Frye FONIX FP40D - Manual (Page 104)

96 FONIX FP40 Portable Hearing Aid Analyzer
13. Output limit status
14. Selected ear
15. Graph containing unaided and aided gain response
5.5.2 Performing AI measurements
Performing AI measurements is just like performing normal insertion gain measurements. Follow
the instructions in Section 5.3.2 and 5.3.3. Instead of choosing IG in step 2 of Section 5.3.2, use
F2 to choose the AI display. Alternately, perform the insertion gain measurements as normal in the
Insertion Gain display, and then press F2 to switch to the AI display. All measurements will be auto-
matically converted from insertion gain to dB HL.
5.6 DSL Coupler Measurements
Since the DSL fitting method is often used on small children who are hard to fit using conventional
real-ear testing methods, often coupler measurements are performed to match corresponding cou-
pler targets.
If possible, it is recommended to perform a real-ear to coupler difference (RECD) measurement on
the child in order to generate an accurate coupler target. When it is not possible to perform a mea-
sured RECD, an average RECD corresponding to the child’s age can be used.
5.6.1 Performing the RECD measurement
RECD is the real-ear-to-coupler difference: the difference between the acoustical resonance of a 2-cc
coupler and the acoustical resonance of a person’s unaided ear canal. It is calculated by subtracting
the frequency response of an insert earphone inside a 2-cc coupler from the frequency response of
the same insert earphone placed inside the client’s ear.
Why would you want to take the RECD? Well, DSL was developed for fitting hearing aids on chil-
dren, and, as anyone who has fitted an aid on a child knows, it is sometimes hard to make the
infant or child sit still long enough to perform good real-ear measurements on them. So, if you can
just make them sit still long enough to get a real-ear unaided response, you can get the RECD and
use it to convert real-ear targets to coupler targets. Then, you can test the aid all you want in the
coupler and send the child to stay with his parents in the waiting room while you program and test
the hearing aid in the sound chamber. If you have a really uncooperative patient, you can even just
rely on the average RECD for the child’s age group and forgo any real-ear measurement entirely. Of
course, when the child gets old enough to sit still long enough to get a good real-ear measurement,
real-ear measurements are the way to go.