For large concerts, loudspeakers are sometimes used to amplify a singer’s sound. The human brain interprets sounds that arrive within 50 ms of the original sound as if they came from the same source. Thus if the sound from a loudspeaker reaches a listener first, it would sound as if the loudspeaker is the source of the sound. Conversely, if the singer is heard first and the loudspeaker adds to the sound within 50 ms, the sound would seem to come from the singer, who would now seem to be singing louder. The second situation is desired. Because the signal to the loudspeaker travels at the speed of light (3 × 10 8 m/s), which is much faster than the speed of sound, a delay is added to the signal sent to the loudspeaker. How much delay must be added if the loudspeaker is 3.0 m behind the singer and we want its sound to arrive 30 ms after the singer’s?
For large concerts, loudspeakers are sometimes used to amplify a singer’s sound. The human brain interprets sounds that arrive within 50 ms of the original sound as if they came from the same source. Thus if the sound from a loudspeaker reaches a listener first, it would sound as if the loudspeaker is the source of the sound. Conversely, if the singer is heard first and the loudspeaker adds to the sound within 50 ms, the sound would seem to come from the singer, who would now seem to be singing louder. The second situation is desired. Because the signal to the loudspeaker travels at the speed of light (3 × 10 8 m/s), which is much faster than the speed of sound, a delay is added to the signal sent to the loudspeaker. How much delay must be added if the loudspeaker is 3.0 m behind the singer and we want its sound to arrive 30 ms after the singer’s?
For large concerts, loudspeakers are sometimes used to amplify a singer’s sound. The human brain interprets sounds that arrive within 50 ms of the original sound as if they came from the same source. Thus if the sound from a loudspeaker reaches a listener first, it would sound as if the loudspeaker is the source of the sound. Conversely, if the singer is heard first and the loudspeaker adds to the sound within 50 ms, the sound would seem to come from the singer, who would now seem to be singing louder. The second situation is desired. Because the signal to the loudspeaker travels at the speed of light (3 × 108 m/s), which is much faster than the speed of sound, a delay is added to the signal sent to the loudspeaker. How much delay must be added if the loudspeaker is 3.0 m behind the singer and we want its sound to arrive 30 ms after the singer’s?
A sound wave with intensity 2 x 10 -3 W/m2 is perceived to be modestly loud. Your eardrum is 6 mm in diameter. How much energy will be transferred to your eardrum while listening to this sound for 1 minute?
Two students hear the same sound and their eardrums receive the same power from the sound wave. The sound intensity at the eardrums of the first student is 0.93 W/m2, while at the eardrums of the second student the sound intensity is 1.16 times greater.
If the diameter of the second student’s eardrum is 1.1 cm, how much acoustic power, in microwatts, is striking each of his (and the other student’s) eardrums?
For Exercise, the formula L = 10 log (£) gives the loudness of sound L (in dB) based on the intensity of sound I (in
W/m2). The value 10 = 10-12 W/m2 is the minimal threshold for hearing for midfrequency sounds. Hearing impairment is
often measured according to the minimal sound level (in dB) detected by an individual for sounds at various frequencies.
For one frequency, the table depicts the level of hearing impairment.
Category
Loudness (dB)
Mild
26 sLs 40
Moderate
41 90
a. If the minimum intensity heard by an individual is 3.4 x 10-8 W/m2, determine if the individual has a hearing
impairment.
b. If the minimum loudness of sound detected by an individual is 30 dB, determine the corresponding intensity of sound.
Chapter 16 Solutions
Physics for Scientists and Engineers with Modern Physics
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