Krell Industries MASTER REFERENCE SUBWOOFER - Manual (Page 13)

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Active Motion Control is a unique circuit topology developed by Krell specifically
for the Master Reference Subwoofer. An instrument grade accelerator, mounted to
one of the drivers, relays information about the driver’s position to the Active Motion
Control circuit, where it is compared to the musical waveform at the amplifier input
stage. Amplifier parameters are then adjusted to ensure that driver motion is faithful
to the input signal, and feedback is precisely applied to preserve sonic impact. Krell
Active Motion Control allows the Master Reference Subwoofer to achieve complete
driver control and deliver true-to-life low frequency sound at the same time.
Enclosure
The enclosure is an essential part of any loudspeaker and is particularly significant
in subwoofer design. Low frequency energy causes some of the most stable materials
to resonate. Enclosure resonance degrades performance and destroys linearity. Krell
engineering has attacked these design challenges with a vigorous application of
technology, know-how, and innovative build materials.
The enclosure for the Master Reference Subwoofer is made of 1 in. thick, aircraft-
aluminum billet. Each of the two driver baffles is a substantive 2 1 / 4 in. thick. The
subwoofer assembly is held together by 68 machine screws, size 1 / 4 20 x 1 in. The
precision machine finish is black anodized to a pearl-like luster. Fully assembled, the
Master Reference Subwoofer weighs 396 pounds. This subwoofer does not resonate.
Drivers
The high performance demands of the Master Reference Subwoofer require drivers
of exceptional capability. Krell has researched every aspect of driver design and
construction to produce remarkable transducers. The Master Reference Subwoofer
contains two 15 in. drivers, which have been custom crafted to Krell’s own rigorous
specifications. The drivers are mounted at opposite ends of the case, firing outward,
away from one another. They are wired in phase: One driver’s motion has the effect
of canceling the motion of the other, rendering the enclosure free of operationally
induced vibrations.