Sound – Part 2
Physiological characteristics of sound perception
The identical states of a sound wave (areas of thickening or rarefaction) are called phases. The distance between the same phases is called the wavelength. Low sounds, in which the phases are far from each other, are characterized by a long wavelength, high sounds with a close phase position – small (short).
Phase and wavelength are important in the physiology of hearing. Thus, one of the conditions for optimal hearing is the arrival of a sound wave at the windows of the vestibule and cochlea in different phases (anatomically, this is provided by the sound conduction system of the middle ear). High sounds with a short wavelength cause vibrations of a low column of labyrinthine fluid (perilymph) at the base of the cochlea, low, with a longer wavelength, propagating to its apex. This circumstance is important for understanding modern theories of hearing.
The physical characteristics of sound also include the frequency and amplitude of sound vibrations. The unit of measurement for vibration frequency is 1 hertz (Hz), which is the number of vibrations per second. Amplitude of vibrations: the distance between the middle and extreme positions of the vibrating body. The amplitude of the vibrations (intensity) of the sound body largely determines the perception of sound. By the nature of vibratory movements, sounds are divided into three groups: pure tones, complex tones, and noise. Harmonic (rhythmic) sinusoidal vibrations create a clean and simple sound tone (that is, a tone of the same frequency sounds), like the sound of a tuning fork. An inharmonious sound that differs from simple tonal sounds in a complex structure is called noise. The noise spectrum consists of a variety of vibrations, the frequencies of which are chaotically related to the pitch frequency, like different fractional numbers. The perception of noise is often accompanied by unpleasant subjective sensations. Complex tones are characterized by an orderly relationship of their frequencies to the frequency of the main tone, and the ear has the ability to analyze complex sounds. In general, the ear decomposes each complex sound into simple sinusoidal components (Ohm’s law), that is, what happens in physics is called “Fourier’s theorem (series)”.
The ability of a sound wave to bend around obstacles is called diffraction. Low-frequency sounds with a long wavelength have better diffraction than high-pitched sounds with a short wavelength. The phenomenon of reflection of a sound wave from obstacles in its path is called an echo. The multiple reflection of sound in closed rooms from various objects is called “reverberation”. With good sound insulation of rooms, the reverberation is weak, for example, in a theater, cinema, etc., with poor sound insulation, it is strong. The phenomenon of superposition of the reflected sound wave on the primary sound wave is called “interference”. With this phenomenon, an increase or decrease in sound waves can be observed. When sound passes through the external auditory canal, its interference takes place and the sound wave is amplified.
