ANSI C63.19: Establishing Compatibility Between Hearing Aids and Cellular
A new standard sets performance requirements for the interoperability
of two increasingly common appliances.
As U.S. baby boomers age, their use of personal hearing aids for sound
amplification will surely increase. At the same time, the high-technology
device called a cellular telephone has been increasing in popularity
as its price comes down and its perceived usefulness grows. (The United
States had more than 76 million cellular telephone subscribers in 1999,
up from 61 million in 1998 and up 74 million in 10 years.) These developments
have led the electromagnetic compatibility engineering community to
begin to look at the interaction between the two electronic devices.
This investigation has been encouraged by two key U.S. agencies, the
Food and Drug Administration and the Federal Communications Commission
The American National Standards Institute (ANSI) Accredited Standards
Committee C63 on Electromagnetic Compatibility was asked by representatives
of the cellular phone and hearing aid industries to investigate the
electromagnetic interaction between the electronic hearing aid and the
wireless communications device (or cellular phone, referred to in this
article as WD). The full committee voted to examine the situation and
assigned the task to its Subcommittee 8 on EMC and Medical Devices.
Subcommittee 8 formed a working group to take up the issue. Cochaired
by Steve Berger of Siemens Business Communications Systems Inc. and
Tom Victorian of Starkey Laboratories, the working group began meeting
in 1996 and arrived at a final version of a standard in 2000. The standard
was approved by the C63 committee and then published in the American
National Standards Institute Standards Action for public review
in November. No comments on the proposed standard were received during
the 45-day public comment period. The standard is expected to be generally
available in the second quarter of 2001.
This article itemizes elements of the standard and briefly describes
its key technical sections.
The new ANSI standard is designated C63.19 and entitled "American National
Standard for Methods of Measurement of Compatibility between Wireless
Communications Devices and Hearing Aids." It encompasses both methods
of measurement and definitions of limits for establishing hearing aid
compatibility and the accessibility of wireless communications devices
to wearers of hearing aids.
The document consists of an overview; a list of references; a glossary
of definitions, acronyms, and abbreviations; three major technical sections
entitled "Wireless DeviceRF Emissions Test," "Hearing Aid RF Near-Field
Immunity Test," and "Wireless Device Audio BandMagnetic Signal
Test"; sections on acceptable performance for interoperability, test
equipment calibration and measurement uncertainty, and the test report;
and a bibliography. Appended to the standard are four normative and
five informative annexes, which are outlined in the discussion below.
Overview. ANSI standard C63.19, in its "Overview," announces
a frequency range of interest of 8003000 MHz (800 MHz to 3 GHz),
although it focuses on the two bands of 800950 MHz and 16002000
MHz (or 1.62.0 GHz). A revision already being planned will incorporate
The primary purpose of the standard is to furnish the tests and parameters
that will accurately predict the ability of a hearing-aid user to employ
a wireless communications device. Its intent is to match hearing aids
and WDs by category such that a desired level of performance is achieved.
For example, a hearing aid with above-average radio-frequency (RF) immunity
could be matched with a WD exhibiting below-average emission qualities,
and the wearer of the hearing aid would be satisfied with the quality
of hearing while enjoying the benefits of the WD.
The standard calls for wireless communications devices to be measured
RF electric-field emissions.
RF magnetic-field emissions.
T-coil mode, magnetic-signal strength in the audio band.
T-coil mode, magnetic-signal frequency response through the audio
T-coil mode, magnetic-signal and noise articulation index.
The hearing aid must be measured for
T-coil is an abbreviation for telecoil, an inductive coil used in some
hearing aids to allow reception of a magnetic-field signal instead of
an acoustic signal. The magnetic, or inductive, mode of reception is
commonly employed in conjunction with telephones, auditorium loop systems,
and other systems that provide the required magnetic-field output.
The standard is intended to apply to all types of hearing aids with
acoustic output, including behind-the-ear, in-the-ear, in-the-canal,
and completely-in-the-canal types.
Two principal conditions of exposure subject hearing aid users to undesirable
RF emissions. A far-field condition reflects the type of field a hearing
aid would experience if its wearer were standing next to someone using
a WD. A near-field condition corresponds to the more intense fields
that a hearing-aid wearer is susceptible to when using a cellular phone
or other WD. ANSI C63.19 addresses the latter case, the near-field situation.
