[1] In China at the present time (1902) certain ports are designated
"free and open." This phrase means that the ports in question are (1)
open to foreign trade, and (2) that vessels engaged in oversea
voyages may freely resort there. Exemption from payment of customs
duties is not implied, which is a matter distinct from the permission
granted under treaty engagements to foreign vessels to carry cargoes
to and from the "treaty ports."
FREE REED VIBRATOR (Fr. _anche libre_, Ger. _durchschlagende Zunge_,
Ital. _ancia_ or _lingua libera_), in musical instruments, a thin metal
tongue fixed at one end and vibrating freely either in surrounding
space, as in the accordion and concertina, or enclosed in a pipe or
channel, as in certain reed stops of the organ or in the harmonium. The
enclosed reed, in its typical and theoretical form, is fixed over an
aperture of the same shape but just large enough to allow it to swing
freely backwards and forwards, alternately opening and closing the
aperture, when driven by a current of compressed air. We have to deal
with air under three different conditions in considering the phenomenon
of the sound produced by free reeds. (1) The stationary column or
stratum in pipe or channel containing the reed, which is normally at
rest. (2) The wind or current of air fed from the bellows with a
variable velocity and pressure, which is broken up into periodic air
puffs as its entrance into pipe or channel is alternately checked or
allowed by the vibrator. (3) The disturbed condition of No. 1 when acted
upon by the metal vibrator and by No 2, whereby the air within the pipe
is forced into alternate pulses of condensation and rarefaction. The
free reed is therefore not the tone-producer but only the exciting
agent, that is to say, the sound is not produced by the communication of
the free reed's vibrations to the surrounding air,[1] as in the case of
a vibrating string, but by the series of air puffs punctuated by
infinitesimal pauses, which it produces by alternately opening and
almost closing the aperture.[2] A musical sound is thus produced the
pitch of which depends on the length and thickness of the metal tongue;
the greater the length, the slower the vibrations and the lower the
pitch, while on the contrary, the thicker the reed near the shoulder at
the fixed end, the higher the pitch. It must be borne in mind that the
periodic vibrations of the reed determine the pitch of the sound solely
by the frequency per second they impose upon the pulses of rarefaction
and condensation within the pipe.
[Illustration: From J. B. Biot, _Traite de physique experimentale_.
FIG. 1.--Grenie's organ pipe fitted with free-reed vibrator.
A, Tuning wire.
D, Free reed.
R, Reed-box.
B, C, Feed pipe with conical foot.
T, Part of resonating pipe, the upper end with cap and vent hole being shown
separately at the side.]
The most valuable characteristic of the free reed is its power of
producing all the delicate gradations of tone between forte and piano by
virtue of a law of acoustics governing the vibration of free reeds,
whereby increased pressure of wind produces a proportional increase in
the volume of tone. The pitch of any sound depends upon the frequency of
the sound-waves, that is, the number per second which reach the ear; the
fullness of sound depends upon the amplitude of the waves, or, more
strictly speaking, of the swing of the transmitting particles of the
medium--greater pressure in the air current (No. 2 above) which sets the
vibrator in motion producing amplitude of vibration in the air within
the receptacle (No. 3 above) serving as resonating medium. The sound
produced by the free reed itself is weak and requires to be reinforced
by means of an additional stationary column or stratum of air. Free reed
instruments are therefore classified according to the nature of the
resonant medium provided:--(1) Free reeds vibrating in pipes, such as
the reed stops of church organs on the continent of Europe (in England
the reed pipes are generally provided with beating reeds, see REED
INSTRUMENTS and CLARINET). (2) Free reeds vibrating in reed compartments
and reinforced by air chambers of various shapes and sizes as in the
harmonium (q.v.). (3) Instruments like the accordion and concertina
having the free reed set in vibration through a valve, but having no
reinforcing medium.
The arrangement of the free reed in an organ pipe is simple, and does
not differ greatly from that of the beating reed shown in fig. 2 for the
purpose of comparison. The reed-box, a rectangular wooden pipe, is
closed at the bottom and covered on one face with a thin plate of copper
having a rectangular slit over which is fixed the thin metal vibrating
tongue or reed as described above. The reed-box, itself open at the top,
is enclosed in a feed pipe having a conical foot pierced with a small
hole through which the air current is forced by the action of the
bellows. The impact of the incoming compressed air against the reed
tongue sets it swinging through the slit, thus causing a disturbance or
series of pulsations within the reed-box. The air then finds an escape
through the resonating medium of a pipe fitting over the reed-box and
terminating in an inverted cone covered with a cap in the top of which
is pierced a small hole or vent. The quality of tone of free reeds is
due to the tendency of air set in periodic pulsations to divide into
aliquot vibrations or loops, producing the phenomenon known as harmonic
overtones or upper partials, which may, in the highly composite clang of
free reeds, be discerned as far as the 16th or 20th of the series. The
more intermittent and interrupted the air current becomes, the greater
the number of the upper partials produced.[3] The power of the overtones
and their relation to the fundamental note depend greatly upon the form
of the tongue, its position and the amount of the clearance left as it
swings through the aperture.
[Illustration: FIG. 2.--Organ pipe fitted with beating reed.
AL, Beating reed.
R, Reed box.
Ff, Tuning wire.
TV, Feed pipe.
VV, Conical foot.
S, Hole through which compressed air is fed.]
Free reeds not associated with resonating media as in the concertina are
peculiarly rich in harmonics, but as the higher harmonics lie very close
together, disagreeable dissonances and a harsh tone result. The
resonating pipe or chamber when suitably accommodated to the reed
greatly modifies the tone by reinforcing the harmonics proper to itself,
the others sinking into comparative insignificance. In order to produce
a full rich tone, a resonator should be chosen whose deepest note
coincides with the fundamental tone of the reed. The other upper
partials will also be reinforced thereby, but to a less degree the
higher the harmonics.[4]
For the history of the application of the free reed to keyboard
instruments see HARMONIUM. (K. S.)