GB2133201A - Sound reproducing device - Google Patents

Abstract

A sound reproducing device has a speaker diaphragm 2 attached to the inner top face of a casing 1, an acoustic cylinder 3 attached to a central aperture in the diaphragm, into which a plunger- type vibration rod 4 is slidably mounted, a stylus-pressure coil spring 13 between the plunger-type vibration rod and the casing urging a sound transmitting member 5, and pick up 6, toward the face of a record disc 9, the sound transmitting member being coupled by the plunger-type vibration rod to the speaker diaphragm. Stylus pressure releasing means for returning pick up 6 to the start utilises cam (20) and return arm (18) (Fig. 2). Silicone grease (16) (Fig. 3) may be present within cylinder 3. Circuit operation is described. This device suppresses high frequency sounds, offensive to the human ear, thereby accomplishing satisfactory amplification of sounds, music or speech, over a wide but not excessive range. <IMAGE>

Description

SPECIFICATION Sound reproducing device This invention relates to sound reproducing devices of a simple, mechanical construction, comprising a speaker diaphragm fixed to the inside face of a casing, a stylus-pressure coil spring, a sound transmitting member urged toward a recording on one face of a record disc and connected to the speaker diaphragm, so that adequate stylus pressure can be imparted to a pickup.

Known sound reproducing devices of this simple type include the construction described in the United States Patent No. 3,467,393, in which a speaker diaphragm is formed as an integral part of a sound transmitting member, and this speaker diaphragm is urged by a stylus pressure spring toward the recorded face of the record disc to impart a stylus pressure to a pickup.

However, in this device, the combined weight of the unit consisting of the speaker diaphragm and the sound transmitting member is too heavy to permit a satisfactory performance when reproducing low frequency tones, and in addition, as the speaker unit is mounted in the casing in a swingable manner by only end end of the sound transmitting member, it is not able to withstand shock and is liable to allow the reproducing stylus to hop or jump out of the groove.

Another known construction is described in the United States Patent No. 4,004,815, which comprises a speaker diaphragm fixedly disposed inside the casing, on the top of which a sound transmitting member is fixed, a pickup being located so as to slidably contact the lower face of the sound transmitting member and a turn table supported by a centre pin being urged by a stylus pressure spring toward the pickup.

With this construction, since the speaker diaphragm is fixed to the casing, reproduction of low tones is improved to some extent by a socalled buffer effect. However, since the stylus pressure is derived via the turn table, the stylus spring cannot be sufficiently strengthened, due to the relationship required between the weight of the turn table and the stiffness of the stylus pressure spring. As a result, the sound reproduction stylus of the pickup cannot fully follow the recorded groove of the record disc, and the stylus is liable to jump or to hop to a different track, which damages the record face.

Other known devices, for example, the sound reproducing device described in the Japanese Patent Publication No. 23861/78 (corresponding to U.S.P. 3,992,016) comprise a casing containing a speaker diaphragm fixed thereto, an acoustic cylinder fixedly attached to the top of the speaker diaphragm, a vibration rod of much smaller diameter than the inside diameter of the acoustic cylinder received therein to project out and be carried by a sound transmitting member in such a manner that the sound transmitting member is urged diametrically toward the acoustic cylinder to forcibly urge the vibration rod against the inner face of the acoustic cylinder, and a pickup which is disposed below to slidably contact the lower face of the sound transmitting member, confronts the recorded face of the record disc so that the second reproducing stylus is urged by a stylus pressure spring to engage the recorded face.

This device has been found effective for suppressing high frequency tones but suffers the following drawbacks.

The casing of the device must contain, in its narrow space, both the stylus pressure spring and the spring for biasing the vibration rod toward the diametric direction of the acoustic cylinder, so the construction inevitably becomes complicated. In addition, even if the vibration rod is biased by the spring diametrically toward the acoustic cylinder, the forced contact of the vibration rod with the inner face of the acoustic cylinder becomes insufficient, due to the overall weight of the sound reproducing member and the friction between the mounting parts, and this results in erratic surges that degrade the tone quality.

The United States Patent Specification No.