References. In this section, the standard lists 52 relevant
documents ranging from other ANSI standards to International Electrotechnical
Commission (IEC) standards to government standards developed by the
Definitions, Acronyms, and Abbreviations. Definitions of key
words used in the standard appear in this section. Important acronyms
pertinent to the cellular phone and hearing aid industries are also
explained, including esoteric technical acronyms such as IRIL, which
stands for input-referenced interference level, the equivalent acoustic
input sound-pressure leveltypically at 1 kHzthat would produce
the same acoustic output in a hearing aid as that produced by an RF
Bibliography. Leaving aside for the moment the technical sections
of the standard and skipping to the end, the standard concludes with
a bibliography of 23 technical papers treating the challenges involved
in measuring either hearing aids or WDs.
Annexes. The following nine annexes supplement the text of the
standard. The first four are normative; that is, part of the standard's
requirements. Annexes EI are informative, which means that they
add information but are not requirements of the standard. Together they
constitute 45 pages of very valuable details regarding measurement of
the devices concerned with reference to the parameters of interest in
Annex A: Definitions of Reference Axes.
Annex B: Acoustic Test Frequencies.
Annex C: Equipment and Setup Calibration.
Annex D: Test Equipment Specifications.
Annex E: Sample Measurement Uncertainty Estimates.
Annex F: Use of Helmholtz Coils for Calibration.
Annex G: RF Envelope Comparison for U.S. WD Systems.
Annex H: Explanation of Rationales Used in This Standard.
Annex I: Alternative Test Method for RF Immunity.
Wireless DeviceRF Emission Test. The first major technical
section of ANSI standard C63.19 covers measurement of the near electric
field and the near magnetic field generated by wireless communications
devices. It is sufficient for the purposes of the standard to measure
the devices at the frequencies at which each WD is capable of transmission
as part of its normal operation. The measurements must take place in
a laboratory that complies with ANSI C63.4, "American National Standard
for Methods of Measurement of Radio-Noise Emissions from Low-Voltage
Electrical and Electronic Equipment in the Range of 9 kHz to 40 GHz."
Two small probes (one E-field, one H-field) are used in conjunction
with a probe-positioning system. The goal of this setup is a measurement
uncertainty of ±2 dB. A 5 x 5-cm region, 1 cm from the surface
of the WD, is controlled so as to be usable by a hearing aid (see Figure
1 for the test setup). To be usable, the hearing aid emissions must
be minimized to avoid excessive self-interference. This 25-cm2
area is searched via the probe-positioning system in order to find the
highest RF emissions.
|Figure 1. Magnetic field measurement test setup.
The standard describes detailed pretest and test procedures that include
both a manual scanning method and an automatic scanning method.
Hearing Aid RF Near-Field Immunity Test. This part of the standard
treats the method of measuring the level of immunity of a hearing aid
to radiated electromagnetic fields originating from a wireless communications
device. It specifies a near-field illumination technique because that
is a more realistic simulation of the near-field condition in actual
interaction between the hearing aid and the WD. The microphone-mode
evaluation of the interference effect of RF emissions from WDs is procedurally
very similar to that employed with the T-coil mode. However, in the
T-coil mode, an evaluation of the effects of base-band interference
sources must be made in order to fully appraise the signal quality a
user would receive.
The test facility must have a reasonably low ambient for acoustic noise
and must be an environment of moderate temperature and humidity. The
hearing aid must be tested with a fresh battery installed, and the battery
must be within ±5% of its rated voltage in a no-load condition.
The necessary test equipment consists of the same set of two dipoles
that was used to measure the WD, plus a signal generator, a power amplifier,
an RF directional coupler, an RF power meter, and microphones. Also
needed are a microphone preamplifier, an ear coupler, a microphone calibrator,
an audio signal generator, an acoustic transmission line, a hearing
aidimmunity test fixture, and RF cables.
The standard provides a detailed test setup and a procedure for validating
the experimental setup in order to ensure accuracy of results. The validation
procedure includes a check of RF interference to test equipment, a characterization
of tubing attenuation and resonances, an audio input-source setup (see
Figure 2), and selected pretests taken from ANSI S3.22, "American National
Standard, Specification of Hearing Aid Characteristics."
|Figure 2. Setup of the near-field immunity test for hearing
The planned revision of ANSI C63.19 would aim to improve the correlation
between this test method and the use of a gigahertz transverse electromagnetic
(GTEM) cell for immunity testing hearing aids.
