The physics of playing guitar - Oscar Fernando Perez - video Dailymotion

TED-Ed

Guitar masters like Jimi Hendrix are capable of bending the physics of waves to their wills, plucking melody from inspiration and vibration. But how do wood, metal, and plastic translate into rhythm, melody, and music? Oscar Fernando Perez details the physics of playing the guitar, from first pluck to that final shredding chord.   Lesson by Oscar Fernando Perez , animation by Chris Boyle.

Transcript

00:00Hendrix, Cobain, and Page, they can all shred.

00:12But how exactly do the iconic contraptions in their hands

00:16produce notes, rhythm, melody, and music?

00:21When you pluck a guitar string,

00:23you create a vibration called a standing wave.

00:26Some points on the string, called nodes, don't move at all,

00:30while other points, anti-nodes, oscillate back and forth.

00:34The vibration translates through the neck and bridge to the guitar's body,

00:39where the thin and flexible wood vibrates,

00:42jostling the surrounding air molecules together and apart.

00:46These sequential compressions create sound waves,

00:49and the ones inside the guitar mostly escape through the hole.

00:53They eventually propagate to your ear,

00:56which translates them into electrical impulses that your brain interprets as sound.

01:01The pitch of that sound depends on the frequency of the compressions.

01:06A quickly vibrating string will cause a lot of compressions close together,

01:10making a high-pitched sound,

01:12and a slow vibration produces a low-pitched sound.

01:16Four things affect the frequency of a vibrating string—

01:19the length, the tension, the density, and the thickness.

01:24Typical guitar strings are all the same length and have similar tension,

01:28but vary in thickness and density.

01:31Thicker strings vibrate more slowly, producing lower notes.

01:35Each time you pluck a string, you actually create several standing waves.

01:40There's the first fundamental wave, which determines the pitch of the note,

01:44but there are also waves called overtones,

01:47whose frequencies are multiples of the first one.

01:50All these standing waves combine to form a complex wave with a rich sound.

01:56Changing the way you pluck the string affects which overtones you get.

02:01If you pluck it near the middle, you get mainly the fundamental and the odd multiple overtones,

02:06which have anti-nodes in the middle of the string.

02:09If you pluck it near the bridge, you get mainly even multiple overtones and a twangier sound.

02:15The familiar Western scale is based on the overtone series of a vibrating string.

02:21When we hear one note played with another that has exactly twice its frequency,

02:26its first overtone, they sound so harmonious that we assign them the same letter

02:32and define the difference between them as an octave.

02:37The rest of the scale is squeezed into that octave,

02:40divided into 12 half steps whose frequency is each 2 to the 1 12th power

02:46higher than the one before it.

02:48That factor determines the fret spacing.

02:51Each fret divides the string's remaining length by 2 to the 1 12th power,

02:57making the frequencies increase by half steps.

03:00Fretless instruments like violins make it easier to produce the infinite frequencies between each note,

03:06but add to the challenge of playing in tune.

03:10The number of strings and their tuning are custom tailored to the chords we like to play,

03:15and the physiology of our hands.

03:17Guitar shapes and materials can also vary,

03:20and both change the nature and sound of the vibrations.

03:24Playing two or more strings at the same time allows you to create new wave patterns,

03:29like chords and other sound effects.

03:32For example, when you play two notes whose frequencies are close together,

03:36they add together to create a sound wave whose amplitude rises and falls,

03:41producing a throbbing effect, which guitarists call the beats.

03:45And electric guitars give you even more to play with.

03:49The vibrations still start in the strings,

03:51but then they're translated into electrical signals by pickups,

03:55and transmitted to speakers that create the sound waves.

03:58Between pickups and speakers, it's possible to process the wave in various ways,

04:04to create effects like distortion, overdrive, wah-wah, delay, and flanger.

04:11And lest you think that the physics of music is only useful for entertainment,

04:16consider this.

04:17Some physicists think that everything in the universe

04:20is created by the harmonic series of very tiny, very tense strings.

04:27So might our entire reality be the extended solo of some cosmic Jimi Hendrix?

04:33Clearly, there's a lot more to strings than meets the, uh, ear.

The physics of playing guitar - Oscar Fernando Perez

Category

Transcript

Be the first to comment

Recommended