Hearing aid parts
List the basic hearing aid components and what they do
Mic: P/u signal and changes it to an electrical signal
Receiver: takes electrical signal and changes it to sound and delivers it to the ear.
Batter: power source
Amplifier: increase sound volume and passes it to the speaker
Everything between the mic and the receiver
Define compression
takes the range of sounds an compress it so its useable for the listener while applying different amounts of gain to different inputs.
in mutlichannel processing, how many channels are standard to fit the prescription target?
5-7
In EMs what does venting due?
Reduce low Hz amplitude, provide pressure relief, reduce OE
What is a transducer and what are the three transducers of a hearing aid?
a device that converts energy from one form to another. H/A transducers include mic, rec, telecoil
Name the steps of the digital hearing aid
mic, pre-amp, A/D, DSP, D/A, receiver
AGCi affects what?
Gain, MPO, KP
gain and MPO not KP
What is frequency lowering?
moves high hz to the lower hz
What does the sound bore do?
Modifications made here can modify/alter frequency response
What type of condenser is used for today's mic? How do they differ from older versions
electret condenser- holds a charge
Define gain. How do you calculate
How much volume the hearing aid can give output-input
AGCo affects what?
Gain, MPO, KP
gain/KP but not MPO
How do directional mics work?
two omnidirectional mics used with an electronic time delay to output of rear mic.
what does a dampener do?
eliminate or lessen unwanted peak resonances created by earhooks
How do air conduction receivers work?
Work on the magnet principle, the magnet reacts to current coming from the amplifier which moves the diaphragm of the receive creating noise.
What is OSPL 90? What is a frequency response curve?
OSPL90 is the max output when using a 90 dB SPL input
frequency response curve is the curve showing the grain of a hearing aid over the frequency range the hearing aid will amplify
Describe output limiting compression
compression waits until a high input before compressing but once it does, it REALLY compresses
How does digital noise reduction work?
Reduces gain in channels where noise is dominant or have schemes that use DM to manage background noise.
What are the materials used for finished earmolds? What HL are they good for?
Acrylic/vinyl: mild to severe
Silicone: profound
Explain how a t-coil and induction loop works
t-coil converts electromagnetic energy to electrical energy for the hearing aid to use. this field picked up by the coil is generated by an electrical current having the same waveform as an audio signal.
Induction loop: the audio signal turns into an electrical current that flows through the wire, and into magnetic field. This field is sensed by coil and induces electrical charge.
explain bands vs channels
Bands are segments of the frequency response which help with gain manipulation
Channels are range of frequencies that is created by a digital filter.
Bands are grouped into channels
What is WDRC? WHat does it do?
Wide dynamic range compression. has a weak degree of compression over a wide raange of input
Dr. Brandes gave use a pyramid diagram with patient needs. Can you tell me the diagram from bottom to top?
Audibility and comfort in quiet
comfort in noise
speech intelligibility in noise
convenience, ease of use, simplicity
Purpose of an earmold
couple H/A to ear, retention, provide good seal, comfy, acoustically modify gain, frequency response and output, can be aesthetically acceptable to wear