The Acoustic Reflex

Human ears are amazing. They can distinguish half a million tones and detect sound levels from 0 to 135 decibels. Zero dB is a very faint sound, and 135 dB is extremely painful and damaging to hearing. Decibels are measured on a logarithmic scale, so 135 dB is 10 trillion times as loud as 0 dB. Anything over 85 dB can damage hearing with long exposure, but God has given us an automatic protection system that activates between 70 and 100 dB. It is called the acoustic reflex.

Here is how the human acoustic reflex (also known as the stapedius reflex or auditory reflex) works. High-intensity sounds trigger an involuntary muscle contraction in the middle ear. Tiny muscles in the middle ear, primarily the stapedius and tensor tympani muscles, contract to dampen the movement of the ossicles or stapes (the small bones in the middle ear). Because of this reflex, chain saws, loud engines, or hair dryers can make it difficult to hear conversations, which are typically not more than 60 dB, but it helps protect the inner ear from damage caused by loud noises.

 When the acoustic reflex activates, the stapedius muscle pulls the ossicles (stapes) of the middle ear away from the cochlear window, and the tensor tympani muscle stiffens the stapes by pulling on the eardrum and malleus (hammer bone). This is essential to protect hearing in everyday environments. However, the acoustic reflex is not fast enough to react to sudden loud noises, such as gunshots. Also, extremely loud noises or prolonged exposure to loud noises can still harm your hearing, and for that reason, wear ear protection when around loud noises. We should be thankful for God’s design of ears and for the automatic protection He provided as part of the amazing design of the human body.

— Roland Earnst © 2026

Reference: Stuart Burgess, Ultimate Engineering, Discovery Institute Press, © 2026, pages 127-128, and Wikipedia.