The flagship powered subwoofer in the PINNACLE^® line is the Digital Sub^TM 350. It packs a bundle of high tech engineering and performance into its tiny 15-inch cube-shaped enclosure and still costs less than $1,100. It is exactly the same size as its little brother, the Digital Sub^TM 150, and looks identical from the front. Just like the 150, the box is finished in a premium black vinyl material, and the removable black, cloth-covered grille cloaks nearly the entire surface of the front of the cabinet. There is a gold PINNACLE^® badge at the bottom, center. Solid brass, cone-shaped feet are furnished to improve bass definition by minimizing cabinet movement in reaction to cone movement. These feet are effective and should be used whenever the subwoofer sits on carpet. The appearance is simple and not particularly outstanding in any way, but this subwoofer is so small and unobtrusive that it will be all but invisible in the room.

On the back things are a little different from the entry level model. Like the 150, the back panel has no protruding heat sink as this product uses a digital switching amplifier which does not require one, due to its high efficiency and low heat operation. High quality five-way binding posts replace the blade-type connectors on the 150 for speaker-level inputs and outputs. There are RCA line-level inputs, a volume control, a low-pass frequency control calibrated from 50-150 Hz, a phase switch and a power switch marked Off and Auto-on.

The top-of-the-line PINNACLE^® powered subwoofer uses two 12-inch heavyweight polycone drivers with 2-inch voice coils and 40-ounce magnets in a compound (Isobarik) configuration. Both drivers face in the same direction, one behind the other, and are wired in phase and in parallel. The enclosure is sealed. The Class D digital switching amplifier produces 350 watts RMS continuous power (555 watts dynamic power). The active low-pass filter is fourth-order, 24 dB/octave, and variable from 50-150 Hz. The passive, speaker-level high-pass filter is first-order, 6 dB/octave, and fixed at 80 Hz.

Using two drivers in a compound (or Isobarik) configuration allows the enclosure to be half as large for the same cut-off frequency, or remain the same size and go much lower than a single driver system. Or a little of both, as is the case here. Only the volume of the space behind the internal driver (the one you can't see) is considered, so even though the outside of the enclosure of the Digital Sub^TM 350 is the same size as the outside of the 150 model, the internal volume is less. Using two motors to essentially drive the one cone that actually vents into the room, improves definition and control at low frequencies.

Because the rear driver is loaded by the sealed volume of the enclosure and the front driver is loaded by a sub-enclosure pressurized by the rear driver, their resonant frequencies will be different. The loose coupling between the drive elements allows these dissimilar resonances to damp each other, producing very high quality bass that is near-aperiodic. I really like the tight, highly defined sound of Isobarik bass systems.

The Digital Sub^TM 350 reached 108 dB at 40 Hz, 107 dB at 35 Hz, and 106 dB at 30 Hz. It could manage 96 dB at 25 Hz and 86 dB at 20 Hz before doubling set-in. With a sine wave input, it could easily be driven to doubling, a form of harmonic distortion, at any frequency below 40 Hz. This is usually caused by the voice coil leaving the gap. Levels over 105 dB are extremely loud for music and loud enough for all but the most enthusiastic sound effects, so the doubling problem was never troublesome during listening tests, but I would prefer that limiting be employed so that this could not occur at all.

Music listening is a joy with the Digital Sub^TM 350. Bass is tight and well controlled with excellent tonal definition. The rhythm and pace of music are easy to follow and the subjective impression of very low bass is excellent. Details that are obscured by conventional designs on low frequency sound effects are revealed clearly by PINNACLE's flagship powered subwoofer. Bass impact is quite punchy, and film sound effects are reproduced surprisingly well for such a compact unit, but for the ultimate sense of slam, two units are recommended. Two subwoofers will load the room better for smoother response, give you stereo all the way down, and allow you to hear this fine quality compound bass at higher levels-and still cost about the same as one of the more expensive units in the review.

The high quality of Isobarik bass used to be associated with high cost. The PINNACLE^® Digital Sub^TM 350 allows us regular guys to afford a compound-loaded subwoofer system too. The outstanding musical performance of this subwoofer makes it outshine the competition in the hotly contested near-$1,000 category and it's very, very good for movie soundtracks too. Get thee to a dealer soon, and listen to this miniature powerhouse. It's a performance winner that's also affordable.

Richard Hardesty / Widescreen Review Volume 6, Number 4, Issue 26