US3391250A - Reverberation unit - Google Patents

Description

July 2, 1968 G. s. KLAIBER ETAL REVERBERATION UNIT 2 Sheets-Sheet 1 Filed Dec. 21, 1964 (lfgpa m4 flan did R 05 mm F L RP m EM M a A K J/ w u 1 E 0 c L MM m5 R R an a5 MW MN VA 5 m L y 1968 G. s. KLAIBER ETAL 3,

REVERBERATION UNIT Filed Dec. 21 1964 2 Sheets-Sheet 2 United States Patent 3,391,250 REVERBERATION UNIT George Stanley Klaiber, Tonawanda, and Anthony C.

Ippolito, North Tonawanda, N.Y., assignors to The Wurlitzer Company, Chicago, 11]., a corporation of Ohio Filed Dec. 21, 1964, Ser. No. 419,730 11 Claims. (Cl. 179-1) ABSTRACT OF THE DISCLOSURE A reverberation unit for electrical musical instruments and the like utilizing a helica'ly coiled spring as a signal time-delay element, combined with dampers on transducers at either end thereof to produce satisfactory results with but a single spring.

This invention relates to apparatus for producing timedelay or reverberation effects in musical instruments, phonographs, tape recorders and the like.

It has been recognized heretofore that one defect of home reproduction of music is that the music is generally reproduced or produced in a room which is substantially smal'er than is desirable for proper acoustic effects. It will be recognized that the reverberation time of a large concert hall is inherently much greater than that of a domestic living room. Various attempts have been made to produce reverberation synthetically in order to simulate a large concert hall. Probably the most successful artificial or synthetic reverberation devices have utilized eectromechanical devices for delaying a signal, preferably introducing echoes therein. It has been recognized heretofore that this can be done by way of one or more springs having motion imparted thereto at one end in accordance with an electrical signal and having an electrical signal derived at the opposite end from the mechanical movement of the spring.

The production of delayed sound transmission by imparting vibrations to one end of a spring is well known. The spring may vibrate in a torsion, compression or transverse mode alternatively, as taught in Wegel US. Patent 1,852,795. Such spring time-delay systems have also been used specifically in the musical arts, see for exampe Hammond US. Patent 2,230,836 and Meinema U.S. Patent 2,982,819.

It is recognized that any spring inherently has its own natural period of vibration. Obviously, if the spring tends to resonate at an audio frequency which is to be delayed in time to produce a reverberation effect, this frequency will be emphasized. In any event, the motion imparted to a spring electromechanically will travel back and forth through the spring with a plurality of echoes, as is essential to simulate concert hall reverberation wherein there are many echoes. Some of the echoes or reflected waves will be in phase with one another and produce an augmented result. On the other hand, some of the reflections or echoes, will be out of phase and will cancel one another. As a result, there is not a smooth frequency curve, but rather a curve having alternate peaks and valleys wherein the reflected and direct signals reinforce and cancel one another. I

Due to this cancellation effect and the peaks and valleys of the response curve, it heretofore has been thought essential to have two or more strings of different natural periods of vibration. It has been assumed that the peaks of one spring will fill in the valleys of the other, and vice versa. Unfortunately, it has been found that although this does sometimes happen, there are also reinforcement and cancellation effects of the peaks and valleys of the two springs. It also has been thought essential to have a rather limply suspended spring so that it will not tend to resonate at an audio frequency in which it is desired to develop reverberation. This has necessitated the provision of rather large gaps in the transducers at either end of the spring to avoid bumping together of parts of the transducers upon movement of the springs other than compressionally or torsionally. This, in turn, has led to low efliciency of transducing. Limp suspension has also necessitated various provisions to prevent the spring from swinging around upon any physical shocks being imparted to the reverberation apparatus. Bumping together of adjacent coils of the spring, bumping of parts of the transducer, or bumping of the spring against the frame cause extremely unpleasant percussive sounds in the output.

It is an object of the present invention to provide an artificial reverberation system utilizing but a single helical spring.

It is a further object of this invention to provide an artificial reverberation apparatus of greater efliciency than those heretofore known in the art.

Yet another object of the invention is to produce an artificial reverberation apparatus having extended frequency response.

