If you or someone you know has hearing loss, you’ve probably noticed that the hearing impaired person has particular difficulty understanding a conversation (even if they are wearing hearing aids) when the speaker is at a distance or has their back to them. Some of the reasons for this are obvious and some not so obvious.

An obvious reason is that a hearing impaired person subconsciously tends to lip read and rely more on visual cues such as facial expressions and hand gestures.

One not so obvious reason is that quite often hearing losses are in the higher tones which also happen to be where most consonants are located. In addition, higher tones diminish in their intensity over distance more readily than do lower tones.

To illustrate, imagine you strike one low pitch and one high pitch key on a piano such that the initial volumes are the same. Over distance however, a listener will experience that the high pitch note becomes quieter than the low pitch note. When speaking with your back to someone, sound waves effectively have to bounce off of an object in front of you, such as a wall, and travel backwards to the listener. This increase in distance makes the conversation sound much more muffled and vowel-like, not to mention distorted due to the echo effect.

Another consideration is that all electromagnetic waves, such as sound, obey a physical property known as the inverse square law.

In short, if you speak directly into someone’s ear and then repeat yourself at the same intensity but just two feet away, they will experience what you are saying at 1/4th the volume. At eight feet way, the listener will hear you at 1/64th the volume and so on. This property of sound coupled with the fact that many hearing aids are designed to filter out low volumes in an effort to decrease background noise makes conversation very difficult for the hearing impaired when the speaker is facing away.