Grotto i deploys the full array of MartinLogan's advanced subwoofer technologies to achieve deep, rich, satisfying bass while preserving electrostatic-like accuracy and detail. Its advanced low-distortion switching amplifier and sophisticated servo control system extract the very best possible performance from Grotto i's high-resolution 10-inch aluminum-cone driver.

Grotto i subwoofer X-ray view.

A powerful 300 watt (900 watt peak) low-distortion, high-reliability amplifier gives Grotto i extremely articulate bass without need of exaggerated amplifier power ratings or transient-blurring ported or passive radiator enclosures common to many modern subwoofers. A proprietary servo system further ensures that output from Grotto i's 10-inch high-resolution aluminum cone woofer is dramatically free of distortion and provides a faithful replica of the audio input signal.

An optimized selection of connections and controls allow connection of both 2-channel stereo music and multi-channel home theater while allowing each connection to have unique crossover and level settings. LFE input effectively uses no low-pass filter, leaving crossover control to the processor. Left/right line level and speaker level inputs integrate six discrete audiophile grade low-pass filters between 30-80Hz allowing a different level and crossover point when playing back two channel music.

RCA output allows multiple Grotto I subwoofers to operate in series. A unique 25Hz level control allows adjustment of system response by 10dB to eliminate low-frequency build-up or suck-out at a room's most problematic bass frequency. ETC™ spikes couple the sub directly to the floor, minimizing lost energy and allowing tight, well defined bass in any system.

Aluminum cone woofer.

Rigid, Low-Mass Aluminum-Cone Diaphragm

By eliminating cone flexure, even at long voice-coil excursions, low-mass yet extremely rigid aluminum diaphragms help our advanced-technology bass drivers achieve the very low distortion necessary for proper blending with MartinLogan electrostatic speakers.

Servo Correction System

A highly sophisticated control system compares input to output from the woofer and applies automatic electronic correction for any deviation. The advanced servo combines with the drivers' inherent low distortion to yield the cleanest, most accurate bass possible.

Comprehensive Inputs and Outputs with Simultaneous-Connection Option

Grotto i provides a direct, unfiltered LFE input for connection to surround preamp/processors and receivers with built-in subwoofer crossovers as well as line- and speaker-level stereo inputs that connect to its internal crossover. The LFE and stereo inputs can be connected simultaneously with separate level and crossover settings for each, enabling precise optimization for home-theater and stereo music playback in the same system. For those who desire a multiple subwoofer setup, line-level outputs include a mono jack that carries the sum of all inputs. Further, stereo outputs pass a signal from the stereo inputs either directly or through switch-selectable high-pass filters.

Grotto i control and connection panel.

Precision Low- and High-Pass Crossover Filters

Grotto i offers six switch-selectable low-pass crossover frequencies between 30 and 80 Hz, implemented with filters precision-designed for optimum attenuation slope and minimum group delay. This ensures cohesive integration with smooth response through the crossover range with any type of main speaker. The similarly designed high-pass filters on the line-level outputs can be switched between 40- and 70-Hz settings or bypassed.

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 i'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.

Full-Rotation Phase Switch

Grotto i's phase control can be switched from 0 to 270 degrees in 90-degree increments, allowing precise adjustment for optimum blending with the main speakers.

Advanced Proprietary Vojtko™ Switching Amplifier

Grotto i'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 300 watts continuously and 900 watts peak.

Subwoofer level control.

Extended-Range Master Level Control

Crave a little heavy-metal thunder from time to time? Ordinary level controls top out at '10'; ours goes to '11'!

Sealed Cabinet with Asymmetrical Driver Chamber

Grotto i's sealed cabinet eliminates port and passive-radiator resonances and minimizes low-frequency group delay. And its internal asymmetry breaks up standing waves within the enclosure to further minimize resonance and coloration.

Aesthetically Extraordinary (Yet Practical) Cabinet Design

Let's face it – most subwoofer cabinets are just nicely finished boxes. That leads people to hide their subwoofers in corners behind plants or to buy models that look like end tables. Grotto i's cabinet is the anti-box, with a unique architectural look that is both visually engaging and easy to integrate into a room. It features a selection of wood finishes for the top, which enable the Grotto i to blend into any décor. The cabinet body, meanwhile, has a durable, black tough-coat finish, with rubber bumpers at the bottom to minimize damage from stray impacts, such as vacuum cleaners and errant footsteps. Durable, crushproof grilles complete the package.

ETC spikes.

Asymmetrically Configured Energy Transfer Coupler Spikes

Grotto i is supplied with sturdy, 3/8-inch ETC™ spikes, which can be used in place of the standard feet to enhance stability on thick carpets or to create tighter coupling between subwoofer and floor. The spikes are arrayed asymmetrically in a configuration designed to minimize the chance of grille damage if the cabinet is tipped.

Descent i, Depth i, and Grotto i.