Once again, the field of automotive racing has stolen some ideas from audiology. If I had a nickel for every time this happened (rather than the other way around) I would have at least … several dollars (Canadian, which is about $1.91 US).
The field of audiology and room acoustics is not shiny, does not have neat doors that swing up, and does not travel in excess of 200 mph. But the laws of room acoustics do have something in common with the McLaren F1 racing car, specifically with the McLaren F1 racing car’s windshield wipers.
Why so? Well, the answer is that 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 all but the few physicists among us. It states: “The acoustic impedance of the acoustic inertance is proportional to frequency.” Translated into English, this means that higher frequencies “see” obstructions while 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.
Those of us who work for the CIA or other spy agencies will find that if we try to listen in on a conversation on the other side of a wall, all we will be able to hear will be the lower frequency vowels. The higher frequency consonants such as “s” and “sh” will be inaudible to us. As spies, we will be relatively unsuccessful because these inaudible high-frequency consonants contribute so much of the clarity to speech.
BACK TO THE McLAREN
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 even a 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 a 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, 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.