US 2481911 A
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Sept, 13, 1949. K. DE BOER ETAL 2,431,911
DEVICE FOR ADJUSTING THE STEREOPHONIG EFFECT IN DEVICES FOR STEREOPHONIC TRANSMISSION Filed April 26, 1946 7 PRELIMINARY AMPUHER F AMPLIFIER RI K v ARY Ma Pfzmg 1 AMPLIHER L2 V EVg INVENTORS KORNELIS DE BOER 8: ROELOF VERMEU LEN GENT Patented Sept. 13, 1949 DEVICE FOR ADJUSTING THE STEREO- PHONIC EFFECT IN DEVICES FOR STEREOPHONIC TRANSMISSION Kornelis de Boer and Roelof Vermeulen, Eindhoven, Netherlands, assignors, by mesne assignments, to Hartford National Bank and Trust Company, Hartford, Conn, as trustee Application April 26, 1946, Serial No. 665,028 In the Netherlands May 20, 1942 2 Claims. 1
This invention relates to a device for adjusting the stereophonic eect in devices for stereophonic transmission, in which the sound to be transmitted is received by means of two microphones which are mounted in an artificial head and respectively connected to a transmission channel.
In order to conserve the sense of direction in electrically transmitting sound the sound must be supplied to both ears of the listener with the correct relative time and intensity diiierences. This can be realised by replacing in the pick-up space the absent listener by a so-called artificial head carrying two microphones at the ears, each microphone feeding, through an amplifier and transmission line or radio link (channel) of its own one of two head phones on the ears of the listener or two loudspeakers placed at a suitable distance.
In such a stereophonic sound installation the perceived location of the sound image depends on the intensityand time diiierences occurring at the microphones of the artificial head. The perceived deviation of the sound image increases as these differences are greater and it will be appreciated that the deviation is larger as the diameter of the artificial head is larger. For various purposes the diameter may vary irom about to 22 cm. Now it is objectionable for various purposes to have various artificial heads at ones disposal so that it is desirable that one and the same artificial head may be sufficient for all cases.
According to the invention this is achieved by coupling together the two transmission channels through an adjustable network of impedances in such manner that the deviation of the represented sound image can be increased or reduced at will.
When making use of the invention we obtain electrically the eiiect of an artificial head having a variable size, which yields a great simplification of the recording technique. The device according to the invention can be directly used at the transmitter side. However, the use of this device is also of importance for reproduction. In fact, the sound records may in all cases be given an exaggerated stereophonic effect and during reproduction the stereophonic eiiect may be ad- .iusted at will in accordance with the conditions imposed by the reproduction space.
The sole figure of the drawing represents one form of construction of a device according to the invention used in a stereophonic installation. M1 and M2 represent two microphones placed on either side of an artificial head K. Each microphone is connected to a reproducing device, the loudspeaker L1 and Le respectively, through the intermediary of a transmission channel including a preliminary amplifier V1 and V: respectively and an output amplifier EV1 and EV: respectively. The two transmission channels are interconnected through a network in T-connection comprising three adjustable resistances R1, R2 and R3. If R3=8 the two channels are not coupled together and the deviation of the sound image during reproduction is mainly determined by the distance between the microphones M1 and M2, i. e. by the diameter of the artificial head. If, in contradistinction thereto, both R1 and R2 are zero, so that the two channels are completely coupled together, the loudspeakers L1 and L2 receive electrical sound oscillations without relative timeor intensity differences with the result that no deviation of the sound image occurs. By adjustment of the resistances R1, R2 and R3 to a value lying between the extreme values just referred to any desired deviation of the sound image can be adjusted.
Moreover it is still remarked that the device according to the invention may also be used in sound-film installations designed for stereophonic recording or reproducing purposes in which case sound-film recording and reproducing devices are interposed in the transmission channel.
1. A binaural transmission system comprising an artificial head having a predetermined diameter, a pair of microphones disposed at opposite sides of said head to simulate the aural response of ears, a pair of receiving devices, a first transmission channel connecting one of said microphones to one of said devices, a second transmission channel connecting the other of said microphones to the other of said receiving devices, and means to vary efiectively the diameter of said head, said means including an adjustable impedance network intercoupling said first and second channels, said network being constituted by three variable resistors arranged to form a T type section.
2. A binaural transmission system comprising an artificial head having a predetermined diameter, a pair of microphones disposed at opposite sides of said head to simulate the aural response of ears, a pair of loudspeakers, a first amplifying channel connecting one of said microphones to one of said loudspeakers, a second amplifying channel connecting the other of said microphones to the other of said loud speakers, and means for varying the effective diameter of said head, said means including an adjustable impedance network intercoupling said first and second channels, said network being constituted by three variable resistors arranged to form a T type section.
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UNITED STATES PATENTS KORNELIS DE BOER. Number Name D t ROELQF VERMEULEN 1,624,486 Fletcher Apr. 12, 1927 5 2,019,615 Maxfield Nov. 5, 1935 REFERENCES CITED 2,093,540 Blumlein Sept. 21, 1937 H 2,114,019 Friebus Apr. 12, 1938 The following references are of record in the 2126929 Snow et a1 "In" Aug 16, 1938