AC40 Service Manual Page 29
Phasing of headphones
Before headphone calibration of DD45/TDH39 take place the phase of the speakers must be checked.
Phasing of the Headset
Start the audiometer in user mode1.
Select Left ,Tone, Rev. 125 Hz 70dBHL in channel 1.2.
Connect channel 1 of an oscilloscope to the socket on the left headphone ( set the trigger to 3.
channel 1).
Connect the Left earphone to Left output on the Audiometer and place it on the artificial ear, which 4.
again is connected to a sound level meter.
The sound level meter must be in the range 110 to 115dB.5.
Connect the channel 2 on the oscilloscope to the output of the sound level meter.6.
The oscilloscope must display both channels.7.
Looking at the oscilloscope, notice the phase difference between channel 1 and channel 2.8.
Exchange the Left earphone plug with the Right earphone plug. Replace Left earphone with Right 9.
earphone on the artificial ear
Connect channel 1 of the oscilloscope to the socket on the right speaker.10.
Looking at the oscilloscope, notice if the phase difference between channel 1 and channel 2 is the 11.
same as it was in point 8
If the phase difference is identical the headset is correct connected.12.
If not identical, the plug on the headphone must be turned 180 degrees. Make a new control to be 13.
sure that the oscilloscope picture is the same for point 8 and 11.
Calibration of test equipment
All test equipment used for the calibration of audiometers is to be calibrated annually. Calibration of all test
equipment is to be performed by a laboratory which is traceable to the National Institute of Standards and
Technology (NIST) or equivalent. Test equipment calibration documents are to be kept on file.
Calibration Mode Entering
The calibration program is activated by selecting:
Windows XP: C:\Program Files\Interacoustics\Diagnostic Suite\Calibration AD629AC40.exe
Windows 7: C\program files(X86)\Interacoustics\Diagnostic Suite\ Calibration AD629AC40.exe Follow the
instructions on the screen.
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