Introduction: Understanding the Tools of the Trade

When an audiometric testing van pulls up to your workplace, what’s inside? WHS managers and operations teams often wonder about the technical specifications of the equipment being used to test their workers’ hearing. This guide explains the key components of mobile audiometric testing setups, the standards they must meet, and how to verify that a testing provider is using compliant, properly maintained equipment.

Understanding audiometric equipment builds confidence in the validity of your testing results and helps you verify compliance with Australian standards.

Overview: The Mobile Audiometric Testing Setup

A complete mobile audiometric testing system includes:

• Audiometer: The device that produces calibrated sound at specific frequencies and measures hearing thresholds
• Earphones: Circumaural or insert earphones that deliver sound to the worker’s ears with precision
• Sound-attenuating booth: An enclosure that minimises external noise, creating the quiet environment required by standards
• Microphone: For monitoring ambient noise levels during testing
• Software: For controlling the test sequence, recording results, and generating audiograms and reports
• Calibration equipment: Biological check devices and calibration couplers for ongoing quality assurance
• Environmental monitoring: Equipment to verify that acoustic conditions meet AS/NZS 1269.4 limits

The Audiometer: Heart of the Testing System

What Is an Audiometer?

An audiometer is an electronic device that produces pure-tone sounds at specific frequencies and sound levels. The audiometrist uses the audiometer to determine the quietest sound level at which a worker can hear a tone at each of several frequencies (typically 500 Hz to 8000 Hz for occupational testing).

AS/NZS IEC 61672 Type 1 Compliance

Occupational audiometers in Australia must comply with AS/NZS IEC 61672, which specifies the accuracy standards for sound measurement and presentation equipment. Type 1 is the highest accuracy class, suitable for precise occupational testing.

What this means practically: A Type 1 compliant audiometer produces tones at exact dB levels (no “drift” or calibration error), responds predictably across the frequency range, and maintains accuracy over years of use when properly maintained.

How the Audiometer Works in Testing

1. The audiometrist presents a pure tone (e.g., 1000 Hz) at a starting level (e.g., 20 dB HL)
2. The worker raises their hand or presses a button when they hear the tone
3. The audiometrist lowers the level incrementally until the worker no longer responds
4. The audiometrist raises the level again until the worker responds once more
5. This process is repeated at each test frequency, establishing the worker’s hearing threshold at that frequency
6. The results are plotted on an audiogram, showing hearing thresholds across frequencies

Test Frequencies

Occupational audiometric testing typically includes test frequencies of: 500 Hz, 1000 Hz, 2000 Hz, 3000 Hz, 4000 Hz, 6000 Hz, and 8000 Hz. Some providers offer extended frequency testing (up to 16000 Hz) for workers with potential high-frequency hearing loss.

Sound-Attenuating Booths: Creating the Quiet Environment

Why Acoustic Control Matters

Testing must occur in a controlled acoustic environment. If background noise is too high, it interferes with the worker’s ability to hear subtle test tones, making thresholds appear higher than they actually are. This creates false results and undermines the validity of monitoring.

AS/NZS 1269.4 Ambient Noise Limits

The Australian standard specifies maximum ambient noise levels at each frequency:

• 250 Hz: 39.5 dB
• 500 Hz: 39.5 dB
• 1000 Hz: 39.5 dB
• 2000 Hz: 43 dB
• 3000 Hz: 47 dB
• 4000 Hz: 47 dB
• 6000 Hz: 51 dB
• 8000 Hz: 51.5 dB

These limits are critical. A testing environment that doesn’t meet these limits produces unreliable results and fails to comply with AS/NZS 1269.

Portable Sound-Attenuating Booth Specifications

Mobile audiometric testing uses portable sound-attenuating booths — self-contained enclosures lined with acoustic foam. These booths typically:

• Accommodate 1-2 workers at a time
• Measure approximately 1.2m x 1.2m x 2.2m (height)
• Use multiple layers of acoustic foam (50-75 mm thickness) to absorb sound
• Achieve 20-30 dB noise reduction between the outside and inside at mid-range frequencies
• Include ventilation to prevent worker discomfort during longer testing sessions
• Have a small window for the audiometrist to observe the worker

Verifying Acoustic Adequacy

A compliant testing provider will measure the ambient noise levels within the booth before and during your testing session using a sound level meter. This measurement confirms that the environment meets AS/NZS 1269.4 limits. You can request to see these measurements or ask the audiometrist whether environmental noise issues affected any workers’ tests.

