The Why and How of Line Arrays
Line array loudspeakers have an obvious appeal. The use of multiple drivers produces increased acoustic efficiency and power handling ability. There is also a subtler, but very real benefit. The physical span of the array produces a more life like sound image-adding height to a listening experience often missing with more conventional loudspeakers. The benefits of a line array are not simply bought, however. Designing a good line array presents unique challenges differing substantially from those of conventional designs. Using many drivers spread out vertically over a distance of 7-8 feet causes sound from the individual drivers to arrive at the listener's ears at different times and therefore with different phases. If these effects are not accounted for the result will be very uneven frequency response. Placing the drivers on the arc of a circle can focus the sound of all the drivers at a single point, but this greatly limits the choice of listening position. Construction of a circular arc array is also more difficult. The line array design challenge is to provide uniform coverage over a broad range of distances and heights using a simple to build linear arrangement of drivers. Several line array concepts were subject to extensive computer simulation and acoustic testing to arrive at the design finally presented here. By appropriate series connections within a group of twelve mid-bass drivers, the effect on array response of drivers more distance from the array centerline was tamed. As a result, the listener will experience little change in frequency response over a broad range of heights at distances of 10 feet or more from the array. (Because it has a much smaller height, the tweeter array does not need any special treatment.) The resulting array sensitivity is 96dB SPL/2.83v/1m. Frequency response is uniform from 50Hz to 20kHz. Sound pressure levels of 115dB can be generated with a 100watt amplifier. Impedance is 8( with an angle no greater than +30), making ideal for tube amps.
May 19, 2000