Translations of Encyclopedia about Physics

Acoustics

Acoustics (in Greek "akustikos", which relates to the act of listening) is concerned with sound, for which reason it has become part of the study of the characteristics and spread of waves or vibrations. The main point of interest in acoustics is vibrations between the lower end of sound waves we hear (16 Hz) and the upper end (20,000 Hz).

Vibrations are caused by the concurrent effect of forces which deviate an object from its calm or balanced stated and other forces which work to bring an object to its balanced state.

Each vibration is made up of a constant back and forth movement. If the vibration spreads or travels further, we refer to them as waves. The speed of sound is understood as the speed that it travels in the form of sound waves. However, this value varies depending what substance it pass through. The unit of measurement of a vibration’s frequency is the herz (Hz). With the rippling of these waves, there is a transformation of energy but not mass.

A vibrating object creates a change in the air’s pressure, which then spreads further. Molecules in the air move cyclically to and away from each other. The length of a wave is the distance between its amplitudes of compression. Sound waves can also spread or travel through solid objects and liquids.

Thanks to these natural qualities, we are able to receive sound waves, meaning we are able to hear.

Mechanical vibrations below the frequency of 16 Hz are referred to as infrasound, and ultrasound if above the frequency level of 20,000 Hz. Ultrasound is used for example when examining the human body. There are no physical difference between infrasound, ultrasound and the sound we, as humans, are able to hear but these definitions were created in reference to the range of sound that we, as humans, are able to discern.

Sound behaves differently in different environments. As with light, sound reflects, breaks, bends and interferes.

In loudspeakers, constant magnets and electromagnets are used to convert acoustic signals from electrical signals. Electrical signals are magnetised by electric coils and magnets create waves of various lengths.

The human ear can perceive sound as being pleasant or unpleasant, depending on the regularity or irregularity of its waves.

Music is made of "standing" waves and is based on musical tone scales. However, the same tones may be reproduced differently if they are created using different [musical] instruments. Besides creating tone frequencies, higher tones are also produced which give each musical instrument its characteristic.

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