3,682,484 describes yet another similar arrangement of the stylus pressure spring, and its associated components, but has many of the above-mentioned drawbacks, and the purpose and the technical concept of the arrangement is not the same as that of the present invention.

One object of the present invention is to provide a construction for a simple sound reproducing device that obviates the various drawbacks mentioned above, and suppresses amplification of high frequency sounds offensive to human ear but is suitable for reproduction of low frequency sounds, using a sound transmitting mechanism of simplified construction that is free from any tendency to jumping or track hopping of the reproducing stylus during use, and does not result in lowering of tone quality due to variations in playing speed.

In accordance with a preferred embodiment of the present invention there is provided a sound reproducing device comprising a casing, a speaker diaphragm fixed to an inner face of said casing, a hollow acoustic cylinder fixed to a central aperture in said speaker diaphragm to extend toward said inner face, a plunger type, hollow vibration rod fitted in said hollow acoustic cylinder to slide in the axial direction, a sound transmitting member coupled to said speaker diaphragm via said vibration rod, a pivotted tone arm having a pickup in sliding contact with said sound transmitting member, a turn table rotatably supported by a centre-pin and carrying a record disc having one or more recorded grooves into which a sound reproducing stylus of said pickup engages, a stylus-pressure coil spring imparting stylus pressure to said pickup through said sound transmitting member, a stylus pressure releasing means for returning said pickup to the starting point of sound reproduction after completion of a cycle of sound reproduction, and a motor for rotating said turn table, said stylus pressure spring being compressed between said plunger type vibration rod and said casing to urge said plunger type vibration rod toward said record disc, and said pickup having the necessary pressure imparted via said plunger type vibration rod and said sound transmitting member.

Since the speaker diaphragm is fixed to the inner face of the casing, amplification of shrill, keen sounds of high frequency can be suppressed to some extent. The acoustic cylinder fixed to the central aperture of the speaker diaphragm holds the plunger type vibration rod inserted therein so that it can only slide in an axial direction, and accordingly, sounds of high frequencies can be absorbed by the sliding surfaces, so that it is only sounds of low frequencies, which are nonoffensive, that can be amplified.

In addition, as the vibration rod is a sliding fit in the acoustic cylinder there can be substantially no side play of the vibration rod normal to the axis of the acoustic cylinder.

This helps to eliminate poor sound reproduction by eliminating frequency fluctuations.

Furthermore, slidable contact fitting of the vibration rod with the inner face of the acoustic cylinder eliminates the necessity of providing any spring to provide smooth, slidable contact. It is also to be noted that the stylus pressure spring is composed of a coil spring compressed between the plunger type vibration rod and the casing to urge the plunger type vibration rod toward the record face. In fact, this construction contributes to the simplification of the device, as a whole.

Filling of the gap between the acoustic cylinder and the plunger type vibration rod with a grease further improves the tone quality of the device, because the grease absorbs high frequency sounds.

The present invention can be applied to simplified sound reproducing devices of the type using an electric motor drive, and to pull string types using a constant-torque spring motor.

The invention will now be described with reference to the drawings, in which:~ Figure 1 is a cross-section of one exemplary embodiment construction in accordance with the present invention; Figure 2 is a schematic plan view of the embodiment shown in Figure 1 with its upper housing removed; and Figure 3 is an enlarged cross-section showing details of the acoustic cylinder and vibrating rod assembly.

The embodiment shown in the drawings is a motor driven sound reproducing device, wherein a casing 1 consists of a chassis 1 a and an upper housing 1 b fitted thereon. A speaker diaphragm 2 is fixed to the inner face of a speaker jacket 1 c formed on the housing 1 b. This speaker diaphragm 2 has a conical configuration with a central aperture downwardly disposed in the casing 1, in which aperture there is fixed an acoustic cylinder 3. Within the acoustic cylinder 3, a plunger-type, hollow vibration rod 4 is inserted as a sliding fit to be freely movable in the axial direction. This plunger-type vibration rod 4 is cylindrical in shape and has a bottom plate of enlarged diameter to form a flange. The open upper end of the hollow rod 4 faces the speaker jacket 1 c and the hollow rod 4 houses a styluspressure coil spring 13 which bears upon the bottom plate.The upper end of the stylus-pressure coil spring 1 3 resiliently contacts the inner face of the speaker jacket 1 c, being compressed between the plunger-type vibration rod 4 and the casing 1.

