Sound waves: concept and features

The world that surrounds us, it is possible with certaintycall the world of sounds, because around us there are always voices, music, twitter of birds, the sound of the wind. Sound waves help people communicate, receive information about the world around them. For animals, sounds are no less important. From the point of view of physics, sounds are mechanical oscillations that propagate in an elastic medium: water, air, solid, and so on. The human ears are able to hear the sound when the audio frequencies are in the range of 16 to 20,000 Hz. Oscillations with higher or lower frequencies are not audible for a person.

Science acoustics deals with the solution of variousquestions, including issues related to the features and properties of hearing. The subject of studying physiological acoustics is directly the organ of hearing, its structure, action and device. Architectural acoustics deals with the study of how sound waves propagate in the room, examines the influence of the shape and dimensions of the room on sound, studies the properties of materials with the current view of propagation and suppression of sounds. Musical acoustics deals with the study of musical instruments, explores the conditions for the best sound of a particular instrument.

Physical acoustics studies the sound vibrations themselves, sound waves, recently it also began to cover fluctuations that lie beyond the capabilities of the human auditory system.

Basic concepts of acoustics

The appearance of sound is due to mechanicalvibrations of elastic bodies and media. Air is a conductor for sound. This is proved by the experience of Robert Boyle. If you put a sounding body under the bell of an air pump, then as the air is pumped out from under the bell, the sound will become weaker. When the air under the bell is over, the sound will stop altogether.

During oscillation, the body alternately createsdischarge in the layer of air adjacent to its surface, then compresses this layer. As a result, the propagation of waves in airspace begins with the oscillations of the air layer at the surface of the body.

As sound waves propagatein space, sound attenuation is observed, which is associated with certain irreversible processes. The meaning is that some of the energy carried by the sound wave is absorbed by the medium.

The coefficient of absorption is a quantity,which is equal to the ratio of the sound energy absorbed by the medium to the energy that entered the medium. The absorption coefficient is affected by internal friction or viscosity of the medium, its thermal conductivity, the density of the medium, and the velocity of propagation of the wave.

Spreading in the medium, the wave somedayreaches its border. After this boundary, another medium begins, which consists of other particles and in which another speed of sound. At this boundary, sound is reflected. In this case, the rarefaction of particles turns into a thickening, and condensation into a vacuum.

This effect occurs because the oscillations,which the wave brings to the boundary of the medium, are transmitted to particles of another medium and become the source of a new wave. The secondary wave will spread not only in the second environment, but also in the one from which it originally came. This is the reflected sound wave.

At the boundary of the medium, a partial passage takes placesound into the second medium and a partial absorption of sound. The fraction of reflected energy will depend on the ratio of the media densities, and also on the state of the interface. For example, the reflection of a sound wave propagating in the air, from a liquid surface or solid body, occurs almost completely. Sound waves propagating in a solid are almost completely reflected at the boundary with the air.

With the phenomenon of reflection directly relatedoccurrence of an echo. The essence of this phenomenon is that sound comes from the source to some obstacle, which becomes the boundary of the media, and reflects from it, returning to the place where the wave originates.