SOUND

From Big Medical Encyclopedia

SOUND — the oscillating motion of particles of elastic medium extending in a wave mode. Waves which distribution happens in the direction of fluctuation of particles of the environment, received the name longitudinal, and the waves extending perpendicular to the direction of fluctuation of particles — cross. Longitudinal waves are formed in firm, liquid and gaseous environments, cross — only in firm. In fabrics of a live organism 3. can extend in shape both longitudinal, and transverse waves. 3. it is characterized by the frequency of fluctuations, i.e. number of full waves in unit of time (second). One fluctuation in 1 sec. makes unit of frequency — hertz (Hz), and time, during to-rogo the fluctuating body makes full wave, is called the period of fluctuation.

The distance between two consecutive condensations or depression in a sound wave is called its length. Wavelength (l) is directly proportional to the speed of a sound (C) and it is inversely proportional to the frequency (v):

l = With / v

Physical. the concept «sound» includes fluctuations with a frequency from shares to billions of hertz. In biol, the relation 3. represents a specific irritant acoustic analyzer (see) the person and animals perceiving fluctuations in the range from 16 Hz to 20 kHz. Fluctuations lower than 16 Hz designate as infrasounds (see), it is higher than 20 kHz — as ultrasounds (see). However such classification is conditional since many animals use in acoustical communication sound vibrations with a frequency considerably exceeding 20 kHz. It is shown, as the person is capable to perceive ultrasounds with a frequency up to 225 kHz on condition of their bone and fabric carrying out.

the Diagrammatic representation of decomposition of difficult tone on harmonious components: 1 — difficult tone; 2 — 5 — the simple true tones making in the sum difficult tone 1.

Audibles signal as an irritant of the acoustic analyzer can be divided into two main types: tones and noise. Under tone mean sound vibrations of a constant or the frequency which is strictly changing in time. Tone corresponding to the smallest frequency of fluctuations in a range difficult 3., call the main tone. In the nature true tones meet seldom. Usually as audibles signal serve the difficult fluctuations made of the main tone and overtones (fluctuations of more high frequency, multiple to the frequency of the main tone). Set of simple fluctuations to which it is possible to spread out difficult fluctuation received the name of a harmonious range (fig).

Noise (see) represents a chaotic combination of various difficult tones. The frequencies making a difficult range of noise belong to the frequency of the main tone as fractional numbers. Depending on width of a range distinguish narrow-band and broadband, continuous and line (discrete) noise. Narrow-band noise differ from broadband in the fact that their power range is limited by limits of the fixed main frequency. Continuous noise are characterized by insignificant intervals between separate frequency components, and line — considerable intervals.

Area of the environment, in a cut sound waves extend, is called a sound field. Properties of the environment define rate of propagation of a sound in it. Wavelength upon transition from one environment to another changes, but at the same time the frequency of fluctuations remains. So, in air at t ° 0 ° distribution of longitudinal waves happens to speed of 331 m/s, in water at t ° 25 ° — 1497 m/s, in tissues of a human body — 1445 — 1600 m/s. Rate of propagation of sound waves does not depend on the frequency of fluctuations. At the same time the sound waves arising, e.g., at explosions have the speed much surpassing usual for this environment in the initial site of distribution; this speed decreases to the norm inherent to this environment, only after a distance from a source 3.

Sound transmission of various substances and biol, fabrics depends on their density and rate of propagation in them a sound wave. 3. dies away during the passing in Wednesday owing to its absorption (energy conversion of sound vibrations in energy of thermal agitations). Considerable easing 3. comes due to reflection at distribution of a sound wave from one environment in another in connection with distinctions of acoustic resistance of environments. Acoustic resistance represents the work of density of the environment on the speed of a sound (see. Impedance ). Big differences of sizes of acoustic resistance of air and liquid of an inner ear cause power loss of the audibles signal perceived by an acoustical receptor. The balancing unit smoothing distinctions of sizes of an impedance during the passing of a sound wave through an ear is the tympanic membrane. For understanding of mechanisms hearing (see), diagnoses of its disturbances and development of methods of acoustical correction also studying of patterns of carrying out 3 is very important. through bones of a skull and soft covers of the head.

At distribution in the environment of two sound waves there can be their geometrical addition — an interference (see. Interference of waves ). Depending on that, match or the developing waves on the frequency and the direction do not match, amplitude of the resulting wave increases or decreases. Great interest for understanding biol, actions 3. has ability of sound waves to deviate from rectilinear distribution at interaction with an obstacle, received the name of diffraction. A special case of diffraction is rounding by a sound wave of an obstacle.

If the frequency of the sound wave operating on a body matches own frequency of fluctuations of a body, there is a phenomenon of a resonance consisting in significant increase in amplitude of sound vibrations. Thanks to a resonance there is strengthening of a sound wave in outside acoustical pass.

Power properties of a sound wave are defined by intensity of a sound, i.e. amount of the energy transferred by a wave for a unit of time through unit of area of a surface perpendicular to the direction of the movement of this wave. In unit of intensity 3. the watt on square meter serves (W/m 2 ).

Amount of the energy radiated by a source 3. in unit of time in surrounding space, is called 3. also it is measured in watts. At the solution of practical tasks usually choose pressure of a sound wave (sound pressure) as the measured parameter of a sound field. Intensity of a sound (I) is connected with sound pressure (R) a ratio:

I = P 2 /2ρC

where ρ — density of the environment, in a cut extends a sound, and C — the speed of a sound. Sound pressure in newtons upon square meter is expressed (N/m 2 ) or pascals (1 N/m 2 = 1 pases).

