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May 2012

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by Bruce Borgerson

There was an ancient era (1960s and 1970s) when column loudspeakers were all the rage in church installations. After that was a long period when, as Rodney Dangerfield would have said, “They didn’t get no respect.” Perhaps for good reason.

Today, however, sleek and slender column loudspeakers are making a comeback. Thanks to improved transducer technology and computer-aided design, newer column loudspeakers offer improved performance across the board. Beyond that, when you give each little driver its own amplifier and put everything under advanced DSP control, the column can do tricks never dreamt of in the age of the Shure Vocalmaster.

First, regarding nomenclature, the industry shows little agreement. These devices are variously called “column arrays,” “line source arrays,” “architectural columns” and combinations thereof. For the sake of uniformity, we’ll call them “column arrays.”

A Matter of Principles

Next in order is a review of relevant acoustical principles. Loudspeakers are placed in a vertical column in order to provide a wide horizontal dis- persion pattern (typically 120 degrees or more) in combination with a far more restricted vertical pattern—usually between 10 and 30 degrees. That spreads the sound power across a wide seating area, yet also throws it effectively toward the rear of the room without splattering useless sound on the ceiling. That’s a good thing, if you can do it uniformly across the whole audio spectrum—something not easily done.

Two basic physical characteristics determine the upper and lower limits, as well as the uniformity, of a column array’s vertical control pattern:

The driver (loudspeaker cone) diameter defines the upper frequency limit, assuming all drivers are adjacent to each other. The smaller the loud- speakers, the higher the frequencies you can reproduce without losing your desired vertical pattern and generating unwanted discontinuities (“lobing”). A column with six-inch cones will couple smoothly to nearly 1,200 Hz, while one with three-inch cones won’t start serious lobing until about 2,400 Hz. Obviously, having smaller drivers will extend your high frequency performance, which is why many new columns are far skinnier than older models. Two-way column arrays, usually with cone drivers four-inch or larger, will add either small dome tweeters or a magnetic planar (“ribbon”) driver to extend the highs.

The total length of the column defines the low-frequency limit of pattern control. A column four feet long will hold its pattern below 300 Hz, generally considered the bottom of the vocal range. For meaningful bass control, however, you’ll need a column at least double that length.

But will the skinnier columns still deliver? Amazingly, with proper powering and processing, new high-excursion two-inch and three-inch drivers produce solid low-frequency response. With enough of them lined up—24 little three-inch drivers have about the same cone area as a 15-inch woofer. So you can push some serious air with small drivers.

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Bruce Borgerson networks around the industry via Wavelength Communications while monitoring technologies at the First United Methodist Church of Ashland, Ore.