The RECD is the “real-ear to coupler difference.” It is the difference between the acoustical resonance of a 2-cc coupler and the resonance in the ear canal. There are actually two difference measurements performed to obtain the RECD: the coupler measurement and the real-ear measurement.
To do this procedure on the FP35, you will need a 50-ohm insert earphone. You can obtain this from Frye Electronics. You can use an insert earphone from an audiometer, but make sure that it is a 50-ohm earphone, and you will probably need a 1⁄4 inch to 3.5 mm adapter. The resistance of the insert earphone is printed on the box for each ear.
Coupler measurement
The coupler measurement is considered a calibration procedure. The resonance inside a 2-cc coupler is constant, so it does not have to be measured for every patient. For this reason, the coupler part of the RECD is performed in an FP35 calibration screen.
- Plug the insert earphone into the “earphone” jack on the back of the analyzer.
- Remove the foam eartip from the insert earphone and attach the insert earphone tubing to the tubing of the HA-2 coupler.
- Insert the coupler microphone into the HA-2 coupler. See Figure A.
- Press [MENU] from the Opening screen.
- Press [F4] to enter the Earphone Calibration screen.
- The selection “Calibrate Ins. Earphone” should be selected.
- Press [START] twice to perform the measurement.
- Select “Calibrate Ins. Earphone (RECD)” with the down arrow key.
- Press [START] twice to perform the measurement.
- Press [F5] to save the calibration into permanent memory.
- Press [EXIT] three times to return to the Opening screen.
Figure A: Coupler setup for the RECD
The coupler measurement will need to be re-measured after the analyzer microphones are calibrated.
Real-ear measurement
The real-ear measurement is performed in the Audiogram Entry screen.
- From the Opening screen, press [F2] to enter Real-ear mode
- If the screen title does not say “Real-ear Audiogram Entry”, press [NEXT] until it appears.
- Press [MENU] to open the local menu.
- Select the desired ear using the left-right arrow keys.
- Select ASSESSMENT with the up-down arrow keys.
- Use the left-right arrow keys to select INS. EAR.
- Press [EXIT] to close the local menu.
- Press [F2] repeatedly until “RECD Select” is displayed above F2.
- Look at the bottom right corner of the display. If you see the message “Earphone not calibrated,” you will need to perform the coupler measurement described in the section above.
- Press [F3] to select MEASURE RECD.
- Plug the insert earphone into the “earphone” jack on the back of the FP35. Make sure you use the same earphone that was used for the coupler measurement.
- Insert the probe microphone into the patient’s ear as usual.
- Carefully insert the foam eartip or custom earmold attached to the insert earphone into the patient’s ear without moving the probe tube. See Figure B.
- Press [START/STOP] on the analyzer to take the RECD. The results will be displayed in graphical and numerical format on the display.
Figure B: Real-ear setup for the RECD
Troubleshooting
If the RECD values do not seem right:
- Make sure the probe tube is inserted correctly and that the probe tube is clear of debris.
- Make sure the insert earphone is inserted correctly and connected to the analyzer.
- Check the validity of the coupler measurement.
To check the validity of the coupler measurement, you can use the black probe adapter:
- Thread the probe tube through the black probe adapter and secure in place with a dab of Fun Tak.
- Insert the adapter into the HA-2 coupler. Connect the insert earphone to the HA-2 coupler.
- Follow the steps for the real-ear measurement described in the section above except keep the probe adapter setup described here. This performs the “real-ear” measurement with the probe microphone connected a 2-cc coupler. If the coupler measurement part of the RECD is valid, the resulting RECD should be within 2 dB of zero between 200-4000 Hz. The RECD response at 6000 and 8000 Hz is susceptible to noise and not always consistent.
- If the coupler measurement is greater than 2 dB at any value between 200 and 4000 Hz, it is recommended to repeat the coupler measurement.