Module 9

Question 1

T/F: microphones create about 10-15 dB SPL of noise themselves

Answer 1

FALSE: usually 25-30 dB SPL

Question 2

Microphones convert ___ energy into ___ energy

Answer 2

Acoustic, electrical

Question 3

Microphones of hearing aids are ____ microphones

Answer 3

Electret: must be protected in the devices themselves and from electromagnetic interference

Question 4

T/F: omni directional microphones have one port while directional microphones have two ports

Answer 4

TRUE

Question 5

Omnidirectional vs Directional Microphones

Answer 5

-Omni:
·One port
·Sound hits one side of the diaphragm
·Responsive to all sounds regardless of their direction
-Directional:
·Two ports
·Sound will hit both sides of the diaphragm
·More response to sound originating from a certain direction (usually the front-most microphone on the hearing aid user)

Question 6

Possible microphone arrangements in a HA

Answer 6

-One omnidirectional (no directionality)
-One directional (2 ports)
-Two omni microphones: microphones communicate with one another to look at phase and time delays

Question 7

T/F: directional microphones have higher low frequency sensitivity compared to omnidirectional microphones

Answer 7

FALSE: they have LESS low frequency sensitivity

Question 8

What are some factors that may lead to mismatched omnidirectional microphones?

Answer 8

Dirt, debris and physical damage can cause mismatch

Question 9

Main advantage of directional microphones

Answer 9

-Provides better speech understanding in noise by improving the signal to noise ratios (SNR) and create a comfortable listening environment for users
-DMs can improve SNR by ~3 dB when noise is to the rear of the listener
-Directionality most effective when patient is within 10 feet of sound source

Question 10

What plane is preferred for analysis in polar plots?

Answer 10

Horizontal: using a 180 degree plot

Question 11

What is the directivity index (DI)?

Answer 11

-The difference (in dB) in sensitivity of sounds arriving in the front relative to other directions
·An omni mic would have a DI of 0, while directional mics have DIs between 2-6 dB

Question 12

What is articulation weighted directivity index (AI-DI)?

Answer 12

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)

Question 13

Generally, omnidirectional mics are best suitable in ___ environments and directional in ___ environments

Answer 13

Quiet, noisy

Question 14

When is directionality not possible, feasible, or desired?

Answer 14

-Hearing aid form (is directionality possible?)
-Wind noise
-Sounds from direction other than the front are desired
-Patient restrictions (physical or cognitive)
-Venting effects: reduces the effect of directionality
-Reverberation