Terminology

for Hearing Aid Coupler, Real-Ear Measurements & Formulae

by

Robert de Jonge, 2004

 


ANSI S3.46-1997. American National Standard Methods for Measurement of Real-Ear Performance Characteristics of Hearing Aids.

ANSI S3.6-1996. American National Standard Specification for Audiometers

 



2. SPL
3. fieldReferencePoint
4. inputLevel
5. micLocation
6. RESPL
7. REAR and REAG
8. Curve
9. RESR
10. 2ccSPL_HA1
11. 2ccSPL_HA2
12. 2ccSPL
13. 3mmBore

14. 6ccSPL
15. 2ccGain

16. OSPL90
17. RECD
18. RECD_HA1, RECD_HA2
19. DialReading
20. RETSPL
21. RETSPL6cc
22. RETSPL6cc

23. CalibrationError
24. REDD

25. REUR
26. REUG
27. REIG
28. REOR and REOG
29. RECD_6cc
30. CORFIG
31. GIFROC
32. ThresholdHL
33. ACL
34. LDL or UCL



Sound pressure level

The SPL is measured in dB re: 20 µPa. SPL may be measured in a free or diffuse sound field, a hearing aid test box, an NBS-9A coupler, a 2-cc coupler, the ear canal of a real ear, KEMAR (i.e., the "average" person), or some other reference point.

SPL

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The field reference point

The location of the sound inlet to the reference mic used for equalization or measurement (during coupler or real-ear measures).

Real-ear measures of gain (like REUG and REAG) are referenced to the "field reference point" (ANSI S3.46 - 1997). This point may be at the surface of the head, or at the "subject reference point" (the midpoint of the imaginary line connecting the two ear canals).

fieldReferencePoint

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Stimulus level used to define the input level

The SPL developed in the sound field, either free or diffuse field, or in a hearing aid test box, at the fieldReferencePoint.

inputLevel

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Microphone location correction

The increased SPL at the hearing aid microphone location (as compared to the inputLevel at the fieldReferencePoint) is due to baffle effects of the head and external ear.

MicLocation varies for BTE, ITE, ITC, and CIC aids. For linear aids, increases in input are reflected in the same changes in output. If the aid is in saturation, then changes in input due to micLocation don't produce any changes in the output. For wide dynamic range compression aids (say with a 2:1 compression ratio), the output will change less (only half as much) than the micLocation correction (i.e., a 5 dB micLocation correction will only cause a 2.5 dB change in output).

micLocation

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Real-ear SPL

The SPL developed in a real ear canal, close to the eardrum (usually 5 mm or less for accurate measurements to 6 kHz).

RESPL

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Real-ear aided response/gain

The REAR is the RESPL created during aided listening.

REAR = REAG + inputLevel

REAR and REAG

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Curve

The term "curve" may be appended to any gain or response measure (REAG curve, REUR curve, etc.) to indicate a frequency response (a plot of gain or output as a function of frequency).

Note: Previously, the term "response" was used to denote the curve. What was formerly called the REAR would now be called the REAG curve.

Curve

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Real-ear saturation response

The maximum (or close to maximum) RESPL the aid is capable of delivering, measured with the aid in saturation, or the level produced by a 90 dB SPL input. The measurement may be performed with the hearing aid gain control set to use-gain.

RESR = OSPL90 + RECD - 3mmBore

RESR is not defined by S3.46-1997.

RESR

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SPL developed in the HA-1, 2-cc coupler

This is the SPL developed at the microphone located inside the HA-1 coupler.

2ccSPL_HA1

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SPL developed in the HA-2, 2-cc coupler

This is the SPL developed at the microphone located inside the HA-2 coupler.

2ccSPL_HA2

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2-cc coupler SPL

Refers to either 2ccSPL_HA1 or 2ccSPL_HA2.

2ccSPL

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18 mm long, 3 mm diameter earmold bore in HA-2 coupler

When compared to the HA-1 coupler, the horn effect of this bore produces greater high frequency output in the HA-2 coupler. The 3mmBore = 0 dB for HA-1 coupler measures.

2ccSPL_HA2 = 2ccSPL_HA1 + 3mmBore

3mmBore

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6-cc coupler SPL

The SPL developed in the coupler used to calibrate supra-aural earphones, the NBS-9A coupler.

6ccSPL

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2-cc coupler gain

The gain for a hearing aid measured in a HA-1 or HA-2 coupler.

2ccGain = 2ccSPL - inputLevel

2ccGain

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Output SPL in a 2-cc coupler for a 90 dB input, formerly called SSPL90

The maximum (or close to maximum) 2ccSPL, measured with the aid in saturation (or close to it) for a 90 dB SPL input.

