from audio to hi style, gain, & output

From Audiogram to HI Style,Gain & Output

The pure tone audiogram provides an indicator for those who might benefit from hearing instruments.

Those presenting with more hearing loss (especially in the low frequencies), will generally perceive a greater disability and will investigate hearing instrument benefit.


Let’s review in Dillon page 257-261 and Figure 9.2 for more detail regarding hearing threshold hearing levels and hearing instrument ownership vs. “usership”.


As we discussed last week, those hearing impaired who are more aware of their hearing disability and lifestyle activity limitation i.e. self reported disability, are often the ones seeking assistance from hearing instruments.


When they access your clinic for hearing help, there are factors which must be addressed.

1. What are their hearing thresholds and residual hearing performance abilities?

Comprehensive audiogramAcceptable hearing-in-noise levelsHearing-in-noise abilitiesLoudness Discomfort Levels by frequency


2. What is their listening/communication environment, needs, and expectations?Quiet environmentNoisy environmentSedentary lifestyleActive lifestyle

NOTE: Lifestyle preferences will often dictate hearing-in-noise ability testing.


3. Stigma and perceived age including cosmetic concerns. They believe HI use will make them

appear “old”Fear & concern of reduced self-image

Note: The size of the hearing instrument transcends all age categories of HI users.


4. Hearing instrument manipulation and management.

Hand the patient/client a style of instrument you are considering to fit and assess their reaction

Determine if they can manipulate the controls and change the battery

NOTE: An elderly patient may regard the ease of management as the most important aspect to the hearing instrument selection.


5. Age & PersonalityAging often involves health problems which

often may preclude the decision to access hearing instruments

Various personalities will respond differently to the acceptance of hearing instrument use

NOTE: Personalities and their reactions to rehabilitation with hearing instruments is described in Dillon page #271


Let’s discuss the summary of potential obstacles to the acquisition and use of hearing instruments as described in the summary box found upon page #273 of Dillon.


Dillon describes three types of unwilling patient/clients on pages #274—277. They are:Unwilling due to lack of awarenessUnwilling to accept hearing loss

conditionUnwilling to try HI’s or other

rehabilitation activity


It should be noted that for any of these three unwilling patient/client types, that a demonstration of instant-fit hearing instruments may provide them with first-hand information to consider.


The audiogram and electroacoustics have often been a challenge when attempting to apply the audiometric data to the audibility requirements of the patient/client—much less their loudness comfort!

Let’s first discuss audibility (electroacoustic gain)


Let’s look at the audiogram as a picture of a damaged cochlear bio-amplifier.

We learned that the outer-hair cell function of the cochlea contributed to the Wide Dynamic Range Amplification of the cochlear bio-amplifier performance.


The audiometric “picture” of hearing loss, at about fifty decibels HL, reveal to the dispensing professional that there are very few outer hair cells contributing to the cochlear amplifier process.

NOTE: Past fifty decibels will often result in modified gain requirements for patient/client audibility.


Electroacoustic Gain for Audibility

First, calculate the average hearing loss at 500Hz, 1000Hz, & 2000Hz (decibel level of hearing loss for each frequency added and then divided by three)


Electroacoustic Gain for AudibilitySecond, locate the required ANSI high frequency gain (HFA gain) information supplied for/with hearing instrument electroacoustic specifications.

This is information may be obtained by placing the HI into a ANSI test box or viewing the specification information supplied by the manufacturer.



Third, take the three frequency pure tone average, divide that decibel level by two and add six.

(PTA divided by two plus six = Gain)



This will provide the information to determine the amount of electroacoustic HFA gain to select for your patient/client with fifty decibel or less pure tone average hearing loss.


Electroacoustic Gain for AudibilityTo select the HFA electroacoustic gain for audiometric pure tone average hearing loss greater than fifty decibels, you add twelve.

(PTA divided by two plus twelve = Gain)



This is due to the reduced performance of the outer-cells within the cochlear amplifier; and a greater reliance upon electroacoustic stimulation from the hearing instrument.


Dillon has described the rationale for modifying the NAL-NL1 formula into NAL-NL2 formula.

This rationale is described on page #314 of his second edition text.

You will notice the new formula has been modified to use more recent loudness model information.


Dillon’s loudness model detailed description may be found in table 10.2 on page #328.

You will notice it calculates the output sound pressure levels based upon the pure tone average at 500Hz, 1000Hz, & 2000Hz.

It converts the HL information into sound pressure level information.


OUTPUT = COMFORTIt is stated within the first paragraph below this table that these output values should be correct eighty percent of the time.


To be correct eighty percent of the time:you would calculate the three frequency

average pure tone hearing loss as revealed by the audiogram

then refer to the ANSI electroacoustic specification information supplied by the ANSI test box and/or manufacturer.

select the output parameters from table 10.2 in Dillon


OUTPUT = COMFORT

This output matching to the table detail, will give you the opportunity to select the correct output eighty percent of the time!


OUTPUT = COMFORT

To have the opportunity to be closer to one hundred percent, you may measure frequency specific LDLs using a warble or masking tone.


This should be performed for four primary reasons. They are:1. Most hearing instruments fit today are

multi-channel digital

2. Predicted LDL values may be off by as much as thirty decibels

3. Fully stimulate residual dynamic range

4. Address frequency specific recruitment


Multi-channel digital hearing instruments which have the ability to limit maximum output by channel should also have further output modification as listed in Dillon table 10.4 on page #330.

This is due to frequency summation as most received signals are frequency complex in nature.


There are many reasons for not exceeding LDL with electroacoustic output as well as for fully stimulating the residual dynamic range of each ear.The most obvious for not exceeding is

avoiding loudness discomfort for the patient/client.

The less obvious is reducing the affects of auditory deprivation over years of hearing instrument use.


For a comprehensive list of considerations for the selection of hearing instrument style, let’s review table 11.1 in Dillon on page #337.

Their detailed descriptions upon the following pages #338--#346 will assist with specific considerations for the style selection process.


We will continue our discussion next week regarding the physical components required for the custom fitting of various hearing instrument styles.

from audio to hi style, gain, & output

Education

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gain output dillon

hearing disability

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hearing help

style of instrument

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