GRAS RA0401 Externally Polarized High-Frequency Ear Simulator

Two Improved Versions of the IEC 60318-4 (711) Ear Simulator

The ever-increasing demand from consumers for new features, better quality and lower prices put a constant strain on audio and electronics manufacturers to differentiate on cost efficiency, shorter time to market and outstanding performance. At GRAS, we acknowledge your challenges and try to overcome these by pushing the boundaries of what is possible within precision measurement microphones.

For more than three decades, the IEC 60318-4 ear simulator has been the recognized industry standard for testing audio transducers with a realistic simulation of the acoustical load presented by the human ear. However, its undamped resonance at 13.5 kHz makes it difficult to use for high-frequency testing. Therefore, GRAS has introduced two improved variants of the IEC 60318-4 ear simulator. They retain a firm footing in the standard but improve the ability to measure at high frequencies. Discover the evolution of the IEC 60318-4 ear simulators here.

The GRAS RA0401/02 High-Frequency Ear Simulator is based on the standard IEC 60318-4 ear simulator, but extends the useful frequency range to 20 kHz. 

The GRAS RA0403/04 Hi-Res Ear Simulator is based on the standard IEC 60318-4 ear simulator, but extends the useful frequency range to 50 kHz and beyond. You can learn more about and its specifications here.

The New Normal 

The Standard IEC 60318-4 (711) Ear Simulator (GRAS RA0045) has a step half-wave resonance at 13.5 kHz which effectively limits its usefulness to below at least 10 kHz and it uses a ½" microphone.

However, the RA0401/02 has a damping system that attenuates the half-wave resonance at 13.5 kHz and thus extends the useful frequency range to 20 kHz. It uses the same ½” microphone as the original version and fully complies with the standard. This is why we recommend it as the first choice when you are looking for a “standard” 60318-4 ear simulator - but without its shortcomings at high frequencies. We think of it as “the new normal”.

It is now possible to measure up to 20 kHz. Total Harmonic Distortion (THD), frequency response and driver resonance related phenomena can now be investigated, and an objective supplement to the ”golden ear” approach is now available for concept validation, R&D, and production testing – all based on a ”human-like” test method. In the High-Frequency Ear Simulator, the length-related resonance is damped and the resulting frequency response is much clearer. It is now easier to distinguish the headphone driver resonance from the ear simulator resonance. THD measurements are now less influenced by resonance-related peaks. 

Explore the benefits

Our new ear simulators build on industry standards- and improve upon them in important ways. They introduce major improvements: High-frequency capability and improved repeatability. When combined with our anthropometric pinna, improved collapsibility, fit and seal are added benefits.



GRAS Pinna with RA040X coupler

High-Frequency Ear Simulator

Drop-in replacement for 60318-4 ear simulator in any test setup

Improved distortion measurements

Improved repeatability           

Human-like load up to 10 kHz

Extended and stable requency response

IEC 60318-4 compliant

100 Hz to 10 kHz according to IEC 60318-4
10 to 20 kHz:  ± 2.2 dB test tolerance
Damped resonance, with peak @ 13.5 kHz
Volume 1260 mm³ @ 500 Hz according to IEC 60318-4
Sensitivity 12.5 mV/Pa
Based on ITU-T Rec P.57

The GRAS RA0401 is a high-frequency ear simulator with an acoustic input impedance closely resembling that of an average human ear.  It includes a 40AG 1/2" pressure microphone and is individually calibrated with this specific microphone. It features a special dampening system that extends its useful frequency range to 20 kHz. Its prepolarized equivalent is RA0402.



The GRAS RA0401 is a high-frequency version of the well-known standardized 60318-4 ear simulator, which has gained wide acceptance as the preferred tool for measurements with simulation of the acoustic load presented by the human ear.

Below 10 kHz, the standardized ear simulator does a good job at this. However, above 10 kHz its performance starts rapidly to deteriorate. The primary reason for this is its high Q resonance at 13.5 kHz. This resonance makes the acoustic load that the ear simulator constitutes more complex and imposes an un-linearity on the output above 10 kHz where repeatability is poor and measurements of frequency response and distortion are unreliable.

