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Every guitar player runs into these at least once (and probably way more often, too): power chords. This is a general term for chords consisting of the root note, the fifth, and an octave.

In most situations, these chords are played on the lower strings, often with distortion/overdrive. In my view, that's why power chords never contain thirds; with the distortion and the low tones, this small interval would sound a bit messy.

I wonder if this kind of chords is ever used in other situations though. In rock music, you'll sometimes find chord schemes consisting entirely of power chords played on guitars, with not a single third note anywhere. Is this something that appears in other kinds of music, and on other instruments as well? Additionally, is there a specific kind of emotion/feeling that you create by omitting the third note of your chord(s)?

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Gotta love a well placed power chord :-) –  user2808054 Jul 3 at 8:30
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I agree completely, @DougusMaximus. But also: gotta hate powerchords when overused. –  Lee White Jul 3 at 8:31
    
lol you get that thing where you're begging to hear a 3rd .. somewhere. . anywhere .. –  user2808054 Jul 3 at 8:32
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Note that thirds can actually sound great through distortion. Unfortunately, 12-edo has blessed us with thirds which are rather far off from just intonation; it's mainly this difference that makes full chords so messy through distortion. In Bohlen-Pierce tuning (which is pretty weird because it has no octaves, but has much more precise third and harmonic-seventh intervals) even 7th chords sound pretty amazing distorted. –  leftaroundabout Jul 3 at 15:07
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A major fifth does not exist. Fifths and octaves can't be major or minor (so fourths and primes neither). –  11684 Jul 3 at 16:18

7 Answers 7

up vote 11 down vote accepted

Like you and others said, the main reason of using power chords is to avoid the intermodulation distortion: Thirds sound muddy with distortion.

I think that they generally have two functions in rock music. One function is to use it as a substitute for a triad. Here, the third is generally implied. But it may be played by a solo guitar or sung by the vocalist for example. In this case it has the same function as the triad it replaces.

In some riffs, though, it doesn't make sense to analyze them as chords. They're just fuller sounding monophonic melodic notes. The fifth is not heard independently, it's just part of the timbre.

In classical music, they're called bare, open or empty fifths. According to Wikipedia:

The closing chord of the Kyrie in Mozart's Requiem and of the first movement of Bruckner's Ninth Symphony are both examples of pieces ending on an empty fifth.

My personal impression is that, open fifths give kind of an ancient sound in classical music alluding to the Middle Age music where thirds were considered dissonances.

Also, omitting the third opens up the possibility for leaving the triad ambiguous, ambiguity is a fairly common tool in romantic period music. Beethoven starts his ninth symphony with an open fifth if I remember correctly.

You can also think of Strauss's Also sprach Zarathustra, where you have to wait quite a bit for the third to appear and when it does finally appear as a major third, it instantly shifts to minor, and doing it the other way next time before finally concluding with a convincing cadence in C major. Until then, the modality is left ambiguous.

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They are also called horn fifths on the dominant. They are so called because valveless horns could not make the leading tone (B in the key of C), so omitting the third was common for that chord. (source) –  trlkly Jul 3 at 18:05

Bagpipes come close, even though their drones are at a pitch and its octave. The harmonics come into play here (pun intended), because every instrument produces not only the fundamental note that we think we hear, but some/lots of others too.Each instrument will have particular overtones, partials or harmonics that it will produce in different proportions. The first harmonic is an octave above the fundamental. As such, it's quite easy to miss the fact that it's sounding. The second is a perfect (not maj. or min.) fifth above that, and this one is quite clear on some instruments. The next is two octaves above the fundamental, as such, difficult to discern against the original and its octave already sounding.

With no third sounding in a chord, one can't tell if it's major or minor - a feature the Western world of music seems to appreciate when it's there.So it's a sort of 'hard' sound, with not much flavour.

The other factor is that with distortion/ overdrive the harmonics of a note are accentuated. Those of a fundamental and its fifth work without sounding too discordant. Put a third in - maj. or min. - and those harmonics, as well as the note itself, start to make the sound too crowded.

Another possibility, and I'm not knocking guitar players, is that it's quite easy to just play power chords - particularly with the bottom string tuned to D - one finger will do. Instant success !

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I would venture that ONE of the functions of a power chord is to provide an open melodic soloing space. I recall an interview with Eric Johnson in which he referred to fifth/power chords as "open chords" -- meaning that the soloing space over the chord was unrestricted. That was a different perspective than I had ever used for that terminology(*). I concede that each voice added to a chord restricts (or more tightly defines) the available [traditional] melodic/harmonic choices.