Wireless Device Audio BandMagnetic Signal Test. In this
chapter, the standard describes the method for measuring the audio-band
magnetic signals from the WD. Three quantities are measured and evaluated:
first, the field intensity of the desired signal at the center of the
audio band; second, the frequency response of the desired signal measured
across the audio band; and third, the signal quality, which is defined
as the difference between the desired and undesired magnetic field levels.
The equipment used is similar to that characterized in the previous
section of the standard. The basic test configuration is shown in Figure
|Figure 3. Setup of the magnetic-field test for the WD audio
band. The optional power supply is permitted for base-band signal
measurements only; it is not allowed for noise measurements.
Calibration and Measurement Uncertainty. Under this heading,
the standard describes the baseline conditions necessary for the measuring
equipment and the ambient conditions of measurement. For example, the
measuring instruments should be marked with the date of last calibration,
date of next calibration, and validation initials or source and location
of calibration records. The measurement uncertainty is calculated with
reference to NIST Technical Note 1297, "Guidelines for Evaluating and
Expressing the Uncertainty of NIST Measurement Results."
Test Report. The test report is the means by which the test
results are presented to the appropriate procuring or regulatory agency
or to the testing laboratory for archival purposes. The report is expected
to include the test plan, the applicable standards, identification of
the unit of equipment tested, the test configuration, a list of test
equipment used (including calibration dates), units of measurement,
location of the test site, measurement procedures employed, measurement
data obtained, general and special test conditions, a summary of test
results, required signatures, and test report annexes. The document
is to be maintained by the testing organization for a period of at least
three years following the date of the test.
The "Performance" chapter of the standard presents the performance
requirements for acceptable interoperability of hearing aids with WDs.
When these parameters are met, as determined by the tests described
in the standard, a hearing aid operates acceptably in close proximity
to a wireless communications device.
Research has shown that a signal-to-interference ratio of 20 dB provides
a signal quality that is acceptable for normal operation of the hearing
aid. A 10-dB degradation (that is, a signal-to-interference ratio of
10 dB) puts the performance into an area of unacceptability. A 10-dB
improvement (from 20 to 30 dB) removes almost all the interference.
Using these research data, the standard provides tables that categorize
hearing aids and cellular phones and systems of the two on the basis
of performance. The information in these tables is reproduced here as
Tables I and II.
E-field immunity CW dB (V/m)
H-field immunity CW dB (A/m)
E-field emissions CW dB (V/m)
H-field emissions CW dB (A/m)
||30.035.0 dB (V/m)
||23.0 to 18.0 dB (A/m)
||4651 dB (V/m)+0.5 x AWF
||4.4 to 0.6 dB (A/m)+0.5
||35.040.0 dB (V/m)
||18.0 to 13.0 dB (A/m)
||4146 dB (V/m)+0.5 x AWF
||9.4 to 4.4 dB (A/m)+0.5
||40.045.0 dB (V/m)
||13.0 to 8.0 dB (A/m)
||3641 dB (V/m)+0.5 x AWF
||14.4 to 9.4 dB (A/m)+0.5
||>45.0 dB (V/m)
||>8.0 dB (A/m)
||<36 dB (V/m)+0.5 x AWF
||<14.4 dB (A/m)+0.5 x AWF
|Table I. Hearing aid and cell phone near-field
categories as defined in draft ANSI C63.19. During testing, the
hearing aid must maintain an input-referenced interference level
of less than 55 dB and a gain compression of less than 6 dB.
U Category Sum
4 or more
|Table II. System classification by joint performance
of hearing aid and wireless device, as defined in draft ANSI C63.19.
The U-category sum is the sum of the numbers of the categories in
which any two devices in question belong.
It can be seen from Table II, for example, that combining a low-immunity
hearing aid in Category U0 with a Category U3 telephone that has low
emissions produces a numerical score of 3, which means the combination
is acceptable for normal use.
More than four years of sustained effort by many individuals from the
hearing aid and wireless communications device industries have culminated
in the publication of ANSI C63.19. The measurement techniques provided
by the standard are quite complicated and exacting; they will challenge
both captive laboratories of manufacturing companies and independent
testing laboratories. But the end result of the application of this
standard should be improved accessibility to modern communications devices
for anyone wearing any type of hearing aid who wishes to communicate
A final note of interest: In December 2000, FCC released a public notice
entitled "Wireless Telecommunications Bureau seeks comment on request
to reopen the petition for rulemaking regarding hearing-aid-compatible
telephones." The C63 Committee of ANSI commented on the notice by making
the C63.19 standard its proposed answer to the challenge of the successful
coexistence of cellular phones and hearing aids.