History of Reverse Action Design on the Autoharp
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Autoharp Evolution
The invention of the autoharp is commonly credited to Charles F. Zimmermann of Philadelphia. A US Patent 257808 was granted in 1882. Zimmermann certainly contributed much to the popularisation of the instrument in the United States of America, but the instrument that he produced and popularised was based more closely upon the design work of Karl Gütter. Ivan Styles’ “The True History of the Autoharp” is considered the authoritative historical re-construction and Styles unhesitatingly credits Gütter as the true inventor (Styles, 1990, pp. 1–3). A comparison of the patent drawing submitted by the two supports this view (Zimmermann, 1882)
A photograph of Zimmermann playing a version of this instrument is produced within Styles' article (right) and this shows a similar instrument to that which is depicted in the patent drawings above.
However there are extant examples of the instrument that Zimmermann actually produced (photograph below). This is a type 1 Zimmermann production model dated at c. 1885–88, it is a diatonic tuning in the key of C, with three chord bars providing IV, I and V7 from the toe to dead end of the instrument.
The instrument here is clearly the same as described in the Gütter patent. Styles reproduced these original drawings from his research in the foreign patents section of the US patents office. (The drawings of this patent remain absent from commonly available online databases, and this image is reproduced directly from the Styles article (Styles, 1990).
Styles identifies a trip to Germany as a source of Zimmermann's knowledge of this instrument. He speculates that Zimmermann might have felt this design to be easier to manufacture than his own. The design is certainly a more straightforward playing interface; note the playing position in 
the Zimmermann photograph above — the instrument is placed horizontally upon a hard surface such as a table, rather than held.
Whilst there are some autoharp traditions that still use this playing position, precise and virtuosic players more commonly hold the instrument against the trunk of the body, and strum across the surface. This is a far more natural strum/pluck position. 
Zimmermann subsequently manufactured Gütter's design under the auspices of his own patent. This sleight of hand was challenged by Herman Lindemann, a German manufacturer who had bought the rights to Gütter's design in 1883. Lindemann issued a statement in 1890 “Warning: I warn hereby especially not to buy or sell the recently sold instrument under the name of Chordzither or Autoharp that are in the market as imitations of my patent ‘Volkszither’", but the challenge appears to have come to nothing.
The first commercially available autoharps had extremely limited chord choice, and the instrument was at once subjected to selective pressure to extend its chromatic capability. We can trace three lineages of design thinking to allow this. One lineage saw autoharps produced with increasing numbers of chord bars, examples of 15 bar and 21 bar autoharps became common; this is the standard contemporary design approach, and these types of autoharps are by far the most numerous.
Another approach introduced a further set of secondary damping control to the system. The Meinhold autoharp (left) is one of the more straightforward examples. The twelve chord bars can be crooked a semi-tone in either direction, immediately increasing the chromatic potential. The Victoria autoharp, perhaps the closest formulation to Zimmermann’s original, is another example of this. Unlike the maximised chord bar approach, extant manufactured examples are limited to 19th-century examples; though these are relatively numerous.
A third approach is to integrate a keyboard in a way similar to the ReAPH. Examples of such instruments do exist, but are exceedingly rare as we shall see.
Without doubt, the design concerns of the innovation are in accord with the Victorian ethos, and it is no surprise that the earliest keyboard-integrated examples also date from this time. This was an era of widespread experimentation with mechanical and mechanically enabled musical instruments of all kinds, and this history begins with four designs, covering the period 1888 to 1915, all of which seem to have been written without knowledge or reference to each other. Three of these, Wigand, Back and Millington/Young bear striking similarities in the playing interface (if not in all aspects of the design). Because of these similarities we will consider these three in isolation and subsequently in comparison.