News About Measuring ITEs in FONIX 5000 and 6000 Series Test Chambers
by Larry Revit, hearing scientist
The loudspeaker in the chamber is not mounted at the bottom and pointing up, as you might have thought. Instead, in order to achieve the most consistent sound field possible in such a compact space, the loudspeaker is located at the lower right, pointing at an angle upward and to the left (see drawing #1)
This orientation of the loudspeaker has a practical implication for those interested in measuring ITEs with close precision for comparing to ANSI measurements. With ITEs, the faceplate has some directional properties. Therefore, the orientation of the faceplate within the sound field affects the measured frequency response. With the FONIX system, in order to match the measuring conditions called for by the ANSI standard, the faceplate of the hearing aid should be at "grazing incidence" to the axis of the loudspeaker (see drawing #1). "Grazing incidence" means that sound coming from the loudspeaker travels across the faceplate, not towards it.
The easiest way to achieve a grazing incidence orientation of an ITE faceplate in a FONIX chamber is to place the hearing aid and coupler so the faceplate faces upward and to right (as in the drawing), the surface running from upper left to lower right. Also, it is best to have the microphone opening as close to the reference circle as possible. It's all right (although not as precise) to have the faceplate vertical and facing the right, but never angle the faceplate downward.
New Recommended Placement of the QUICK-Probe Reference Microphone
For results that are even more consistent every time you measure, and for leveling made even easier, we now recommend a slightly different position of the QUIK-Probe reference microphone . Instead of placing the reference microphone. Instead of placing the reference microphone with front surface above and in front of the pinna, place the microphone further back, so the front surface is in line with the apex (highest part) of the pinna (see drawing #2).
Happy measuring! (Accuracy is bliss.)