Four-channel Headphone

Abstract

A four-Channel headphone comprises a pair of left and right headphone body casings, a front channel speaker and a rear channel speaker respectively provided in each casing and electrical signal supplying means for supplying rear channel signals to the rear channel speakers with shifted phase. When the signals shifted in phase are reproduced and sounded from the rear channel speakers in the headphone body casings, the sounds produce a panoramic surrounding sound effect for a listener who uses the four-channel headphone.

Description

The invention relates to a four-channel headphone and, more particularly, to a four-channel headphone in which four speakers respectively corresponding to each of four channels are mounted for producing a panoramic surrounding four-channel sound effect which gives a listener an impression that he is entirely surrounded by sound.

In a system for reproducing an audio signal, there has recently been employed a reproducing apparatus including a four-channel tape or a four-channel record for reproducing a sound field which closely resembles to the original sound field. There have been proposed various arrangements of speakers in a reproducing apparatus for four-channel system. The most prevailing speaker arrangement is a so-called 2--2 system in which speakers for first, second, third and fourth channels are respectively disposed at left front, left rear, right front and right rear of the listener. In this system, four-channel signals have a sound image orientation corresponding to a sound source and different phases, levels and information contents in connection with reproducibility of a sound field. A listener placed in the center of this speaker arrangement has an impression that he exists at the center of the sound field surrounded by sound all around, due to a sound field effect produced by sound planes formed between respective speakers which reproduce and sound the four-channel signals.

With a view to affording this four-channel effect to a headphone, a four-channel headphone has been proposed. This headphone has four speakers in its two headphone bodies, namely two in the left headphone body and two in the right one and the respective speakers are adapted to reproduce four-channel signals. However, the four-channel headphone system is different from the system in which the speakers are arranged in a large space in a room to form a sound field in a room space, because in the headphone system both ears of the listener are respectively in tight contact with the left and right headphone bodies and each ear receives only sound produced in the space of either left or right headphone body. Consequently, in the four-channel headphone in which the left front and left rear speakers corresponding to the first and second channels are mounted on the left headphone body and the right front and right rear speakers corresponding to the third and fourth channels on the right headphone body, the sounds of the first and second channels are mixed together in the left headphone body and reaches only the left ear of the listener whereas the sounds of the third and fourth channels are mixed in the right headphone and reaches only the right ear of the listener. In this case, the sounds of the left side channel (the first and second channels) and those of the right side channel (the third and fourth channels) are not mixed in the air and neither the sounds of the left side channels nor those of the right side channels reach the listener's ear on the opposite side. Further, the headphone essentially has a limitation in its size and the two speakers mounted in either headphone body are relatively close to each other. This prevents the listener from having impresssion of spread of sound between the two speakers.

As a result, the prior art four-channel headphone is disadvantageous in that the left and right headphone bodies which have two speakers respectively reproduce sounds of four different channels but the headphone can only give the listener a binaural effect produced by the sound from the left headphone body and the sound from the right headphone body, and cannot give the listener a panoramic surrounding sound effect which gives the listener an impression that he is really and entirely surrounded by the sound. Further, the conventional headphone is disadvantageous in that the listener has a feeling that the sounds concentrate on his occipital region which is quite unpleasant to him.

The inventor of the present invention has discovered that if the signals which should be reproduced and sounded from the rear channel speakers, i.e., the second and the fourth channel speakers, of the above described four-channel headphone have been shifted in phase from the second and fourth channel signals which were originally to be reproduced, the listener using the headphone can obtain a truly effective panoramic surrounding sound effect. The reason for the above effect is theoretically quite unclear. It is presumed, however, that the effect is due to the construction of the headphone itself according to which the sounds of the first and second channels and those of the third and fourth channels respectively reach the left ear and the right ear separately, since in case in the room disposed with four-channel speakers the signals of the second and fourth channels are reproduced and sounded with their phases shifted from the signals of the second and fourth channels which were originally to be reproduced, it only gives the listener an unpleasant feeling, whereas the above described effect is produced in the headphone.

It is, therefore, a general object of the invention to provide a novel and useful four-channel headphone which has eliminated the above described disadvantages of the conventional headphone.

Another object of the invention is to provide a four-channel headphone which produces a panoramic surrounding sound field effect and gives a listener an impression of spread or expanse of sound.

