Whirly tube
The whirly tube, corrugaphone, or bloogle resonator, also sold as Free-Ka in the 1960's-1970's, is an experimental musical instrument which consists of a plastic tube or hose, open at both ends and possibly wider at one end, 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 non-idiophonic interruptive free aerophone, but is usually included in the percussion section with sound effects such as chains, clappers, and thunder sheets.
Sound
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 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, it is difficult to skip over harmonics, as this requires a jump in speed, 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, 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. 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.
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.
Use
A corrugated plastic tube whirling instrument became an instant, if short-lived, cultural phenomenon in late 1960's 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 1970's 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, You're the One |Paul Simon, Macy Gray, Loch Lomond, and Yearbook Committee. Also in Brett Dean's Moments of Bliss 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, Missa Hilarious, and Shepherd on the Rocks with a Twist. Schickele, who calls it the lasso d'amore, gives a tongue-in-cheek explanation of the instrument's evolution: Viennese cowboys twirled "their over their heads with such great speed that a musical pitch was produced.... The modifications that had made this development possible rendered 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, 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.