PSD213's - $219.95
• Rear coaxials - MBQuart DKD110's - $64.99
• Amplifier - Kenwood KAC-959 - $234.99
• Subwoofer - JL Audio 6w0 - $79.95
• Sub Enclosure - $275.00
• Approx 3-6 hours install time @ $50/hour - $150.00-$300.00

Total: $1000 - $1150

Additional Thoughts

The Z3 stereo upgrade is a tough one to do in stages if you are trying to save a little money. Any upgrade of the amp requires an upgrade to the front speakers and vice versa, as the crossovers for the speakers are built into the amplifier. An obvious place to save money is to retain the stock head unit as I did and utilize it's low-level outputs. Even a crappy CD player (which the BMW CD-43 unit is not) is acoustically very good, so unless you want to play MP3 CD's or require some other feature the stock unit doesn't have I highly recommend keeping it. You also save by waiting to do the rear fill speakers or the subwoofer, or by simply lowering the quality of the components themselves.

I think the amplifier setup has the most leeway for a good, different implementation from what I chose. I have seen many different setups using different size and numbers of amps and different install locations. In the end I chose what I did to preserve all trunk space. Others may rather lose some trunk space than cut holes in the trunk liner.