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CHAPTER 19: Reflections, Images, and the... > A COMPARISON OF REAL AND PHANTOM IMA... - Pg. 564

PART VII Acoustics and Sound Reinforcement FIGURE 19.9 A comparison of the absolute thresholds shown in Figure 19.8, with measured energy-time curves (ETCs) for the three spaces within which the tests were done. All data from Olive and Toole, 1989. ETCs at the listening location compared with the detection thresholds for a single reflection in that same space. Signal: speech. 10 "live" IEC listening room 0 Relative level (dB) -10 In terms of spatial aspects, Bech (1998) con- cluded that those sounds above 2 kHz contrib- uted to audibility and that "only the first-order floor reflection will contribute to the spatial aspects." The effect was not large, and, as before, speech was less revealing than broadband noise. Again, this is a case where a good carpet and underlay would appear to be sufficient to elim- inate any audible effect. In conclusion, it seems that the basic audible effects of early reflections in recordings are well preserved in the reflective sound fields of ordin- ary rooms. There is no requirement to absorb first reflections to allow recorded reflections to be heard. -20 -30 -40 0 10 20 30 40 50 60 70 80 Delay (ms) 10 IEC room with attenuated first reflections The "Family" of thresholds Figure 19.11 shows a complete set of thresholds, like those shown in Figure 19.5, determined in an anechoic chamber but here determined in the "live" IEC listening room. The curves are slightly irregular because the data were based on a small number of repetitions. As expected, the 0 level (dB) -10 -20