Kevin in Wappinger Falls New York (wherever that is) asked me an interesting question recently.
This is a really good question and one we don’t talk about much. Perhaps it’s a good idea to first get on the same page. The classic two-way or three-way loudspeaker has two or three drivers in a box. The multiplicity of drivers—tweeter, midrange, woofer—is needed to break apart the frequencies so each driver only has to handle a specific range: tweeters handle the higher frequencies about 2kHz and the woofer handles everything from that point down.
A line source handles the frequency divisions in exactly the same way—tweeters, midrange, and woofers—but instead of relying upon a single driver for each range multiple drivers are instead employed, typically with a line of many tweeters and sometimes many midranges. The advantages of multiple drivers in a line are manifold: each driver has fewer demands and the waveform comes out in a long, vertical, cylinder rather than a single driver’s ever-expanding circular wave.
The advantages of a line source vs. a point source can be summed up fairly easily. A point source sound radiates in all directions from the driver and quickly loses energy as it floods the room in a 180˚ plane. Worse, this expanded radiation pattern hits the ceiling, walls, and floor and reflects back into the room out of synch (time) with the initial launch. Only those listeners in a narrow sweet spot get to enjoy the best sound. A line source radiates a more focused pattern in the shape of a tall vertical cylinder that, above about 500Hz, has nearly no floor, ceiling, or sidewall reflections to dissipate energy and add to sonic confusion.