US2967447A - Apparatus for translating electrical musical tone signals into sound - Google Patents

Description

Jan. 10, 1961 J. M. HANERT 2,967,447 APPARATUS FOR TRANSLATING ELECTRICAL MUSICAL TONE SIGNALS INTO SOUND Flled March 6, 1957 2 Sheets-Sheet 1 VOICE COlL TEiZMlNATlONS OF ELECTZKAL MUSlCAL INSTRUMENT, PHONOGIZAPH,

EADIO, OR o NHCIZOFHONE AMPLIFIER ELECTEO-MECHAI\HCA\ ELECTEICAL.

ZEVEEBEEATIVE SOUND WAVE DELAY APPARATUS Jan. 10, 1961 J. M. HANERT 2,967,447

APPARATUS FOR TRANSLATING ELECTRICAL MUSICAL TONE SIGNALS INTO SOUND Filed March 6, 1957 2 Sheets-Sheet 2 FFZEQUENCY- CYCLES PER SECOND RELA'HVE INTENSITY-DECIBELS FEEQUENCY- CYCLES PER SECOND RELATIVE. lNTENSlTY-DEClBEL5 FEEQUENC.Y cxcLEs PER SECOND 50% M. 35M

EELAT\VE (NTENSITY-DECIBELS United States Patent APPARATUS FOR TRAN SLATIN G ELECTRICAL MUSICAL TONE SIGNALS INTO SOUND John M. Hanert, Des Plaines, Ill., assignor to Hammond Organ Company, Chicago, 111., a corporation of Delaware Filed Mar. 6, 1957, Ser. No. 644,266

Claims. (Cl. 84-1-26) My invention relates generally to electrical musical instruments and more particularly to the transmission of electrical musical tone signals and the translation of the tone signals into sound, to produce novel binaural chorus and reverberation effects, and incidentally to improve the attack and decay characteristics of the tones.

It is the primary object of the invention to provide a method and apparatus for producing binaural reverberation effects without objectionable frequency distortion and nulls, whereby electrical musical tone signals delivered from tone signal generators of electronic organs, sound on film, phonograph recordings and microphonic pickups for public address systems, may be translated into sound having a binaural effect.

Other objects will appear from the following description, reference being bad to the accompanying drawings in which:

Fig. 1 illustrates a preferred form of the invention in schematic wiring and block diagram form;

Fig. 2 is a frequency response curve of the reverberative component of a known reverberation apparatus;

Fig. 3 is a frequency response curve of the output of the known reverberation apparatus combined with a nonreverberative output of a tone signal source;

Fig. 4 shows two curves illustrating the frequency response characteristics of music being heard respectively by the ears of a listener, when the music from a monaural source is heard through two separate electro-acoustic channels, one transmitting the musical signal directly from the source and the other transmitting the signal from the source through a sound delay reverberation apparatus.

There have been a number of attempts made to secure reverberative acoustic output from an electrical signal source initially lacking in reverberation, as shown for example, by the patent to S. J. Begun No. 2,327,956 and the patent to L. Hammond No. 2,230,836. The apparatus shown in the Hammond patent has proved satisfactory in thousands of installations but has a number of undesirable features in that the frequency response of the output is not uniform, but instead, displays such a high deviation from the desirable uniform frequency reresponse that in fact it had nulls, that is, certain frequencies are not transmitted by the apparatus. This is shown by the frequency response curves of Figs. 2 and 3, Fig. 2 being for the reverberation apparatus alone and Fig. 3 being of the reverberative and electrically superposed direct signals.

The apparatus of the patent to Begun likewise does not have uniform frequency response in its acoustic output for the following reasons.

For example, if a tone signal having a frequency of 440 c.p.s. is recorded on a magnetic tape moving 44 inches per second, one cycle will extend 0.10 of an inch along the tape. Therefore, if the length of the tape between the air gap of the recording head and the air gap of the pickup head is any odd multiple of 0.05 of an inch, the signal at the recording head will be at its "ice positive peak while the signal at the pickup head will be at its negative peak phase difference), so that when the two signals are of equal amplitude and are electrically mixed, they will completely cancel one another. On the other hand, if the length of the tape between the recording and pickup heads is any even multiple of 0.05 of an inch, the signals at the two heads will be in phase and reinforce one another. Such irregularities in response cannot be tolerated by the musically trained ear.

