MUSICAL FLAMES
2
TECHNICAL NOTES AND RESEARCH BRIEFS 5.16, 5.18; 7.8, 7.10 MUSICAL FLAMES W. R. Babcock,K. L. Baker, and A. G. Cattaneo United Technology Center, Sunnyvale, California 94086 INTERACTION BETWEEN •FLAMES and sound was first reportedby John Lecontein 1858 and has since been studied by Rijke, Rayleigh, Tyndall, Andrade, • and many others.It was the subject of a special ses- sion at the fourth symposium of the Com- bustionInstitute in 1952 under the heading "Oscillatory Combustion." Leconte had noticed that a gasflame at a concert responded to certain beats of the music. Subsequent work attempted to analyze and explain this effect in terms of the properties of sound waves and those of flames. • Because very characteristic changes in the shape of a flame can be produced by soundwaves of specific frequencies, flames have been used as sound detectors in acous- tic research. 3 Experimenters have observed that the response of the flame is more ener- getic than the sound intensitywhich caused it; the flame thus acts as an amplifier, and feedback occurs. l Others have shown that flames can in fact accept and reproduce soundand music and act as loudspeakers, confirming the wordsattributed to Leconte • that we must "look upon all jets as musi- cally inclined." A very simple experiment (Fig. 1) uses a natural-gas flame into which a jet of oxygen is blown at right angles. The flow of oxygen is modulated by motions of the membrane M, whichin turn are imposed by the coil C (in practice, a commercial loudspeaker membrane with its driving unit is easily AUDIO INPUT adapted to form the flow-modulation unit). Any electrical vibrations imposed on the coil, membrane, and oxygen flow will now be reproducedas audible sound by the flame. If these vibrations are taken from a tape recorder and constitute Beethoven's Fifth Symphony, a very fine rendering is ob~ tained with a fidelity apparently limited only by the quality of the recording and the modulation unit. The "beats" that Leconte observed are clearly evident in the flame. Many other arrangements are possible, of which we sketch only one (Fig. 2) con- veniently operatedfrom the acetylene and oxygen supply of a weldingunit, with the samefine reproducing qualities. In the experiments described, the modu- lation unit really produces the sound waves OXYGEN ------ I• N __ INPUT •••••"•C Fig. 2. FUEL GAS Fig. 1. and the flame merely amplifies them-- although the amplification, even on the laboratory scale described, is of the order of several hundred. We have found, how- ever, that it is not necessary to modulate the flame physically; it can be done elec- trically as well, as was observed, on the shape of the flame and its wake only, by Zickendraht. 5 For thispurpose, a voltage is imposed on the flame between pointsnear the base and near the end of the visible region. The voltage is taken from the secondary windings of a transformer, and it has to be biased to allow symmetrical oscillations. The desired input is fed to the primary transformer windings,and will be audibly reproduced by the flame. The ex- periment is sketched in Fig. 3. The acety- lene and oxygen used do not contain suffi- cientionizable species, but these are readily added by touching to the base of the flame an asbestos wick feeding an alkali salt like potassium nitrate in water solution. The arrangement shownwill fill a large room with musicor speech. The observations described show that the production of sound by the flame is associated with the surface in which the chemical energy is liberated,corroborating the concept of flame surface tension. ø This is also the place where the strongest light emission takes place, and the latter also contains the imposed modulation. By opti- cally forming an imageof the light from this region of the flame in one of the above ex- periments on a suitable photocell, amplify- ing its output, and feeding it to a loud- speaker, one can again recover the input from the tape recorder in audible form. When the experiments in Figs. 1 and 2 are used,a delay will occurcaused by the time the gas takes to flow from the modulation unit to the flame;but no delayis apparent with the experiment in Fig. 3. The optical photocell arrangement can be used to show that even the weak flame of a candlehas the properties described. If one The Journalof the Acoustical Society of America 1465 Redistribution subject to ASA license or copyright; see http://acousticalsociety.org/content/terms. Download to IP: 132.75.80.183 On: Mon, 08 Dec 2014 12:15:21
Transcript of MUSICAL FLAMES
TECHNICAL NOTES AND RESEARCH BRIEFS
5.16, 5.18; 7.8, 7.10
MUSICAL FLAMES
W. R. Babcock, K. L. Baker, and A. G. Cattaneo
United Technology Center, Sunnyvale, California 94086
INTERACTION BETWEEN •FLAMES and sound
was first reported by John Leconte in 1858 and has since been studied by Rijke, Rayleigh, Tyndall, Andrade, • and many others. It was the subject of a special ses- sion at the fourth symposium of the Com- bustion Institute in 1952 under the heading "Oscillatory Combustion."
Leconte had noticed that a gas flame at a concert responded to certain beats of the music. Subsequent work attempted to analyze and explain this effect in terms of the properties of sound waves and those of flames. • Because very characteristic changes in the shape of a flame can be produced by sound waves of specific frequencies, flames have been used as sound detectors in acous-
tic research. 3 Experimenters have observed that the response of the flame is more ener- getic than the sound intensity which caused it; the flame thus acts as an amplifier, and feedback occurs. l Others have shown that
flames can in fact accept and reproduce sound and music and act as loudspeakers, confirming the words attributed to Leconte • that we must "look upon all jets as musi- cally inclined."
