2 15.1- Properties and Detection of Sound Importance of Sound
3 Place your hand on your throat. Speak to someone next to you for 30 seconds.Sing to someone next to you for 5 seconds.What do you feel?
4 Movement forward compresses air particles- increases pressure Movement backwards separates air particles- decreases pressure
5 Sound waves- longitudinal waves with pressure variation that is transmitted through matter (cannot move in a vacuum)Speed of sound depends on temperature0.6 m/s per 1oC343 room temperature sea levelSpeeds increase in liquids and solids
7 Detection of Pressure Waves Human ear takes vibrations in the air and transmits them into electrical impulses
8 Perceiving Sound Pitch- depends on the frequency of the vibration Human Ear can hear20 Hz-16,000 Hz20 Hz-10,000 Hz (older people)20 Hz-8,000 Hz (age 70-cannot understand speech)
9 Find the wavelength in air at 20oC of an 18 Hz sound wave, which is one of the lowest frequencies that is detectable by the human ear.
10 Loudness- perceived by our sense of hearing, depends primarily on the amplitude of the pressure wave 1 billionth of an atmosphere or 2x10-5 Pa to 20 Pa (pain)Sound level-logarithmic scale measured in decibels (dB).10 dB increase is about 2x as loud
12 The Doppler EffectDoppler Effect- frequency shift
13 Fd=fs(v-vd/v-vs) v=velocity of the sound wave vd=velocity of the detectorvs=velocity of the sound sourcefd=frequency received by the detectorfs=waves frequency
14 Setting up Parameters + from source to detector - from detector to sourceThe velocity of sound is always positive!
15 You are in an auto traveling at 25 You are in an auto traveling at 25.0 m/s toward a pole mounted warning siren. If the siren’s frequency is 365 Hz, what frequency do you hear? Use 343 m/s as the speed of sound.
16 A sound source plays middle C (262 Hz) A sound source plays middle C (262 Hz). How fast would the source have to go to raise the pitch to C sharp (271 Hz)? Use 343 m/s as the speed of sound.
22 Resonance in Air Columns Closed pipe resonator- a resonating tube with one end closed to airHigh pressure reflects back on high pressureOpen pipe resonator- resonating tube with both ends openLow pressure reflects back on high pressureIncreased amplitude from constructive interference causes the sound to get louder
24 Resonance on StringsEach end is clamped and therefore has a node on each end.Speed of the wave depends on the tension and mass per unit length.Must attach to a sounding board (which must resonate as many frequencies) to intensify sound
25 Sound QualityTuning fork- uses simple harmonic motion which can be uninterestingInstruments and Voices- use superposition to blend many frequencies which seems more pleasing to hearTimbre, tone color, tone quality
26 The sound spectrum: fundamental and harmonic Fundamental- lowest frequency (f1)Closed pipe- f1=λ/4Open pipe- f1=v/2LHarmonics- multiples of the lowest frequencyClosed pipe- odd multiplesOpen pipe- even multiples
27 Consonance and Dissonance Dissonance- unpleasant set of pitchesConsonance- please set of pitches (pitches with small whole number ratios)Ex: 1:2, 2:3, 3:4
28 Musical Intervals Octave- 2 notes with frequencies related 1:2 Ex: 440 Hz: 880 HzEx: Fundamental: 1st Harmonic: 2nd Harmonic