The Physics Of Sound

Have you ever wondered just what you're hearing when you listen to music? This will explain that to you.

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Have you ever wondered why you hear something? OK, probably not. Ever wondered why something sounds the way it does? Possibly, huh? This will explain all of that to you. You hear sound when something vibrates. These vibrations disturb air currents around the vibrating object, which in turn creates variations in air pressure. "Sound waves" are created from varying air pressures, and these sound waves are transmitted through the air to your ears. They make your eardrum vibrate at a certain frequency, and then you hear the sound that the wave has transmitted. They travel through the air at around 1100 feet per second. Diagram of a sound wave: Now that you know just what sound is created from, it's time we delve into the three components of sound: Pitch, Loudness, and Timbre.

Pitch

Remember those vibrations we talked about earlier? Well, these air patterns are repetitive in nature. This means that they stay at relatively the same "shape" throughout the sound wave. This pattern of a sound is called a "waveshape" or "waveform." The number of repetitions that occur from a specific waveshape is called "frequency." The frequency of a sound is what gives it it's pitch. So, for example, the waveshape of an A "looks" different from the waveshape of a B, and so forth. A sound with a very high pitch is said to have a high frequency, and a sound with a low pitch has a low frequency. Frequency is measured in "hertz" or "Hz." So when your tuner says "A440," that means that the A note you're tuning to has a frequency of 440 cycles per second. When a note octaves, it's frequency doubles. So if your tuning pitch is A440, then an octave above that would be A880. And if you wanted to go an octave below A440, it would be A220. Simple, right? In addition to measuring frequency, we can also measure just how long an actual wave is. This is called "wavelength." The wavelength of a frequency can be calculated by dividing the velocity of sound (1100 fps) by the frequency. So if we wanted to find the wavelength of A440, this is the equation we would have: 1100/440, which comes out to about 2.5 feet. The range of frequency for human hearing is from about 20 Hz to 20000 Hz.

Loudness

The strength of the vibrations in air pressure determines the loudness, or volume of a sound. The greater the air pressure variations, the louder we perceive the sound. This is referred to as the "amplitude" of a sound. To fully understand this, think of font sizes. Here is a letter A at a certain font: A And here is a letter A at a larger font:

A

It's still the letter A, but one is just bigger than the other. When I play a note on my guitar, the waveshape will be a certain size. Now, if I play that same exact note, but alot louder, I'll get the same waveshape, but it will just look bigger. It has the same shape, but the proportions are just a bit larger. That's why a note doesn't change it's pitch the louder or softer we strike it. Sound volume is measured in Decibels (dB). The "threshold of hearing" to "threshold of pain" range is from 0 dB to 120 dB. Decibel relation chart:

Timbre

Timbre (pronounced TAM-ber) is what lets us distinguish a guitar sound from a piano sound. Timbre means "tone colour" and different timbres occur because most sounds perceived as pitch actually contain many frequencies other than the fundamental. (The fundamental being the main tone we hear.) So when someone hears the note "middle C" on a piano, many frequencies besides the C frequency are audible. The other frequencies present occur in a series called the "harmonic" or "overtone" series. The frequency of each harmonic is a whole number multiple of the fundamental frequency. (i.e., 2X, 3X, etc.) The harmonics of the note A: So, the second harmonic (the fundamental being considered "one") is and octave above the fundamental, the third harmonic is an octave plus a fifth, and the fourth harmonic is two octaves above the fundamental. The number of harmonics audible determines the timbre of the sound. Most sounds have timbers that change over time. For example, a low note struck heavily on a guitar will sound bright at first, but as the sound decays, it will become "duller." This shows that the higher harmonics die out quicker than the low ones.

In Conclusion...

So, in conclusion, while each of the three components of sound are independant of each other, they work together to give each type of sound we hear it's own unique properties. Think about the complexity of sound the next time you pick up your guitar. Maybe you'll appreciate the science and mathematics behind music a little more. -Mike