The new GRAS High-Frequency Ear Simulator mitigates this limitation. The steep resonance at 13.5 kHz has been replaced by a much-damped resonance and the useful frequency range is now extended to 20 kHz within a narrow tolerance band.

It complies with IEC60318-4 and its acoustic transfer impedance is within the tolerance band specified by IEC60318-4. From 10 to 20 kHz the transfer impedance is within ± 2.2 dB, resulting in much-improved repeatability. Also, realistic THD measurements are now possible. It is measured and calibrated according to the ITU-T Recommendation P.57 and delivered with a calibration chart specifying its sensitivity and frequency response.

Its prepolarized equivalent is GRAS RA0402


  • Transfer impedance in compliance with IEC60318-4
  • 10 to 20 kHz the response is within ± 2.2 dB
  • The 13.5 kHz resonance dampened by about 14 dB


  • Measurements below and above 10 kHz in the same test sequence - results below and above 10 kHz can be compared/analyzed in the same process.
  • Measurements below and above 10 kHz both at the eardrum reference point, i. e. with the same acoustical load.
  • Better distortion measurements, even from as low 3-5 kHz and upwards.

It is based on the following international requirements:

  • IEC 60318-4: Occluded-ear simulator for the measurement of earphones coupled to the ear by ear inserts.
  • ITU-T Recommendations P.57 (08/96) Series P: Telephone transmission quality, Objective measuring apparatus: Artificial ears.


The RA0401 embodies a number of carefully designed volumes connected via well-defined and precisely tuned resistive grooves. In an equivalent electrical circuit, capacitors would represent the volumes, and inductance and resistance would represent respectively air mass and air flow within the resistive groves.

It is delivered with a built-in GRAS 40AG 1/2" externally polarized pressure microphone and an individual calibration chart for the ear simulator.

Where the standard ear simulator has a high Q resonance at about 13.5 kHz, the high-frequency version has a built-in damping system that attenuates the volume related resonances by about 14 dB. Also, the shape of the resonances has been softened. 

In this way, the useful frequency range of the coupler is extended to 20 kHz.

Comparison: The Standard 60318-4 Ear Simulator versus the RA0401 High-Frequency Ear Simulator

The advantages of the design with resonance dampening can easily be seen when comparing the standardized RA0045 Ear Simulator and the RA0401 Ear Simulator.

The curve below shows the transfer impedance of a standard RA0045 60318-4 Ear Simulator (Fig. 1)


Fig 1. Comparison of the resonance of a typical standard 60318-4 Ear Simulator and a High-Frequency Ear Simulator

The transfer impedance of the High-Frequency Ear Simulator with the IEC tolerance and the GRAS tolerances from 10 to 20 kHz are shown in Fig. 2. 


Fig 2. The half-wave resonance of a typical RA0401 High-Frequency Ear Simulator with IEC and GRAS tolerances

It can readily be seen that the amplitude and shape of the half-wave resonance are very different. Where the standardized ear simulator has a peak that tops above 36 dB, the RA0401 is 14 dB lower. At the same time, the slopes of this resonance are more rounded in the RA0401. The overall result is a much more useful response, whose effects on measurements are much easier to identify.

Typical applications and use

The RA0401 is for measurements on earphones and hearing aids coupled to the human ear by ear inserts such as tubes, ear molds, or ear tips and for measurements where the influence of the pinna and the head and torso are part of the investigation.

GRAS has a large portfolio of test devices for such measurements, ranging from fairly simple tabletop test setups to comprehensive configurations based on the KEMAR manikin, with or without mouth simulation.


A drop in-replacement for KEMAR already configured with RA0045 for testing

  • Hearing aids, monaural or binaural

  • Headphones, in-ear, supra- and circumaural

  • Headsets

GRAS 43-series tabletop Ear Simulator Kits

If you already own one of our tabletop testbeds, the RA0401 is a drop-in replacement for 43AC, 43EA and 43AG already configured with RA0045


Low and High Leak Pinna Simulators

In accordance with ITU-T Recommendation P.57, it can be used with the following GRAS pinna simulators for testing telephones:

A comprehensive range of accessories for making measurements in accordance with IEC 60318-4 is available.

For upgrade information, contact GRAS.


