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Amplification I > Lecture 7 > Flashcards

Lecture 7 Flashcards

1
Q

Define gain

A

Gain refers to the difference between the input intensity (reaching the HA microphone), and the output intensity (from the HA reciever)

Gain = output - input

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2
Q

Define frequency response

A

The gain at various frequencies

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3
Q

Define saturation response

A
  • Maximum output that the HA can produce
  • In a saturation response, a higher input does not translate to a higher output
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4
Q

Define input-output function

A
  • Output as a function of input (the gain provided by the hearing aid will depend on the input level)
  • Depending on the input, we will see a certain level of output (on the graph, at 45 dB, input and output are equal which is a 1:1 compression ratio)
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5
Q

How does the sound signal get into the HA?

A

Microphones convert acoustic energy into electrical energy and deliver sound into the HA

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6
Q

Do microphones have to be protected? If so, what from and how?

A
  • Microphones of HAs are “electret” microphones, and must be protected in the devices themselves and from electromagnetic interference
  • A microphone is typically surrounded by metal (microphone can)
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7
Q

What makes the microphone work?

A
  • Backplate amplifier
  • FET
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8
Q

What is the frequency range of microphones?

A

HA electret microphones have a wide frequency response (very suited for speech and environmental signals)

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9
Q

What two things are HAs sensitive to?

A
  1. Moisture
  2. Humidity
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10
Q

What is essential to microphones?

A

Highly important to keep the microphones clear of debris (which can block the mic port or damage internal components)

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11
Q

Do microphones create noise? How much?

A

Yes, usually between 25-30 dB SPL

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12
Q

What are some ways to keep a HA dry?

A
  • Desiccant bead kit
  • Electrical dryer
  • Built in dryer to charger
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13
Q

Where are the microphones located on a custom HA?

A

On the face plate

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14
Q

The microphone is on the ____ of the HA

A

Outside

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15
Q

What is telling the HA how to work and function?

A

The DSP (digital signal processing chip)

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16
Q

What 5 things does the DSP chip do?

A
  1. User settings (volume control, audiogram)
  2. The processing algorithms (how to treat sound based on the environment)
  3. Instruction sets (battery usage, on and off)
  4. Timing and sequencing information (how quickly things happen, different environments)
  5. Memory (manual programs, data logging)
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17
Q

What do hearing aids have to do first in order to process sound?

A

Convert the signal!

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18
Q

What are the steps of signal conversion?

A
  1. Mic picks up sound
  2. Conversation from analogue to digital
  3. DSP chip does the processing of the signal
  4. Sound is changed back to acoustic energy and is delivered back to the ear through the receiver
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19
Q

How does the sound get delivered?

A
  • Though the receiver
  • Receivers are the speakers of the HA: processed sound exits the HA to be delivered to the ear
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20
Q

Do receivers vary in gain?

A

The smaller receivers have less gain potential than the larger receivers

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21
Q

Where is the receiver in a custom HA?

A

Sound outlet

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22
Q

Where is the receiver in a RIC?

A

Sitting in the canal covered by a custom piece or dome

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23
Q

Where is the receiver in a BTE?

A

outside of ear delivered into ear by ear hook

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24
Q

Explain wax guards

A
  • Wax filters should be changed at least once a month
  • If HA is sounding muffled, change the wax filter
25
Q

Where is a wax guard in a custom HA?

A

Right at the end of the device

26
Q

Where is a wax guard in a RIC?

A

When you take the dome off, the wax guard is there

27
Q

What are 4 different options to change the volume on a HA?

A
  1. Toggle/rocker switch (indents when you push it)
  2. Wheel (on custom HAs, rolling forwards turns it up, rolling backwards turns it down)
  3. Push button (great for 2 HAs: R HA turns both up, L HA turns both down)
  4. Touch-sensitive surface (not the best because no tactile response)
28
Q

What are some off-ear devices to adjust volume on HAs?

A
  • Connection through app
  • Remote control
29
Q

Can you manually change program buttons?

A
  • Changing between automatic and manual program stored in the HA
  • Programs may also be changes by remote or app
  • If there is a single button, change can be determined by how long you press the button
30
Q

What are telecoils (t-coils)?

A
  • An alternative way to introduce a sound signal to a HA wirelessly
  • Picks up sound through an electromagnetic induction signal to provide a wireless signal direct to the HA
  • Generally in a public venue with connection to landline phones (phones have a T-rating)
  • Different models will denote if a t-coil is available (look for “T” on the model description)
31
Q

How do t-coils work in public venues?

A
  • Loop systems have great benefits when competing with background noise or distance
  • various configurations to the HA microphones selected in the program settings (T, MT, mT)
32
Q

What can t-coils be affected by?

A

Interference: fluorescent lights and electrical wires

33
Q

What is a T tele-coil

A

Microphone muted, full induction signal (just telecoil)

34
Q

What is an MT tele-coil

A

We want the microphone and telecoil signal to be equal (people get a boost from the telecoil, but still have access to the microphone)

35
Q

What is an mT telecoil?

A

Reduce microphone quite a bit, but the telecoil is dominant

36
Q

Explain assistive listening devices?

A

FM systems & DAIs

37
Q

How does an FM system work? How is the sound recieved?

A
  • FM receivers bring frequency-modulated sound from one source, directly into the HA
  • The signal is received through a direct-audio input device, such as a “boot” or “Shoe”
38
Q

What is the benefit of an FM system?

A

Improved SNR, and overcome distance

39
Q

Who benefits most from FM system?

