A Career in Sound

To Work in Acoustics Means You Learn About the Sound of Sound

Acoustics is the study of sound propagation, it is a field of physics, the theory of wave propagation, almost always discussed in the language of mathematical expressions. It is related to the studies of ocean waves, earthquakes, radio waves, light and heat waves and other types of waves.

In traffic engineering for example there is a wave like behavior in the overall movement of traffic, when one person suddenly applies the brakes, the person behind sees and then applies the brakes and so on, resulting in a wavelike “shock wave” that travels upstream. Similar studies involve the movements of huge flocks of birds or fish. How they travel in a straight line may not be so wavelike but how they turn as a group is very wavelike.

A wave is how a huge number of things, that pretty much don’t move away from each other, can still manage to relay some sort of movement. It is the opposite of a ball. A ball is thrown, travels through the air and hits something somewhere else. A wave, let’s say a wave in a pond, can be created in one place and a little while later the wave arrives somewhere else, where it can be felt. In both cases energy is injected into one location and delivered some time later to another location. But with the wave, nothing actually moved between the two locations, as with the ball, and yet, energy was still delivered between the two locations..

And so as I learned about waves, they seemed to be magical, subtle, nothing like the studies of blunt, finite objects, which make up regular world of mechanics, balls and bats, levers and gears and chains… Here was a mechanical world that didn’t have separate parts. A world that still worked but here it was because of the relationships between the multitude of parts of that world, not parts made from the world.

Let’s think about water. If we freeze it, cut out chunks, and throw the chunks, then we have the traditional mechanical world made up of objects. Now if we unfreeze it and have a liquid we see something different. Liquids flow, they move from one place to another but not as an object, like a chunk of ice but as a whole bunch of separate things in contact with each other, moving downhill, like a crowd of people leaving the football stadium. But water has another kind of behavior. It can also support a wave. Now a wave is not like a stream. A stream flows away from where it was created, but always downhill. A wave also “flows” away from where it was created, but it isn’t limited to flowing downhill, it can flow in any direction, as long as it is away from where it was created.

Next we boil the water and create a huge cloud of steam, water molecules. Now water molecules act like all molecules do when in the form of a gas. Gas molecules individually travel at very fast speeds, thousands of feet per second and they are usually so crowded together they keep crashing into each other very frequently, maybe 100 thousand times a second. If a gas is heated, the hot molecules have a faster speed than the cooler gas molecules along side. The hot molecules hit the neighboring molecules harder and more often than usual and that makes the neighboring molecules move faster. This is how heat is conducted through the air. Cold is the opposite, cold molecules travel slower.

Air can flow. Like water that flows from high locations to lower locations, air flows from higher pressure locations toward lower pressure locations. The wind moves over the earth, driven between huge high and low pressure zones, continent size pressure zones. And air can have a wave like action. If we push a bunch of air quickly in one direction, maybe using a loudspeaker, the closest group of air molecules get pushed by the movement of the speaker cone. They move away and crash into their neighbors, who move away and who crash into their neighbors and so on….Then the speaker come backs up, and molecules fall into the partial vacuum created in front of the cone…the next group of molecules fall in the same direction and so on. A sound wave is the back and forth movement of air combined with changing pressure. When the speaker pushes the air in front of it forward, it compresses that air a little and pushes it away. A little while later the speaker cone pulls back, decompressing the air a little and letting it move in the opposite direction. The pressure changes and movement of air near the speaker cone is relayed away from the speaker con in all directions and we call this action a sound wave.

When the sound wave passes by our ears, the pressure part of the sound wave pushes our ear drum back and forth, which pushes part of our hearing organ back and forth, causing tiny hairs to move inside our hearing organ, which create the sensation we perceive as sound.