Advances in hearing-aid design have made it possible to increase the frequency range of hearing aids. This is the basis for a need for a method for measuring above 10 kHz, in ways that are precise, consistent and offer good repeatability. A traditional 60318-4 ear simulator has poor repeatability above 10 kHz and is ill-suited for measurements on wide-band hearing aids.

The High-Frequency Ear Simulator meets the demand for an accurate broadband measurement method where the measurements at high frequencies can be trusted. It is within the IEC limits, so the link to historical data can be maintained and existing test procedures can still be used - full backwards compatibility is ensured.

It is therefore well suited as a high resolution supplement to the standardized 60318-4 (former 60711 ) ear simulator – or as a new reference tool for hearing aids manufacturers R&D testing and design verification.

Consumer electronics: Headphone testing

Realistic test of headphones and earphones requires that they are presented with an acoustic load that simulates the human ear. The traditional 60318-4 ear simulator does exactly that, but testing above 10 kHz does not produce reliable and reproducible results because of the sharp and very dominant resonance at 13.5 kHz. In practice this limitation has made it necessary to measure the high frequency behavior of the transducer under test with other means, such as mounting it on a baffle and measure in the near field with a ¼” microphone.

With the RA0401, it is now possible to measure below and above 10 kHz in the same measurement setup, at the drum reference point and with the same acoustical loading of the transducer under test. This makes tests of headphones much easier, with improved repeatability.

RA0401 can be used as a development tool for the development of insert type headphones as well as supra- and circumaural types.

For R&D of headphones, the RA0401 can be mounted in a KEMAR. When furnished with the anthropometric pinna, tests of supra-aural and circum-aural headphones can be done to a much higher degree of realism than previously possible. When a headphone is mounted, the anthropometric pinna collapses against the head much like the real ear, and sealing and leakage related effects can better be investigated. For insert type of headphones the better shape of the ear canal improve seal and fit, vastly improving repeatability of measurements.

The combined advantage of the anthropometric pinna and the RA0401 is better test results at low frequencies and improved resolution at high frequencies and much-improved repeatability.

For QC purposes, the RA0401 can be mounted in a 45CA Headphone/Hearing-protector Test Fixture.



The RA0401 can be used with a standard LEMO preamplifier, e.g. the GRAS 26AK 1/2" Preamplifier or the GRAS 26AC-1 1/4" Preamplifier fitted with an adapter. For the 1/4" preamplifier, use either the straight RA0003 Adapter or the right-angled RA0001 Adapter.

Like the RA0045 the RA0401 has a dust protection filter to prevent dust and dirt from entering the internal volume. This filter should be kept clean and replaced when needed as dust build-up will influence the performance of the ear simulator.


200 V / Traditional
Theoretical dynamic range lower limit with GRAS preamplifier
Theoretical dynamic range upper limit with GRAS preamplifier @ +28 V / ±14 V power supply
Theoretical dynamic range upper limit with GRAS preamplifier @ +120 V / ±60 V power supply
Set sensitivity @ 250 Hz (±3 dB)
Set sensitivity @ 250 Hz (±3 dB)
dB re 1V/Pa
Resonance frequency
Coupler volume
1260 @ 500 Hz
Temperature range, operation
°C / °F
-30 to 60 / -22 to 140
Temperature coefficient @250 Hz
dB/°C / dB/°F
Humidity range non condensing
% RH
0 to 90
ANSI standard
IEC standard
60318-4 (former 60711)
ITU-T recommondations
CE/RoHS compliant/WEEE registered
Yes/Yes, Yes
g / oz
52 / 1.8


Ordering info

 Optional items


In Ear Adapter


Calibration Adapter


Stop Washer


Tube Adapter


Ear-mould Simulator


Retention Ring


Tube Adapter


Low-leak Pinna Simulator


High-leak Pinna Simulator


26AK 1/2'' Standard Preamplifier with Integrated Connector


26AC-1 1/4" Standard Preamplifier with Integrated Miniconnector


Right-angled Adapter for 1/2" microphone and 1/4" preamplifier


Adapter for 1/2" microphone and 1/4" preamplifier

GRAS Sound & Vibration reserves the right to change specifications and accessories without notice.