Frye FONIX FP40D - Manual (Page 122)

114 FONIX FP40 Portable Hearing Aid Analyzer
5.10 FM Systems
For users who test FM Systems, a comprehensive guidebook is available free of charge. Contact the
factory and request the publication Testing FM Systems with FONIX FP40 Analyzers
5.11 Testing Directional Aids
Perhaps the most convenient way to test directionality is with a real-ear measurement. You can use
the Insertion Gain screen on the FP40 analyzer to show you the forward and reverse responses as
well as a curve showing the directional advantage. All you need is a swivel chair to turn the client
around during testing, or an external speaker on a swing arm to move the speaker around the cli-
ent.
Since we’re going to use the Insertion Gain screen for this measurement in order to show the differ-
ence between the forward and reverse responses, we’re going to treat the reverse measurement as
the “unaided” measurement and the forward measurement as the “aided” measurement.
5.11.1 Reverse Measurement
1. Set up the analyzer as you would for any real-ear measurement. Use a 0° azimuth position-
ing when you level the sound field speaker. See Section 5.1 for details.
2. Insert the probe tube and the hearing aid.
3. Turn OFF the reference microphone. To do this, press F1 from any real-ear measurement
screen and change the REFERENCE MIC setting to OFF under Probe Settings. Use the
AMPLITUDE and FREQUENCY knobs and the START/STOP button to make this selection.
Press F1 again to return to the real-ear measurements screen.
4. Look above F2 on any real-ear measurement screen. IG should be highlighted. If it is not,
select IG with F2.
5. Select the source type with F7. If available, choose one of the Digital Speech signals or the
Composite signal. Otherwise, select the pure-tone FAST signal.
6. Make sure UNAIDED is highlighted above F2. If it is not, you may need to press F2 to high-
light it.
7. Select the source signal using the AMPLITUDE knob. The source should be above the noise
floor of the room, but as quiet as you can make it and still get accurate real-ear measure-
ment. The reason for this is that you don’t want the aid to go into compression while you are
trying to test the directionality characteristics. If possible, use a source of 50 dB SPL; noisy
test environments may force you to use a louder level.
8. Turn the patient around so the speaker is pointed towards the “null” spot of the hearing aid.
For some aids, this is 180°. For other aids, it might be a different angle. Alternately, if you
are using an external speaker on a swing arm, you can swing the speaker around to the back
of the patient. Maintain the distance from the patient and the speaker that you used for lev-
eling. See Figure 5.11.1.