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DICTIONARY OF ORGAN STOPS. S3
is not desired. It will be seen that in this type of Diaphone the
valvular movement is less sudden than that of the preceding patterns.
The smoother the action of the valve, the smoother the tone quality
generated. If, on the contrary, the valve beat forcibly on its seat, the
resultant tone will be rough and coarse. This Roller-Valve Diaphone is
here described mainly on account of its theoretical interest ; it is scarcely
a form adapted to practical use.
In the above Diaphones the quality and power
of the tone can be controlled within limits by the
shape and sue of the resonators, the tension of the
springs, etc. By the substitution of cylindrical
resonators, Clarinet tones have been obtained.
Their satisfactory tonal effect is very dependent on
the suppleness of the valve. A somewhat serious
objection to which all these forms of Diaphone are
open is their lack of durability. It will be evident
that the wear and tear of motors vibrating, in the
case of high notes especially, at the requisite
rapidity, must be very great. On the other hand,
no single note is ever in continuous motion for
a protracted period of time, and were some
mechanism to be invented for computing the
number of minutes in a year that a Diaphone
pipe was in action, the number indicated would
probably be found to be small It is but fair to
observe that the Diaphones at Worcester and
Edinburgh, referred to above, although probably
somewhat decayed, are still in excellent working
order. Moreover, it is a matter of no very great
difficulty to replace worn-out motors.
In 1897 Mr. Hope-Jones patented an improved
variety of Diaphone, known as the Diaphonic
Horn, or sometimes as the "valvular reed." In
it the motor bellows is dispensed with, the
vibrating pallet or disc being carried on the free
end of a spring. It is thus a variety of beating
reed. The construction of this form of Diaphone
will be explained by reference to Fig. D. The
spring s is made of aluminium, a pliable metal
readily admitting the correct adjustment of the
disc in relation to the block against which it beats.
Whereas the Tremulant Diaphones are tuned by
the resonator or pipe, the valvular reed is properly
Fig. D—" Valvular Reed'
or Diaphonic Horn.