The Technology Behind the Q7

Equipment report
Magico Q7
The Technology Behind the Q7

Although the Q7’s woofers, midrange driver, and tweeter look identical to those of the Q5 (except that the woofers are bigger and there are more of them) the Q7’s drivers are actually quite a bit more sophisticated. The tweeter is a third-generation beryllium design (the Q5’s tweeter was a first generation) with several key improvements. This new tweeter features a fully under-hung motor structure with a more powerful neodymium magnet to increase sensitivity (to a whopping 95dB). The term “under-hung” describes a short voice-coil mounted in a long gap. This design results in more linear operation because the voice coil remains within the gap’s magnetic field regardless of the voice-coil’s position or excursion.

The 6" midrange is an all-new design with a massive 55mm voice coil driving the Magico Nano-Tec cone. This cone is woven from a carbon-nanotube material originally designed for helicopter blades where light weight and stiffness are absolute requirements. The under-hung motor uses a massive magnet (5" in diameter) made from N48H-grade neodymium (the higher the number in the grade the stronger—and more expensive—the magnet). The magnetic field strength in the gap is a stunning 1.7 Tesla, a value seen only in field-coil drivers (in which the magnetic field is created by an electro-magnet rather than a fixed magnet). The voice coil is a vented titanium design and is mated to a new composite spider material that allows +/-6mm of excursion. The driver, which was designed specifically for the Q7, can reportedly produce 120dB SPL at 1m distortion-free within its passband. Incidentally, while visiting the Magico factory (see sidebar) I visually compared the Q5’s midrange driver with this new Q7 midrange unit. Although the look the same when mounted in an enclosure the Q7’s midrange was considerably more massive and elaborate. I was able to lift the Q5’s midrange driver from a metal table, but not the Q7’s midrange, which felt like 100 pounds because of the magnet’s strength.

Looking next at the 10" mid/bass unit that’s mounted at the top of the enclosure, the driver is again all-new for the Q7. Its design is very similar to that of the midrange, with a massive motor structure and top-grade neodymium magnets for high magnetic field strength in the gap. The voice coil is a whopping 127mm, half the cone diameter. (An engineering textbook in my library shows a photo of a 15" subwoofer driver with a “large” 3" voice coil.) Again, the cone is Magico’s Nano-Tec material. Magico claims that this 10" mid/bass driver has the lowest inductance of any driver extant (0.085mH at 10kHz).

The dual 12" woofers are again all-new for the Q7. They use the same 127mm voice coil and underhung motor as the 10" mid/bass. These drivers have an excursion of +/-15mm and can reportedly produce 120dB SPL at 1m at 50Hz.

The drivers were designed using a state-of-the-art finite element analysis software package that allowed Magico Chief Technical Officer Yair Tammam to model the driver behavior in the thermal, magnetic, mechanical, and electrical domains simultaneously. Previously, Tammam told me, he had to model each of these domains separately in different software.

The drivers are designed for maximum magnetic field strength in the gap, low moving mass, and minimal inductance. In addition, Magico has also gone to extreme lengths to minimize eddy currents in the drivers. Eddy currents impede the motion of the voice coil by creating magnetic forces that oppose the voice coil’s motion. Eddy currents are so effective in slowing down moving objects that train brakes are based on the phenomenon. One way of reducing eddy currents is by fully saturating the iron in the motor. If the iron is saturated, magnetic flux cannot be induced in the iron, and thus no opposing magnetic force is generated. Magico found just one facility in the world that could saturate the iron in the driver motors to their specification, and it happened to be in England. The drivers start life in Israel, are shipped to England, back to Israel, and then to the US. Magico’s Web site shows a pair of plots comparing the saturation of its 10" woofer with a “high-end” woofer.

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