Introducing Bosca Dubh!

The Bosca Dubh (circa 2020)

I’ve been living with Bosca Dubh for a month now and learning about its unique personality. Bosca Dubh is the next generation of The Black Box, which is essentially a D/G diatonic accordion redesigned to allow traditional Irish ornamentation. Bosca Dubh began its life as a club accordion, apparently designed by Excelsior. There are no identification numbers anywhere on the box or inside. I contacted Excelsior for information about this box, but they have no idea about it other than it could be one of a few specimens of a test model. This makes it even more unique and mysterious.

Compared to The Black Box, Bosca Dubh has two more treble-side buttons (on the inner-most row), and four more bass-side buttons. Here’s the layout:

The green buttons are identical to those of The Black Box. The other buttons are new. Here are the ranges of the two boxes, also showing the rolls that are possible:

The range of Bosca Dubh is one semitone lower than The Black Box, and has the high f natural. Bosca Dubh also can do rolls on F3 and G3. Neither box allows a traditional-style roll on F4 — but a triplet suffices. Everything else is the same on the treble side.

The bass side of Bosca Dubh is expanded. Like The Black Box, all thirds are removed. But Bosca Dubh now has A and F# on the press, and F and C# on the draw. These add lovely color to tunes in the keys/modes common to Irish traditional dance music. The C# is useful for tunes in A, and the F# is useful for tunes in D. The F adds a nice modal flavor to tunes in G.

Like The Black Box, the Bosca Dubh has LMMMH reeds (L = octave below; M = middle; H = octave above); but it has more couplers. Here’s a picture of all the voicings available on Bosca Dubh. (The dots and their position denote which reeds are active.)

The coupler pressed is “ALL REEDS GO!”. One can also choose just L, or just M, or just H. Then there are four couplers that choose combinations of these. There are three couplers choosing combinations of the middle reeds — let’s call them Ml (middle low), Mm (middle middle), and Mh (middle high). “Traditional” Irish tuning makes the Mm reeds right on concert pitch and then the Ml and Mh are detuned relative to that by up to 15 cents, lower or higher, respectively. This makes a “wet” or warbly sound. (Some traditional players, like Jackie Daly, use very little to no detuning of these reeds.)

The Ml+Mm coupler selects the middle reeds located in a cassotto chamber. This is another unique aspect of Bosca Dubh over The Black Box. Cassotto makes for a very mellow sound. Here’s a picture of the treble side showing the reed batteries in the cassotto chamber (top):

The most odd feature of Bosca Dubh is the coupler isolating Ml+Mh. The expert that converted this accordion (Erik Simons, highly recommended!) believes this is a mistake of the manufacturer. I’ve never seen such a coupler before. BUT, I love the sound. I call it the “circus setting”. This “mistake” lends credence to the theory that this box was a test model.

Now for a demonstration of Bosca Dubh, including its “circus” setting:

How does Bosca Dubh compare with the typical B/C accordions played in Irish traditional music? Below are the ranges of Bosca Dubh compared with the standard B/C layout of the popular Paolo Soprani boxes:

We can see several things. Bosca Dubh doesn’t go as low as the B/C, but it does go higher. The longest chromatic run of notes on the B/C is two on the press and four on the draw; but on Bosca Dubh it is ten on the draw and five on the press (in the middle of the range). Each roll on the B/C can only be performed in one direction of the bellows, but on Bosca Dubh many rolls can be performed in both directions. The only rolls Bosca Dubh cannot perform that the B/C can are E3 and F4. The B/C cannot perform rolls on C# or F#.

Another typical system in Irish traditional accordion is C#/D, which is just tuned a semitone higher than the B/C. Thus it shares much of the same characteristics:

As for the B/C, Bosca Dubh doesn’t go as low as the C#/D. As for the B/C, the longest chromatic run of notes on the C#/D is two on the press and four on the draw. Each roll on the C#/D can only be performed in one direction of the bellows, but on Bosca Dubh many rolls can be performed in both directions. Unlike the B/C system, the C#/D can perform rolls on C# and F#, but not on F natural.

A big advantage of Bosca Dubh and The Black Box over B/C and C#/D accordions is the expanded harmonic possibilities on the treble side. Many more note combinations are possible, which makes them versatile instruments for accompaniment. Here’s a table showing several of the chords that can be played on the treble side: “M” is major, “m” is minor, “M7” is major with raised 7th, and “dim” is minor with diminished fifth.


For a given root, the major 7 chord resolves to the IV, while the diminished chord resolves to the V. So in Irish traditional music, several of these wouldn’t be useful, e.g., C#dim, Adim, B7 and Bdim. More often, however, intervals of octaves, fifths and fourths are used on Irish accordion.

In conclusion, the expanded bass on the Bosca Dubh is the biggest and most useful change from The Black Box. The two additional buttons on the treble side aren’t really that useful. The cassotto on Bosca Dubh is very nice, as is the organ/melodeon sound. The circus setting is a fun unique one. If I were to look toward the next design, I might trade some of the high notes for the low ones available on B/C and C#/D, e.g., remove everything from the Eb6 up and add in the B2 to D3. This however would make the box have a sixth button start, shifting my hand position down one, which might actually be beneficial ergonomically.

One thought on “Introducing Bosca Dubh!

  1. Pingback: Tunes from the Ai Frontiers | Folk the Algorithms

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