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"The Basics of" series continues with an article on sound.
Vibrations and Hearing
When you place a ping pong ball inside a vibrating speaker cone, the vibrations cause the ball to bounce around. If the frequence is very high, then the speaker is vibrating too quickly for the eye to see, and at an extreme high, for the human ear to hear.
How quickly something vibrates is measured in Hertz (or Hz for short). This measures how many vibrations are set up in one second. Now, human ears can only hear certain vibrations. A young person can hear between 20 Hz and 20,000 Hz. The range gets smaller with age.
Sound in the Air
Sound is a form of energy. It is produced when an object is made to vibrate. It travels in waves through any substance, solid, liquid or gas. Sound can travel through air but not through empty space. This is because molecules in the air can be made to vibrate. The molecules are alternatly pushed together and pulled apart to form the sound waves. Sound waves come examples of transverse waves. Astronauts can not speak in space because there is a vacuum between them. Radio waves can transfer the waves.
Frequency and Pitch
The pitch of a sound means how high or low a sound is. This is dependant on how fast the producer of the sound vibrates. The frequency is a measurement of the pitch. This is measured i Hertz. All musical instruments have a range in Hertz. An "A" tuning fork is 440Hz for an example. The top string of a guitar is 660Hz. A drumskin is 20Hz, so it moves vibrates up and down by 20 times per second.
A high pitched scream will have a high frequency. This means that the vocal cords will move quicker, while a low-pitched growl will have a lower frequence so the vocal cords move slower.
NOISE!
In a classroom you would expect to get 60dB, while in a canteen about 75dB. At the fun fair you would expect between 80 and 90 dB. It is not just how high the sound is, but how frequently you hear it. If you work all day with noise all round you, you are more likely to get hearing damage, but at a disco for example, you only get one night, so it is unimportant for you to have ear protection.
ECHOES,CHOES,HOES,OES,ES,S,S!
An echo is made when a sound hits a wall and bounces back. A room without things like carpets, tiles and bricks cause more echoes. Rectuangular rooms and plain walls means no sound escapes making you have more echo. Eco can be a real pain for sound engineers as if an echo bounces back to a microphone, it causes feedback, which gets worse as the sound bounces back to the mic. This can be stopped using a noise gate, compressor or changing the EQ, or just checking the venue before a gig. People also absorb sound, so "sound checks" are always more echoey than the live performance.
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