_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 5/8
diameter, through the rack-board and to the depth of 1 inch in the
upper boards.
The rack-board now being put aside for the present, all the holes may
be bored through the upper boards, sliders, and table with bits of
various sizes. From what has been said above it will be seen that it is
not the sizes of these holes, but of the apertures in the pipe-feet,
which regulate the volumes of wind supplied to the pipes; but you will,
of course, use bits proportioned to the pipes you have in view. The
upper, or treble, holes must not let the little pipes slip into them,
nor must the larger holes throttle or check the flow of the wind. In
the bass the holes may be as large as the grooves will allow; and if
these are narrow, or if there is secondary grooving or conducting, it
will be well to cut the round hole at its interior aperture with a
sharp chisel into a square or rectangular opening; or to bore two round
holes and connect them by taking out the intervening wood. Afterwards,
with iron rods of various sizes, heated to redness, scorch all the
holes through the three thicknesses of wood, leaving a clear and smooth
charred passage for the wind.
We have not yet done with grooving. This seems to be the proper place
for pointing out how the use of this system may further assist us in
the arrangement of an organ.
Our bass pipes, we have said above, may be planted on holes cut _in any
part_ of the covering or roof of their respective secondary channels.
It follows readily from this that the secondary groove or channel may
be extended or prolonged for the express purpose of locating the pipes
in situations convenient for them. Quite apart from any necessity which
may exist for supplying a common bass to two or more sliders, we may
evidently plant our larger pipes almost where and how we please by
cutting grooves in the substance of the upper board, extending from the
table beneath to the point where we wish the pipe to be. So long as the
holes are of sufficient diameter and the grooves of ample dimensions,
the wind will reach a pipe located at a distance even of 2 or 3 feet
from its source of supply without any appreciable interval between the
impact of the finger on the key and the production of the sound; and
the grooves may be curved almost as we please, though sharp angles
should be avoided.
Even if, in consequence of alterations of original plans or other
circumstances, the upper boards should not be of sufficient thickness
or size to admit of grooving, we may still avail ourselves of this
convenient system by using an additional or supplementary upper board,
which we will here call a conducting board, screwed down upon the main
upper board, and containing the grooves. To fix the exact places for
the holes in the under side of the conducting board, corresponding
with those in the table, spread a sheet of white paper over the upper
board at the part where the conducting is to be, making the edges or
corners of the paper coincide with those of the board, and rub the
paper with the finger so as to take clear impressions of the holes;
then transfer the paper to the under side of the conducting board,
guided by the edges and corners as above, and prick out on this under
side the centres of the circular impressions made on the paper. It is
evident that when the conducting board is applied to the upper board,
edges and corners coinciding as before, these punctured marks will be
exactly over the wind holes in the table. The holes in the upper side
of the conducting board will be marked as before from the rack-board,
and grooves cut and roofed in with thin wood, as previously described.
Note further, that the grooving may be, if necessary, on both sides of
the upper boards. All that is needful in such case is, that after the
grooves on the under sides, next the sliders, are cut, the _whole of
the board_, and not merely the grooved part of it, shall be covered or
veneered with thin stuff. This must be dressed perfectly true, as in
the case of the solid or ungrooved board, and all the holes will be
bored through it. The upper sides will also have a neater appearance
if the roofing of thin mahogany or cedar is carried over its entire
surface. Upper boards so treated are, in fact, compounded of three
layers of wood, a central thick slab containing the grooves, and two
coverings or veneers. The gluing on of these latter must, of course,
be very sound and effectual in every part, or a running of wind might
ensue--a most provoking and really fatal defect, incurable without
complete reconstruction.
Short grooves may be made by boring holes with a centre-bit in the
_edges_ of the upper boards, and making the wind-hole beneath and the
pipe-hole above communicate with this concealed tunnel. On plugging up
the external aperture in the edge of the board, or on stopping a whole
row of such apertures by gluing a band of leather, parchment, or thick
paper over them, it is clear that the wind will pass to the pipes at
pleasure. All such holes and channels must be scorched with hot irons.