The particular example chosen for illustration is not unique, because no matter what spacing of the recording and pickup heads may be employed there will be certain bands of frequencies attenuated and intermediate bands will be reinforced resulting in an undesirable formant effect.

The frequency response curve of the system would appear as a series of scallops, similar to a curve showing the output of a conventional full wave rectifier. This type of frequency response tends to produce an extensive series of tone formants, or resonances, in the quality of any harmonically complex tone. This is very unnatural sounding.

The disadvantages of both the Hammond and Begun apparatuses stem from the fact that the original electrical tone signal and the tone signal produced by the reverberation apparatus are electrically superposed and the vectorial addition of the two alternating current signal waves inevitably results in cancellation at certain frequencies and augmentation in amplitude at other frequencies, depending up the relative phase angles and relative amplitudes of the reverberative and original or direct signal.

Furthermore, in each of these types of reverberation apparatus there is a pronounced directional effect in that the combined direct and reverberative signals are translated into sound as a single signal, and even if the electrically superposed reverberative and direct signal were translated into sound through two or more speakers the effect would still be perceived by the listener as a single monaural sound devoid of presence.

The music is perceived merely as originating from the loud speaker as a point source of sound. As a result, music which was projected over these electrical reverberation systems sounded no better than a radio receiver reproducing music which originated in a reverberative hall. In fact, because of the undesirable nulls, the general effect rendered is even less satisfactory. The effect on the listener that he is actually present in a reverberative hall was not produced. This was due to the fact that there actually existed only a single signal or source of sound which was the electrical output of the superposed direct and reverberative signals transmitted by the amplifier.

Experience gained through many thousands of installations of the electrical reverberation apparatus of one of these types has shown that no array of speakers connected to the amplifier could remove this monaural deficiency in the sound produced.

In accordance with the present invention the direct electrical tone signal and the electrical tone signal forming the output of the reverberation apparatus are not electrically superposed, but instead, are separately amplified and translated into sound. In this way the otherwise unavoidable poor frequency response characteristics of the prior apparatus are avoided.

Due to the virtually infinite number of acoustic reflections from the various points on the walls of the enclosure as well as the propagation of sound from the various points on the speakers radiating surfaces, the resulting acoustical combination becomes a statistical summation of a virtually infinite number of waves of random rela,

tive phases adding according to the square root relation. On the other hand, if the direct and the reverberative signals are electrically superposed they add to produce the simple vector sum of the two alternating current signals coupled together electrically to form a single output signal which may be radiated as sound with a suitable loud speaker or system of loudspeakers. In the present invention, the acoustic addition of the original and the delayed signals results in a highly desirable statistical summation in which the direct and reverberative signals do not cancel each other.

In the preception of musical tones, as well as other sounds, the ears receive stimuli from entirely difierent sets of acoustical paths due to the reflections of the sound from the source through paths of varying length. The phases of identical frequencies stimulating the individual ears may be in any phase relation but the brain does not add these stimuli of the same frequency from the ears vect-orially, but instead, adds them in a more or less arithmetric manner, as will hereinafter be explained in connection with the discussion of the curve of Fig. 4.

In the prior art of the production of audio tones derived from a single source, the sound produced had the deficiency of being perceived as monaural. This deficiency is overcome by the present invention in that the speaker translating the reverberative signal commences to speak approximately 7 0 milli-seconds after the speaker connected directly to the source commences emitting sound, and upon the interruption of the signal supplied from the source the speaker connected directly to the source stops sounding immediately upon such interruption, while the speaker connected to the source through the reverberation apparatus will continue to sound 70 or more milli-seconds thereafter. This creates a genuine two source musical production and results in an extremely efiective binaural presence. This is highly effective not only as an adjunct to electrical musical instruments which are played by a musician, but is also of utility in greatly enhancing the music of high fidelity (hi-fi) phonograph systems, sound on film, radio, and microphone pickup for public address and other systems in which the reverberative effect is not sufficient, as for example if the surroundings are such as to lack the ability to cause natural reverberation.