Other and further objects and advantages of the present invention will be apparent from the following description when taken in connection with the accompanying drawings wherein:

FIG. 1 is a block diagram illustrating a system utilizing the reverberation apparatus of the present invention;

FIG. 2 is a perspective view of a reverberation apparatus constructed in accordance with the present invention;

FIG. 3 is a longitudinal sectional view through the apparatus of FIG. 2 as taken along the line 3-3 in FIG. 2, FIG. 3 being on a larger scale and with the center portion broken away to foreshorten the figure;

FIG. 4 is an end view of an insulating form or support forming a part of the reverberation apparatus;

FIG. 5 is a cross sectional view on the same scale as FIG. 3 and taken along the line 55 in FIG. 8;

FIG. 6 is a cross sectional view taken along the line 66 in FIG. 8;

FIG. 7 is a detail view of the attachment of the spring to the spring anchor taken in longitudinal section and on an enlarged scale;

FIG. 8 is a fragmen ary longitudinal. sectional view taken along the line 8-8 in FIG. 3 and on a larger scale;

FIG. 9 is an exploded perspective view of one of the transducers and adjacent parts; and

FIG. 10 is a sectional view along the line 1010 in FIG. 6.

Circuits utilizing artificial reverberation apparatus are known, and one such circuit is shown in FIG. 1. Thus, there is an electrical tone source providing electric oscillations corresponding to a tone which is to have reverberation thereto. This may be, for example, the tone generators of an electronic organ. Alternatively, it can be the pickup of a phonograph, or tape recorder, or a signal source in a radio. The electric signal from the tone source 20 is fed to an amplifier 22, and through a resistor 24 to a loudspeaker 26. In addition, the output from the amplifier is taken by means such as a wire 28 to the reverberation apparatus 30 which in turn is connected to a reverberation amplifier 32. This amplifier is shown as being connected to the loudspeaker 26, although it is known that it could be connected to a separate loudspeaker.

Referring now to FIGS. 2 and 3, there will be seen a reverberation apparatus 3t] constructed in accordance with the principles of this invention, and including a channelshaped frame 34 having a relatively wide and elongated web 36 with longitudinal flanges 38 along the edges thereof. At the ends of the flanges are holes 40 for receipt of diagonally tensioned springs 42 to suspend the reverberation apparatus substantially free of external vibrations. Relatively adjacent the ends of the flanges 38 there are provided somewhat larger semicircular openings 44. Intermediate the openings 44 the edges of the flanges are turned out at an acute angle to form longitudinal lips 46. These lips provide additional rigidity and inhibit any resonance of the frame.

Adjacent the left end of the frame 34 there is disposed a transducing unit or transducer 48, for clarity of nomenclature hereafter referred to as a sending transducer. An identical transducer or transducing unit 48a is secured to the frame near the right end thereof, and this transducer will for the sake of distinction be referred to as a receiv ing transducer. It will be understood that electrical energy could be fed into either of the transducers 48, 48a and taken from the other.

A helically coiled elongated spring 50 is tensionally supported between the two transducers, extending substantially from end to end of the frame. This spring normally is wound with initial tension so that the adjacent convolutions initially are in contact with one another. The spring is stretched somewhat during installation so that the adjacent coils or convolutions are pulled apart. This provides for a uniform, but close spacing between adjacent turns. The spacing is sufliciently small that it is diflicult to show it in the scale of FIG. 3. However, it will be seen in FIG. 8.

As has been noted, the two transducers 48 and 48a are identical. Hence, attention will now be directed to the left or sending transducer 48 for the details thereof. The transducer 48 is mounted by means of a stud 52 staked at 54 in a hole provided therefor in the web 36 of the channel 34. The stud is provided at its other end with a tapped axial bore receiving a screw 56 which holds down a U-shaped cover plate 58 having a web 60 and a pair of side flanges 62. Also held by the screw 56 and beneath the cover 58 is a U-shaped bracket 64 of relatively heavier material. Although the cover 58 may conveniently be formed of sheet steel, the bracket 64 is made of brass or other nonmagnetizable material. The bracket includes a web 66 and side flanges or legs 68 having extending tongues 70 at the ends thereof received in transverse slots 72 in the web 36 of the supporting frame 34 for proper positioning of the frame or bracket 64. Other details of the frame or bracket 64 will be set forth hereinafter. It will be observed that the cover 58 is rotated 90 from the position of the bracket 64, whereby the flanges 62 of the cover fill in the space between the flanges 68 of the bracket.

