User manual ELECTRO-VOICE 715SR DATASHEET

[. . . ] The multiple coverage curves are overlaid on the same graph. This makes it easier to judge whether the array is providing constant tonal balance over the coverage area. Figure 1. Three-frequency prediction By default, the three frequency bands are centered at 500, 3000, and 8000 Hz, and are each 1/3 octave wide. You may change these values as you wish. [. . . ] This is true even at great distances from the array. This means that the sound from outlying loudspeakers is delayed. 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. The result is less summation at high frequencies. The higher the frequency, the less the summation. This is true of all line arrays, regardless of size, cost, or manufacturer. 4 715SR · 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. The light gray trace shows the frequency response of a single XLC-DVX box, as measured in the laboratory. The blue trace shows the target frequency response. 4. 3. Practical Advice: Creating the LAPS EQ Curve "Dialing in" a LAPS EQ curve usually requires three or four parametric sections. All EQ curves are different, but here is a starting point that we have found useful: # 1 2 3 4 Type 6dB low shelf Bell Bell or 12B high shelf Bell Freq 600 3kHz 7-12kHz varies Gain -6 +3 varies varies Q n/a 0. 5 varies varies Note LF rolloff Mid-high contour HF contour Optional, to fix small wiggles Table 1. Suggested starting point for setting up LAPS EQ 6 715SR · SELECTED TECHNIQUES REV. Gain Shading Here at EV, our experience with LAPS advanced prediction features has highlighted the importance of gain shading for line arrays. By "gain shading", we mean adjusting the gains of the signals driving different parts of the array, and particularly reducing the gains for loudspeakers at the top and bottom of the array. Many line array designers will have used gain shading at the bottoms of their arrays, to reduce excessive loudness in the first few rows. In this application, gain shading is thought of as a simple nearfield technique -- "if a box is too close to a seat, turn it down. " However, gain shading is more than that, as we will describe. 5. 1. 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. [. . . ] Figure 11 shows the same array, with Box 1 (the top box) turned down 3dB, Box 9 turned down 2dB, and Box 10 turned down 4dB. Blue Red Teal 500 Hz 3000 Hz 8000 Hz Figure 11. As mentioned above, in current practice it's common to turn down boxes down at the bottoms of array, but not at the tops. What would happen if we turned down only the bottom boxes in this example?Figure 12 shows the same configuration as Figure 11, except that the top box is at 0 dB instead of -3 dB. [. . . ]