CHAPTER 4

Horizontal Coverage. Horizontal coverage for a single array can be considered constant regardless of the number of array elements or the angles between them.

TIP: The angle between two or more line arrays can also be changed to meet

additional design requirements (for example, wall reflections).

Given these factors, designing and deploying a line array system will typically have the following objectives:

Even horizontal and vertical coverage

Uniform SPL

Uniform frequency response

Sufficient SPL for the application

With two different technologies (low-frequency line array and high-frequency wave guide) built into each M2D cabinet, achieving these goals becomes a multi-step process, with different strategies for the lower and higher frequencies for long throws and short throws.

NOTE: THE Meyer Sound MAPP Online prediction program, covered in greater detail

later in Chapter 5, “System Design and Integration Tools,” enables you to make accurate and comprehensive predictions for optimal coverage(s) during the design phase.

High-Frequency Design Strategies

Planning for high-frequency coverage is a matter of fine- tuning the splay angles between cabinets while keeping an eye on the number of far-throwing elements in the array. The number of elements does not necessarily have a significant impact on SPL at high frequencies (it will at low frequencies), but can profoundly affect throw.

For the far field, a smaller mechanical splay angle achieves superior throw through better coupling to compensate for energy lost over distance. In the near- to mid-field, larger splay angles increase vertical coverage.

Low-Frequency Design Strategies

While the wave guide provides isolated control over various mid to high-frequency coverage areas, the low-frequency section of an M2D line array still requires mutual coupling

—with equal amplitude and phase — to achieve better directionality.

Low frequency directionality is less dependant on the array’s relative splay angles and more dependent on the number of elements of the array. At low frequencies, the more elements in the array, the more directional the array becomes.

Electronically Driving the Array

Once the design (number of elements, vertical splay angles and horizontal splay angles between arrays) has been determined, you can effectively optimize the array by driving it with multiple equalization channels, or zones. Typically arrays are divided in two or three zones depending on

the design and size of the array; to optimize EQ, different strategies are used for the low and high frequencies for long throws and short throws.

High-Frequency Equalization Strategies

For the far field, air absorption plays a critical role. The farther the distance, the greater the attenuation at high frequencies. In this zone, very high frequencies generally need a boost to compensate for energy lost over distance; the gain needed is usually proportional to the distance and high-frequency air absorption.

In the near- to mid-field, the air absorption is not nearly as critical; in this zone, high frequencies need little or no additional gain.

TIP: If your M2D array uses a third zone for short throws, high frequencies there may

need to be attenuated to avoid excess levels in the near field.

Low-Frequency Strategies

Although the array can (and usually should) be zoned for implementing different equalization curves for high frequencies, similar or identical equalization should be maintained in all the low-frequency filters. Different low- frequency equalization settings in the same array will degrade the desired coupling effect.

For the same reason, gain tapering is not recommended for line arrays, since adjusting various zones with an overall amplitude control for each zone results in the following:

1.Directionality decreases.

2.Low-frequency headroom decreases.

3.The length of the line array column is effectively shortened.

TIP: The LD-3 compensating line driver was designed to implement both low- and high- frequency strategies with its array and atmospheric

correction functions. The LD-3 line driver’s array correction function compensates for low-frequency build-up, while the atmospheric controls correct for the attenuation of sound in air at high-frequencies. For more information on the LD-3 line driver’s atmospheric and array correction features, please refer to the LD-3 datasheet, operating instructions or visit www.meyersound.com.

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