US2008825A - System for reproducing sound from a sound record - Google Patents

Description

July 23, 1935. J. H. HAMMOND, JR 2,008,825

SYSTEM FOR REPRODUGING SOUND FROMA SOUND RECORD Filed Oct. 14, 1931 5 Sheets-Sheet 1 July 23, 1935. J. H. HAMMOND, JR 2,008,825

I SYSTEM FOR REPRODUCING SOUND FROM A SOUND RECORD I Filed Oct 14, 1931 s Sheets-Sheet 2 July 23, 1935. J. H. HAMMOND, JR

SYSTEM FOR REPRODUCING SOUND FROM A SOUND RECORD Filed Oct. 14, 1931 5 Sheets-Sheet 3 ATTORNEY S Patented July 23, 1935 PATENT. OFFICE SYSTEM FOR BEPBODUCING SOUND FROM A SOUND RECORD John Hays Hammond, In, Gloucester, Mass.

Application October 14, 1931, Serial No. 568,688

17 Claims. (01. 179-100.!)

This invention relates to amplifying systems and provides a system for separating electrical energy into a plurality of frequency groups and for amplifying the energy in any or all of the groups in accordance with the strength of the applied energy in that group. The outputs of these systems may be combined and reproduced by a single means, or the output of each system may be reproduced independently.

The invention provides a method by which various frequency groups may be amplified independently, the amplification or gain ratio being greater for strong signals than for weak ones.

signals.

The system may be used in connection with the pickup from a phonograph or from a photographic sound record and may also be applied to a piano in order to accentuate the high frequencies and give them a greater range of amplification than the low frequencies.

The construction of a. piano is such that the high notes are produced by thin short strings and therefore have a relatively small amount of energy. By using the present system for these notes it is possible to expand the volume range and to cause the high frequency notes to be relatively stronger when the piano is played forte and weaker when it is played pianissimo, thus producing a more balanced effect in the music.

The invention also consists in certain new and original features of construction and combinations of parts hereinafter set forth and claimed. Although the novel features which are believed to be characteristic of this invention will be particularly pointed out in the claims appended hereto, the invention itself, as to its objects and advantages, the mode of its operation and the manner of its organization may be betterunderstood by referring to the following description taken in connection with the accompanying drawgraph.

Fig. 2 illustrates diagrammatically a modified form of the invention.

Fig. 3 is a front elevation partly in section of a piano constructed in accordance vention.

with thisin- Like reference characters denote like partsin the several figures of the drawings.

Inthe following description and in the claims, parts will be identified by specific names for convenience, but they are intended to be as generic 5 in their application to similar parts as the art will permit.

Referring more particularly to the form of the invention shown in the accompanying Fig.

1, a phonographic pick-up i0 is connected to one side of a double-pole double-throw switch II, the other side of which is connected through a transformer 12 to a photoelectric cell l3 of a talking moving picture projector. This cell is illuminated by means of a lamp II the light from which 15 is focused by means of a lens 15 through an aperture 15 in an aperture plate 11 upon the sound record of a moving picture film It. The light transmitted through this film is then focused by means of a lens 15 upon the photoelectric cell 13.

The blades of the switch II are connected through a transformer 21 to three filter circuits 22, 23, and 24. The circuit 22 is a high pass filter allowing only the high frequency currents to be transmitted. The filter 23 is an intermediate pass filter and the filter 24 is a low pass filter. Each of these circuits is connected to the input circuit of a space discharge means 25, 26 and 21, respectively. In the output circuit of these de- 30 vices are the primaries of three transformers 3|,

32 and 33, the secondaries of which are connected to potentiometer-s 34, 35 and 36, respectively. These potentiometers are connected across the input circuits of three amplifiers 31, 38 and 35 39. The output circuits of these amplifiers are connected through transformers 4 I, 42 and 43, respectively, to the input circuits of three push-pull amplifiers 44, I5 and 4B. The output circuits of these amplifiers are connected through trans- 4o formers 41, 48 and 48 to the moving coils of three loud speakers, 51, 52 and 53. The field windings 54, 55 and 56 of these loud speakers are energized by suitable sources of power. The three loud speakers 5], 52 and 53 may be of difierent sizes, each being suitable to the frequency range which it is to reproduce.

