Sounds that cannot be heard (inaudible) at lower frequencies have not been considered harmful to the ear, but this may not be the case. This is the conclusion of a study from the Ludwig Maximilian University in Munich, Germany. The study shows that being exposed to inaudible sounds for only 90 seconds can have an effect on the inner ear.
Low frequency sounds can be harmful
Human beings are normally able to detect sounds in the range of 20-20,000 Hz and it is well known that sounds within this range can damage the hearing. However, sounds under the frequency of 20 Hz can also affect the ear even though we are unable to hear them.
The German study was conducted on 21 volunteers who were placed in sound proof booths. The volunteers were exposed to a frequency of 30 Hz for 90 seconds. After this, the activity in their ears was recorded.
Whistling sounds from the ear
The activity of the ears was measured from faint whistling sounds that are constantly being emitted from the human ear. The phenomenon is called spontaneous otoacoustic emissions, SOAEs. The whistling sounds cannot be picked up by the human ear and were detected with a microphone.
The researchers found that after being exposed to low frequency sounds for 90 seconds, the whistling sounds or SOAEs changed. The SOAEs became temporarily stronger or weaker, which tells the researchers that sounds can be harmful even though we are not able to hear them.
According to researcher of the study, neurobiologist Markus Drexl, the results do not indicate that exposure to sounds with low frequencies leads directly to hearing loss, but it makes the ear more prone to being damaged.
The study was published in Royal Society Open Science.