A

Do a SIN test to see who will benefit most from FM (these are ideal candidates)

40
Q

How does wireless streaming work?

A
  • Bluetooth allows the wireless streaming of audio signal from one device to another
  • Bluetooth connections can be from several devices
41
Q

Explain ingress protection

A
  • How HA components are protected
  • IP ratings suggest how well HAs can stand up to debris and moisture
  • First digit: solid material debris/dust (1-6)
    • Wax, dust, skin
  • Second digit: moisture (1-8)
  • Ex) IP65
42
Q

How does a HA perform compared to how it should perform?

A
  • It is imperative that prior to fitting a HA for a patient, we first are certain it has passed a level of quality control, which can be done:
    • With the manufacturer: when aids arrive, there should be documentation that determines if it has passed
    • In clinic
43
Q

What do we do in clinic to see if a HA is performing well?

A
  • We can perform an electroacoustic analysis (ANSI) of hearing instruments with the verification equipment to determine if it is performing well
  • Verifit
44
Q

What is ANSI?

A
  • The american national standards institute
    • Sets the standards for hearing instruments
  • Defines parameters and the allowable tolerances for hearing instrument function (within specs)
  • Quantifying if a HA is weak, distorted, noisy (measured in a test box)
  • If a device does not meet specifications, it may indicate a need for repair
45
Q

What does our hearing instrument analyzer (test box) do?

A
  • We set the aid in the test box for ANSI testing, connect to the programming software to test mode
  • We will determine if the HA is set to FULL ON GAIN (FOG) or REFERENCE TEST SETTINGS (RTS)
  • All adaptive features of the HA should be turned off (feedback managers, noise reduction features, and compression setting)
46
Q

ANSI testing - output sound pressure level with 90 dB input (OSPL90)

A
  • What are we measuring?
    • How much power output is the HA capable of?
  • How are we measuring?
    • A 90 dB stimulus, across a frequency range is presented, and the output is measured in the coupler
  • Tolerance: within 3 dB of specifications
  • Note: this is different than setting the MPO of the HA in fitting verification
47
Q

ANSI testing - high frequency average output sound pressure level 90 dB input (HFA-OSPL90)

A
  • What are we measuring?
    • What is the average output of the frequencies of 1000, 1600, and 2500 Hz (unless a manufacturer sets a different set of frequencies)
  • How are we measuring it?
    • A 90 dB stimulus, across a frequency range is presented, and the output is measured, and the average of the frequencies aforementioned
  • tolerances: within 4 dB of specifications
48
Q

ANSI testing - response curve full-on gain with 50 dB inputs (FOG)

A
  • What are we measuring?
    • What is the output of the HA when HA gain is set to maximum, with a softer input?
  • How are we measuring it?
    • A 50 dB stimulus, across a frequency range is presented, and the frequency response output is measured
  • Tolerances: within 5 dB of specifications set by the manufacturer
49
Q

ANSI testing - high frequency average full-on-gain (HFA-FOG)

A
  • What are we measuring?
    • What is the average output with the 50 dB input of the frequencies of 1000, 1600, and 2500 Hz (unless the manufacturer sets a different set of frequencies)
  • How are we measuring it?
    • A 50 dB stimulus, across a frequency range is presented, and the output is measured, and the average of the frequencies aforementioned
  • Tolerances: within 5 dB of specifications set by the manufacturer
50
Q

ANSI testing - reference test gain (RTG)

A
  • What are we measuring?
    • The response of the HA at an appropriate user setting with a softer input (near average speech)
  • How are we measuring it?
    • A stimulus is presented (usually at 60 dB) across a wide range of frequencies, the response is measured with the volume control at a normal level (60 dB input = speech)
  • Tolerances: informational purposes only, no tolerances specified by ANSI
51
Q

ANSI testing - total harmonic distortion (THD)

A
  • What are we measuring?
    • Is there good fidelity of the signal from input to output? Are there any other frequencies or harmonics generated?
  • How are we measuring it?
    • Distortion is measured in percentages
  • Tolerances: no more than 3% compared to manufacturing specifications
52
Q

ANSI testing - equivalent input noise (EIN)

A
  • What are we measuring?
    • How much internal noise is the HA itself creating
  • How are we measuring it?
    • Calculation of the noise creating by the HA with no signal present
  • Tolerances: no more than 3 dB above the manufacturers specifications
53
Q

Where is noise created in a HA?

A

Microphone

54
Q

What is expansion?

A
  • Reduce the output for low-level inputs
  • Can effect this measurement and the specifications sheets must note if expansion was used during measurement
55
Q

ANSI testing - battery current drain

A
  • What are we measuring?
    • If the drain of the battery is reasonable, and is measured in mA
  • How are we measuring it?
    • Testing the draw of the battery in the following setting
    • Quiescent, with 65 dB input, and 90 dB inputs
  • Tolerances: should not exceed 20% of the maximum value specified by the manufacturer
56
Q

What can battery drain depend on?

A
  • Where the volume control is set
  • The inputs
  • The use of streaming
57
Q

When is it a good idea to have ANSI testing performed?

A

Before the devices are set for patients

58
Q

What are the 8 ANSI tests?

A
  1. Output SPL with 90dB input (OSPL90)
  2. High frequency average output 90dB input (HFA-OSPL90)
  3. Response curve full on gain with 50dB input (FOG)
  4. High frequency average full on gain (HFA-FOG)
  5. Reference test gain (RTG)
  6. Total harmonic distortion (THD)
  7. Equivalent input noise (EIN)
  8. Battery current drain

Amplification I (14 decks)

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