A very simple experiment (Fig. 1) uses a natural-gas flame into which a jet of oxygen is blown at right angles. The flow of oxygen is modulated by motions of the membrane M, which in turn are imposed by the coil C (in practice, a commercial loudspeaker membrane with its driving unit is easily
AUDIO INPUT
adapted to form the flow-modulation unit). Any electrical vibrations imposed on the coil, membrane, and oxygen flow will now be reproduced as audible sound by the flame. If these vibrations are taken from a
tape recorder and constitute Beethoven's Fifth Symphony, a very fine rendering is ob~ tained with a fidelity apparently limited only by the quality of the recording and the modulation unit. The "beats" that
Leconte observed are clearly evident in the flame.
Many other arrangements are possible, of which we sketch only one (Fig. 2) con- veniently operated from the acetylene and oxygen supply of a welding unit, with the same fine reproducing qualities.
In the experiments described, the modu- lation unit really produces the sound waves
OXYGEN ------ I• N __
INPUT •••••"•C
Fig. 2.
FUEL GAS
Fig. 1.
and the flame merely amplifies them-- although the amplification, even on the laboratory scale described, is of the order of several hundred. We have found, how- ever, that it is not necessary to modulate the flame physically; it can be done elec- trically as well, as was observed, on the shape of the flame and its wake only, by Zickendraht. 5 For this purpose, a voltage is imposed on the flame between points near the base and near the end of the visible region. The voltage is taken from the secondary windings of a transformer, and it has to be biased to allow symmetrical oscillations. The desired input is fed to the primary transformer windings, and will be audibly reproduced by the flame. The ex- periment is sketched in Fig. 3. The acety- lene and oxygen used do not contain suffi- cient ionizable species, but these are readily added by touching to the base of the flame an asbestos wick feeding an alkali salt like potassium nitrate in water solution. The arrangement shown will fill a large room with music or speech.
The observations described show that the production of sound by the flame is associated with the surface in which the
chemical energy is liberated, corroborating the concept of flame surface tension. ø This is also the place where the strongest light emission takes place, and the latter also contains the imposed modulation. By opti- cally forming an image of the light from this region of the flame in one of the above ex- periments on a suitable photocell, amplify- ing its output, and feeding it to a loud- speaker, one can again recover the input from the tape recorder in audible form. When the experiments in Figs. 1 and 2 are used, a delay will occur caused by the time the gas takes to flow from the modulation unit to the flame; but no delay is apparent with the experiment in Fig. 3.
The optical photocell arrangement can be used to show that even the weak flame of a
candle has the properties described. If one
The Journal of the Acoustical Society of America 1465
Redistribution subject to ASA license or copyright; see http://acousticalsociety.org/content/terms. Download to IP: 132.75.80.183 On: Mon, 08 Dec 2014
12:15:21
TECHNICAL NOTES AND RESEARCH BRIEFS
TUNOSTEN ELECTRODES
'•'--"KNO 3 IN WATER
'•----WE L DING TORCH
OXYGEN ACETYLENE
talks at a candle flame, the monitoring photocell will reproduce the voice, albeit volume and fidelity are deficient in this case.
While this has considerably entertain- ment value, its implications may apply to
Fig. 3.
a number of combustion phenomena in- cluding, for example, the instability of chemical rocket engines.--•
(Nature 216, 676-678, 1967, by permission) x Andrade, E. N. da C. 1941 Proc. Phys. Soc.
(London) 53,229.
2 Brown G. B. 1935 Proc. Phys. Soc. (London) 47, 703.
a Humby, S. R. 1927 Proc. Phys. Soc. (London) 39, 435.
• Zickendraht, H. 1941 Helv. Phys. Acta 14, 195.
• Zickendraht, H. 1941 Helv. Phys. Acta 14, 132.
s Behrens, H. 1951 Z. Physik. Chem. 197, 6.
7.8, 7.10
REDUCTION OF FLAME NOISE BY APPLIED ACOUSTICS
A KZND O• CONV•.RS•. of the effects de-
scribed in the foregoing paper was pre- sented in an earlier issue of Nature maga- zine. x In this case, experiments were per- formed that showed that the application of acoustic energy transversely to ignited jets of gas reduces the audible noise output markedly. The effect occurred with applied
frequencies from about 2 kHz upwards. Re- ductions of about 6 dB in total audible out-
put were observed when using ultrasonic frequencies of about 40 kHz. The applied sound-pressure level was 100 dB at the nozzle orifice; this applied energy was less than 0.01% of the heat energy released by the plasma.
The effect of the acoustic field on the
ignited gas jet was to slightly shorten and broaden the flame. Near the nozzle, an in- tensification of the emission of blue light
(indicating stabilization) was observed. Shadowgraphs of the jet under acoustic treatment showed that the jet core tip oscillated at a relatively low frequency.
Experiments with unignited jets and with both aerated and nonaerated Bunsen
flames showed that, in these cases also, sig- nificant reductions in noise could be achieved.---
x Briffa, F. E. J. and Fursey, R. A. E. 1967 "Reduction of Audible Flame Noise by the Appli- cation of Ultrasonics," Nature 214, 75-76 (1 Apr.) 1967.
10.2
BEAUTY AND THE BUZZ
W•. HAVe. NOT•.D from time to time in these pages the rapid expansion in the ap-
1466 Volume 43 Number 6 1968
plications of ultrasonics into new fields. Now the spreading ultrasonic waves are quite literally lapping at Milady's feet via the beauty industry. We heard on the radio this morning a commercial for a new ladies'
stocking called Ultrason ; 'tis said its exotic sheerness derives from a secret ultrasonic process. Obviously, neither ultra- sonics nor Madison Avenue is on its last legs/--,
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