Intensity refers to the amount of energy carried by sound waves, and it can be measured in different ways depending on the context. In acoustics, intensity is commonly measured in watts per square meter (W/m²). In audiology, it is measured in decibels (dB). Intensity can also be measured in terms of pressure or amplitude, but these are less commonly used units.
Sound intensity and loudness are closely related but different concepts. Intensity is a physical measure of the energy carried by sound waves, while loudness is a subjective perception of how loud a sound is. Loudness depends on factors such as the sensitivity of our ears, the frequency of the sound, and the distance from the sound source, whereas intensity is solely based on the physical properties of the sound wave.
The decibel (dB) scale is a logarithmic scale used to express the loudness or intensity of a sound. It is based on the ratio between two sound intensities, with 0 dB representing the threshold of human hearing and 120 dB representing the threshold of pain. This means that a sound with an intensity of 10 times that of a reference sound will be 10 dB louder or more intense.
As sound waves travel through space, their intensity decreases due to the spreading out of the energy. This means that at a greater distance from the source, the sound will be quieter and have a lower dB level. The decrease in intensity follows an inverse square law, meaning that doubling the distance from the source will result in a 6 dB decrease in intensity.
Common examples of sound intensity and their corresponding dB levels include a whisper (30 dB), normal conversation (60 dB), a lawnmower (90 dB), a rock concert (110 dB), and a jet engine (140 dB). It's important to note that prolonged exposure to sounds above 85 dB can cause hearing damage, and sounds above 120 dB can cause immediate hearing loss.