Sound Ranges of Hearing Frequency / Wavelength / Period / Speed AUD202 Audio and Acoustics Theory.
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Transcript of Sound Ranges of Hearing Frequency / Wavelength / Period / Speed AUD202 Audio and Acoustics Theory.
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
Sound is Vibrations
When an object vibrates it causes nearby molecules to vibrate causing a chain reaction
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)
Frequency range of hearing
The human ear is capable of hearing frequencies between 20 and 20,000 cycles per second
(20Hz to 20kHz)
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 = 0.00002 Pascals (20
µPa)120dBSPL = 20 Pascals
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)
Units of Measurement
= velocity of sound (in metres per second)
f
v = wavelength (in metres)
= frequency in Hertz (Hertz is cycles per second)
= period of one cycle (in seconds)
Wavelength (m) = speed of sound / frequency (Hz)
What is the wavelength of 20Hz?
= 344 / 20
= 17.2 metres
Frequency (Hz) = speed of sound / wavelength (m)
vf
f = 344 / 0.0172
f = 20,000Hz
What frequency has a wavelength of 1.72cm?
Tf 1frequency in Hz = 1 / period (in seconds)
f = 1/.002
f = 500Hzms = millisecds.
There are 1000ms in 1 second
What frequency has a period of 2 milliseconds?
period in seconds = 1 / frequency (Hz)
fT 1
What period has a frequency of 200Hz? Answer in milliseconds.
T = 1/200T = 0.005 secondsT = 5 milliseconds
Velocity of Sound in Various Mediums
Air > 344 m/sHydrogen > 1284 m/sWater > 1482 m/sHuman Brain > 1540 m/sGold > 2000 m/sSteel > 5200 m/sDiamond > 12000 m/s
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)
Range of Hearing
The ‘accepted’ range of hearing of a young undamaged ear is 20Hz to 20kHz
The typical amplitude range is 120dBSPL
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
LoudnessLoudness is a subjective term describing the strength of our perception of sound.
Loudness is measured in Phons
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.
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