Survey of Sound class 3
Speed of Sound
The Speed of sound is measured in meters per second.The speed of sound is affected by several factors: temperature, humidity, and elasticity.
SOS ~ 344 m/s or 1130 f/s
NOTE: for class we will assume the speed of sound in air @ 20 degrees Celsius an 75% humidity is 344m/s
Speed of sound Calculator http://www.measure.demon.co.uk/Acoustics_Software/speed.html
Sound is a periodic event. This means that there is a fixed amount of time between different events.The Frequency component of a sound wave affects the pitch of the sound.
Frequency if the measure of how many cycles a wave complete per second.
Frequency (f) is measures in Hertz
Period (T) in the inverse of infrequency is is measured in seconds
Frequency = Cycles/Second Period = Seconds/Cycle
f = 1/T T = 1/f
Different types of frequency components periodic / aperiodic.
- sound that has a measurable frequency
- sound that is mostly random
It is assumed the humans can hear frequencies from 20Hz to 20,000 Hz.
- http://iam.colum.edu/sound/media/sweep20-20.wav 41kb,16 bit 3.7megs
Wavelength is measured in distance (ft. of m)
The actual physical length of a single cycle of a wave
Wavelength = speed of sound / Frequency in Hz
- λ = SOS/f
wavelength = speed of sound * period
- λ = SOS*T
The wavelength of a sound wave varies greatly with the frequency of the wave. A 20 kHz wave has a wavelength of 1.72 (0.7 in)cm while a 20 Hz wave has a wavelength of 17.2 m (~56 ft.).
Perception of Amplitude and Frequency
Humans do not hear all frequencies equally. We perceive different frequencies with equal energy to have different amplitudes. The Fletcher Munson Curves show the phons scale, how amplitude is perceived by frequency
Fletcher Munson Curves 1 http://arts.ucsc.edu/EMS/Music/tech_background/TE-02/AcNumbers/AcNumbers.html
Fletcher Munson Curves 2 http://www.allchurchsound.com/ACS/edart/fmelc.html
Fletcher Munson Curves 3 http://hyperphysics.phy-astr.gsu.edu/hbase/sound/eqloud.html