OK, that’s the idea behind waves in general and in particular, sound waves. This roughly outlines what the science of waves is about. It’s fantastic on one hand, but on the other…so what? Fair question…so what. We humans have 5 different sensing systems which we use to perceive our world, to figure out what is going on in our world, to us and around us. They are smell, taste, touch, sight and hearing. The smell, taste and touch senses means something has to physically contact us before we sense it. That doesn’t give us much time to prepare ourselves, we’ve been exposed to whatever it is before we can even have an opinion about it. Ugh.

Now sight is pretty neat. We can see things far away, long before then ever come close to us. It is a good early warning system. We can see as mean dog long before it ever bites us and we have time to take evasive maneuvers, like climb a tree. This is all good except for one thing. We have to be looking in the right direction to see something. And so, we can sometimes still be surprised, because what ever it was, we didn’t see it coming.

Finally we come to sound and hearing. It too is an early warning system. We not only can see the dog running, but we can hear it barking. Even better, we can hear the dog barking even if the dog is coming at us from behind. Then we turn around to face the sound and see what is going on. We like sound and our ability to hear sound because it is the only long range detector that we have that works in all directions at the same time. This means that if we listen, we minimize the surprises we get jolted with.

Something else about sound. When we move, we make sound. When we talk or even just walk, we make sound. Our ears hear the reflections of the sounds we make while moving which tells us that an object is nearby, without use even having to see it. When people become blind, this natural ability becomes greatly intensified, and the blind can easily hear the reflections off the space around them, and they can know where they are. As they walk, they can hear the curb, or a tree, or a fence, or a gateway opening into a yard. We always are doing this even though most of us never even think of it.

Think about how we listen to something, if we really want to listen. The first thing we do is to shush the noise around ourselves, as much as possible. Then we try to concentrate on the sound. We usually find that if we quit looking around, and stare as if in a trance, seeing nothing in particular, that our ears really open up. Actually they are always open, but our brain is so full of visions and thoughts that we don’t hear much. To hear, we have to turn off all other senses and zoom in on the one sense, the hearing sense.

Sorta zone out, for a minute, yes, right now….zone everything out except the sounds you are hearing. While I’m talking you can hear much more of the intonation, articulation and character in my voice as you intently listen to it. And that leads you to a better understanding of what’s behind my voice, for example my intensions appear as some kind of characterization in my voice. Evil intentions, generous intentions…the gamet of human intention is expressed through the voice. Not what I am saying so much as to how the sound of what I’m saying sounds like.

There is a difference between the logical message I am communicating, the words and sentences being used, and the emotional intention behind those words, which is solely communicated in the tonality of the voice. Does someone say a sentence in a kind voice, a humorous voice, a snarling voice…..How many kinds of voices are there….Actors have to master the skill of making the sound of the voice fit the intent of the character they are playing. Learning to listen to the sound of the sound is a critical listening skill and you get it by practicing it.

We can hear the words of a sentence and understand them without being able to hear the subtle tonalities with which it was delivered, especially in a noisy space. And so to hear the sound of the sound, we want the noise around us to be quiet. But our hearing system has something to say about this as well.

By the way, listening to the sound of the sound is not just for talking, it’s for musicians who are trying to get their instrument to sound a certain way. The note may be the correct note but the intonation, the character of the note may not be right. Singers also strive to get their voice to mimic the sound they imagine it should sound like, inside their mind.

Back to our hearing system. Let’s imagine we have gone outside, far away from houses, buildings, trees or any other solid object. We might be in the dunes at the coast. We might be in the middle of a golf course or a large sports field. When we talk to ourselves or each other out there, something is missing from the sounds we are trying to make and the sounds we expect to hear. If we make one hand clap, and listen, the sound of what we hear feels vacant, empty, without life and without energy. When we talk, we feel like we have to raise our voices to even be heard, even though there is no loud noises around. What is missing are the reflections of sound. Not just any reflection but those special reflections called “early reflections”.

