Can loudspeakers play ultrasound

They are inaudible, but everywhere: there are sound waves in train stations, schools and even in libraries and museums. And even if we cannot hear them, our bodies can certainly hear the constant noises.

Tim Leighton from the University of Southampton determined how we are literally continuously exposed to noises that are imperceptible to the human ear in everyday life. Even loudspeakers, door openers and other devices emit these high frequencies.

There is as yet no hard evidence that these are harmful to our health, but Leighton can imagine it. He has compiled studies from the past 40 years that deal with ultrasound and its effects on the human body. As Leighton explains in "Proceedings A" of the British Royal Society, it cannot be ruled out that intense sound waves can be harmful to health.

Ultrasound is the frequency of sound waves that are above our hearing threshold of around 16 kilohertz. So far, the motto has been "what a person does not hear does not harm him". On the other hand, however, it has been shown that ultrasound can temporarily render rats sterile, especially at high intensities. Even trees use ultrasound waves. They send them out when there is a lack of water, which French researchers have found out with very fine microphones.

If people could hear it, the signal would resemble a high-pitched, piercing whistle. Signals that are usually emitted by loudspeaker systems in public buildings such as train stations and schools, but also in cinemas or sports facilities. They occur between amplifiers and loudspeaker circuits and serve, among other things, as an acknowledgment of receipt. The result of the measurements: In many places there are ultrasonic tones or pulses of high intensity. In the great hall of a train station, for example, Leighton recorded a load of 94 decibels for sounds around 20 kilohertz, in a school and museum it was still between 60 and 80 decibels.

Ultrasound could cause headaches or tinnitus According to the researcher, this uninterrupted exposure to the sound could cause health problems. Leighton suspects that the inaudible sound pulses could be behind unspecific complaints such as nausea, tinnitus, headaches and migraine attacks or a feeling of pressure. "Although such symptoms have been reported with ultrasound for 40 years, their non-specific nature makes them difficult to attribute to a clinical cause."

There are regulations to avoid strong ultrasound exposure in the workplace. However, these are decades old and mostly relate to high broadband frequencies - an ultrasonic noise, so to speak, as the researcher explains. The "acoustic smog" of narrow-band, pointed tones generated by modern devices has not yet been taken into account. The consequences have not yet been investigated in more detail. Many devices do not even state which intensities of ultrasound they would emit, criticizes Leighton. He therefore urgently advises further investigations into the exposure to ultrasonic smog and the possible effects on health.

The number of ultrasound sources has increased significantly thanks to modern technology in particular: a few decades ago they only occurred in certain drillings, cleaning devices or as a side effect of great noise. Today there is hardly any escape from the ultrasonic smog Even computers and wireless chargers can emit ultrasound.

In order to find out how strongly these inaudible frequencies dominate our everyday life, Leighton measured this in various public places. The tool for this: a simple smartphone or tablet. "Many of these devices have microphones that can register frequencies above 20 kilohertz," explains the researcher. "If you use an app that displays spectrograms, you can recognize the ultrasound as a tone or pulse."

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