In real-ear sound pressure level measurements using a probe microphone, insufficient probe-tube depth will most likely cause which effect on the measured high-frequency response?

• A. Increase the high-frequency response
• B. Decrease the high-frequency response
• C. Decrease the response at all frequencies
• D. Increase the low-frequency response

Answer: (B)

The point of focus here is how the exact location of the probe microphone inside the ear canal influences the accuracy of real-ear measurements, especially at high frequencies. The ear canal acts like a resonator, and the pressure at the eardrum shows a notable boost around a few kilohertz due to this resonance. If the probe-tube depth is insufficient, the microphone sits too close to the open end of the canal and does not sample the pressure peak produced by the canal’s resonance near the tympanic membrane. This misplacement leads to an underestimation of the high-frequency portion of the response. Low frequencies are less affected by small changes in insertion depth because their wavelengths are long and less sensitive to exact probe position. So, insufficient depth tends to reduce the measured high-frequency response without necessarily altering the overall low-frequency or mid-frequency results.