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24 | Chapter 2
compact disc player (CD720, Philips, The Netherlands) and presented by the speech loudspeaker at a fixed
level of 65 dB SPL, measured at the position of the listener’s head. The soundtrack with noise from the CD
was extracted to the computer. The track was split into parts and divided over the different sound channels
in order to prevent any correlation between the channels.
Microphones
The cochlear implant users involved in the experiment were all implanted with Clarion CII (Advanced
Bionics Corp., Sylmar, CA) cochlear implants. The microphone of this implant is omnidirectional and
incorporated in the headpiece. The headpiece was located on the skull, approximately 4 cm behind the ear.
Two directional microphones systems were tested: the handheld FM-system TX3 Handymic (Phonak,
Bubikon, Switzerland) and the Linkit array microphone system (Etymotic Research Inc., Elk Grove Village,
IL), which is worn on the head. The Handymic has been designed as a wireless FM-system and can be
Fig. 2.
Results of sound level measurements on a sphere with a diameter of 30 centimeters. Measurements are done at 3 cross-sections of
the sphere for 500 and 5000 Hz.