Questions, questions

I could very well expect already the following questions:

• What is a BBb contrabass clarinet, after all ? What kind of music can be played with it?
  
• Why would somebody want to investigate the acoustics of clarinets, and let alone of a contrabass clarinet? Surely there are nice of-the-shelf instruments to be bought, played and enjoyed.
  
• What is this project about? It was already announced many times, but never discussed in detail.
  
• What is the final goal of this project, if any? Is it going to be a real instrument on the table ever?

Well, let's start with the first question, at least.

A contrabass clarinet is the largest and lowest member of the clarinet family. The common instrument that comes to mind under the concept clarinet is the soprano Bb clarinet, measuring about 66 cm. The Bb bass clarinet is twice as long and reaches a full further octave down and the BBb contrabass clarinet is four times as long and reaches two octaves lower. Under "family" it is understood a series of instruments that share common characteristics, such as sound emission by means of single reed and mouthpiece, cylindrical bore, similar tone hole design and placement, similar keywork. Here it is essential to underline that for woodwinds a different air column length means a different instrument, even if belonging to the same family. There is not such a concept as for stringed instruments like violin or cello, where a 1/2 or 1/4 scaled instrument can be made for children or young people with small hands, being essentially the same instrument. There are bassoons for children, in fact, as the fagottino by Guntram Wolf, but it is actually a different instrument of the bassoon family. Technically, it is a tenoroon (or quart bassoon), an instrument used in medieval times, of course with a much more primitive keywork .
This means that we can not scale up a soprano clarinet by a factor of 4 and expect to get the same acoustic behaviour as for the original instrument, but for a lower voice. Even if the length will be roughly 4 times as large, this does not hold true for bore diameter, tone hole diameters, tone hole placement and register hole (instead of one, even three may prove necessary. Bah, .. as for a standard oboe!)
And here is where the "BBb" issue plays a role. The family of instruments share a similar pattern of tone holes that are closed by means of keywork. A certain specific fingering will not produce the same tone or frequency in different instruments of the family, of course, due to different air column lengths. However, for the musician it is very practical to call the fingering a name, rather than calling the tone a name. Therefore, when the C fingering is played in a Bb soprano clarinet, the pitch of the resulting sound is Bb (if you are in tune), a whole interval lower. On the other hand, if you use the same C fingering in a Eb alto clarinet, what sounds is a frequency commonly known in western conventional 12-tone equal temperament tuning system as Eb, one and a half steps higher. Of course, ethnomusicologists would probably frown upon the western temperament system. So many microtones that nature created for us, are just being wasted! Well, to be fair, in western music and specially among players of stringed instruments without frets in the neck as the violin, enharmonic pair of pitches could be distinguished (as F# and Gb, for example). On the other hand, there were many western composers experimenting and composing with microintervals, notably Karlheinz Stockhausen. Additionally, musicians in Middle East and Far East have been giving these microtones good use, for centuries.
Ok, I am back from the digression. The bottom line is that using this trick called transposition, instruments of the same family can be switched easily without the need to learn new fingerings. This brings us to the lovely feature of the BBb contrabass clarinet, that the lowest note Bb0, corresponding to a frequency of 29,14 Hz is written in G-clef, a clef used for soprano register. Consider that the lowest note in a piano is A0, 27.5 Hz and only half a step lower. Here you can hear some scales in a Eppelsheim Bb contrabass clarinet. For testing the lower notes being in tune, better than an electronic tuner a seismograph would be required.

As regards to the second part of the first question, it has to be borne in mind that the contrabass clarinet is a rather recent instrument in history of music. Adolphe Sax developed a rudimentary contrabass clarinet in mid 19th century, which did not see much success. Only in late 19th century and early 20th century some instruments with reasonable flexibility and intonation were developed. Therefore, most compositions for contrabass clarinet are from the 20th century and contemporary.
Here is a list of literature and composers for contrabass clarinet.
Here is Marco Mazzini playing some contemporary and electronic music.