Broadband sounds, which combine low, medium and high frequencies in a single sound, affect users differently. In medium frequency sounds, around 3Khz, listeners are able to detect the difference in intensity of sound at each ear, allowing them to locate the source to their left or right. Higher frequency sounds, above 5Khz, through a learnt skill known as ‘head related transfer function’ and based on the shape of our heads and ears, allow listeners to tell a sound’s forward or backward position. This combination of effects allows listeners to instantly locate a broadband source to within five degrees.
The alarms have already been fitted in a number of prominent and safety conscious institutions, including the US Pentagon and on electric passenger carts at UK airports.
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