sound noise

Tape recorders either open reel or cassette are used in homes , offices , schools and cars everywhere , either for recording and playing back or simply for playing back, The basic principle which tape recorder functions on is that of magnetism .

The sound to be recorded is picked up by microphone which transforms sound waves into impulses of electric current .

The strength of this current varies according to the level of the sound , but at this stage it is comparatively weak and has to be passed through amplifier before reaching the recording head, The head consists of electromagnet which records the electrical signal on the tape as it passes .

The tape is ribbon of plastic coated with powdered Iron and Chrome oxide , substance which can be magnetized and demagnetized readily

Recording takes place when this iron oxide film is magnetized by the magnetic field of the recording head.

When recording is played back , the process is reversed . The magnetized parts of the tape induce weak magnetic field in the reproducing head , also electromagnet . This field produces varying current in coil of the electromagnet and the current is then amplified before the sound emerges from the loudspeaker . Tapes can be erased (De-magnetized ) and Re-used .

Now look at the noise levels indicated on the table and see how much noise you have to put up with..

Noise and its Effects

Noise may be defined as any sound which causes annoyance .

the music from our neighbor's cassette recorder may be pleasant sound to him but noise to us the twentieth century is very noisy century

it is getting noisier , some booms , jet engines discotheques , traffic and various industrial processes all contribute to the general increase in noise and people regularly exposed to levels over 80 Decibels are risking their health.

Here are some of the possible effects of high noise levels.

It damages the hearing and causes deafness.

It causes inflammation of the lining of the stomach and brain

It makes small blood vessels constrict

It cuts down the blood supply to the heart

It dilates the retina of the eye , causing color blindness and inaccurate vision.

It causes stress and deafness .

Ultrasonics

The normal range of human bearing is between the frequencies of 20 to 20,000 HZ ((HZ=Hertz (cycles per second)) , There is whole area of sound beyond this range known as ultrasonics which we can not hear .Some nocturnal animals, notably bats . communicate ultrasonically . But ultrasonic sound waves with frequencies up to 10 million HZ . can also be produced by special apparatus .

The basic principle involved is the production of vibrations in current of air under high pressure.

One method known as magnetostriction , relies on vibrations and changes of dimension in magnetic material placed in magnetic field created by alternating current.

A piezoelectric sound transmitter can provide even higher frequencies , produced by the vibrations of quartz disc (cut from hexagonal crystal )in contact wit two thin metal foils .

The power of ultrasonic sound waves to penetrate all forms of matter means that they have useful applications in medicine the pasteurization of milk the degasification of liquids , welding and echo-sounding