Earphones: Delivering the Test Signal

Circumaural Earphones (Over-the-Ear)

Circumaural earphones are the most common choice for occupational audiometric testing. They:

• Sit over the outer ear, with soft cushions creating an acoustic seal
• Provide good acoustic isolation (block some ambient noise naturally)
• Accommodate workers of varying ear sizes with adjustable headbands
• Are durable and withstand repeated use across multiple workers
• Feel familiar and comfortable to most workers

The earphones are connected to the audiometer via a cable, allowing the audiometrist to deliver precisely calibrated tones to each ear independently.

Insert Earphones (In-Canal)

Some providers also offer insert earphones — small foam or rubber tips that fit directly into the ear canal. Benefits include:

• High acoustic isolation due to direct ear canal placement
• Greater portability (useful for extreme remote sites)
• Better comfort for workers with sensitivity to headband pressure

Drawbacks include potential discomfort for longer-term use and the need for multiple tip sizes to fit different workers adequately.

Earphone Calibration and Checking

Earphones must be calibrated to ensure they produce precise sound levels. This is verified through:

• Biological check: A daily measurement of earphone output using a biological check coupler (a small cavity designed to simulate the ear canal’s acoustic properties)
• 6-monthly electroacoustic check: A more detailed measurement using calibration couplers to verify frequency response and output at each test frequency
• Annual NATA calibration: Full laboratory calibration confirming compliance with AS/NZS IEC 61672

Calibration Requirements: Ensuring Accuracy and Compliance

Daily Biological Check

Before any worker is tested, a biological check is performed. A small sound level meter (biological check coupler) is inserted into the earphone, and the audiometer is set to specific frequencies and levels. The meter verifies that the earphone produces the expected sound level. If the earphone is significantly out of calibration, testing is not performed until the equipment is recalibrated.

This daily check takes approximately 10 minutes and is your assurance that the equipment starting testing on your site is functioning correctly.

6-Monthly Electroacoustic Calibration Check

Every six months, a more detailed electroacoustic calibration check is performed. This involves measuring the audiometer’s output at multiple frequencies using precision calibration couplers and verifying compliance with AS/NZS IEC 61672. If any drift or malfunction is detected, the equipment is recalibrated or serviced before returning to use.

Annual NATA-Accredited Calibration

Once per year, the entire audiometric system (audiometer, earphones, microphone, and booth) undergoes full calibration by a NATA-accredited laboratory. This external, independent verification confirms that all components meet Australian standards.

This is not optional — NATA accreditation is essential for WHS compliance. When booking a testing provider, always ask to see their annual NATA calibration certificate. If they don’t have one, don’t proceed with testing.

What to Look For in Calibration Documentation

Ask your testing provider to provide:

• Current annual NATA calibration certificate (dated within the past 12 months) — this should list the organisation conducting the calibration and the equipment serial numbers
• Most recent 6-monthly electroacoustic check report
• Confirmation that daily biological checks are performed before testing begins

The Mobile Testing Van: Integration of Systems

Van Configuration

A mobile audiometric testing van is a purpose-built vehicle integrating all audiometric testing components:

• Acoustic isolation: The van body is lined with sound-absorbing material, and one or two sound-attenuating booths are installed within the van. The overall setup achieves the ambient noise limits specified in AS/NZS 1269.4.
• Power supply: The van includes a generator or inverter to power the audiometer, software systems, lighting, and climate control.
• Climate control: Air conditioning or heating keeps the testing environment comfortable for workers, which is important because body temperature can subtly affect hearing thresholds.
• Software and networking: A laptop or computer runs the audiometric testing software, which controls the audiometer, records results in real-time, and generates audiograms and reports.
• Accessibility: Ramps or steps allow safe access for workers with mobility limitations.

Parking and Setup Logistics

When scheduling mobile audiometric testing, ensure:

• Adequate parking space (vans typically need an area with no heavy vehicle movement during testing)
• Level ground (to minimise vibration that could affect test results)
• Proximity to power supply if the van’s generator isn’t being used
• Weather protection (ideally a covered area to minimize temperature fluctuations during testing)
• Quiet location away from high-noise work areas

Software for Audiogram Generation and Reporting

What the Software Does

Audiometric testing software controls the entire testing sequence and data management:

• Test protocol: The software runs the standardized testing sequence, presenting tones at the correct frequencies and levels and recording the worker’s responses.
• Audiogram generation: Results are automatically plotted on an audiogram graph, with hearing thresholds for each ear shown at each frequency.
• Comparison to baseline: If a baseline audiogram exists (from previous testing), the software overlays the current results for visual trend monitoring.
• Threshold shift detection: The software automatically flags significant threshold shifts (typically defined as 10 dB or more at 2, 3, or 4 kHz) for follow-up action.
• Report generation: Individual worker reports and group summary reports are generated automatically, ready for distribution.
• Data security: Worker hearing data is stored securely with limited access.

