Real Ear Measurements & Real Ear to Coupler Differences

Real Ear Measurements (REM) & Real Ear to Coupler Difference (RECD)

Some Common Terms

Real-Ear Unaided Response (REUR): SPL, or band SPL, in the open (unaided) ear canal for a given stimulus

Real-Ear Unaided Gain (REUG): Difference, in dB between the REUR and the stimulus SPL, or stimulus band SPL

Real-Ear Aided Response (REAR): SPL, or band SPL, in the ear canal for a given stimulus, with a working hearing aid in place.

Real-Ear Aided Gain (REAG): Difference, in dB, between the REAR and the stimulus SPL, or stimulus band SPL

Real-Ear Saturation Response (RESR): The REAR obtained using a narrow-band signal at a level high enough to saturate the hearing aid (usually 85-90 dB SPL)

Real-Ear-to-Coupler Difference (RECD): Difference, in dB, between the SPL produced in the ear canal and the SPL produced in a coupler by the same sound source.

Audioscan Wideband Coupler (AWC): A cylindrical coupler having a volume of 0.4cc

Thin-tube and Receiver in Canal (TRIC) adapter: Silicone attachment to the AWC which accepts the nozzle of a thin-tube or RIC type hearing aid. It will also accept the nozzle of the RECD transducer, an ER-3A insert earphone and #13 standard earmold tubing.

Wideband Real-Ear-to-Coupler Difference (WRECD): The difference in SPL produced in an occluded ear canal and in the 0.4cc coupler by a high impedance coupled sound source.

On Ear Measures - Setup

For accurate, repeatable measurements, the Verifit must be properly set up and calibrated, the client must be properly positioned and the probe tube must be properly positioned in the ear canal

Calibration of the on-ear probe microphone

For convenience, the probe microphones can be calibrated while seated in the probe dock. Ensure the connectors of both probe microphone assembles are plugged into the appropriate jack on the bootom of the probe dock. See microphone connection and On-ear calibration facts.

Right-click to raise the home menu and click on (Calibration) under (On-ear measures.)
Press the enlarged end of a probe tube as far as it will go, into the recessed opening at the top of the probe module.
Position the open end of the probe tube in front of the reference microphone inlet and press it between the posts as shown
Hold the probe dock 15-90cm (6-36in) away from and directly in front of the sound field loudspeaker with the microphone to be calibrated facing the speaker.
Left-click calibrate. The resulting curve should be similar in shape to that shown but may be shifted +/-5dB
To change the calibration interval, toggle

Positioning the Client

Sound reflections from nearby surfaces (including the operator) can cause large measurement errors, especially if the client moves between REUR and REAR measurements. Room noise can increase test time, cause errors and alter the operation of the hearing instrument being evaluated.

Choose a quiet location and position the client and the sound field speaker at least 1.5m (5 feet) away from any hard surfaces
Position the client directly in front of, and facing, the sound field speaker at a distance of 45 to 90 cm (18-36in) from the center of the head. For success in simultaneous binaural on-ear measurements, minimizing this distance is helpful.
Position the back speaker (if used) directly behind and facing the back of the client's head so that front and rear speaker are at the same height and are the same distance from the center of the clients head.

Positioning the probe tube

Use an otoscope to ensure there is no ear canal obstruction (e.g. cerumen) and to get a sense of ear canal length.
Install a new probe tube on the probe module. set the black marker ring approximately 28mm from end of probe tube for adult females, approximately 30mm from end of probe tube for adult males and approximately 20-25 mm from end of probe tube for children. These positions may be modified based on the otoscopic examination.
Clip the probe dock to the client's clothing, near the middle or to one side. If more convenient, it can alternatively be clipped to the chair back or to a lanyard. It needs to be positioned so that the probe microphone(s) will easily reach the subject's ear(s).
Hang the probe microphone on the ear, as shown below. The reference should face outwards.
Adjust the blue or red lanyard until the probe microphone module is snug against the head, directly below the earlobe (cheek level). Use the probe cables adjust clip to take up slack in the cables where necessary to ensure correct positioning.
Pull the front lanyard so that it passes behind the ear canal entrance and pass the end of the probe tube in front of the lanyard and into the ear canal.
Carefully slide the probe tube into the ear canal until the marker ring approaches the intertragal notch. Then let the front lanyard move forward to hold the probe tube in place. Use an otoscope to verify that the tube is 2 to 5 mm from the eardrum.