The transducer further includes an insulating mounting block or base 74, preferably molded of plastic material. On the front face of the block, which is of generally square outline (the side viewed in FIG. 4 and on the right in FIGS. 3 and 8-10), the block is recessed at 76, leaving a peripheral wall 78. A magnetic structure 80 of open rectangular outline is received in this recess within the wall 78. The magnetic structure is made of magnetically susceptible material, but is not permanently magnetized. It is of an open square shape with a pair of confronting inward protrusions 82 having screw holes 84 therethrough. There are mating screw holes 86 in the plastic block extending completely therethrough. The magnetic structure 80 is permanently retained in the plastic block, as by means of a suitable adhesive.

The block further is recessed on the front face at 88 to accommodate a coil 90 wound on a magnetically susceptible core 92, and having plastic end pieces 94 and leads 96. As will be seen particularly in FIG. 9, the core 92 has a small cylindrical protrusion 98 on its upper end. The plastic end piece 94 has a central square opening complementary in shape to the core, and the cylindrical protrusion 98 is recessed slightly below the upper surface of the plastic end piece 94.

The back side of the plastic block 74 (see particularly FIG. 5) is provided with a generally V-shaped cut out 100 extending through the block into communication with the recess 88. Parallel legs 102 form an upward extension of the cut out. The leads 96 from the coil extend into the V-shaped cut out and up the extensions 102 past edge flanges 104 on the back side of the block. The coil 90 and associated parts are permanently held in the recess in the front face of the block, as by a suitable adhesive.

Screws 106 pass through the screw holes 84 in the magnetic structure, through the screws 86 in the block, and threaded into tapped apertures 108 in the adjacent leg or flange 68 of the bracket 64 to mount the block thereon.

The back or outer flange 68 of the bracket 64 is provided with a pair of ears 110 struck out at right angles thereto. The cars are coplanar, being relatively toward adjacent sides of the flange, and are provided at their outer ends with V-shaped notches 112. A beryllium copper Wire 114 is bent over the upper ear 110, through the V-shaped notch thereof, and is held in place by a lump of solder 116. The opposite flange 68 is provided with bores 118 substantially aligned with the surfaces of the ears 110 disposed opposite the frame or mounting channel 34. The beryllium copper wire 114, which serves as an anchor or torsion wire, as will be brought out hereinafter, is mounted on only one of the ears 112 and extends through the corresponding aperture or bore 118. More importantly, the wire extends through a damper or damping member 120 made of rubber or other suitable elastomeric material of particular characteristics and suiting a particular purpose, as hereinafter brought out.

The rubber damper 120 of generally cylindrical nature is provided with an axial pin hole substantially less in diameter than the wire 114, and the wire extends therethrough. The substantially cylindrical damper is provided near one end, the left end as viewed in FIG. 8 with a circumferential, radially outwardly extending flange 122. This provides a cylindrical protrusion 124 at the left end which extends into the hole 118 in the flange 68, being held therein by a suitable adhesive with the flange 122 abutting the face of the flange. There is a longer cylindrical protuberance 126 at the opposite end, and this extends into a bore 128 in the plastic mounting block 74. The bore or pin hole through which the wire 114 extends in the plug 120 is identified by the numeral 130, and this bore flares outwardly at 132 at either end.

Within the plastic block 74 and extending therefrom a stainless steel tube 134 (see particularly FIG. 7) is crimped onto the wire 114, and is bent into a hook shape at 136, the adjacent end of the spring 50 having a hook 138 interen-gaging therewith. The end of the steel tube is spaced .015 inch from the end of the rubber damper 120, the wire being .007 inch diameter. In addition, there is disposed on the stainless steel tube a ceramic magnet 140 of cylindrical configuration, being .062 inch outside diameter, and of substantially the same length as the transverse dimension of the core 92, the ceramic magnet being aligned with the end of the core 92, and particularly the protuberance 198 thereof. The ceramic magnet 140 is polarized diametrically, rather than axially, and this polarization is ideally in a plane perpendicular to the core 92, i.e., parallel to the plane of the adjacent face of the core. It will be observed particularly in FIG. 8 that the ceramic magnet 140 is centralized bet-ween the confronting face of the core 92 and the adjacent portion of the square magnetic structure 80.

