US2821878A - Stereophonic organ - Google Patents

Description

Feb. 4, 1958 G. R. STlBlTZ 2,821,878

I STEREOPHONIC ORGAN Filed March 15, 1954 2 Sheets-Sheet 1 CDEF'GA comns PEDAL I 5 PEDAL I com-eta 2 c*n"'rs4a U MANUAL MANUAL 1 IN V EN TOR. GEORGE R. STIBITZ ATTORNEY Feb. 4, 1958 G. R. STIBITZ 2,821,878

STEREOPI-IONIC ORGAN Filed March 15, 1954 2 Sheets-Sheet 2 FROM TONE GENERATORS 36 INVENTOR.

. GEORGE R .STIBITZ BY M ATTORNEY.

This invention relates to electric organs and has for its primary purpose, in an electric organ, the production of a spatial or stereophonic effect, whereby the tone appears to come from a number of divergent directions, thus simulating the spatial effect of a pipe organ.

in the conventional pipe organ, the pipes in any rank within one division are arranged in a row that is roughly ten feet long; moreover, the swell, great and other organs or divisions may also be separated in space. As a result, the sound does not appear to come from a single point, but is perceived by the listener as coming from these distributed sources, thus lending richness and a distinctive quality to the music, which is not ordinarily obtainable when the sound is obtained from one or even more than one loud speaker actuated by an electric organ. Of course, the spatial effect could be produced by using a number of speakers in different locations corresponding to the various divisions, pipes or ranks of the organ, and having each one energized only by the notes corresponding to the similarly-located respective divisions or units. However, this would be inordinately complex and expensive, and would therefore be in conflict with a prime object of electric organ production, namely, economy and compactness.

According to the invention, the desired stereophonic effect is obtained, and the above noted objections obviated by using only two speakers, which may be spaced according to the maximum span of the divisions of a pipe organ, and proportioning the intensity of the sound of the various divisions between these two speakers so that the sound will appear to come from any point on the line between the two speakers in accordance with the proportionate intensity of output from each speaker for any given division or unit. This can be accomplished by simple electrical circuit means in reliable fashion and at little cost. Of course, it will be apparent that the invention is not restricted to the use of two speakers, since more may be employed if desired, but it is a feature of the invention that satisfactory performance may be obtained with only two speakers.

According to another form of the invention, two or more speakers may be ernpolyed as before, but the stereophonic effect is produced by delaying that part of the signal generated by a given tone-producing unit and transmitted to one speaker with respect to that generated by the same unit but transmitted to an adjacent speaker. Such non-simultaneous production of a sound from two sources is known to produce in a listener the effect of a change in the apparent source of the sound as compared with its production by two speakers exactly in synchronism, and by changing the relative delay, the apparent source of sound can also be changed.

It is thus a major object of the invention to produce a stereophonic effect in an electric organ by relatively simple and inexpensive means, and by compact, reliable and readily reproducible construction.

The specific nature of the invention as well as other objects and advantages thereof will clearly appear from a States Patent i ice description of a preferred embodiment as shown in the accompanying drawing, in which:

Fig. 1 is a schematic diagram showing one form of the invention;

Fig. 2 is a diagram illustrating the principle of a second form of the invention;

Fig. 3 is a schematic diagram of an arrangement according to the second form of the invention; and

Fig. 4 is a schematic diagram of an alternative arrangement for practicing the second form of the invention.

Electric organs having two or more speakers are known, in which the speakers are either operated simultaneously but over different respective frequency ranges or else respectively connected to different divisions of the organ whereby each speaker, when it sounds, represents only its divisions of the organ. In all of these cases, the result is the production of a point-source effect which compares unfavorably with the spatial effect of a pipe organ. Even if a number of speakers are spaced widely apart and operated simultaneously, the effect is still not realistic, and at any given listening point appears always to come from the same source, no matter what note or rank is sounding.

