BMR drivers, on the other hand, behave very differently than traditional piston drivers do, and in ways that are frankly a bit difficult (at least for me) to picture in the “mind’s eye.” Here’s the deal:
• Rather than being shaped like “domes” or “cones,” all of the BMR drivers I have seen to date feature diaphragms that look like flat paper or cardboard disks.
• At the lowest end of their intended operating ranges, BMR drivers behave like traditional piston-type drivers (that is, the drivers pump inward and outward, producing sound waves).
• But, as frequencies climb higher and higher, the entire motion of the BMR driver changes in a radical way, transitioning from “pistonic motion” to a so-called “ripple motion” where—instead of moving inward and outward like a piston—the entire surface of the disc-shaped diaphragm begins to ripple, with waves of motion spreading from the center of the disc outward toward its rim (almost like the concentric ripples you would see on the surface of a pond if you threw a pebble in).
• One very desirable property of the BMR driver’s distinctive ripple motion is that it offers inherently excellent dispersion. In practice, this means you can typically get away with using a single BMR driver to serve as both a midrange driver and as a tweeter—and without need for a crossover network.
Until now, I have only seen BMR drivers used in relatively expensive high-end loudspeakers, such as the Naim Audio Ovator-series loudspeakers from England. But now, the Cambridge Audio Minx system makes BMR technology available at (by far) the lowest price point we have seen thus far.
Blogs Discussing Speakers Featuring BMR drivers
• My blog entitled, “RMAF (Rocky Mountain Audio Fest) 2009, Day One: Loudspeakers Under $20k” (click here). This blog discusses multiple loudspeakers, including Naim Audio’s Ovator S-600 loudspeaker ($10, 450/pair), which was arguably the first hi-fi product to use a BMR driver.
• “The Absolute Sound at RMAF 2010: Neil Gader on Electronics Under $20k and Loudspeakers under $20k” (click here). This blog discusses multiple loudspeakers, including the BMR driver-equipped Naim Audio Ovator S-400 loudspeaker ($5250/pair).
• My blog entitled, “Radical BMR Drivers Make Cambridge Audio’s Minx System Different & Better” (click here). This blog provides an expanded discussion of BMR driver technology.
Highlights: Minx Min 20 Satellite Speaker
• Dual 2.25-inch BMR driver housed in compact enclosures.
• If described in conventional loudspeaker parlance, the Min 20 would probably be called a “1 ½-way” loudspeaker. In practice this means the Min 20’s dual BMR drivers together handle frequencies from about 130Hz up to around 800-900Hz, at which point a simple “low pass filter” rolls off output from the lower of the BMR drivers while the upper BMR driver is allowed to run all the way up to 20kHz—crossover free!
• Precision molded enclosures finished in gloss black or white.
• Extremely compact dimensions (6-inch x 3.1-inch x 3.3-inch).
• Banana jack-type speaker terminals adapt easily to various types of speaker wires.
• Rear of enclosure has recessed fitting that can accommodate wall mount brackets (included) or optional tabletop or floor stands.
• Snap-on speaker grilles with logos suitable for vertical (standard) or horizontal (optional) positioning. One horizontal-logo grille is included with the S325 system package to allow one Min 20 to be positioned on its side for center channel use.
Highlights: Minx X300 Powered Subwoofer
• Forward-firing, 8-inch woofer driver.
• Downward-firing, 8-inch passive radiator.
• 300-watt, DSP-controlled, digital amplifier.
• Subwoofer controls: volume, phase (continuously adjustable, 0 – 180 degrees), crossover frequency—complete with markings to show ideal settings for use in systems with Min 20 or Min 10 satellite speakers, main power switch, separate on/off mode switch with an “always on” setting or an “automatic signal-sensing” setting.
• Subwoofer inputs/outputs: wireless input port, stereo analog audio inputs via RCA jacks (left input jack labeled as LFE input for use with AVRs), stereo analog audio outputs via RCA jacks.
• Enclosure styled and finished to complement the Min 20 satellites.