US3092792A

US3092792A - Electro-acoustical delay line useful for producing reverberation in electrical musical instruments

Info

Publication number: US3092792A
Application number: US121431A
Authority: US
Inventors: Nathan I Daniel
Original assignee: Individual
Current assignee: Individual
Priority date: 1961-07-03
Filing date: 1961-07-03
Publication date: 1963-06-04
Anticipated expiration: 1980-06-04

Description

I. DANIEL 3,092,792

INE USEFUL FOR PRODUCING ELECTRO-ACOUSTICAL DELAY L REVERBERATION IN ELECTRICAL MUSICAL INSTRUMENTS Filed July 3, 1961 INVENTOR. M d 47/a BY ATTORNEY United States Patent Oil ice This invention relates to electrical musical instruments and more particularly to an apparatus for producing mechanical reverberation in the transmission of sound signals. The apparatus is, in general, of the type disclosed in Hammond Patent No. 2,230,836, dated February 4,

1941. It was pointed out in the above patent that the apparatus there disclosed was capable of producing tones having reverberation eifects which simulated the reverberation characteristics of a large auditorium even though the apparatus was being used in a small non-reverberative' room or out-of-doors. This invention also has that objective but it is a considerable improvement in that the character of the reverberation is controlled substantially completely by the tone signals and is not affected by other considerations such as physical vibrations of the apparatus whether originating externally of the unit or produced through sound waves emanating from the speaker.

I have produced a simplified reverberation unit wherein an electrical transducer, such as a piezoelectric crystal functions as a sending element in applying sound vibrations through a coil spring system, the lower end of which system is in turn connected to a piezoelectric receiving transducer which essentially reproduces the sound signals but with a delay caused by the travel of the vibrations along the spring system. Broadly this initself is old. However, the piezoelectric crystals must be anchored at one end thereof so that the stimulation of the other end mal be translated into physical movement, in the case of the sending transducer, and electrical signals in the case of the receiving transducer.

However, such anchoring has itself caused difficulties in that external physical vibrations would often be introduced into the system so as to produce spurious and undesired reverberative effects. For example, assume that the receiving crystal is physically actuated by the spring to producerever berative signals. Assumealso that an outside eiiect such as persons dancing in the room would agitate the crystal and produce reverberation effects which were completely unrelated to the sound signals through the apparatus. This results in spurious reverberation effects and, indeed, can even cancel the properly transmitted signals.

With the above in mind, I have provided a reverbera tion system wherein the transducer crystals are anchored only so far as they must respond to the stimulation of the sound signals through the apparatus. They are, however, tree to move in both horizontal and vertical planes in such a manner that they are substantially isolated from external noises and will respond substantially solely to the desired signals. This last description assumes the use of a piezoelectric crystal which responds with or reacts to twisting or torsional effects.

The invention will be further understood from the following description and drawings in which:

FIGURE 1 is a longitudinal cross-sectional view of a reverberation unit constructed according to the instant invention;

FIGURE 2 is an elevational view thereof, partly broken away; and

FIGURE 3 is an enlarged fragmentary view illustrating the connection of the spring system to the end walls.

It will be understood that the reverberation unit herein disclosed translates audio waves or signals into mechanical vibrations, effects a delay in the vibrations, and then translates the vibrations back into electrical audio waves or signals. Accordingly, the unit may be interposed substantially anywhere in the audio amplifier system as will be readily understood. For example, in the above mentioned Hammond Patent No. 2,230,836, such a system was interposed at about the center of the audio channel circuitry whereas in Hannert Patent No. 2,967,447 the signals applied thereto were taken from the voice coil terminations and thereafter amplified after having been mechanically delayed.

