an introduction to physics of sound - ksu...
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An introduction to physics of Sound
Outlines
Acoustics and psycho-acoustics
Sound?
Wave and waves’ types
Cycle
Basic parameters of sound wave
period
Amplitude
Wavelength
Frequency
Outlines
Phase
Types of sounds
Simple sounds
Complex sounds ( periodic and aperiodic)
• Resonance Frequency
Acoustics
What is Acoustics?
It’s defined as the science that deals with the production, control, transmission, reception, and effects of sound (as defined by Merriam-Webster).
It’s the branch of physics that deals with study of sound.
Psycho-acoustics
What is psychoacoustics?
It’s the branch of science concerned with the physical features of sound as it relates to the psychologic and physiologic aspects of the sense of hearing in the normal hearing ear.
http://medical-dictionary.thefreedictionary.com/psychoacoustic
It’s the study of the relationship between physical stimuli and the psychological responses to them
Sound
What is sound?
It’s the wave that is created by vibrating objects and propagated through an elastic medium from one location to another.
Air is an example of elastic medium
Elasticity of the medium increased as the distant between the molecules decreased
Cont. Sound
Solid is more elastic than liquid which is in turn more elastic than air
Examples of sound sources
vibration of human vocal cord.
Vibration of Tuning fork tines.
Vibration of radio speaker diaphragm.
Wave
What do we mean by wave?
It described as the disturbance that travels through a medium from one location to another location.
Types of waves
Wave known to be a compressional wave as it travels through the air as a series of compressions and rarefactions.
Cont. Types of waves
wave is stated to be a longitudinal wave when the air particles move back and forth along the wave line.
Cont. Types of waves
•The other waveform is transverse wave, where the particles move up and down along the wave line. Like waves created in water surface
Cycle
What is a cycle?
It’s any complete round or series of occurrences that repeats or is repeated.
http://dictionary.reference.com/browse/cycle
Basic parameters of sound wave
1. Period (Time) It’s the time taken for a particle to complete one
vibrational cycle.
So, it’s the duration of one full cycle.
P (period ) = T2 – T1 T1: time at the beginning of the cycle. T2: time at the end of the cycle. It’s measured in seconds, miliseconds…etc
Illustrated figure for period
Basic parameters of sound wave
2. Amplitude
It is the maximum positive displacement of the particles from the undisturbed position of the medium to the top of a crest".
It’s a magnitude, number, represents how big the wave is.
Cont. amplitude
It is measured in sound pressure level for sounds. (SPL)
The greater the displacement, the louder the sound heard .
The amplitude reflects the energy in the wave, low energy represented by a wave with short amplitude and vice versa.
Cont. amplitude
The amount of energy a sound wave owns reflects how intense the sound is. (Intensity)
So, the larger the amplitude ( greater particles displacement), the greater the owned energy, the greater intensity sound has, the louder sound would be heard.
Illustrated figure for amplitude
Cont. amplitude
Loudness is the perceptual concept of the intensity.
It’s the human perception of the intensity.
It’s measured in Decibels (dB).
Cont. amplitude
dB : deci ( a unit), Bell ( a scientist name, Graham Bell)
Because humans can hear a wide range of sound pressures, a log scale is used to condense the scale.
Basic parameters of sound wave
3. Wavelength
It is the distance between identical points in the adjacent cycles of a waveform.
The distance between 2 peaks (crests) or 2 troughs in the waveform.
Illustrated figure for wavelength
Basic parameters of sound wave
4. Frequency
It’s the number of complete cycles per a unit of time.
It’s measured in cycles per second or a unit Hertz (Hz) can be used.
The Frequency is the reciprocal of the pitch
Cont. Frequency
Frequency and period are inversely related F = 1/ T , T = 1/F
Human ear can hear from 20-20000 Hz.
Pitch is the perceptual correlate of the
frequency. High frequency sounds, perceived with high
pitch. Low frequency sounds, perceived with low
pitch.
Illustrated figure for frequency
Basic parameters of sound wave
5. Phase
• Any points in sine wave ( expressed in degrees), may be compared to standards
• The standard considered to be as (0) degree
• If the oscillation begun at 0 or 360 degree, it said to be in phase with the standard
Cont. phase
If the oscillation begun at any points other than 0 or 360 degrees, it stated to be out of phase from the standard
In phase vs. out of phase wave
Out phase wave
Cont. phase
Interference
Belongs to when more than one tone presented
If the presented tones have identical frequency and phase, intensity will be increase
Cont. phase
If the presented tones have same frequency but 180degree out of phase, the resulted amplitude will be 0, as each wave will cancel the other one
Cont. phase
Beats
When tow tones of different frequencies presented, there will be a noticeable difference in the resulted sound
These changes in the amplitude perceived as beats
Cont. phase
When the difference between the presented frequencies increases, number of beats per seconds increases
Types of sounds
1- simple sounds.
Sounds that have single frequency (one cycle per second).
It’s produced artificially like pure tone that produced by the audiometer,
Waveform presents as a sine wave, sinusoidal.
Illustration for simple wave (sine wave)
Types of sounds
2- complex sounds
They’re a combination of more than one sine wave.
All environmental sounds are complex sounds.
They have got irregular shape like sawtooth waves, square wave…etc.
They have got multiple frequencies.
Illustration for complex wave
Types of complex sounds
1- periodic
Consists of many frequencies that are mathematically related.
So it consists of fundamental and harmonics
Cont . Periodic complex sounds
Cycles are repeatable I.e. all cycles take same time and same pattern. (even if it is with irregular shape).
Square waves and some speech sounds like vowels are example of periodic complex sounds.
Cont . Periodic complex sounds
Periodic complex waveform
Cont . Periodic complex sounds
Fundamental Frequency F0
It’s the basic frequency of the complex sound.
The lowest frequency of the vibrating system.
the lowest harmonic produced by a periodic sound, generally corresponding to the sound's pitch.
Cont . Periodic complex sounds
Harmonics
They’re the integral multiple of F0 (fundamental frequency).
Fundamental & Harmonics
Types of complex sounds
2- Aperiodic
Random waveforms with unrepeatable pattern.
Consists of multiple frequencies that are mathematically unrelated.
Noise and some speech sounds are examples of these sounds.
Example of aperiodic sound wave ( Noise)
Resonance frequency
It is the natural frequency of vibration determined by the physical parameters of the vibrating object.
The energy at only certain frequencies will be enhanced.
Ear canal RF
For example, ear canal Resonance frequency is about 3000 Hz ( 2000-4000 Hz) so, the sound amplification will be boosted at this frequency.
ME RF
Another example, ME resonance frequency from 800-1200 Hz in air conduction mood while it is from 1500-2000 Hz for bone conduction . Where the greatest sound transmission is possible.
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