Thus, when the coil 90 is energized with audio frequency, electrical energy, it imposes a twisting or torsional force on the magnet 140. This, in turn, excites the reverberation spring 50 in a torsional mode. A signal corresponding to that applied to the coil 90 travels down the spring 50 to twist the ceramic magnet 140a at the opposite end thereof, and thereby to induce a signal in the coil 90a of similar nature, but delayed in time. As will be appreciated, not all of the energy imparted to the spring is taken up in inducing an electric current in the coil 90a. Part of the energy is reflected at the point where the spring is hooked on to the magnet 140a and associated structure, travels back to the sending end, and again is reflected to the receiving end. There will be a rather large number of such echoes, andthis results in a received signal remarkably similar to that in a reverberative concert hall or auditorium.

Several details of construction of the present invention, heretofore described, are worthy of amplification. Thus, it will be observed that the structure of the transducers is symmetric. There are two ears 110, two holes 118, and two bores 128, even though there is only one spring and anchoring structure including wire 114, etc. With this symmetrical construction, exactly the same parts can be used at either end. Thus, only one part need be formed instead of two, thereby materially reducing the cost of dies, inventory, etc.

The spring 50 is made of music wire. Springs of beryllium copper, Phosphor bronze, tempered silver, and stainless steel have been found to work satisfactorily under some circumstances, but the music wire works best. The wire itself is of .014 inch diameter, and the spring is wound on a helix so that the spring has an outside diameter of inch. The spring is wound with initial tension so that the adjacent turns or convolutions initially abut one another. The initial spring length is 9% inches, and the spring in installed position is stretched to 13 inches and is under 8 /2 ounces tension. The spring has a natural frequency of about 9 cycles per second. Peaks and valleys in transmission are produced about every 13 cycles on the spring.

Transmission efficiency is increased with increasing axial tension on the spring. However, there is a tendency to produce chattering with undue tension on the spring. Furthermore, with increased tension producing increased efficiency, there is a tendency for a burst of energy imparted on the spring to travel up and down the spring substantially indefinitely, and thereby masking a subsequent note being played. The problems of chattering and of practically infinite hanging on of reflected energy are concurrently solved by the rubber dampers 120. These dampers are made of butyl rubber, and preferably are of 40 durorneter hardness. Dampers with durorneter readings of 40, 50, 60, 70 and 80 all have been satisfactory, but a 40 durorneter reading is best. The position of the damper is quite important, and this is as close as possible to the magnet and stainless steel tube, or stated otherwise, it is as far as possible away from the point of attachment of the torsional anchoring wire 114. The damping is four or five times greater than has been used heretofore with two spring units. Nevertheless, since the initial efficiency is so much higher, the output is still enough higher that a stage of amplification can be omitted.

By and large, the single spring unit sounds better than previous two spring reverberation units, partially due to lack of cancellation effects inherent in the use of two springs, and also due to longer hanging on of the reverberation effect due to the higher efliciency and greater output in the first place.

Many prior helical spring type reverberation units have been quite restricted in frequency response. Some of these have been found to have no significant output much above 3,000 cycles per second, and at least one unit has been found to cut off above 2,800 cycles per second. A reverberation unit constructed in accordance with the principles of the present invention has been found to have very good response up to 6,000 or 7,000 cycles per second. Propagation of energy through a helical spring as in the present invention is at the same rate as if it were through a straight wire equal to the length of the spring uncoiled. Thus, it will be appreciated that the same results could be obtained in a shorter length by using a coil of greater diameter. However, the present dimensions have been found to be optimum. Increasing the diameter of the coil results in there being less coils for a given wave length of a higher note, such for example on the order of 5,000 cycles per second. If, for example, there were only about two coils to a wave length, instead of about six as in the present invention, then there would be a tendency for the wire itself to twist, instead of just twisting of the spring, with resultant undesired damping out of vibrations.

It will be understood that the particular example of the invention as shown and described herein is set forth by way of illustration. Various changes in structure will no doubt occur to those skilled in the art, and will be understood as forming a part of the present invention insofar as they fall within the spirit and scope of the appended claims.

