THE SOUND-BOARD.—(Continued.)
The time has come when we must decide what our five stops are to be, since the sizes and places of the holes must be in accordance with the quality and character of the pipes supplied by them.
The Stopped Diapason we have already made; and in our organ it will be the chief or foundation stop of 8-feet tone. We shall assume that the second stop in the 8-feet pitch will be a metal Dulciana, or small open Diapason. The 4-feet stops will doubtless be a Principal (or some equivalent) and a Flute. The 2-feet stop we will call simply Fifteenth for the moment. For convenience of reference we will number the stops thus:—
| 1. | Dulciana or open | } | 8 | feet pitch |
| 2. | Stopped Diapason | } | " | " |
| 3. | Principal | } | 4 | " |
| 4. | Flute | } | " | " |
| 5. | Fifteenth | 2 | " |
The pipes of No. 1, being the tallest in the organ, will be planted nearest to the back; all the others, occupying the successive sliders, will present a gradation of heights agreeable to the eye and convenient for the tuner.
No. 1, we say, is the tallest in the organ; but be it carefully observed that in our small instrument it will not be carried down to its lowest note CC, which would be 8 feet in speaking length; it will not descend lower than tenor C, 4 feet, and the last or lowest twelve notes or sounds will be obtained by using the corresponding pipes of the Stopped Diapason as a bass for both stops.
This will be done by "grooving;" and it will now be seen why, in cutting out the upper boards, we were careful to have a single board for the pipes of 8-feet pitch, and another single board for those of 4-feet pitch. For it is plain that by boring holes through the upper board, sliders, and table into any groove of the sound-board, and by connecting these holes together by means of another deep groove or score cut in the wood of the upper board, and then covered in with an air-tight covering, we obtain a secondary channel, supplied with air by either or both of the sliders at pleasure; and by boring one hole through the air-tight covering, and planting a pipe on that hole, that pipe will speak whenever a connection is made between the secondary channel on which it stands and the main channel or groove below, which is receiving air at the moment from the bellows.
Clearly, therefore, if we bore holes through the upper boards and sliders of Nos. 1 and 2 into the twelve grooves of the bass octave, and then connect these twelve pairs of holes by cutting upper grooves in the surface of the boards, covering them in by thin boards of wood well glued down, we have then only to plant our twelve largest stopped pipes on twelve new holes bored in these thin boards last mentioned, and we have at once a bass common to both stops, and each of the two stops will be practically, and for ordinary purposes, complete down to the lowest note when its slider is drawn. When both sliders are drawn, the secondary groove will receive air from both holes in the upper board; but this will not have the effect of over-blowing the pipe, since the pressure or weight of the air remains the same, and since the pipe can only receive the quantity of air which is permitted to pass through the aperture in its foot.
It will now be seen why we did not at once bore the holes, or rather mark their places, on the rack-board. Plainly, we must make these twelve grooves first, and cover them in. Then, replacing the rack-board as before, carefully mark on the latter the exact place of each bass pipe, as it will stand on any part of its secondary groove. Afterwards, with a bradawl or other sharp-pointed borer, prick quite through the rack-board at every one of the points which you have marked throughout its whole extent. At these points there will hereafter be circular holes of various sizes for the reception of the pipe-feet, but in the upper boards, sliders, and tables there will be smaller holes, adapted for conveying its stream of air to each pipe. Before removing the rack-board, decide upon the places where the rack-pins, or pillars which will hold the rack-board up above the sound-board, are to be. Have plenty of these, say six or eight if you have a single rack-board, or five to each if you have two, in order to insure a firm plantation of the pipes, and bore holes for them with a centre-bit, say ⅝ diameter, through the rack-board and to the depth of 1 inch in the upper boards.