User manual ELECTRO-VOICE 2710 DATASHEET

[. . . ] Close to the array, there is too much high-frequency level and too little midbass; at middle distances, the midbass is more in balance, but the high frequencies are still excessive; at the back of the room, things are more or less in balance, but the high-frequency coverage is still uneven. 1 / SEPTEMBER 18, 2009 Figure 4 shows the result of revising the box angles and introducing gain shading at the ends of the array. Gain shading is an important topic, and will be discussed in detail below. These changes required no additional investment in loudspeakers, amplifiers, or cabling. Blue Red Teal 500 Hz 3000 Hz 8000 Hz Figure 4. [. . . ] However, the distance from your ear to the loudspeakers in the array varies, especially with curved arrays (and all practical arrays are curved). Therefore, the sound takes longer to reach your ear from parts of the array not pointing directly at you. At low frequencies, these delays are not large enough to matter because the path length differences are small compared to wavelength. All of the loudspeakers sum together at low frequencies because the phase differences between the delayed arrivals are small. At high frequencies, however, the delays are significant - often with many wavelengths different in arrival times - and cause the highfrequency waves not to add up well because the delayed arrivals are not in phase. This is true of all line arrays, regardless of size, cost, or manufacturer. 4 2710 · SELECTED TECHNIQUES REV. 1 / SEPTEMBER 18, 2009 Figure 7 shows the frequency response of a theoretical line array of loudspeakers, each with perfectly flat frequency response. The loudspeakers in this example are 10. 5" high, approximately the size of an EV XLD-281, and are curved and flown in a typical arrangement. the point at which the frequency response is measured) is on the central axis of the array, 100 feet distant. Figure 7. From this curve, it is apparent that for good tonal balance, equalization will be required. For typical line arrays, the equalization curve will take the form of a fairly smooth ramp that rises from low to high frequency. Theory In physics and electronics, sharp discontinuities often have side effects. For example, when a light wave beam passes through a narrow slit, a phenomenon called "single-slit diffraction" occurs, which causes the beam to be split into a set of narrowly divergent beams of graduated strength: Figure 9. Single-slit diffraction Single-slit diffraction is an example of what is known as an "aperture effect", and it occurs for all kinds of waves, including sound waves. The properties of the effect (number of beams, strength of each, etc. ) depend on the slit size and the wavelength. A line array is like the slit in Figure 9 -- it's a long, narrow wave source -- and it exhibits aperture effects of a similar nature. Physical theory tells us that the severity of aperture effect can be reduced by gradually reducing the amplitude of the wave to zero near the edges of the aperture. For line arrays, this means reducing the gain at the top and bottom of the array. It's also called "tapering". 7 2710 · SELECTED TECHNIQUES REV. 1 / SEPTEMBER 18, 2009 5. 2. Example 1 Figure 10, Figure 11, and Figure 12 give an example from an actual installation -- a large church with arrays of ten XLC-DVX boxes. Figure 10 shows the starting point, for both main floor and balconies. Horizontal scale is 25 feet per division. Blue Red Teal 500 Hz 3000 Hz 8000 Hz Figure 10. [. . . ] Flat venue, (6) XLE181, no gain shading Blue Red Teal 500 Hz 3000 Hz 8000 Hz Figure 14. Flat venue, (6) XLE181, 2dB bottom box gain reduction 9 2710 · SELECTED TECHNIQUES REV. 1 / SEPTEMBER 18, 2009 Blue Red Teal 500 Hz 3000 Hz 8000 Hz Figure 15. Practical Advice At EV, we have generally found that gain shading often works best with a bit less tapering on top, and with a bit more careful and gradual tapering on the bottom to maintain good control of the nearfield. [. . . ]