US2048508A - Pneumatic sound reproducer - Google Patents

Description

I July 21, 1936. R. F, MALLlNA 2,048,508

PNEUMATIC SOUND REPRODUCER Filed May 5l, 1934 2 Sheets-Sheet 1 /NVENTOR By* R/-TMALL/NA A TTORA/EV July 21, 1936.'

PNEUMATI C S OUND REPRODUCER R. F. MALLINA 2,048,508

Filed May 51' 1954 2 sheets-sneer 2 I l y I l /N/ENTOR REMALL//VA ATTORNEY Patented July 21, 1936 UNITED STATES Bell Telephone Laboratories,

Incorporated,

New York, N. Y., a corporation of New York Application May 31, 1934, Serial No. 728,201 e claims. (ci. 179-113) This invention relates to improvements in sound reproducing devices and particularly to loudspeakers of the pneumatic type in which currents representing the sounds to be reproduced operate 8 suitable means for modulating an air stream to produce large volumes of sound.

The object of the invention is an efficient and inexpensive modulator for loud-speakers of this type.

v According to one important feature of the invention, the modulator is held in static balance by the action of the air stream thereby eliminating the turning movement of the air pressure on the modulator.

1'5 The preferred structure, according to the invention, comprises a rubber damped balanced armature mounted for vibration about its medial axis which is disposed transversely in the center of the air conduit to form two orifices equal in area between the 'tips of the armature and the walls of the conduit. The armature extends through signal current coils -which are surrounded by bifurcated pole-pieces suitably contoured in the direction of the air ow and disposed to form working gaps with the armature. Flux is fed to the pole-pieces by permanent or electromagnets external to the conduit vand the vibrations of the armature produced by the interaction of the steady and alternating fluxes are damped by rubber blocks engaging both sides of the armature near the armature tips.

The armature may be mounted either at right angles to the axis of the conduit or at a suitable angle (such as 30 to 45) to the transverse axis of the conduit. The right angle construction is inherently of higher efciency but requires that the inner wall of the conduit be contoured to form the necessary oriiices. With the angular arrangement the efiiciency is somewhat decreased but the axes of the oriiices may be parallel to the axis of the conduit.

In the drawings. Fig. 1 is a sectional view of a modulator mounted at right angles to the axis of the conduit;

Fig. 2 is a sectional view taken as indicated in Fis- 1; l

Figs. 3 and 4 are detail views of the armature damping structure; 4

Fig. 5 is a sectional view of the alternate construction in `which the amature is mounted at an angle to the transverse axis of the conduit, Aand Fig. 6 is an assembly view showing the housing 55 for the orice adjusting members of Fig. 1 and an arrangement of the magnets which-is applicable to either embodiment of the invention.

In Fig. 1, the conduit Il composed of -brass or other non-magnetic material is connected at lone end to a source of compressed air by means of 5 the pipe I2 and at the 'other end to a suitable horn of which only a portion of the throat I3 is shown. The pole-'pieces I4, I5 extend across the conduit and project through the walls on either side to4 make contact with the magnets I6, I1 which are 10 shown in Fig. 6 as permanent magnets but for loud-speakers of great output capacity the large magneto-motive force required may be supplied by electro-magnets. The signal current coils I8,

I9 are housed between the pole-pieces and the 15 armature 20 is pivoted at its center between the coils on the shaft 2I which is journaled in the pole-piece spacing member 28 as shown in Fig. 2. The pole faces are recessed to receive the rubber damping members 22, 23 which surround the 20 armature as shown more clearly in Figs. 3 and 4 and hold it in its proper position at right angles to the axis of the conduit. At the section where the armature is pivoted, the conduit is substantially rectangular in cross-section and has slots 25 29, 30 extending the full Width o1' ythe armature. The slots are closed by housings 3|, 32 in' which the sliding blocks 33, 34 are fitted to form the orifices 24 and 25. By means of the screws 35, v 36 the blocks may be accurately adjusted to make 3o the oriiices equal and ot any desired size. This adjustment is preferably made with the air applied to the modulator so that the slight 'deflection of the armature due to the air pressure will not result in orifices of unequal areas. 35

