I've dabbled with double-tonguing for a number of years. (Is double dabbling acceptable?) It seems everyone but clarinetists do it. My sister is a flutist and learned double-tonguing early, as do all flutists. My woodwind colleagues in the orchestra, flute, oboe and bassoon, all double-tongue.
The accepted tradition says clarinetists just don't double tongue. Since we keep our tongue quite high for voicing, double tonguing interferes with the air stream and changes the sound, especially in the clarion and altissimo registers. Only a few clarinet soloists, considered "freaks" of nature, can double tongue effectively.
Additionally, many recordings of famous orchestral excerpts, such as Mendelssohn's Scherzo from the Midsummer Nights Dream or Beethoven Symphony # 4, last movement, suggest that it is acceptable to add slurs to troubling passages. Larry Combs, retired Principal Clarinetist of the Chicago Symphony, admitted he slurs over the sixteenth before the grace note in the Beethoven excerpt. In the Mendelssohn Scherzo recording by the Cleveland Orchestra, Marcellus adds a slur at the beginning of the two measure run starting on E.
Those are the ideas I grew up with and have found little reason to change. My single tongue is acceptably fast. I can tongue about 132 to the quarter for short bursts, maybe a bar or two, and at 126 for longer, functional tempos for most excerpts. (In college days, I wondered if I would ever tongue fast enough, being unable to do sixteenths faster than 112-116, but I had a breakthrough when I realized I tightened my tongue in attempts to tongue faster, hindering its natural speed)
I have noodled with double tonguing on the Beethoven 4th excerpt for a few years, but have never been able to use it in performance. My double tongue was too fast and uncontrolled for the "real" thing, where the tempo and dynamics make it difficult to control.
But recently I have heard more soloists in recordings who can double tongue effectively and without interfering with the sound. Kari Kriikku and Martin Frost come to mind. Bob Spring has made a name for himself with his ability to double tongue AND circular breathe in his recording of Paganini's Perpetual Motion. I asked Bob about double tonguing a few years ago, and he gave me a printed copy of his routine and method. He also gave me one important piece of advice: keep your throat relaxed.
During the '08-'09 Season of the Columbus Symphony, we played Saint-Saens Organ Symphony, for what seems like the 50th time in the past ten years. The conductor wanted a brisk tempo in the tricky first movement, with its alternating sixteenth passages in 6/8 time, and which begin after a sixteenth rest.
Since all the woodwinds played the lick together, I hated having to add slurs to keep up, and was barely able to get the notes in at that tempo without a slur or two. So I hunkered down the day before the performance and tried to double tongue the lick. It's in the low register, and so is not too dicey.
The problem was that it begins on a sixteenth upbeat, meaning you have to begin on a "Goh", or shift the whole lick over a sixteenth, making the offbeat quite accented. I tried both, with uneven results in either case. To be clear, even the double tonguing flutes, oboes and bassoons had trouble with these same issues.
During the performance I made it through, by the skin of my teeth, or my tongue. It was not a recording quality event, to say the least! But I managed to use a crude form of double tonguing in a performance for the first time! Since then, I have persisted in chipping away at the issues around double tonguing in my regular practice sessions.
Following Bob Spring's advice, I focused on the throat and air, not the tongue. I had heard that the consonants "T-K" are inappropriate for clarinet use, since they close off the air, so I use "D-G".
I wasn't particularly disciplined about the practice. I just kept at it, playing around (I emphasize the "playfulness" of the process) with lots of single note repetitions in the low register, moving to changing notes. At first I didn't use a metronome, wanting to focus on air and throat, and not tempo or rhythm. Then I added metronome to steady the technique.
I gradually moved up to the clarion register, keeping focus on a soft throat. I found that if I kept the air speed fast (or better yet, "falling" fast, which is less tense), it helped me maintain an "un-collapsed" voicing during the guttural "goh" sound.
Another colleague, Steve Secan, Principal Oboist of the Columbus Symphony, mentioned the importance of the vowel sound in addition to the consonant. I use "Doh-Goh", to help keep air flow fast and throat and soft palette loose. Also keep the consonants very light and tongue relaxed. Let it flop in the air, like a flag flapping in the wind. The flag has no muscles to tense. Let your tongue be like the flag in a brisk breeze.
After 6 months, I can double tongue fairly comfortably up to a clarion "C", though it's not perfect yet up there, and still difficult to play soft dynamics.
I emphasize the importance of keeping the air speed moving quickly, and keeping the throat, jaw and soft palette uninvolved. It is a common tendency to tighten the throat, jaw, tongue and everything else when attempting a new technique. Worry less about quality of sound and more about quality of air, and you will progress quickly.
The Saint-Saens excerpt would be a piece of cake now. I hope we perform it again soon, even though we've played it way too much already.
I strongly recommend all serious clarinet students begin their exploration of this vital technique early in their studies. I believe it is becoming standard practice for any competitive clarinetist. Don't wait to motivate until you have lost an audition because you didn't learn double tonguing!
Before publishing this article, I did a quick search for double tonguing articles on the web, and I found one by David Pino on Woodwind.org. He describes a double tonguing technique of flapping the tongue back and forth, or up and down in Pino's suggestion, using the word "tuttle" as the basis for the articulation. (It's like slapping the reed up and down with the tongue) I and my colleague Robert Woody Jones have used this style occasionally in loud tutti passages such as in parts of Strauss, Don Juan, where the woodwinds have extremely fast triplets on single notes. Pino goes on to use this style for triple tonguing as well.
I'll have to play around with this style of double tonguing. My first attempts just now created a hollow sound, since the tongue needs to stay flat to implement it. But it may come in handy with a little refining.
I also found this article by Clark Fobes called "Synthetic Speed", in which he suggests mixing double and single tonguing. Clark details the double tonguing technique and his hybrid variant in impressive detail.