Basic concepts of acoustics

Acoustics is one of the branches of physics that is dedicated to studying sound, infrasound and ultrasound. These are mechanical waves that are propagated through matter by means of physical and mathematical models. Within acoustics we can find countless concepts, some more complex than others, although in this article we want to talk about the most basic, since it is very important to keep them in mind to learn more about acoustics.

Sound and noise

Sound is a sensation that we have inside the organ of hearing produced by the undulating movement of an elastic medium. It is caused by rapid changes in pressure, produced due to the vibratory movement of a sound body. Noise is a complex mixture of sounds of different frequencies and they are differentiated into stationary and non-stationary noises. The former do not have fluctuations as a function of time and the latter show fluctuations that are more or less strong.


The oscillogram consists of a noise or sound that represents the variation of sound pressure, always as a function of time. Normally it is usually the instantaneous pressure and not the effective pressure.

Sound pressure

The quantity that is measured with a microphone is the effective sound pressure and many other quantities can be deduced from the pressure. As the field of acoustic pressure values ​​is too large, the sound pressure level in decibels with respect to a reference pressure corresponding to the auditory pressure threshold is included as a practical magnitude.

Acoustic power

Power is an intrinsic parameter of the noise source. We can say that it is the amount of energy radiated per unit of time and is expressed in Watts. Because the power values ​​are large and disparate, the sound power term is dB.


The number of times that a compression-dilation of the air must link per unit of time is what is known as frequency. The higher the number of repetitions, the higher the frequency. The fewer repetitions, the lower the frequency. The number of repetitions per second is called Hertz or Hz for short.


In order to characterize a sound or noise from a physical point of view, in addition to its intensity or energy transmitted per unit of time through the unit of surface, it is very important to know the frequencies that compose it. Noise can be broken down, thanks to the Fourier transform, into a convergent series of complex terms whose addends correspond to all the frequency components of the signal itself. Each addend is multiplied by a constant, the amplitude. In this case, the study of the frequency components of a noise is considered in acoustics as frequency analysis and the result of the Fourier transform is the spectrum of the signal itself.