When the coils I8 and I9 are not carrying currents, the armature 20 is stationary in its midposition as shown and a continuous stream of air ilows through the orifices to the horn but when currents representing the sounds to be repro- 40 duced are supplied to the terminals 26, 21 of the coils, an 'alternating flux is set up longitudinally in the armature and the armature vibrates between the pole faces in the well known manner. The vibrating armature tips vary the areas of the 45 orifices to produce variations in the air stream corresponding to the signal current variations which are accordingly reproduced as audible sounds from the horn.

Since the armature is rigidly pivoted at its center. the areas exposed to the air pressure on opposite sides of the axis are equal and the steadyl'air pressure therefore has no tendency to displace the armature from its center or neutral position. It is well known that pneumatic loud-speakers `Lili are capable of producing* sounds oi great volume since a large proportion of the acoustic energy is derived from the compressed air. Modulators which are not statically balanced, however, must be extremely rugged to withstand the unbalanced varies substantially directly with the armature displacement.

Thevalternate form shown in Fig. 5 is, in general, similar in construction and operation to the structure just described. 'Ihe essential difference is that the armature 40 is mounted at an angle of from 30 to 45 to the transverse axis of the conduit so that axes of the orifices are parallelto the walls of the conduit 4I The configuration of the pole- pieces 42, 43, the coils 44, 45 and the damping members 46, 41 is modified to adapt them to the inclined position o! the armature but obviously their functions are the same as inthe structure of Fig. 1. While the area of the orifices 48, 49 does not vary directly with the armature displacement but rather `asthe cosine of the angle of displacement wlth a consequent decrease in percentage modulation as compared with the structure-of Fig. 1, this disadvantage may be more than compensated by the advantages of a straight path on the flow of the air through the orifices.

What is claimed is: y

ll. In an acoustic device, a conduit for a fluid stream, a valve disposed midway said conduit, said valve being mounted for rotation about its medial axis transversely of the conduit so that it is statically balanced in said conduit and electromagnetic means including-pole pieces within the conduit defining streamlined passages adjacent the valve for moving said valve in accordance with the sound to be reproduced.

2. In an acoustic device, the combination with a conduit for a fluid stream and a modulator pivoted on its medial axis mounted in the conduit with its axis disposed transversely of the conduit, of means for ariiusting the area of the uid path around the ends of the modulator, and means for vibrating the modulator in accordance with the sounds to be reproduced. Y 6

3. In an acoustic device, the combination with a conduit for a fluid stream, a pair o! furcated polepieces within the conduit and a pivoted modulating member disposed between the pole-pieces and extending toward opposite walls ot the conduit, of l0 means for vibrating the member between the polepieces in accordance with the sound to be reproduced, and means for independently adjusting the oriiices between the conduit walls and the modulating member. f,

4. In an acoustic device, the combination with a conduit for a fluid stream, a pair oi' furcated pole-pieces within the conduit and an armature pivoted on its medial axis in static balance between the pole-pieces and having end portions 2.0 v

forming 4I.equal oriflces adjacent the walls oi.' the conduit,of means for vibrating the armature in accordance with the sounds to be reproduced, and means for damping the armature vibrations. 5. In an acoustic device, the combination with a conduit for a uidstream, a pair o f furcated pole-pieces dividing the conduit into two passages adjacent the walls ot the conduit, an armature pivoted on its medial axis and extending into said 30 passages, means for resiliently holdingv the armature between the pole-pieces at an angle to the transverse axis of the conduit, and means for vibrating the amature in accordance with the sounds to be reproduced. 6. In an acoustic device, a conduit for a iuid stream, and an electromagnetic structure within the conduit comprising pole pieces dciiningl air gaps and dividing the conduit into two restricted passages, and a vibrating armature pivoted bef tween the pole pieces projecting through the gaps into the passages and varying the ilow oi' iiuid through the passages in accordance with its own vibrations.

RUDOLPH F. MALLINA. 45

Images