Basic Concepts: Physics 1/25/00

Sound Sound= physical energy transmitted through the air Acoustics: Study of the physics of sound Psychoacoustics: Psychological response to acoustic stimuli (loudness, pitch & timbre)

Wave Motion Sound Wave: transfer of energy through a medium –Particles attached and interconnected –Collide to transmit energy (condensations) –Rarefaction: particle separation –Longitudinal waves: back & forth motion of particles Slinky

Condensation & Rarefaction of Particles

Particle Collision & Rarefaction

Sinusoid Projected, uniform circular motion or simple harmonic motion Motion produced by constant velocity Specified by: Frequency, amplitude & phase –Frequency: rate of vibration of sound –Amplitude: magnitude of vibration –Phase: point on the sinusoidal function which the waveform commences

Frequency Increased frequency= more cycles per second –Frequency- # of vibrations per second –Hertz –One cycle of vibration = period (t 0 ) –f=1/t 0 and t 0 =1/f 1000 Hz = 1 ms 100 Hz = 10 ms The lower the frequency of vibration, the longer the time needed for a complete cycle of vibration

Frequency Woman= 240 Hz, What is the period? 4.2 ms Man= 120 Hz, What is the period? 8.3 ms Human hearing: frequency range= ,000 Hz

Harmonic Integer relations among elements –Related to one another: series- 2nd is 2x the frequency of the first etc. 100 Hz200 Hz300 Hz Octave is a 2:1 relation between two sounds 440 Hz & next octave 880 Hz

Amplitude Magnitude of displacement of a sound wave Types of magnitude: –Intensity- Sound energy per second over an area of 1 square meter –Sound Pressure Level- Amount of force per unit area Both expressed on a logarithmic scale (decibel)

Fourier Analysis Complex sounds = many sinusoids Amplitude Spectrum (Frequency, Amplitude, Phase) Summation of sinusoidal components

Signal to Noise Ratio Relative intensity of a signal compared to the intensity of the background noise (S/N). Large positive values = Strong signal Small positive & Negative values= noise meets or exceeds the signal Human voice also has noise elements.

Resonance Occurs when a vibrating system is driven by a periodic force at the natural frequency of the system. –Frequency-dependent Examples: –Cars on a bridge, regular intervals, sway of bridge –Glass resonates when running your finger over the rim at a certain rate

Resonance External, periodic, driving force creates vibration in a physical object –Vibration occurs because external force has the same frequency –Additive to natural frequency of object Can determine the natural frequency of an object: –Mass, length, & tension

Damping Sound energy is propagated & dissipated as it moves Damping = The diminution of amplitude of vibration due to friction (resistance) –Energy dies out –Related to bandwidth (frequency range of energy of the sound) Large bandwidth = wide range of frequencies Narrow bandwidth = small range of frequencies Larger bandwidth = more damping

Reverberation Opposite of damping Sounds reverberate or move Bounce back and forth from wall to wall Echoes that are not damped to inaudibility within 50 ms can interfere with the next sound

Applied Mathematics Estimation of loudness does not change linearly to the physical increase in intensity –Human judgment of pitch is nonlinear –Range of perception is great (scale is large) –Transforming a number scale to convenient range

Logarithms Number expressed as a power of 10 or natural log –ex. 100 is 10 2 (10 to the 2nd power) –10 is the base and 2 is the exponent

Bel Strength or magnitude of sound expressed in decibel’s Bel = logarithm of a ratio –Useful to express large #’s of intensities that the ear responds to. –Ratio: intensity of any given sound (I 1 ) is compared to a reference intensity (I 0 ) –The bel is a log to the base 10 of an intensity ratio N (bels) = log 10 I 1 /I 0

Decibel Because the bel is such a large unit, the decibel was introduced Decibel = 1/10 of the ratio of the bel Decibel: N (dB) = 10 Log 10 I 1 /I 0 –ex. I 1 were 1,000 times as great as I 0 the power ratio = 1,000; the dB would be 30 (log to the base 10 or 1,000 is 3 & 10 x 3=30)

Sound Pressure Level Used as a measure of sound in speech & hearing: –most measurement devices respond to sound pressure (ear & microphones) –SPL is also determined by a ratio –Reference pressure is equal to 20  Pa SPL (dB)= 20 Log 10 P 1 /P 0 = 20 Log 10 P 1 /20  Pa Hearing ranges = 140 dB

Readings Copies of readings on reserve in the library: –First reading for Feb 3 (also available in the text: Respiratory Function in Speech and Song.