The rich sonority and tonal depth which results by adding binaural reverberation to electrical tone signals derived from a single source becomes of inestimable value in the production of interesting and truly live music through the use of two loud speakers in a small non-reverberative room. Very fine musical results may be obtained in which the speakers are only four or five feet apart or even immediately adjacent each other. The binaural effect is achieved through the fact that the listener perceives that the sound is originating from several sources and that the sounds from these sources are not duplicates of each other but rather are of entirely different characteristics. One of these characteristics is the effect of a slight delay and reverberation, whereas the other of these characteristics is the eifect of no delay and no reverberation. These efiects are obtained on tone signals of the same frequency or pitch range and are not to be confused with the effect obtained when separate speakers are used for the low and high frequencies respectively, as in woofer-tweeter installations in which, by means of a suitable filtering mesh, the higher frequencies are transmitted to one or a group of speakers having good high frequency response, while the low bass frequencies are transmitted to another speaker, or group of speakers, having good bass response characteristics.

To be of most utility the apparatus of the invention must have its speakers spaced reasonably close to one another so that the listener receives sound from both speakers at approximately the same intensity and at approximately the same time, except for the delay introduced by the reverberation apparatus or other similar sound delay means.

From the foregoing general description of the method and apparatus employed in utilizing the invention, it will be apparent to those skilled in the art that the apparatus may assume a number of different forms. Fig. 1 shows diagrammatically and schematically one form of an apparatus incorporating the invention. In this figure the block 10 represents a source of musical tone signals such as an electronic organ, a phonograph, radio receiver, or the amplified output of a microphone. The output signals of the instrumentality 1%} are supplied directly to a speaker 12 and through a blocking capacitor C14 to the input terminals of a driver 16 of a reverberation apparatus 18. The driver 16 is an electromechanical transducer of either the electromagnetic or crystal type and the mechanical sound vibrations produced thereby are transmitted through suitable linkages 20 and 22 to a plurality of coil springs 24 which are suitably anchored at their lower ends and some of which may have their lower ends immersed in a damping fluid. The rightmost coil spring 24 has its lower end anchored to a mechanical-electrical transducer, indicated as crystal 26. Means such as knife-like blades 28 may be wedged between the successive turns of the springs to prevent damage to the crystal pickup 26 and the electromechanical transducer 16 due to shock while the apparatus is being moved.

This reverberation apparatus 18 is of well known construction, being more fully shown and described in the above mentioned patent to Hammond No. 2,230,836 and also in Hammond Patent No. 2,211,205, the latter relating principally to the spring locking mechanism for preventing damage during shipment of the apparatus.

The output of the crystal pickup 26 is transmitted through conductors 30 and 31, capacitors C32 and C33, respectively, to the grids of double triode 34. Both cathodes of this double triode are connected to ground through a cathode resistor R36 while grid return resistors R38 and R39 respectively connect the two grids to ground. The latter resistors have capacitors C40 and C41 parallel therewith respectively. Current is supplied to the plates of the double triode 34 from a suitable source, indicated as a terminal +265 v. of the power supply, through a filter comprising a resistor R44 and capacitor C46, as well as individual plate load resistors R48 and R49 respectively. The plates of the double triode are respectively coupled to the grids of a second double triode 50 through blocking capacitors C52 and C53 respectively. The cathodes of the double triode it) are connected by a capacitor C54 and are respectively connected to ground through resistors R56 and R57. The grids of the double triode 56 are connected to ground by grid return resistors R58 and R59 respectively. The plates of the double triode 50 are connected to a suitable source of plate current voltage, indicated as a terminal +265 v., through load resistors R60 and R61, respectively, and are coupled to the control grids of tetrodes 64 and 65 by blocking capacitors C66 and C67 respectively.

A suitable control grid bias viltage is supplied from a -19 v. terminal of the power supply through grid resistors R68 and R69. Spurious superaudio frequency signals are bypassed by capacitors C70 and C71 connected between the cathodes and control grids of the tetrodes 64 and 65 respectively. The screen grids of the tetrodes 64, 65 are maintained at a constant potential by connection of a +265 v. terminal of the power supply, while the plates thereof are connected to a 280 v. terminal of the power supply through the two halves of a transformer primary winding L1. The secondary L2 of this transformer has its center tap grounded and its other terminals respectively connected to the cathodes of the tetrodes 64 and 65 to provide negative feedback for the purpose of reduction of distortion. The tertiary winding L3 of this transformer is connected through a variable resistance R72 to a speaker 74. While the speakers 12 and 74 appear from the diagram to be spaced a substantial distance from one another they should, in fact, be placed rather close together so that the sound from both speakers, except for the delay introduced by the reverberation apparatus 18, will reach a listener at substantially the same time. In other words, there should be no substantial difference in acoustic delay in the transmission of the sound from the two speakers to the listener.

