16. SCIENCE OF SOUND:
DIFFERENCE IN SOUNDS:
There are many different sounds such as Fire alarms
which are loud, whispers which are soft, sopranos that sing high, tubas that
play low. Every one of us has different voices. The differences between sounds
are caused by intensity, pitch, and tone.
Intensity:
Sound is a wave and has amplitude or height as
that of other waves. Amplitude is a measure of energy. The more energy a wave
has, the higher its amplitude. As amplitude increases, intensity also
increases. Intensity is the amount of energy a sound has over an area. The same
sound is more intense if you hear it in a smaller area. In general, we call
sounds with a higher intensity louder. The sound of someone yelling is loud,
while the sound of breathing is very soft. Loudness cannot be assigned a
specific number, but intensity can. Intensity is measured in decibels.
The human ear is more sensitive to high sounds, so
they may seem louder than a low noise of the same intensity. Decibels and
intensity, however, do not depend on the ear. They can be measured with
instruments. A whisper is about 10 decibels while thunder is 100 decibels.
Listening to loud sounds, sounds with intensities above 85 decibels, may damage
ears. If noise is loud enough, over 120 decibels, it can be painful to listen
to. One hundred and twenty decibels is the threshold of pain.
Pitch:
Pitch helps to distinguish between low and high
sounds. Imagine that a singer sings the same note, one on an octave and another
on an octave above the other. There is a difference between the two sounds. That
is because their pitch is different.
Pitch depends on the frequency of a sound wave.
Frequency is the number of wavelengths that fit into one unit of time. A
wavelength is equal to one compression and one rarefaction. Even though the singer
sang the same note, because of the different frequencies of sounds, they are
heard as different. Frequencies are measured in hertz. One hertz is equal to
one cycle of compression and rarefaction per second. High sounds have high
frequencies and low sounds have low frequencies. Thunder has a frequency of
only 50 hertz, while a whistle can have a frequency of 1,000 hertz.
The human ear is able to hear frequencies of 20 to
20,000 hertz. Some animals can hear sounds at even higher frequencies. The reason
humans cannot hear dog whistles is that the frequency of the whistle is too
high to be processed by ears. Sounds that are too high for a man to hear are
called ultrasonic.
Ultrasonic waves have many uses. In nature, bats
emit ultrasonic waves and listen to the echoes to help them know where walls
are or to find prey. Captains of submarines and other boats use special
machines that send out and receive ultrasonic waves. These waves help them
guide their boats through the water and warn them when another boat is near.
Tone & Harmonics:
Another difference that could be noticed between
sounds is that some sounds are pleasant while others are unpleasant. A
beginning violin player sounds very different than a violin player in a
symphony, even if they are playing the same note. A violin also sounds
different than a flute playing the same pitch. This is because they have a
different tone or sound quality. When a source vibrates, it actually vibrates
with many frequencies at the same time. Each of those frequencies produces a
wave. Sound quality depends on the combination of different frequencies of
sound waves.
Imagine a guitar string tightly stretched, and if
it is strummed, the energy from the finger is transferred to the string, causing it
to vibrate. When the whole string vibrates, the lowest pitch is heard. This
pitch is called the fundamental. Parts of the string vibrating at frequencies
higher than the fundamental are called overtones, while those vibrating in
whole-number multiples of the fundamental are called harmonics. A frequency of
two times the fundamental will sound one octave higher and is called the second
harmonic. A frequency four times the fundamental will sound two octaves higher
and is called the fourth harmonic. Because the fundamental is one time itself,
it is also called the first harmonic.
The usefulness of Tone and Harmonic in Everyday life:
The more harmonic the sound is, it has better
quality sound. All the different overtones of a sound give it a unique pattern.
This is especially true for a person’s voice. Everybody in the world has a
different voiceprint, or pattern of overtones. Detectives can track a criminal
if they know his voice print just as they would use his fingerprints. Voice
identification equipment is used in advanced security systems to recognize and
let in only one authorized person. Voice prints are also used in modern
technology, for example, voice-activated telephones. In the future, for turning
the lights on, it may be more common to say by words to turn on lights, than to
flip a light switch.
DIFFERENCE BETWEEN MUSIC AND NOISE:
Both music and noise are sounds but there is a
difference in both. Some sounds, like construction work, are unpleasant. While
others, such as a favorite band are enjoyable to listen to. Also, the sound of rain might be pleasant music to some, while
the sound of a child practicing piano might be an unpleasant noise. To
help classify sounds, there are three properties that a sound must have to be
musical.
A sound must have an identifiable pitch, a good or
pleasing quality of tone, and a repeating pattern or rhythm for it to be pleasing music. Noise on the other hand has no identifiable pitch, no pleasing
tone, and no steady rhythm.
FREQUENCY AND RESONANCE
Sound waves traveling through the air or other
mediums sometimes affect the objects that they encounter. Sound is caused by
the molecules of a medium vibrating. Frequency refers to the number of
vibrations that an individual particle makes in a specific period of time,
usually a second. The frequency of a wave is different than the speed of a
wave. Frequency refers to how often a wave passes through a certain point,
while speed refers to how fast a wave passes through the point.
Different articles vibrate at a specific frequency,
called natural frequency. Steel, brass, and wood and all have different
natural frequencies. Occasionally, objects vibrating at their natural
frequencies will cause resonance. Resonance is when objects with
the same natural frequency as the vibrating source also begin to vibrate.
Resonance does not happen very often and only affects objects close to the
vibrating source. Sometimes, the effects of resonance can be powerful. A singer
can make glass vibrate enough to shatter, just by singing a note with the
glass’s natural frequency!
CHANGING PITCH
A string vibrates with a particular fundamental
frequency. It is possible to produce pitches with different frequencies from
the same string. The four properties of the string that affect its frequency
are length, diameter, tension, and density. These properties are described
below:
· When the length of
a string is changed, it will vibrate with a different frequency. Shorter
strings have a higher frequency and therefore higher pitch. When a musician
presses the finger on a string, the length of the string is shortened with
increasing pitch.
· Diameter is the
thickness of the string. Thick strings with large diameters vibrate slower and
have lower frequencies than thin ones. A thin string with a 10 millimeter
diameter will have a frequency twice as high as one with a larger, 20
millimeter diameter. This means that the thin string will sound one octave
above the thicker one.
· A string stretched
between two points will have tension. Tension refers to how tightly the string
is stretched. Tightening the string gives it a higher frequency while loosening
it lowers the frequency. When string players tighten or loosen their strings,
they are altering the pitches to make them in tune.
· The density of a string will also affect its frequency. Remember those dense molecules vibrate at slower speeds. The denser the string is, the slower it will vibrate, and the lower its frequency will be. Instruments often have strings made of different materials. The strings used for low pitches will be made of a more dense material than the strings used for high pitches.
