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.