Consequently, the bottom plate of the plungertype vibration rod 4 is urged downward, away from the lower end of the acoustic cylinder 3.

The peripheral inner surface of the acoustic cylinder 3, and the outer surface of the plungertype vibration rod form a sliding fit, but some clearance may be left therebetween, which may be filled with grease 16, as shown in Figure 3.

Silicone grease is preferred, and the available space is filled so as to lubricate the gap between the acoustic cylinder 3 and the plunger type vibration rod 4, and to transmit vibrations therebetween.

The bottom plate of the plunger-type vibration rod 4 engages a sound transmitting member 5, having one bifurcated end, (Fig. 2).

This sound transmitting member 5 is supported at the ends of the bifurcated portions, on a pair of supporting posts 17 and the opposite end is swingable downwardly toward the chassis 1 a and upwardly towards the upper housing 1 b.

There are also pivotally mounted on the chassis 1 a a tone arm 7 having a pickup 6 at its forward end, and a return arm 18.

Both the pickup 6 and the free end of the return arm 1 8 are mounted to permit movement to or from the face of the chassis 1 a, and transverse movement across the chassis face.

The tips of both the pickup 6 and the return arm 1 8 are positioned to contact the lower face of the sound transmitting member 5 and slide thereon.

As can be seen in Fig. 1, a centre pin 11 is disposed upright on the bottom plate of the chassis 1 a, and a turn table 12 is rotatably received thereon. A record disc 9 is fixed on the turn table 12. Accordingly, the pickup 6 and the tip of the return arm 18 are positioned between the sound transmitting member 5 and the record disc 9.

The tone arm 7 and the return arm 18 are biased by respective return springs, 21 and 22, to move them away from the central part of the turn table 12 and from the recorded face of the record disc laid thereon, respectively. On the lower tip end of the pickup 6, a sound reproducing stylus 8 is disposed to protrude toward the record disc.

By virtue of the construction mentioned above, the necessary stylus pressure is given by the stylus pressure-spring 13, imparted to the sound reproducing stylus 8 of the pickup 6 via the plunger-type vibration rod 4 and the sound transmitting member 5.

The turn table 12 has a pulley groove formed around its sidewall, around which a driving belt 19 is extended to embrace the turn table 12 and the output shaft of a motor 15 fixedly disposed on the chassis 1 a.

An upstanding return-cam 20 is disposed at the centre of the turn table 1 2. As can be clearly seen in Figure 2, the free end of the return arm 18 is positioned adjacent to the return-cam 20 so that these two members can constitute a means for releasing stylus pressure. That is to say, due to the rotation of the turn table 12 together with the record disc 9, the pickup 6 engaged in a groove on the face of the record disc 9 by its sound reproducing stylus 8, will arrive at the end point of sound reproduction, when the pickup 6 runs against the end of the return arm 1 8 and urges it to ride on the return-cam 20.

Since the return-cam 20 rotates together with the turn table 12, it raises the return arm 18, lifting up the sound transmitting member 5 against the resilient force of the stylus-pressure spring 13.

In this manner, the pickup 6 is released from engagement with the sound transmitting member 5, and thus the stylus-pressure force is released, so that the pickup is free to move back toward the starting point of sound reproduction, aided by the return spring 21.

At the same time, due to the removal of the pickup 6, the return arm 18 is free to leave the cam face 20 and return to its rest position under the influence of the return spring 22.

A battery 23 (Figure 1) serves as a power source to supply electric current to the motor 15 via an electric circuit whose operation will now be described with reference to Figure 2.

A connection path between the battery and the motor 15 contains the series combination of a first switch 24 and a second switch 25.

The first switch 24 is held OFF by the pickup 6 when the pickup is resting at the starting point of sound reproduction, while said second switch 25 is held ON until the pickup reaches the end point of sound reproduction and urges the return arm 18 to move, when the second switch 25 is turned to its OFF position.

