Real Ear Measurement (REM) is a verification procedure used by hearing healthcare professionals to ensure a hearing aid delivers the precise amount of sound intended for a patient’s ear. This process is considered the most reliable method for accurately fitting hearing aids, moving beyond simple estimates or manufacturer presets. It involves measuring the actual sound pressure level created by the hearing aid directly in the ear canal while the patient is wearing the device. The goal of REM is to confirm that the amplification perfectly matches the ideal prescription target for the individual’s specific hearing loss.
Why Ear Acoustics Demand Custom Testing
Fitting a hearing aid based solely on a patient’s audiogram and default settings is insufficient because it fails to account for the unique acoustics of the individual ear. Every person’s ear canal varies in length, shape, and size, and these anatomical differences significantly influence how sound travels and resonates. The manufacturer’s initial “first-fit” software setting relies on an average ear canal model, which rarely matches an actual person’s anatomy. This “click-to-fit” approach frequently results in the incorrect level of sound reaching the eardrum.
The physical characteristics of the ear canal cause natural acoustic effects, such as resonance, that amplify certain sound frequencies before the sound reaches the eardrum. A shorter or narrower ear canal, for example, will affect sound pressure differently than a longer or wider one. Without measuring this unique acoustic variability, the hearing aid’s programming will be based on an inaccurate assumption of sound delivery. REM is the only objective way to measure and compensate for these individual differences, ensuring the sound output is tailored exactly to the person’s needs.
How the Measurement is Performed
The REM procedure involves using specialized equipment, primarily a probe microphone system, to obtain objective data about the hearing aid’s performance. The professional first examines the ear canal to ensure no wax or debris will interfere. A very thin, flexible silicone tube, known as the probe tube, is then carefully inserted into the ear canal, placing the tip within a few millimeters of the eardrum.
The hearing aid is then placed into the ear, over the probe tube, and the patient sits facing a small loudspeaker. A reference microphone rests outside the ear to monitor the sound level coming from the speaker, ensuring the stimulus remains consistent. The system then plays various test signals, often using a calibrated speech-like signal called “speech mapping” that represents the complexity of human conversation. The probe microphone measures the sound pressure level generated by the hearing aid at the eardrum while the device is actively amplifying the test stimulus.
Translating Results into Hearing Aid Settings
The data collected by the probe microphone is displayed on a computer screen, graphically showing the actual sound output of the hearing aid across different frequencies. This measured output is then compared against a “prescriptive target,” the ideal amplification curve calculated for the patient’s specific hearing loss. The prescriptive target is a scientifically derived formula, such as NAL-NL2 or DSL, that specifies the exact gain required at each frequency to make soft sounds audible and loud sounds comfortable.
If the measured output curve falls below the target line, it indicates the hearing aid is under-amplifying sound at those frequencies, which the professional can correct immediately. Conversely, if the curve exceeds the target, the device is over-amplifying, which could lead to discomfort or sound distortion. The audiologist adjusts the hearing aid’s programming—including gain, compression, and maximum output—in real-time until the measured output precisely matches the prescriptive target. This accurate calibration ensures the device delivers the optimal performance level, resulting in improved speech clarity and listening comfort.
The Risk of Inaccurate Fittings
Skipping Real Ear Measurement carries significant consequences for the patient’s experience and the ultimate success of the hearing aids. When a hearing aid is programmed based only on a manufacturer’s average setting, the patient risks having a device that is either too loud or too quiet. Over-amplification can cause sounds to be uncomfortably loud or distorted, potentially leading to the patient removing the devices due to discomfort.
Under-amplification is a more common issue, resulting in poor speech understanding, especially in noisy environments. The user may also struggle to adapt to a sound quality described as “tinny” or unnatural, which often causes the individual to stop using the hearing aids. Patients fitted with REM achieve better hearing outcomes and report higher satisfaction, minimizing the need for multiple follow-up appointments for adjustments missed in the initial fitting.