US3286204A - Reverberation unit having vibration-isolating suspension - Google Patents

Description

3 Sheets-Sheet l I N VENTORI dlllz w mm Cofa%e,% L

BY 71/ M Na HMM mm SW i WNW w Nov. 15, 1966 w. c. LAUBE, JR

REVERBERATION UNIT HAVING VIBRATION-ISOLATING SUSPENSION Filed April 26, 1962 NOV. 15, 1966 w, c, LAUBE, JR 3,286,204

REVERBERATION UNIT HAVING VIBRATION-ISOLATING SUSPENSION Filed April 26, 1962 5 Sheets-Sheet 2 INV NTOR:

Nov. 15, 1966 w. c. LAUBE, JR

REVERBERATION UNIT HAVING VIBRATIONISOLATING SUSPENSION 5 Sheets-Sheet 5 Filed April 26, 1962 IN VEN TOR: Mm 0 XM,%/@

United States Patent O 7 Delaware Filed Apr. 26, 1962, Ser. No. 190,444 4 Claims. (Cl. 333-30) This invention relates in general to reverberation units for use with musical instruments, such as electrical organs, radios or phonograph-s, and more particularly relates to an improved andmore economical transmission spring and suspension system for a reverberation unit assembly.

Reverberation units generallyv comprise several coil springs which serve as transmission lines to convey signals in different time intervals to an output circuit for the. purpose of simulating the acoustical effect of an auditorium. In such a unit there must be provided a signal generating assembly'or driver comprising an input coil, at one end of the spring. The input coil responds to an input electrical signal for controlling a tiny magnet attached to the adjacent end of the respective transmission lines. This introduces a corresponding mechanical wave into the transmission line which is sensed byv a signal receiving assembly or pickup atthe other end of. the line. The pickup assembly comprises another magnet and coil which respond to the transmitted mechanical wave by providing an. output electrical signal having a delayed interval dependent on thelengthiofthe spring and the rateof wave transmission. This output signal is then applied through suitable amplifying devices to an output transducer, such as a loud speaker, for the purpose of simulating the effect described above.

The usual reverberation unit incorporates springs of considerable length in. order to secure delay intervals of appreciable magnitude, and in order to provide different time delay periods, the springs in the respective transmission lines are of differing unstretched length, Since one of the lines incorporates a long spring in order to provide long delay intervals, it governs the overall dimension of the unit and therefore all springs may be stretched to the same length but differ in the number of turns and helix angle. In addition, the springs are extremely sensitive to external sources of vibration.

The latter problem while not too acute in certain circumstances becomes of extreme importance if the reverberation unit is mounted in a movable assembly such as an automobile or adjacent the bass speakers of an audio system. The problems then are to reduce the overall longitudinal dimension of the reverberation unit while also isolating, the reverberation unit springs from sources of external vibration.

To reduce the length of the springs, and therefore the reverberation unit, of course, resultsin shorter delay periods. In order to overcome this problem it would ordinarily be necessary to provide the springs with a larger helix diameter, but this in turn militates against the vassage of the higher frequencies through the spring. Here it was realized that while at least two transmission lines are necessary to provide adequate reverberation, at the higher frequencies only one transmission line is necessary since such frequencies are largely lost in an auditorium in any event and therefore would not be detected by the ear. This is also true in a reverberation unit if the difference in cut-off frequency between the two transmission lines is not too great. In addition, since the signal velocity and therefore the delay is dependent on the helix angle of the springs, the overall length of the springs may be reduced by providing a minimum stretch in the springs 3,286,204 Patented Nov. 15, 1966 just sufficient to enable the adjacent turns to clear each other.

In view of this the present invention utilizes two springs of differing helix diameter for the purpose of introducing different time delay periods with the smaller helix diameter spring operating into the higher frequency range. All springs are wound to the same length and number; of turns, with their turns in compression. In mounting the springs in the reverberation unit, they are stretched by the-smallest increment necessary to insure that the adjacent turns clear, so that the helix angle is heldsmall while the number of turns that may be provided is quite large. The signal velocity is therefore reduced sufficiently to enable a delay of a character similar to that achieved by springs of twice the length in theprevious units, while at the same time sufficient high frequency signals are passed by the smaller diameter spring to simulate theeffect of an auditorium.