If we go outside and stand near the wall of a building, that is at the edge of a huge field, and we clap our hands, we hear a hand clap. What we really hear is the noise of the clap from our hands that travels straight or directly past our ears. And a second noise, the reflection of that part of the sound that expanded out, hit the wall of the building and then went past our ears. We heard the direct signal and a reflected signal off the wall of the building. We can take a couple steps back, away from the wall and again clap. The sound seems normal and it is clear we are still hearing the direct sound and a single reflection, except this reflection traveled a longer path between our hands and our ear than the other one.

As we keep stepping back and clapping, we discover that when we are about 25 to 30 feet from the side of the building we no longer hear a single clap, but we hear a double clap sound, one clap from our hands and the other off the wall of the building. We are beginning to hear an echo. As we step farther away from the building the echo becomes more distinct.

Notice how early reflections seemed to undetectable and late reflections, echoes were easily detectable. Our hearing system collects early reflections and adds them to the direct signal, making the direct signal louder than it is by itself. Early reflections fuse with the direct signal. Early reflections help us hear better. When we talk in a small office we don’t hear echoes, we just hear sound, comfortably loud sound. The walls of the office create many early reflections which greatly amplify the direct sound we are listening to.

If we have the same conversation in a big gym, there are no early reflections, because the walls and ceiling are too far away, and there are only late reflections and reverberation, both of which obscure or mask the clarity of the sound we are trying to hear. If we go stand near the side wall or the corner of the gym, we can get at least a few early reflections to pass us by, which will make it easier to understand what the other is saying.

And so early reflections amplify sound. These are reflections that arrive within about 1/20th of a second after we hear the direct signal. Early reflections bounce off objects that are within 25 feet of us. All kinds of spaces where hearing is important are actually designed by architects and interior designers with this early reflection principle in mind. Concert halls, class rooms, doctor offices, and recording studios are just some of the acoustic spaces that use or otherwise control early reflections.

Let’s talk a little more about critical listening. Critical listening is not about understanding what someone is telling you, or noticing the tune being played. Critical listening is to hear what the sound of the sound sounds like. In music theory class everyone learns about the lifeline of a sonic event, in this case, a musical event, typically a sound. Someone plucks just one note on a guitar and what do we hear. Basically before the sound starts we hear quiet. Then we hear some sort of a thump sound, quickly followed by the tone of the note, which slowly dies away. The life of a musical event is outlined as the Attack, Release, Sustain and Decay….ARSD.

When you pluck a guitar, the first thing that happens is that the string is pulled aside and then released with a snap. That sound is the Attack part of the musical sound event. Then the string swings across the fretboard and stretches out again on the opposite side, and stops. That’s called the Release. Then the string rebounds and twangs back and forth, making its tone, which stays loud for a while. This is called the Sustain. And finally the twang begins to die away, which is called the Decay.

Normal people listen to the Sustain of the note and hum or sing along with it, if they like the music. Critical listeners, hear this too, but their listening mind focuses on the sound of the Attack Transient. How that sting is released says a lot about the mood, the intention of the player. It’s not the tone so much as it is how the tone is created, that conveys the meaning of the sound. Critical listeners aren’t jumping around and dancing because that would be having too much fun. Critical listeners are trying to be still, shut out all distractions and concentrate on the sound made during the birth of each sound being made.

And so, we come to an end of our visit into the world of acoustics. Then science of acoustics is just about sound waves. But most people who work in then field of sound or acoustics are working with the effect sound has on people. From acoustic engineers, to recording engineers, from ear, nose and throat doctors to audiologists, from sonograms of the heart to sonograms of an unborn baby, from architects and interior designers to acousticians and sound designers. There is a whole world of support, research and service helping people hear what they what to hear and to not have to hear what they don’t want to hear.

You don’t learn acoustics in recording school, you learn how to run the equipment in a recording studio. A sound engineer is not an acoustic engineer; they run a sound board at concerts and in church. To work in the field of acoustics you have to take math, physics, electronics and engineering courses and complete an undergraduate degree in that area. Then, in grad school, you finally get to learn acoustics.

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