Ch. 15 Sound Milbank High School

Sec Properties of Sound Objectives –Demonstrate knowledge of the nature of sound waves and the properties sound shares with other waves. –Solve problems relating the frequency, wavelength, and velocity of sound. –Relate the physical properties of sound waves to the way we perceive sound. –Define the Doppler shift and identify some of its applications.

Sound Waves Are pressure variations that are transmitted through matter Air molecules colliding Longitudinal waves Speed depends on air temperature –Warmer=faster

Sound Waves Can’t exist in a vacuum Echoes –Reflected sound waves –Sonar

Loudness Depends on amplitude We hear based upon pressure differences –Larger amplitudes create a higher pressure differences Sound level –Decibels (dB) –0 dB (most faintly heard), 2 x Pa –Tenfold increase, 2 x Pa is 20 dB –110 is painful (most concerts)

Pitch Difference in frequency –Middle C: 262 Hz –E: 327 Hz Human hearing – Hz –SIM – Pitch/Beat FreqSIM – Pitch/Beat Freq –SIM – Pitch/Beating FreqSIM – Pitch/Beating Freq

Doppler Shift Police siren as it drives bySIMSIM More sound waves reach you when the vehicle is moving towards you Vehicle + waves = higher frequency Waves – vehicle = lower frequency Bats: –Insects flying away: lower frequency –Insects flying towards: higher frequency

Sec The Physics of Music Objectives –Describe the origin of sound. –Demonstrate an understanding of resonance, especially as applied to air columns. –Explain why there is a variation among instruments and among voices using terms timbre, resonance, fundamental, and harmonic. –Determine why beats occur.

Sources of Sound Produced by vibrating objects –Vocal cords –Brass instruments –Reed instruments –Stringed Instruments –Others

Resonance When one object vibrating at the same natural frequency of a second object forces that second object into vibrational motion. Sometimes occurs in a column or tube (trombone) Length of air column determines the frequency

Closed pipe resonance One closed end (marimba, pipe organ, sea shell) First sound heard at ¼ wavelengths Additional resonance lengths found at half-wavelength intervals

Open-end Resonance Woodwinds, brass Sounds loudest at half-wavelengths Wavelengths half as long as in a closed ended tube Leads to twice the frequency

Sound Quality Fundamental –Lowest frequency Harmonics –Odd-numbered multiples of the fundamental frequencies Dissonance –Unpleasant set of pitches Consonance –Pleasant set of pitches

Musical intervals Octave –Frequencies in a 1:2 ratio –Ex: 1 st note-440 Hz, octave higher would be 880 Hz –Also corresponds to harmonics

Beat Notes Beat –Oscillation of wave amplitude –Beat frequency is the difference between the two frequencies