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53 Cards in this Set
- Front
- Back
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What does the absorption coefficient depend on |
the frequency of the sound wave and the properties of the boundary |
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How is the absorption Coefficient calculated |
the sound intensity arriving at the boundary over the amount of energy absorbed by the area |
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Properties of absorption coefficient |
soft materials absorb more sound energy than hard materials so soft materials have higher absorption coefficients; usually increase with sound frequency except for some stiff materials where it is higher for low-frequency sounds |
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What is the reflections coefficient |
the reflective property of a boundary; varies from 0 to 1 |
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how is the reflection coefficient calculated |
the sound intensity at the boundary over the energy reflected back from the boundary to space |
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what does the reflection coefficient depend on |
the frequency of the arriving sound wave and the properties of the boundary medium |
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Total sound intensity |
must equal the sum of absorption coefficient and reflection coefficient; must equal 1 |
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What is external absorption |
sound absorption by boundaries; result of the transfer of sound energy from one medium to another |
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How does sound reflection differ based on the shape of a wall |
if a wall is flat and smooth - all sound energy reflected in same direction, may create unusually loud areas; better to disperse sound via curved walls and rough surfaces |
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How does an echo happen |
when sounds are reflected from a boundary, the listener receives direct and reflected sounds; reflected sounds arrive later than the direct sound; so late that its a repetition rather than a continuation of the original sound |
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What is reverberation |
reflected sound energy within an enclosed space; large spaces with highly reflective walls produce a lot of reverberation; small spaces and spaces with walls covered with absorbing material = little reverberation |
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What is reverberation time |
how the amount of reverberation is measured; that time it takes for a brief sound to decrease in sound pressure by 60 dB; depends on the volume of a room and the absorption provided by the boundaries of the room |
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What is the RT of a live room |
1-2 seconds; highly reflective surfaces |
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What is the RT of a dead room |
0.3-0.5 seconds; lots of highly absorbing surfaces |
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What is a reverberation chamber |
built to reflect as much sound energy as possible |
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What is an anechoic chamber |
absorb all of the sound energy arriving at the walls |
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What is the signal to noise ratio |
difference between the desired signal and the background noise |
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What are the ideal classroom RTs |
<0.6s for small classrooms; <0.7s for medium classrooms; special guidelines provided for control of reverberation for large classrooms; a high level of reverberation has a negative impact on learning environment; classrooms with high RTs have reflected speech sounds that cover subsequent speech sounds |
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What is the ideal Signal to Noise ratio |
+10-15 dB; need to to be positive for optimum learning |
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What is the doppler effect |
a shift in frequency of a sound wave resulting from the movement of a sound source, the movement of an observer/listener, changes in the medium, or a combination of these factors; heard as an increase in frequency of an approaching sound source followed by a similar decrease in frequency of a departing sound source |
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what is being compared when talking about the doppler effect |
comparing the frequency the sound source is oscillating at to the frequency hard by the listener |
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what physically causes the perceptual changes in frequency when a sound source moves toward the listner |
the wavelength of sound in the medium (relative to the listener) is affected and it gets shorter |
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What physically causes the perceptual changes in frequency when a sound source moves away from the listener |
The wavelength of sound in the medium (relative to the listener) is affected and it gets longer |
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What happens when a listener is moving away or towwards a sound source |
if the listener is moving, the wavelength of sound is not changing in the medium, but the listener's velocity changes how fast the wave fronts are hitting the listener's ear, changing the perception of frequency |
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What is impedance |
the opposition to the flow of energy through a system; measured in ohms; relates the velocity of a system to the force acting on the system; the greater the impedance, the greater the amount of force needed to make the system move at a given velocity |
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What is resistance |
the form of opposition to motion of the particles due to friction; produced by the particles moving against one another or moving against surfaces with which they come into contact; does NOT change with frequency of the driving force |
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How does frequency correlate with stiffness reactance |
As the frequency of the driving force increases, the stiffness reactance decreases; as the compliance increases, the stiffness reactance decreases |
