Having two ears has many advantages over having one ear. Although verbal communication is generally not hampered much by using just one ear, accurate sound localisation relies heavily on using two ears. Sound localisation occurs based on a comparison between the difference in sound that reaches both ears.
The figure above illustrates that sound from a narrator (S) takes longer to reach the right ear of the listener (L) than it takes to reach the left ear. Besides, in order to reach the right ear of the listener, sound has to travel around (and through) the head of the listener causing the sound to be quieter in the right ear.
The difference in time and volume provide information about the location of the sound. These differences, together with other factors, are interpreted by our brain and translated into a given location.
Difficulty in locating environmental sounds can be inconvenient, or in some situations it can put us in danger (e.g. not knowing the location of an approaching car). Hearing loss does not always result in poor localisation ability. However, very soft signals will be inaudible and can therefore not be located. The larger the hearing loss, the more difficult it becomes to work out where sounds are coming from because we struggle to hear them well. Apart from the volume of the sound, the type of hearing loss we have can also affect our ability to locate sounds and some hearing losses make it harder to locate sounds than others . In addition, if the hearing loss in one ear differs from the other ear (asymmetrical hearing loss), or in the case where one ear has a hearing loss and the other does not (unilateral hearing loss), localisation performance decreases.