Each of the amplifiers 31, 38 and 39 consists of a space discharge amplifier 6| in the output circuit of which are the primaries of the transformers I], I2 and I3. Across the primaries of these transformers are resistances 62. The grid return circuits of the space discharge means ii are connected through resistances 63 and batteries 54 to the movable contacts of potentiom- 55 eters 65. The resistances 63 are shunted by condensers 3i and by rectifiers 31, which are in series with the secondaries of transformers l3. The primaries of these transformers are connected in the plate circuits of space discharge amplifiers II, the grids of which are connected through blocking condensers I2 to the input circuits of the space discharge devices SI.

In the operation of the form of the invention shown in the accompanying Fig. 1 the switch II is thrown downwhenit isdesiredtousethe phonograph, and is thrown up when it is desired to use the moving picture projector. In either case, the energy received passes through the transformer 2I to the three filter circuits 22, 23 and 24. These separate out the energy of various frequency groups, the filter 22 allowing the high frequencies to pass; the filter 23, the intermediate; and the filter 24, the low frequencies. These three frequency groups are then amplified by the space discharge means 25, 23 and 21, the output of which passes through the transformers 3I 32 and 33 to the potentiometers 3|, 35 and 33, where any desired amount of energy from each of the groups may be selected.

The energy from these potentiometers then passes into the input circuits of the space discharge amplifiers iI of the amplifiers 31, 33 and 33. Parts of these energies pass through he blocking condensers I2 to the input circuits of the space discharge amplifiers II. The output currents from these amplifiers then pass through the primary windings of the transformers 53. The currents in the secondaries of these transformers are rectified by the rectifiers 31 and fiow in the direction of the arrows through the resistances 63. This causes potential differences to be built up across these resistances which are proportional to the cln'rents flowing therein and therefore proportional to the input signal strength of each of the amplifiers. These potential dif ferences cause a decrease of the biases of the space discharge devices SI, thereby decreasing their impedances and'increasing their amplification ratios. It is thus seen that the amplification or gain ratios of these devices vary in accordance with the input signal strength, being greater for strong signals than for weak ones. By making the resistance 53 zero and by reducing the potential of the battery 64 to that for normal bias any of the stages 31, 33 or 39 may be made to act as normal amplifiers.

The outputs of the space discharge devices 3| pass through the primaries of the transformers I, 42 and I3, and through the resistances 82. These resistances are of the order of the internal impedance of the space discharge devices GI, and maintain the frequency characteristics of these devices independent of the amplitude characteristics. The currents from the secondaries of the transformers II, 32 and 43 are amplified by the push-pull amplifiers ll, 45 and 46. The amplified outputs from these devices then pass through the transformers l1, l3 and 43 to the loud speakers 5|, 52 and 53, where the high frequency, intermediate frequency, and low frequency tones are reproduced in the usual manner.

Itisthusseen thatbythissystem the high, intermediate, and low frequency tones are amplified separately, each amplification being accomplished by means of amplifiers in which the'amplification or gain ratios vary in accordance with the input signal strength, being greater forstrongsignalsthanforweakones. Inthis way, each group of tones is amplified independently and to the best-advantage, each group being reproduced by a separate loud speaker which is constructed to work most'eiliciently tage of this system is that by having three separate amplifiers a loud note in any particular frequency group will notcause notes in the other frequency groups to be amplified out of their true proportions. In this way it is possible to prevent what is known as blasting, which is caused by one very loud note causing the amplifier to amplify the whole scale instead of that particular note.

Referring to the modified form of the invention Fig. 2 shows an amplifying system which receives its energy from a mechanical pick-up III, or a photoelectric cell III. This cell receives light from a lamp II2 which is energized from a source of power III. The light from this lamp is focused by a lens III through an aperture 5, in an aperture plate IIB, upon the soimd record of the moving film Ill. The light which passes through this film then strikes the photoelectric cell III. This cell is connected through a transformer II8 to two contacts I2I of a double-pole double-throw switch I22, the other contacts I23 of which are connected to the mechanical pick-up III]. The blades of the switch I22 are connected to the primary of a transformer I23, the secondary of which is connected to two filter circuits I25 and I26, the former being a high pass filter, which allows onb the upper harmonics to pass, and the latter being a low pass filter which allows only low frequencies to pass. These filter circuits are connected to the primaries of two transformers I21 and I23, the secondaries of which are connected to potentiometers I3I and I32, respectively.

