National Physical Laboratory

Sound in air header image Sound in Air

Accurate and consistent measurements of airborne sound fulfil a wide range of regulatory, health, safety and commercial needs both within the UK and in support of international trade. 

Accurate and consistent measurements of airborne sound fulfil a wide range of regulatory, health, safety and commercial needs both within the UK and in support of international trade. Applications arise in the measurement of machinery and product noise, environmental and workplace noise, hearing protection, audiometry, and the quality control of acoustical devices.

NPL's airborne sound and audiometric expertise includes:

  • Provision of primary standards for sound pressure in air, including the requirement to demonstrate equivalence of our standards with those of our trading partners.
  • Dissemination of standards, largely achieved through the development, and where appropriate, delivery of specialised measurement services for the calibration of sound measuring instrumentation. These include calibration both for general purpose measurements and for specific applications having a widespread impact on the community.
  • Addressing the need for instrumentation to comply with certain minimum performance requirements beyond the need to simply be calibrated. This is achieved through being involved in the development of international specification standards through IEC and OIML for example.
  • Development of the infrastructure to underpin the measurement of hearing in the population.
  • Undertaking of research into new test methodologies to underpin calibration applications, an example of this is the qualification of free-field rooms.
  • Development of optical techniques as the basis of the next-generation measurement standards for the calibration of airborne sound measuring instruments.
  • Development and application of novel MEMS-based microphones
  • Calibration techniques for low-cost microphones.
  • Measurement and guidance related to measurement of environmental and machinery noise.
  • Technical Guides on Sound in Air, Ultrasonics and Underwater Acoustics.
  • NPL provides input to the working groups of international and national standards bodies and is aiding development of internationally standardised methods for testing DSP hearing aids.
  • A guide for all parties who commission, undertake or use environmental sound predictions for commercial or industrial operations, of whatever type or scale, for which an environmental noise assessment may be required.
  • NPL is pursuing the development of MEMS (Micro Electro-Mechanical System)-based measurement microphones.
  • NPL provides imaging and characterisation of materials using infrared Fourier domain optical coherence tomography and large scale dispersion profiling using optical wavefront assessments.
  • Research work is currently being undertaken towards the development of a new optically-based primary standard for the free-field calibration of airborne measuring instruments based on photon correlation spectroscopy.
  • NPL provides primary measurement standards appropriate for the wide range of acoustical measurements in air. These standards support sound pressure measurements for manufacturing and product QA, health, safety and hearing conservation, environment noise measurement and monitoring, and many other applications.
  • Secondary calibration of working standard microphones can offer the most direct and cost-effective traceability path for sound-in-air measurements.

Sound in Air products & services

  • A wide range of consultancy services are available, from solutions to specific measurement problems to the bespoke design of a complete primary calibration system.
  • A range of calibration services are available for the whole spectrum of acoustical instrumentation. Measurement services cover the common types of acoustical and audiometric instruments.


Please note that the information will not be divulged to third parties, or used without your permission