Issue link: https://www.e-digitaleditions.com/i/1327492
January/February/March 2021 I 53 FIGURE 9: Finding example coverage. Divide speaker dispersion angle in half for a right triangle. FIGURE 10: Recommended sound pressure level (SPL) overlap varies depending on mobility of listeners. Ceiling 9' 0" 5' 6" 3' 6" 120° 90° (120° / 2) = 60° 66" h d D Standing Height Seated Height Floor Step 5: To calculate the coverage distance or conic section, use right triangle trigonometry to first calculate one-half of the distance. To start, divide the dispersion angle in half to obtain a right triangle. For this example, it is 120°/2 = 60° (Figure 9). Since this is a right triangle, use the Tangent function to solve for the opposite side, as the formula TAN(60) = d/h leads to d = Tangent 60° X 66 inches and then 1.732 X 66 in = 114.3 inches. The Excel formula =TAN(RADIANS(60)) * 66. Since the full distance D is twice the length of d, then 2 X 114.3 in = 228.6 inches or 19.0 feet (5.8 m). This is the coverage distance for each speaker at seated height. Similarly, the calculation for standing height (5 feet and 6 inches standard listening height) that is 42 inches from the ceiling yields a coverage distance of 12.1 feet or 3.69 m. It is important to note that the Figure 9 diagram is a look from the side. The view from the ceiling speaker would represent D as the coverage diameter of the speaker. No Overlap Minimum Overlap Maximum Overlap -1.4dB -2.0dB -4.4dB SPL Variation throughout sound field Distance between speakers = Conic Section SPL Variation throughout sound field Distance between speakers = 75% of Conic Section SPL Variation throughout sound field Distance between speakers = 50% of Conic Section Step 6: In the example, listeners are seated and not normally moving around the room, so they cannot improve the sound clarity by moving to be within the range of a speaker. Speaker overlap is important to eliminate locations where an individual is not within the sound field. On the other hand, if the listeners are standing or mobile, there is no need for overlap of sound coverage because they naturally move slightly to improve the sound level. The more mobile the listeners are, the further apart speakers can be placed. A good guide is shown in Figure 10. Because the listeners in the example are normally stationary, space the speakers with maximum overlap.