Burmester Audiosystems B99 loudspeaker
The B99's shape is slightly reminiscent of an airfoil and with an aluminum veneer modeled on the riveted wings of turboprop aircraft. It is a three-way, full-range, floorstanding loudspeaker whose midrange and high-frequency drivers are installed in a D'Appolito configuration; the two woofers are mounted on the side.
The B99's ribbon tweeter consists of heat-treated Kapton foil. Its motor consists of aluminum conductors laminated on the diaphragm foil, and uses neodymium magnets with an energy density 20 times higher than similar ferrite magnets. Silver conductor wires are soldered directly to the diaphragm foil. The ribbon's 28cm2 area (4.34 sq.in.) is protected by a plastic ridge that also serves to broaden the dispersion angle of the tweeter over its working frequency range. The ribbon covers an area about 10 times the size of conventional dome tweeters, allowing for a low crossover frequency of 1.8kHz.
The two 5.6" midrange drivers use magnesium cones that are said to be free from resonant modes to above 3kHz—an octave above the crossover point. Each driver has a large gold-colored, bullet-shaped phase plug of copper to prevent compression effects in the center of the driver, and is supported by a rigid, diecast, magnetically nonconductive support.
The bass frequencies are managed by two 10" woofers with air-dried, resonance-damped paper cones. The woofer has a large vent hole in the pole core behind the dustcap to reduce compression effects, and the 1" coil is said to have a long linear throw. The two woofers are mounted either side of the ports and vent through 40 lateral openings, each 10" by 0.5", in the curved aluminum panels on one of the loudspeaker's sides.
Burmester makes the B99 in matched pairs. The process begins with setting tight tolerances for the OEM drive-unit suppliers. The drivers received from the supplier are then burned in for two weeks, using a 10Hz continuous sinewave for midrange units (at 110W) and woofers (at 250W), and a 7W continuous pink-noise signal for the ribbon tweeters. The drivers are then measured and computer-sorted; the 10 units that go into a given pair of B99s are trimmed within ±5dB for their respective frequency responses. All technical specifications for each driver are filed, so that a loudspeaker in the field can receive a new driver identical to the one being replaced.
The B99's enclosure is double-walled. The inner chamber is made of 1"-thick, ultrastiff MDF strengthened with a complex internal bracing system. The midrange driver and tweeter are mounted in their own internal cabinets and the outer housing and inner chamber are insulated from each other by a layer of damping material. Like all Burmester speakers, the B99 is not damped by wool stuffing, because "the woofer has to pull the air through the wool." Rather, the B99 contains mats of a felt-like material in various thicknesses. The thickness of these mats has been calculated precisely in relation to their placement in the enclosure.
The B99's crossover—which weighs more than 11 lbs—sits in its own completely sealed enclosure at the bottom of the speaker cabinet, protected from the "sonic storms" that rage inside the main enclosure. Second-order crossover slopes are used, and impedance correction is used so the theoretically correct filter behavior is not affected by changes in the driver's impedances. Heavy-gauge copper plating is used for the crossover's printed-circuit board. The woofer connections are made with high-purity 10mm2 copper wire, and the midrange drivers and tweeters are wired with pure silver.
The four speaker binding posts—two for the woofer section, two for the midrange-tweeter—are located on the underside of the enclosure just below the crossover. Two people are required to change the speaker cables: one to tilt and hold the front end of the 220-lb speaker, the other to crawl underneath and screw down the four large plastic wing nuts.