In my unit, the electrical audio signals are applied by the usual shielded coaxial cable 10 through an opening inend wall 11 to the conventional flexible met-a1 terminals of a piezoelectric crystal 12. Crystal 12 is in itself rigid and is preferably of the type which reacts to electrical signals by twisting physically. Such crystals are most commonly used in phonographs where they translate twisting motion derived from the needle into electrical signals. Of course, they also operate in reverse, i.e., they produce a mechanical twisting motion in response to electrical signals applied thereto. Actually, for convenience of mounting and protection of the terminals, I provide a covering of ordinary electrical friction tape 13 over the crystal and its flexible terminals as will be hereinafter described. For grounding purposes, I ooat the inner surface of wall 11 with metal foil 14. The shield of cable 10 is effectively grounded to foil 14 as is conventional and as will be hereinafter more fully explained.

The spring delay system comprises the two

coil springs

15 and 16 which are hooked to each other and serially connected together as by solder at their meeting point 17. The springs are of the type described in the above mentioned patents, it being understood that the springs are largely conventional and are not critical in either length, tension or caliber. As an example, however, it may be noted that in a satisfactory embodiment the smaller caliber spring 16 (about 1 diameter) was about 2 inches long, the larger caliber spring (about V 3 diameter) being about the same length. In such embodiment, the connected springs were extended to about 6 inches, serially. The spring system is enclosed within a nnetal or other rigid tube 18 which is shock mounted at both ends in foam rubber or plastic blocks 19 which are adhered to a rigid supporting base 20.

Notwithstanding the mounting of the unit in the highly resilient blocks 19, the unit is nevertheless subject to external vibrations which produce spurious signals as above described. Accordingly, the connection of the springs to the piezoelectric crystals is of great importance, as I have above set forth.

Referring now to larger spring 15, the end two coils thereof are bent perpendicularly to the axis of spring 15 so as to form a fastening element 21 comprised of said two end coils. Said fastening element 21 is then glued to the friction tape 22 which embraces the crystal 23. A firm connection is thus eifected which allows no play between the fastener element 21 and the rigid crystal 23. The glue may be of any common variety which will bond steel coils to the fabric friction tape 22.

The length of the crystal 23 is about as is the 'crystal 12. The other end of crystal 23 is similarly adhesively secured to the fastening spring coil 24 which in fact may constitute about 1 /2 turns. However, a single annulus will suffice. Coil 24 is, of course, of metal as are the

springs

15 and 16. Fastening

coils

21 and 24, although of spring metal, comprise horizontally rigid con- Patented June 4, 1963 necting elements capable of transmitting physical movements without losses.

The enlargement of FIGURE 3 best illustrates the connection which forms the subject of this invention. Thus end wall 25 duplicates the structure of the opposite end wall 11. It includes an inner foil 26 and is formed with an offset hole within which is disposed a tubular rivet 27 serving as a passageway. The rivet further mechanically secures the fastening member 28 to wall 25.

The construction of fastening member 28 is of importance. It comprises a connecting arm 29 and an end hook 30. End hook 30 has a planar floor 3-1. Coil 24 although being connected firmly by adhesive 32 to the crystal, or rather its tape cover 22, is pivotally received within hook 30 so that it is free to swing upwardly in the direction of arrow 33 or downwardly in the direction of arrow 34.

As a result of the foregoing connection, the springs may partake of various motions relative to the tubular casing 18. Thus, the crystal 23, which is rigid with respect to the fastening end coils 21 of spring 15, may swing upwardly or downwardly in a vertical plane in the direction of

arrows

33 and 34 and it may also slide perpendicularly thereto in a horizontal plane on floor 31, all without generating and transmitting electrical signals to its flexible

metallic terminals

35 and 36.

Terminals

35 and 36 are the usual flexible Phosphor bronze (or the like) terminals connected to the crystal and which are in turn connected to the

wires

37 and 38 of the output coaxial cable 40, the shield 3-9 of which is grounded to the arm 29 as illustrated in FIGURE 3.

It will be understood from the foregoing that when the receiving crystal 23 receives a twisting impulse from the

springs

15 and 16, it will produce corresponding electrical signals in its

terminals

35 and 36 which are then amplified, although after some delay. However, should the springs be jarred through external vibrations, the described structure will effectively screen out such movements by the connection of the coil 24 to the hook 30 which will produce a response only to twisting of the crystal and not to movement thereof bodily. In other words, by virtue of the construction shown if fastening coil 21 is twisted, then coil 24 will hold fast in hook 30 so as to produce twisting of the crystal and corresponding electrical signals. However, should substantially any other type of motion be applied to the receiving crystal 23, it will simply move bodily and produce no signals.

