Week 2 Sound Physics, Ranges of Hearing Frequency, Wavelength, Period, Velocity Audio Engineering & Sound Production Unit code: AUD202 AUDIO & ACOUSTICS.

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Presentation transcript:

Week 2 Sound Physics, Ranges of Hearing Frequency, Wavelength, Period, Velocity Audio Engineering & Sound Production Unit code: AUD202 AUDIO & ACOUSTICS THEORY

Sound is Vibrations When an object vibrates it causes nearby molecules to vibrate causing a chain reaction

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

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)

One complete cycle is one compression and one rarefaction 1000 cycles per second = 1000Hz = 1kHz

The sine wave is a pure tone with no harmonics Sine Wave

Simple Waveforms Sine Square Triangle Sawtooth

HIGHER FREQUENCY shorter wavelength LOWER FREQUENCY longer wavelength

Frequency range of hearing The typical range of hearing of a young undamaged ear is between 20Hz and 20kHz

A3 = 220 Hz A4 = 440 Hz A5 = 880 Hz

C4 = Hz D4 = Hz E4 = Hz F4 = Hz G4 = 392 Hz A4 = 440 Hz B4 = Hz C5 = Hz

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

Dynamic Range of Hearing 60 decibels of amplitude -60dBFS to 0dBFS

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

Velocity of Sound Formula The velocity of sound through air at 21 degrees Celsius is 344m/s

THE SOUND BARRIER

The Sound Barrier

SPEED OF SOUND AIR WATER STEEL DIAMON D 344 m/s 1482 m/s 5200 m/s m/s

The Decibel The Bel is named after Alexander Graham Bell 1847 –1922. The decibel (dB) is a tenth of a Bel Amplitude is measured in decibels

Loudness is Subjective Amplitude is Objective

Loudness Loudness is a subjective term describing the strength of our perception of sound. Loudness is measured in Phons

Threshold of Pain 120dB Threshold of hearing is