The potentiometer I3I is connected in the input circuit of a space discharge amplifier I33. The

grid return of said amplifier includes resistance I42 and batteries I31 and I38 and is connected to a potentiometer I36. A control amplifier I35 is also connected across potentiometer I3I through a stoppage condenser I43. The output circuit of this amplifier I35 is connected through a transformer I 45 to a rectifier circuit including a rectifier I46 and resistance I42. The output circuit of the space discharge means I33 is connected to the primary of a transformer I" across which is a resistor I48, for thepurpose of keeping the input resistance of the transformer practically constant and independent of the impedance change between the plate and filament of amplifier I33.

The potentiometer I 32 is connected in the input circuit of a space discharge amplifier I5I, the output circuit of which is connected to the primary of a transformer I52. The secondaries of the transformers I I1 and I 52 are in the input circuits of two space discharge means I53 and I, the output circuits of which are connected in parallel to the moving coil of a loud speaker I55, the field winding I 56 of which is energized fromasource ofpower I51.

tions from the loud speaker I55 are transmitted In the operation of the form of the invention shown in the accompanying Fig. 2, when it is desired to use the pick-up IIII the switch I22 is thrown down, and when it is desired to use the photographic sound record I", the switch I22 is thrown up. In either case, energy is fed to the transformer I24 from the secondary of which it passes to the two filter circuits I25 and I26. The former allows only the high frequencies to pass. The energy from this circuit passes through the transformer I21 to the potentiometer I3I, where any desired amount may be fed to the input circuit of the space discharge means I33. Some of the energy in thiscircuit passes through the stopping condenser I43 to the control amplifier I35. The output from this amplifier passes through the transformer I45 and is rectified by the rectifier I46, causing a D. C. current to flow in the direction of the arrow, through the resistor I42. The amount of current flowing through this resistor varies the voltage drop therein. Thus, as this current is increased the potential drop of resistance I42 will be increased which causes a decrease of the negative potential of the grid of the space discharge amplifier I33 allowing more current to pass therethrough. In this way an increase of amplification for loud signals is obtained. The energy from the transformer M1 is then amplified by the space discharge means I53, the output of which passes through the moving coil of the loud speaker 55, thereby causing the high frequency tones to be reproduced in this loud speaker. The volume of these tones is controlled by the potentiometer I3I and the amplification varies according to the strength of the original tones so that the amplification ratio is greater for louder tones than for weak ones.

The low frequencies are passed through the filter I26 and the transformer I29 to the potentiometer I32. The energy from this potentiometer is amplified by the space discharge amplifier I5I, the output of which passes through the transformer I52 and is applied to the space discharge amplifier I54, the output of which passes through the moving coil of the loud speaker I55 where it is combined with the output of the space discharge means I53. Thus the low frequencies are reproduced in the loud speaker I55, the volume being controlled by the potentiometer I32. These frequencies, however, are amplified by a straight system of amplification so that the tones of high and low intensities are amplified in the same ratio.

Referring to Fig. 3 a piano I6I is shown which is provided with the usual sound board I62 strings I63 and action I64. Mounted on the cross bracing I65 of the piano is the electric magnetic pickup device H0, such as that shown in Fig. 2. The armature I66 of this device is secured to the sound board I62 and the winding is connected to the primary of the transformer I24 of Fig. 2. Secured to the under surface of the sound board I62 is the loud speaker I 55 which to the sound board I62, thus causing a regenerative action and also adding the tonal qualities of the sound board to the reproduced music.

This system is particularly useful as applied to a piano inasmuch as the higher frequency notes are ordinarily of .relatively low intensity and do not produce as 'much audible response as the low notes unless struck-with greater force. The present system avoids this difiiculty and permits the notes of the higher register to be amplified in any desired ratio with respect to the lower frequency notes whereby various audible effects may be obtained.

Although only a few of the various forms in which this invention may be embodied have been shown herein, it is to be understood that the invention is not limited to any specific construction, but might be embodied in various forms without departing from the spirit of the invention or the scope of the appended claims.

What is claimed is:

1. A system for the production of sound from a sound record'comprising in combination a'sound record, a pick-up device therefor, a receiver of sound energy, a plurality of paths connecting said pick-up device and receiver, means in said paths for passing different frequency bands of the sound energy, and means in at least one of said paths controlled by the dynamics of the frequency bands passing through said path for controlling the intensity of the sound passed through said path.

2. A system for producing sound from a sound record comprising a pick-up device, three amplification channels, means for separately selecting the high frequency, intermediate frequency and low frequency tones and applying the selected tones to the respective channels, means for independently controlling the gain ratio of each of said channels by the average intensity of energy passing through the particular channel and means for producing sound effects thereby.

