Study Guide: Sources of Sound G6
Vocabulary
- Echo (Reflection Phenomena)
- Amplitude (Volume)
- Pitch
- Percussion
- Friction
- Vibration
- Resonance
- Tone
- Notes (Musical Notation)
- Sound Qualities
- Noise
- Music
- Intervals
- Beat and Rhythm
- Speed of Sound
Sources of Sound
- Wind (air)
- String (plucking, strumming, bowing)
- Percussion (includes pianos!)
- Friction (scratching a chalkboard, etc.)
- Electronic (a variety of sources from vibrating crystals to electromechanical devices)
Qualities of Sound
Some sounds are high and others low; some are loud and others barely audible; some are pleasant and others harsh.
The three basic properties of any pure sound are pitch, its volume, and quality.
Higher tones seem to pierce through the noise better than low tones.
Different materials produce different pitches. If an object vibrates quickly we hear a high-pitched sound. If an object vibrates slowly we hear a low-pitched sound.
The stronger the vibration, the louder the sound. Sounds are fainter the further we are from the source because the vibrations spread out like ripples on the surface of a lake.
Most sounds we hear are a mixture of many different individual sounds.
Random Noise
Random sounds can be soothing, such as the wind in the trees or waves on the beach, of they can be irritating, such as when scratching our nails on a chalkboard. Irritating noises often have the following qualities: chaotic, tense, confusing, irritating, painful.
Music
- Beat and rhythm
- Singular focus
- Organized into patterns of melody and harmony
- Importance of intervals, the space between the notes.
- Can strongly effect us: Interesting, beautiful, emotional, inspiring, fun…
- Teamwork: Everyone plays their part.
Train Whistle
- Combines the sounds of four different flutes.
- The pitches are F#, D#, G#, A#
Source: Jesse
Sound is created when something vibrates and sends vibrations (waves of energy) through a medium to someone’s ears. Sound depends on three things.
- A source to create the vibrations.
- A medium (such as air) to carry the vibrations. Sound waves cannot travel through a vacuum.
- A receiver (such as ears or microphones) to detect the vibrations.
Vibrations
Vibrations can travel through gasses (air), liquids or solids. The vibrations themselves are silent, but when they reach someone with ears to hear, the vibrations are converted to electrical impulses that travel along nerves to our brains where they are interpreted as sound. If our ears can’t detect the vibrations, perhaps because the frequency is too high or too low, we don’t hear a sound.
If a Tree Falls in a Forest…
There is an ancient riddle about sound. If a tree falls in a forest far from any sound detector (such as a human ear or a microphone), does the tree’s crash make a sound?
The answer depends on how “sound” is defined.
- If it is thought of as the waves carried by the air, the answer is yes—wherever there are sound waves there is sound.
- If sound is defined as what someone or something hears, the answer is no. In that case sound does not exist unless there is a receiver detect it.
The two answers are equally correct and incorrect!
Echos (Reflection Phenomena)
Reflection phenomena (or echos) are commonly heard with sound. When we yell into a canyon, we can hear the the canyon yell back at us. The sound travels through the air, reflects off the canyon walls and returns to us. The result is that we hear the echo (the reflected sound) of our own yell.
The Ancient Riddle of Return
Speaking of things returning… What do you call a boomerang that never returns?
Speed of Sound
Auto-focusing cameras use the time it takes for sound to return to the camera to measure the distance from the camera to the objects in view.
The distance of lightening can be measured by counting the seconds. Sound travels about one mile in five second. The actual speed depends on the temperature of the air and the medium through which the sound is travelling The speed of sound in air at sea level is about:
- 343 m/sec
- 1,235 km/h
- 1,125 ft/sec
- 767 mph
- 1 km in 2.9 sec
- 1 mi in 4.7 sec