In the use of the apparatus shown in Fig. l the apparent binaural effects described above will be obtained due to the fact that the listener will hear the music from two different sources and will be able to discriminate between the effect produced, and that of hearing reverberative tones from one speaker. The music will appear to the listener as being live, that is, as if he were in the enclosure in which the music was being produced all around him.

The intensity of the output of the speaker 74 is preferably adjusted by means of the variable resistor R72 to equal that of the intensity of the output of the speaker 12, although such adjustment may be varied somewhat to suit the desire of the listener.

The undesirable poor frequency response characteristics of prior devices are not present in the practice of my invention because the acoustic outputs of the several speakers are always additive at all frequencies in accordance with the square root law of acoustics. Thus, if the intensity of the acoustic outputs of four speakers, each having an acoustic power output assumed to be unity, the aggregate acoustic power output of the speakers will not be perceived as being four times that of one speaker but, instead, the intensity will be the square root of four, namely, 2. In the particular structure disclosed herein if the speakers are assumed to have equal acoustic power outputs, the most probable intensity will be the square root of 2, namely, 1.4 times as great as the acoustic power output of one of the speakers.

The invention may be summarized by critical reference to Figs. 2, 3, and 4. Inasmuch as the variations in output intensity from the reverberative device occur at very closely related frequencies, that is, at frequencies which are spaced approximately 17 cycles apart, a frequency response curve for the entire audio response spectrum would have over a hundred reversals and would be impractical to show on a Single graph. In view of the fact that it is important closely to examine the phenomena occurring between reversals, the exemplary frequency range for the three curves shown in Figs. 2, 3, and 4, is between 200 and 300 c.p.s. It will be recalled that Fig. 2 shows the frequency response characteristic of a reverberation apparatus such as the type described and referred to in this application. It will be noted from Fig. 2 that there are at least seven small bands of frequencies which are inaudible as indicated by the fact that the intensity of the signal drops below approximately 5 decibels, which, under the conditions usually present for providing comfortable listening, is below the lower intensity range of audibility. From this curve it is readily apparent that an organist playing on an electrical organ with a pure flutelike tone quality would experience undesirable dead notes in playing, that is, depression of a key would not result in the production of the desired tone.

superficially, it might be thought that adding a signal component in which the frequency response was fiat would improve this undesirable frequency response condition. In the prior art, as for example in the said Hammond Patent No. 2,230,836, this addition is provided as shown in Fig. 1 of said patent with adjustable resistors 24. These resistors are effective to superpose the direct signal upon the reverberated signal, the latter having a frequency response characteristic similar to that of Fig. 2 of this application. Fig. 3 illustrates the resulting frequency response by employing such superposition of the direct and the reverberative components. An examination of Fig. 3 discloses that the violent attenuations of certain bands of frequencies which are productive of the undesirable nulls, referred to above, are still present.

It is therefore seen that adding the direct to the reverberative signals does not improve the poor frequency response of the reverberative transmission system. The nulls are still present.

The above mentioned nulls, shown in the frequency response characteristic of Fig. 3, may be caused by the vectorial cancellation of certain frequencies having direct and reverberated signals of opposite phase and of approximately equal amplitude. It is readily apparent from Fig. 3 that the addition of the direct component to the reverberated component is ineffective to improve the undesired frequency response characteristic shown in Fig. 2. It is also to be understood that no woofer-tweeter speaker installation, multiple speaker installation, or any reverberative or other acoustical surrounding, can be effective to reinstate the cancelled frequencies. This, of course, is because they are absent in the final signal produced when the reverberative and direct components are electrically superposed.

Fig. 4 comprises two curves, respectively in dotted and full lines, which are the frequency response characteristics taken in a normal small nonreverberative room in which two microphones wer'eprovi'ded and positioned and oriented as are the ears of-a listener. The sound pickup also includes a sound attenuating element placed between the microphones, corresponding, in attenuating effect, to the sound attenuating characteristics of the head of the listener. The sound was emitted by two independent and separate loud speakers, one of which was supplied with a reverberative electrical signal from a source, and the other of which was supplied with the direct or non-reverberative signal from the same source. As is characteristic of all frequency response data taken with a microphone in a room having reflecting walls, the response curve exhibits many high peaks, and low valleys produced in part by the standing wave phenomena caused by the walls of the room, and also by phase shifting effects caused by the moving cones of the speakers.