In standard organ practice, the notes C, D, E, Flt, Git, All, form one group and those for Cit, Di, F, G, A and B, form another, and these groups may be divided by stops or claviers into further groups. Referring to Fig. 1, it is assumed that four groups are formed consisting of pedal C-side, manual C-side, manual Cliside, and a pedal Cit-side, whose electrical outputs appear respectively on lines 1, 2, 3 and 4 in the drawings. Two speakers, 5 and 7, are provided, preferably placed about ten or more feet apart in the room in which the organ is to be sounded, the spacing being adapted to the size and acoustic properties of the room. The electric outputs of lines 1-4 may be the output signals of any conventional electric organ, but the invention is intended for use with an electric organ such as is described in my copending application, Serial No. 298,669, filed July 14, 1952, now Patent No. 2,770,995, issued November 20, 1956, in which the output leads, instead of all leading directly to the speaker system, are grouped as shown by leads 1-4 inclusive.

Leads 1-4 are connected to resistance dividers 11-14 respectively. Resistance divider 11 has a 1K resistance on the left side and a 10K resistance on the right side, thus the right speaker will sound much louder due to a sound signal on lead 1 than will the left speaker, and the effect to the listener will be that musical tones from the C pedal come from a point closer to the right speaker 7. Similarly, since the dividing network is so arranged that ninety percent of C3 pedal signal is applied to the left speaker and 10 percent to the right speaker, the acoustic effect will be that the C3? pedal will appear to come from a point near the left speaker 5. Since sixty percent of the C1? manual signal is applied to the left and forty percent to the right, the Cit manual tones will appear to come from a point between the speakers 5 and 7, but somewhat to the right of the Ci pedal, and the reverse will be true of the C manual. A separate amplifier, 16 and 18 respectively, is provided for each speaker.

It will be apparent that the division shown in Fig. l is only exemplary and that any desired numbgr of resistance dividers may be used with a corresponding number of organ units, to provide different sterophonic arrangements as desired, thus presenting a realistic spatial effect corresponding to the physical construction of the organ and avoiding the spatial point-effect of prior electric organs. It will also be apparent, that instead of two speakers, three or more speakers may be used with the respective signals divided in any desired manner among Flute String Trumpet Diapason Mixture Clarinet C# OC# CC# CC# CC# 'ooao This arrangement does not follow the conventional pipe organ pattern, which is largely dictated by mechanical convenience,'but instead attempts a pattern based on musical considerations.

The reason for this choice is that the flute, string and clarinet may be used as solo instruments, and might well be separated, the trumpet and diapason are powerful foundation stops easily distinguishable in timbre and should notbe separated too far, while the diapason and mixture form a unified chorus. The flute being some whatdelicate may profit by being well separated.

'Inthis example, 'theC side of the string rank (C, D, E, FL, Ft, At?) is located of the Way from the left end and of the way from the right end of the array. We may then feed roughly five times :as'much of thesignal from this 'half rank into the amplifier for the left speaker as for the-right, by means of the standard potentiometer, for which purpose I prefer to use an adjustable potentiometer, and to vary the ratio until the positions appear correct=to the listener, in order to obtain initially a'set of suitable permanent values for theresistancemetwork. For a given organ, of course, it is not necessary to use an adjustable network once the correct values are known, so that productionunits may be provided with a fixed network, whose values have been empirically determined.

It will be noted that the stereophonic efiect produced is not particularly related to pitch, but represents specifically the physical-arrangement of an idealized pipe organ with a degree of realism previously unattainable.

Instead of using'two-spaced-apart speakers and a resistance network, a similar effect may be attained by using two speakers whose sound division, instead of being in terms of relative amplitude, is in terms of relative time delay. -In order'to-approximate a sound coming from a definite direction, the listener receives two (or more) component waves from spaced speakers at various delays. These combine to form a wavefront that is approximately plane, or, at any rate, the normal to which is in the desired direction for the apparent sound source.

Referring to Fig. '2, suppose that there are several sources that emitted pulses at times, t, t+ T t+T2,etc., in the past. The apparent direction of the wave front is at an angle whose sine is VT /.d where V is the velocity of sound at d the'spacing between speakers.

Ina room, the spacing, a, may be ten or twelve feet.

If we want thesound toccme from an angle of, say 30?,

"by-a wire of magnetic material as shown in Fig. 3. The

wire 20 (or thin ribbon) could be driven at several points'hy electro-magnetsZZ, each carrying signals from a 'group of "tone generators. Pick ups 24 and 26 atthe 4 ends of the wire would lead to separate amplifiers and speakers, 28 .and 30 respectively.

