Text of Chapter 15 The Nature of Sound What is Sound??? Sound is a Longitudinal Wave traveling through...
The Nature of Sound What is Sound??? Sound is a Longitudinal Wave traveling through matter.
Longitudinal Waves Matter vibrates in the same direction as the wave travels.
Longitudinal Waves Compression Rarefaction
Sound from a Tuning Fork
Speed of Sound Sound is transmitted through matter. The Velocity of Sound depends on the matter that carries it.
Sound travels at a velocity of 332m/s in air at 0 C. Sound travels faster through warm air than through cold air. The velocity of sound increases about 0.6m/s for each degree in temperature. Sound travels much faster through liquids and solids than through gases. At 20 C sound travels at 344m/s.
Comparing Media MediaSpeed of Sound Air at 0C331m/s Air at 20C343m/s Water at 25C1493m/s Sea Water at 25C1533m/s Iron at 25C5130m/s Rubber at 25C1550m/s
Human Hearing Frequency of Sound 20 Hz to 20,000 Hz. Sound above 20,000 Hz - Ultrasonic Sound less than 20 Hz Subsonic (Infrasonic)
Frequency is Pitch
Detection of Pressure Waves
Intensity and Loudness Intensity of Sound Depends on the amplitude of the wave. Loudness Describes a persons response to sound intensity.
Loudness is measured in Decibels(dB) For every 10dB change the sound doubles!! 70dB is twice 60dB 80dB is four times 60dB
Resonance A resonant frequency is a natural frequency of vibration determined by the physical parameters of the vibrating object.
Harmonics Vibrations which occur at a particular frequency is known as a harmonic.
First Harmonic The lowest possible frequency at which a string could vibrate to form a standing wave pattern is known as the fundamental frequency or the first harmonic.
Resonance in Air Columns Closed Air Column = 4L L = 4 / 3 L = 4 / 5 L
Resonance in Air Columns Open Air Column = 2L L = L = 2 / 3 L
Example A tuning fork is placed above an open-pipe resonator in which the length can be changed. The loudest sound is heard at a length of 67cm and the next loudest was heard at 100.5cm. If the temperature of the air is 20C what is the frequency of the tuning fork?
Example = 67cm = 0.67m v@20C = 343m/s v = f f = v/ f = 512Hz f = 343m/s 0.67m
Homework #15-2 PP: 5-9 Page: 362 Due: 3/17/03
Music to Your Ears A back and forth motion is set up in a string, resulting in a regular vibration. The vibration is called a standing wave the location of the crests and troughs are always in the same place.
In a wind instrument, holes are opened and closed, changing the length of the vibrating column of air. This changes the size of the standing wave.
Noise Sound with no regular pattern or definite pitch.
Tone Quality The differences among sounds of the same pitch and loudness.
Music Musical Sounds Based on a series of notes called a musical scale.
The Sound Spectrum: Fundamental and Harmonics
Open Air Column = 2L L = L = 2 / 3 L f 1 = v/ f 1 = v/2L f 2 = v/L f 2 = 2f 1 f 3 = v/ 2 / 3 L f 3 = 3f 1
Fundamental Frequency First Overtone Second Overtone Third Overtone 262Hz 524Hz 786Hz 1048Hz
Closed Air Column = 4L L = 4 / 3 L = 4 / 5 L f 1 = v/4L f 2 = v/ 4 / 3 L f 2 = 3f 1 f 3 = v/ 4 / 5 L f 3 = 5f 1
Fundamental Frequency First Overtone Second Overtone Third Overtone 256Hz 768Hz 1280Hz 1792Hz
Harmony Notes that sound pleasing together. The ratio of the frequencies of tones that are in harmony are small whole numbers. Notes that are one octave apart. Middle C and C 524/262 = 2/1 Notes E and C 330/262 = 5/4
Dissonance and Consonance Dissonance combination of pitches that sound unpleasant. Consonance combination of pitches that sound pleasant.
Musical Intervals Octave: Two notes that have a ratio of 1:2. Example: 440Hz 880Hz one octave higher. 220Hz one octave lower.
Interference Constructive Interference Occurs when the compressions and rarefactions of two or more waves come together. Louder Sound
Interference Destructive Interference Occurs when a compression of one wave arrives at the same time as a rarefaction of another wave. Quieter Sound
Interference Beats The result of compressions and rarefactions of two slightly different frequencies reaching your ears together. Beats
f 1 = 512Hz f 2 = 514Hz Beats = f 1 - f 2 Beats = 2Hz (beats/s) = 514Hz - 512Hz
Homework #15-3 Practice Problem:10 Section Review Page: 367 Due: 3/18/03
Homework #15-4 Study Guide Due: 3/19/03 Test: 3/20/03