Universal pulsato unit
FIELD OF INVENTION 
     This invention relates to musical instruments, and more particularly to pulsato rotors of the type shown and described in U.S. Pat. No. 3,315,760 to Jacob M. Schwendener issued Apr. 25, 1967 and entitled ACOUSTIC DAMPING DRIVE FOR PULSATO ROTOR. Such pulsato rotors form an acoustic link between the speaker output of an electrical musical instrument and the room or space in which the sounds are perceived by the listeners. The operative element of the pulsato rotor is a rotary sound channel whereby the sound radiation pattern is rotated to impart the desired pulsato or phase shift effects. 
     BACKGROUND OF THE INVENTION 
     Pulsato rotors of the general type shown in Schwendener&#39;s patent have been used extensively. There are two basic modes of use. In the so-called free standing organization illustrated in the Schwendener patent, the pulsato rotor is mounted between spaced panels or partitions in a speaker cabinet. A speaker is mounted on one panel in line with the rotor axis but on the opposite panel side. The speaker registers via a large opening with the throat of the sound channel. In the so-called built-in organization illustrated in U.S. Pat. No. 3,245,284 to Donald J. Leslie issued Apr. 12, 1966 and entitled ROTOR DRIVE FOR PULSATO APPARATUS, the pulsator rotor is mounted on one side of a single panel or board while the speaker is mounted on the other side. In order to provide outboard support for the pulsato rotor, a generally U-shaped yoke or bracket is mounted on the panel. The panel together with the pulsato rotor and speaker is typically then mounted by an organ manufacturer in the console. The organ manufacturer is ordinarily responsible for back enclosure of the speaker so that the pulsato effects are not diluted by back radiation. 
     In addition to the problem of proper back enclosure of the speaker for full strength production of pulso, there have been certain noise problems in the pulsato unit of this general type. One noise is a flutter effect due to the rather substantial width of the yoke or bracket. Thus the yoke or bracket serves as a baffle or reflector that imposes a certain acoustic impedance that recurs twice every revolution. A slight, but objectionable flutter or buffeting takes place. 
     Another problem is the propogation and mechanical amplification of shaft and bearing noises that are most noticeable at low speeds and during speed changes of the rotor. Noises due to belt slippage and lateral movement are controlled by adjustment of the motor bracket and possible replacement of the pulley belt. In the past, a complex noise isolation pivoted motor bracket arrangement was provided that was not always stable in certain panel orientations. 
     The primary object of the present invention is to provide a simplified pulsato rotor that not only has improved musical characteristics in terms of noise reduction, flutter elimination and back speaker radiation, but which also has improved mechanical characteristics in terms of low weight, ease of assembly, standardization of parts, reduction in number of parts, and ease of pulley adjustment. 
     SUMMARY OF INVENTION 
     In order to accomplish the foregoing object, we provide a new shaft and bearing assembly in which the shaft ends are, with a positive bias, caused to engage the thrust bearing surfaces of the bearings. Rattling and squeaking is largely eliminated. In the built-in organization, three identical angled rods quick fitted to an outboard hub serve to support a cup like shaft bearing through the intermediary of a noise reduction neoprene grommet. An identical bearing and grommet arrangement is provided at the inboard end which is supported by a simple strap that spans the port between the speaker and rotor throat. By utilizing the spring characteristics of the angled rods, a controlled end thrust is imposed upon the shaft. In the free standing organization, the identical bearing and grommet assembly is used at both panels or partitions, but since the panels themselves are in fixed spaced relationship, the shaft itself is multipart with an internal spring that serves not only to allow for variations in the spacing of the panels, but also provide the necesary positive bias to ensure a positive contact between the shaft ends and the thrust bearing surfaces. 
     The outboard hub supporting rods are quite narrow and hence impose very minimal acoustic impedance whereby the flutter or buffeting effect is minimized. 
     In order to minimize transmission of pulley belt noises, a simplified motor mounting bracket is provided in which biconical acoustic damping pads mount the motor on a rectilinearly movable adjustment bracket. During normal operation, the motor weight is supported with very minimum contact at the apices of the biconical pads in order to minimize noise transmission to the panel. The conical configuration provides a spring constant that increases as a function of displacement whereby adequate shock support is provided notwithstanding the minimal contact during normal operation. The pads are interposed between an adjustment bracket and the motor rather than between the adjustment bracket and the panel. Parallel slots in the adjustment bracket make possible simple belt tension adjustment that is stable in all orientations of the panel. 
     In order to provide an efficient back enclosure for the speaker, we provide a molded expanded polystyrene cap that adds very little weight. The lightweight and flexible characteristics of the polystyrene would ordinarily be expected to result in buzzes and rattles as well as reradiation of sound. However, by imposing a compressive load upon the cap, the cap acts as a massive and rigid body quite equivalent to a heavy enclosure. The compressive load is readily imposed by a plate attached to the rear of the speaker magnet. 