We claim:

1. A reverberation unit comprising a supporting base; a pair of electromagnetic transducers mounted on said base in spaced apart relation; and a helical spring stretched between said transducers; each of said transducers including an insulating base, means supporting each insulating base from said supporting base, a coil mounted centrally of each insulating base, a core in each coil, a surrounding magnetic structure on each insulating base substantially symmetrically disposed about said coil, there being an air gap at each end of said core between said core and said magnetic structure, a pair of apertures through said insulating base respectively aligned with said air gaps and a pair of anchor means supported from said supporting base and respectively aligned with said apertures, a single torsion wire anchored to only one of the anchor means of each transducer and passing through the corresponding aperture in said insulating base, means mounting a permanent magnet on said torsion wire in only one of said air gaps of each transducer, means joining said spring at its opposite ends to said torsion wires; en ergization of the coil of one transducer with an audio frequency electric signal imparting a twisting motion to the corresponding permanent magnet and torsionally exciting said helical spring, said spring in turn imparting a twisting movement to the permanent magnet of the other transducer and inducing in the coil of said other transducer an audio frequency signal similar to the energizing frequency but delayed in time therefrom, and a damper of elastomeric material mounted in the aperture in said insulating base through which said torsion wire passes and engaging said torsion wire.

2. A reverberation unit comprising a supporting base, a pair of electromagnetic transducers mounted on said base in spaced apart relation, and a. helical spring stretched between said transducers, each of said transducers including a base, an elongated torsion wire suported at one end from each transducer base, a magnetic member mounted on said torsion wire and free to move therewith, complementary electromagnetic structure mounted on each insulating base in proximity to the magnetic member on the torsion wire, an elastomeric damper mounted from each insulating base in damping engagement with the respective torsion wire and having a hardness between substantially 40 and durorneter, and means interconnecting each torsional wire and the adjacent end of said helical spring.

3. A reverberation unit comprising a supporting base, a pair of electromagnetic transducers mounted on said base in spaced apart relation, and a helical spring stretched between said transducers, each of said transducers including a base mounted on said supporting base, an elongated torsion wire secured at one end thereof to each of said transducer bases and secured at the other end to the respective ends of said spring, a magnetic member secured to each of said torsion Wires adjacent the end thereof secured to said spring, magnetic structure including a coil carried by each of said transducer bases in proximity to the respective magnetic members, and a damper acting on each torsion wire, each of said dampers comprising an elastomeric member supported from the respective transducer base with said wire passing through and in intimate contact with said elastomeric member, said elastomeric members being disposed immediately adjacent said magnetic members.

4. A reverberation unit as set forth in claim 3 wherein each of said magnetic members comprises a cylindrical permanent magnet having a predetermined length, and wherein the spacing between each damper and the adjacent magnetic member is less than said predetermined length.

5. A reverberation unit as set forth in claim 4 wherein each of said magnetic members comprises a cylindrical permanent magnet having a predetermined diameter, the spacing between each damper and the adjacent magnetic member being less than said predetermined diameter.

6. A reverberation unit as set forth in claim 3 wherein each of said transducer bases has a bore in which the respective damper is mounted, each said bore having a predetermined diameter, the spacing between each damper and the adjacent magnetic member being less than said predetermined bore diameter.

7. A reverberation unit as set forth in claim 3 wherein said torsion wire has a predetermined diameter, and wherein the spacing 'between each damper and the adjacent magnetic member is on the order of twice said predetermined diameter.

8. A reverberation unit as set forth in claim 3 wherein each of said dampers is a cylindrical member having a predetermined diameter, and wherein the spacing from each damper to the adjacent magnetic member is less than said predetermined damper diameter.

9. A reverberation unit comprising a supporting base, a

pair of electromagnetic transducers mounted on said base in spaced apart relation, and a helical spring stretched between said transducers, each of said transducers including a base, anchor means on said transducer bases, a

torsion wire secured to one anchor means of each transducer Ibase and secured at the other end to the adjacent end of said helical spring, a magnetic member on each torsion wire adjacent said spring and remote from the corresponding anchor means, and a cylindrical damper mounted on each transducer base and having an axial hole through which the corresponding torsion wire extends, each damper being cylindrical in configuration and having a greater axial length than the diameter thereof.

10. A reverberation unit as set forth in claim 9 wherein each damper further has a circumferential mounting flange thereon.

11. A reverberation unit as set forth in claim 10 wherein the circumferential flange extends radially out from each damper and is disposed relatively adjacent one end of the damper, said one end being the end remote from said spring.

References Cited UNITED STATES PATENTS 2,982,819 5/1961 Meinema et a1 179-1.6 3,106,610 10/1963 Young 179--1.6 3,159,713 12/1964 Laube 1791.6 3,270,300 8/1966 Van Leer 333-30 R. P. TAYLOR, Assistant Examiner.

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