In the apparatus of this invention further peaks and valleys are caused by the reverberation device as shown by the curve of Fig. 2. However, a close examination of Fig. 4 reveals very interesting phenomena. It is seen that, despite the various peaks and nulls produced at the listeners two ears, there are no particular relations between them, and that a peak in the round heard by one car may very likely be accompanied by a null heard in the other ear. The curves of Fig. 4 show that at no frequency is there a null for both ears. To produce a null at both ears is virtually impossible because of the very pronounced tendency for the reflected signals from the various points on the walls of the room to add according to the square root law. As the room in which the signals are heard becomes larger and more complex, the contours of these variations in intensity tend to become less violent and the response at the two ears tends to become more nearly uniform. The net acoustic result of the listener perceiving the sound with both ears is remarkably smooth and exhibits a very desirable uniformity of loudness as the frequency of the electrical signal generating source is slowly varied. In examining Fig. 4 it is important to understand that no consideration need be given to phase relations occurring between signals of the same frequency as represented by the two curves. This is because, as explained before, the brain does not function in a manner vectorially to add the sounds perceived by the two ears, but rather, adds them logarithmically in a purely arithmetic sense due to the independent hearing mechanisms of the two cars. It is thus seen that the nulls which were present in the response curves of Figs. 2 and 3 are not present in the summation of the curves shown in Fig. 4. Furthermore, the latter curves shows that adding the direct component acoustically to the reverberative component results in reinstatement of the frequencies which are absent in the reverberated signal shown in Fig. 2.

The fact that the two ears hear the signals with different frequency response characteristics provides the listener with an apparent sense of binaural or stereophonic hearing. In others words, these differences in the frequency response curves, together with the delay in the initial onset of the reverberative sound, serve as a means through which the listener perceives that the source of sound is not a point source but rather emanates from several different points in the room to produce a spacial acoustic binaural effect, characteristic of hearing several musical instruments separated in space. In the apparatus of this invention this effect of presence is achieved by utilizing two independent loud speaker systems, one of which is differentiated from the other through the addition of reverberation and also through the addition of a time delay. These two elements are sufficient to cause the desirable binaural presence efiect even though the room in which the music is head is very small.

It is thus seen that the apparatus of this invention overcomes both of the deficiencies inherent in the prior art, namely, the non-uniformity of frequency response and the point source effect. in the beginning of this specification it was mentioned that monaural sound is readily identifiable by the listener, regardless of the acoustical surrounding, as beiru produced by some from of loud speaker, or public address system, which is reproducing the music which originated in sound reverberative halls. This is the characteristic which so many musicians and other people having musically sensitive ears refer to as canned music. In other words, the expression canned has the connotation that it is not the actual sound, but rather is a reproduction of the sound, that is being heard. It is this sensation of being a reproduction, as contrasted with the original sound, which has caused so much criticism of sound movies, radio receivers, and other monaural music. in hearing this reproduced music the listener does not actually feel that he is in the enclosure in which the musicians are located. In the apparatus of this invention this sensation of hearing canned music is entirely overcome. in fact, the effect of binaural presence is so strong as to cause the listener to experience a mental conflict between the perception of the sound he actually hears, which suggests the rich sonority of actually being present in an auditorium, and the obvious lack of presence as conveyed by the listeners eyes in viewing his small non-reverberative surroundings.

It is of great importance to understand that the results obtained by this invention are not the same as the binaural effects which are achieved by the use of two earphones respectively supplied with signals from a pair of microphones spaced and oriented as are the ears. In this latter earphone arrangement the effect of a binaural perception is created only for the single condition that the listener does not move his head. Motion of the head causes no change in the frequency response phenomena heard by the listener. This, of course, is unnatural because in a large auditorium the very slightest motion of a listeners head causes the frequency response to be violently shifted. In fact, moving the listeners head is the means by which he is enabled to localize the sources of the various sounds. In the present invention, in Which there are two separate loud speakers in an enclosure, the frequency response characteristics do violently shift when a listener moves his head. In other Words, the binaural efiect produced has a distinct genuine ness as opposed to the pseudo-binaural effect produced by the earphone system. With the apparatus of this invention there is in fact more than a single source of sound, indeed, there are two completely different sources of sound, albeit that both transmit the same frequency spectrum to produce the effect of a plurality of spacial sources, which they actually are. This fine effect is readily achievable with musical tone signals derived from any monaural source, such as electrical musical instruments, phonograph records, radio receivers, hi-fi systems, etc.