    
    
     BRIEF DESCRIPTION OF DRAWINGS 
     A detailed description of the invention will be made with reference to the accompanying drawings wherein like numerals designate corresponding parts in the several figures. These drawings, unless described as diagrammatic or unless otherwise indicated, are to scale. 
     FIG. 1 is a pictorial view of a pulsato unit incorporating the present invention. 
     FIG. 2 is a plan view thereof from the rotor side of the mounting panel. 
     FIG. 3 is a plan view from the speaker side, a portion of the enclosure cap being broken away. 
     FIG. 4 is a diagrammatic view showing the axial assembly of the shaft, rotor and speaker cap. 
     FIG. 5 is a diagrammatic view illustrating the assembly of one of the supporting spider legs with the hub plate. 
     FIG. 6 is an enlarged pictorial view of the motor and mounting bracket. 
     FIG. 7 is a sectional view taken along a plane corresponding to line 7--7 of FIG. 6. 
     FIG. 8 is a fragmented axial sectional view of a modified shaft assembly for use in mounting a pulsato rotor between two fixed panels. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENT 
     The following detailed description is of the best presently contemplated modes of carrying out the invention. This description is not to be taken in a limiting sense, but is made merely for purposes of illustrating the general principles of the invention since the scope of the invention is best defined by the appended claims. 
     Structural and operational characteristics attributed to forms of the invention first described shall also be attributed to forms later described, unless such characteristics are obviously inapplicable or unless specific exception is made. 
     In FIG. 1 there is illustrated a pulsato rotor 10 mounted on one side of a panel or board 12 for rotation about an axis x perpendicular to the panel 12. A speaker (FIG. 3) is coaxially mounted on the other side of the panel. The rotor 10 has an angled sound channel 14 having a throat end registering via a panel opening 16 with the speaker and a laterally opening mouth to provide a rotating sound radiation all in a well understood manner. 
     The rotor 10 is made of light weight molded expanded polystyrene dynamically balanced to provide stable rotating characteristics. The light weight construction minimizes inertia for rapid speed changes as required by the musician. 
     The rotor is supported for rotation upon a one piece shaft 18 by the aid of a pair of apertured neoprene grommets 20. The grommets are attached at opposite ends of the central hub 22 of the rotor. These grommets are tapered or frusto-conical at the inner ends to fit correspondingly tapered recesses 24 in the rotor hub. 
     The grommets 20 are preferably cemented in place all in the absence of any compressive load upon the grommets. The grommets provide high acoustic impedance to limit transmission of noises to the rotor and at the same time provide suitable shock mounting for the rotor. Washers 26 locate the rotor on the shaft. 
     The shaft ends project beyond the rotor and are received in low friction plastic bearing cups 28 which have tapered seats for the rounded ends of the shafts. The bearing cups 28 in turn are mounted in neoprene supporting grommets 30. The rotor is supported simply by providing mounting holes in supporting brackets for the bearing grommets 30. One hole 32 is provided in a strap or plate 34 that extends diagonally across the panel opening 16. Another hole 36 is provided in a hub plate 38 at the outboard end of the shaft. 
     The hub plate is supported by the aid of three spider legs 40 that form a cage about the rotor. Each of the spider legs comprises a light rod bent at its center to provide an angularity of slightly less than 90°. Each spider leg is stamped near both ends to provide a lug 42 located in the plane determined by the rod bend. The lug 42 at one end serves to attach the spider leg to the panel 12 while the lug 42 at the other serves to attach the spider leg to the hub plate. The spider legs are symmetrical for simplification of assembly. 
     Each spider leg is attached to the panel 12 by the aid of a stop washer 44 and a speed nut 46. A recessed attachment pad 48 (FIG. 3) of a speaker cover 50 as well as a soft paper gasket 52 are interposed between the panel and the speed nut whereby the cover 50 is mounted. The cover 50 will be described more fully hereinafter. 
     The outboard end of each of the spider leg extends skew to the rotor axis x (FIG. 2) to form with the companion spider legs a generally triangular array about the mounting hole 36. The hub plate is lanced and stamped (FIG. 5) to provide three knuckle strap attachments for the three spider legs. The three attachments are identically formed but located in angularly spaced array. One of the attachments, for example, is formed in part by two spaced parallel cuts 54 and 56 defining therebetween a strap 58 that is bowed laterally of the hub plate in one direction. Another part is formed by stamping the hub plate between the outer cut 54 and the edge of the plate to form a lateral arcuate depression 60 in the opposite direction. The third part of the knuckle strap attachment is formed by stamping between the inner cut 56 and a hole 62 to form an arcuate depression 64 extending in the same direction as the outer depression 60. The spider leg is inserted into the attachment from the outer edge, passing under the strap 58 and across the hole 62 until it abuts the edge of the hole. By turning the spider leg, its lug 42 wedges against the strap 58 until the leg is slightly bowed by the interaction. An exceedingly tight, rattle free joint is achieved notwithstanding the simple quick fit connection. The preassembled three spider legs and the hub plate 38 are readily attached to the mounting board over the preassembled rotor, bearings 28 and grommets 30. The bearing grommets 30, in combination with the rotor grommets provide noise isolation as well as shock protection. 
