History of Columns
The line array effect of the narrowing of the beam with increasing frequency was first demonstrated by acoustical pioneer Harry Olson. He published his findings in his 1957 text, Acoustical Engineering. Olson used line array concepts to develop the column speaker in which vertically aligned drivers in a single enclosure produced mid-range output in a wide horizontal and narrow vertical pattern. Line arrays have been around for over half a century but until recently most were voice range only. The application for these columns was for highly reverberant spaces where a narrow vertical design kept from exciting the reverberant field.
The next generation of bands, working at a higher level of the business, moved beyond the popular Vocal Masters (among other large columns) of the day, toward higher-output loudspeaker systems, with large woofers and HF (high- frequency) horns. Small bands followed suit with similar but scaled–down systems, and the column loudspeaker was largely forgotten in the US. But small column speakers continued successfully in speech PA application, such as for airports and traditional places of worship, where speech intelligibility is all–important.
The EU loudspeaker manufacturers continued to advance the design of column loudspeakers. It was L-Acoustics' V-DOSC line array in the mid-1990s that would show the concert world that more projection and a smoother frequency response can come from fewer boxes in a line array. As soon as people realized that there was no destructive interference in the horizontal plane and waves combine mostly in phase in the vertical plane, the race was on for pro-sound loudspeaker manufacturers.
I did a review, for a church AV magazine, of the Bose MA12s, shortly after they came out in 2003 (it is taller than the version with electronics at music stores). Like other modern, thin column-shaped loudspeakers coming to market, they excel in reverberant rooms like classical churches and airports. The Bose column is Ok at its primary task of PA systems and is a good value. But the Bose, it’s smaller versions and many newer imitators, represent only the entry-level line-array (column speaker) class.
The MA12 is made from just (12) two in. drivers; it has neither woofers nor tweeters included. They do offer some small woofers as an option & certainly need them for any use with music (even then they are not subwoofers). I find the use of even smaller versions of the slim Bose columns in music clubs sometimes ill-advised, they are especially inadequate when bands try to use them outside. All of the basic, thin column speakers have real limitations, although not the same. Most of these loudspeakers are intended primarily for PA/speech, because they have limited output and/or bass response (most have decent high-end).
Line arrays disperse sound differently than conventional loudspeakers. As my MA12 review pointed out, a challenge with basic cost-effective (1-way) column arrays, like the Bose, is the way that their main lobes get tighter with rising frequency (see graphics at top & bottom), causing the frequency response to change with distance; this is not a good thing. Slim columns typically are single-band units (do not have tweeters), so the horizontal and vertical directivity vary with frequency too much. This narrowing radiation pattern (w/increasing frequency) effect causes the rate of fall off to vary with frequency, so then each seat gets a different frequency response of direct sound, making it very difficult to design or EQ the system for uniform-good sound.
If a line array is long, verses the frequency that it is reproducing, it will have a sound level drop-off, at one-half the typical rate of conventional, point sources. This is a great idea, but low-cost, 1-2-unit, (column shaped) line arrays are not long enough to control the lower frequencies – thus the big difference between the “Representation of Dispersion” graphic (above Left) showing the simplified radiation pattern of a leading column-shaped speaker array in the upper mid-range (at 4kHz.) and the real radiation polar pattern, at top (three different freq.), of a similar column.
Column speakers with superior fidelity
There are now several alternative column loudspeaker types that have superior music fidelity (some at much greater cost), from several manufactures. I have wanted to specify column loudspeakers for my some of my smaller church clients. As you might guess, I have been following this trend closely. There was a lot of room for improvement in this product class.
A few other column loudspeakers are “shaded” loudspeaker arrays. This means that the drivers at the end of the array receive just the lower frequencies, with less drivers being used as the wavelength is reduced (higher frequencies) – some, like JBL’s, use special shading EQ.
These shaded loudspeaker arrays are less directional at higher frequencies (not as tight polar lobe the other column loudspeakers), so they have more consistent polar lobes (sound coverage) and frequency response. A few of these small, shaded-column speaker arrays have one AMT or planar tweeter with superior fidelity, from small specialty manufacturers like Innovox Audio.
Other brands like Alcons, Atlas and SLS offer larger two-way column speaker arrays (shown at Top-Right) with ribbon/planar drivers the full-length of the arrays – these sound great and the polar radiation starts to be usable if the arrays are at least 5ft tall, at the right height and pitched to ensure that the tight HF polar lobe is covering all of the seating area. LF extension modules are available to improve the radiation pattern (that tends to broaden too much at lower frequencies).
A new trend in thin column-shaped speakers is the move toward optimized shape/profile, to improve the consistency of the radiation pattern. Slightly and much larger columns are recently coming to market that offer much higher output. A few higher-cost column speakers are self powered with DSP, allowing them to steer their lobes down as needed. So these column loudspeakers are starting to get interesting!
Principal Audio Design