It cannot be overemphasized that the essence of the invention, in its preferred form, resides in the translation of an electrical musical signal into sound in the same acoustic region by transmitting the signal thereof to two independent channels, the output of one of the channels producing the music delayed and predominantly reverberative in character, while the other channel produces the music substantially Without delay and without reverberation.

in the foregoing, and in some of the claims, the phrase in the same acoustic region in referring to the positions of electroacoustic translating means is intended to mean that the speakers are located sufiiciently close together that the sound outputs thereof reach the listener at substantially the same time, allowing for the delay produced by the reverberation or time delay apparatus, as distinguished from location of speakers such that a distinct echo effect is heard from one of the speakers most remote from the listener. For simplicity in the foregoing description and in most of the following claims, the term speaker is used in the generic sense as meaning any electroacoustic translating means.

This application is a continuation-in-part of my copending application Serial No. 286,952, filed May 9, 1952 (now abandoned).

While I have shown and described particular embodiments of my invention, it will be apparent to those skilled in the art that numerous modifications and variations may be made in the form and construction thereof, without departing from the more fundamental principles of the invention. I therefore desire, by the following claims, to include within the scope of my invention all such similar and modified forms of the apparatus disclosed, by which substantially the results of the invention may be obtained by substantially the same or equivalent means.

I claim:

1. An apparatus for improving the musical acoustic output derived from a source of electrical musical tone Signals comprising two speakers located in the same acoustic region; a channel to transmit the signals from the source to one of said speakers, said channel including means to introduce a substantial reverberative time delay in the major portion of the acoustical output, said delay introducing means comprising a reverberative solid sound wave carrier, means for impressing the signal on the carrier and means for picking up the signal from the carrier a predetermined short interval after the signal is impressed upon it; and a second signal transmission channel coupling the source to the other speaker and operative to transmit the majority of the signal without said amount of time delay.

2. The combination set forth in olaim 1 in which the solid sound wave carrier comprises at least one helical coil spring.

3. The combination set forth in claim 1 in which the source produces signals varying at a vibrato rate, and in which the means for introducing delay operates to introduce a delay approximating one-half of the vibrato periodicity.

4. The combination set forth in claim 1 in which the solid sound wave carrier comprises a helically coiled spring, in which the means for impressing the signal on the carrier comprises an electromechanical transducer, and in which the means for picking up the signal from the carrier comprises a mechanico-electric transducer.

5. The combination set forth in claim 1, in which the References Cited in the file of this patent UNITED STATES PATENTS McCutchen Sept. 13, 1927 Hitchcock Sept. 13, 1932 0 10 Schreiber Feb. 20, 1934 Kellogg Oct. 15, 1935 Goldsmith Jan. 11, 1938 Hammond Feb. 4, 1941 Stack Mar. 9, 1948 Becker Jan. 7, 1958 FOREIGN PATENTS Germany May 31, 1955 Disclaimer -John M. Hamert, Des Plaines, I11. APPARATUS FOR TRANSLATING ELECTRICAL LKUSIOAL TONE SIGNALS INTO SOUND. Patent dated Jan.

Oct. 19, 1964:, by the assignse, H ammon 10, 1961. Disclaimer filed Org cm Company. Hereby enters this disclaimer to claims 1, 2 and 4; of said patent.

[Oyfioial Gazette N o'vember 24, 1964.]

2,967,44;7.-J07m M. Han

Disclaimer 1. APPARATUS FOR TRANSLATING wt, Des Plaines, Il

INTO SOUND. Patent dated J an.

ELECTRICAL MUSICAL TONE SIGNALS 10, 1961. Disclaimer file OTgcm Company. Hereby enters this disclaimer to claims 1, 2 an [Oyfioz'al Gazette N o vembey' 24, 1.964.]

(1 4-. of said patent.

(1 Oct. 19, 196i, by the assignee, Hammond

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