The field of room acoustics is not shiny, does not have neat doors that swing up, and does not travel in excess of 100 mph. But the laws of room acoustics do have something in common with the McLaren F1 racing car. Specifically, what do the laws governing room acoustics have to do with the McLaren F1 racing car’s windshield wipers?
This is an obvious question and I am sure that most would have asked this immediately. This is all about the acoustic behavior of various wavelengths.
As we know, low frequency sounds have long wavelengths and high frequency sounds have shorter wavelengths. There is an important rule of physics which is almost indecipherable to most of us- “the acoustic impedance of the acoustic inertance is proportional to frequency”.
Other than the few physicists among us, in English, this means that higher frequencies “see” obstructions when lower frequencies go right through them. As long as the wavelength of sound is significantly greater than the width of an obstruction such as a wall or a head, that obstruction will be acoustically invisible to the sound.
Low frequency vowels in our voice have long wavelengths so they can go through walls with minimal attenuation. In contrast, higher frequency consonants, see the wall as an obstruction and reflect back into the room, contributing to room reverberation.
For those of us who work for the CIA or other spy agencies, if we were to listen in on a conversation on the other side of a wall, all we would be able to hear would be the lower frequency vowels. The higher frequency consonants such as “s” and “sh” would be inaudible to us. As spies, we would be relatively unsuccessful because these inaudible high frequency consonants contribute so much of the clarity to speech.
So, what does this have to do with the McLaren F1 racing car’s windshield wipers?
Since as the frequency increases, the wavelength decreases, what happens when we get to the very, very high frequency region- the region of ultrasonics?
As frequency increases, the wavelength can become so short that any miniscule molecule or object will act as an obstruction. These high frequency, very short wavelength sounds can bump into very small objects and move them around. And if these very high frequencies are aimed correctly they can even levitate an object- this is called acoustic levitation.
Short of levitation, a very short wavelength sound can also move small objects such as droplets of water, and if very, very short wavelength sound, can move actual molecules of matter. And this is how the new proposed windshield wipers can work on the McLaren F1 racing cars. A series of ultrasonic emitters are arranged around the windshield and the annoying rain is just pushed off the windshield. This would be more streamlined than using actual mechanical windshield wipers that would alter the air flow over the front window.
Obviously the engineers who designed this new ultrasonic, windshield wiper-less, windshield wiper knew all about room acoustics and audiology, even if they didn’t know what the sentence “the acoustic impedance of the acoustic inertance is proportional to frequency” means.
MARSHALL CHASIN, AuD
Dr. Marshall Chasin is Director of Audiology at the Musicians’ Clinics of Canada, Adjunct Professor at the University of Toronto (in Linguistics), and Associate Professor in the School of Communication Disorders and Sciences at Western University. He is the author of over 200 articles and 8 books including Musicians and the Prevention of Hearing Loss. He writes a monthly column in Hearing Review called Back to Basics. Dr. Chasin has been the recipient of many awards over the years including the 2012 Queen Elizabeth II Silver Jubilee Award and the 2017 Canada 150 Medal. He has developed a new TTS app called Temporary Hearing Loss Test app. And he is not as boring as this bio makes him sound!