Speechmap

Speechmap presents hearing threshold, UCL and amplified speech spectra as SPL in the ear canal. The fitting goal is to make amplified speech audible and comfortable while avoiding discomfort of loud sounds.

Speechmap may be accessed by right clicking and selecting Speechmap under Test box or On-ear.

Speechmap is only used in SPL and this guide describes only this usage.

Speechmap facts

Speechmap is a trademarked hearing instrument fitting environment introduced by Audioscan in 1992. It presents hearing threshold, UCL and amplified speech spectra as SPL in the ear canal. The fitting goal is to make amplified speech audible and comfortable while avoiding discomfort for loud sounds. Originally speech was simulated using amplitude-modulated tonal signals. The Verifit replaces these simulated speech signals with real speech, both recorded and live.

Speechmap departs from insertion gain target methods in presenting amplification goals in the context of the residual auditory area, not as an isolated target line, and in the use of real speech, not tones or broad-band noise. This is extremely important for non-linear hearing aids, analog or digital because their processing is signal-dependent. It also makes provision to correct audiometric data and coupler measurements for age-related or individually-measured acoustic differences real ears and the couplers used for calibration and testing.

NAL-NL1 in Speechmap

the NAL-NL1 procedure seeks to amplify speech such that all bands of speec are perceived with equal loudness while maximizing speech intelligibility and ensuring that the wearer perceives speech to be no louder than that which a normal hearing person would perceive. Although NAL-NL1 states its goals for speech, it derives insertion gain targets assuming noise as a verification signal. Because it is more accurate to verify a non-linear fitting using the signal for which the procedure was developed. Audioscan converts the NAL-NL1 insertion targets to LTASS targets for amplified speech in the Speechmap environment, resulting in Speechmap NAL-NL1. The conversions use the same adult average RECD and REUG as used in DSL. The RESR targets are from Hearing Aids (Dillon, Thime Publishing, 2001, p274)

Using Speechmap

The speechmap fitting environment provides a number of distinctly different stimuli. Speech and noise are analyzed in 1/3 octave bands and for most speech stimuli data are presented as 3 curves. The tope curve is the level exceeded 1% time (speech peaks), the lower curve is the level exceeded 70% of the time (speech valleys) and the middle curve is the average. Clicking "play" causes the signal to be presented continuously - the speech signals run in a loop - and the curves are updated frequently to show any changes you make to the hearing instrument. Clicking on "record" restarts the speech passage and the curves are then calculated for the entire passage, producing an accurate display of the speech region and LTASS, and an accurate SII calculation. When using live speech, a pause button captures short-term speech features.

To access Speechmap: right click and then select Speechmap under On-ear or Test box
to change screen setup: See On-Ear Measures Screen Setup and On-ear or Test box mode
To set up hearing instruemtn type: click on the Audiometry section and select BTE, ITE, ITC, CIC, RITE (receiver in the ear - test box mode).
To enter audiometric data: see Assessment data entry
To start a test, click on "play" in any of the test areas
To select stimulus type: click the down arrow beside the stimulus window and select from the list
To select stimulus level: click the down arrow beside the stimulus window and select from the list
To complete a measurement and store the result: click on "record" while the stimulus is running
To stop a test without recording any test data: click on "stop."
To capture the current screen curves when using live speech: click on the pause button

Speechmap Screen Tour

Max TM SPL
Estimated UCL (black asterisks)
Unaided long-term average speech spectrum (LTASS; center black line in shaded region)
Impaired threshold (red line)
Normal threshold (MAP; dotted line on bottom)
Turn on/off display of unaided speech region (far right highlighted button mid-screen)
Unamplified speech (shaded region)
LTASS + 12dB (top line of shaded region)
LTASS - 18dB (bottom line of shaded region)

Speechmap Fitting Procedures

The Speechmap fitting screen provides a number of choices for inputting and applying audiometric data for the verification of hearing instrument fittings.

