Real-ear measurement is an essential verification tool used during the hearing aid fitting process to measure the sound pressure level in the ear canal when a hearing aid is worn. To complete this measurement, a thin silicone probe tube is placed in the ear canal. The tube is connected to a microphone that measures the output of the hearing aid to ensure that the hearing aid is meeting the user’s prescriptive targets (based on the patient’s hearing test results). Common practice is to use real-ear measurements to verify that soft, average, and loud speech is meeting the patient’s prescription. Real ear measures also verify that loud sounds are not too loud through the hearing aid.
History of Real Ear Measurement
The first commercial real-ear measurement systems became available in the early 1980’s when they were able to create a system with a thin, silicone microphone to place comfortably in the ear canal. Now there are many available real-ear systems that allow for tone sweep and speech mapping measurements. Improvements in the systems now allow for both ears to be run simultaneously, and compatibility with hearing aid programming softwares to make changes in the programming while measurements are being run for more accurate fine-tuning. Consistent, widespread utilization of real-ear measurements in audiology clinics has been disappointingly slow since that time though it is widely accepted as an important component of ‘best practices’ for hearing aid fittings.
Why perform Real Ear Measures?
Real ear measures are a vital component of the hearing aid fitting to ensure an accurate fitting. Each patient’s ear canal has a unique shape and size, which ultimately affects the amount of amplification, or intensity of the sound at the eardrum. To conceptualize this, imagine the difference in sound created when singing in a small closet vs singing in a large, reverberant concert hall. Much different, right? The same thing happens when you program a hearing aid based on the same test results but place it into a very small human ear canal vs a very large human ear canal. These individual differences in anatomy must be taken into account to obtain an accurate hearing aid fitting. When real-ear measurements are NOT performed, the hearing care provider is just “guessing” the amount of amplification that the patient is ultimately receiving. Conversely, when real ear measurements are performed, the provider can ensure that the patient is receiving the prescribed amount of amplification for different speech levels across the frequency spectrum. Real-ear measurements also confirm that loud sounds are not TOO loud, which is another important component of a successful hearing aid fitting.
What is the basic process of REM?
To perform real-ear measurements, the audiologist first looks into the ear canal with an otoscope to ensure the canal is free of wax or debris that would affect the measurement. Next, a soft, thin silicone probe tube is placed in the patient’s ear canal approximately 5 mm from the ear drum. The soft probe tube may “tickle” the canal slightly. The patient is placed 12-15 inches from a speaker that will present the test stimulus. He/she is instructed to remain quiet while the test stimulus is being presented to measure the amplification from the hearing aid in the ear canal.
Calibration of the Probe Microphone
Real-ear measurement equipment has probe calibration guidelines outlined by the equipment manufacturer. Most units require you to complete a probe tube microphone calibration prior to testing to account for individual differences in probe tubes prior to playing the test stimulus. For probe tube calibration, the probe tube is secured directly in front of the ear level microphone, the calibration tone is presented and the calibration is completed.
Real Ear Unaided Gain (REUG)
The external ear canal is able to create a natural amplification or gain with it’s unique “S” shape, which can be measured using real-ear measurements and defined as the real ear unaided gain (REUG). The peak of this amplification typically occurs around 2600-3000. REUG can be calculated by subtracting the level of the incoming input signal from the real ear unaided response (REUR). REUR is essentially the resonance of the external auditory canal (ear canal). This resonance is calculated by measuring the absolute sound pressure level from an input signal using a real- ear probe tube which is placed approximately 5 mm from the tympanic membrane (eardrum).
Real Ear Occluded Gain (REOG)
The Real Ear Occluded Gain (REOG) from a hearing aid or earpiece is measured by placing the hearing aid (or earpiece) in the ear, but turned OFF. This measurement can be useful to obtain in order to determine the amount of attenuation caused by occluding the ear with a hearing aid or earpiece. This is used to help the audiologist determine appropriate venting for an earmold or hearing aid, or select the appropriate dome size during the hearing aid fitting process.
Real Ear Aided Response (REAR) or Real Ear Aided Gain (REAG) 100-150 words
Real ear aided response (REAR) is measured when a hearing aid is placed in the ear canal turned ON and set to desired settings; the frequency response generated from the hearing aid to a particular input signal (above the ambient noise level). Real ear aided gain is used as a reference for calculating real ear insertion gain.
