16. SCIENCE OF SOUND

 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.