GRAS RA0404 Prepolarized Hi-Res Ear Simulator

Introduction

The GRAS RA0404 is an ear simulator for hi-res audio testing. It is developed to meet the increasing demand for realistic and accurate high-frequency measurements with simulation of the acoustic load presented by the human ear. It is intended as a research and development tool for high-resolution capable headphones.

Using a ¼” microphone and a special dampening system to attenuate the internal resonances, the RA0404 offers an unprecedented high-frequency capability for headphone testing.

The RA0404 is based on the standardized IEC60318-4 Ear Simulator but has been modified to improve its high-frequency response. It has the same internal design and its acoustic input impedance closely resembles that of the human ear and, as a result, loads a sound source in very much the same way. Below 10 kHz, the standardized ear simulator does a good job at simulating the human ear. 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 RA0404, however, uses a resonance dampening system to dampen the steep resonance at 13.5 kHz. This resonance is attenuated by more than 14 dB. This greatly improves the linearity above 10 kHz and makes it possible to use a ¼” microphone in the coupler and benefit from its extended frequency range. Therefore, the RA0404 is well suited for research and the development of high-resolution capable headphones up to 50 kHz.

It is compatible with IEC60318-4 and its acoustic transfer impedance is within the tolerance band specified by IEC60318-4 up to 10 kHz. From 10 to 20 kHz the transfer impedance is within ±2.2 dB, from 20 kHz to 50 kHz it is within ±3.2 dB. Therefore, it is now possible to make measurements up to 50 kHz with good repeatability.

It is measured and calibrated according to IEC60318-4 and delivered with a calibration chart specifying its sensitivity and frequency response.

When mounted in a KEMAR in combination with an anthropometric pinna you have the possibility of performing high-frequency tests including the effects from head diffractions.

Its externally polarized equivalent is GRAS RA0403.

Features

• Transfer impedance compatible with IEC60318-4
• 10 kHz to 20 kHz the response is within ± 2.2 dB
• 20 to 50 kHz the response is within ± 3.2 dB
• The 13.5 kHz resonance dampened by more than 14 dB
• Calibrated to 100 kHz

Benefits

• Measurements with realistic acoustic load of the test object
• 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 as 3-5 kHz and upwards.

Design

The RA0404 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 40BD 1/4″ prepolarized 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-resolution version has a built-in dampening system that attenuates the volume related resonances by about 14 dB. Also, the shape of the resonances has been softened. The effects of the internal resonances are well controlled. At the same time, the slopes of the resonances are more rounded, making it possible to achieve reliable and reproducible measurement results.

The overall result is a much more useful response, whose effects on measurements are much easier to identify and the useful frequency range of the coupler is extended to 50 kHz.

Typical applications and use

The RA0404 is for measurements on earphones 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.

45CA Headphone Test Fixture

The RA0404 is a drop-in replacement for 45CA already configured with an externally polarized ear simulator.

A preconfigured version available is the 45CA-12 Headphone Test Fixture – Hi-Res Audio & Anthro. Pin CCP.

An externally polarized equivalent is available, the 45CA-11 Headphone Test Fixture – Hi-Res Audio & Anthro. Pin LEMO.

KEMAR

RA0404 is a drop-in replacement for KEMAR already configured with an RA0045-S1 or a RA0402.

Two configurations are available:

45BB-16 KEMAR for Test of Ear & Headphones with Hi-Res Audio Ear Simulator, 2-Ch CCP.

45BC-16 KEMAR with Mouth Simulator for Test of Headset with Hi-Res Audio Ear Simulator, 2-Ch CCP.

The externally polarized equivalents are:

45BB-15 KEMAR for Test of Ear & Headphones with Hi-Res Audio Ear Simulator, 2-Ch LEMO.

45BC-15 KEMAR with Mouth Simulator for Test of Headset with Hi-Res Audio Ear Simulator, 2-Ch LEMO.

GRAS 43-series tabletop Ear Simulator Kits

If you already own one of our tabletop testbeds, the RA0404 is a drop-in replacement for a 43AG already configured with RA0045-S1.

A preconfigured version is available, the 43AG-9 Anthro. Ear and Cheek Simulator with Hi-Res Audio Ear Simulator, CCP.

The externally polarized equivalent is 43AG-8 Anthro. Ear and Cheek Simulator with Hi-Res Audio Ear Simulator, LEMO

Two versions of the 43AC Ear Simulator Kit configured for hires testing are available:

43AC-S6 with Hi-Res Ear Simulator, LEMO, and 43AC-S7 with Hi-Res Ear Simulator, CCP.

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 coupler 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 RA0404 ear simulator, 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.

RA0404 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 RA0404 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 improves seal and fit, vastly improving the repeatability of the measurements.

The combined advantage of the anthropometric pinna and the RA0404 is better test results at low frequencies and improved resolution at high frequencies and much-improved repeatability.

For QC purposes, the RA0404 can be mounted in a 45CA Headphone/Hearing-protector Test Fixture.

Compatibility