The research performed in our laboratory covers a number of areas related to inner ear function and the physiology of the cochlear fluids (apparent from the rest of the Cochlear Fluids website). Our group has for years been using infrasonic tones to study how the ear works. These are often described as “biasing tones”, because they allow the structures of the ear to be displaced slowly while measurements are made. For almost 10 years we have been using infrasonic 5 Hz bias tones at levels as low as 85 dB SPL (shown as the green diamond in the graph at the right) to manipulate cochlear responses in guinea pigs. The guinea pig is LESS sensitive to low frequencies than the human, so this makes you realize that low frequency infrasonic sounds ARE AFFECTING THE FUNCTION OF THE EAR at levels well below those that are heard by humans.
The reason humans can only hear frequencies between 20Hz and 20kHz is due to the limitations of our auditory system. Our ears are able to detect sound waves within this range and convert them into electrical signals that are then processed by our brain as sound. Frequencies below 20Hz and above 20kHz are not as easily detected by our ears and are therefore not perceived as sound.
Our ears have tiny hair cells called cilia that are responsible for detecting sound. Different cilia are sensitive to different frequencies, allowing us to hear a range of frequencies within the 20Hz-20kHz range. When sound waves enter our ear, they vibrate these cilia, and the signals are then transmitted to the brain, where they are interpreted as different frequencies.
If we are exposed to frequencies below 20Hz or above 20kHz, our ears may not be able to detect it, but our bodies can still sense it. For example, low frequencies can be felt as vibrations in the body, while high frequencies can cause a ringing sensation in the ears. Prolonged exposure to frequencies outside of the audible range can also lead to hearing damage.
Different animals have different ranges of hearing due to variations in their auditory systems. For example, some animals, like bats and dolphins, have a much wider range of hearing than humans, allowing them to detect high-frequency sounds that are used for echolocation. Other animals, like elephants and whales, can hear frequencies as low as 5Hz, which is below the human range.
Yes, with the help of technology, we can hear frequencies outside of the 20Hz-20kHz range. Devices like hearing aids and cochlear implants can help people with hearing impairments detect sounds at different frequencies. Additionally, specialized equipment, like ultrasonic or infrasonic microphones, can also capture sounds outside of the audible range for scientific research and other purposes.