270 E.C. Stasiunas et al. Fig. 25.3 Microphone and speaker circuit placement an overhead crane was used to lift the entire assembly high enough to rotate the test unit into a vertical configuration, and place it at the center of the speaker stacks, 1 foot above the floor. Casters installed on the VT-99 speaker stacks allowed for easy opening and closing of the speaker enclosure. Acoustic instrumentation for the Flight System DFAT consisted of a total of 18 microphones, located no closer than 3-ft to the speakers in order to measure a more uniform sound field, and no closer than 1-ft to the test article to reduce microphone distortion due to reflections and surface effects (per standard DFAT practices [1]). Microphone heights varied from 2-ft to 11-ft above the floor. The exact locations of the individual microphones, represented by the green squares, are shown in the top-view diagram of Fig. 25.3 and listed in Table 25.1. Pre-polarized ¼-inch diameter pressure-field microphones were used for this test, with sensitivities ranging from 0.7 mV/Pa to 1.2 mV/Pa. The diagram of Fig. 25.3 also displays the individual speaker cabinets that make up each speaker stack along with their corresponding amplifier circuits. In this diagram, Full Range cabinets represent the VT-99s which contain low-mid-high speakers, and the Sub cabinets represent the VS-Q low frequency speakers. The speakers are stacked as the radius increases out from the center—for example, Stack 1 consists of a Full Range—Circuit 1 cabinet on the bottom, a Full Range—Circuit 1 cabinet in the middle, and a Full Range—Circuit 5 cabinet on the top. Each of these amplifier circuits was driven by an independent output from the MIMO control system which was determined by a corresponding control microphone placed nearby. If placed too far away, there was a potential of speaker damage due to the control system outputting more voltage than speaker could withstand in order to reach the desired specification. Therefore, as seen in the diagram, control microphones (Microphones #1–6) were placed near their associated speaker circuits and at various heights to aid in achieving the acoustic field gradient. The remaining response microphones (Microphones #7–18) were placed randomly in the field. As mentioned previously, the test was designed with six independent speaker circuits/control system drives, which accounts for the twelve Full Range cabinets (two cabinets per circuit). In order to supplement the low frequency portion
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