A discussion on evaluating the effect of head-of worn devices on directional sound localization in the horizontal plane

Spatial auditory awareness while wearing hearing protection devices is critical to safety in noisy environments. ANSI/ASA S3.71-2019, “Methods for Measuring the Effect of Head-worn Devices on Directional Sound Localization in the Horizontal Plane” defines four protocols to evaluate and quantify the effects of headgear on the ability of the user to localize sound in one dimension. Method 1 is low complexity, using an array of eight speakers. The key metrics are stimulus location and front-back reversal identification. Method 2 is a more robust method using an array of 36 speakers in 10° increments. This method quantifies angular error and reports a more detailed assessment. Method 3 combines the 36-speaker array with a grid of four LEDs. The report includes response time degradation between the headgear on and off conditions. Method 4 is a high-resolution test using 180 speakers, each situated 2° apart on the horizontal plane. This detailed method aims to determine a subject’s localization acuity or their ability to determine minimum resolvable angular separation between two sound sources. Regardless of method, front-back reversals affect most subjects and are naturally present in this type of human subject testing. Experiences will be discussed for this interesting and unique psychoacoustic phenomenon.