Difference Between Sound Intensity and Loudness

Sound Intensity vs Loudness

Loudness and sound intensity are two concepts discussed in acoustics and physics. Sound intensity is the amount of energy carried by sound whereas loudness is a measurement of the audible sound. The concepts of sound intensity and loudness are vital in fields like music, audio engineering, acoustics, physics and various other fields. In this article, we are going to discuss what sound intensity and loudness are, their applications, the similarities between sound intensity and loudness, the definitions of sound intensity and loudness and finally the difference between sound intensity and loudness.

Sound Intensity

Sound intensity is the amount of energy carried by sound per unit time through a unit area of a selected surface. In order to understand the concept of sound intensity, one must first understand the concept of sound energy.

Sound is one of the main methods of sensing in the human body. We encounter sounds every day. A sound is caused by a vibration. Different frequencies of vibrations create different sounds. When the source vibrates the molecules of the medium around it also starts to oscillate, creating a time varying pressure field. This pressure field is propagated throughout the medium. When an audio receiving device such as the human ear is exposed to such a pressure field the thin membrane inside the ear vibrates according to the source frequency. The brain then reproduces the sound using the vibration of the membrane.

It can be obviously seen that to propagate sound energy there must be a medium that is capable of creating a time varying pressure field. Thereby sound cannot travel inside a vacuum. Sound is a longitudinal wave because the pressure field causes the particles of the medium to oscillate in the direction of the energy propagation. The SI unit of sound intensity is Wm^-2(Watt per square meter)

Loudness

Loudness is defined as “the attribute of auditory sensation in terms of which sounds can be ordered on a scale extending from quiet to loud,” by the American National Standards Institute. Loudness is a measurement of the sound perceived by the human ear. Loudness may depend on several qualities of the sound such as the amplitude, frequency, duration. The unit “Sone” is used to measure loudness.

Loudness is a subjective measurement. Loudness depends on the properties of the source as well as the properties of the medium and the observer.

Loudness vs Sound Intensity

Sound intensity is a property of the sound source but loudness depends on the sound source, the medium and the receiver, as well.

Sound intensity holds a small significance in problems involving human hearing system, but loudness is a very important property to consider in such problems.