Speechmap Fitting Procedures

Speechmap screen choices are made by clicking on the relevant buttons for (On ear or Test Box), (Graph or Table), (dual view or Single view), (L or R or L+R), (Audiometry), (BTE + HA-4, BTE + mold, ITE, ITC, CIC, RITE, Body, Open, CROS or FM) and (Loss simulator). cliciking on (Audiometry) will cause a related section poster to be presented. Changes made on this poster are applied and the poster closed by clicking on the green checkmark. The poster may be closed without applying the changes by clicking the red x.

Defaults are the last-used choices if test setup memory has been turned on

Targets: Fitting rule: select from DSL Adult, DSL Child, NAL-NL1, NAL-NL2, Camfit restoration, Camfit equalization or none.
HL Transducer: Sound source used to obtain the audiogram. Select from (Headphone, Insert + foam, insert + mold). If Headphone is selected, average adult real-ear to dial difference is used to converted entered HL values to ear canal SPL. If insert + foam is selected the appropriate real-ear to coupler difference (RECD) is used to convert entered HL values to ear canal SPL values. If insert + mold is selected, the audiometer is no longer calibrated and a measurement protocol is provided for accurate conversion 0of entered HL values to ear canal SPL. If Measure is not selected, entered HL values are convereted to ear canal SPL as if a foam tip had been used to obtain the audiogram. If LS 45 is selected appropriate real-ear unaided gain (REUG) values at 45 decrees azimuth, will be used to convert HL values to ear canal SPL values.
Bone Conduction: Select from (N/A or Enter). If (Enter) is selected, an entry screen will be provided after the air conduction thresholds have been entered.
UCL: Uncomfortable Level. Select from (Enter or Average). If Average is selected, UCL will be estimated from entered thresholds. If (Enter) is selected an entry screen will be provided after the air (and bone) conduction thresholds have been entered. If measured UCL values are entered, these values will be converted to real-ear SPL and used as real-ear saturation response targets.
RECD: Real-ear to coupler difference. unless otherwise indicated, RECD is the difference between the SPL in an occluded ear and the SPL in the HA-1 2cc coupler produced by the same high (acoustic) impedance sound source with the same acoustic coupling. Because of standing waves in the 2cc coupler, it is not useful above 6kHz. The Verifit has adopted a 0.4cc coupler to extend the capabilities of Speechmap Test box to the 1/3 octave band at 12.5 kHz. The term Wideband real-ear to coupler difference (WRECD) has been coined to denote an RECD based on a 0.4 cc coupler rather than the HA-1 Coupler. The WRECD is the difference between the SPL in an occluded ear and the SPL in the 0.4 coupler produced by the same high (acoustic) impedance sound source with the same acoustic coupling.

Open fittings in Speechmap

On-ear mode should be used for open and vented fittings. There are no special real-ear SPL targets for open fittings - it doesn't matter how the sound reaches the TM, the perception is the same. However, the sound that escapes from a vent or open fitting may be detected by the on-ear reference microphone, interfering with the sound field equalization. for this reason, the hearing instrument must be muted during sound field equalization!

With Speechmap in the (On-ear) mode, click the instrument pull-down menu and select (Open)
Position the client and probe tube and enter audiometric data.
Place the open-fit hearing instrument on the ear with the probe tube in place, MAKING SURE TO MUTE THE HEARING INSTRUMENT.
Access Test 1,2,3 or 4. If this is the first test since selecting Open, you will be prompted to mute or turn off the hearing instrument and click the Equalize button on the setup poster. After equalization, unmute or turn the instrument on and follw the fitting procedures presented previously in this section. IT IS NECESSARY TO REPEAT THE EQUALIZE PROCEDURE WHENEVER THE CLIENT OR NEARBY OBJECTS ARE MOVED!

Binaural fitting in Speechmap

When Speechmap is set to Dual view, it is possible to analyze both left and right hearing instruments simultaneously.

