I have now got around to measuring the paper speed on my Triola.
Harald Mueller is correct in spotting that John Wolff's speed is the
average, since he has divided the total length by the total time.

It is important to know the initial paper speed when arranging for any
instrument using a relatively small take-up spool which is rotating at
a constant speed.  On the Triola, this, and using spiral compensation,
are particularly important as you don't want to speed up the crank
speed towards the end of the roll as this will have the effect of
speeding up the rate of reiteration.

When checking three rolls I come up with an initial speed of 33 mm/sec.
"O Sole Mio" and "Over The Waves" gave this speed, whereas "Sheik Of
Araby" requires a slightly faster speed of 36 mm/sec.  Of course,
music speed is at the choice of the player.  I think my speed
measurements tally with John Wolff's when you take into account the
speed compensation.  Incidentally, "Sheik Of Araby" must be the most
difficult roll to play in the bass if one is to interpret correctly the
bass instructions.

The actual degree of spiral compensation will depend on the paper
thickness.  This means that if one is copying an original roll it is
important to use exactly the same thickness of paper on the copy as is
used on the original.  This assumes you are using the old fashioned way
of marking through, rather than scanning and digitising.

As regards long chord strengthening, rolls tend to use 'choral
breathing' as Harald puts it.  This is the standard technique used on
keyed fair organ books and on the Triola is even less audible than on
the organ, due to the reiterating effect and the lack of dampers.  May
I correct a minor error in Harald's posting.  The Triola strings are
not operated by rotating starwheels.  The entire jack carriage is
oscillated back and forth by a three lobed cam fitted to the crankshaft.
The vertical movement between the keys ( which have to be fixed
laterally for obvious reasons ) and the plucking jacks is facilitated
by a short thin cord on the back of each key, lifting the jack above
the string when there is no hole in the paper.

There are six sets of four bass strings.  These are used for both
bass and accompaniment and are not just strummed.  Quite complex
accompaniments can be achieved.  Harald, please see my earlier posting
where I describe in detail the three different ways in which these
strings are marked on the roll, and should be played.

Finally, I had the pleasure of meeting Harald at Waldkirch earlier
this year and was most impressed by his ambitious arranging for 20-note
street organ.  Is there anyone else who has put Jelly Roll Morton tunes
onto 20-notes and made it work?

Kind regards to you all,
Nicholas Simons,
in the windy and wet East Midlands of Great Britain.