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What’s louder than loud? The Auxetophone
By Dan Gilmore


“Be it known that I, Horace Lenoard Short, a subject of the Queen of Great Britain, residing at New Malden, in the county of Surrey, England, have invented certain new and useful Improvements in Sound-Increasing Devices; and I do hereby declare the following to be a full, clear and exact description of the invention, such as will enable others skilled in the art to which it appertains to make and use the same.” -----------Text of US Letters of Patent No. 677476, applied for on April 29, 1899 and granted July 2, 1901, lines 1-11

Since the first work on commercial sound recording and reproduction, one of the major goals was to make the sound reproduced as loud as possible. There were many schemes designed to accomplish this during the ‘Acoustic Era’ before the advent of commercial electrical sound recording. Many of these schemes were effective and some unique. Yet none were as unique and effective as the “Auxetophone”.

The principles behind the Auxetophone are based upon a very simple theory: that sound could be substantially amplified (in the true sense of the word) by modulating a column of pressurized air. This was accomplished by interrupting the column of air with valve of some sort and thus modulating it response to some kind of audio input. The input could be a mechanical diaphragm assembly into which someone spoke, a telephone speaker, or the groove of a record.

[Image source: US Patent No. 677,476; USPTO ]

The text of the patent clearly explains how this device works:

“In the drawings, Figure 1 is a central sectional view of my invention. Fig. 2 is a front view of part of Fig. 1. Fig. 3 is a detail view relating to Fig. 1. Figs. 4 and 5 represent further detail views. Fig. 6 is a detail sectional view of a modified portion of Fig. 1. Fig. 7 is a similar view of a modification of 'Fig.5.

In Fig. 1 the voice is used to speak into a mouthpiece u and set in corresponding vibration the telephonic diaphragm g. The diaphragm g is shown connected with a Spindle v, which passes through the cap w, fitted upon the end of the chamber a, of suitable diameter, into which air under sufficient pressure is forced through pipe a‘. Across chamber a is a rigid diaphragm, or partition x, having a series of parallel slits through it, forming a grating, as shown in front view in Fig. 2. To the partition x is hinged at x‘ a plate consisting of a series of light tongues or strips y of such size as just to close the holes forming the grating in x. This plate of tongues is connected at y‘ to the spindle v, operated by the diaphragm g of the telephone when the latter is spoken to, and the vibrations of the diaphragm g are therefore transmitted to the tongues y, which open and more or less close the passages through the grating x at a speed and in a manner exactly corresponding with the movements or vibrations of the diaphragm g and cause corresponding undulations in the column of air which is forced in at a' and is discharged through the trumpet_mouthed pipe z, the words or other sounds uttered into the telephone at u being reproduced, very greatly magnified and strengthened, and capable of being heard, at a great distance by the more or less complete closing at very rapid intervals of the apertures or grating through which the air is forced. This form of apparatus is especially adapted to be used where the loud sounds to 8 be produced are obtained by the undulations of the column of air forced through the valve, as shown. Aspring m assists in bringing back the tongues.

In Fig. 6 the same apparatus is shown partly broken off, but operated by movements of the style or point M of a phonograph upon a properly_indented cylinder N or disk.

Fig. 7 shows a regulating_screw P, by which the pressure on the spindle between the valve y and the phonograph_cylinder N can be exactly adjusted and regulated.”

In 1900, Horace Short demonstrated his phonographic version of this device (the Auxetophone) from the top of the Eiffel Tower.1 Charles Parsons purchased the rights to Short’s patents in 1903.2

Charles Algernon Parsons filed on April 12, 1904 for a patent on a phonograph reproducer using Short’s compressed air amplification method (Granted April 17, 1906, US Patent No.817,686).
[Image Source: US Patent 817,686; USPTO]

Parsons mentions the work of others in this patent and in particular the work of Thomas A Edison as it relates to compressed air amplification of sound. Also noted is the finding that the moving parts of the reproducer (in this case those parts associated with the moving grating in figures 2 through 6 above) should be on the low-pressure side of the apparatus. The reasoning for this is that were the movable grating on the high-pressure side there would develop the tendency for the grating to vibrate like the reeds in a harmonica. The stated operating pressure was approximately 5 psi, more or less. Volume could be controlled by adjusting spring tension on the lever arm attached to the movable grate.
[ Image source: US Patent 816,180; USPTO]

Parsons’ also patented a violin that used his modified reproducer to amplify the instrument. Needless to say this would have been a clumsy affair given the needed air-line to the instrument (US Patent No. 816,180, applied for April 12, 1904, granted March 27, 1906. See illustration above)

[Image source: US Patent 814,561; USPTO]

In the figure above, we see what is essentially the final form of the Auxetophone reproducer (US Patent No. 814,561, filed for September 26, 1904, granted March 6, 1906). One unique feature of this early design is the diamond shaped socket on the needle chuck. The idea of this shape (figure 2, item e) was to cause the steel needle to effectively wedge into the narrow point of the chuck. A horseshoe magnet (f) was employed to hold the needle in place while the reproducer was in the up position. Later versions of the Auxetophone reproducer lacked this chuck and magnet design, opting for a standard thumbscrew chuck.

There are a scarce few complete examples of Auxetophones in existence, and even fewer in operating condition. Was the Auxetophone loud? It was painfully loud.


1 Brian Jewell, Veteran Talking Machined, History and Collectors’ Guide, Midas Books, Turnbridge Wells, Kent, England, 1977; ISBN 0 87069 222 4; pg 36.

2 ibid, pg 36.

Copyright ©2004 by Dan Gilmore. All rights Reserved.