Digitally Steerable Arrays ("DSA") are a relatively new type of loudspeaker system that are not only self-powered, but also employ individual processing for each transducer to control the coverage of the entire array. Using advanced, but well-known techniques of gain-, delay- and frequency-shading, the polar response of an array of transducers can be steered differently than it would behave passively. Steve "Woody" LaCerra discussed DSAs at length in last month's issue.
DSAs employ a line-source form-factor, a vertical column of identical transducers that are closely spaced for the most part. Like unprocessed architectural columns, DSAs typically provide fixed horizontal coverage of about 100 degrees. However, their vertical coverage, usually fairly narrow in tall enough passive line sources, can be directed downwards, can be opened up to cover a wider vertical angle or can sometimes even be split to fire above and below architectural obstructions, such as balcony fascia.
Architectural columns originally found favor for announcements and spoken word in public spaces like train stations, airports and churches: cavernous buildings with reflective surfaces that challenge intelligibility with diminished direct-to-reverberant ratios when distributed point-source speakers are employed. While columns provide wide coverage with limited vertical spill, aiming them down to better address listening areas requires tilting the enclosures at an angle, less aesthetically pleasing than mounting them flush to a wall. More importantly, physically angling passive columns tips coverage at the farthest reach, but doesn't change coverage at the sides.
Both passive columns and DSAs are getting a boost from changes to the National Fire Code that require Emergency Voice Alarm Communications Systems (EVACS) and Mass Notification Systems (MNS) for non-fire emergencies, and there's an intelligibility requirement. Additionally, a variety of modern public spaces, from shopping malls to auditoriums and symphony halls, don't want or need to own a high-power concert-quality sound system, but have regular use for a Public Announce (PA) system that also satisfies fire and emergency enunciation requirements.
In addition to DSAs' ability to steer coverage, a further benefit is that most can be programmed with presets that can adjust coverage for different applications. One setting might only cover the floor or orchestra level of a hall, while another might reach further into the room or split coverage into a second beam to hit a balcony.
Columns of drivers have a limit to coupling at higher frequencies, determined by the distance between acoustic centers, limiting their ability to project the highest octaves. The high-fidelity solution is to supplement a column of cones with a high frequency array. Some products integrate these into the enclosure, while others provide them in a second box. Low frequency pattern control is determined by array length, so many provide supplemental low frequency columns to extend the array's length. For musical applications, even a fairly tall array benefits from the addition of subwoofers.
Finally, a recent development is modular multi-way DSAs, systems made of multiple identical two- or three-way enclosures that are assembled into vertical arrays to provide high SPL and full bandwidth audio for larger concert applications.
To download a PDF of the June 2011 FOH Buyers Guide, CLICK HERE .
