The ultimate guide to ambient noise monitoring: Tools, methods, and benefits

Monitoring ambient noise plays a crucial role in accurately measuring hearing thresholds. Uncontrolled environmental noise can cause subjects to misinterpret test stimuli, resulting in false responses or invalid results. By monitoring ambient noise levels, clinicians and hearing health professionals can minimize these interferences and improve diagnosis and treatment outcomes.

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Why measure ambient noise?

Audiometric tests are invalid if conducted in environments with unsuitable ambient noise levels. Excessive ambient noise can ‘mask’ the pure-tone test signal, making it inaudible to the test subject, and thus falsely elevating the resulting hearing threshold.

Evidence may be necessary to confirm that audiometry has been performed in an appropriate, noise-free environment; if such evidence cannot be provided, test results should be rejected.

Organizations such as the BSA (British Society of Audiology), ANSI (American National Standards Institute), ISO (International Organization for Standardization), and OSHA (Occupational Safety and Health Administration) define specific noise level criteria for audiometric testing environments. Measuring ambient noise ensures adherence to these requirements.

How to evaluate and monitor ambient noise

The location in which audiometry is performed should be both assessed and monitored:

• ‘Assessment’ should ensure sound levels fall within specified limits in every third-octave frequency band. This must be carried out with a calibrated class 1 or class 2 sound level meter (SLM) capable of accurately measuring low sound levels in each frequency band. Assessments should be performed periodically, when locations change, or when noise conditions vary.
• ‘Monitoring’ should confirm that sound levels remain consistent during each test session (e.g., daily in one location). This can be performed using a broadband sound level meter (i.e., a calibrated meter that provides a single dB(A) reading instead of readings for each frequency band). Trained audiometry personnel should always remain aware of the potential effects of background noise.

What to use for measuring ambient noise

Sound level meters or sound room microphones can be used to measure ambient noise. These devices measure the frequency content in octave or third-octave bands. It should be noted that some level of ‘measurement uncertainty’ exists, due to factors such as environmental conditions (ambient noise and distractions), equipment, the subject, technique, and the tester.

What is an acceptable level of background noise?

Acceptable background noise levels for audiometry are outlined in the British Society of Audiology (2025) guidance ‘Acoustic Considerations for Audiology Clinics’, based on ISO standards. These requirements are based on both the ambient noise level in the room and the headphones' attenuation of ambient sound during testing. Supra-aural headphones offer the lowest attenuation, so noise-reducing headphones may be preferred.

Some audiometers include a microphone that measures the ambient noise during testing. This provides assurance that tests are performed under appropriate conditions. However, these microphones are not class 1 or 2 SLMs, meaning they are suitable only for monitoring sound levels and cannot replace the need to assess the location.

According to the BSA (2023) ‘Surveillance Audiometry’ guidance, “in general, the ambient noise should not exceed 35 dB(A)”. While this provides reasonable assurance for monitoring, assuming the test uses headphones that attenuate ambient noise, it does not meet the environmental assessment requirements outlined in the BSA acoustics document (2025).

How to ensure the suitability of an environment for audiometry

Ensuring that non-clinical environments, such as workplaces, meet ambient noise criteria can be challenging. However, it is important to remember that inadequate control of ambient noise can invalidate test results and put the organization at legal risk if testing conditions are later disputed.

Noise levels often fluctuate and, if the noise is fleeting and infrequently intrusive, testing may be temporarily suspended or rescheduled. Trained personnel performing audiometry must be aware of this.

Noise levels slightly above the stated limits may be acceptable if noise-reducing headphones are used, provided their attenuation is known. Noise can also be decreased by installing an audiometry booth in a room. In such cases, ambient noise levels should be measured inside the booth.

As previously outlined, the ambient noise in a test room should be adequately assessed and monitored, with results compared against recommended limits (BSA, 2025). When headphones are used, their attenuation should be known and added to the acceptable noise limit.

Ambient noise monitoring solutions

Incorporating a Sound Room Microphone (SRM) into the testing process enables monitoring of environmental conditions, helping to ensure high-quality audiometry outcomes. Amplivox offers multiple solutions that incorporate SRM technology:

The Anova^™ provides unparalleled precision with the option of an external SRM. The microphone is placed in the test environment and delivers real-time feedback when noise surpasses the ‘ideal level’ for accurate measurements, ensuring optimal testing conditions.^*

The Amplivox modelONE, a PC-based audiometer, includes noise-attenuating headphones with an integrated SRM.^*

^*Please note: the use of an SRM does not replace the need for an IEC 61672 class 2 microphone (as stated in the HSE L108 'Controlling Noise at Work' 2005 publication). 

References and further reading

1. HSE (2015). HSE - Noise: Health surveillance. (online) HSE. Available at: https://www.hse.gov.uk/noise/healthsurveillance.htm.
2. British Society of Audiology (2014). British Society of Audiology - BSA. (online) British Society of Audiology. Available at: https://www.thebsa.org.uk/.
3. ANSI (2019). ANSI-American National Standards Institute. (online) ANSI. Available at: https://www.ansi.org/.
4. ISO (2025). ISO - International Organization for Standardization. (online) ISO. Available at: https://www.iso.org/home.html.
5. OSHA (2025). Occupational Safety and Health Administration. (online) OSHA. Available at: https://www.osha.gov/.

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