The isolation of the springs from external vibration presents several problems in that the most necessary isolation should occur in the. range ofbetween. and

4000 cycles through which the unit is intended to function most effectively and the cutoff frequency-of-the iso-' to findlothe'r means for reducing thetransmitted external lower frequency vibrations. The unit can of course be shock mounted on springs,- which is a common expedient; however, this may be self defeating and expensive since the mounting springs also have optimum frequencies which they will pass and since the unit must be capable of being held in any of several positions. As the system is orthogonal, a unilaterally-compliant spring would normallybe-requiredfor each direction from which vibrations may betransmitted.

In such a spring supported arrangement the static sag of the unit corresponds to a resonant frequency at which harmfulvibrations are passed most effectively. Below this resonant frequency the stiffness of the spring system is to great to provide isolation while above this 'fre-' quency the mass of the unit controls. It is therefore necessary to provide a mounting inwhich the static sag' The, light springs may be self resonant at-a high frequency but this frequency is one at which the mass of the unit controls.

The compliant springsare generally incapable'of any stable stress except under tension, but stable equilibrium will occur at the juncture between a plurality of compliant helical springs provided the springs are mounted along non-parallel axes so that they have lateral as well as axial compliance. Such a mounting system can easily be provided by considering the reverberation unit as being at the juncture of the springs and suspending the unit from the mounting by means of coiled springs which each have an axis normal to a respective plane of a tetrahedron.

It is therefore an object of the present invention to provide an improved reverberation unit.

It is another object of the present invention to provide an improved arrangement of the transmission l nes of a reverberation unit to, permit shortening the lines.

It is still another object of the present invention to provide an improved compliant supporting arrangement for a reverberation unit for the purpose of isolating the unit from external vibrations.

Other objects together with the features of the present invention will become apparent on examination of the following specification, claims and drawings, wherein:

FIG. 1 is an elevational view of the reverberation unit assembly;

FIG. '11: is an end view of the assembly shown in l with certain details omitted;

FIG. 2 is a' sectional view taken along the line 22 in FIG. 1;

FIG. 3 is asectional view taken along the line 33 in FIG. 2;

FIG. 4 is a sectional view taken along the line 44 in FIG. 3;'

FIG. 5 is a sectional view taken along the line 55 in 20. The channel member 12' comprises opposite longitudinal side walls'22 and a back'wall 23 therebetween.

Each wall is provided with apertures adjacent the pickup and driver assemblies for receiving respective coiled springs 24'24c. The springs 24-24c' serve to suspend the reverberation unit from a suitable, mounting channel 25 for isolating the unit10 from extraneous vibrations.

The springs 24-24c are all wound so that they. are in. compression, and when assembled between channel meme ber 12' and the mounting channel 25 they are stretched so that their turns are spaced apart for preventingthe transmission of high frequencies and for permitting axial compliance in both directions. It will be noted from FIG. la that the springs are all stretched due to the spacing between the connections at channel 12 and the connections at the mounting channel 25, while the stretch of springs 24a and 24b is also dependent on the mass.

of the unit 10. The mass of the unit 10 therefore results in a so-called sag which is dependent on the spring constants and the mass of theiunit. The greater the sag, the lower the resonant frequency which will be transmitted. The springs 24-240 are therefore light so that the sag is of such nature that the resonant frequency will be below 30 cycles, for example. It 'will also be noted that the unit 10 will be supported in the same manner regardless of whether the mounting channel 25 is upright, as shown, or inverted, and that the. sag will be nearly the same.

The springs being light will of course resonate at a high frequency and self resonance could be induced therein. The mass of the unit 10, however, is such that it will not respond to such high frequencies.

In addition, the arrangement of the four springs 24- 240 provides isolation for vibrations originating in substantially all directions since the unit is in effect mounted at a juncture of the springs which do not have parallel axes and are laterally as well as axially compliant. Thus reference to FIGS. 1, 1a and 2 shows the relative disposition ofthe spring axes between the channel 12 and the mounting channel 25 is each normal to a different plane paralleling a tetrahedron so that any'force transmitted by one spring to the channel will interact at a transverse angle to the axis of each of the other springs and thereby damp the force out. The unit 10 at the juncture of the springs'therefo re remains in a condition of substantial equilibrium.

