exam 1

Question 1

what are some problems that people face when they have sensorineural hearing loss?

Answer 1

• decreased audibility
• decreased dynamic range
• decreased frequency resolution
• decreased temporal resolution

Question 2

auditory processing disorders

Answer 2

disorders of the brainstem, mid-brain, or auditory cortex that can exist independently of any peripheral HL or can be the direct consequence of an impaired cochlea sending deficient signals to the brainstem

Question 3

spatial processing disorder

Answer 3

a deficit that occurs even when sounds are made comfortably audible by individually prescribed amplification

• does fall under auditory processing disorder (is a type)
• hearing impaired have and EXTREMELY hard time separating the sound from noise/masker

Question 4

frequency

Answer 4

• cycles per second

- Hz

Question 5

period

Answer 5

1/frequency

-seconds or milliseconds

Question 6

phase

Answer 6

timing of a sound, or 1 component of a sound, relative to some other aspect of the sound/or relative to another sound.
-360 degrees

Question 7

wavelength

Answer 7

distance a sound wave travels during 1 period

Question 8

diffraction

Answer 8

the way the sound is altered by an object

Question 9

pressure

Answer 9

force per unit area

-pascals

Question 10

sound pressure level

Answer 10

number of dB by which any sound pressure exceeds the arbitrary, but universally agreed reference sound pressure of 2x10 (^-5)

Question 11

RMS

Answer 11

root mean square:

represents the strength of a fluctuating signal over a certain time.

Question 12

waveform

Answer 12

how the pressure of a sound wave varies from moment to moment in time.

Question 13

spectrum

Answer 13

added mixture of puretones that produce a complex sound over a portion of time

Question 14

fourier transform

Answer 14

enables the spectrum to be calculated if the waveform is known

Question 15

impedance

Answer 15

how easily a medium vibrates when a sound pressure is applied to it.

Question 16

linear amplifier

Answer 16

everything gets bigger by multiplying the input signal by a fixed amount

Question 17

gain-frequency response

Answer 17

the gain of a linear amplifier is necessary to state its gain at every freq w/in the freq range of interest

Question 18

essential components for hearing aids

Answer 18

• 1 or more mics (sound –> electrical signal)
• an amplifier to increase the strength of the electrical signal; in the process it provides balance of the sound, usually giving more emphasis to HF sounds and weak sounds than it does to LF sounds and intense sounds
• a mini loud speaker (receiver), to turn electricity back into sound
• a means of coupling the amplified sound into the ear canal
• battery to provide the power needed by the amplifier

Question 19

RITE

Answer 19

receiver in the ear canal

Question 20

RICA

Answer 20

receiver in the aid

Question 21

microphone

Answer 21

aka transducer

-takes an electrical waveform and turns it into an acoustic waveform

Question 22

diaphragm

Answer 22

-inlet port that is thin and flexible
-sound pressure causes movement to move the diaphragm towards/away from the electret. this change in distance changes the electrical force btwn opposing charges means that the voltage btwn the backplate and diaphragm changes.
sound wave to electric wave

Question 23

back-plate

Answer 23

small air space behind the diaphragm that separate it from the rigid metal plate
-on the back plate is the “electret”

Question 24

what are other names for microphone amplifier

Answer 24

aka FET: field effect transistor, buffer amplifier, follower

Question 25

what are other names for completely electronic microphones

Answer 25

silicon microphones, solid-state, integrated or micro-electro-mechanical system (MEMS)

Question 26

why does resonance occur?

Answer 26

it occurs btwn air in the inlet port (acoustic mass) and volume of air next to front of diaphragm (acoustic compliance)

Question 27

Helmholtz resonance

Answer 27

mechanical compliance of diaphragm and air behind diaphragm. | this resonance can cause a 5dB gain at about 4-10kHz in the frequency response

Question 28

what are microphone imperfections?

Answer 28

- major imperfection: mics breakdown if exposed to adverse chemicals (sweat) - random electrical noise (sometimes audible in HA in quiet) [greatest in mic that use internal acoustic path to roll-off LF] - sensitive to sound AND VIBRATIONS: when mic is shaken (like running) any vibe gets amplified - feedback loop when mechanical transmission of vibes from receiver to the mic are strong enough they make an oscillation - mic will overload & distort sound with increased pressure - bad design/construction of the HA - subject to wind noise (turbulence increases the pressure, and mic converts that to sound

Question 29

Internal feedback

Answer 29

can be detected w/coupler or by an oscillation. | -indicated by bumps in the frequency response at increased volume, but disappear at lower volume.

Question 30

how does a directional microphone work?

Answer 30

1. sound comes from rear and hits the front part later 2. sound in rear is delayed as it passes thru internal low pass filter 3. if internal and external delays are equal, sound from rear will hit both sides of diaphragm at the same time so there will be no net force on the diaphragm = insensitive to sound from rear 4. if internal delay is less than external delay, mic will be insensitive 2 sounds from other directions

Question 31

maximum external time delay

Answer 31

time btwn sounds arriving from front to rear to the other is equal to the distance btwn the ports receiving sound after they diffract around the head to the other ports.

Question 32

internal time delay

Answer 32

rear port has acoustic damper (resistor). the resistor and cavity at the back make a low pass filter (passes most freq w/o attenuation, but w/some delay is apparent to all filter.)

Question 33

why are directional microphones important/

Answer 33

they suppress noise coming form some direction while keeping sensitivity to sounds from 1 direction. -good for HAs cuz it processes signals to improve SNR and increase intelligibility

Question 34

polar sensitivity pattern:

Answer 34

directional sensitivity of mic on a circle graph. | -by changing the ratio of internal/external delay we can change the pattern.

Question 35

omni directional microphone

Answer 35

opposite of directional microphone - a single port with a circle polar pattern - non-directional

Question 36

Directivity index (DI)

Answer 36

ratio of sensitivity for frontal sounds relative to sensitivity averaged across all other directions. 2D-DI = horizontal plane 3D-DI = all directions

Question 37

front-to-back ratio

Answer 37

ratio of frontal/rearward sensitivity. -says nothing about effectiveness of HA in suppressing noise arriving from directions other than precisely behind the aid wearer

Question 38

dual microphone technique

Answer 38

2 omni mics both w/1 inlet port. | the output of 2nd mic is electronically delayed and subtracted from the 1st

Question 39

total harmonic distortion

Answer 39

power of all distortion products are added and expressed relative to power of wanted output signal component

Question 40

intermodulation distortion

Answer 40

distortion products arise from modulation (mutual alteration) of every component in the input signal

Question 41

compression amplifier

Answer 41

aka Automatic gain control (AGC) or automatic volume control.