Lower- and upper-mid frequency reproduction is provided by the QWD 100 4" midrange. Like the QTD 25, it uses a neo magnet motor system. This not only makes for a very lightweight driver (if you want to go fast, you've got to lose as much weight as possible!), but a fairly shallow profile for mounting in cramped areas. The depth goes from about 1.94" to 1.44" depending on whether the driver is flush- or surface-mounted. Built on a custom-designed forged aluminum frame, the motor fits inside the frame rather than being attached to it, as with the majority of ferrite motor woofers. The QWD 100 also has a substantial ring of heat sink fins that surround the neo motor's location. For mounting, MB supplies all the hardware required for custom (or stealth), surface, and flush mounting.
The QWD 100's cone assembly includes a WPC (Wet Powder Coating) coating over a polypropylene cone, a butyl rubber surround, inverted poly dustcap, elevated Nomex spider, 1" edgewound voice coil wound on a Kapton (a high temp Dupont plastic material) former and gold-plated screw-down and connector terminals. Two things are kind of unique here: the WPC cone compound and the edgewound voice coil. The WPC is a surface coating compound that contains titanium and does seem to make the cone stiffer. Edgewound coils are nothing new, but you don't often see them in car audio woofers. The advantage is a lot of woofer Bl (read that as horsepower) in a fairly lightweight single-layer coil and less inductance than a multi-layer round wire voice coil, which means better high frequency response.
MB supplies a two-way crossover for each channel with the QSD 210. As with previous MB networks, the company uses high-grade component parts, including ferrite bobbin inductors, film capacitors, gold connecting terminals, and a cast aluminum chassis with a clear plastic cover.
The tweeter section of this crossover has a 2nd-order highpass filter topography that results in roughly a 3rd-order highpass slope on the tweeter. Components in this filter section are a high quality polypropylene film capacitor and a ferrite bobbin inductor. The tweeter level can be adjusted in four increments using the gold-plated jumpers provided and can be adjusted from 0dB to -1.5dB, -3dB, -4.5dB, and -6dB.
For tweeter protection, Quart uses what it calls an HPCCR Optical tweeter protector, which is a fancy term for a type of light bulb. Light bulbs work well for tweeter protection and in some ways are better than PTCs (Poly switches) or fuses. A poly switch will conduct right up to its cutoff voltage and then turn your tweeter off completely (usually right in the middle of a great tune) and take a few minutes to reset. This does protect the tweeter but it can be a bit annoying. The filament bulb method gradually turns down the tweeter as you try to put too much damaging voltage into the tweeter. The result is that your tweeter volume decreases somewhat at very high volumes, which does provide protection without shutting the tweeter down altogether like a fuse or PTC.