The driver and pickup units 18 and 20 are substantial- 1y identically constructed and dimensioned. Each in cludes an integrally formed case 26 having a pair of spaced apart depending L-shaped lugs 27 that extend through the back wall 23 as best seen in FIGS. 4 and 5 and project towards each other. A shoulder 28 on each lug limits the downward movement of the case. A leaf spring 30 is inserted between the respective lugs 27 along the lower side of wall 23 to seat the respective cases 26 in position. An angle stop 32 on the leaf spring engages the edge of wall 23 as best seen in FIGS. 2 and 3, while a detent '33 engages an aperture in wall 23 to control the position of spring 30 and prevents its shifting. In addition, a ground strip 36 is inserted between the shoulders 28 and the top of wall 23 and is held firmly engaged against the wall 23 when clip 30 is inserted.

Each case 26 comprises a generally rectangular main body 3 8 having side faces 40, a front face 42, a back face 44, a top face 46, and a bottom face 48 from which the lugs 27 depend.' A groove 50 in both the top and bottom faces extends back from the front face 42 towards the rear of the body 38 and a sloping stop element 52 having .a vertical rear wall 53 is located in each groove as best seen in FIGS. 4 and 5.

The .body 38 is provided with a deep substantially rec-tan gularly shaped recess 54 in its front face 42. The recess 54 has side walls 55 intersected by vertical stop walls 56. In the posterior portion of the recess 54, as seen in FIGS. 3 and 5, the vertical walls converge and .a narrow aperture 58 connects the recess 54 to the back [face 44 of the body. The aperture 58 is adapted to receive a connector strip 60 which extends through the recess. 54 for the purpose of enabling electrical connections to be extended to a coil 62. The coil 62 comprises part of a coil and pole piece assembly 64 adapted to be received in the recess 54 and in a pair of horizontal slots 66.

A horizontal slot 66 connects each side of the recess 54 withthe side faces 40 of the body 38 for a predetermined distance from the front face 42. Each slot 66 is'define-d by flat upper and lower wall portions 68 from the front face 42 to a position intermediate the slot ends and then by arcuate top and bottom wall portions 70 which terminate at a stop wall 72 as best seen in ,FIG. 6. A narrow horizontal passageway 74 connects each slot 66 through the wall 72 to the back face 44 where the respective passageways terminate in a circular' opening recess 76. Narrow recesses 77 aligned crosswise to the passageways 74 extend inwardly from the opening 76.

The' coil and pole piece assemblies 64, as best seen in FIGS. 7 and 8, each comprise a bobbin 78 on which the coil 62 is wound in a conventional manner. The

bobbin 78 has a rectangular passageway 80 therein and generally rectangular spool heads 82. A pair of pole pieces 84 are each adapted to be engaged on a respective spool head 82 and each has a core portion 86 for engagement in the passageway 80.

The pole pieces .84 each comprise an elongate web 88 of magnetic material and the respective core portions 86 depend therefrom adjacent the transverse axisof the web and to one side thereof. An L-shaped flange- 90 is provided at opposite ends of each pole piece and each flange has an arm 92 extending in opposing direc-' tions. The core portions 86 are inserted through spool heads 82 into opposite ends of passageway 80 and in abutting relationship. The webs 88 are thus supported so that the arms 92 on one pole piece .are in a more closely spaced relationship to an .arm on the other pole piece than the pole piece webs. This reduces the area of flux leakage to that of arms 92 since only these areas are in close proximity to each other.

The spacing between respective arms 92 defines the gaps 93 of identical magnetic circuits and a tiny cylindrical magnet 94 at the end of each transmission line is 10- cated in each of the gaps. The magnets 94 each have an axial dimension substantially the same as the transverse dimension of the associated arms 92. It will be noted that the magnets 94 intersect the confined main flux path in the limited area traversed by arms 92 so that maximum signal efiiciency is achieved. In addition the construction enables the gaps for the magnets at each end of both transmission lines to be effectively defined by a single pair of pole pieces and these are all interchangeable.

It will be noted that each of the spool heads 82 is provided with a boss 98 along one end and that a recess 100 is provided in one end of each boss. Each recess 100 is adapted to receive respective arms 102 of the connector stnip 60. The connector strip 60 is a flat elongate insulating plate 103 upon which is afiixed a pair of thin conductive layers 104 to which respective ieads 106 of the coil are extended at 'lugs 107. The strip 60 has top and bottom stop portions i108 which abut the back of recess 54 when the coil and pole .piece assembly 64 is inserted in recess 54. A tab portion 110 onconnector strip 60 extends through aperture 58 for the purpose of extending external electrical leads 11-2 to the coil. The leads 112 are positioned by a tab 114 that is staked onto wall 23.

