Music Trade Review
Issue: 1922 Vol. 74 N. 17 - Page 9
Music Trade Review -- © mbsi.org, arcade-museum.com -- digitized with support from namm.org
APRIL 29,
1922
THE MUSIC TRADE
REVIEW
9
vVB^raBfiflg^BfSB^^
The Problems Involved in Providing for the Various Pressure Levels Which
Are Necessary in the Operation of the Reproducing Piano Have Engaged the
Attention of Pneumatic Engineers for Years—Some of the Systems in Use
The problem of attaining the different pressure
levels which are needed for the practical work of
reproducing piano playing in the automatic-ex-
pression or reproducing types of player-pianos
has engaged the attention of many inventors dur-
ing the last ten years. In consequence a multi-
tude of devices for this purpose has been brought
into existence, some of which, of course, are much
better than others. The principle on which they
depend is, of course, the same in all cases, but
its application may, in the practical sense of the
term, be extremely varied. It will be interesting
to examine some of these.
Definition of Pressure Level
The general problem, of course, is simply that
of producing needed pressure levels at will and
according to some scheme deduced from the re-
quirements of a given piece of music. A pressure
level may be defined as the relation at any mo-
ment existing between the pressure of the atmos-
phere and the pressure of air inside a player
action. The difference between this outside fixed
pressure and the pressure inside is obtained by
withdrawing from the inside some part of its
air. If air is simultaneously entering the action
it becomes necessary to assure that more air
will be in process of withdrawal than can enter,
or, more accurately, that the rate of withdrawal
shall be greater than the rate of entry. This can
be assured by the use of suitable suction bellows
or fans, whose capacity is greater than that of
all sources of leakage combined.
The Ratio of Pressure
Now, upon the relation between the rate of
withdrawal and the rate of inleak will depend
the relation between the inside pressure and the
pressure outside. Therefore, changes in pressure
level might be brought about by causing changes
in the rate of motion of the suction machinery.
This, however, would be a very clumsy and in-
effective method. Much simpler, more efficient
and generally more practical is the simple method
of changing the area of the passageway through
which the air must flow in process of withdrawal.
The Suspended Valve Method
Suppose that in such a passageway a turn is
made, to provide a short vertical chamber. Let
this chamber be provided with a floor in which
is bored a hole communicating with the player
action. At the other end, or near the roof, of
this chamber let a hole of the same size be bored
in the wall. If now a valve is suspended so that
it can rest right in contact with the hole in the
floor of the chamber, or be raised above it, as
required, then plainly means will have been pro-
duced for effectively modifying the area of the
passageway through which the air passes from
action to bellows. For if the valve be placed so
as nearly to touch the upper surface of the hole
then no matter how powerfully the suction ma-
chinery may work no more air can pass through
from the action than can find its way out through
the narrow space between valve and hole.
The suction machinery might, indeed, be speed-
ed up, which would have the effect of bringing out
a larger quantity of air from the action by in-
creasing the difference between the reduced and
the atmospheric pressures. But this process could
be compensated by the simple device of a gov-
ernor controlled by the pressure itself.
In one very practical method, then, the re-
quired changes in working pressure are to be
considered as produced by mechanism which will
cause a valve to be brought into various posi-
tions with relation to a hole. Let us consider
how this may conveniently be worked out, with
the kind of pneumatic mechanism which is avail-
able in a player action.
The Question of How Many Positions
The first question which will be asked is, of
course: "How many different positions of the
valve must there be?" The answer is that there
cannot in effect be too many such positions, but
in practice their number may be limited. Let us
suppose, for the sake of example, that four such
positions are considered to be sufficient for the
purpose aimed at. Then there are several ways
in which these positions of the valve may be at-
tained. Imagine, for one of such ways, that the
valve is suspended upon a rod, at the other end
of which is pivoted loosely a fulcrumed lever. On
the other side of the fulcrum let there be four
pneumatics, arranged side by side. Let each pneu-
matic correspond with a perforation in the mar-
gin of the tracker bar. Between each such per-
(Continued on page 10)
Pratt Read Player Actions
"built to play"
MODEL A
for high-priced pianos
10-point motor
Transposer
Pedal throwout
Automatic tracker
Automatic hammer rail
Automatic pedal
Silencer
Soft bass and treble buttons
MODEL F
for moderate-priced pianos
Automatic tracker
6-point motor
Covered metal tubing
Simplified bellows
Sustaining pedal lever
Soft bass and treble levers
Materials and Workmanship Guaranteed
Over 48,000 in Use. Worth Trying!
The Pratt Read Player Action Co.