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What is mass reactance |
opposition to the motion due to the mass of the objects or particles; changes with frequency of the driving force; very massive systems transmit low frequency energy better; very stiff systems transmit high frequency energy better |
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What is mass dominated |
If mass reactance is greater than stiffness reactance |
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What is stiffness dominated |
If stiffness reactance is greater than mass reactance |
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What are some general ways to increase the impedance of a system |
increase the mass of the system; increase the friction on the system; increase the stiffness of the system |
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What is admittance |
inverse of impedance; used for diagnostic purposes to measure the function of the middle ear system; the ease with which a system can vibrate due to an applied force; measured in until called siemens (reciprocal of ohms) |
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What is conductance |
the inverse of resistance; the ease with which energy travels through a friction element in a system |
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What is susceptance |
the inverse of reactance; the ease with which energy travels through a mass or spring (stiffness) element in a system; can have mass susceptance and stiffness susceptance |
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What is impedance matching and how is it relevance to the auditory system |
to transfer the greatest possible amount of energy from one system to another, the impedances of both objects (the source of energy and the load/receiver of energy) should be equal |
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What is the impedance of a medium related to |
the density and elasticity of a medium |
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What are the three parts of the ear |
outer, middle, inner |
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What are the parts of the outer ear |
pinna/auricle; external auditory canal (ear canal) |
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What are the structures of the pinna |
helix (outer fold of the pinna); antihelix (second ring of the cartilage); triangular fossa (near the top of the anti helix above the tragus); tragus and antitragus (project from the pinna near the opening of the EAC); concha (two parts - cavum concha and cymbal concha) |
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What are the functions of the pinna
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several pinna cavities have resonant effects, but not the primary resonance cavity |
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Describe the EAC |
2.5 cm long with a 3 cm effective length; 25% longer due to the "end effect" (an acoustic elongation of the anatomic length of the canal due to the opening at the concha); forms an s-shaped curve ending at the TM; isthmus (narrowing) 4mm from the TM; Ear canal cavity if the primary resonance cavity acting as a on-quarter wavelength resonator |
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What are the two portions of the pinna |
Outer one third = cartilaginous portion; inner two thirds = osseous or bony portion of the ear canal |
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How are the pinna and EAM inspected |
visual inspection and otoscopy |
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What are the two functions of the outer ear |
sound transmission and directional function |
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How are sounds reaching the body affected |
affected by the body, head, and outer ear; each part of the body creates modification in sound intensity; ear canal is the most with greatest change in sound pressure at lowest frequency; changes in sound pressure caused by various parts of the body depends on the direction of the incoming sound |
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What are the two parts of spatial orientation |
localization (where in space its coming from) and distance estimation (how far away it is) |
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What is azimuth localization |
the process of determining the direction of an incoming sounds on the horizontal plane; circle around us; front is 0; right is 90; left is 270; and being center is 180 |
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What is elevation localization |
is the sound coming from above the ears, below the ears, or at the same level as the ears |
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What is distance estimation |
the process of determining how far we are from a sound source |
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What are localization cues |
created by reflection and refraction of sound by the folds, cavities, and ridges of each outer ear |
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What are monaural localization cues |
primary cues for elevation estimation; sound entering ear canal consists of original sound wave and reflected sound from various folds of the pinna; reflection cases subtle changes in the spectrum of the incoming sound if it approaches the listener from above the ear, below the ear or at the same level of the ear; difference are interpreted by the CANS and we can determine where in the vertical plane the sound is coming from |
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What are binaural cues |
created by differences in sounds arriving at the right ear and left ear; primary cues for azimuth estimation; created by interaural (between ear) differences in the intensity and arrival time of sounds between ears; interaural intensity difference cues result from intensity differences between the ears; sound arriving from the left will be earlier in the left ear |
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How does the outer ear protect the middle ear |
protects the TM and the middle ear from physical damage and abuse because it is narrow and curvy; dust and other very small objects that enter the ear are trapped by the small hairs in the ear canal; ear wax (cerumen) provides a lubricating protective layer for the skin |
