Tutorial Effects of Tubing Length and Coupling Method on Hearing Threshold and Real-Ear to Coupler Difference Measures Samantha Gustafson, a Andrea Pittman, a and Robert Fanning b Purpose: This tutorial demonstrates the effects of tubing length and coupling type (i.e., foam tip or personal earmold) on hearing threshold and real-ear-to-coupler difference (RECD) measures. Method: Hearing thresholds from 0.25 kHz through 8 kHz are reported at various tubing lengths for 28 normal-hearing adults between the ages of 22 and 31 years. RECD values are reported for 14 of the adults. All measures were made with an insert earphone coupled to a standard foam tip and with an insert earphone coupled to each participant’s personal earmold. Results: Threshold and RECD measures obtained with a personal earmold were significantly different from those obtained with a foam tip on repeated measures analyses of variance. One-sample t tests showed these differences to vary systematically with increasing tubing length, with the largest average differences (7–8 dB) occurring at 4 kHz. Conclusions: This systematic examination demonstrates the equal and opposite effects of tubing length on threshold and acoustic measures. Specifically, as tubing length increased, sound pressure level in the ear canal decreased, affecting both hearing thresholds and the real-ear portion of the RECDs. This demonstration shows that when the same coupling method is used to obtain the hearing thresholds and RECD, equal and accurate estimates of real-ear sound pressure level are obtained. Key Words: earmolds, audiometry, real-ear measures T he use of real-ear measures is the preferred method for verifying hearing aid (HA) fittings because real- ear measures allow for the measure of HA output near the tympanic membrane. This enables the unique characteristics of a client’s ear canal to be taken into account to ensure that speech is audible and that HA output matches prescribed targets. Real-ear measures are commonly per- formed by placing a probe microphone near the tympanic membrane and using an HA analyzer to measure sound pressure level across frequency. Verification of and adjust- ments to HA output can be made in real time with the use of these systems. To compare HA performance in the ear to hearing thresholds on one graphic display, it is necessary to convert the client’s hearing threshold levels from decibels of hearing level (dB HL) to decibels of sound pressure level (dB SPL), as measured at the plane of the probe microphone. Modern HA analyzers use individually measured or stored average values to make this conversion through a series of steps represented in Figure 1. The steps are similar to those of Revit’s (1997) Circle of Decibels but are arranged in a triangular fashion. In this configuration, the points of the triangle represent measured levels (e.g., dB HL), and the sides of the triangle represent calculated transforms required to convert one measured value to another. A sound-level meter is substituted for an HA analyzer in this illustration and, as shown, levels may be transformed in either a clockwise or counterclockwise direction. Going counterclockwise, a hearing threshold level can be converted from dB HL (dial) to dB SPL near the tympanic membrane (real ear) by adding the real-ear-to-dial difference (REDD) to the dial value. One method of obtaining the REDD is by delivering a signal from the audiometer through an earphone at a specified level (e.g., 70 dB HL), measuring the SPL of that signal with a probe microphone near the tympanic membrane, and then subtracting the dial value from the real-ear value. Once this transform is obtained, it can be used to convert any given HL to SPL near the tympanic membrane and vice versa. Although this (dial + REDD = real-ear SPL) is the most direct route from the audiometer to the real ear, it is impractical to obtain these measures in a busy clinical setting, particularly with clients who are unable or unwilling to sit for prolonged probe-microphone measures. a Arizona State University, Tempe b Phoenix Children’s Hospital, AZ Correspondence to Samantha Gustafson, who is now at Vanderbilt University, Nashville, TN: samantha.gustafson@vanderbilt.edu Editor: Larry Humes Received August 15, 2012 Accepted December 20, 2012 DOI: 10.1044/1059-0889(2012/12-0046) 190 American Journal of Audiology N Vol. 22 N 190–199 N June 2013 N ß American Speech-Language-Hearing Association