Main Office and Factory, Deep River, Conn.
Foreign Office, 21, Mincing Lane, London.
APRIL 29,
1922
THE MUSIC TRADE
REVIEW
9
vVB^raBfiflg^BfSB^^
The Problems Involved in Providing for the Various Pressure Levels Which
Are Necessary in the Operation of the Reproducing Piano Have Engaged the
Attention of Pneumatic Engineers for Years—Some of the Systems in Use
The problem of attaining the different pressure
levels which are needed for the practical work of
reproducing piano playing in the automatic-ex-
pression or reproducing types of player-pianos
has engaged the attention of many inventors dur-
ing the last ten years. In consequence a multi-
tude of devices for this purpose has been brought
into existence, some of which, of course, are much
better than others. The principle on which they
depend is, of course, the same in all cases, but
its application may, in the practical sense of the
term, be extremely varied. It will be interesting
to examine some of these.
Definition of Pressure Level
The general problem, of course, is simply that
of producing needed pressure levels at will and
according to some scheme deduced from the re-
quirements of a given piece of music. A pressure
level may be defined as the relation at any mo-
ment existing between the pressure of the atmos-
phere and the pressure of air inside a player
action. The difference between this outside fixed
pressure and the pressure inside is obtained by
withdrawing from the inside some part of its
air. If air is simultaneously entering the action
it becomes necessary to assure that more air
will be in process of withdrawal than can enter,
or, more accurately, that the rate of withdrawal
shall be greater than the rate of entry. This can
be assured by the use of suitable suction bellows
or fans, whose capacity is greater than that of
all sources of leakage combined.
The Ratio of Pressure
Now, upon the relation between the rate of
withdrawal and the rate of inleak will depend
the relation between the inside pressure and the
pressure outside. Therefore, changes in pressure
level might be brought about by causing changes
in the rate of motion of the suction machinery.
This, however, would be a very clumsy and in-
effective method. Much simpler, more efficient
and generally more practical is the simple method
of changing the area of the passageway through
which the air must flow in process of withdrawal.
The Suspended Valve Method
Suppose that in such a passageway a turn is
made, to provide a short vertical chamber. Let
this chamber be provided with a floor in which
is bored a hole communicating with the player
action. At the other end, or near the roof, of
this chamber let a hole of the same size be bored
in the wall. If now a valve is suspended so that
it can rest right in contact with the hole in the
floor of the chamber, or be raised above it, as
required, then plainly means will have been pro-
duced for effectively modifying the area of the
passageway through which the air passes from
action to bellows. For if the valve be placed so
as nearly to touch the upper surface of the hole
then no matter how powerfully the suction ma-
chinery may work no more air can pass through
from the action than can find its way out through
the narrow space between valve and hole.
The suction machinery might, indeed, be speed-
ed up, which would have the effect of bringing out
a larger quantity of air from the action by in-
creasing the difference between the reduced and
the atmospheric pressures. But this process could
be compensated by the simple device of a gov-
ernor controlled by the pressure itself.
In one very practical method, then, the re-
quired changes in working pressure are to be
considered as produced by mechanism which will
cause a valve to be brought into various posi-
tions with relation to a hole. Let us consider
how this may conveniently be worked out, with
the kind of pneumatic mechanism which is avail-
able in a player action.
The Question of How Many Positions
The first question which will be asked is, of
course: "How many different positions of the
valve must there be?" The answer is that there
cannot in effect be too many such positions, but
in practice their number may be limited. Let us
suppose, for the sake of example, that four such
positions are considered to be sufficient for the
purpose aimed at. Then there are several ways
in which these positions of the valve may be at-
tained. Imagine, for one of such ways, that the
valve is suspended upon a rod, at the other end
of which is pivoted loosely a fulcrumed lever. On
the other side of the fulcrum let there be four
pneumatics, arranged side by side. Let each pneu-
matic correspond with a perforation in the mar-
gin of the tracker bar. Between each such per-
(Continued on page 10)
Pratt Read Player Actions
"built to play"
MODEL A
for high-priced pianos
10-point motor
Transposer
Pedal throwout
Automatic tracker
Automatic hammer rail
Automatic pedal
Silencer
Soft bass and treble buttons
MODEL F
for moderate-priced pianos
Automatic tracker
6-point motor
Covered metal tubing
Simplified bellows
Sustaining pedal lever
Soft bass and treble levers
Materials and Workmanship Guaranteed
Over 48,000 in Use. Worth Trying!
The Pratt Read Player Action Co.
Main Office and Factory, Deep River, Conn.
Foreign Office, 21, Mincing Lane, London.
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