Characteristics of a Sound Wave
Characteristics of a Sound Wave
Since sound is a wave, we can relate the properties of sound to the properties of a wave. The basic properties of sound are: pitch, loudness and tone.
Pitch and loudness of sound. Sound B has a lower pitch (lower frequency) than Sound A and is softer (smaller amplitude) than Sound C.
Pitch
The frequency of a sound wave is what your ear understands as pitch. A higher frequency sound has a higher pitch, and a lower frequency sound has a lower pitch. In the figure above, sound A has a higher pitch than sound B. For instance, the chirp of a bird would have a high pitch, but the roar of a lion would have a low pitch.
The human ear can detect a wide range of frequencies. Frequencies from 20 to 20 000 Hz are audible to the human ear. Any sound with a frequency below 20 Hz is known as an infrasound and any sound with a frequency above \(\text{20 000}\) \(\text{Hz}\) is known as an ultrasound.
The table below lists the ranges of some common animals compared to humans.
Table: Range of frequencies
| lower frequency (\(\text{Hz}\)) | upper frequency (\(\text{Hz}\)) | |
| Humans | \(\text{20}\) | \(\text{20 000}\) |
| Dogs | \(\text{50}\) | \(\text{45 000}\) |
| Cats | \(\text{45}\) | \(\text{85 000}\) |
| Bats | \(\text{20}\) | \(\text{120 000}\) |
| Dolphins | \(\text{0.25}\) | \(\text{200 000}\) |
| Elephants | \(\text{5}\) | \(\text{10 000}\) |
Optional Activity: Range of Wavelengths
Using the information given in the table above, calculate the lower and upper wavelengths that each species can hear. Assume the speed of sound in air is \(\text{344}\) \(\text{m·s$^{-1}$}\).
Loudness
The amplitude of a sound wave determines its loudness or volume. A larger amplitude means a louder sound, and a smaller amplitude means a softer sound. In the figure above, sound C is louder than sound B. The vibration of a source sets the amplitude of a wave. It transmits energy into the medium through its vibration. More energetic vibration corresponds to larger amplitude. The molecules move back and forth more vigorously.
The loudness of a sound is also determined by the sensitivity of the ear. The human ear is more sensitive to some frequencies than to others. The volume we receive thus depends on both the amplitude of a sound wave and whether its frequency lies in a region where the ear is more or less sensitive.
Video: Sound + Fire = Rubens' Tube
Sound waves in a tube of gas create flames of different heights that dance to the music. A metal tube with holes in it is filled with gas. The gas is lit to create a row of tiny flames. A speaker at one end plays sound into the tube, which creates a standing wave of sound: areas where air molecules are vibrating rapidly separated by areas where the air is fairly still. This produces the different heights of flames and allows the wavelength of the sound wave to be estimated. Watch the video by Veritasium below.
This lesson is part of:
Mechanical Waves and Sound