We began investigating quartal harmony— voicings constructed from stacked fourths, rather than thirds—in last month’s column (“Exploring Quartal Harmony,” April 2011PG). It was the first of a three-part series, and this month we’ll be building on what we covered previously. If you missed that introduction or want a quick refresher, check out the lessonhere.

So far, we’ve played three-note quartal voicings on string sets 3–2–1 and 4–3–2. In this lesson, we’ll map out three-note forms on the lower string sets and then test-drive larger four- and five-note quartal voicings. Ready?

InFig. 1, we harmonize E Mixolydian (E–F#–G#–A–B–C#–D) in fourths along string set 5–4–3. For starters, slowly play the middle note in each voicing by itself, ascending on the 4th string from E, 2nd fret, to E on the 14th fret. This one-octave crawl establishes E Mixolydian as our parent tonality, which you can think of as a note pool or construction kit for our quartal voicings.

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Now, return to measure one and play each three-note grip. Again, we’re ascending through a one-octave stretch of E Mixolydian, but this time we’re moving a pair of stacked fourths along three strings. As you work through these voicings, notice how the fourths are either perfect (which is most of the time) or augmented, depending on where you are in the scalar ascent.

For example, the first two grips consist of a pair of perfect fourths. But when we hit grip three, the interval stack changes—the bottom one becomes an augmented fourth (D-G#), while the top remains a perfect fourth (G#-C#). We also depart from stacking perfect fourths in the penultimate voicing, A–D–G#, at the 12th position. This time our bottom interval is a perfect fourth and the top interval is an augmented fourth. In each voicing, we adjust the intervals to conform to the parent tonality of E Mixolydian.

Quartal harmony is inherently dissonant— many would saydeliciouslyso—and our ears are more willing to accept this restless, edgy sound in higher registers. It’s not that youcan’tplay quartal voicings on the bass strings at the lowest frets, but you have to be careful not to let the harmony get too murky. Muddy fourths just don’t sound appealing.

That said, one advantage of fretting quartal forms on the bass strings is physical: It allows you to slip in a pedal tone or drone on a higher string, as inFig. 2. Here, an insistent open E adds a welcome sparkle to the dark-sounding chords. This technique isn’t limited to E Mixolydian, so as you explore quartal voicings on the bass strings in other keys and different parent tonalities, try plucking open E or B (or both) to see if you like adding a bit of jangle to the block-chord sound.

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Up to this point, we’ve been working with three-note grips, but the real fun begins with four- and five-note quartal stacks.Fig. 3opens the door to this sound with four-note voicings composed of three stacked fourths. This time, we’re using E Dorian (E–F#–G–A–B–C#–D) as our parent tonality. And instead of restricting ourselves to a given string set, we’re now moving across the fretboard, as well as up and down.

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But the basic concept hasn’t changed: Each voicing contains various combinations of perfect and augmented fourths, and the mix of intervals within each grip is determined by the parent tonality. For example, the first voicing in bar 1 comprises three perfect fourths, while the arpeggio in bar 3 is built on an augmented fourth with two perfect fourths stacked above it. For extra points, record or loop this four-bar phrase and then try jamming over it in E Dorian.

Fig. 4consists of five-note quartal voicings drawn from the parent tonality of E Aeolian (aka E natural minor). One way to keep these lumbering babies from sounding too muddy or dissonant is to borrow a trick from Brazilian guitarists. First, fret the voicing as a single large grip and then selectively pluck notes from within it, darting back and forth with your picking-hand thumb and fingers to create syncopated rhythms from smaller clusters of sound (measures 1 and 3). Playing arpeggios (as in measures 2 and 4) is another way you can keep the harmony distinct and reduce muddy dissonance within five-note forms.

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Okay, it’s time to incorporate the 6th string into our quartal grips and actively comp across and along the entire fretboard. With its three-octave-plus range and booming low-E pedal tone,Fig. 5gets us into piano-like territory. Notice how we’re venturing all the way up to the 15th fret while juggling highly mobile, three-note grips on string sets 6–5–4, 4–3–2, and 3–2–1. Cool!

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A quick recap: We’ve learned how to stack perfect and augmented fourths to construct quartal voicings, and we’ve played them in three-, four-, and five-note forms on all six strings and all over the fretboard. Next month, we’ll conclude this journey by looking at ways to integrate quartal harmony with more traditional tertian (third-based) chords. This way, you get the best of both worlds—familiar chord progressions laced with hip, quartal colors.

Andy Ellisis a veteran guitar journalist and Senior Editor atPG. Based in Nashville, Andy backs singer-songwriters on the baritone guitar, and also hostsThe Guitar Show, a weekly on-air and online broadcast. For the schedule, links to the stations’ streams, archived audio interviews with inspiring players, and more, visittheguitarshow.com.