Real ear aided gain (REAG) is the amplification or the gain measured in the ear canal across the frequency spectrum. REAG is calculated by subtracting the input signal level from the REAR.
Real Ear Insertion Gain (REIG)
Real ear insertion gain (REIG) is the quantified gain added by the hearing aid alone in the ear canal. REIG can be calculated by either subtracting the REUG from the REAG across frequency spectrum or by subtracting the REUR from the REAR across the frequency spectrum. Real ear insertion gain is useful when compared against prescriptive targets to determine if a hearing aid at its current setting is meeting a prescribed insertion gain target. The prescriptive target most commonly used in clinical settings is the NAL-R target.
Real Ear Measurement Method
Real ear measurements provide an objective, reliable means for verifying a hearing aid fitting and determining that the prescribed gain targets are being met with the user’s hearing aid(s). However, proper calibration, probe tube placement, and loudspeaker location must be accurately controlled in order to ensure accurate results. In addition, otoscopy by a qualified hearing care professional must be completed prior to conducting real ear measurement to ensure that the ear canal is healthy & not blocked by cerumen (ear wax) or debris.
Proper probe tube placement requires a trained professional. The probe tube is placed ~5 mm from the eardrum to ensure the response is accurately measured, especially in the high frequencies which can be most affected by a bad probe tube placement.
Real Ear Measurement Speech Mapping
Speech mapping is a form of real-ear measurement that uses speech or calibrated speech-like stimuli as the test signal. There are a number of advantages to speech mapping over traditional real-ear measurements with artificial stimuli; thus, speech mapping has become the preferred and most commonly clinically utilized type of real-ear measurement conducted in clinical practice.
The effective amplification from the hearing aid can be determined with speech mapping using realistic, relatable stimuli (speech) with the hearing aid in its prescribed user settings in its normal mode of operation. The influence on the response of the hearing aid features such as noise reduction, feedback cancellation, compression speed, etc are automatically taken into account and the interferences created by artificial test signals are avoided.
The typical clinical protocol is to present soft speech, average speech, and loud speech stimuli and measure the response with a probe tube in the ear canal to confirm that all of these speech levels are being appropriately amplified by the hearing aid to meet prescriptive targets across the frequency spectrum. If too much or too little amplification is recorded in a particular frequency region for a particular input level, the gain in the hearing aid can be adjusted accordingly and the measurement is re-run to re-verify that prescriptive targets are being met.
Are real ear measurements necessary?
Real ear measurements are a vital component of a successful hearing aid fitting. Without real ear measurements, the hearing care provider is blindly “guessing” at the amount of amplification generated by the user’s hearing aid because individual differences in ear canal anatomy are not taken into effect. For two patients with the exact same hearing test results, the hearing aid needs to be programmed very differently for someone with a very small ear canal vs an individual with a large ear canal; without performing real ear measurements these individual differences are not accounted for. As an informed consumer, patients are encouraged to ask your provider if real ear measurements are performed as a part of the fitting process.
Programming hearing aids is truly an art, and accurately performing real ear measurements is just one important component of the picture. Trained hearing care professionals take into account the patient’s ear anatomy, comprehensive hearing test results, previous hearing aid experience (or lack of experience that may have led to auditory deprivation effects), sensitivity to loud sounds, dexterity, technology needs (phone, tv, video conferencing, etc), medical conditions, and cognitive concerns when fitting a hearing aid. Even the most advanced and most expensive hearing aid is truly only as good as it is professionally programmed and fit to the user.
Utilization of real-ear measurements provides a reliable, clinically validated way to ensure that hearing aids are meeting prescriptive targets and allows audiologists to take into account individual differences in ear anatomy when programming devices. At Clarity Audiology & Hearing Solutions, our highly trained Doctors of Audiology are committed to providing best practices and so we consistently utilize real-ear measurements (speech mapping) as part of our hearing aid fitting process. We perform speech mapping measurements not only at the initial fitting, but also when changes in hearing aid programming, or hearing aid venting are made to confirm that hearing aids are meeting prescriptive targets (and adjusting them accordingly) when acoustical parameters are changed. Because we are committed to making sure our patient’s hearing aids continue to work optimally for the long run, speech mapping measurements are then also performed at all of our patients’ routine hearing aid check appointments, which are typically scheduled every 6 months, to verify that the devices are still meeting prescriptive targets.