THE SCIENCE AND APPLICATIONS OF ACOUSTICS - H. H. Arnold ...

10.7 Prosthetics for Hearing 231Table 10.6. PSIL (in dB) at Which Effective Speech Communication isBarely Possible.Normal Raised Very Loud ShoutingDistance (m) M F M F M F M F0.3 68 63 74 69 80 75 86 811 58 53 64 59 70 65 76 712 52 47 58 53 64 59 70 653 48 43 54 49 60 55 66 614 46 41 52 47 58 53 64 59The speech-interference level (PSIL = 68 dB) has been identified as the levelat which reliable speech communication is barely possible in a normal male voiceat a distance of 0.3 m (or 1 ft) outdoors. If a male speaker talks in a raised voice, avery loud voice, or in a shout, the speech interference levels have been identified,respectively, as PSIL = 74, 80, and 86 dB. A female speaker, on the average, hasPSIL levels 5 dB less than the corresponding values for a male. Table 10.6 liststhe PSIL (in dB) at which effective speech communication is barely possible. Thetable is based on minimally reliable communication, at which about 60% of thecommunication of uttered numbers and words out of context can be discerned. Inorder to roughly approximate PSIL in terms of dBA, 7 dB can be added to thevalues of PSIL.Example Problem 2: SILBackground noise levels for an industrial plant were measured to be 62, 65, and74 dB, respectively, in the 500-, 1000-, and 2000-Hz center-frequency bands. Whatare the implications for speech interference at a distance between a speaker and alistener standing 1 m apart?SolutionTo solve this problem, the arithmetic average of the noise level in three bandsare first determined. This will be (62 + 65 + 74)/3 = 67 dB. From Table 10.6 weestablish that reliable speech is barely possible for a male, speaking in a raisedvoice or a female speaking in a very loud voice.10.7 Prosthetics for HearingHearing AidsA conventional hearing aid works by amplifying sound and delivering that amplifiedsound to the eardrum. Sound is received by a miniature microphone thatconverts acoustic signals into electrical signals that is amplified and then relayed to