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Martin Logan


Frequency Response:
22–150 Hz ±3dB; Anechoic through LFE effects input

Input Impedance:
20,000 ohms
Low Pass Filter Frequencies:
30, 35, 45, 55, 65, 80 Hz
High Pass Filter Frequency:

0°, 90°, 180°

25Hz Level Control:
±12 dB

Woofer Type:
10" (25.4cm) high excursion, aluminum element woofer with extended throw drive assembly, non-resonance asymmetrical chamber format

250 watts rms (350 watts peak)

RCA line level; RCA LFE; speaker level
RCA for multiple subwoofer connection
40 lbs. (18.2 kg)
Dimensions (HxWxD):15.4" × 15" × 12.9" (39.1 × 38.1 × 32.8 cm)




Active Subwoofer (250watt)


Looking more like contemporary sculpture than exotic audio equipment, the attractively priced Grotto makes it easy to add great bass to your home's audio system. It's not just a pretty face, however. Grotto's compact cabinet houses some serious performance-enhancing technology, starting with the same low-mass, long-excursion driver used in our flagship Descent subwoofer. A proprietary advanced-design amplifier and a highly sophisticated servo monitoring and control system work together to extract from that driver the greatest possible low-frequency extension and power with absolute minimum distortion. It's amazing to hear deep bass so clear and detailed emerge with so much impact from such a small enclosure. A precision crossover and 25-Hz level control facilitate integration into any stereo music or multi-channel home theater system.
Low-Distortion Aluminum-Cone Driver
Borrowed from our state-of-the-art Descent subwoofer, Grotto's high-resolution driver combines a 10-inch aluminum-cone diaphragm with a high-intensity magnet structure to achieve huge excursion and output capability without sacrificing detail. By eliminating cone flexure, even at long voice-coil excursions, aluminum diaphragms help our advanced-technology bass drivers achieve the very low distortion necessary for proper blending with MartinLogan electrostatic speakers.
Advanced Servo Control
All dynamic drivers have nonlinearities in their suspension and motor systems, which increase dramatically at large diaphragm excursions. The resulting distortion can rise to 20 percent or more with typical woofers and subwoofers reproducing strong deep-bass signals. MartinLogan's advanced servo system uses a sophisticated monitoring and control circuit to detect and instantaneously correct any deviation between acoustical output and electrical input. The result is a three- to ten-fold reduction in distortion for the purest possible low-frequency reproduction.
Precision Low-Pass Crossover Filters
Grotto offers six switch-selectable low-pass crossover settings ranging from 30 to 80 Hz, each implemented with filters precision-tuned for optimum contouring in both the amplitude and time domains. This enables seamless integration with any MartinLogan main speakers as well as with speakers from other manufacturers.
Crossover-Bypass LFE Input and Daisy-Chain Output
For home theater systems in which the surround processor supplies the crossover, Grotto provides an LFE input that completely bypasses its internal filters. It also has an unfiltered line-level output to allow operation of multiple subwoofers in a serial configuration.
25-Hz Level Control
At very low frequencies, all rooms exhibit a phenomenon known as room gain, which produces a mild bass boost. The smaller the room, the higher the frequency at which this starts. Grotto's 25-Hz level control enables you to compensate for excessive room gain by cutting output in the 20- to 30-Hz range or, if you prefer, to accentuate the feeling of deep-bass energy by augmenting those frequencies.

Advanced Proprietary Vojtko™ Switching Amplifier
Grotto's amplifier belongs to recently developed class of switch-mode designs that incorporate a variety of innovative techniques to reduce noise, distortion, and heat to the lowest possible levels. In particular, the switching frequency is much higher than in typical subwoofer amplifiers of this type. It can produce a true 250 watts continuously and 350 watts peak.

Portless Enclosure
Although ports are a convenient and cost-effective way of increasing low-frequency output, they rely on resonant energy in a way that impairs bass quality. A good sealed system will exhibit less transient-blurring group delay while maintaining smooth, consistent response regardless of output level or voice-coil temperature. Listen carefully to the sound of a bass drum, and you'll hear the difference.
Installation Versatility
Grotto excels in all installation configurations, including in corners, inside cabinets, and underneath or behind furniture.
Energy Transfer Coupler Spikes
The Grotto is supplied with sturdy, 1/4-20 MiniETC™ spikes, which can be used in place of the standard feet to enhance stability on thick carpets or to create tighter coupling between speaker and floor.