User manual ELECTRO-VOICE 642 DATASHEET

[. . . ] No more costly delay lines or cheap seats!!The unique, patented throat and flare structure of the VI horn delivers a 6-10 dB hotter signal to the rear of the room, eliminating earstrain at the back of the seating area and painful ears at the front. VI horns deliver sound to fill only the floorplan, providing uniform direct-field SPL and an order of magnitude less energy into the reverberant field. This provides an increase in mid- to high-frequency intelligibility of 6 dB in most applications. [. . . ] By contrast, a typical two-way system with a 60° x 40° CD horn in the same mounting location as Figures 1 and 2 (see Figure 3) produced a floor plan that sounded tonally fairly consistent with a 20- to 24-foot width and 30-foot depth with an offset of nine feet to the front row. On paper, this seems like adequate performance, but in the room it has very noticeable (6 dB or greater) variation in overall level from side to center, and in some aiming cases over 10 dB of variation from front to back as well as a pronounced lemon shape. The sides of the first three to five rows in a church and the last few rows were noticeably muted and much lower in overall level. As mentioned before, a two-horn system can work fairly well, but the physical offsets required for installation inevitably result in some amount of destructive interference throughout the room (see Figure 4). Figure 4 was produced using a 90° x 40° CD horn aimed down by 65° and a 60° x 40° horn aimed down by 30°. The actual physical offsets were used to simulate the floor response in direct-field SPL. The displayed figure agrees very well with the measured response, showing a 14-dB variation at 4kHz in a distance of 3 feet horizontally. Tonal changes as a result of interference pattern change versus frequency were clearly audible in an acoustically well-behaved room, but were overall much less audible than for a single system with a conventional CD horn. Locating drivers 3 and horns closer together than possible with medium-format horns will produce somewhat better results, but will always result in fairly severe lobing. Polar measurements in 2° increments show the lobing very well, but the smoothing required for translation to the EASE 10° resolution database will eliminate the vast majority of peaks and dips, resulting in what appears to be a fairly smooth simulation. In contrast, the new VI systems have no problems with interference, and maintain very good tonality even far to the sides and to the back, outside the "equalSPL" pattern area. The enclosure is tilted back by 5° to provide a 50-foot throw, with the outskirts of the pattern filling in the rear aisle area with tonally accurate but reduced overall SPL. If the under-balcony seating area is only 35 feet deep, then the enclosure should be tilted down by about 10° relative to the floor in order to prevent excess slap echo and preserve intelligibility. Figure 12 shows a typical small-room application, perfect for a 20-foot by 30-foot boardroom or meeting hall. In this case, the head height is actually defined by a standing height of approximately 6 feet, so the long-throw axis should be very close to horizontal. Then the included 40 degree angle points directly towards the entire listening area, minimizing slap echo while retaining a full width, high intelligibility and even SPL throughout the listening area. Q vs. Intelligibility: The "Q" of a system is a good measure of the system's directivity, and in some ways a good measure of whether the system's in-room response will be consistent across the frequency range. A typical 12-inch two-way system with a 60o x 40o horn will maintain a fairly constant Q from 16-30 or 12-15 dB (normally about 26, or 14dB) from 3, 000­20, 000 Hz, and a 90o x 40o a Q of 13-15 (11-12dB). The net result 4 is that 3dB of long-throw SPL and 1. 5-2dB of sidefill level has been lost. A higher resolution data file is needed to provide a "real world realistic" simulation. Figure 5 shows the raw 2° polar data with the averaged 10° data superimposed. Also shown are floorplans from our 2° modeler, DCSO, the 5degree AcoustaCADD and 10-degree EASE. [. . . ] In this case, the enclosure may be rotated upwards by at least 15°, more than sufficient for nearly any application (see Figure 15). The brackets are supplied with friction washers that will prevent the enclosure from rotating over time, but to be absolutely certain, the installer should use a set screw in the threaded hole to fix the enclosure permanently in position. The described hanging methods are rated for suspending only one speaker (with a minimum of an 8:1 safety factor). Hanging any additional weight from the speaker will exceed its strength rating and create an unsafe condition. [. . . ]