The whirly tube, corrugaphone, or bloogle resonator, also sold as Free-Ka in the 1960s-1970s, is an experimental musical instrument which consists of a corrugated (ribbed) plastic tube or hose (hollow flexible cylinder), open at both ends and possibly wider at one end (bell), the thinner of which is rotated in a circle to play. It may be a few feet long and about a few inches wide. The faster the toy is swung the higher the pitch of the note it produces, and it produces discrete notes in the harmonic series like a valveless brass instrument, but the fundamental and second harmonic are difficult to excite. To be played in concert the length of the tube must be trimmed to tune it. Hornbostel–Sachs number: 412.22, the tube is a whirling (turns on its axis) non-idiophonic (reedless) interruptive free aerophone, but is usually included in the percussion section with sound effects such as chains, clappers, and thunder sheets.
Hopkin describes a single whirled corrugaphone as capable of producing three or four different pitches. Crawford describes harmonics two through seven as reachable while whirling, though seven takes, "great effort." Hopkin describes that with a corrugahorn, "with tubes of suitable length and diameters, the range extends well up the [harmonic] series, where the available tones are close together and you can, with practice, play quite melodically." In fact, since each harmonic plays throughout a range of speeds (rather than at one specific speed), it is difficult to skip over harmonics, as this requires a jump in speed (rather than gradual change), though this is easily done using one's tongue and throat to interrupt the air flow with a corrugahorn. Many sales offers describe the tubes as producing up to five distinct notes (presumably the bugle scale: harmonics 2, 3, 4, 5, and 6 Play (help·info)), and while higher harmonics may be possible, if hard work, dissonant adjacent harmonics may sound simultaneously, such as 15 and 16. The fundamental and harmonics of a corrugated tube are lower than those of an uncorrugated tube of the same length and diameter, and, "audible vibration in the whirly tube appears only when air flow velocity exceeds a certain minimum, which may preclude the sounding of the fundamental or lower harmonics." The timbre of the notes produced by the whirly tube are, "almost all fundamental," according to Fourier analysis (similar to sine waves). Tubes longer than many feet may have one end whirled while held near its middle or may be held out a car window.
The equations describing the sound produced when the tube is whirled are as follows, where a "bump" is when air bumps into the corrugations.
Thus the faster the tube is swung or the more dense the corrugation the higher the pitch of the note produced.
The difference in speed between the moving end of the tube and the stationary, hand-held end creates a difference in air pressure. A higher pressure is at the fixed end and a lower pressure is at the moving end. This difference pulls air through the tube and the air's speed changes (making the changes in the tones) with the speed of the spin. The pitch, loudness, and tone of the sound come from the tube's length and diameter, the distance between each ridge, and the speed the tube spins around, which moves the air faster or slower through the tube changing the tone in steps. ... [Only corrugated tubes sing] As the air flows first over one ridge then over a second it tumbles into a vortex. The faster the air flows through the tube, the higher the frequency of the sound produced by the vortex. When the frequency of the vortex matches one of the natural resonant frequencies of the tube [harmonics], it is amplified.
According to Bernoulli's principle, as speed increases, pressure decreases; thus the air is sucked into the still or inside end of the tube as higher pressure air moves up the tube to fill the lower pressure air at the faster moving spinning or outside end of the tube.
The characteristic speed is the mean flow through the pipe U and the characteristic length must be a multiple of the spacing between corrugations, nL, where n is an integer number and L is the distance between corrugations. At low speeds, the unstable interior flow needs to travel several corrugations to establish the feedback loop. As the speed increases, the loop can be established with fewer corrugations. The Strouhal number
was used as the scaling factor. A unique aspect of this whistle is that the internal flow carries both the unstable vortex downstream and the returning feedback signal upstream.
An ensemble of whirlies produces astounding musical patterns of vibrant clear pitch, sometimes hauntingly beautiful, sometimes dramatic, sometimes soft, sometimes strong and robust, but at all times inspiring and thought provoking.
A corrugated plastic tube whirling instrument became an instant, if short-lived, cultural phenomenon in late 1960s New York City under the name "Free-Ka", sold by street vendors, as captured by The New Yorker in 1970. It was used by Peter Brooks in the early 1970s in his production of Shakespeare's A Midsummer Night's Dream. It has been used by a number of artists including Peter Schickele, Frank Ticheli, Paul Simon, Macy Gray, Loch Lomond, and Yearbook Committee. Also in Brett Dean's Moments of Bliss (2004) and by The Cadets Drum and Bugle Corps in 2011. It has been employed in some of Peter Schickele's comic P. D. Q. Bach compositions such as the Erotica Variations: IV (1979), Missa Hilarious (1975), and Shepherd on the Rocks with a Twist (1967). Schickele, who calls it the lasso d'amore (a pun on oboe d'amore), gives a tongue-in-cheek explanation of the instrument's evolution: Viennese cowboys twirled "their lariats over their heads with such great speed that a musical pitch was produced. . . . The modifications that had made this development possible rendered [the lasso] useless for roping cattle."