     The length of the rotor shaft is so designed that, in the assembled position, the hub plate flexes the spider legs outwardly. A positive spring interaction is thereby generated to impose a controlled end thrust upon the shaft bearings. Squeaks, rattles and resonant buzzes are thus prevented, particularly when the speaker is not rotated. 
     The small thickness of the rods makes them acoustically transparent whereby buffeting sounds are eliminated. 
     In order to rotate the rotor, a pulley 70 is provided (FIG. 4) that is mounted on the shaft between the rotor 10 and the panel 12. The pulley is apertured in order to make it as acoustically transparent as possible. It is coupled to the rotor by the aid of a resilient strap (not shown) of the type shown and described in the Schwendener patent identified above. The rotor pulley 70 is coupled to a drive pulley of a motor 72 (FIGS. 2 and 6) by the aid of a pulley belt 74. The motor 72 is mounted on the panel 12 alongside the rotor 10 by the aid of a two part bracket 76. 
     The two parts of the bracket are acoutically isolated, one of the parts mounting the motor and the other of the parts being adjustably mounted on the panel independently of the acoustic isolation means. One of the bracket parts 78 comprises a pair of parallel channels 80 and 82 extending generally radially of the rotor axis for movement inwardly and outwardly thereof for adjustment of pulley tension. For this purpose, the channel sides in engagement with the panel 12 have slots 84 and 86 for cooperation with clamping screws 88. The second bracket part is a plate 90 that bridges the tops of the channels 80 and 82. As shown in FIG. 7, the plate 90 has four holes arrayed as a square in which biconical grommets 92 are captured. For this purpose, each grommet has a peripheral mounting groove 94. The bottom tips of the grommets rest upon the top flanges of the channels 80 and 82 and are held in that position by the aid of washers 96 that rest on the upper tips of the grommets and by the aid of screw fasteners 98. The screw fasteners include screws threaded through the washers 96, grommet 92 and top flanges of the channels 80 and 82. The motor 72 is directly mounted on the plate 90 so that the driving pulley is suitably accessible. 
     By virtue of the two part bracket, acoustic isolation is provided between the motor and the panel while a simple belt tension adjustment means is provided. In normal operation, the noise circuit between the motor and the panel 12 includes only very small areas at the soft upper tips of the biconical washers. The acoustic impedence is large. Nevertheless the biconical washers provide effective shock mounting. Thus as the grommets flatten under shock load, the compressive force increases approximately as the square of displacement rather than merely linearly. This occurs due to the conical configuration of the grommets. The grommets are effective for both noise isolation as well as for extreme shock loads. 
     As shown in FIGS. 3 and 4, the speaker is enclosed by a molded expanded polystyrene cover 50. The cover, although extremely light weight, is inhibited from vibrating and from reradiating sound by virtue of its being stressed. This is achieved by a stress plate 100 that overlies a substantial area of the cover behind the speaker magnet. A draw screw 102 that attaches to a screw hole in the rear of the speaker magnet imposes a compressive force on the cover so that it acts as a substantially solid, massive body that absorbs back radiations. Dilution of the tremolo effect by back radiation is avoided by means normally considered unsuitable for the purpose. The soft fibrous or paper like gasket 52 not only provides a seal, but also prevents vibrations between imperfectly fitting parts. 
     In an organization where an effective back enclosure is provided by the particular console structure, the back cover may be deleted. In that case, a soft multilayer paper insulation can be stapled over the speaker for optimum results. 
     DESCRIPTION OF ALTERNATE EMBODIMENT 
     In the form of the invention illustrated in FIG. 8, the pulsato rotor is installed between fixed panels 110 and 112 of a free standing speaker enclosure. One of the panels 110 mounts a speaker 114 about an opening 116. A bracket 118 like the bracket 34 is mounted across the opening. The opposite panel 112 simply has a hole 120 for insertion of a bearing grommet 122. 
     In order to generate end thrust on the bearings 124 and 126, the shaft 128 includes two hollow telescoping parts with a coil spring interposed therebetween. The requisite end thrust is thereby provided in a manner equivalent to that provided by the spring action of the spider legs of the previous form. Additionally, the spring serves to compensate for slight deviations in the spacing between the panels.