Real Ear Measurement (REM) is recognized as the most accurate method for verifying a hearing aid’s performance on an individual. This process ensures that the sound amplification delivered is precisely tailored to the unique acoustic properties of a person’s ear. REM is considered the gold standard for hearing aid fitting because it measures the true output of the device inside the ear canal. It provides objective data necessary to maximize the device’s effectiveness, ensuring successful hearing correction.
Defining Real Ear Measurement
Real Ear Measurement is an objective test that gauges the actual sound pressure level (SPL) produced by a hearing aid directly at the eardrum. It is often referred to as “in-situ” or probe microphone measurement. The process uses specialized equipment to determine the exact acoustic output of the hearing device while it is worn by the patient.
REM contrasts sharply with standard manufacturer default settings or 2cc coupler measurements, which are performed in a standardized test box. Manufacturer defaults are based on average ear canal dimensions and do not account for individual anatomy. Relying on these generic settings can lead to a significant difference between the prescribed sound level and the sound level actually delivered to the eardrum. REM eliminates this guesswork by measuring the sound in the unique environment of the patient’s ear.
The Importance of REM for Hearing Aid Success
Generic hearing aid programming often fails because the sound delivered is altered by the patient’s individual ear anatomy. The size, shape, and resonance characteristics of the ear canal vary significantly from person to person, even between a person’s two ears. Without an in-ear measurement, the prescribed amplification could be over- or under-delivered at the eardrum.
The ear canal acts as a natural resonator, providing an acoustic boost of up to 15 to 20 decibels in the high-frequency range. This natural amplification is captured during the measurement, ensuring the hearing aid’s programming compensates correctly. If this natural resonance is not accounted for, the resulting amplification may be inaccurate, leading to sound that is either too sharp or too weak for speech clarity.
The geometry of the ear canal is dynamic, changing shape when a person talks, chews, or moves their jaw, which affects sound delivery. REM provides the data for “target matching,” which compares the actual measured output to a prescriptive fitting formula, such as NAL-NL2 or DSL. This comparison verifies that the hearing aid delivers the precise level of gain and frequency response needed to make speech audible without causing discomfort. This precision is linked to better speech understanding and overall patient satisfaction.
The Procedure: How Real Ear Measurements are Taken
The REM procedure begins with an otoscopic examination to ensure the ear canal is clear of debris that might interfere with the measurement. A flexible probe microphone tube is then inserted into the ear canal, with its tip positioned approximately two to six millimeters from the eardrum. This close proximity is necessary to capture the sound pressure level right at the point of hearing.
Next, the audiologist performs a measurement without the hearing aid in place, called the Real Ear Unaided Gain (REUG). This measurement records the ear canal’s natural resonant characteristics. After this baseline is established, the hearing aid is placed in the ear and activated.
The system then plays a calibrated test signal, often a speech-like signal called the International Speech Test Signal (ISTS), from a loudspeaker positioned in front of the patient. The probe microphone records the sound levels produced by the hearing aid, resulting in the Real Ear Aided Gain (REAG). The REAG value shows the net amplification provided by the device across various frequencies.
Using REM Data for Hearing Aid Programming
The culmination of the REM process is verification, where the collected data is used to fine-tune the device settings. The REAG measurement is displayed on a screen as a curve overlaid with the prescriptive target curve, which represents the ideal amplification for the patient’s hearing loss. The goal is to make the measured curve match the target curve.
If the measured curve falls short of the prescriptive target, the audiologist increases the gain within the hearing aid’s software at those frequencies. Conversely, if the measured output exceeds the target, the gain is reduced to prevent over-amplification and discomfort. This objective, data-driven adjustment ensures the patient receives optimal amplification for soft, average, and loud speech inputs.
Modern hearing aid software often features “automatic target matching” tools that streamline this process, allowing the audiologist to quickly adjust the gain to meet the targets. Once the measured REAG matches the prescribed target curve (typically within a tolerance of plus or minus five decibels), the audiologist can be confident that the hearing aid is programmed to provide the best audibility and comfort for that individual.