A further object of the invention is to provide a four-channel headphone in which each pair of the speakers provided in each of the left and right headphone bodies reproduce and sound signals which have a phase difference between each other. According to the headphone of the invention, the listener has an impression that he is surrounded by sounds and has a feeling of reality which is much superior to the binaural effect produced by the prior art headphone. Further, the listener feels a spread of sound. Furthermore, he has no unpleasant feeling that the sound concentrates on his occipital region.

Other objects and features of the invention will become apparent from the description made hereinbelow with reference to the accompanying drawings, in which:

FIG. 1 is a schematic plan view of the speaker arrangement of the four-channel headphone according to the invention shown in its state in use;

FIG. 2 is an elevational view showing one embodiment of the four-channel headphone according to the invention;

FIG. 3 is a side view of the four-channel headphone shown in FIG. 2 taken along the line III--III;

FIG. 4 is a left side view of the four-channel headphone shown in FIG. 2;

FIG. 5 is a sectional plan view of the headphone taken along the line V--V of FIG. 4;

FIG. 6 is a circuit diagram of one embodiment of the electric circuit of the four-channel headphone according to the invention;

FIG. 7 is a circuit diagram of another embodiment of the electric circuit of the four-channel headphone according to the invention; and

FIG. 8 is a diagram showing a frequency-phase shift characteristic.

FIG. 1 shows a schematic plan view of the four-channel headphone according to the invention shown in its state in use. A four-channel headphone 10 generally comprises a left headphone body 11 and a right headphone body 12. In a casing 3 of the left headphone body 11, there are a first channel speaker 14 and a second channel speaker 15 mounted at positions at which a line connecting the centers of the two speakers runs substantially parallel to a line connecting through the front and back of the listener's head. Similarly, a third channel speaker 18 and a fourth channel speaker 19 are arranged in a casing 17 of the right headphone body 12 at positions at which a line connecting the centers of the two speakers runs substantially parallel to a line connecting the front and back of the listener's head. Signals which are applied to these first to fourth channel speakers 14, 15, 18, 19 are the same first to fourth channel signals as are applied to the conventional 2--2 system speakers disposed at left front, left rear, right front and right rear positions to the listener. The casings 13 and 17 are respectively provided in the middle of their outside surface with phase shifting slide switch knobs 20 and 21 to be described later.

One embodiment of a concrete construction of the four-channel headphone according to the invention with the above described speaker arrangement is illustrated in FIGS. 2 to 5. Throughout these figures, illustration is made only for the left headphone body 11. As to the right headphone body 12, description of a concrete construction thereof is omitted because the right headphone body 12 has exactly the same construction as the left headphone body 11 except only that the first and second channel speakers 14 and 15 are replaced by the third and fourth speakers 18 and 19.

The left and right headphone bodies 11 and 12 are connected with each other by means of a curved and elastic support plate 32 which is secured at either end thereof to holding frames 30 and 31 which, in turn, are respectively pivotally supported on the casings 13 and 14. The support plate 32 is covered with a head pad 33 made of a soft material. An electrical signal transmitting code 34 to be connected to a headphone jack of the reproducing apparatus is connected in the lower portion of the casing 13 of the left headphone body 11. A code 35 for transmitting the third and fourth channel signals extends from the upper portion of the casing 13 through the head pad 33 and is connected to the upper portion of the casing 14 of the right headphone body 12. The casing 13 and 14 are both provided with ear pads 36 and 37 made of a soft material at the surfaces which contact the listener's ears and portions of the head around the ears.

The ear pad 36 is of an annular shape with openings 38 which are large enough to receive the listener's ears. The speakers 14 and 15 respectively generally consist of magnetic poles 39 and 40, magnets 41 and 42 and diaphragms 43 and 44 which are respectively mounted on a unit mounting plate 45 with an angle of less than 180.degree. relative to each other as shown in cross section in FIG. 5. In the present embodiment, the angle made between planes which are vertical to the central axes of the magnets 41 and 42 of the speakers 14 and 15 is 150.degree. and the angle made between the directions of the center of radiation of sound which are equal to the central axes of the magnets 41 and 42 is 30.degree.. The speakers 14 and 15 are disposed at positions at which the line connecting the centers of the two speakers runs parallel to the line connecting the front and back of the listener's head as shown in the side view of FIGS. 3 and 4. The front surfaces of the diaphragms 43 and 44 are covered with an acoustic planes 46 made of a punching metal. The speakers 14 and 15 are separated from each other by partitions 47, 47 so that the sounds will not leak into the other speaker side on the rear side of the speakers 14 and 15 (on the side of the magnetic poles and the magnets). Between the two partitions 47, 47, there is provided a phase shifting slide switch 48 with its knob 20 exposed outside of the casing 13.

