Real ear measurement (REM) is a way for an audiologist to verify that your hearing aids are actually delivering the right amount of sound to your ear canal. A tiny microphone on a thin tube is placed inside your ear alongside your hearing aid, and it measures exactly what sound is reaching your eardrum. Without this step, your hearing aids are programmed based on averages that may not match your ear at all. In fact, research published in the American Journal of Audiology found that 71% of hearing aids failed to hit their prescribed targets at one or more frequencies when using the manufacturer’s default settings alone.
Why Default Settings Often Miss the Mark
Every hearing aid comes with a “first fit” algorithm from the manufacturer. This software estimates how much amplification you need based on your hearing test results and a set of average ear canal dimensions. The problem is that ear canals vary significantly from person to person in both size and shape. A larger ear canal has different resonance properties than a smaller one, and those physical differences change how sound behaves before it reaches your eardrum. Two people with identical hearing loss on paper can receive very different sound levels from the same hearing aid programmed the same way.
The research on first-fit accuracy is striking. When researchers compared manufacturer defaults to established prescription targets, the sound levels delivered were systematically lower than what patients actually needed. The gap was as large as 22 dB at some frequencies, with the biggest shortfalls at 1 kHz, 1.5 kHz, and 4 kHz. These are frequencies critical to understanding speech. At 1 kHz alone, 37% of fittings missed the target by more than 10 dB. At 4 kHz, 32% missed. After the audiologist adjusted the hearing aids using real ear measurements, the failure rate dropped from 71% to just 18%.
How the Measurement Works
The core equipment is simple: a thin silicone probe tube connected to a microphone, a reference microphone that sits near your ear, and a loudspeaker. You sit in a chair, typically facing the speaker at a distance of about half a meter. The audiologist threads the probe tube into your ear canal, positioning the tip within about 5 to 6 millimeters of your eardrum. For adult women, the tube is usually inserted about 28 mm past a visible landmark at the ear canal opening. For adult men, it’s 30 to 31 mm. For children, 20 to 25 mm.
The loudspeaker plays a calibrated sound signal. With the probe tube in place but no hearing aid inserted, the system first measures how your ear canal naturally handles sound. This is your baseline. Then your hearing aid is placed in the ear alongside the probe tube, and the measurement is repeated. The system now shows exactly how much amplification the hearing aid is providing at each frequency, displayed against a target curve that represents what you should be receiving based on your hearing loss.
The audiologist can then adjust the hearing aid’s programming in real time, watching the measured output move closer to or further from the target. Speaker placement matters for accuracy: 0 degrees (directly in front of you) or 45 degrees to one side both produce reliable results, while 90 degrees to the side introduces significant measurement errors.
Prescription Targets: What Your Hearing Aid Should Hit
The target curves displayed during real ear measurement come from one of two widely used prescription formulas. Each takes your hearing test data and calculates how much amplification you need at each frequency, but they approach the problem differently.
The first, called NAL-NL2, aims to maximize your ability to understand speech while keeping overall loudness at a comfortable level, no louder than what a person with normal hearing would experience. The second, called DSL v5, focuses on making sounds at each frequency feel as loud as they would for someone with normal hearing. In practice, DSL tends to prescribe more amplification and produces a louder overall experience. Both formulas provide separate targets for children and adults, with children receiving higher gain because they need stronger signal levels to reach the same speech recognition performance as adults.
Neither formula is universally “better.” Your audiologist selects one based on your age, hearing loss profile, and listening needs. What matters is that whatever target is chosen, the hearing aid actually meets it. That’s what real ear measurement confirms.
Live Speech Mapping
A newer variation of real ear measurement uses live speech instead of generated test signals. Called live speech mapping, it displays the hearing aid’s output in real time while someone talks, whether that’s the audiologist, a recording, or even a family member’s voice. The display shows the amplified speech signal against the prescription target and your hearing thresholds, making it immediately visible whether conversational speech is being amplified into your audible range.
This approach has a practical advantage beyond precision: it’s a powerful counseling tool. When your spouse speaks into the system, both of you can see on screen exactly where their voice falls relative to what you can hear. Research by Cunningham and colleagues found that using live speech mapping during fittings reduced follow-up visits and saved money, likely because patients left their initial appointment with a better understanding of what their hearing aids were doing and more confidence in the fit.
What Professional Guidelines Say
The American Speech-Language-Hearing Association (ASHA) identifies probe microphone measurement as the preferred method for verifying hearing aid performance. Their guidelines strongly support real ear measures as the primary verification tool and recommend they be performed unless a physical limitation prevents it, such as an unusually narrow ear canal, active drainage, or excessive earwax blocking the tube.
Despite these recommendations, not every hearing aid fitting includes real ear measurement. Some providers rely on the manufacturer’s software to estimate performance, or use the patient’s subjective impressions to guide adjustments. The evidence consistently shows this is less accurate. Multiple studies over decades have concluded that first-fit programs cannot be relied on to provide gain consistent with a prescription formula, and that real ear measurements should be used to make corrections.
Does REM Affect Whether You Keep Your Hearing Aids?
Hearing aid return rates are a major concern for both patients and providers. A recent study published in ASHA’s Perspectives journal tracked 532 hearing aid recipients and found an overall return rate of about 9%. The group that received a full audiology-based best practice fitting, which included real ear measurement, had the lowest return rate: 8 out of 176 patients returned their aids, compared to 15 out of 165 in a consumer-directed group and 23 out of 171 in an “efficient fit” group that streamlined the process.
Interestingly, the study found that the degree of match to prescription targets alone didn’t statistically predict returns. What did correlate with keeping hearing aids was a patient’s self-reported benefit score. Those who kept their aids rated an average 14% improvement on a standardized benefit questionnaire, compared to 7.5% among those who returned them. This suggests that real ear measurement matters most as part of a thorough fitting process. Getting the sound right is necessary, but so is ensuring the patient perceives a meaningful difference in daily life.
What to Expect at Your Appointment
The entire process typically adds 10 to 15 minutes to a hearing aid fitting. You won’t feel the probe tube once it’s placed, though the insertion can feel slightly unusual for a moment. The sounds played through the speaker are moderately loud but not uncomfortable. You’ll sit still and avoid talking during measurement periods, which last only seconds each.
If you’re getting new hearing aids, ask your audiologist whether they perform real ear measurement as part of their fitting protocol. If you already wear hearing aids and have never had this verification done, it’s worth requesting. Given that the majority of default fittings miss their targets at one or more frequencies, there’s a reasonable chance your hearing aids could be performing better than they are right now.