(*) I had always employed that terminology to differentiate chords that contained one or more open strings.

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I think they do evoke an emotion, which is quite hard to describe ..

I wish I could remember the song but there's a solo in said tune where a fiddle player plays a power chord for a bar or two. It's an american folk/country song- the power chord shines right through everything, even though it's not that loud. The rest of the fiddle solo involves a lot of notes (probably 3rds all over the place) so when it settles on the power chord it kind of has a "home" feeling and a notion of "and I mean it".

That's similar-but-different-to power chords on a distorted electric guitar; as you say, the usual reason to miss out the 3rd is to allow the distortion to be more harmonious.

I'm sorry I can't remeber the tune, if it comes to me I'll post it as an edit.

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In the middle ages and before that, they used a system of tuning called Pythagorean tuning (as opposed to 12 tone equal temperament which we use today). This basically meant that you tuned with a stack of fifths until you got 12 notes (and moved the octaves around), as opposed to equally spacing them out. This meant that there were really nice fifths, but awful (well actually not that bad) sounding thirds that were considered dissonant. Because of that, medieval western and Chinese music uses a lot of power chords. Also, Chinese music uses only the pentatonic scale so there aren't many chord options other than power chords. It has a very stable, solid sound to it like the chord of a brick, and now with rock music it makes you think of rock music if it's played on piano or guitar, but not on medieval instruments really, especially since they need to be in a really low octave to sound like rock.

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Actually not that bad? A Pythagorean major triad does sound pretty awful to me indeed (though inversions and minor chords are rather more bearable). Remarkable enough that 12-edo is merely half-way between Pythagorean and just intonation. –  leftaroundabout Jul 3 at 21:23
    
Everyone's different. I asked a bunch of people what they thought of a Pythagorean major triad and they said it sounded fine, but the people in the middle ages must have thought it sounded awful, since they avoided it. I think we only like 12-edo major thirds because we're so used to them, though. –  Nick of Music Jul 3 at 21:34

Power chords and shell chords both serve a similar function. A power chord strips a triad down to the root and fifth; a shell chord uses the root, seventh, and sometimes the third.

Power chords and shell chords both sacrifice some of the chords’ character but still drive the chord progression. They simplify the harmony, which has a couple of major benefits:

  • They are easier to play, which not only helps less-skilled musicians, it also enables pianists to focus more on right-hand melody and less on left-hand harmony.

  • They reduce overtones, which makes the overall sound less muddy. This is a well-known issue for distorted guitars, but it’s also important for the lower octaves on a piano, which have their own kind of distortion.

Depending on the overall instrumentation, other voices may fill in the missing chord tones, or the arrangement may simply use a sparser, more ambiguous voicing. In the latter case, natural overtones may lend the piece a subtle major-key feel.

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Shell chords are one of the reasons I love the sound of many Faith No More songs - they use thirds and sevenths extensively with heavy distortion, leading to some lovely harmonics. –  Dr Mayhem Jul 7 at 9:14

A "power chord" under this name is used for distortion play, period. If you have frequencies f and its harmonics, and 3/2f and its harmonics, the intermodulation frequencies are all multiples of f/2. So that basically means that the harmonics "hint" at a fundamental frequency of f/2 which is in line with the bass note of the power chord.

Organs do have fifth registers which are a perfect fifth (not! a tempered fifth) plus some octaves above other pipes they are combined with. You use them to give a different tone color to some registration by adding overtones. You can also use them for "hinting" at non-existent lower bass notes: combining a 5⅓' register with an 8' register "hints" at a 16' register psychoacoustically. However, on a guitar the notes don't have constant volume, so the characterics and composition of the distorted tones varies with the dynamics of the notes, leading to a much more lively action than the static harmonic composition of organ registers provides.

With smaller intervals than a fifth, the intermodulation frequencies become messier and the resulting spectrum so sparse and irregular that it does not really point convincingly to an underlying bass note in the audible spectrum (power chords tend to be played on the lower strings of a guitar or even bass guitar). Also a fifth tends to be the purest interval in any kind of tempered, particularly equally tempered, tunings and thus gives the clearest approximation to some bass frequency when looking at the sums and differences of the frequencies of fundamental and harmonic frequencies.

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