sound is pressure waves. it propagates based on pressure difference
longitudinal wave, amplitude of oscillation is in direction of propagation
human hearing range 20-20khz
female higher frequency , so it reaches longer distance
sound is perceived when vibration in air is detected by ear. ear converts vibration to electrical impulse
impulses are transmitted to brain by nervous system and brain detects pitch,timber and loudness
sound travel by compression and rarefaction of air molecules
v -= sqrt(T)
T is in kelvin
v1/v2=sqrt(T1/T2)
at 20 degree 344 m/s
measurment
Lp=20 log (p/p0)
p0=refrence pressure 2*10^-5
which is often considered as the threshold of human hearing (roughly the sound of a mosquito flying 3 m away).
Lw=10log(w/w0)
w0=10^-12 W
Li=10log(i/i0)
i0=10^-12 W/m^2
Intensity of sound
unit W/m^2
threshold of hearing intensity = 1 pico W/m^2
threshold of pain = 10 W/m^2 , pressure 63 N/m^2
phon
loudness of sound intensity in db over threshold of hearing at 1000hz is phon
sone
used to determine increase in loudness
loudness sensation produced by 1000hz sound of 40db is 1 sone
10logL = (p-40) log2
p is loudness in phon
L is loudness in sone
pitch
frequency of sound
in speech and music, pitch depend on intensity , unit is MEL
1 MEL is tone of 1000 hz and 40db intensity
relation between pitch and frequency is non-linear
higher frequency lower loudness,
human need higher intensity to listen to low frequency and lower intensity to listen higher frequency
timbre
tonal characteristic of sound
we distinguish sound based on timbre
our voices also have different timber
timber is defined as per sets of different frequency proportion
overtones and harmonics
frequencies other than fundamental frequencies
harmonics is integral multiple of fundamental frequency
interval and octaves
ration between two frequencies is interval
interval = f2/f1
octaves = log(f2/f1)/log2
natural frequency : all sound transducers wit moving parts have frequency based on mass and compliance
f=1/[2*PI* sqrt(LC)]
f=1/2PI * sqrt(K/M)
M=L , K=1/C, X=Q, V=I, F=V
diaphragm has natural frequency
lower frequency is attenuated due to spring
higher due to mass
microphone
sensitivity : how weak sound signal is detected by microphone
o/p of mic (in mv) for sound pressure ( 0.1 pa) at 1000 hz
normal pressure has 0.1 pa
some manufacturer given sensitivity in dbm i.e db milli volt
SNR
represented in terms of sound pressure level(SPL)
ratio of db of output (with SPL of 0.1 pa) to output in absence of sound
bandwidth of audio within +/- 1db is frequency response
40 hz - 15k hz flat responce winthin +- 1db is hifi audio
80-8k hz for normal mic
carbon,crystal,condenser,moving coil,ribbon microphone
distortion
non-linear : distorted harmonics in amplitued
for hq less than 5 , for hifi less than 1
phase
multiple mic with diffrent path of source
directivity
D=E/E0
E = actual o/p
E0 = o/p of omnidirectoinal mic
must match output impedance for max power transfer
moving coil mic
dynamic microphone , based on em induction
Sensitivity 30uv for 0.1 SPL
snr 30db
freq response 60-8k hz for +-1db
distortion less than 5%
omnidirectional
robust,heavy,no bias,low cost,25 cm distance
use for PA(public address), broadcast
poor high freq response due to heavy coil
ribbon microphone
use lightweight aluminum ribbon as diaphragm and coil assembly
corrugated ribbon = having grooves like bump
horse shoe magnet
freq response= 20-12k hz
reflectivity = bidirectional, no signal at 90 degree
lite ribbon so careful
wind will make noise
excellent transient response
no external bias
high cost
crystal microphone
piezoelectric effect
pressure difference on crystal produce potential difference
quartz,tourmaline,Rochelle salt, ceramic
rochelle salt : high piezo but temp 50degree moist
quartz and tourmaline : low piezo
ceramic : suitable as high temp and moisture sustain
Sensitivity 50uv for 0.1 SPL
snr 40db
freq response 100-8k hz for +-1db
distortion less than 1%
omnidirectional
op impedance 1 Mhz
can be spoken at close range
high impedance
no need bias
long direct sunlight damage crystal
low cost
capacitor or condenser microphone
https://en.wikipedia.org/wiki/Sound_pressure
https://en.wikipedia.org/wiki/Absolute_threshold_of_hearing
https://en.wikipedia.org/wiki/Octave
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