Nextly, the circuit diagram of the first embodiment of the electric circuit of each speaker including the phase shifting switch is shwn in FIG. 6. Terminals 60, 61, 62 and 63 for the first to fourth speakers 14, 15, 18 and 19 are respectively connected to amplifiers of the first to fourth channels in the reproducing apparatus through the code 34. As to the front channels, i.e., the first and third channels, the speakers 14 and 18 are directly connected to the terminals 60 and 62. The speakers 15 and 19 of the rear channels, i.e., the second and fourth channels are connected to the terminals 61 and 63 through phase shifting switches 48 and 49 respectively provided in the casings 13 and 17.

When the switches 48 and 49 are connected on the side of contacts a by means of the knobs 20 and 21, the speakers 15 and 19 are connected to the terminals 61 and 63 in the same phase with the original phase. Accordingly, the second and fourth channel signals are reproduced and sounded from the speakers 15 and 19 in their original phase. When, on the other hand, the knobs 20 and 21 are slid to connect the switches 48 and 49 on the side of contacts b, the speakers 15 and 19 are connected to the terminals 61 and 63 in opposite phase. Accordingly, the second and fourth channel signals are reproduced and sounded in a phase opposite to the original phase.

If, accordingly, the switch knobs 20 and 21 provided on the casings 13 and 17 of the headphone bodies 11 and 12 are operated to connect the switches 48 and 49 on the side of the contacts b, the second and fourth channel signals are respectively reproduced and sounded from the second and fourth channel speakers 15 and 19 of the headphone bodies 11 and 12 in opposite phase to the original phase of the second and fourth channel signals, i.e., with a phase difference of 180.degree.. The second and fourth channel signals have phases (normally, phases having slight phase differences .+-..DELTA..theta.) which are related with the first and third channel signals, so that the reproduced sounds of the second and fourth channels have a large phase difference (180.degree. .+-..DELTA..theta.) relative to the reproduced sounds of the first and third channels. Accordingly, if the listener applies the headphone body 11 containing the speakers 14 and 15 to the left ear and the headphone body 12 containing the speakers 18 and 19 to the right ear, the panoramic surrounding sound effect which gives him an impression that he is surrounded by the sound is produced. In this case, he is entirely free from the feeling that the sounds concentrate on his occipital region. Further, the sound of each channel in the four-channel system is different from one another and the signals of the rear channels (the second and fourth channels) seldom coincide in phase and level with the signals of the front channels (the first and third channels). Accordingly, the sounds of the front channels are not greately cancelled by the sounds of the rear channels.

In the foregoing embodiment, the changing of phase between an original phase and an opposite phase is effected by means of the phase shifting switches 48 and 49. Instead of provision of the switches 48 and 49, the speakers 15 and 19 may be fixedly connected to the terminals 61 and 63 in opposite polarity, so that the signals may be reproduced in opposite phase to the original phase.

FIG. 7 shows a circuit diagram of the second embodiment of the electric circuit of the four-channel speakers according to the invention. In the above described embodiment in which the phases of the second and fourth channel signals reproduced and sounded are changed by 180.degree. to make them opposite phase to the original phases, the above described surrounding effect is produced. This construction, however, has a problem that the listener may sometimes have an unpleasant feeling due to unnaturalness accompanying such surrounding effect. Furthermore, if the first and the second (or the third and the fourth) channel signals happen to completely in the same phase and same level, the sound of the first channel signal will be cancelled by the sound of the second channel signal which is in opposite phase to the sound of the first channel. This particularly apts to become a problem in low frequencies in which the two signals often have components which are in phase or almost in phase with each other. The present invention is directed to settle these problems by variably adjusting the phase shift so that a natural surrounding sound effect will be produced in accordance with phases of the signals.

In FIG. 7, the speakers 14 and 18 for the front channels, i.e., the first and the third channels, are directly connected to the terminals 60 and 62, as in the first embodiment previously described. The speakers 15 and 19 for the rear channels, i.e., the second and the fourth channels, are respectively connected to the terminals 61 and 63 through phase adjusting circuits 70 and 71. The phase adjusting circuits 70 and 71 generally consist of transformers 72 and 73, variable resistors 74 and 75 and capacitors 76 and 77. One end of a voice coil of the speaker 15 is connected to a connecting point of the variable resistor 74 and the capacitor 76. One end of a voice coil of the speaker 19 is likewise connected to a connecting point of the variable resistor 75 and the capacitor 77. The other ends of the voice coils of the speakers 15 and 19 are respectively connected to one ends of primary windings and intermediate taps 78 and 79 of the secondary windings of the transformers 72 and 73.

