Real ear measurement is the measurement of sound pressure level in a patient's ear canal developed when a

hearing aid A hearing aid is a device designed to improve hearing by making sound audible to a person with hearing loss. Hearing aids are classified as medical devices in most countries, and regulated by the respective regulations. Small audio amplifiers su ...

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 The American Speech–Language–Hearing Association (ASHA) is a professional association for speech–language pathologists, audiologists, and speech, language, and hearing scientists in the United States and internationally. It has more tha ...

(ASHA) and

American Academy of Audiology American(s) may refer to: * American, something of, from, or related to the United States of America, commonly known as the "United States" or "America" ** Americans, citizens and nationals of the United States of America ** American ancestry, pe ...

(AAA) recommend real ear measures as the preferred method of verifying the performance of hearing aids. Used by

audiologists Audiology (from Latin , "to hear"; and from Greek , ''-logia'') is a branch of science that studies hearing, balance, and related disorders. Audiologists treat those with hearing loss and proactively prevent related damage. By employing various ...

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 The American National Standards Institute (ANSI ) is a private non-profit organization that oversees the development of voluntary consensus standards for products, services, processes, systems, and personnel in the United States. The organi ...

specification Methods of Measurement of Real-Ear Performance Characteristics of Hearing Aids, ANSI S3.46-2013 (a revision of ANSI S3.46-1997).ANSI/ASA Standard S3.46-2013 "Methods of Measurement of Real-Ear Performance Characteristics of Hearing Aids," Acoustical Society of America, Melville, New York, http://acousticalsociety.org/

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 manufactures had introduced this new type of computerized probemicrophone 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 An otoscope or auriscope is a medical device which is used to look into the ears. Health care providers use otoscopes to screen for illness during regular check-ups and also to investigate ear symptoms. An otoscope potentially gives a view of ...

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 In the anatomy of humans and various other tetrapods, the eardrum, also called the tympanic membrane or myringa, is a thin, cone-shaped membrane that separates the external ear from the middle ear. Its function is to transmit sound from the air ...

. Next the hearing aid is put in place. The REM system will typically produce a test stimulus from a loudspeaker situated 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 In telecommunication, insertion gain is the gain resulting from the insertion of a device in a transmission line, expressed as the ratio of the signal power delivered to that part of the line following the device to the signal power delivered to tha ...

, 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 An audiogram is a graph that shows the audible threshold for standardized frequencies as measured by an audiometer. The Y axis represents intensity measured in decibels and the X axis represents frequency measured in hertz. The threshold of hear ...

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 Frequency is the number of occurrences of a repeating event per unit of time. It is also occasionally referred to as ''temporal frequency'' for clarity, and is distinct from ''angular frequency''. Frequency is measured in hertz (Hz) which is eq ...

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.

References

{{reflist, 30em Hearing Audiology Ear procedures

History

Method

Insertion gain

Speech mapping

See also

References