To the true joiner this may seem an unworkmanlike expedient, but it is
necessary to prevent the weakening of the currents of air which would
ensue from friction against rough surfaces, and to preclude the risk of
carrying tiny chips and particles of wood into the pipes. If conducting
boards are used, they should be faced with soft white leather on their
under surfaces before they are screwed down in their places, unless,
indeed, they are glued down immovably. The places for the screws, as
well as for those which secure the whole upper board to the table, must
be carefully determined with reference to the grooves.
Fig. 12 is intended to show, in a rough way, how in an upper board BB
grooves may conduct the wind from the holes in a slider AA to a row of
pipe-holes near the margin of the board, resulting in an arrangement
like that shown in Fig. 8. The dotted lines are meant to indicate
grooves cut in the under side of the board. It is clear that these
might be made to cross the others, so that different plantations of
pipes might be obtained, as in Fig. 9.
[Illustration: Fig. 12.]
_Remark._--These figures, however, must be understood rather as
illustrations of our meaning than as representations of actual work.
Conveyancing tubes are in constant use, not only as substitutes for
grooving, but as ancillary to it. They are made of pipe-metal, and from
about 5/8 inch in diameter to much larger sizes. To manage them neatly
and well you should be adroit in the use of the soldering-iron. They
are commonly smeared over with a composition which will not receive
the melted solder; this composition is scraped off at the points where
a junction is to be made at an angle, and with the usual copper tool,
a little resin and tallow, the solder is applied. Much practice is
needed to give mastery of this process, apparently so easy; we have
known instances in which it has been avoided altogether by covering
the junctions of the conductors with white leather secured by thick
flour paste. It is right, also, to add, that we have seen successful
conveyances made of cartridge paper rolled upon wooden mandrels with
paste. Any tin-plate worker in your town or village would make them of
his own material or of zinc, and in an hour or two would solder all the
junctions for you when you had planned your arrangement thoroughly.
Assuming, however, the use of the usual tubes, we may say that they are
thus applied. Let us suppose that the large pipe shown in Fig. 10 is to
be conducted off from the sound-board at the higher level to the plank
on which it stands. Bore the hole in the upper board a trifle larger
than the outside diameter of the tube. Glue a patch of white leather
over the hole, and cut out the aperture in this leather somewhat
smaller than the hole, leaving an excess of leather all round the hole
of about 1/8 inch. Then, making the end of the tube a little conical,
thrust it into the hole; it will carry in with it the surplus margin of
the leather, which will form around it an air-tight joint or collar. A
right angle may be allowed in the tube at this first commencement at
the hole itself, but in its subsequent course sharp corners should be
avoided. The pipe is planted on a hole bored to a sufficient depth in
a plank; a second hole, suited to a conducting tube, is bored at any
convenient distance from this, and communication made between these
two holes by a groove in the under side of the plank closed in with
leather, parchment, thick paper, or wood; then the end of the tube is
forced as before into the hole bored for it and provided with leather
packing, and all is complete.
It is by these means that "speaking fronts" are arranged according to
any design.
_Remark._--If you have all your pipes, metal as well as wood, ready
at hand, it might be well to pierce the rack-board and fit them in
their places at this stage of the proceedings, because chips and dust
are inseparable from the operation, and may be more troublesome and
mischievous after the pallets are put in than now. Those readers who
resolve on this course may turn, then, to the subsequent pages, in
which they will find all the directions which are necessary for their
guidance. For our own part, we prefer to continue in the next chapter
our account of the mechanism of the sound-board.
We may further remark, that while the boring-tools are in use we may
perhaps do wisely in piercing holes also for the screws which are to
hold the upper boards down upon the sliders. If the planing has been
perfectly true, about four pairs of screws should be enough for each
upper board, and no extra screws should be required to force the boards
into closer contact at any intermediate part. The screws should pass
clear and easily through the holes in the boards, and should bite
well in the table beneath. The heads of the screws should be let down
below the level of the upper surface of the boards by counter-sinking,
and it is a useful practice to mark the places of these screws on the
rack-board as well, and to bore corresponding holes in this latter, in
order that if hereafter a slider should be pinched too tightly between
the upper board and table, the end of a long screw-driver may be
introduced to ease it by slackening the screws without disturbing the
pipes.
But we shall have to return to this part of our subject.