A Very Short Introduction to Sound
A quiet and studious audience packed their way into the old-fashioned circular Anatomy Lecture Theatre in Summerhall, and it was interesting that for a lecture about sound, neither the acoustics not the microphone were optimized for easy listening. Mike Goldsmith was a fascinating lecturer, with books’ worth of knowledge tumbling forth in a steady stream for almost an hour. He is a freelance acoustician and science writer and the former Head of Acoustics at the National Physical Laboratory. One of his many books for adults and children is Discord: the Story of Noise and a slimmer book called, as the lecture, ‘A Very Short Introduction to Sound’.
He began with the basics, for us mere mortals, and sped off from there. He talked about the inherent difficulties with the objective and subjective dichotomy of the discussion of sound, but decided to define sound simply as an object oscillating; unless it’s an explosion of some kind or due to variations in heat. He discussed how important sound is, due to the fact that it can go through lots of different media, like water, air etc. He went on to explain the origin of sound, and that the first sound occurred very early on after the Big Bang. Sound is so important to us on a career level as such a wide variety of professions deal with sound, not just the obvious ones like musicians, but also including vehicle designers, sound artists, politicians, and generally that sound is so precious to us in our experience of daily life as humans.
He covered the dangers of sound, and the thresholds of sound that are comfortable and safe for the human ear, up to about 120 decibels, but also allowing for variation, as showed that some people are just more sensitive to the effects of sound. 90 decibels is just starting to become dangerous for our hearing. He discussed musician’s hearing being damaged by playing regularly in orchestras due to the noise level. The frequencies that we can hear change as we age, due to either the ageing process and general exposure to noise over a lifetime. There were chuckles in the audience as he talked about the rather cruel ‘mosquito device’ that vibrates at 16-17kHz and is supposed to be used for repelling teenagers, as by the time we reach adulthood we can no longer hear at those frequencies. One lady confided in me that she needed one for her challenging 26yr old son with ADHD who was refusing to leave home! Most people can hear up to 20kHz but there’s a small minority of people who can hear up to 30kHz. I’m always interested in learning about exceptions and why they happen, and made a mental note to find out more about their genetics and/or environment. He talked about the dangers of the frequency and level of noise in modern cities, and the effect it has on us as humans, and singled out that the type of frequency used in audio addresses in places like airports subways etc. have such a new, strong frequency that they may be doing damage to our hearing.
One of most fascinating parts of the lecture was when he showed a diagram of the density of cosmic sounds soon after the Universe was formed, and explained the patches you could see clearly were density variations due to ionised plasma falling into an area of local matter – like mini black holes. An in and out effect created, and basically a sound wave. He explained the low and long pitch of the sound of the universe expanding, and showed the density imbalances leading to the formation of planets. I wished he could have played a clip of the sound in the lecture, but instead I listened to the sound on the internet when I got home and it had a bizarre, grounding but also unsettling effect on my body.
He talked about sound in the ocean and its importance to sea creatures for quite a significant part of the talk. How sounds in the ocean are so much more important that light. Scientists measuring temperature change using sound-measuring devices. The ‘sound traps’ in the ocean that span large distances and both animals and humans send sound through them. Of course the whales beat us humans to this a long time ago; and use it for their communication over vast distances. Scientists think perhaps there was a time that the oceans were such that even Antarctic and Arctic whales could hear and communicate with each other!! The speed of travel of the sounds depends on the saltiness of the sea. I thought it was fascinating that under the water, sound frequencies split up, and touched on the fact that different sound frequencies in speech relay both the informational and the emotional components of speech, and I wondered if the different tonal aspects of various languages and dialects directly affect not just the population’s emotional expressions but emotional states .
He continued on to the basics of music, of course, and the fact that the foundations of music are in based firmly on physics. He touched on the makeup of a piano keyboard and the relationship between the C notes on a piano key board; the fact that if you double the frequency you get the next C along. Relationships of notes to each other depending on wavelengths. It made me think about different music systems in different cultures and how that affects people psychologically and physically. Also the fact that under colonial regimes, banning of ‘native’ instruments are often amongst the first laws to suppress a colonised people. He discussed the social and emotional effects of music, which are universal amongst all peoples, to a point. Which sounds create feelings of agitation and aggression, and which sounds are soothing to the human body/mind. The repetitive sound of trains are always more popular and experienced as less intrusive than aircraft noise. Aircraft are so much more disturbing to humans that house price goes down but it’s the opposite for trains. Prices can go up 10 per cent more for being near a train station! Helicopters are considered even more annoying, but studies have found that the experience is quite subjective, depending on what he helipcopter is being used for, people experienced it as more or less annoying. A little like if you are invited to the noisy party next door or not! Or whether you like the people!
One of the more mindblowing revelations, was the fact that recently, using ultrasound, we can actually listen to the sounds of plants growing, and in experiments done on maize, it’s been found that as a plant dries out, it generates ultrasonic signals, detected by special microphones. Plants give off sounds like high pitched squeaks when they need water! These experiments have lead to a whole science of agro-acoustics, for example, measuring the rate at which sap moves, using sound.
To wrap up the lecture, Goldsmith suggested the possible applications of sound and acoustics in the future. For example, ultrasonic levitation that comes from the packed force of the ultrasound. This could have great applications for useful things like invisible keyboards and possibilities of which now being explored for use in space stations. He touched on the use of acoustic microsurgery, using ultra high frequencies getting into dimensions less that the width of a molecule. At this stage, you begin to leave behind the idea of ‘sound’ as a wavelength, as the frequency increases and becomes higher. As various physicists like Einstein have touched on, the laws that govern the universe don’t match up with the laws of the atom, yet the study of sound may give us this bridge of understanding. Mindblowing stuff, indeed.
Reviewer: Lisa Williams
Mumble Words 