Real-ear-to-coupler Difference Research Articles

Optimizing your RECD measurements

The real-ear-to-coupler-difference (RECD) measurement captures an individual's occluded ear canal acoustics for the purposes of selecting and fitting amplification. A practical, step-by-step guide to measuring the RECD is offered.

Perforation of the tympanic membrane and its effect on the real-ear-to-coupler difference acoustic transform function.

It is not always possible to undertake extensive real-ear measurements, especially in infants and young children. An alternative approach is to estimate the real-ear SPL by use of an acoustic transform function such as the real-ear-to-coupler difference (RECD). This may be used to estimate the real-ear sound pressure level (SPL) obtained from an insert transducer or a hearing instrument. The aim of the present study was to investigate the effects of tympanic membrane perforation on the RECD transform function. Subjects in the study comprised two groups of 12 individuals aged between nine and 65 years. One group of subjects had a tympanic membrane perforation and was recruited to the study before admission for myringoplasty. There was no evidence of middle ear pathology in the remaining subjects who comprised the control group. An RECD transform function for an insert transducer was measured on each subject using the standard clinical protocol on the Audioscan RM500 real-ear measurement system. There was a statistically significant difference between the two groups; mean RECD transform value of the perforation group was 9-12 dB lower than the corresponding value in the control group at audiometric frequencies below 1.5 kHz. This difference is probably due to the perforation acting as a vent and allowing low-frequency acoustic energy to escape into the middle ear cavity. Use of an average RECD transform function to estimate real-ear SPL in subjects with a perforation will overestimate the SPL reaching the tympanic membrane. As a result, the derived real-ear SPL obtained by use of either an insert transducer or a hearing instrument will be overestimated. This has implications for the selection and verification of a hearing instrument. The difference in the mean RECD transform function between the control group and subjects with a tympanic membrane perforation supports the use of individually measured RECD values wherever possible.

Practical Considerations of Real-Ear-to-Coupler Difference Measures in Infants

The purpose of this study was to investigate some of the practical issues surrounding the use of the real-ear-to-coupler difference (RECD) measure in infants in clinical settings. Twenty-two newborns were seen once a month during their first year of life for the purpose of obtaining RECD measurements. Two methods for obtaining the RECD were examined: the commonly used constant insertion depth method and the acoustic method. Differences between the results of the two methods were examined as well as test-retest reliability for each. Findings suggest that no compelling evidence exists to support the use of one of these methods over the other. Use of either method resulted in good test-retest reliability in the midfrequency range of the RECD, with poorer reliability on both ends of the frequency spectrum. Test-retest reliability decreased with increasing age for both methods. In addition, reliability of between-ear RECD values was examined. Between-ear measurements were most reliable in the midfrequency range, and reliability decreased slightly with increasing age.

Insertion gain measurements using two low-powered analogue hearing aids.

Differences between insertion gain measurements and coupler measurements were investigated using two different hearing aids, to assess the accuracy of hearing aid fitting methods which involve the use of real-ear-to-coupler differences (RECDs). The hearing aids used were the NHS BE19 and the Lavis X11. They were allocated alternately to 80 new adult hearing aid users, and insertion gain measurement was carried out with the allocated aid on all subjects, and with both hearing aids on 36 subjects. Coupler measurements were also carried out with both hearing aids, at two different gain settings. Comparison of the coupler measurements and the insertion gain measurements suggests that the differences in insertion gain produced by different hearing aids cannot be predicted accurately from the differences in coupler gain measurements produced by the same aids. Although the use of RECDs measured using insert earphones may accurately predict the real-ear performance of some models of hearing aid, this method may not produce equally satisfactory results with other models.

Probe-Tube Microphone Measures in Patients with Open-Mastoid Surgery: Real-Ear-to-Coupler Differences and Real-Ear Unaided Responses

Real-ear-to-coupler differences (RECDs) and real-ear unaided responses (REURs) were measured using a probe-tube microphone system in 15 patients who underwent open mastoid surgery. The results show that RECDs are significantly smaller at higher frequencies (1.5, 2.0, 3.0, 4.0 and 6.0 kHz) in mastoid ears. The intrasubject variability of RECDs measures in these patients is on average 2.6 dB larger than for controls. For REURs, mastoid surgery significantly reduced the mean peak resonant frequency without affecting the amplitude and bandwidth. In operated ears, mean resonant frequency is by a factor of 1.4 lower than that for normal ears. Reduced responses (negative gains) at frequencies above the resonance peak occurred in 7 out of the 15 patients. These reduced responses corresponded to the smaller RECD at the middle and high frequencies. The results support the need for individual RECD measures to be made in operated ears instead of using average values from normal subjects. Otherwise, real-ear measures of the aided response should be made for each patient with open-mastoid cavity and the fitting should be done in terms of the target response at the eardrum rather than by defining a target insertion gain.

