Stroh Violin

The creation of the phonograph by T. Edison in 1877 made it possible to record sounds by means of a groove in a wax cylinder. For this recording to be effective, the sound source, be it a musical instrument or a voice, had to be loud enough. However, this was not the case with the violin, whose sound was not loud enough.

To address this problem, in 1899, engineer John Matthias Augustus Stroh sought an innovative solution. He applied for a patent for a design that greatly improved the directionality of the violin's sound, making it suitable for phonographic recording. His design was patented on 4 May 1899 under British patent GB9418, entitled ‘Improvements in Violins and Other Stringed Instruments’, and accepted on 24 March 1900. The patent described the use of a flat metal diaphragm (although other materials were also mentioned) inside the violin to amplify the sound mechanically. Subsequently, on 16 February 1901, Stroh applied for an additional UK patent (GB3393), entitled ‘Improvements in the diaphragms of phonographs, musical instruments and similar devices for the production, recording and transmission of sound’, which was accepted on 14 December 1901. This second patent expanded the original concept, introducing a conical resonator with corrugations at its edge, which allowed for a stiffer diaphragm.

Stroh's proposals resulted in significant modifications to the classical design of the wooden violin, leading to the birth of the Stroh violin:

• A rigid structure replaced the traditional soundboard, with the sole purpose of supporting and tuning the four strings of the instrument.

• The movement of the bridge was adjusted to favour its rotation around an axis parallel to the strings.

• The bridge was connected to a membrane between the strings and an acoustic horn, which amplified the sound.

The bridge of the Stroh violin was designed to oscillate laterally, fixed on an axis. The friction of the bow on the string produced vibrations which were transmitted to the bridge and from there to the membrane. This rotational movement of the bridge was converted into a translational movement of the diaphragm, similar to that of a piston.

All components of the Stroh violin's acoustic-mechanical design were intended to allow the membrane to oscillate. This membrane functioned as a loudspeaker, being light and rigid to achieve the right balance. The vibrations of the membrane moved the internal air column of the horn, producing a highly directional acoustic radiation, comparable to that of a trumpet or trombone.

Due to the high directionality of this device, musicians had difficulty hearing their own sound. To solve this, Stroh added a smaller secondary horn to provide sound feedback to the player. This feature made the Stroh violin much easier to record with a phonograph compared to the classical violin.

The Stroh violin was an expensive instrument. In 1911, London dealers Barnes & Mullins sold it for nine or twelve guineas, at a time when a reasonable factory violin cost around two guineas. It was considered particularly suitable for use in small theatres and music halls.