Question

Dolphins emit sound bursts that range in frequency from 1 Hz to 120 kHz. Say that a dolphin is using a sound burst consisting of these frequencies as a form of sonar, like bats. Let the burst last for a time interval of 10 ms, after which it listens for 100 ms. Say that the logarithmic intensity (loudness) of the dolphin's sound is 50 dB as measured at 1 m away. Dolphins can hear sounds that are 2 dB below our threshold of hearing.

a. How far ahead can the dolphin 'see' using this approach?

b. What is the smallest object it can 'see'?

c. What is the largest object it can 'see'?

d. What would be the amplitude of the pressure wave at 20 m from the dolphin?

e. How far from the dolphin producing the sounds does another dolphin have to be before the sound intensity is below the threshold of hearing for dolphins?

Answer 1

In amplitude means sound pressure as a sound field quantity and not sound intensity as a sound energy quantity.

In loudness is a personal feeling of the volume and a correct value is not easy to decide.

Threshold of hearing for human beings in air is the reference sound pressure level

{Lpo = 0 dB}

that is sound pressure in air po = 20 Pa = 0,00002 Pa = N/m.

The reference sound pressure level in water

[Lpo = 0 dB]

that is sound pressure in water po = 1 �Pa, which was chosen by the US Navy for their underwater work for sound in water. Approximately the same level of detail for air and water at their respective reference pressure in level differ by approximately 62 dB. So withdraw from the sound level of water about 62 dB to compare with sound level of air.