Question

phons 100 9 80 60 A 40 20 20 10k 1000 100 10 Frequency Hz) a) At approximately what frequency is the human ear most sensitive? How can you tell? b) If you heard a 300-Hz tone with a sound level of 60 dB, approximately how many phons would you perceive? toward you with a speed v, starting a distance of 1 km away att 0. If the train moves very slowly (that is, v is extremely small compared to the speed of sound in air), then at what time tss will you hear a sound of 55 phons? c) A train blowing a 400 Hz whistle at 100 dB (as measured at a distance of 1 m) is moving (~340 m/s), but its whistle still has an emitted frequency of 400 Hz and it still produces a sound level of 100 dB at 1 m. If you perceive a sound of 45 phons when the train is at a distance of 1 km from you, what is its speed v? d) Suppose now that the train in part c) is moving at a significant fraction of the speed of sound

Answer 1

a) the human ear can sense the pressure variations in the air. If the pressure variations are in the audible frequency range, then we will be able to hear it. In the curve, the lowest pressure variation is below 20 dB. The loudness of the wave with 20 phons is same throughout the curve. But, in the range of 2000 Hz to 5000 Hz, the loudness of 20 phons is same as compared to more decibel levels. This can be compared for all loudness levels. This means that the human ear can listen these waves with equal loudness even if the pressure variation is less. This tells about the sensitivity of the ear for lower pressure variations. Thus, for frequency range 2000 Hz to 5000 Hz, the human ear is more sensitive. b) Phons Decibles dB "10 - 100 1000 TOK Frequency Hz From the above curve, the blue dot represents the 300 Hz tone with sound level of 60 dB. The corresponding phons will be approximately 55 phons.