The minimum intensity of a sound causing an acoustical feeling at the person makes 10-12 W/m 2 also is called a hearing threshold. In terms of sound pressure it corresponds to 2•10 - 5 N/m 2 . The smallest intensity 3., at Krom perception 3. sense bodys causes sensation of pain, is called a threshold of sensation of pain. The threshold of sensation of pain, as well as a hearing threshold, depends on frequency 3. At the same time in practice the quantitative characteristic 3. in acoustic measurements usually give in the form of determination of level of intensity 3. or level of sound pressure. At the same time level (L) is calculated in decibels (dB) in relation to the stated above threshold values on a formula:

L = 10 lg (I/I 0 ).

where I 0 — hearing threshold equal 10 - 12 W/m 2 , I — intensity 3. As intensity 3. it is proportional to a square of sound pressure, the level of pressure is calculated on a formula:

L — 20 lg (P/P 0 ),

where P 0 — a hearing threshold in terms of the sound pressure, P — sound pressure.

Determination of level of sound pressure is more preferable since intensity of a sound (I) depends on environmental conditions (temperatures, Wednesdays, forms of a sound wave etc.).

The average level of sound pressure created by a business conversation of people in rooms reaches 60 dB (at shout 80 dB), noise of the moving car and the train of the subway reaches 80 — 100 dB. The same level of sound pressure creates fortissimo big orchestra. Already at level 80 — 90 dB speech signals cause a feeling of acoustical discomfort at the healthy person; influence of sound incentives with level 120 dB is followed by feeling of pain, and it is higher than 140 dB — damage of structures of a middle and inner ear (see. Acoustic injury ).

Biol, action 3. on a human body it is in many respects connected with existence in the environment of noise surrounding it. Adverse impact on a human body is exerted by production and utility noise. This influence affects not only the acoustic analyzer, but also a functional condition of all organism. At the same time change of functions of an organism happens as owing to primary impact of noise on the acoustic analyzer, and irrespective of it. Depending on these or those conditions 3. high intensity and noise can lead to an acute acoustic injury or slowly developing relative deafness (see). Along with it changes and vibration sensitivity (see), functions of cardiovascular system, a motor analyzer, c are broken. N of page and other systems so in general it is possible to speak about development of a noise disease.

For understanding biol, actions 3. the established Cheymbersom and Flosdorf (L. Chambers, H. Phlosdorf, 1936) the fact of a denaturation of fabric proteins under the influence of 3 is of interest. an upper part of the heard frequency range of high intensity. By D. N. Nasonov and K. S. Ravdonik's works (1947, 1950) it was shown that sounds with a frequency of 200 — 10 000 Hz strengthen sorption of neutral dyes the isolated muscle of a frog and neurons spinal gangliyev rats; at the same time the most active intravital absorption by fabrics of paint was observed under the influence of 3. that frequency area, in a cut the maximum acoustical sensitivity of the person is shown, and its attenuation range depended on intensity 3. The same is later it was revealed concerning sensory cells of a kortiyev of body. On the basis of it Ya. A. Vinnikov (1971) made the conclusion about a community of perception of sound energy cytoplasm as specialized in relation to 3. cells of an inner ear, and unspecialized cells of other fabrics.

Key parameters 3. have subjective equivalents in acoustical feeling. Intensity 3. its loudness, frequency — height, and existence of overtones — a timbre defines.

As unit of loudness the background — feeling is accepted, a cut arises at action of tone with a frequency of 1000 Hz. For the frequency of 1000 Hz the scale of backgrounds corresponds to a scale of decibels. For other frequencies loudness is defined by comparison with intensity of ravnogromky tone 3. with a frequency of 1000 Hz. For receiving a linear scale of loudness special unit — a dream is entered (the loudness in 1 dream corresponds to loudness in the 40th background). At measurement of loudness various 3. on this scale comparison of feeling with loudness in 1 dream is made (loudness increases as a cube root from intensity 3.). In dignities express the loudness of true tones. Loudness difficult 3. and noise define by their comparison with standard tone with a frequency of 1000 Hz. Subjective feeling of height of tone also not in proportion to the frequency or its logarithm. As unit of height 3. use chalk (height in 1000 chalk corresponds to tone of 1000 Hz at intensity 40 dB).

In the equipment sources 3. various devices in the form of the electro-acoustic converters transforming electric fluctuations of acoustical frequency to mechanical oscillations of the radiating device and allowing to reproduce the most various audibles signal serve. As receivers 3. in the equipment hl are used. obr. the converters turning fluctuations of elastic medium into electric signals. Such converters for reception 3. in air microphones, serve in water — hydrophones, in dense environments of the land surface — geophones.

To biol, to sources 3. the voice device belongs (see. Voice ). The person on the basis of a voice had a specific form of activity, the employee to communication between people — speech (see). Receiver 3. the person and animals the ear is (see). See also Hearing .



Bibliography: Akkerman Yu. Biophysics, the lane with English, M., 1964; Vinnikov Ya. A. Cytologic and molecular bases of reception, L., 1971, bibliogr.; Sagalovich B. M. and Pokryvalova K. P. About a possibility of perception by a human ear of sounds of ultrahigh frequency, Biophysics, t. 9, No. 1, page 138, 1964; With to at-chik E. Bases of acoustics, the lane with English, t. 1 — 2, M., 1976; Tsvikere. and Feld-keller of R. Ukho as the receiver of information, the lane with is mute., M., 1971, bibliogr.; Noise and a noise disease, under the editorship of E. Ts. Andreyeva-Galanina, L., 1972, bibliogr.; In yo k yo s at G. Experiments in hearing, N. Y. a. o., 1960, bibliogr.; D j u p e s-land G. Zwislocki J. Sound pressure distribution in the outer ear, Acta oto-laryng. (Stockh.), v. 75, p. 350, 1973.

B. M. Sagalovich.

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