Stroh's Automatic Phonograph

This vowel sounder, known as an "automatic phonograph", from the Whipple Museum's collection was designed by the German-born engineer J. M. Augustus Stroh (1828-1914) and built by W. Groves. It is one of the many so-called 'talking machines' that were constructed in the late 19th and early 20th centuries, along with Helmholtz's synthesizer and eventually Edison's phonograph. This was a period of great public and scientific interest in the potential for the recording and transmission of sound. This machine was used by William Preece and Augustus Stroh in demonstration of their paper Studies in Acoustics: On the Synthetic Examination of Vowel Sounds to the Royal Society in February 1879.

How it works

The automatic phonograph was used to imitate five different vowels. Five discs, mounted on a rotating axle, are cut with grooves resembling the sound waves associated with various vowel sounds. When the axle rotates one of the discs rubs against a thin metal rod transmitting the ensuing vibrations to a circular diaphragm. This results in an audible sound being produced. The metal rod and diaphragm are able to slide between the five discs depending on which vowel sound is required (the machine is inscribed with 'oo', 'o', 'ah', 'a', 'e').

Invention

Hermann von Helmholtz (1821-1894) argued that vowels are compound tones, defined by the combination of non-harmonic resonances known as formants. The nature of the vowel depends on the relative intensities of these different formants, which in turn depend of the positioning of the vocal tract. The grooves in the discs of this machine are cut in such a way as to cause the vibrations of the diaphragm to reflect the combination of frequencies found in vowel sounds, resulting in the production of a similar sound.

Stroh built four talking machines in early 1878, the third of which was this phonograph. The second machine etched the sound waves of the formants of vowel sounds onto the brass discs used in the phonograph, and the fourth played discs with complete words such as 'mama' and 'papa'. One year earlier, Thomas Alva Edison (1847-1931) had made his first phonograph, a device for recording and replaying sound that also used the idea of spiral discs. However, Stroh's research focused more on the scientific understanding of the composition of sound rather than Edison's more popular appeal.

Horny violins

History also remembers Stroh today for his invention of the Stroh violin, patented in 1899, which looks at first glance to be a hybrid of a violin and a trumpet (Image 2). He invented this instrument in response to the growing market for recorded music. At this time recording technologies required a powerful and focused sound source, but conventional string instruments with their hollow wooden resonator bodies produced a relatively low volume that was highly dispersed. The Stroh violin uses a metal resonator and horn to amplify and direct the sound of the strings, thus producing much more volume than conventional wooden-body string instruments. This also made the instruments popular in jazz bands and in small theatre settings, where they could be heard without amplification. The smaller horn points toward the player so that they can hear the instrument clearly.