Bowers & Wilkins DB1 subwoofer
The last applies to the Bowers & Wilkins Group's new DB1 subwoofer: In addition to its automated room-compensation system, which samples over a wider bandwidth and adjusts for more room modes than does that of the competition, the DB1's menu-driven controls can be conveniently adjusted from a laptop computer rather than the user having to stretch to reach them on the sub's front panel.
Like most subwoofers these days, the DB1 has its own amplifier, uses equalization to generate powerful deep bass output from a small enclosure, and contains a self-optimizing setup program. This approach has proven more popular with buyers than subs that rely on a large enclosure to generate deep bass.
Measuring about a foot and a half wide and tall and 16" deep, the DB1 has two opposed, 12" drive-units. On the rear panel beneath the styling groove that runs all the way round the enclosure's base are the input connectors: mono RCA for low-frequency effects (LFE) from a home-theater processor; stereo unbalanced RCA from a stereo preamplifier's auxiliary main outputs; mono XLR; minijacks for a trigger on/off signal and for the room-compensation test signals from the system's soundcard; a DB-9 serial input to receive control signals via RS232 from the owner's PC (sorry, Mac users); and an IEC inlet for the detachable power cord.
Beneath the groove on the DB1's front are the large on/off switch (with power-on LED) and the controls, grouped in a diamond pattern of five pushbuttons (up, down, left, right, and Set-Up), for navigating the various menu screens that come up on the extremely bright but tiny (1" square) organic LED display next to them. When the DB1 is first turned on, the left and right control buttons can be used to toggle between different presets, while the up and down buttons control the subwoofer's output gain. Pressing and holding the central button brings up the DB1's setup mode. The left- and right-arrow buttons bring up various menu screens, while the up and down buttons select items within a menu, and the center button saves selections and moves on to the next menu. Selecting Audio from the Setup menu brings up a menu of adjustable output features, including choice of preset, low-pass filter settings (slope and turnover frequency), the input sensitivity level (a red LED flashes if you overload the input), gain, normal or inverted polarity, and phase. There is a separate menu for a five-band equalizer (20, 28, 40, 56, and 80Hz), each band adjustable from +5 to 10dB. With all the levels of the DB1 set to their default value of 0dB, the subwoofer has the THX standard sensitivity of 109dB spl at 1m for an input of 1V RMS.
Because I found its display panel difficult to see from my listening chairmy right-channel Quad ESL-989 speaker blocked my viewI controlled the DB1 with B&W's SubApp program, which is compatible with Windows XP as well as Vista and Windows 7 (both 32 and 64-bit versions). Not shipped with the subwoofer, it must be downloaded from www.bwgroup-support.com. SubApp provides graphical user interface controls for the DB1's gain, phase, polarity, and equalization, and enables two additional functions not available on the control panel: naming the presets, and launching the DB1's Room Acoustics Compensation routine. The tools needed to run that last itema calibration microphone, four connector cables, and a USB-connected soundcard that generates the necessary test signalsare included with the subwoofer. With SubApp, the DB1 can take measurements of the room, then adjust its internal equalizer to compensate for up to four room-mode peaks within its operating range.
The DB1's construction, fully described in a white paper posted at the B&W website, includes: two mechanically opposed 12" woofers separated by a partially open internal partition; 1"-thick walls of MDF with ¾"-thick bracing panels to minimize vibration; digital signal processing (DSP) circuits to run the menu-based control system rather than physical switches; home automation capability; and the 1000W switching amplifier, equalized to produce linear output. Like the JL Audio Fathom f212, the DB1 lacks a high-pass filter to shape the bass response of the main speakers, it being assumed that this will be taken care of by the preamplifier/processor or A/V receiver's bass management function.
B&W stuffed two 12" drivers into the smallest enclosure possible and reduced the resistance of the drivers' spiders and dampers at the extremes of the cones' 1.6" range of travel by using a pliable progressive-roll spider, a voice-coil of relatively small diameter (75mm). The woofer cones are made stiff by using a composite of carbon-fiber skins over a core of Rohacell. A highly flexible cable is used to prevent "tinsel fractures" from developing in the DB1's internal wiring from the drivers' constant motion.
The DB1's internal electronics include a signal input circuit board that converts the analog input to digital, a motherboard, a DSP board, the amplifier and its power supply, and an auxiliary power supply to run the digital circuits when the sub is in standby mode. The DSP functions are handled by an Analog Devices Sigma chip; this equalizes the subwoofer, provides low-pass filtering and phase control, adds a five-band graphic equalizer, runs the room-compensation software, and generates an "impact overlay" preset to enhance home-theater sound effects. The DB1 can store five user presets.
Automatic Room Acoustics Compensation
Other subwoofers I have reviewedincluding the Velodyne DD-18, REL Studio III (October 2004), and Revel Ultima SUB-30 (November 2004)have provided test tones and equalizer controls, but require the owner to interpret the findings and make the appropriate adjustments. More recently, JL Audio's Fathom f113 (September 2007) and Fathom f212 subs (April 2010) are shipped with a self-adjusting firmware routine that uses calibration microphones and internal signal generators and processors to optimize the sub's frequency response in the listener's room by adjusting its output to compensate for a single peak room mode. However, only the B&W DB1 lets its owner run its automatic optimization program and adjust its set-and-forget controls (eg, gain, polarity, phase) from the listening chairthough it's necessary to connect a PC to the subwoofer with the long line-level cables (supplied).