Lesson 2 - Physics of Sound
OBJECTIVE: In the last lesson you were introduced to a brief history of the major developments in electronic music in addition to the major contributors and terminology related to electronic music. This unit will explore more closely, a major component of electronic music: Sound. You will learn basic terminology and parameters of sound, sound production and its relationship to music. The terminology and concepts discussed will be enhanced through unit activities, an online workbook assignment and a quiz.
Components of Sound
There are 4 perceptual properties of sound: Pitch, Loudness, Articulation and Timbre.
Pitch is the relative highness or lowness that we hear in a sound.
The vibration pattern of a sound or pitch is called a waveform.
Each repetition of a waveform is called a cycle.
Measuring the physical length of a cycle or wave is called the wavelength.
Physics of Sound
Sound - Is produced when something vibrates.
It disturbs the air around the vibrating object, creating variations in air pressure.
These variations are called sound waves.
As the sound wave travels through the air, the molecules are pushed together with a higher pressure called compression.
When the sound waves are pulled apart with a lower pressure called rarefaction.
Sound waves travel through the air at an average rate of 1,100 feet per second (depending on air temperature), which is slow compared to the speed of light (983,571,056 feet per second). This is why we see lightning that is a few miles away several seconds before we hear the thunder.
The number of repetitions that occur per second is called the frequency.
The pitch of sound is decided by the frequency of its vibrations.
Frequency is measured in Hz (Hertz) or kHz (kilohertz) for in the thousands.
The normal range of human hearing is from 20 Hz to 20 kHz.
(About 10 octaves from the lowest to the highest distinguishable pitch.).
Frequency spectrum of sound is greater than the range of human hearing.
Many animals can transmit and hear frequencies that are far below or above what we can perceive.
Blue Whale Call: As low as 5 Hz
Dogs Here frequencies well above that of humans.
The distance between the lowest and highest tones that a voice or instrument can produce is called the pitch range.
Cycles Per Second
In music a sound that has a definite pitch is called a tone.
Has a specific frequency (440 cycles per second).
The pitch between any two tones is called an interval.
Tones that are separated by the interval called an octave, sound very much alike.
For a example: A tone at 440 cycles per second would be at 880 cycles per second an octave higher. An octave below 440 cps would be 220 cps.
The relative strength of the deviations in air pressure created by a vibrating object is what determines the loudness (or volume) of a sound.
Greater variations in air pressure=The louder we perceive the sound.
Deviations=Amplitude of the waveform
As sound emanates from the source, the concentration of power becomes less and less as the distance from the source increases.
The amount of power per square meter=Intensity of the sound.
Humans do not perceive sound in a linear fashion.
For a sound to be perceived as twice as loud, the intensity must be ten times as great.
We measure the perceived intensity level of a sound using a logarithmic scale called the decibelor dB.
The following might prove helpful in understanding this concept:
To double the perceived loudness of a sound, the power (measured in watts) must be increased by 10 times and the sound pressure level will increase by 10 dB.
Example: A sound pressure level (SPL) of 90 dB produced with 10 watts of power will double in apparent loudness when the power is increased to 100 watts and the SPL increases to 100 dB.
Doubling the power of a sound nets a 3 dB gain in perceived loudness.
Example: A sound pressure level (SPL) of 90 dB is produced with 10 watts of power. If the power is doubled to 20 watts, the SPL increases to 93 dB.
Moving twice the distance from a given sound source will result in one-fourth the loudness (i.e., a 6 dB loss.)
Example: At a distance of 20 feet from a sound source, a sound pressure level (SPL) of 90 dB is produced. Doubling the distance from the source to 40 feet results in a SPL of 84 dB. (90 dB - 6 dB loss = 84 dB).
??=The average Rock Concert!