Handbook for Sound Engineers

Loudspeaker Cluster Design 659

18.7.5.4 Array Height versus Wavelength (Ȝ)

Driver-to-driver spacing sets the highest frequency at

which the array operates as a line source. The total

height of the array sets the lowest frequency at which it

has any vertical directivity.

Figs. 18-29 though Fig. 18-32 show the effect of

array height versus wavelength.

At wavelengths of twice the array height, there is no

pattern control, the output is that of a single source with

very high power handling, Fig. 18-29.

As the frequency rises, wavelength approaches the

height of the line. At this point there is substantial

control in the vertical plane, Fig. 18-30.

At higher frequencies the vertical beamwidth

continues to narrow. Some side lobes appear but the

energy radiated in this direction is not significant

compared to the front and back lobes, Fig. 18-31.

Still further vertical narrowing, with side lobes

becoming more complex and somewhat greater in

energy, Fig. 18-32.

18.7.5.5 Inter-Driver Spacing versus Wavelength (O)

The distinction between side lobes and grating lobes

should to be maintained. Side lobes are adjacent to and

radiate in the same direction as the primary lobe.

Grating lobes are the strong summations tangential to

the primary lobe. Side lobes will be present in any real-

izable line array, grating lobes form when the inter

driver spacing becomes less than ½ wavelength. It

Figure 18-27. O(1 wavelength).

Figure 18-28. Increased wavelength to inter-driver spacing.

Figure 18-29. Wavelength is twice the loudspeaker

height.

Figure 18-30. Wavelength is the loudspeaker height.