The QWD 100 circuit is a bit more complicated. First off, since the QXD 210 has a very flexible setup that allows both bi-wiring and bi-amplification, and the ability to combine with another woofer via the QSD 164 midbass kit, it also has a highpass filter for the QWD 100. This filter can be bypassed when using an electronic crossover and biamping (using one amp for the QSD 210 and a separate amp for the QSD 164) the system. With the filter in place, you are ready to connect the QSD 164 for passive three-way operation. Switching from highpass to bypass mode is done with a jumper on the crossover circuit board that is accessible when you remove the clear plastic cover on the QXD 210. I should also note that Quart used a film-type capacitor to bypass the non-polar cap in the 250Hz highpass filter (the inductor in this circuit is also a high quality ferrite bobbin type). This tends to improve the sound quality, if for no other reason than the two capacitors in parallel have less series resistance.
Lowpass filtering takes the form of a contour circuit and a standard 2nd-order filter. The contour filter takes the shape of a series inductor with a parallel resistor and together form a 1/2-order filter that works to correct the frequency response of the QWD 100. Both inductors in this circuit are also ferrite bobbin types and the capacitor is a single non-polar type. Crossover between the QWD 100 and QTD 25 is specified at 2.4kHz.
Probably the most unusual feature in the QXD 210 network is the use of what MB Quart calls Balance Temperature Technology. Like woofers, certain parts of your crossover network can heat up dramatically and cause network values to change. The worst offenders are resistors and inductors. To minimize this value change that comes from resistance changes as these parts heat up, Quart builds the entire network on a cast aluminum plate rather than the usual plastic case the majority of component crossovers use. All of the ferrite bobbins are screwed down to this plate (this provides a thermal path to the aluminum chassis) and all the resistors are the expensive ceramic type that have metal cases with heat fins. This type of resistor is superior in its heat dissipation capability, but MB takes it a step further and actually uses heatsink paste to thermally couple the resistor metal bodies to the crossover aluminum chassis. The result is a more thermally stable crossover. Given the high SPL use many car systems are subjected to, this is a reasonable, although expensive, way of dealing with the issue of heat buildup in crossover filters.
Low-frequency for this three-way system is provided by the QSD 164 add-on midbass kit. The kit consists of the QWD 160 6.5" woofer and the QXD 164 crossover network stereo (one network for both channels). Features for the QWD 164 woofer are similar to the QWD 100. Like the QWD 100, the 6.5" diameter QWD 160 woofer uses a neo motor in a forged aluminum frame with cooling fins, butyl surround, WPC poly cone, inverted poly dustcap, Nomex flat spider, a 1.50"-diameter edgewound voice coil wound on a Kapton former and gold plated screw and connector terminals. Also, like the QWD 100, the QWD 160 is very lightweight, and has a mounting depth between 2.72" and 2.25", depending on whether it is mounted with the provided surface- or flush-mounting kit. The QXD 164 crossover is a stereo crossover (a single box with two-channels) with the heat sinked resistor and inductors thermally coupled to the aluminum chassis like the QXD 210 format. Terminals are provided to drive the QXD 210 and the crossover frequency is specified at 250Hz.
I performed two levels of testing on the MB component system. The first was to measure the T/S (Thiele/Small) parameters and simulate enclosure operation and the second was to measure the on- and off-axis frequency response, individual driver response, and the midrange out-of-phase response (I'll explain this later).