Ocean acoustics is the study of sound and its behavior in the sea. But sound also exists all around us in the air. When objects vibrate, they create sound-pressure waves that compress and decompress the surrounding air molecules. These waves radiate outward from the source, similar to ripples on a pond. Our ears, and instruments like microphones, detect these compressions and decompressions as changes in pressure, allowing us to perceive sound. So, Can Sound Travel Through Air? Absolutely, and understanding how it does is crucial to understanding acoustics in general.
The Building Blocks of Sound Waves
To understand how sound travels through air, we need to understand the components of a sound wave: frequency, wavelength, and amplitude.
-
Frequency: This is the number of pressure waves passing a point per unit of time, measured in Hertz (Hz). A higher frequency sounds like a higher pitch, while a lower frequency sounds like a lower pitch. Humans typically hear sounds between 20 and 20,000 Hz. Sounds below 20 Hz are infrasonic, and those above 20,000 Hz are ultrasonic. Middle “C” on a piano is around 261.63 Hz.
-
Wavelength: This is the distance between two peaks of a sound wave. Wavelength and frequency are inversely related; lower frequency waves have longer wavelengths.
-
Amplitude: This describes the “loudness” of a sound and is often measured in decibels (dB). Larger pressure variations (taller waves) mean louder sounds, while smaller variations mean quieter sounds.
These characteristics determine how we perceive sound in the air.
Frequency and Amplitude in Air
The examples below show sound waves that vary in frequency and amplitude.
These two waves have the same frequency but different amplitudes.
The decibel scale is a logarithmic scale used to measure sound amplitude. Our perception of loudness doesn’t increase linearly with amplitude; equal steps in amplitude result in successively smaller perceived increases in loudness. A decibel expresses a ratio between measured pressure and a reference pressure. It’s important to note that the reference pressure in air differs from that in water, so a 150 dB sound in water is not the same as a 150 dB sound in air.
| Amplitude of Example Sounds | In Air (dB re 20µPa @ 1m) |
|---|---|
| threshold of hearing | 0 dB |
| whisper at 1 meter | 20 dB |
| normal conversation | 60 dB |
| painful to human ear | 130 dB |
| jet engine | 140 dB |
| supertanker | 128 dB (example conversion) |
Hydrophones measure sound pressure, normally expressed in units of micropascals (µPa). Early acousticians working with sound in air, realized that human ears perceive differences in sound on a logarithmic scale, so the convention of using a relative logarithmic scale (dB) was adopted. In order to be useful, the sound levels need to be referenced to some standard pressure at a standard distance. The reference level used in air (20µPa @ 1m) was selected to match human hearing sensitivity.
The Speed of Sound in Air
Sound travels at different speeds depending on the medium. The speed of sound in air is approximately 340 meters per second, while in water it’s much faster (around 1500 meters per second). This difference is due to the different mechanical properties of air and water.
Temperature also affects the speed of sound in air; sound travels faster in warmer air than in colder air. The wavelength and frequency of a sound wave are related by the speed of sound. Specifically, wavelength equals the speed of sound divided by the frequency. Therefore, a 20 Hz sound wave in air has a wavelength of approximately 17 meters (340/20 = 17).
Sound in Air: A Fundamental Phenomenon
Understanding how sound travels through air is fundamental to many areas of science and technology. From the design of concert halls to the development of communication systems, the principles of acoustics in air are essential. By studying frequency, amplitude, and the speed of sound, we can better understand and manipulate the sounds that surround us every day. So, yes, sound can travel through air, and this phenomenon shapes our world in countless ways.
