Probe Tube Microphone Probe Tube Microphone MeasurementsMeasurements

(Basics and Definitions)

Greg Nassar Greg Nassar

MCHAS Team

University of Manchester

Prescriptive Prescriptive TargetsTargets

Best Fit within Best Fit within Fitting SoftwareFitting Software

Probe Tube Probe Tube Microphone Microphone Measures Measures

2cc Coupler2cc Coupler

Targets Targets Based on Based on

Pure TonesPure Tones

KemarKemar

Different Different Input levelsInput levels

Individual ear Individual ear canal sizecanal size

Individual Individual ear canal ear canal acousticsacoustics

Targets Targets based on based on SpeechSpeech

Probe tube

Measurement microphone

Reference microphone

Supporting wire

Probe TubeLight Reflex

Umbo

ULL

HTL

Real Ear Unaided Response

Clinical measurement of Real EarUnaided Response (REUR)

Real Ear Unaided Response

REURThe SPL as a function of frequency in the unoccluded ear canal. Is expressed as either SPL or gain in dB relative to the stimulus level.

Real Ear Unaided Response

REURThe SPL as a function of frequency in the unoccluded ear canal. Is expressed as either SPL or gain in dB relative to the stimulus level.

Real Ear Unaided Response

Real Ear Aided Response

REURThe SPL as a function of frequency in the unoccluded ear canal. Is expressed as either SPL or gain in dB relative to the stimulus level.

REARThe SPL as a function of frequency in the ear canal with the hearing aid in place and turned on.Also known as in situ response and is normally displayed as dB SPL

Real Ear Aided Response

Real Ear Unaided Response

REARThe SPL as a function of frequency in the ear canal with the hearing aid in place and turned on.Also known as in situ response and is normally displayed as dB SPL

REURThe SPL as a function of frequency in the unoccluded ear canal. Is expressed as either SPL or gain in dB relative to the stimulus level.

Real Ear Unaided Response

Real Ear Aided Response

REARThe SPL as a function of frequency in the ear canal with the hearing aid in place and turned on.Also known as in situ response and is normally displayed as dB SPL

REURThe SPL as a function of frequency in the unoccluded ear canal. Is expressed as either SPL or gain in dB relative to the stimulus level.

Clinical measurement of real ear aided response (REAR)

Real Ear Unaided Response

Real Ear Unaided Response

Open Ear Gain

Open Ear Gain

Insertion Gain

Open Ear Gain

Insertion Gain

Target Insertion Gain

Open Ear Gain

Insertion Gain

Target Insertion Gain

The difference in dB as a function of frequency between the REUR and the REAR (REIR=REAR-REUR).The real ear insertion gain is the value in dB of the REIR at a specific frequency

In adults the REIR is the measure of choice in verifying the electroacoustic characteristics of the chosen hearing aid meet the prescribed gain and desired frequency response.

PTM’s on Children

REAR should be used rather than REIR. The REAR will prescribe the same gain at the eardrum for a given hearing loss, regardless of ear canal size and shape.

This ensures target speech levels at the child’s eardrum will meet the requirements of the hearing impaired ear despite changes in resonant frequencies of the child’s ear canal over the first few years of life.

ULL

HTL

RESR

Is the SPL as a function of frequency in the ear canal with the hearing aid in place and turned on. The measurement is obtained with the stimulus level sufficiently intense as to operate the hearing aid at its’ maximum output level.

RECD

Is the difference in dB as a function of frequency between the outputs of a hearing aid measured in the real ear versus a 2cc coupler.Using these measurements the real ear performance of the hearing aid can be predicted.

Key Points to Take Away!

REIG target based upon the average adult ear canal resonance

Not appropriate to ear canal with different acoustic properties to average adult ear

REAR target based upon the desired SPL at the eardrum

This is always the same for a given hearing threshold (dB SPL) regardless of the size of the ear canal…..

However the output of the hearing aid still needs to be corrected for differing ear canal sizes