Demystify science | The impact of infrasound and ultrasound

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Posted at 6:00 a.m.

Ultrasounds do not seem harmful, but infrasounds are associated with psychological and cardiovascular disorders. It is not known, however, whether they are impacts of sounds on health directly, or the impact of the disturbance they cause.

Infrasons start at 20 Hertz (Hz), either at very low frequencies, while ultrasound are at the other end of the spectrum, at more than 20,000 Hz. By way of comparison, a nightclub issues bass in the 200 Hz region and an ambulance will go up to 2000 Hz. One of the difficulties of studies on ultrasound and infrasions is that they require more expensive research devices That clinical devices, which cost thousands of dollars rather than hundreds of dollars. Clinical devices generally examine the frequencies between 250 and 8000 Hz.

Ultrasound, or acute sounds bordering on the noticeable, are only frequent in dentist offices, in certain industrial environments and in zoos housing dolphins or bats. “There have been some studies on dentists’ offices, and nothing has been observed as an impact on health,” said Professor Richard Neitzel.

Our ability to detect infrasound stems from the need to hear the steps of predators slowly approaching at night, according to Mr. Neitzel. The latter directs a vast study, launched in 2019, to measure the ambient noise from Apple earphones. Apple Hearing Study brings together more than 160,000 Americans from 50 states. “Before wind turbines, less than 1 % or even less than 0.1 % of our noise exposures concerned infrasounds or very low frequencies. »»

The sounds of wind turbines have been greatly studied by public health organizations. They generate very low frequencies by their movement in the air, which is called “aerodynamic noise”.

Anxiety

“There seems to be with sounds with very low frequencies an increase in the risk of depression, anxiety and cardiac palpitations with the proximity of turbines,” explains Richard Neitzel.

The problem of infrasound is that they are difficult to block, because they have a larger wavelength and therefore can cross the obstacles against which shorter wavelengths are collided. “We know when you live near a nightclub, a railroad or a road where many trucks pass. Or when you are stopped at a red light near a car in which music plays with a lot of bass. »»

On the other hand, infrasounds do not seem to damage the eyelashes of the inner ear which transmit noise to the auditory nerve, like the other types of strong noise. “The eyelashes responsible for the perception of high frequencies are near the opening of the inner ear, so they are damaged the first. Lower frequencies should go further in the inner ear, so they lose power and make less damage. »»Do you have a scientific question? Write us