One of the ranks, containing the string-toned reeds, has some additional features that have to be refurbished.  Unlike the five other ranks, there is no array of Helmholz bottles on the reed cell outlets.  But this rank contains two reeds per note.  In the higher ends of the scale, one of these reeds is tuned slightly high, so if both reeds play simultaneously, the beat frequency (F₁ + F₂, inaudible, and F₁ - F₂, about 4 to 8 Hz) produces a pleasant warble effect, called the "Aeolian Harp".

    The mutes are covered with the same composite of thick white felt and kidskin as all the other valve pallets described elsewhere.  Using the same techniques, a composite of felt and leather was made; glued to the mutes, and trimmed.

    While I was at it, I made a new felt cover for the big mute that covers the outlet of the sub-bass resonator.  This mute is opened when the louder "Double Bass" stop is pulled, and closed when the softer "Contra Bass" is selected.

    When reinstalling any reed organ mutes, it is desirable to plug the existing hinge screwholes, and start at new spots.   It is impossible to make the mute covering exactly the same thickness as the original, and if one attempts to reuse the old hinge screwholes, the mutes will not end up flat and tight.  To hold the mute flat, drill small holes through them, and nail them in place with small finishing nails.

    After the mutes are hinged to the reed board surface, the old wire torsion springs are reinstalled, and a couple of loops of bushing cloth are tacked around the springs to keep them from rattling against the hinges.  Note that the  much longer treble end mute is in two pieces, with a little felted cleat which open the middle one when the right end one is opened by the linkage.

    An interesting feature are the little extension blocks on the outer ends of the mutes.  These extend through holes in the walls of the swell box, and are connected to the linkages that operate the mutes from the stop rail.  See Chapter 22.2 for details of this linkage.  To remove the rank chest, one has to unscrew these blocks from the mutes.  Since each block has only one screw, there is a considerable tendency for the forces from the linkage to rotate the block. rather than pulling it straight.  To prevent this, sandpaper is glued to the inner surface of the blocks, to improve the frictional grip.  This is a common trick in piano building, to keep one-screw flanges from turning, but this is the only instance of this in the Orchestrelle I found.

    Now a problem arose.  When the rank was tested, a few of the celest reeds still played even when the mute was closed, especially at the treble end.  For the very small reeds, only a tiny flow is required to make them speak.  After a lot of trial and error, it seems that a very slight curvature or warpage of the mute sticks made them seat unevenly.  The torsion springs are not very strong, and the total area of the felt and leather is comparatively large.  There is not enough unit force to make the felt compress enough to insure seating all along the width of the sticks.  No mater how I adjusted the hinges, either the top or bottom edge of the sticks would not seat flatly, depending where along the stick I tired.

    I could have installed stronger torsion spring wires, but I did not want to increase the force required to draw the stops.  Instead, I cut off part of the width of the felt and leather.  There remained plenty of leather width to fully cover the sound outlet holes.  But now the leather area was centered over the holes, and the compression area was reduced by half.  Now the mutes sealed themselves reliably over the holes, all long their length.  Not original, but it worked.

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