Data Quality and Validation

The software also performs quality checks:

• Flags tests where environmental noise exceeded limits during testing
• Identifies inconsistent responses suggesting worker error or misunderstanding
• Highlights potential equipment malfunctions

Quality Assurance Equipment and Procedures

Biological Check Coupler

A small device that simulates the acoustic properties of the human ear canal. It’s used daily to verify that earphones produce the correct sound levels before testing begins.

Sound Level Meter

Used to measure ambient noise levels within the testing booth, confirming that the environment meets AS/NZS 1269.4 specifications.

Calibration Couplers (Mechanical Ears)

Used in 6-monthly checks to verify that the audiometer and earphones produce correct output at each frequency.

Environmental Monitoring During Testing

Most modern systems continuously monitor ambient noise during testing, flagging results if noise levels briefly exceed limits (e.g., if a loud vehicle passes nearby during a test).

Frequently Asked Questions

What is AS/NZS IEC 61672 Type 1 audiometer compliance?

AS/NZS IEC 61672 Type 1 means the audiometer meets the highest accuracy standard for sound measurement devices. Type 1 audiometers are calibrated to precise dB levels and are suitable for occupational hearing testing as required by AS/NZS 1269.

How often must audiometric equipment be calibrated?

Audiometric equipment requires: daily biological checks (earphone output verification before testing begins), 6-monthly electroacoustic calibration checks, and annual NATA-accredited full calibration to maintain AS/NZS compliance.

What are the acoustic noise limits in AS/NZS 1269.4?

The ambient noise limits for testing environments are: 250 Hz: 39.5 dB, 500 Hz: 39.5 dB, 1000 Hz: 39.5 dB, 2000 Hz: 43 dB, 3000 Hz: 47 dB, 4000 Hz: 47 dB, 6000 Hz: 51 dB, and 8000 Hz: 51.5 dB. Sound-attenuating booths ensure the testing environment meets these limits.

What’s the difference between circumaural and insert earphones?

Circumaural earphones (over-the-ear) are more commonly used in occupational testing and provide good acoustic isolation. Insert earphones fit directly in the ear canal and are more portable but may be less comfortable for extended use or workers with sensitive ears.

How is a mobile testing van configured acoustically?

A mobile testing van integrates sound-attenuating booth(s) within the vehicle body, using acoustic foam and structural isolation to meet AS/NZS 1269.4 ambient noise limits. The van provides climate control, power supply, and software connectivity for audiogram recording.

What quality assurance checks are performed during testing?

Quality assurance includes: biological checks (sound level verification), environmental noise monitoring during testing, equipment functioning checks, and software validation. Results are flagged if environmental noise exceeds limits during testing.

Is NATA accreditation essential for audiometric testing equipment?

Yes, NATA (National Association of Testing Authorities) accreditation is essential. Annual NATA-accredited calibration confirms that equipment meets AS/NZS standards and is suitable for occupational hearing testing, which is required for WHS compliance.

Can I check that mobile testing equipment is properly calibrated?

Yes, you can request to see the annual NATA calibration certificate, the most recent 6-monthly electroacoustic check report, and confirmation that daily biological checks are performed before your testing session begins.

Conclusion: Ensuring Valid Results Through Equipment Quality

Mobile audiometric testing relies on a sophisticated ecosystem of equipment, calibration procedures, and quality assurance. Understanding these technical specifications helps WHS managers verify that testing providers are using compliant, well-maintained systems.

When you book audiometric testing, you’re investing in accurate baseline and monitoring data for your hearing conservation program. Verify that your provider uses Type 1 compliant, NATA-calibrated equipment tested in acoustically controlled booths. This assurance ensures that your testing results are valid, your compliance records are defensible, and your workers’ hearing health is being monitored with scientific precision.

Always request to see calibration documentation before testing begins — this is not an unreasonable request; it’s a fundamental component of WHS diligence.