A VIBRATING REED OSCILLOGRAPHF. J. Shollenberger Citation: Review of Scientific Instruments 3, 365 (1932); doi: 10.1063/1.1748946 View online: http://dx.doi.org/10.1063/1.1748946 View Table of Contents:http://scitation.aip.org/content/aip/journal/rsi/3/7?ver=pdfcov Published by the AIP Publishing Articles you may be interested in Vibrational modes of accordion reeds. J. Acoust. Soc. Am. 126, 2216 (2009); 10.1121/1.3248800 Vibrational modes of clarinet reeds J. Acoust. Soc. Am. 102, 3085 (1997); 10.1121/1.420211 Theory of the vibrating ferromagnetic reed J. Appl. Phys. 59, 3224 (1986); 10.1063/1.336903 Studies of the Vibrations of Clarinet Reeds J. Acoust. Soc. Am. 32, 935 (1960); 10.1121/1.1936551 The Mode of Vibration of a Clarinet Reed J. Acoust. Soc. Am. 12, 529 (1941); 10.1121/1.1916135

This article is copyrighted as indicated in the article. Reuse of AIP content is subject to the terms at:

http://scitationnew.aip.org/termsconditions. Downloaded to IP: 128.138.73.68 On: Mon, 22 Dec 2014 02:48:20

A VIBRATING REED OSCILLOGRAPH

By F. ]. SHOLLENBERGER

[MOUNT UNION COLLEGE, ALLIANCE, OHIO. RECEIVED MARCH 8th, 1932]

It is hardly necessary to emphasize the value of the oscillograph in physics; its numerous uses in the study of wave motion make it a neces­sary laboratory instrument. This device, developed by Blondel (1893) and Duddell, has been used successfully for the analysis of electrical impulses, but not without mechanical and electromagnetic difficulties which have caused appreciable errors in the reproduction of wave forms.

FfSb G )

A 8

FIG. 1.

The instrument to be described makes use of a closed core type of magnetic field such as is employed in the standard electrodynamic loud speaker, but differs somewhat from the conventional design. The elec­tromagnet is energized by a six volt storage battery connected to the leads A and B. An air gap E of about one sixteenth of an inch separates the center core D from the outside cylindrical shell C. A coil F, of ten turns of number thirty wire wound on a paper form, is suspended in the air gap and is held in position by the reed C.

In order to eliminate lags due to hysteresis, metals possessing mag­netic properties are not used in connection with the movable coil. Vari­ous forms of diaphragms were tried, but the reed gave greatly increased

365

This article is copyrighted as indicated in the article. Reuse of AIP content is subject to the terms at:

http://scitationnew.aip.org/termsconditions. Downloaded to IP: 128.138.73.68 On: Mon, 22 Dec 2014 02:48:20

366 F. J. SHOLLENBERGER [R.S.L, 3

sensitivity. Directly above the reed is a steel spindle mounted in jeweled bearings, of the type used in D. C. Miller's phonodeik, to which a small mirror M is fastened. A fine silk thread attached to the reed is wrapped once around the spindle and then to a spring of variable tension. Paral­lel light rays are directed first on the mirror, which imparts a vertical motion, and then to a horizontally revolving mirror which reflects the light spot sidewise and thus forms a wave on a screen.

An alternating current in the coil F sets up corresponding attractions and repulsions and causes a displacement of the reed and a rotation of the mirror proportional to the change of current in the coil. Varying direct currents will cause similar effects, except that the restoring forces will be dependent upon the elasticity of the reed.

This device may be used with a microphone, battery, and transformer for the projection of sound waves, or, where great sensitivity and fidelity of reproduction are desired, a condenser type microphone and push-pull amplifier are most satisfactory. \Vith this latter arrangement, waves a foot or more in height may be shown on a screen eight feet from the oscillograph, the sound being produced by a one-half pound tuning fork several hundred feet distant and making two hundred and fifty six vibrations per second.

Interference of sound, resonance, and the complex waves of musical instruments and the human voice are readily shown. One of the most interesting applications of this device may be had by connecting it in series with the loud-speaker of a radio. The vizualization of the electrical impulses synchronized with the sound waves illustrates the wide field of application of this instrument.

•

This article is copyrighted as indicated in the article. Reuse of AIP content is subject to the terms at:

http://scitationnew.aip.org/termsconditions. Downloaded to IP: 128.138.73.68 On: Mon, 22 Dec 2014 02:48:20