Acoustic sagas. What is a sound? Welcome
, one of the most fragile and difficult systems in a human body - acoustical. About 20 percent of people perceive information aurally much better, than at its visual receipt. Radio, an audioplayer, phone, lecture, conversation, an alarm clock - these concepts without the word “ sound “ would become an empty phrase or would change to unrecognizability.
the People deprived of ability to perceive a sound admit society disabled people.
In what an essence of the phenomenon serving as object of perception one of feelings of the person - hearing? First we will rigidly define: the sound is fluctuations of the environment. From this, at least, follows: there is no Wednesday - there is no sound. The astronauts in an outer space deprived of a radio communication, being in several centimeters from each other, can shout as much as necessary something each other, seeing only a movement of lips in pitch silence. And only adjoining viewing glasses of space suits, theoretically they will be able to hear each other.
Speaking about a sound it is simple, it is possible to present it in the form of the consolidation of the environment moving rectilinearly in the direction away from a source of fluctuations. The second comparison - a sea wave. Like a sound, the wave can be considered as some “ consolidation “ Wednesdays, moving in space with a certain speed. As well as the sound, a sea wave loses the “ compaction “ with distance, gradually dying away. Fading of a sound much more intensively, than at a sea wave. It in inverse proportion to a distance square from a sound source.
Speed of distribution of a sound in gases depends by nature gas, density of the environment, temperature and static atmospheric pressure. For liquid and gaseous environments - generally by nature Wednesdays. So, in air this size makes from 330 to 345 m/s at change of temperature from 0 to 20 degrees Celsius, in water - about 1 500 m/s, in steel - 6 000 m/s. A champion on the speed of distribution of a sound is metal beryllium - 12 500 m/s.
It is comparable all these speeds with velocity of light and we will notice that they it is insignificant are small. In vacuum velocity of light makes about 300 000 000 m/s. Becomes clear why the explosion which happened in the distance from us is heard not at once. Approximately each 330 meters from us to a source of a sound add 1 second to a difference between the picture visual and sound. The same treats also lightning flash. Noting time from the flash moment to the first sounds of a peal, you with ease define at what distance from you it occurred. Just share quantity into about three seconds - and receive distance to the next to you a flash point in kilometers.
We will consider the mechanism of emergence of sound waves and their distribution in space. Imagine the loudspeaker with the fluctuating membrane. For certain, each of you saw trembling of this membrane. Each movement of a membrane on the direction to us creates air consolidation, the subsequent movement of a membrane from us creates depression in air. Frequency of it “ tremblings “ determines the frequency (height) of a sound, and amplitude of trembling of a membrane, i.e., distance on which it is displaced - volume of sound. The sequence of such consolidations - depression moves with a speed stated above to our ear. It should be noted that the speed of a sound does not depend on its frequency.
Interesting feature of a sound is change of its frequency in a case when the source moves with a constant speed. Sound of a siren of the approaching fire truck moving towards us, above than at standing still, and from removed - respectively below. Having read reasonings is lower, it is possible to imagine the reason of such phenomenon.
For those who like to visualize all faces, we will represent a sound graphically. System of coordinates: amplitude (a vertical axis, ordinate) - time (a horizontal axis, an abscissa). It is possible to understand as amplitude:
and) the provision of the fluctuating loudspeaker membrane concerning rest position when it does not make any sounds (this determination of amplitude close to reality, we will enter for relief of understanding);
) value of the excessive (insufficient) pressure created by a membrane in the environment as a result of the fluctuations (more exact definition). In this case we approach the standard term sound pressure .
The pure sound of a certain frequency on such schedule will look a sinusoid. Increase in volume of sound will lead to stretching of this sinusoid on a vertical axis, increase in frequency - to compression on horizontal. The principle of work of all sources of a sound is approximately identical, whether it be already mentioned loudspeaker or vocal chords of the lecturer. Our ear, owing to constancy of speed of a sound under identical conditions, perceives such sequence of fluctuations as a uniform rumble, a ring, peep. However if the source of a sound moves on us, the frequency of emergence of peaks of a maximum on graphics will increase, leading to increase of frequency of a sound. By analogy, at the movement of the car from us, the frequency of a sound will decrease.
It is necessary only to add that the human ear can perceive air with a frequency from 16 to 20 000 Hertz fluctuations (fluctuations in a second). Range of frequencies of a human voice is also quite extensive - from 70 to 9 000 Hz. In 20 kHz only units from us therefore sometimes specify audibility threshold figure in 16 kHz will be able to catch the top limit. All sounds with a frequency out of the specified range belong to infrasounds (lower than 16 Hz), or ultrasounds (it is higher than 20 kHz).
It does not mean at all that nobody can hear such sounds. For example, it is considered that dolphins are capable to hear sounds with a frequency from 100 up to 200 000 Hz, and cats and dogs possess a perception threshold in 60 and 40 kHz respectively. Perhaps, the sounds inaccessible to us, it is possible to explain with time extraordinary behavior of our pets.]