Follow the instructions in Speechmap screen choices to enter audiometric data and select the fitting rule
Click binaural link between the L and R selections. Both the L and R buttons will highlight wehn binaural operation is active.
click "play" in any of the test areas to start a test. The output from both hearing instruements will be displayed simultaneously.
Once the test is started, click the (Stimulus) list button to select the stimulus type.
When the passage is being presented, adjust the hearing instrument's frequency shaping and gain for average sound so that the middle curve (LTASS) falls within the target range, shown by the "target" symbols, especially between 500-4000Hz. These target symbols are automatically adjusted for the stimulus level you select.
Click "record" to measure and store the long-term signal-averaged result. If the input level at each ear is significantly different, the signal may be repeated twice for accurate results.
Click "stop" to stop the test without recording any test data.

Speechmap Stimuli

A tone burst (MPO) stimuluse provides 128 ms bursts with 128 ms gaps at 1/3 octaves with a level of 90 dB SPL in the test box and 85 dB SPL for on-ear mode

WRECD measurement

The WRECD (Wideband Real-Ear to Coupler Difference) may be individually measured to improve the accuracy of hearing aid fittings. The measurement proceduree may be accessed by selecting WRECD from the On-ear tests list on the home menue or from the Audiometry poster within Speechmap

Calibration of the WRECD Transducer

WRECD values are stored and expressed as referenced to the 0.4cc wideband coupler (silver). A calibration of the Audioscan RECD transducer in this coupler is required at a minimum of weekly.

Connect the WRECD transducer to the WRECD jack on the Probe Dock. Prepare the system for test box tests. See Microphone connection, Calibrating test box reference microphone.
Choose WRECD from the On-ear list on the home menu.
Select the RECD couping method that will be used on the ear. Audioscan software supports both foam eartips and personal earmold, however this choice must be made prior to measurement.
Attach the TRIC adapter to the 0.4cc coupler and attach this to the blue coupler microphone.
Insert the nozzle of the WRECD transducer all the way into the opeing of the TRIC
Click on the green checkmark. This causes a broadband signal to be applied to the WRECD transducer and the 0.4cc coupler SPL to be recorded and displayed.
Select interval to toggle the measurement interval for the coupler response between daily and weekly. If set to weekly, RECD transducer calibration will expire at 12 AM Monday morning

Measure WRECD

Connect the RECD transducer to the RECD jack on the Probe Dock. (See WRECD coupler response)

Prepare the system for on-ear tests. (See Calibration of on-ear probe microphone)

Select (WRECD) on the home menu.
Select the WRECD couping method that will be used on the ear. Audioscan software supports both foam eartips and personal earmolds, however this choice must be made prior to measurement.
If no RECD calibration exists or the measurement interval has been exceeded, go to Calibration of WRECD transducer, if a valid transducer calibration exists, select (Measure real ear).
Couple a standard insert earphone foam eartip to the nozzle of the WRECD transducer. If using an earmold, seal any vent at it's outer surface.
Refer to Positioning the probe tube and insert the probe tube into the ear canal to within 2-5mm of the eardrum.
Insert the foam tip or earmold into the ear, being careful not to advance the probe tube further into the ear canal. Insertion depth should be as used with insert phones. Allow the foam tip to fully expand in the ear. Insertion depth should be as used with insert phones.
Select the green checkmark to generate the real-ear response curve (magenta) and the WRECD curve (blue). If the WRECD curve is negative and unstable in the low frequencies, check the seal of the foam tip. Increase the tip size and/or apply a lubricant to the foam tip to improve the seal. If the WRECD curve deviates more than 10dB from the average in the 4-6kHz region, check for proper probe placement and possible blockage of the tube by the foam tip or cerumen.
When these curves are stable, select the green checkmark to save them

for companion purposes, the age-related average WRECD is shown as a dotted curve on the screen. If you have accessed WRECD from the main menu, you may click the Age box to change the age for this reference curve.

WRECD results

The WRECD measurement screen shows the response of the WRECD transducer in the 0.4 cc coupler (green line; top) and in the real ear (purple line below). The difference between these curves is the WRECD (blue line at the bottom above dotted). The age appropriate average WRECD is shown for reference (dotted line).

Since WRECD uses the 0.4 coupler rather than 2cc. It is normal to see negative numbers since the volume of the wideband coupler more closely matches that of an ear. A WRECD with large negative slope in the low frequencies may indicate a poor seal between the foam tip and the ear canal, or an open vent in an earmold. A negative WRECD above 1kHz often indicates a blocked or pinched probe tube.