science

Real ear measurement

Real ear measurement is a science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Real ear measurement rather than just read about it. In short: Real ear measurement is the measurement of sound pressure level in a patient's ear canal developed when a hearing aid is worn. It is measured with the use of a silicone probe tube inserted in the canal connected to a microphone outside the ear and is done to verify that the hearing aid is providing suitable amplification for a patient's hearing loss.

Key takeaways

Real ear measurement belongs to science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Real ear measurement to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Real ear measurement from memory before moving on to harder problems.

Reference excerpt

Real ear measurement is the measurement of sound pressure level in a patient's ear canal developed when a hearing aid is worn. It is measured with the use of a silicone probe tube inserted in the canal connected to a microphone outside the ear and is done to verify that the hearing aid is providing suitable amplification for a patient's hearing loss. The American Speech–Language–Hearing Association (ASHA) and American Academy of Audiology (AAA) recommend real ear measures as the preferred method of verifying the performance of hearing aids. Used by audiologists and other hearing healthcare practitioners in the process of hearing aid fitting, real ear measures are the most reliable and efficient method for assessing the benefit provided by the amplification. Measurement of the sound level in the ear canal allows the clinician to make informed judgements on audibility of sound in the ear and the effectiveness of hearing aid treatment. The use of real ear measurement to assess the performance of hearing aids is covered in the ANSI specification Methods of Measurement of Real-Ear Performance Characteristics of Hearing Aids, ANSI S3.46-2013 (a revision of ANSI S3.46-1997).

History The first commercially produced real ear measurement available was made by Rastronics. Help soon arrived. In the early 1980s, the first computerized probe-tube microphone system, the Rastronics CCI-10 (developed in Denmark by Steen Rasmussen), entered the U.S. market (Nielsen and Rasmussen, 1984). This system had a silicone tube attached to the microphone (the transmission of sound through this tube was part of the calibration process), which eliminated the need to place the microphone itself in the ear canal. By early 1985, three or four different manufacturers had introduced this new type of computerized probe microphone equipment, and this hearing aid verification procedure became part of the standard protocol for many audiology clinics.

Method

First, the clinician will examine the ear canal with the use of an otoscope to ensure no wax or other debris will interfere with the positioning of the probe tube. The probe tube is placed with the tip approximately 6 mm (1/4 inch) from the tympanic membrane. Next the hearing aid is put in place. The REM system will typically produce a test stimulus from a loudspeaker situated 12–15 inches (30–38 cm) from the patient's head and simultaneously measure the output in the ear canal to determine how much amplification the hearing aid is providing.

Insertion gain The traditional method of real ear measurement is known as insertion gain, which is the difference between the sound pressure level measured near the ear drum with a hearing aid in place, and the sound pressure level measured in the unaided ear. First a measurement is made with the probe tube in the open ear (Real Ear Unaided Response, or REUR), then a second one is made using the same test signal with the hearing aid in place and turned on (Real Ear Aided Response, or REAR). The difference between these two results is the insertion gain. This gain can be matched to targets produced by various prescriptive formula based on the patient's audiogram or individual hearing loss.

Speech mapping Speech mapping (also known as output-based measures) involves testing with a speech or speech-like signal. The hearing aid is adjusted so that the speech is amplified to the approximate middle of the patient's residual auditory area (the amplitude range between the patient's hearing threshold and upper limit of comfort) while observing a real-time spectrum display of the speech in the patient's ear canal. Many multi-channel hearing aids allow each frequency channel to be adjusted separately. The aim is to find a good compromise between intelligibility and loudness discomfort. This approach to hearing aid testing is implemented in most current real ear systems and there has been a significant increase in audiologists selecting to verify using the output method. Using a real speech signal to test a hearing aid has the advantage that features that may need to be disabled in other test approaches can be left active, and the effects of these features in normal use are included in the test.

Illustrations

Worked examples

Example 1 — a first encounter with Real ear measurement

Start with the simplest possible case. Write down what Real ear measurement claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Real ear measurement before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Real ear measurement ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Real ear measurement

In research: Real ear measurement appears in science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Real ear measurement in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Real ear measurement is common in secondary-school and first-year university syllabi. It links to neighbouring topics Audiology, Ear procedures, Hearing, so understanding it makes those chapters shorter.
In everyday life: Look for Real ear measurement outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Real ear measurement in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Real ear measurement means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Real ear measurement out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Real ear measurement in simple terms?

Why does Real ear measurement matter?

Because it connects several science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Real ear measurement?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Real ear measurement.