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Amplification I > Lecture 9 > Flashcards

Lecture 9 Flashcards

1
Q

Explain the frequency response of a hearing aid microphone?

A
  • Hearing aid electret microphones have a wide frequency response- very suited for speech and environmental signals
  • Miniaturization of this microphones are well-suited to hearing aid forms
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2
Q

What are hearing aids sensitive to?

A
  • Moisture and humidity
  • Highly important to keep the microphones clear of debris- debris can block the mic port, or damage the internal components
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3
Q

Do microphones create noise?

A

Microphones create noise themselves— usually between 25-30 dB SPL (which may or may not be audible to the patient)

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4
Q

Microphones convert ____ energy into ____ energy

A

Acoustic, electrical

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5
Q

Besides debris, what else do microphones have to be protected from?

A

Microphones of hearing aids are electret microphones and must be protected in the devices themselves and from electromagnetic interference

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6
Q

What are the two types of microphones?

A
  1. Omni directional microphones
  2. Directional microphones
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7
Q

Do custom hearing aids have one or two microphone ports?

A

Small custom hearing aids are omni directional (one port), and the larger custom hearing aids are directional (two ports)

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8
Q

What type of debris gets in the microphone of a custom hearing aid?

A

Skin

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9
Q

Do BTEs/RICs have one or two microphones?

A

Almost all BTEs and RICs are directional microphones because they have the space to have two microphone ports

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10
Q

Where are the microphones located on BTE/RIC hearing aids?

A
  • Front facing directional mic
  • Back facing directional mic
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11
Q

What type of debris gets in the microphone of a BTE/RIC hearing aid?

A

Dust/lint

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12
Q

Explain the functionality of omi-directional microphones

A
  • One port
  • Sound hits one side of the diaphragm
  • Responsive to all sounds regardless of their direction
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13
Q

Explain the functionality of directional microphones

A
  • Two ports (must have physical space between port openings)
  • Sound will hit both side of the diaphragm
  • More responsive to sound originating from a certain direction (usually be the front-most microphone on the hearing aid user)
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14
Q

What is the range of spacing between directional microphones?

A

Spacing between 4-12mm

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15
Q

What are the three possible microphone arrangements?

A
  1. One omnidirectional (no directionality)
    • Capture sounds equally from all directions
  2. One directional (2 ports)
    • Hearing aid is always in a fixed directional sensitivity (fixed directionality)
  3. Two omni microphones
    • Microphones communicate with one another to look at phase and time delays
    • Note: microphones have to be perfectly matched in function
    • Have fixed directionality
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16
Q

Omni vs. directional frequency response

A

Directional microphones have less low frequency sensitivity compared to omnidirectional microphones

17
Q

Explain mismatched microphones

A
  • When two omni directional microphones, working together to learn directionality the following can happen:
    1. Performance of each microphone may not be identical
    2. Two microphones will have different sensitivity or frequency response
  • This effects the directionality function of the aid
18
Q

What can cause mismatched microphones?

A
  • Dirt, debris, and physical damage can cause mismatch
  • Some hearing aids will monitor the mismatch and adjust gain to compensate
19
Q

Candidacy considerations of directional microphones

A
  • The overriding function and purpose of directional microphone technology is to improve sound from one direction and attenuate sound from another
  • WHY? To provide better speech understanding in noise by improving the signal to noise ratios (SNR) and create a comfortable listening environment for users
  • Patients who have challenges in noise (i.e. show impairment in performance of speech in noise testing) benefit from this technology
    • DMs can improve the signal-to-noise ratio by approximately 3dB when noise is to the rear of the listener
  • Patient should sit with their back to the noise
20
Q

Directionality is most effective when the patient is within ____ feet of sound source

21
Q

What 3 characteristics make up a polar plot?

A
  1. Azimuth
  2. Null (the most amount of attenuation)
  3. Areas of focus
22
Q

What are 5 different polar plots (polar directivity patterns)?

A
  1. Omnidirectional
  2. Bi-directional
  3. Cardioid
  4. Super/Hyper Cardioid
  5. Anti Cardioid
23
Q

What is an anti cardioid polar plot and why might someone have this?

A

Null is forward facing and most sound will be picked up from the back and sides of the patient (someone being pushed in a wheel chair, a patient driving)

24
Q

What are polar directivity patterns for?

A
  • Representation to visualize the amount of attenuation provided by the microphone in a 180 degree plot, generally in the horizontal plane
  • Azimuth is represented between 0 and 180 degrees
  • There can be frequency specific differences in polar plats, often shown in 500, 1000, 2000, and 4000 Hz (can be specific for speech)
25
What 3 ways do you measure directional microphone performance?
- Front to back ratio (FBR) - Directivity index (DI) - Articulation weighted directivity index (AI-DI)
26
What is the front-to-back ratio?
- Difference in what is coming to the front and back speaker in a directional mode In an omnidirectional system those lines would be almost equal - Difference in the frequency response between 0 and 180 degrees - This can be done in test box or with patient wearing devices
27
What is the directivity index (DI)?
- How sensitivity is a microphone? What is the difference in sensitivity of sounds arriving in the front relative to other directions? - The Directivity Index (DI) is a value (in dB) obtained from the polar plot, and can be obtained from individual frequencies - Difference in the frequency response between 0 and 180 degrees
28
An omnidirectional microphone would have a DI of ____
0
29
Directional microphones have DIs commonly between ____ dB
2-6
30
The higher the DI, the more sensitive the hearing aid is to the ____
Front
31
What is the articulation weighted directivity index (AI-DI)?
- An articulation - weighted directivity index (AI-DI) looks at the directivity of the microphones in relation to the sounds specifically important for speech (i.e. more weight is given for 2000 Hz, less to 500 Hz) - Depends on a lot of things (directionality index and how the person wears their HAs in everyday life)
32
What is automatic and adaptive directionality?
- The switching between omni and directional functioning (patient user control vs. automatic change from hearing aid itself) - Generally, omni is best suitable in quiet listening situations and directional in noisy situations - Adaptive polar plots and can change quickly to respond to environmental changes - Hearing aids select the polar plot it believes to be most appropriate for a specific listening situation - How quickly the change is depends on the speed of the processor
33
Why might someone want a beam focus microphone?
Beam focus is best when there is high level ambient noise and an individual is trying to have a conversation with someone right in front of them
34
6 Considerations - when is directionality not possible, feasible, or desired?
- Hearing aid form: is directional microphone technology a possibility? - Wind noise: turbulence on microphones can be problematic - Sounds from direction other than the front are desired? - Patient restrictions: either physical or cognitive - Venting effects: reduces the effect of directionality - Reverberation
35
Why does venting reduce the effect of directionality?
The more venting we have, the less effective directional mics are (sound is already coming in through the canal to the auditory system in a natural way)

Amplification I (14 decks)

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