Real-Ear to Coupler Difference in Patients with Ear Drum Perforation

The aim of this study is to investigate the effects of ear drum perforation on real-ear to coupler difference (RECD) in adults. RECD was measured using a probe tube microphone system in 22 patients with ear drum perforations. Twenty-two normal subjects served as controls. For normal subjects, RECD was in good agreement with the values reported in the literature. For the perforated ears, the RECD was up to 8 dB smaller in the frequency range from 0.5 to 1 kHz. There was no significant difference at frequencies below 0.25 kHz and above 1 kHz. A much larger intersubject variability was found in the experimental group. The mean intersubject standard deviation was 4.4 dB in the experimental group as contrasted with 2.2 dB in the control group. Neither the equivalent ear canal volume nor the perforation size appeared to be correlated with the degree of RECD reduction over lower frequencies. These results strongly suggest the need for individual RECD measurements, rather than using the average normal RECD, to appropriately compensate for the reduced transmission of lower-frequency sounds in fitting hearing aids for patients with ear drum perforations.

Validity and repeatability of level-independent HL to SPL transforms.

The purpose of this study was to evaluate the reliability and validity of the real ear to coupler difference (RECD) and the real ear to dial difference (REDD) in predicting real ear SPL (RESPL). The RESPL, RECD, and REDD were measured in the right ear of 24 normal-hearing subjects using probe microphone equipment and both insert and supra-aural earphones. The phones and probe tube were removed and replaced, and the RECD and REDD were remeasured. RESPL was predicted using the RECD for insert earphone data and the REDD for supra-aural earphone data. Reliability estimates were calculated as the difference between test and retest values for the RECD and REDD. Validity estimates were calculated as the difference between measured and predicted RESPL. Results indicate that the RECD and REDD have equal and high reliability and validity in predicting RESPL. It is concluded that the RECD and REDD may be used as level-independent HL to SPL transforms as a substitute for in situ audiometric procedures.

Real-ear to coupler differences in children with grommets.

Real-ear to coupler differences (RECDs) are important for the selection of appropriate amplification characteristics for hearing impaired children. The aim of this study was to investigate the effects of patent grommets on RECDs in children. Subjects were 32 children aged between 4 and 7 years, 16 had a patent grommet in one or both ears as confirmed by otoscopy and large equivalent ear canal volumes on tympanometry. There was no evidence of middle ear pathology in the remaining 16 who comprised the control group. All real-ear and coupler measures showed good test-retest repeatability across the whole frequency range. The mean difference in RECDs between the two groups in the frequency range 0.125-0.75 kHz was 15 dB. The differences in RECDs were statistically significant (P < 0.01) for all frequencies below 0.75 kHz. There was a strong correlation between the mean RECD and equivalent ear canal volume at all frequencies between 0.125 and 0.5 kHz, and a moderate correlation at 0.75 kHz. Large inter-subject variability was found, with a maximum standard deviation of 6.6 dB at 4.0 kHz. Therefore, this study supports the need for individual RECD measures to be made, particularly for subjects with grommets, rather than using averaged transformation figures. It suggests that more low frequency gain should be given to hearing aid users with patent grommets to overcome the reduced SPL in the ear canal, due to leakage through the vented tympanic membrane.

A modified hearing aid fitting procedure using both real ear and 2cc coupler measurement system.

In order to reduce the test time in real ear hearing-aid fitting for children, the validity of applying the average real ear to coupler differences (RECDs) in prefitting procedure using a 2cc coupler measurement system was evaluated by checking whether the majority of people's RECDs might occur within 5 dB of the average RECDs (N = 116) in each test frequency and age group. The percentages of occurrence were around 90% in test subjects' RECDs in saturation sound pressure levels (SSPLs) and around 70% in gain in each important test frequency. Appropriate test frequencies in prefitting are 500, 1000, 1500 and 2000 Hz.

Repeatability of a Real-Ear-to-Coupler Difference Measurement as a Function of Age

For a given individual, the applicability of an average real-ear-to-coupler transfer function in the fitting of hearing aids is of limited utility, because the acoustical properties of individual ears may differ substantially from average transformation values (Feigin, Kopun, Stelmachowicz, &amp; Gorga, 1989; Fikret-Pasa &amp; Revit, 1992). It has been suggested, therefore, that individual real-ear-to-coupler difference (RECD) measures should be obtained whenever possible and applied within the fitting process (Hawkins, 1992; Nelson Barlow, Auslander, Rines, &amp; Stelmachowicz, 1988). The purpose of this study was to investigate the repeatability of a specific RECD measurement procedure that has been developed for clinical application with young children (Moodie, Seewald, &amp; Sinclair, 1994). The test-retest reliability of this procedure is reported for 10 adults and 90 children in the birth-to-7-year age range.

Impact of "Standard" Earmold on RECD

Output from a moderate-gain behind-the-ear hearing aid was measured in HA-1 and HA-2 couplers. For the HA-1 coupling, a standard full-shell earmold with #13 tubing throughout was used. The results suggest that when this earmold configuration is used, the gain and output assumed from HA-2 specifications may not be realized in the higher frequency region. Questionnaires sent to all U.S. earmold manufacturers indicated that only one of those manufacturers considered a “standard” earmold to be one incorporating a “horn” effect in the canal portion of the mold; over 70% of the manufacturers reported inserting tubing to the end of the canal portion as a standard procedure. Measures of real-ear-to-coupler differences (RECD) should be obtained with consideration for this earmold effect.