CHAPTER 5

CHAPTER 5: LINE ARRAYS AND SYSTEM INTEGRATION

HOW LINE ARRAYS WORK

Line arrays achieve directivity through constructive and destructive interference. For example, consider one loudspeaker with a single 12-inch cone radiator in an enclosure. The loudspeaker’s directivity varies with frequency: When the wavelengths being reproduced are larger than the driver at low frequencies, it is omnidirectional; as the frequency increases (and the wavelength is comparable to the size of the driver), directivity narrows. Above about 2 kHz, it becomes too beamy for most applications, which is why practical system designs employ crossovers and multiple elements to achieve controlled directivity across the audio band.

Stacking two of these loudspeakers one atop the other and driving both with the same signal results in a different radiation pattern. At common points on-axis, there is constructive interference, and sound pressure increases by 6 dB relative to a single unit. At other points off-axis, path length differences produce cancellation, resulting in a lower sound pressure level. In fact, if you drive both units with

a sine wave, there will be points where the cancellation is complete, which can be shown in an anechoic chamber. This is destructive interference, sometimes referred to as combing.

A typical line array comprises a line of loudspeakers carefully spaced so that constructive interference occurs on-axis of the array, and destructive interference (combing) is aimed to the sides. While combing has traditionally been considered undesirable, line arrays use combing to positive effect: to control the directivity.

M’ELODIE CURVILINEAR ARRAY

The M’elodie loudspeaker employs a combination of drivers to enable you to optimize both coverage and directivity in a M’elodie line array system. To achieve optimal results, it is important to understand how these components work together.

In the horizontal pattern of an array of M’elodies, these horns work to produce a wide 100-degree coverage; in the vertical, however, Meyer Sound’s REM technology provides narrow coverage in order to:

■Minimize destructive interference between adjacent elements

■Promote coupling to throw longer distances

As more elements are arrayed in a vertical column, they project mid- and high-frequency energy more effectively through coupling. The amount of energy can then be controlled using the relative splay between the elements:

■Wide angles: Curving a line array can aid in covering a broader vertical area.

■Narrow angles: Straightening a line array provides a longer throw and coverage that more closely matches that of the mid-low frequencies.

Mid to Low Frequencies

For the mid to low frequencies, line arrays must be coupled together to narrow their vertical coverage and project mid and low energy to the far field. The directional control of the array depends on the length of the array (number of elements).

Directional control is achieved when the length of the array is similar or larger than the wavelength of the frequencies being reproduced by the array. As frequencies get lower and wavelengths get longer, the number of cabinets has a critical effect on the directional control. The number of array elements is very important: the more M’elodie loudspeakers used, the more directional the vertical beamwidth becomes at the lower frequencies. However, at low frequencies the splay angle between cabinets has little effect since the total length is not modified substantially.

High Frequencies

For high frequencies, M’elodie uses a very precise Constant Q horn — developed using Meyer Sound’s anechoic chamber — which provides a consistent beamwidth of coverage in the horizontal plane.

17