The same fact applies to the input transducer or sending crystal 12, the mounting thereof being identical to that of the output transducer 23, the fastening member 28 being spaced from its opposed fastening member 41 by the length of tube 18.

Crystals

12 and 23 comprise flat bodies, the

fastening coils

21 and 24 being flatly adhered thereto by having an arc of about 120 thereof adhesively secured to the op posite end portions of the crystal bodies which are rectangular in shape.

Briefly, it may be observed that electrical audio signals translated into sound vibrations by crystal 12 will travel along the length of

springs

16 and 15 and will be reflected from the ends thereof as well as from the connection point 17. The result will be a variety of reflections substantially duplicating or at least simulating the sound reflections or reverberations in a large auditorium. However, outside influences will be screened out as above described.

In the form shown, the output co-axial cable 40 is brought around to the front of the unit for convenience in installation, both cables terminating in plugs 42 and 43.

There has been shown what is now considered a preferred embodiment of the invention but it is obvious that changes and omissions may be made without departing from its spirit.

What is claimed is:

1. Apparatus for transmitting sound comprising opposed end supports, a sending piezoelectric crystal and a receiving piezoelectric crystal respectively connected to said supports, both of said crystals having flat bodies, and an elongated spring means connected to and between said flat bodies, the connection of said spring means to at least one of said flat bodies comprising a portion of said spring means fixedly secured to the said one flat body, said spring means consisting of at least one coil spring, said last-named connection comprising an end coil thereof which is adhesively secured to said one flat body and embraces an end portion thereof, a hook having a substantially planar floor on each of said end supports, and a rigid connecting element fixedly secured to the opposite end portion of said one flat body and being rotatably received by said hook and resting on and across said planar floor thereof whereby said rigid connecting element may rotate in the plane of said floor and in a plane perpendicular thereto but is restrained from twisting movement relative to said hook.

2. Apparatus according to claim 1 and wherein said rigid connecting element comprises an annular coil an arc of which is adhesively secured flatly to said flat body while an opposite arc thereof rests slidably on said hook floor.

3. Apparatus according to claim 2 and wherein the connection of each of said flat bodies to said elongated spring means and to said hooks is identical.

4. Apparatus for transmitting sound comprising a pair of opposed fastening members, means maintaining said fastening members in spaced relationship, a piezoelectric crystal slidably connected to each fastening member for slidable movement relative thereto in one plane and rotating movement in a plane perpendicular to said one plane, said crystal being secured against twisting movement relative to said fastening members, spring means disposed between and connected to said crystals for transmitting sound vibrations, one of said crystals being a sending crystal and the other being a receiving crystal, the sending crystal reacting to sound signals by twisting and the receiving crystal reacting to twisting by generating electrical signals, each of said fastening members comprising a hook having a planar floor, said crystals having flat bodies, a rigid connecting element connected flatly to the outer end portions of each crystal and being also slidably connected to said hook and resting on said planar floor thereof, said spring means comprising at least one coil spring and having an end coil thereof fixedly secured to an inner end portion of one of said crystals.

5. Apparatus according ,to claim 4 and wherein said rigid connecting element comprises an annular coil an arc of which is adhesively secured flatly to the respective crystal bodies while an opposite arc of which rests slidably on the respective hook floors.

6. Apparatus according to claim 5 and wherein said spring means comprises two serially connected coil springs of respectively different calibers.

References Cited in the file of this patent UNITED STATES PATENTS 1,852,795 Wegel Apr. 5, 1932 2,001,132 Hansell May 14, 1935 2,137,852 Nicolson Nov. 22, 1938 2,211,205 Hammond Aug. 13, 1940 2,318,417 Phelps May 4, 1943 2,575,333 Di Toro Nov. 20, 1951 2,600,870 Hathaway June 17, 1952