Mention column loudspeakers to grumpy old soundmen and the Shure Vocalmaster immediately springs to mind, as every ’70s band used it.
But column loudspeakers continue to gain in popularity because they offer a solution for those who need efficiency in the vocal range combined with even coverage and a very slim, unobtrusive profile.
Line sources have been around for well more than a half-century. For portable sound applications, audiences tend to be small. Installed systems are often employed in reverberant public spaces – houses of worship, auditoriums and passenger terminals – predominately for public address.
The characteristics of line source columns – wide horizontal coverage, minimal vertical coverage above and below the enclosure and coherent sound in the vocal range – are all attractive features for these kinds of venues.
Driver spacing determines the highest frequency at which a column of identical drivers acts as a line source, while the height of the column determines the lowest frequency with directivity. As with modular line arrays, a short system might efficiently throw the midrange, but leave a puddle of low-frequency mud behind the enclosure.
Inexpensive column loudspeakers remain popular because they offer a compromise solution to installers who need efficiency in the vocal range combined with even coverage and a skinny profile that makes them acceptable on the walls of public assembly spaces.
Investigations into line source coupling behavior and pattern control tell us that loudspeaker cones exhibit coupling behavior up to a frequency whose wavelength is half the distance between adjacent acoustic centers.
Another old soundguy image is the column of JBL 2123 10-inch midrange drivers in Clair S4 cabinets. With their frames squared off to provide closer coupling, their acoustic centers could be placed 9.5 inches apart, providing coupling to 800 Hz.
In architectural columns 6.5-inch diameter cones, when tightly-spaced, will couple up to about 1 kHz. Four-inch cones couple to about 1,600 Hz and 2-inch cones to 3.3 kHz. Above these frequencies top and bottom lobes appear in the polar response, however restricting the high frequency response of some of the cones can reduce lobing. This can be achieved with passive filters in the cabinet, or with active filters used in DSP-driven steerable columns.
A specialized version of the line source column is called “digitally steerable” with individual amplification, delay and equalization for each driver, allowing the column’s vertical coverage to be tilted down (or up) and focused for short or long throws, though its horizontal coverage remains fixed.
One advantage is that a column loudspeaker can be placed flat on a wall, while its coverage can be tailored to a specific listening area. Another advantage to digital steering is that the entire coverage pattern can oriented downwards. Mechanically tilting a passive array adjusts the farthest coverage, while leaving the coverage towards its sides near the original height.
More demanding applications, such as music, require both greater bandwidth and dynamic range, leading to two-way designs that incorporate separate high-frequency transducers in addition to the column of tightly spaced cone drivers.
In modular line array enclosures, compression drivers are mounted onto “isophasic” manifolds that convert sound from their round opening into a tall, thin opening whose output is in phase along its entire height. Columns lack both the budget or depth for this, so high-frequency drivers in 2-way column speakers are reproduced by a few closely coupled HF drivers, since their height only needs to be a few inches, or by the use of magnetic planar or “ribbon” drivers, which provide the required in-phase output in a tall, thin HF driver.
It’s common for line source columns to be combined as multiple cabinets to achieve better performance as taller systems for bigger rooms. Longer columns provide pattern control reaching to lower frequencies. A 9-foot column can provide control to 125 Hz, so combining three 3-foot columns can increase low frequency performance.
As with miniature line arrays, some systems have companion LF columns which employ long-excursion small-format woofers to extend pattern control to lower frequencies. Alternately, traditional subwoofers can supplement a column’s LF response.
Enjoy our Real World Gear Photo Gallery Tour of the latest available column loudspeaker models.