General Operation 47
5. Choose SPEAKER to enable only the speaker, MONO EAR to enable only the left
channel of the earphone jack, STEREO EAR to enable both channels of the earphone
jack, or ALL ON to enable both earphone jack channels and the speaker.
6. Press [EXIT] to return to the measurement screen.
2.5.6 Using Impulse Rejection
Impulse rejection reduces the amount of noise measured in the testing environ-
ment by working together with the noise reduction setting. When the impulse
rejection is set, the FP35 looks for sudden increases in the signal equal to at
least as much as the set impulse rejection and lasting at least half as many
measurements as the set noise reduction. If an impulse is found meeting those
specifications, that measurement is ignored. For example, if the noise reduc-
tion setting is 8, and the impulse rejection is 12, the FP35 analyzer will look
for (and reject) impulses of at least 12 dB, lasting for up to 4 measurements.
This is useful for noisy testing environments. The USER LEVEL must be set to
ADVANCED in the Default Settings menu. See Section 2.3.3
2.5.7 Using an External Speaker or Sound Chamber
It is possible to use an external sound chamber for performing coupler measure-
ments, and an external sound field loudspeaker for performing real-ear measure-
ments.
In order to make the FP35 analyzer as portable and as lightweight as possible,
its sound chamber necessarily had to be fairly small. We have compensated for
its size by making every effort to occlude exterior noise from entering the sound
chamber, and by recommending that the coupler be included in the chamber
during the leveling process. However, a large chamber will give better sound
isolation and make it easier to position hearing aids.
If you have the Real-Ear Option, you also might find it handy to use an external
sound field speaker for your measurements. The external speaker can be mount-
ed to a floor stand or to a swing arm. A swing arm is especially nice because
you can move the speaker around the patient when you switch ears, rather than
move your patient around the speaker.
The external sound chamber and the external sound field speaker can both
use the external sound field speaker jack on the back panel of the FP35. If it
is desired to connect the external sound chamber and the external sound field
speaker at the same time, the internal speaker can be disconnected entirely, and
the internal speaker jack can be used to connect the external sound chamber. If
this is done, the external sound chamber will be treated as the “internal” speak-
er by the FP35 analyzer’s software..
