toyL,
some guys were discussing these guitars in another thread, when I saw the page I thought you might be interested.
Here are some quotes from the site:
http://www.teuffelguitars.de/instrumente/birdfish/index_e.html
"...Despite their simple construction, guitars are subject to special acoustic and electro-acoustic rules. The fundamental character of the sound is formed by the resonant properties of the body wood. Underneath the strings are the pickups, which, according to their position between the bridge and the neck, transmit the various overtones to the strings. The composition of the pickups, which, simply put, are made out of copper wire and magnets, is tonally significant. These three fundamental principles form the character of the instrument. If one were to make them variable, then one could thereby change the character of the instrument.
This is the theme of the birdfish. The body, as a source of tone, is reduced to two cylindrical resonators, which are available in different materials. They are interchangeable by means of a screw-connection. The pickups are arranged adjustably on a rail and therefore pickup the overtones variably.
Additionally, five pickups with different characteristics are at one's disposal. One can very easily go through all the variations. The two aluminum sculptures "bird" and "fish" assume the connection of all the components. They are bridges of vibration-transfer, and establish contact to the body of the player....."
".....The resonators define the fundamental sound. They are easily exchangeable. Two blue resonators made of swamp-ash are supplied, which are very percussive with clear lows and highs. Two red resonators are also included in the set. They sound more powerful and forceful....."
"....One of the two central elements that connect the components. This part's tonal function is crucial. It requires an extraordinarily careful manufacture......"