Basic Acoustics Flashcards
air pressure is
1000 Pa
air pressure
1000 hPa
is the speed of spreading sound the same as the speed of molecules themselves?
no
speed of sound
340 m/c
longitudinal wave
direction in which molecules oscillate is the same as the direction of the wave itself
is sound a longitudinal or transverse wave
longitudinal
transverse wave
direction in which molecules oscillate is perpendicular to the direction the wave is travelling
microphone measures sound waves how?
transforms air pressure changes into electrical signals, which are then available for future processing
how is a microphone made/set up
- a membrane stretched over a closed compartment
- back plate stable
- front plate mobile (diaphragm)
- sound wave forces membrane inward or outward dues to stable air pressure in the compartment
- the small movements of membrane generate small electrical signals
- thin light coil to make membrane move
sounds journey though microphone
1) front plate
2) back plate
3) battery
4) output audio signal
oscillogram
sound pressure (amplitude) is plotted vertically against a horizontal time axis
frequency equation.
F(Hz)=1/T[s]
speech frequencies typically between
80Hz - 10,000Hz
wavelength calculation of a sound wave when given period
Distance d[m]= c[m/s] * time [s]
Perceptually or acoustically does it make a difference what the phase difference is
it doesn’t make a difference what the phase difference is
is amplitude relative in a digital enviroment
yes
cosine wave is
sine +/- 90 degrees
analog signal
continuous signal
digital (time axis) signal
sampling
digital (amplitude axis) signal
quantization
nyquist theory
If you want to record speech (acoustic signals), then for technical reasons your sampling frequency has to be double the highest frequency you want to record
Sound pressure level equation
SPL= 20* log10 p/p0
2 main types of microphones
- electro(dynamic) microphone
- condensor micropone
microphone capsule size
- big capsule (larger than half inch)
- small capsule (smaller than half inch)