OSPL90 = RESR - RECD + 3mmBore

OSPL90

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Real-ear coupler difference

As compared to the 2-cc coupler, the load impedance of the ear canal and middle ear increases output, especially for higher frequencies in the real ear.

RECD = RESPL - 2ccSPL

RECD

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Real-ear coupler difference for an HA-1 or HA-2 coupler

The RECD differs for the two couplers by the 3mmBore.

RECD_HA1, RECD_HA2

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The audiometer dial reading in dB HL

DialReading is the nominal value. The audiometer may or may not be in calibration.

DialReading

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Reference Equivalent Threshold SPL

The coupler SPL used to represent normal hearing (audiometric zero, or 0 dB HL) for a population. RETSPLs depend on the earphone (ER-3A insert or supra-aural) and coupler (6-cc or 2-cc). RETSPLs convert dB HL to dB SPL, according to ANSI S3.6-1996.

RETSPL

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Reference Equivalent Threshold SPL, 6-cc coupler

The 6-cc coupler SPL used to represent normal hearing (audiometric zero, or 0 dB HL) for a population tested with a supra-aural earphone.

6ccSPL = DialReading + RETSPL6cc + CalibrationError

RETSPL6cc

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Reference Equivalent Threshold SPL, 2-cc coupler

The 2-cc coupler SPL used to represent normal hearing (audiometric zero, or 0 dB HL) for a population tested with an insert (e.g., ER-3A) earphone.

2ccSPL = DialReading + RETSPL2cc + CalibrationError

RETSPL6cc

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Audiometer calibration error, measured in dB

The difference between the expected SPL and the measured coupler SPL. For example:

CalibrationError = 6ccSPL - (DialReading + RETSPL)

CalibrationError

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Real-ear dial difference

The difference between RESPL and the DialReading. The REDD includes any audiometer calibration error.

REDD = RESPL - DialReading

REDD

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Real-ear unaided response

The RESPL due to head diffraction and external ear resonances.

REUR = inputLevel + REUG

REUR

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Real-ear unaided gain

The difference in SPL at the fieldReferencePoint and the RESPL due to external ear resonances.

REUG = REUR - inputLevel

REUG

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Real-ear insertion gain

The increase in RESPL (as compaired to the unaided condition) caused by the hearing aid. Note: the term "real-ear insertion response" or "REIR" is no longer used.

REIG = REAR - REUR = REAG - REUG

REIG

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Real-ear occluded response/gain

The REOR is the RESPL measured with the aid in position but turned off. REOG is the insertion loss.

REOG = REOR - REUR

REOR and REOG

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NBS-9A, 6-cc coupler correction

Converts 6-cc coupler SPL to RESPL.

RESPL = 6ccSPL + RECD_6cc

REDD = RETSPL + RECD_6cc + CalibrationError

RECD_6cc

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Coupler response for flat insertion gain

Converts REIG to 2ccGain.

CORFIG = REUG - RECD + 3mmBore - micLocation

2ccGain = REIG + CORFIG = REIG + REUG - RECD +

3mmBore - micLocation

2ccGain = REAG - RECD + 3mmBore - micLocation

CORFIG

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The opposite of CORFIG is GIFROC

Converts 2ccGain to REIG.

GIFROC = - CORFIG

REIG = 2ccGain + GIFROC

REIG = 2ccGain - REUG + RECD - 3mmBore + micLocation

GIFROC

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Audiogram threshold

Conventional audiometric threshold measured in dB HL.

ThresholdHL

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Average conversational level speech

ACL is often assumed to have an overall sound field level of 65 dB SPL (+12 dB, 99%; -18 dB, 1%). ACL can be expressed in dB HL. For each 1/3-octave band SPL of speech (ACL_dBSPL) the corresponding level above threshold (ACL_dBHL) is:

ACL_dBHL = ACL_dBSPL + REUG - REDD

ACL

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Most comfortable level

MCL is usually measured in dB HL. MCL is usually viewed as the target output for amplified average conversational level speech, measured in dB HL or RESPL, etc. MCL is often calculated from ThresholdHL, or could be measured directly. Figuring out what MCL (and other loudness levels) should be is the general purpose of prescriptive procedures, like NAL-R, POGO II, DSL, etc.

REIG = MCL - ACL

MCL

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Loudness discomfort/uncomfortable loudness level

LDL is usually measured in dB HL. The OSPL90 of the hearing aid is usually set to an SPL slightly less than (i.e., the safety margin) the corresponding RESR computed from LDL. LDL is often calculated from ThresholdHL (using Pascoe's data), or could be measured directly.

RESR = (LDL_dBHL - safetyMargin) + REDD

OSPL90 = RESR - RECD

LDL or UCL

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