Question

7. Sound pressure level measurements were taken in a semi-anechoic chamber at 5 m from the source. A ten point hemispherical array was utilized in this process. The following data was obtained: (1) L,-94 dB, (2) Lp-96 dB, (3) L,-97 dB, (4) L,-93 dB, (5) Lp-92 dB, (6) L,-90 dB, (7) L,-91 dB, (8) L,-95 dB, (9) L,-93 dB, (10) Lp-94 dB From these values a) Determine the sound power level of the noise source b) The maximum directivity index c) The minimum directivity factor

Answer 1

(L_p) = 10 log[1/10(10^9.4 + 10^9.6 + 10^9.7 + 10^9.3 + 10^9.2 + 10^9.0 + 10^9.1 + 10^9.5 + 10^9.3 + 10^9.4)] = 93.982 L_p TildeEqual 94 dB a L_w = L_p + [10 log Q/4 pi r^2] where Q is directivity factor D.I is directivity index Q = 2 in case of hemispherical array Therefore L_w = 94 + 10 log 2/4 pi times (5)^2 = 115.96 dB L_w TildeEqual 116 dB b Max D.I = 10 log Q = 3 c Min Q = 2 (for hemispherical array)