This article addresses the most frequently asked questions about Real Ear-to-Coupler Difference (RECD), with a focus on adult hearing aid fittings. The answers are provided by Dr. Sherman Lord, Au.D., the National Clinical Trainer for e3 Diagnostics.
Please note that the discussion of RECD in this article may not apply to all hearing aid verification systems. For specific information regarding your current system, please contact the manufacturer directly.
Q1: What is the Real Ear to Coupler Difference (RECD)?
A: Real Ear-to-Coupler Difference (RECD) measures the difference in sound pressure levels (SPL) between an individual’s ear canal and a standardized coupler using the same sound source. This measurement ensures accurate hearing aid fittings by accounting for the unique acoustic properties of each person’s ear canal.
The primary use of RECD is for programming hearing aids in a test box. It is not applied during on-ear Real Ear Measurements (REM), except when insert earphones are used to measure a patient’s hearing thresholds. In this case, some REM instruments may use the RECD as part of the formula to convert hearing level (HL) thresholds from the audiogram into SPL for use on the REM system. Others use the Real Ear to Dial Difference (REDD) for the HL to SPL conversion.
RECD is especially important for pediatric fittings, where test box verification is often preferred due to the challenges of performing on-ear measurements with young patients. While not as critical for adults, measuring RECD is still recommended for the most accurate hearing aid programming.
Q2: How does RECD relate to real ear measurements?
A: Real-ear measurements directly measure the sound pressure level inside the ear canal near the tympanic membrane when a hearing aid is in place. RECD, on the other hand, accounts for the differences between the real ear and the standardized coupler that is used when programming the hearing aid in the test box. By incorporating RECD data, HCPs can ensure the hearing aid is programmed to deliver the correct amount of sound to the patient’s ear.
Q3: Do I need to measure an RECD if I verify using real ear measurement?
A: No, but with an important caveat. If you conduct on-ear REMs, the RECD does not influence the measurement results. When insert earphones are used for pure tone audiometry, certain REM systems incorporate the RECD to convert HL thresholds from the audiogram into SPL for REM measurements. Refer to the device’s user manual for specific instructions. The REM system then utilizes these converted levels to calculate audibility targets and uncomfortable loudness levels (LDLs) when LDLs are obtained from the patient and entered in the REM system.
Q4: How is RECD measured?
A: There are two steps required to measure the RECD. The first step involves measuring the SPL of the RECD transducer when connected to either a 2CC or a 0.4CC coupler, depending on the equipment you are using.
The second step requires measuring the SPL of the same RECD transducer in the patient’s ear, with the probe microphone positioned within 5 mm of the tympanic membrane. The RECD transducer can be coupled to the patient’s ear using either a foam ear tip or a custom earmold.
Q5: How do I interpret RECD results?
A: RECD results are often displayed as a graph showing the difference in decibels (dB) across different frequencies. A positive RECD value indicates that the sound level is higher in the real ear than in the coupler, while a negative value indicates the opposite.
If the RECD curve is negative and unstable in the low frequencies, verify the seal of the foam tip or earmold. If the RECD curve deviates by more than 10 dB from the average in the 4-6 kHz range, ensure proper probe placement and check for any blockage in the probe tube.
Q6: Why is RECD important in adult hearing aid fittings?
A: RECD is essential in adult hearing aid fittings because it accounts for individual variations in ear canal anatomy and acoustics. This improves the accuracy of the hearing aid fitting and should improve the overall performance and satisfaction of hearing aid users.
Performing RECD is essential in cases of eardrum perforation and mastoid ear. In both instances the RECD will differ significantly from the average, therefore measuring RECD is imperative.
Q7: How does RECD affect adult hearing aid performance?
A: If a patient’s audiogram was obtained using insert earphones and/or if the hearing aid is programmed in the test box rather than on the patient’s ear, not applying the RECD may lead to a suboptimal fitting. This can result in under- or over-amplification, distortion, poorer speech understanding, and overall patient dissatisfaction.
Q8: How often should RECD be measured?
A: Since an adult’s ear canal size and shape remain relatively constant, it is uncommon for HCPs to measure the RECD more than once. Additional measurements are typically only necessary if there is an observable change in the patient’s ear canal.
In contrast, it is important to measure the RECD regularly in children. As children grow, their ear canals do as well, leading to changes in the acoustics that can affect RECD values. Failing to monitor these changes may result in less-than-desirable outcomes.
Q9: How are RECD measurements different for children compared to adults?
RECD measurements for children can be more challenging than for adults due to the smaller size of the ear canal and the potential for movement during testing. Special techniques and equipment may be required to obtain accurate RECD measurements in children. Additionally, the interpretation of RECD results may need to be adjusted to account for the unique acoustic properties of the pediatric ear canal.
Q10: How does the type of hearing aid coupling (e.g., earmold, dome) affect RECD?
The two coupling methods used for RECD measurements are a form ear tip or the patient’s custom earmold. A dome is never used. Using a custom earmold is generally considered more accurate, as it incorporates the acoustics of the tubing and the earmold into the RECD calculation. To reiterate, the audiologist does not need to manually apply the RECD values when adjusting the hearing aid settings, as the RECD is automatically applied by the REM system.
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