An introduction to physics of Sound

Transcription

1 An introduction to physics of Sound

2 Outlines Acoustics and psycho-acoustics Sound? Wave and waves types Cycle Basic parameters of sound wave period Amplitude Wavelength Frequency

3 Outlines Phase Types of sounds Simple sounds Complex sounds ( periodic and aperiodic) Resonance Frequency

4 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.

5 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. It s the study of the relationship between physical stimuli and the psychological responses to them

6 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

7 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.

8 Wave What do we mean by wave? It described as the disturbance that travels through a medium from one location to another location.

9 Types of waves Wave known to be a compressional wave as it travels through the air as a series of compressions and rarefactions.

10 Cont. Types of waves wave is stated to be a longitudinal wave when the air particles move back and forth along the wave line.

11 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

12 Cycle What is a cycle? It s any complete round or series of occurrences that repeats or is repeated.

13 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

14 Illustrated figure for period

15 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.

16 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.

17 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.

18 Illustrated figure for amplitude

19 Cont. amplitude Loudness is the perceptual concept of the intensity. It s the human perception of the intensity. It s measured in Decibels (db).

20 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.

21 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.

22 Illustrated figure for wavelength

23 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

24 Cont. Frequency Frequency and period are inversely related F = 1/ T, T = 1/F Human ear can hear from Hz. Pitch is the perceptual correlate of the frequency. High frequency sounds, perceived with high pitch. Low frequency sounds, perceived with low pitch.

25 Illustrated figure for frequency

26 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

27 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

28 In phase vs. out of phase wave

29 Out phase wave

30 Cont. phase Interference Belongs to when more than one tone presented If the presented tones have identical frequency and phase, intensity will be increase

31 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

32 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

33 Cont. phase When the difference between the presented frequencies increases, number of beats per seconds increases

34 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.

35 Illustration for simple wave (sine wave)

36 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.

37 Illustration for complex wave

38 Types of complex sounds 1- periodic Consists of many frequencies that are mathematically related. So it consists of fundamental and harmonics

39 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.

40 Cont. Periodic complex sounds Periodic complex waveform

41 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.

42 Cont. Periodic complex sounds Harmonics They re the integral multiple of F0 (fundamental frequency).

43 Fundamental & Harmonics

44 2- Aperiodic Types of complex sounds Random waveforms with unrepeatable pattern. Consists of multiple frequencies that are mathematically unrelated. Noise and some speech sounds are examples of these sounds.

45 Example of aperiodic sound wave ( Noise)

46 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.

47 Ear canal RF For example, ear canal Resonance frequency is about 3000 Hz ( Hz) so, the sound amplification will be boosted at this frequency.

48 ME RF Another example, ME resonance frequency from Hz in air conduction mood while it is from Hz for bone conduction. Where the greatest sound transmission is possible.