dB A vs dB HL

10 mins
01 September 2017


Can dB (A) and dB (HL) be used interchangeably in sound field audiometry?

Well, I’m not really sure they’re used “interchangeably” as such. Either one or the other scale would typically be used. In the sound field, the A-weighting for measuring sound pressure level is often applied to the sound level meter. This provides a measurement that has some resemblance to the 40-phon equal loudness contour, hence the measurements provided will have a closer relationship to loudness than, say, the z-weighting (or zero weighting) measures.

The Reference Equivalent Threshold Sound Pressure Levels (RETSPLs) for sound field testing are provided in ISO 389-7, which are thresholds given under binaural listening conditions and the values it contains are the basis for defining dB HL in these conditions.

Although sounds measured in dB HL are therefore derived using RETSPLs and sounds measured in dB A are measured directly using an SLM, the difference between the two is nonetheless small – on the order of 3dB across most of the audiometric range. This might not be considered a clinically significant amount so it might be acceptable to consider thresholds measured in dB A “as if” they were hearing levels.

References and caveats
ISO 389-7:2005 
Acoustics -- Reference zero for the calibration of audiometric equipment -- Part 7: Reference threshold of hearing under free-field and diffuse-field listening conditions


Michael Maslin
After working for several years as an audiologist in the UK, Michael completed his Ph.D. in 2010 at The University of Manchester. The topic was plasticity of the human binaural auditory system. He then completed a 3-year post-doctoral research program that built directly on the underpinning work carried out during his Ph.D. In 2015, Michael joined the Interacoustics Academy, offering training and education in audiological and vestibular diagnostics worldwide. Michael now works for the University of Canterbury in Christchurch, New Zealand, exploring his research interests which include electrophysiological measurement of the central auditory system, and the development of clinical protocols and clinical techniques applied in areas such as paediatric audiology and vestibular assessment and management.

Popular Academy Advancements

Interacoustics - hearing and balance diagnosis and rehabilitation
Copyright © Interacoustics A/S. All rights reserved.