54 comments sorted by best / new / date

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    suc_mi_wenni
    Stuff like this interests me in a, wierd, boring way but interesting never the less..
    Andrewbiles
    newcomer wrote: And overdrive/distortion changes the wave altering the wave 'points' from sharp to blunt, or even square; the more overdrive/distortion the further from a perfect wave you get. If that makes sense, i hope it does.
    Distortion just adds a load of extra harmonics to the sound. I knew all of this already as it's basically what I do at Uni, but it's still nice to read through this stuff and see the way others write it out. With the decibels chart though you should really have mentioned that people shouldn't listen to music too loudly for long periods of time as it can really mess your ears up (tinitus). Oh, that just one harmonic of a note is the sine wave (say A with the hz of 440) and then adding other harmonics to that will slowly create a square wave and all that. Well written article.
    helpme
    Nice article, but I would still like to learn more about why harmonizing sounds good and what are the physics in distortion and overdrive. 10/10
    newcomer
    good article, good stuff. But don't most people know about pitch and volume? Maybe its just me. I'm curious to know more about Timbre...lots more. And overdrive/distortion changes the wave altering the wave 'points' from sharp to blunt, or even square; the more overdrive/distortion the further from a perfect wave you get. If that makes sense, i hope it does. i liked the article Zamboni. rock on. 10/10
    HelpMeImHungry
    i was literally wondering about this a day before i saw it on the site, thanks man, but I wish you went more into timbre
    Scourge441
    Interesting article, the comments section shows that the people want more. How about a part 2?
    vanceboy
    Pretty Imformative... But what I am really curious about, is why certain harmonies, such as the fifth, sounds good (scientifically speaking) and others (such as 4th Augmented/5th Diminished) sound more unnatural.... Maybe you could explain that in another arcticle. Still, this one wasn't bad.
    That's cuz certain waves correspond with each other, while ones that sound irritating are waves that don't really coincide, the waves don't match up. For example, octaves sound really good with each other. That's cuz playin two octaves, the top one is exactly twice the wavelength of the other. But that's really basic.
    Zamboni
    Scourge441 wrote: Interesting article, the comments section shows that the people want more. How about a part 2?
    I'm thinking about writing another one. Give me some insight as to what you guys would like to see in Pt. 2.
    -x-TheUsed-x-
    less confusing than my physics teacher!!! but why is rock at the top of that decibel chart - u can play rock at any volume?
    Drewsufer
    Well....of course amps can create multiple frequencies...also Your eardrum receives all the waves and creates one pattern...with multiple parts of frequencies...that then travel through a canal... Then, your inner ear has tens of thousands of tiny little hairs dispersed in a tiny canal.... The hairs resonate and vibrate to the frequency they receive...they bounce up and down to this pattern....this signals nerves in your ear to transmit patterns to your brain.... Cool eh?
    psychotim
    something i have been wondering about lately is why can we hear more then one note at the time and how can a speaker make more then one note? A speaker cant make many diffrent frequenceys at the same time, or can it? And how can the ear pick up all these frequenceys?
    DainBramage546
    right now im in school working on a physics project on guitar. this article was well written and it helped me with the project. thanks
    DamoPlaysBass
    I reckon you should do a really in-depth article about the perfect fifth and fourth - I have a theory that the dominant fifth is slightly more consonant than the sub-dominant fourth, and there is a deeper reason for the 'dominant'/'sub-dominant' labels. If you already know anything about this though, don't keep it to yourself!
    will102387
    i'd like to know why when it gets hotter the strings become more sharp and when its colder they get flat. in physics, when something this warmer it expands and shouldn't that make the strings flat? i dunno, ive always wondered.
    Towlie
    It would have been nice to see some stuff about harmonics, and standing waves etc... , but for a start its not bad. Nothing new for me though...
    Yongyot
    cool article... I've heard that there is a note from a certain machine that doesnt have any notes other than the fundametal... Think it was called the "Sinus note", would be cool to hear a little about that one, otherwise really interesting!
    black_sabbath85
    Very basics well written. There is a tremendous amount of engineering and physics going into sound amplifiers.
    atc228
    wow that was a lot of information, and u didnt ramble on at all. i liked it, and learned a lot, 10 stars or whatever the rating is now. keep up the good work
    EZLN libertad
    nice man, i knew a little bit about it, but now i know more i liked that comparison of noise levels chart too, of course rock is the loudest :p
    kostya
    very enjoyable and as a mathmatician gave me a new understanding of guitar
    Nome
    Pretty Imformative... But what I am really curious about, is why certain harmonies, such as the fifth, sounds good (scientifically speaking) and others (such as 4th Augmented/5th Diminished) sound more unnatural.... Maybe you could explain that in another arcticle. Still, this one wasn't bad.
    Snipe
    Pretty good, I skimmed it and it looked like you had at least the basics. I'd read it, but I did a huge report last year on the science of guitar.
    starbomb13
    ^i did a whole end-of the year 30% of grade proj. on sound/audio,where i mainly focused on music/guitar. Not that interesting, but still good to know.
    fahd
    yes to the point. and understandable u shud b teachin physics in the college i studied. i totally understood this and the proffessor took ages but i took nothing from him maybe bcuz he was'nt teaching with a musical perspective. thumbs up sir.
    jamstation
    well, nothing too new for me, but... not bad. you should probably elaborate on timbre..
    Spanner
    Nice one Zamboni I do physics as well, and we dont cover sound as good as this 10