Procedural considerations in the real-ear measurement of completely-in-the-canal instruments

Conventional procedures for measurement of the real-ear aided response (REAR) of hearing aids are performed by placing the probe tube 5 mm beyond the medial tip of the canal portion of the earmold or shell and within 5 mm of the tympanic membrane. Completely-in-the-canal (CIC) instruments insert more deeply into the ear canal, and thus may make adherence to conventional probe-microphone procedures impossible. The REAR was measured at several probe tube insertion depths, using two insertion methods: through a probe vent and alongside the CIC shell. Results indicated that conventional probe insertion depth is not necessary for CIC instruments and may place some clients at risk for discomfort due to contact of the probe tube with the tympanic membrane. Placement of the probe tube along-side the CIC shell rather than through a probe vent resulted in slit leak venting effects that were highly variable across subjects. A probe tube placement protocol for use with CIC instruments is suggested.