42-44;Ear/Loudness Flashcards
mechanism of ear
pinna = receives sound energy proportional to area of wave front intercepted
tympanic membrane/ossicles= amplifiers to increase effectiveness of reception
ossicles = 3 small bones = passes large fraction of energy received by eardrum to oval window via a lever system = multiplies found force exerted on oval window
the amplified mechanical force transmitted to oval window = hydraulic pressure in cochlear fluid = wave-like ripple in basilar membrane = distinguish different freq of sound
- high freq wave = peaks near oval window = excites basilar membrane = relays signal to brain as high pitch
- low freq wave= peaks near end of cochlea = perceived as low pitched
threshold of human hearing
10^-16W/cm^2 at 10^3
20-20000Hz
10^3 Hz freq change of 3 Hz can be perceived by most
decibel scale
logarithmic scale of intensities to maintain a manageable set of numbers
distinction between loudness and intensity
sound intensity = acoustic power per unit area = objective physical measurement, independent of freq of sound
loudness involves perception of sound to human ear, depends on sensitivity of ear at particular freq of sound
equal loudness curve
measure of avg hearing sensitivity of a larger no. of ppl in controlled tests = subjects asked to compare loudness of test tones w/ standard tone at 10^3 Hz
y axis = intensity levels in dB
x axis = freq in cycles per sec
relative unit of loudness is the phon
using the equal loudness designation, threshold of hearing = 0 phons, regardless of freq
hearing test /audiometery
test for hearing loss: pure tone and speech audiometry
pure tone= tone of single freq, simplest and most common, produces sine wave = diff in waveforms caused by overtones(presence of higher freq) on basic freq
speech audiometry= more complex, using speech sounds that we can interpret
audiometer used = electric oscillator produces pure tones of specified f, attenuator controls loudness and compatible earphones
presbycusis
loss of high freq sensitivity
