1. Audio and Acoustics Theory
Sound
Ranges of Hearing
Frequency / Wavelength / Period / Speed

2. What You Need to Learn Today
What sound is and how it travels The frequency range (Hz) and dynamic range (dB) of human hearing How to calculate frequency, wavelength, period and speed of sound

3. Acoustics: the physics of sound
Psychoacoustics: the human perception of sound

4. Sound is Vibrations
When an object vibrates it causes nearby molecules to vibrate causing a chain reaction
Sound energy is the energy produced by sound vibrations as they travel through a specific medium. Sound vibrations cause waves of pressure which lead to some level of compression and rarefaction in the mediums through which the sound waves travel.
The study of sound and vibration are closely related. Sound, or "pressure waves", are generated by vibrating structures (e.g. vocal cords); these pressure waves can also induce the vibration of structures (e.g. ear drum). Hence, when trying to reduce noise it is often a problem in trying to reduce vibration.
Sound travels through air because air is made of molecules (molecules carry the sound waves by bumping into each other)
Electromagnetic waves (light)don’t need molecules to travel; they form when an electric field couples with a magnetic field.

5. Compressing and rarefacting air molecules

6. Sound is Vibrations
Sound travels as a series of compressions and rarefactions through a medium

7. Sound is a Mechanical Wave
Sound travels through air as a longitudinal wave
However it can also travel as a transverse wave (such as on a guitar string or a wave in water)

8. Units of frequency, logarithmic progression of musical scales.

9. 1 cycle per second = 1cps = 1 Hertz = 1Hz
One complete cycle is one compression and one rarefaction
1 cycle per second = 1cps = 1 Hertz = 1Hz

10. Frequency range of hearing
The human ear is capable of hearing frequencies between 20 and 20,000 cycles per second (20Hz to 20kHz)

11. Frequency range of hearing
20Hz
40Hz
80Hz
100Hz
150Hz
200Hz
10kHz 15kHz 16kHz 17kHz 18kHz 19kHz

13. Dynamic Range of Hearing
The typically accepted amplitude range of human hearing is 120dBSPL
Sound amplitude is referenced to the Pascal (Pa) (the unit for pressure)
0dBSPL = Pascals (20 µPa)
120dBSPL = 20 Pascals
The pascal (Pa) or kilopascal (kPa) as a uit of pressure measurement is widely used throughout the world and has largely replaced the pounds per square inch (psi) unit. Standard car tyres are usually best at 36 Psi which is 248 kPa
Sound pressure or acoustic pressure is the local pressure deviation from the ambient (average, or equilibrium) atmospheric pressure caused by a sound wave. Sound pressure in air can be measured using a microphone, and in water using a hydrophone. The SI unit for sound pressure p is the pascal (symbol: Pa).

14. Dynamic Range of Hearing
The pascal (Pa) or kilopascal (kPa) as a uit of pressure measurement is widely used throughout the world and has largely replaced the pounds per square inch (psi) unit. Standard car tyres are usually best at 36 Psi which is 248 kPa
Sound pressure or acoustic pressure is the local pressure deviation from the ambient (average, or equilibrium) atmospheric pressure caused by a sound wave. Sound pressure in air can be measured using a microphone, and in water using a hydrophone. The SI unit for sound pressure p is the pascal (symbol: Pa).
Decibels relative to full scale, commonly abbreviated dBFS, measures decibel amplitude levels in digital systems such as pulse-code modulation (PCM) which have a defined maximum available peak level.
0 dBFS is assigned to the maximum possible digital level.[1] For example, a signal that reaches 50% of the maximum level at any point would reach -6 dBFS at that point, 6 dB below full scale. Conventions differ for RMS measurements, but all peak measurements will be negative numbers, unless they reach the maximum digital value.
60 decibels of amplitude -60dBFS to 0dBFS

15. Sine Wave
The sine wave is a pure tone with no harmonics. It is a ‘simple waveform’
1kHz sine wave

16. Other Simple Waveforms
Sine
Square
Triangle
Sawtooth

17. HIGHER FREQUENCY LOWER FREQUENCY
shorter wavelength
LOWER FREQUENCY
longer wavelength

18. Characteristics of Waveforms
Frequency
(number of cycles per second)
Wavelength
(length of one cycle in metres)
Amplitude
(strength or power of the wave)
Period
(time for one cycle in seconds)

19. Units of Measurement = period of one cycle (in seconds)
= velocity of sound (in metres per second)
= wavelength (in metres)
= frequency in Hertz (Hertz is cycles per second)
= period of one cycle (in seconds)

20. Velocity of Sound Formula
The velocity of sound through air
at 20 degrees Celsius is 344m/s

21. Wavelength (m) = speed of sound / frequency (Hz)
What is the wavelength
of 20Hz?
Wavelength (m) = speed of sound / frequency (Hz)
= 344 / 20
= 17.2 metres

22. f = 344 / 0.0172 f = 20,000Hz What frequency has a wavelength
of 1.72cm?
Frequency (Hz) = speed of sound / wavelength (m)
f = 344 /
f = 20,000Hz

23. What frequency has a period of 2 milliseconds?
frequency in Hz = 1 / period (in seconds)
f = 1/.002
f = 500Hz
Frequency and period are distinctly different, yet related, quantities. Frequency refers to how often something happens. Period refers to the time it takes something to happen.
ms = millisecds.
There are 1000ms in 1 second

24. T = 1/200 T = 0.005 seconds T = 5 milliseconds
What period has a frequency of 200Hz? Answer in milliseconds.
period in seconds = 1 / frequency (Hz)
T = 1/200
T = seconds
T = 5 milliseconds
Frequency and period are distinctly different, yet related, quantities. Frequency refers to how often something happens. Period refers to the time it takes something to happen.