The electric circuit also comprises a main switch 26, which is connected in parallel with respect to the connection path containing the switch 24 and switch 25.

Due to this electrical connection, when the main switch 26 is turned to ON, the motor 15 starts rotation, to rotate both the turn table 12 and the record disc 9, causing travel of the pickup 6 toward the end point of sound reproduction, and releasing the switch 24, which moves to the ON position. As a consequence, even if the switch 26 is set to OFF by the operator taking his hand from the main switch 26 prematurely, the electric circuit through the first switch 24 and the second switch 25 is conductive and maintains rotation of the motor 1 5. Upon arrival of the pickup 6 at the end point of sound reproduction, the pickup 6 will move the end of the return arm 1 8, and this will set the second switch 25 to OFF, thus making the circuit non-conductive and stopping the motor 15, the turn table 12 and the record disc 9.

In this manner, one cycle of sound reproduction is completed.

A further play-back can be started by setting the main switch 26 to ON, when the pickup 6 proceeds on beyond the end point of sound reproduction, and urges the return arm 18 to be engaged and ride up on the return-cam 20, when the pickup 6 itself can return to the starting point of sound reproduction and move the start switch 24 to set it to the OFF position. If it is required to repeat the play back, continued holding of the main switch 26 to ON for a short period of time allows the pickup 6 to start its travel toward the end point of sound reproduction, and sets the first switch 24 to ON, and thus the sound reproduction can be repeated.

The simplified embodiment of the sound reproducing device can be operated as mentioned above, vibrations of the recorded sounds traced by the pickup 6 being transmitted to the plungertype, hollow vibration rod 4 via the sound transmitting member 5.

The reproduced vibrations of the plunger-type vibration rod 4 is further transmitted, through grease 16 to the acoustic cylinder 3. Since the plunger-type vibration rod 4 is held to directly and resiliently engages the sound transmitting member 5 by the stylus-pressure spring 13, the vibrations can be picked up exactly. In addition, since the plunger-type vibration rod 4 is inserted in the acoustic cylinder 3 and is only capable of being moved in the axial direction, to allow mechanical connection, but no harmful side play, the onward transmission of any unwanted noise, such as frequency variations or vibrations of high frequency sounds to the speaker diaphragm 2 is suppressed. Particularly when silicone grease is filled between the mating surfaces of the acoustic cylinder 3 and the plunger-type vibrating rod 4, it interrupts the transmission of high-frequency sounds in an effective manner, so the reproduced, amplified sound becomes very comfortable to listen to.

Claims (5)

1. A sound reproducing device comprising a casing, a speaker diaphragm fixed to an inner face of said casing, a hollow acoustic cylinder fixed to a central aperture in said speaker diaphragm to extend toward said inner face, a plunger type, hollow vibration rod fitted in said hollow acoustic cylinder to slide in the axial direction, a sound transmitting member coupled to said speaker diaphragm via said vibration rod, a pivotted tone arm having a pickup in sliding contact with said sound transmitting member, a turn table rotatably supported by a centre-pin and carrying a record disc having one or more recorded grooves into which a sound reproducing stylus of said pickup engages, a stylus-pressure coil spring imparting stylus pressure to said pickup through said sound transmitting member, a stylus pressure releasing means for returning said pickup to the starting point of sound reproduction after completion of a cycle of a sound reproduction, and a motor for rotating said turn table, said stylus pressure spring being compressed between said plunger type vibration rod and said casing to urge said plunger type vibration rod toward said record disc, and said pickup having the necessary pressure imparted via said plunger type vibration rod and said sound transmitting member.

2. A sound reproducing device as claimed in Claim 1, wherein said plunger type vibration rod is formed as a cylinder with a bottom plate, and into which said coil spring being inserted into said cylinder to urge said plunger type vibration rod by the force acting upon said bottom plate.

3. A sound reproducing device as claimed in Claim 1, wherein a grease filling is provided between the mating sliding faces of said acoustic cylinder and said plunger type vibration rod.

4. A sound reproducing device as claimed in Claim 3, where said grease is silicone grease.

5. A sound reproducing device substantially as described with reference to Figures 1 to 3.