David Cope, in 1972, discussed a cugaphone, which, in 1997, he describes as an instrument built from a trumpet mouthpiece attached to a long piece of 3/8-inch bore plastic tubing with a kitchen funnel, usually in hand, at the other end acting as the bell; thus sound may be modulated by directing the funnel, applying pressure to the funnel, or by swinging the funnel around one's head and creating a Doppler effect. This version of the instrument would require brass embouchure technique rather than corrugation. By 1997 ensembles of cugaphones existed.
The inventor is not known, though Bart Hopkin credits the late Frank Crawford of the UC Berkeley Department of Physics with, "developing the idea and researching the underlying acoustics," and in 1973 Crawford credits another professor with pointing out to him a toy which, "about a year or two ago...appeared in toy stores across the land," and gives the brand or trade names "Whirl-A-Sound", "Freeka", and "The Hummer"; the last being made by W. J. Seidler Co. of L.A., CA. Crawford invented the method of playing small enough hose by blowing, known as a corrugahorn. This requires a tube with a diameter smaller than commonly marketed as toys (a one inch diameter is too great, a half inch is not), Hopkin recommends 3/8" gas heater hose as the most playable of widely available sizes. Crawford invented an, "inverted-wastebasket water piston," operated version he called the "Water Pipe", with which he could easily reach the eleventh harmonic.
- Sprott, Julien Clinton (2006). Physics Demonstrations: A Sourcebook for Teachers of Physics, Volume 1, p.158. "You can also use a corrugated plastic tube, called a 'corrugaphone,' 'Bloogle Resonator,' or 'Hummer,' to produce a variety of whistling sounds when you spin it around over your head. The frequencies are harmonics of the fundamental organ-pipe mode that are individually preferentially excited depending on the speed of rotation. It is hard to excite the fundamental and even the second harmonic, but the higher harmonics are easily excited." ISBN 9780299215804.
- Hopkin, Bart (2009). Making Musical Instruments with Kids, unpaginated. See Sharp. ISBN 9781937276027.
- Crawford, Frank S. (1974). "Singing Corrugated Pipes", AJP, Volume 42, pp. 278–81, Physics.umd.edu. "A corrugated tube open at both ends, with air flowing through the tube, sings notes which depend on the flow velocity and the length of the tube. The notes it sings are the natural harmonics of the tube."
- Hopkin, Bart (1996). Musical Instrument Design: Practical Information for Instrument Making, unpaginated. See Sharp. ISBN 9781884365836.
- "Sound Hose", SteveSpanglerScience.com.
- Crawford, Frank (1989). "What is a Corrugahorn?", Experimental Musical Instruments, Volume 5, pp. 14–9. Features description and illustration.
- "Whirly Tubes", ScienceWorld.ca.
- "Free-Ka", by Robert MacMillan, The New Yorker, July 11, 1970, p. 20 "
- Barbara Hodgdon, p. 166, in “Shakespeare, Memory and Performance”, ed. Peter Holland
- Morris, Craig (August 7, 2009). "Whirly Tubes and Bloogles", LivMusic.com. Archived 29 August 2016 at the Wayback Machine
- Schickele, Peter (1976). The Definitive Biography of P. D. Q. Bach. New York: Random House. p. unpaginated. ISBN 9780394465364.
- "The Intimate P.D.Q. Bach", Schickele.com.
- "Bach: Erotica Variations, for banned Instruments and Piano", PrestoClassical.co.UK.
- Rickards, Steven (2008). Twentieth-Century Countertenor Repertoire: A Guide. Lanham, Maryland: Rowman & Littlefield. pp. 273–4. ISBN 9780810861039.
- Schickele, Peter. "'Erotica' Variations for banned instruments and piano, S. 36EE" The Intimate P.D.Q. Bach, Vanguard, LP, VSD 79335, 1974. On this recording, Schickele additionally claimed they were 18th century Viennese Cowboys, meaning they likely performed at the Winter Riding School.
- Cope, David (1997). Techniques of the Contemporary Composer, p.146. Schirmer. ISBN 0-02-864737-8. Cites: Cope, David (1972). Margins. New York: Carl Fischer.
- Cope (1997), p.148.
- Sanders, Robert (2003). "Physicist Frank Crawford, who worked on bubble chambers, supernovas and adaptive optics, has died at 79", Berkeley.edu.
- Nakiboğlu G, Rudenko O, Hirschberg A. "Aeroacoustics of the swinging corrugated tube: voice of the Dragon" J Acoust Soc Am. 31, 749–765, 2012.
- Rajavel, B., Prasad, M.G. "Parametric studies on acoustics of corrugated tubes using large eddy simulation (LES)", Noise Control Engineering Journal, 62(4), 2014.
- Lisa R., Taylor, M.E., "Experimental Study of the Acoustical Characteristics of Corrugated Tubing", Noise and Vibration Control Laboratory, Stevens Institute of Technology, Thesis 1994.
- (1974). "Corrugahorns", Scientific American, Volume 230. Munn & Co.