The magents 94 each have a central aperture in which a stepped tube 116 is inserted and cemented thereto. The stepped tube 1.16 has a portion which is cemented to and crimped about a respective straight end 118 of a coil spring 120 or 122. The springs 120 and 122 each form a part of a respective transmission iline 14 or 16. Each transmission line comprises two sp nings 120 or 122 -respectively joined in the center of the line' by an eyelet, for example, and connected at opposite ends to the magnets 94. The springs 120 or 122 are joined so that their windings are of opposite direction for the purpose of suppressing undesired vibrational modes.

It will be noted that although the springs of each transmission line are of identical length that the springs 122 of the transmission line 16 have a helix diameter of, for example, .198" and the springs 120 of line 14 have a smaller helix diameter of .178", for example. Thus the springs of each line are wound to the same length of approximately 1.8" with each having approximately 139 turns, these being in compressive relationship so that adjacent turns are normally touching. When assembled to the driver and pickup assemblies, the springs are stretched to just separate the turns and the smaller diameter line 14 will of course transmit higher frequencies than the larger diameter line 16 with their cutoff frequency differing by a value depending on their helix diameter difference. A stretch of only 1.5" per transmission line so that the total length approaches only 8" with a separation of between .003" and .007" between adjacent turns has been found quite feasible. In the range where the frequency transmitted by line 16 begins to fall off substantially, little acoustical effect is lost since in that range the single line 14 contributes suflicient reverberation effect. Since the helix angle is held small, a delay of appreciable magnitude is also secured within the short total length.

Due to the step in the tube 116, a shoulder is formed which serves as a stop for a flattened end of a support wire 124 inserted partially therethrough as best seen in FIG. 6. The support wire 124 is extended through a rubber damping disc 126 and its end is fastened along one diameter of an anchor disc 128 which serves as a bayonet connection as will be explained. Thus each transmission line 14 and 16 is a self contained subassembly comprising a pair of coiled springs 120 or 122 joined in the center of the line and having at each end a magnet 94, support wire 124, damping disc 126 and anchor disc 128.

To assemble the reverberation unit, a coil and pole piece assembly 64 is inserted in recess 54 in each case 26 with the tab 110 projecting from the rear of the case. The ground strip 36 which has an elongate leg 132 extends towards the front face 42 and this is bent over and inserted 6. between the lower pole piece and associated spool head before the assembly 64 is inserted in recess 54. Each case 26 is mounted on the channel 12 and-held thereto by the leaf springs 30 either before or after the assembly 64 is inserted in recess 54, but in either event the walls 55 and 56 in recess 54 serve to control the position of the assembly 64. The transmission lines 14 and 16 are assembled to the driverand pickup assemblies 18 and 20 by inserting the anchor disc 128 at one end of each transmission line through the passageway 7.4, and on passing therethrough and being aligned with circular opening 76, each is given a slight rotational movement and a slight pull thereon enables the anchor disc 128 to be seated in the recesses 77 to form a bayonet connection. is then no longer aligned with the passageway 74, it cannot be pulled back through it so that one end of each transmission line is held in position. The disc 128 at the other end-of each transmission line is then inserted through a passageway 74 in either the driver or pickup means as the case may be in the same fashion.

The distance between the two ends of passageways 74 is calculated to just stretch the springs so that their turns areseparated by an identicalamount with the turns having a low helix angle to insure the proper propagation of the transmitted waves while at the same time the-total spring length is held short. Thus, by the positioning of the cases 26 the correct spacing between the .turns can be easily achieved. The magnets-94 then lie in the gaps 93 formed between a respective pair of arms 92 of the pole pieces.

In order to properly position and secure the pole pieces with respect to the magnets 94 while securing the coil and pole piece assembly 64 and in order to maintain the damping discs 126 properly positioned, a spring clip 134 is used to complete the positioning of the assembly. The clip 134 is generally U-shaped with the ends of the side legs 135 having ring shaped slotted right angle arms 136 thereon. In addition, a pair of wings 137 are provided at the end of each leg 135 and in the same plane, but projecting back therefrom at a transverse angle.

The back leg 138 of the clip 134 is provided with respective upwardly and downwardly projecting tines 139 and L-shaped arms 140. Each arm 140 has a locking bend 142 at the end thereof.