In Fig. 3, six drivers are shown which might be arranged to accept signals covering about two octaves each, on one side. Thus, an amplifier might deliver to the driver on the left, the signals from Ci Cfi Di F3 Fit etc.

By control of the damping along the wire and at the ends as at 23 and 25 the relative intensity of the signals at the two speakers as well as a residual reverberation can be provided. Damping may be accomplished in ways well known in the acoustic art, as for example by means of felt or rubber cushions pressing lightly against the wire.

Some practical considerations should be noted. The delay along the line is to be .005 second or so; this means that the wire will have a natural frequency of about cycles. A convenient length would be twenty inches. Then a Wave of 1'0;000 cylces will be 0.4 inch long. The drivers and pickups must then act on a portion of the wire that is of the order of 0.2 inch (half wave) or less.

Another obvious method of delay is to record and play back froma magnetic drum or other moving magnetic material, .as shown in Fig. 4.

Magnetic drum 30 has spaced around its circumference a series of magnetic heads; one of these, 32, will record the signals from a unit group of tone generators, corresponding to any one of the four groups shown in Fig. 1. Two spaced pickups, 34 and 36, lead to respective amplifier-speaker units, like units 28 and 30 of Fig. 3. An erase head 38 leaves the magnetic track always clear for signals from recording head 32. The rotary speed of the drum and the spacing of the pickup head 34 and 36 determine the respective delay. A similar track will be needed for each group of tone generators, all of the first pickup heads corresponding to 34 being connected to speaker No. 1 and all of the second heads, corresponding to 36, being connected to speaker No. 2. This arrangement is very flexible, as the spacing may be readily set to any desired value, and a single drum may contain any number of parallel tracks in side-by-side relation and may be driven by the same motor as the tone generator of my aforementioned copending application, or may even be an additional section on the tone drum.

it will thus be seen that the invention discloses means of directions, .thereby giving the music of the organ a spatious and live feeling.

It Willbe apparent that the embodiments shown are only exemplary and that various modifications can be made-in construction and arrangement within the scope ofmy invention as defined in the appended claims.

I claim:

1. In an electric organ having a plurality of units each being capable of generating signals corresponding to different spacially arranged pipes or pipe groups of a pipe organ to be simulated, an output for each ofsaid units, electroacoustic transducer means including .at least two loud speakers spaced according to the maximum span of the divisions of a pipe organ to be simulated, and circuit means coupling said outputs to both of said transducer means including means differentially dividing each of the generated signals between each of said units and both of said transducer means for simultaneously apportioning the signals generated by each of said units between said transducer means toproportion. the intensity of the sound'of'the various divisions of theorgan to be simulated between-said transducer-meansso that the sound will appear to come from a predetermined point on a line betweensaid transducer means in accordance with theproportionate intensity. of the output from each of said transducer means inany given division.

2. in an electric organ as claimed in claim 1 wherein said means differentially dividing each generated signal comprises a differentially dividing impedance network.

3. In an electric organ as claimed in claim 1 wherein said means differentially dividing each generated signal comprises means for dilferentially delaying each of said signals and means for supplying each of said differentially delayed signals between said transducer means, signals to one of said electroacoustic transducers and its delay counterpart to another of said electroacoustic transducers.

4. In an electric organ as claimed in claim 3 wherein the means for differentially delaying said sginals comprises an elongate mechanical member, means for producing transverse acoustic vibrations in said member at spaced points along its length, said vibrations corresponding to said signals, and means for reconverting said vibrations to second electric signals at at least two spaced points on said member, and means for conducting said second electric signals respectively to said electroacoustic transducer means.

5. In an electric organ as claimed in claim 3 wherein the means for difierentially delaying said signals comprises a rotary magnetic surface, means for producing a sound track of said signals on said surface, and means for picking up said signals at respective different points on said sound track.

References Cited in the file of this patent UNITED STATES PATENTS 1,852,624 Nicolson Apr. 5, 1932 1,877,317 Hitchcock Sept. 13, 1932 2,098,372 Blumlein Nov. 9, 1937 2,273,866 Holst et al. Feb. 24, 1942 2,274,199 Hammond Feb. 24, 1942 2,419,894 Hayes Apr. 29, 1947 2,481,576 Boer Sept. 13, 1949 2,599,510 Campbell June 3, 1952 2,600,870 Hathaway et al. June 17, 1952

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