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GUEST BLOG: “Four Main Reasons Why Barbershop Singing Sounds Unique,” by Jon Nicholas

Reason #1: The Melody Is In The Middle.  With many vocal music genres, the melody is sung in the highest part. In barbershop, the melody usually floats around between the tenor and bass and the baritone avoids it.  Barbershop is not the only style that utilizes this structure (gospel quartets, for example, also use it), but it's the first element that starts to separate it from other styles.
Reason #2: The Dominant Seventh Chord.  The dominant seventh chord is so prevalent in traditional barbershop music that it has come to be known as the Barbershop Seventh Chord to many. In a traditional song, 35 to 60% of the chords are dominant sevenths.
Reason #3: Just Intonation.  Though many early barbershop quartets used musical instruments to accompany their singing, most modern quartets sing in the a cappella style so they can use Just Intonation. The human brain can detect when a chord "locks" into place, and most singers, with experience, can automatically adjust their notes to make a chord sound better. A locked chord is called so because once achieved, the singer feels vocally locked into place.
Reason #4: Overtones.  An overtone is a natural phenomenon that occurs when sound waves rub against each other and produce a higher note. In a well-tuned barbershop quartet, overtones are enhanced, even sometimes to the point where the loudest note is not being sung by any of the four singers. Since each voice can produce its own overtones, it's quite possible to have a five, six, or even an eight-part chord being sung by four people. Barbershoppers call this expanded sound. A side benefit of this phenomenon is that the singer can relax his volume a bit because the over-all volume has now increased with the addition of the overtones. Unlike most singers in other musical styles, barbershoppers actively work towards producing overtones.
Of Course, There's More...
I've covered four of the biggest reasons why barbershop singing sounds so unique, but there are more. For one, there's the Circle of Fifths, and a classic barbershop song moves around that circle quite a bit. Most modern songs don't travel around the circle very far, but songs from the early days of American Popular Music, including those from the Tin Pan Alley era, do and this is why so many barbershop songs are from days gone by. Some other elements that set barbershop apart (and may provide some stimulating research on your part):
     Call and Response
     Swipes (Slurs)
     Echos and Patters
     Unexpected Modulations
     Unexpected Chord Progressions
You can READ A LONGER VERSION of this article with demonstration clips.
on February 11, 2014 1:21am
Nice summary!  As to #2, I'd stick with "barbershop seventh" because singers add the sixth overtone (7th harmonic) to nearly any major triad, regardless of its tonal position, and tune it very high, as in the harmonic series.  Generally, that makes a ringing overtone-locked chord, as you say, and a characteristic sound.  But it is not a dominant seventh, which uses the subdominant note, tuned much lower, in order to resolve back to the third of the tonic triad. 
on February 11, 2014 12:33pm
I love #3 Just Intonation!!  It explains soooo much in my musical brain!  Thanks for sharing!
on February 12, 2014 10:03am
You have thought a lot about this and put together a fine essay. The biggest reason Barbershop sounds as it does the sound of men's voices singing in close harmony. It's the sound: rich with a lot of overtones. You won't find this sound with women's barbershop groups. I think it was Thomas Tallis that said, "There is nothing more musically satisfying in the world than the sound of four-part men singing together.", or words to that effect. While I'm not a barbershop fan, i do run four Compline Choirs with various voicings: 1. ATBarB with the male altos singing in falsetto, or as they call it, "the little voice".2. AATB, all male quartet with a couple screamers. 3. ATBarB quartet with a strong female alto, males the rest. 4. And last but not least an all-female Compline Choir (Voces angelorum) SSAT. T? Yep, we have a few 'lady basses' that can sing tenor, so I write for them. Notice not one SATB group. The somber, soothing nature of Compline cries out for that rich, dark sound. No Magnificat here. That's for Vespers. A less bombastic Nunc dimittis: yes.  I write the Sops in the all-women group no higher than 'g' as to stay away from the 'schreek factor'. 
Another technique we use is Faux Bourdon: simply putting the melody (which is usually on top) down in the tenor, and the tenor part up an octave in the highest part. This is as close as we get to the barbershop sound, but it's not really compressing the voices down into close proximity (about a twelfth) like the barbershop sound does. I have found a few pieces from the Renaissance that use the compressed, 'barbershop' voicing but no dom 7ths here.
Four of us guys have a Faux Freshmen quartet with a distinctive, not-barbershop sound using reconstructed sheet music my brother pilfered. This is men singing in very close harmony with not a lot of dom. 7ths. We use Just intonation. Why? To get rid of the beats. For 40 years our trombone section in the L. A. Philharmonic used this way to tune chords. I wrote extensively about this in my workbook on playing bass trombone. Using the 'cent scale', (100 cents per semi tone) we lined up the overtones and came up with this relative direction of travlel for chord tones to be in tune: Warning! This flies in the face of choral conductors' concept of 'in-tune'.
Minor third: adjust to 7 cents sharper than normal.
Major third: adjust to 9 cents flatter than normal.
Perfect fifth: adjust to 3 cents sharper than normal.
Minor seventh: adjust to 17 cents flatter than normal.
Major seventh: adjust to 11 cents flatter than normal.
While I don't have what to do with the 6th degree of the chord handy, I do adjust down as in a major third and this seems to line up with the overtone series. Notice how low the M and m seventh degree of the chord must move to be in tune.
We had a rehearsal last night with the Faux Freshmen (this is with the melody in the highest part) and used all these adjustments and it works out great. The woe is, most folks don't have fine enough ear to automatically move their chord tone, but they respond well to a relative direction of travel if they know what part of the chord they are on. Most singers that can discern micro pitches adjust by the seat-of-the-pants.
Yet another part of the Just intonation is Octave Compression. It took me a long time to figure this one out. Basically, you compress the lowest octave up farther than you think. It's a matter of perceiving the 'composite' sound compared to the induvidual octave tones. Do this test:  Get four brass players (it's easier to hear the beats) to play in four octaves of unison, say Bb. If a pedal Bb is the lowest note, build the remaining octaves over this. Play together until it sounds in tune without beats. Then have three players drop out on cue leaving one of the octaves still sounding. If you leave the bottom note sounding alone, it sounds very sharp compared with the composite sound. The third 8va down, alone sounds slightly sharp to the composite. The second 8va down sounds pretty close. The highest 8va, alone, sounds flat compared to the composite. The reason I bring this up is in my experience with women singing low, they tend to go way flat as they are used to hearing a couple 8vas higher. Male basses have no trouble with this as it's in their dna to sing slightly sharper in the low register, or at least that's my experience. 
on February 12, 2014 7:43pm
The element of tuning is most important - one tunes each chord to to each note of the melody, not to the accuracy of a given key.  Thus each element of the chord not in the melody must be adjusted as if the melody pitch is the root of the chord.  In just intonation, the ratio of c to d in a c major scale is a slightly larger than the ratio of d to e.  Those ratios are slightly adjusted away from a scale in a compromise to make each chord "ring."  When going around the circle of fifths one does not return to the starting pitch without making adjustments along the way!