The clips 134 is assembled to the case 26 by inserting the side legs 135 together with wing 137 in the recess 54 while arms 140 engage grooves 50. The slots in ring shaped arms 136 permit the arms to engage over the wire 126 between the magnets 94 and damping discs 126. As the clip 134 is pressed back, the arms 136 move the damping discs 126 through slots 66 between the arcuate wall portions 70 and 72 to properly seat the same. At the same time the wings 137 press the webs 84 of the pole pieces against the respective upper and lower walls of recess 54 to size the gap 93 therebetween. Simultaneously the Walls 56 serve as stops for the arms 90 so that the pole pieces are positioned properly with respect to the magnets 94.

The tines 139 serve to apply pressure against the coil and pole piece assembly 64 and when the locking bend 140 on the clip passes over the vertical wall 53 of the stop 52, the assembly is securely held in position.

A rectangular resilient shielding element 142 is slipped over the front of the driver unit case 26 preferably before the transmission lines 14 and 16 are assembled thereto. The element 142 has a set of cars 143 which engage around a tab 144 protruding from the sides of each case so that the element 142 is properly seated and supported. The element 142 additionally seats the leg 132 of the ground strip 36 against the bottom face 48 of the case so that it is in no danger of entranglement.

There has been described one embodiment of my invention, and since this embodiment is capable of many adaptations and modifications, there is appended hereto a series of claims for accurately setting forth the limitations of the invention.

Since the anchor disc 128 I claim:

1. A suspension system for a vibration sensitive reverberation unit utilizing electroacoustic transducers, for the purpose of vibrationally isolating the reverberation unit comprising, a subframe for said reverberation unit, said subframe in end elevation providing attachment points arranged in substantially a rectangular pattern with diagonally opposite corners of the rectangle at the same end of the subfrarne, a separate mounting frame, four coil tension springs supporting said reverberation unit, one of said springs being connected at one end to one of said attachment points and to said mounting frame, another of said springs being connected to the diagonally opposite attachment point at the same end of the subframe and to the mounting frame, said springs in tension being angled relative tothe subframe to produce a centering component on said subframe end relative to said mounting frame and also to produce a rotary component on said subframe in one direction, the other pair of springs being connected to beration unit utilizing electroacoustic transducers for the.

purpose of vibrationally isolating the reverberation unit comprising, a mounting frame, four substantially identical coil springs supporting said reverberation unit, said springs being, in tension and connected at one end to said reverberation unit at spaced points and to the mounting frame at their other ends at spaced points, and the angularity of the springs being such that the axis of each spring is normal to a different face of a tetrahedron.

3. In a suspension system for a vibration sensitive reverberation unit utilizing electroacoustic transducers, the combination recited in claim 1 in which the tension springs are angled such that no two have parallel axes.

4. In a suspension system for a vibration sensitive reverberation unit utilizing electroacoustic transducers, the combination recited in claim 1 in which said springs are each normal to a different tetrahedral face.

References Cited by the Examiner UNITED STATES PATENTS 1,016,077 1/1912 Lumley 21754 2,211,205 8/ 1940 Hammond 333-71 2,230,836 2/1941 Hammond 33371 2,480,131 8/1949 Hammond 841.15 2,768,235 10/1956 Knoblauch 179-1 2,799,778 7/ 1957 Stephenson 21754 2,967,447 1/ 1961 Hanert 84-1.26 3,092,792 6/1963 Daniel 33330 3,106,610 10/1963 Young 179-1 FOREIGN PATENTS 677,326 '8/ 1952 Great Britain. 730,729 5/ 1955 Great Britain.

HERMAN KARL SAALBACH, Primary Examiner.

C. BARAFF, Assistant Examiner.

Claims (1)

1. 2. A SUSPENSION SYSTEM FOR A VIBRATION SENSITIVE REVERBERATION UNIT UTILIZING ELECTROACOUSTIC TRANSDUCERS FOR THE PURPOSE OF VIBRATIONALLY ISOLATING THE REVERBERATION UNIT COMPRISING, A MOUNTING FRAME, FOR SUBSTANTIALLY IDENTICAL COIL SPRINGS SUPPORTING SAID REVERBERATION UNIT, SAID SPRINGS BEING IN TENSION AND CONNECTD AT ONE END TO SAID REVERBERATION UNIT AT SPACED POINTS AND TO THE MOUNTING FRAME AT THEIR OTHER ENDS AT SPACED POINTS, AND THE ANGULARITY OF THE SPRINGS BEING SUCH THAT THE AXIS OF EACH SPRING IS NORMAL TO A DIFFERENT FACE OF A TETRAHEDRON.

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