25. What is the speed of sound at 1,263,719°C?
v = (0.6 x 1,263,719)
v = 758,562.8 m/s
Frequency and period are distinctly different, yet related, quantities. Frequency refers to how often something happens. Period refers to the time it takes something to happen.

27. The Sound Barrier

28. The Sound Barrier

29. Velocity of Sound in Various Mediums
Air > 344 m/s Hydrogen > 1284 m/s Water > 1482 m/s Human Brain > 1540 m/s Gold > 2000 m/s Steel > 5200 m/s Diamond > m/s
Human brain is 77 – 78% water
It can be anywhere between 3000 m/s and 6000 m/s depending on the type of steel and the direction of propagation of the sound wave

30. Speed of Sound Through Air
Calculate the speed of sound at:
0°C
5°C
10°C
20°C
30°C
v = (0.6xC)

31. Answers 0°C = 331.4 m/s 5°C = 334.4 m/s 10°C = 337.4 m/s

32. What are the frequencies of the following wavelengths?
3.4m 5m 50cm 80cm
Freq = vel/wavelength

33. Answers
3.4m = 101 Hz
5m = 68.8 Hz
50cm = 688 Hz
80cm = 430 Hz

34. Calculate the Wavelength of:
140Hz in air (at 344m/s)
400Hz in steel (at 5000m/s)
500Hz for an electrical signal in wire (at 300,000km/s)
Answers:
Wavelengths in air at 140Hz = 2.46 metres
Wavelengths in steel at 400Hz = 12.5 metres
Wavelength in wire at 300,000 km/s = 600 metres

35. Range of Hearing
The ‘accepted’ range of hearing of a young undamaged ear is 20Hz to 20kHz The typical amplitude range is 120dBSPL

36. Dogs 40 Hz to 60,000 Hz
Bats 20 Hz and 120,000 Hz
Mice 1 kHz to 70 kHz

37. In 1876, at the age of 29, Alexander Graham Bell invented his telephone. In 1877, he formed the Bell Telephone Company

38. The Decibel
The Bel is named after Alexander Graham Bell 1847 –1922. The decibel (dB) is a tenth of a Bel In audio, amplitude is measured in decibels
A decibel, or its abbreviation dB is a measurement of loudness that ranges from the threshold of hearing, 0dB to the threshold of pain, about 140dB. The term decibel is actually two words: deci, meaning one-tenth, and bel, named after Alexander Graham Bell, the inventor of the telephone, which is why the 'B' is always written in upper case as in dB. So, a decibel is actually one-tenth of a unit of sound measurement known as a bel.

39. Loudness is Subjective Amplitude is Objective
A decibel, or its abbreviation dB is a measurement of loudness that ranges from the threshold of hearing, 0dB to the threshold of pain, about 140dB. The term decibel is actually two words: deci, meaning one-tenth, and bel, named after Alexander Graham Bell, the inventor of the telephone, which is why the 'B' is always written in upper case as in dB. So, a decibel is actually one-tenth of a unit of sound measurement known as a bel.

40. Loudness is measured in Phons
Loudness is a subjective term describing the strength of our perception of sound.
A decibel, or its abbreviation dB is a measurement of loudness that ranges from the threshold of hearing, 0dB to the threshold of pain, about 140dB. The term decibel is actually two words: deci, meaning one-tenth, and bel, named after Alexander Graham Bell, the inventor of the telephone, which is why the 'B' is always written in upper case as in dB. So, a decibel is actually one-tenth of a unit of sound measurement known as a bel.
Loudness is measured in Phons

41. Threshold of hearing is
Threshold of Pain 120dB
Threshold of hearing is
A decibel, or its abbreviation dB is a measurement of loudness that ranges from the threshold of hearing, 0dB to the threshold of pain, about 140dB. The term decibel is actually two words: deci, meaning one-tenth, and bel, named after Alexander Graham Bell, the inventor of the telephone, which is why the 'B' is always written in upper case as in dB. So, a decibel is actually one-tenth of a unit of sound measurement known as a bel. 41

42. To Recap
Sound is audible pressure variations which travel as a series of compressions and rarefaction through a medium. Sound is a mechanical wave which is transmitted as longitudinal and transverse waves.

43. Audio Engineering Society
Username: jmcacademy
Password: student1

44. Papers related to NIHL on AES website
Hearing Loss from Noise and Music
Sound Pressure Levels in Symphony Orchestras and Hearing   
How the Ear Works and Why Loud Sounds Cause Hearing Loss
Preventing Hearing Loss
Investigation of the Loud Music Exposure Hearing Loss

45. Moodle Key to enrol in Trimester 1 classes
amplitude

46. Next Week
Wave Interaction Beat Frequencies Phase Concepts Comb Filtering Waveforms Noise