3. A system for producing sound from a sound record comprising a pick-up device, a plurality of amplification channels, means for separately selecting the high frequency, intermediate frequency and low frequency tones and applying the selected tones to the respective channels. means controlled by the average input energy of each channel for independently controlling the gain ratio thereof so that the energy range is expanded and means for producing sound effects thereby.

4. A system for producing sound from a sound record comprising a pick-up device, a plurality of amplification channels, means for separately selecting various frequency ranges and applying the selected frequencies to the respective channels, means controlled by the average input energy in certain of said channels for independently controlling the gain ratio thereof so that the energy ratio of said certain frequency ranges is expanded and means for producing sound effects in accordance with the energy of each of said channels.

5. A system for producing sound from a sound record comprising a sound record, a pick-up, a pair of amplification channels, filter networks associated therewith whereby the high and low frequency tones are separately amplified in said channels, means for varying automatically the gainratio only of the high frequency channel in accordance with the strength of signal therein and means for combining the sound effects from the various channels.

6. In a sound producing system, a piano having a sounding board and strings, pick-up means for picking up vibrations therefrom, filter circuits for separating the high and low frequency energy derived from said pick-up means, means for separately amplifying said high and low frequency energies and means for controlling the ratio of said energies to produce the desired sound eifect.

7. In a sound producing system, a piano having a sounding board and strings, pick-up means for picking up vibrations from said sounding board, filter circuits for separating the high and low frequency energy derived from said pick-up means, means for separately amplifying said high and low frequency energies, means for va-, rying the amplification ratio of the high frequency energy in accordance with the strength of said energy and means for producing a sound effect by the combined action of the high and .low frequency energies.

8. In a phonographic system, a source of sound energy, a receiver of sound energy, a plurality of paths between said source and said receiver, means in said paths for passing different frequency bands of the sound energy, and means in at least one of the paths controlled by the dynamics of the frequency bands passing through said path for modifying the dynamics of the sound passing through that path.-

9. In a sound reproducing system, a sound record, a pick-up device therefor, a speaker for delivering sound, a plurality of paths between said pick-up device and said speaker, means in said paths for passing different frequency bands of the sound energy, and means in at least one of the paths controlled by the dynamics of the fre-- quency bands passing through said path for expanding the dynamics of the sound passing through that path. I

10. The method of reproducing a recorded selection from a sound record which comprises picking up the selection from said record, dividing said selection into different frequency bands and separately expanding the dynamics of at least the highest frequency band.

11. In a phonographic system, the method of reproducing a recorded selection from a sound record which comprises picking up the selection from said record, dividing said selection into different frequency bands and separately modifying the dynamic contrast between the loud and soft notes of at least one of the frequency bands.

12.Inaphonsraphicsystem,themethodof the dynamics of a selection which comprises picking up said'selection, parately modifying the dynamic contrast between loud and soft notes in each range of the diiferent registers of the entire audible spectrum and delivering the modified selection into an output device.

13. The method of reproducing a recorded sound selection which comprises picking up said selection, separately expanding the dynamic range between the loud and soft notes of the different registers of the entire audible spectrum and translating the modified selection into sound waves.

14. The method of reproducing a recorded sound selection which comprises picking up said selection, expanding the dynamic range of the higher pitch notes while leaving the dynamic range of the lower pitch notes substantially unchanged and translating the modified selection into sound waves. a

15. In a phonographic system, the method of improving a sound selection which comprises picking up said selection, modifying the dynamic range of a part of the audible spectrum while leaving the dynamic range of the rest of the audible spectrum substantially unchanged, and delivering the modified selection into an output device.

16. In a system of amplifying audio frequency signals, means for translating a signal from a sound record, a pair of amplifying circuits, filters associated with each of said circuits and connected with said translating means, one of said filters being adapted to pass the high frequency components of the applied signal and the other of said filters being adapted to pass the low frequency components of the applied signal, and means in each of said amplifying circuits controlled in accordance with the intensity of the signal in said circuit for varying the gain ratio of said amplifier whereby the volume ratio of each of said components is expanded.

17. In a sound record system, an originator of sound energy, a receiver for said sound energy, a plurality of paths connecting said originator and said receiver, filter means in each of said paths for passing different frequency bands through said paths, an amplifier in each path, and means in each path controlled by variations in intensity of the sound energy in that path for controlling the gain ratio of the amplifier in that path.

. JOHN HAYS HAMMOND, JR.

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