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[ MB Quart QM 328.01CX 3-way speaker kit picture ]
MB Quart QM 328.01 CX
There are only speakers in the front of the car, this to create a front sound stage. The speakers used here at a 3-way set consisting of a 0.75inch tweeter, a 4inch midrange and a 6.5inch woofer on each side, as sold as a set by MB Quart called the QM 328.01CX kit. This set is capable of producing 38hz to 32KHz, a very large sound range although the whole set is only fed frequencies above 120Hz from the electronic crossover. The sound quality from these speakers is excellent, producing clear and accurate sound in the front of the vehicle. MB Quart speakers often win awards for the quality of there speakers, the 328.01CX kit winning the AutoSound Grand Prix award by AutoSound Magazine.

The 328 set comes with a slightly adjustable passive crossover network, passive meaning that it comes after the source of amplification and works at a higher voltage than the electronic one. It's very slightly adjustable, in that the tweeters can be set to high or low, potentially making the sound brighter than the normal setting. The crossover has a 12db per octave crossover slope, give the tweeters all frequencies above 4khz, midrange 250hz - 4khz and the woofer 120hz upto 250hz. As this crossover was custom built for these speakers, it works very well with the set, but it's possible to upgrade to MB Quarts MUSiCOMP crossovers. These are of a must higher quality designed without compromise using the best quality components, and aimed towards the competition and very high end audio market, possibly and expensive but rewarding upgrade.

Due to the installation limitations within the front of the E30 3-series BMW, the speakers had to be seperated. The resulting placement of speakers has meant that the tweeter and midrange speakers are in the kick panels, filling the cars standard front speaker position. This was very tricky, as the standard speaker size is 5.25inch and a 4inch and 0.75inch don't fit into this space very well. Also the standard location points the speakers right into the drivers feet, not an ideal situation for sound quality. The 6.5inch woofer was placed in the door panel, built into a custom made door panel. I hope to add full details of the installation of this speaker set as soon as possible. The tech. spec. with all the t/s parameters are below.

[ technical specification ]
  Tweeter Midrange Woofer
Power Rating 75 Watts RMS
Impedance 4 ohms
Crossover Slope 12 db / Octave
Frequency Response 38Hz - 32KHz
Sensitivity 2.0 W (90db / 1m) DIN
Mounting Depth 18mm / .7inch 40mm / 1.6inch 63mm / 2.5inch
External Diameter 65mm / 2.5inch 130mm / 5.1inch 190mm / 7.5inch
Installation Diameter 57mm / 2.25inch 95mm / 3.75inch 149mm / 5.9inch
T/S specifications
Impedance 6 ohms 6 ohms 6 ohms
DC Resistance (Ohms) Re) - 5.8 2.85
Resonant Frequency (fs) Hz - 87 66
Mechanical (Qms) - 3.43 4.41
Electrical (Qes) - 0.93 0.8
Total (Qts) - 0.76 0.68
Voice coil Inductance (Le) mH - 0.42 0.37
Equivalent Volume (Vas) - 0.76 0.68

There is currently no rear-fill but I'm investigating the possibility of adding some, when I find time to test a few different setups. The most likely result will be the rear channel from the electronic crossover running a small Alpine amplifier, which will power the standard rear BMW speakers. This will probably to crossed over in a band-pass setup so as to produce only a mid-range output which will create only rear ambience and not interfere with the front stage.

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