An application guide for the Brüel & Kjær (HBK) Type 5128-C High-Frequency Head and Torso Simulator. Covers what makes it different from earlier HATS, the test workflows it enables for telecom, headphone, and smart-speaker development, and best-practice fixturing for repeatable measurements up to 20 kHz.
What’s Covered
What the Type 5128-C is, and what changed
The Type 5128-C is HBK’s high-frequency Head and Torso Simulator, designed to reproduce the acoustic field around a human head and torso for repeatable measurements of audio products. Unlike earlier HATS, which were optimized for telephone-band measurements (up to roughly 8 kHz), the 5128-C extends performance across the full audible range up to 20 kHz.
The major design change is the ear canal. The 5128-C uses an MRI-derived ear canal geometry, synthesized from anatomical scans of multiple subjects, that maintains realistic acoustic impedance well above traditional HATS’ upper limit. The ear simulator carries a built-in transducer electronic datasheet (TEDS), so calibration data follows the simulator into any HBK measurement front end without manual configuration.
The 5128-C is approved by ITU-T as a standardized solution against P.57 and P.58, meaning it can be used for statutory approval testing of communication devices including mobile phones.
Why high-frequency HATS measurements matter now
Modern audio products operate well outside the speech band. Premium headphones extend frequency response to 40 kHz; smart speakers and soundbars present complex multi-driver radiation patterns; in-ear monitors couple uniquely with each ear canal geometry. None of these are measurable with an 8 kHz limit, and traditional artificial-ear approaches break down above the limit they were designed for.
Bringing high-frequency content into the qualified measurement range matters for three reasons:
- Premium product differentiation depends on the upper bands users perceive as “clarity” and “detail”
- Active noise cancellation and adaptive feedback algorithms operate across the full audible range
- Comparative testing across products requires a consistent acoustic interface, not multiple artificial ears with their own band limits
Application areas
Headphone and earbud testing
The MRI-derived ear canal geometry produces realistic coupling for in-ear, on-ear, and over-ear products. Frequency response, distortion, leakage sensitivity, and active noise cancellation can all be characterized with the same fixture and methodology.
Smart speakers and soundbars
For room-listening products, free-field measurements over the 5128-C in an anechoic or semi-anechoic environment capture the perceptual experience more accurately than coupled-mode measurements. Smart-speaker development teams use the 5128-C to validate beamforming, voice pickup direction, and listener-position frequency response.
Telecom and conferencing devices
Handset, headset, and conference device qualification under ITU-T P.57 and P.58 use the 5128 family directly. The 5128-C maintains compatibility with the standard’s required impedance and geometry, while extending capability beyond the legacy telephone band.
Hearing aids and hearing protection
Hearing aid open-fit, closed-fit, and bone-conduction designs benefit from extended-range coupling. Hearing protection effectiveness is measured by comparing protected and unprotected fields with consistent geometry, exactly what the 5128-C is built for.
Voice assistants and microphone arrays
Far-field voice pickup and microphone array beamforming both rely on consistent source and listener simulators. The 5128-C provides a repeatable mouth simulator and listener model for these tests.
Workflow: from device under test to repeatable result
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Define the standard
ITU-T, IEEE, vendor internal, or comparative? The standard fixes the test geometry, signal type, weighting, and acceptance criteria.
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Configure the simulator
Confirm ear simulator type, mouth simulator if used, and TEDS-loaded calibration. Set the front-end channel map to the simulator’s transducers.
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Position the device under test
Follow the standard’s geometry. For supra-aural and circumaural headphones, force application is part of the test specification. Consistency between operators is the dominant repeatability factor.
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Calibrate the chain
Apply a calibration tone or pistonphone reference at the start and end of the session. Document any drift.
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Run the test
Sweep, pink noise, speech, or pre-recorded reference signal, per the standard. Capture raw audio plus computed metrics.
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Validate before reporting
Inspect for clipping, environmental contamination (HVAC, traffic), and obvious anomalies. Compare against historical baselines for the same device class to flag outliers.
Fixturing, positioning, and acoustic environment
High-frequency measurements are far less forgiving of fixturing and environment errors than telephone-band work. Reflections, room modes, and operator variation that were inconsequential at 4 kHz can dominate at 16 kHz.
- Measure in an anechoic or semi-anechoic environment whenever possible; treat narrow-band fixturing reflections aggressively
- Use the 5128-C’s mounting interfaces, bench-top tabletop or torso configuration, appropriate to the test type, and standardize across operators
- Document seating depth and force for in-ear products; small variations dominate the high-frequency response
- Capture environmental conditions; temperature affects the ear simulator’s acoustic properties, particularly above 10 kHz
Integration with HBK measurement systems
The 5128-C is designed for the HBK acoustic measurement ecosystem: LAN-XI / Fusion-LN front ends for capture, BK Connect or PULSE for analysis, and Sonoscout / dedicated audio test platforms for product development. Built-in TEDS in the ear simulators feeds calibration directly into the front end on connection, see the TEDS technology guide.
For complementary instrumentation, see the Durham Instruments product pages for sound level meters, data acquisition, and acoustic sensors.
FAQ
How is the Type 5128-C different from the Type 4128 HATS?
The 4128 was optimized for telephone-band measurements with traditional ear simulators valid to roughly 8 kHz. The 5128-C uses a redesigned MRI-derived ear canal and matched ear simulators that maintain realistic acoustic impedance up to 20 kHz, suitable for modern wideband audio products as well as standard telecom work.
Is the 5128-C ITU-T compliant?
Yes. The Type 5128 family and the Type 4620 ear simulator are approved by ITU-T as standardized solutions for the requirements of P.57 and P.58, meaning the 5128-C can be used for statutory approval of communication devices.
Can I use the 5128-C for measurements outside the speech band?
Yes, that is its core differentiation. The 5128-C maintains realistic acoustic impedance across the full audible range and is widely used for headphone, smart-speaker, and audio-product measurements above traditional HATS’ upper limit.
Does the 5128-C ship with TEDS calibration data?
Yes. The ear simulators include built-in TEDS so calibration follows the simulator into any HBK measurement front end without manual entry. This is particularly valuable in production-test environments where simulators may rotate between stations.
Where can I get a 5128-C in Canada?
Durham Instruments is the authorized HBK partner for Canada. We supply the Type 5128-C and the supporting LAN-XI / Fusion-LN / BK Connect ecosystem with installation, calibration, and application support. Contact our team for current availability and configuration.
Planning a Type 5128-C deployment?
Talk to a Durham Instruments engineer about complete acoustic test workflows, Type 5128-C, LAN-XI / Fusion-LN front end, analysis software, and standards-compliant procedures.