In the present embodiment, slide knobs of the variable resistors 74 and 75 are provided on the casings 13 and 17 of the headphone bodies 11 and 12 instead of the switch knobs 20 and 21 employed in the first embodiment. As shown in FIG. 8, the phase shift of the signals applied from the terminals 61 and 63 to the speakers 15 and 19 through the phase adjusting circuits 70 and 71 and reproduced and sounded from these speakers 15 and 19 varies with frequency. The phase shift is small in low frequencies whereas it is large in high frequencies, amounting nearly to 180.degree.. A frequency f.sub.c at which the phase shift is 90.degree. is represented by equation f.sub.c = 1/2.pi.CR, where C is capacitance value of the capacitors 76 and 77 and R is resistance value of the variable resistors 74 and 75.

Accordingly, the value of the frequency f.sub.c is changed by changing the value of resistance of the variable resistors 74 and 75 and the characteristic shown by a full line in FIG. 8 varies as shown by a broken line and a chain line in the same figure. If the frequency f.sub.c is selected at about 200 Hz to 1,000 Hz, an excellent effect is produced with respect to a sound image orientation and a sound field reproducibility.

According to the circuit of the present embodiment, a natural panoramic surrounding sound effect can be obtained. Moreover, the cancellation of the level in low frequencies can be avoided.

In the present embodiment, the amount of phase shift varies in accordance with frequency. However, the invention is not limited to this but a constant amount of phase shift may be maintained over the whole range of frequency or the amount of phase shift may be made variable over the whole range of frequency.

Further, this invention is not limited to these embodiments but various variations and modifications may be made without departing from the scope and spirit of the invention.

Claims

1. A four-channel headphone comprising:

a. a pair of left and right headphone body casings respectively applied to the left and right ears of a listener;

b. first and second speakers disposed in said left headphone body casing so that when said headphone is applied to the ears of the listener said first speaker is to the front of the left ear of the listener and said second speaker is to the rear of the left ear of the listener;

c. third and fourth speakers disposed in said right headphone body casing so that when said headphone is applied to the ears of the listener said third speaker is to the front of the right ear of the listener and said fourth speaker is to the rear of the right ear of the listener;

d. first means for supplying to said first speaker a first channel signal which corresponds to a sound emanating from the front and left of the listener;

e. first switch means mounted in said left head-phone body casing and being set to selectively reverse connections, said first switch means having input terminals and output terminals, said output terminals being electrically connected to said second speaker;

f. second means for supplying across said input terminals of said first switch means a second channel signal which corresponds to a sound emanating from the rear and left of the listener;

g. third means for supplying to said third speaker a third channel signal which corresponds to a sound emanating from the front and right of the listener;

h. second switch means mounted in said right headphone body casing and being set to selectively reverse connections, said second switch means having input terminals and output terminals, said output terminals of said second switch means being electrically connected to said fourth speaker; and

i. fourth means for supplying across said input terminals of said second switch means a fourth channel signal which corresponds to a sound

2. The four-channel headphone as defined in claim 1, wherein said first switch means comprises a double pole double throw switch, the switch knob of which is exposed outside of said left headphone body casing, and wherein said second switch means comprises a double pole double throw switch, the switch knob of which is exposed outside of said right

3. The four-channel headphone as defined in claim 2 which further comprises two spaced partitions provided in said left headphone body casing for separating in space said first speaker from said second speaker, said first switch means being provided between said two spaced partitions, and two spaced partitions provided in said right headphone body casing for separating in space said third speaker from said fourth speaker, said

4. A four-channel headphone comprising:

a. a pair of left and right headphone body casings respectively applied to the left and right ears of a listener;

b. first and second speakers disposed in said left headphone body casing so that when said headphone is applied to the ears of the listener said first speaker is to the front of the left ear of the listener and said second speaker is to the rear of the left ear of the listener;

c. third and fourth speakers disposed in the right headphone body casing so that when said headphone is applied to the ears of the listener said third speaker is to the front of the right ear of the listener and said fourth speaker is to the rear of the right ear of the listener;

d. first means for supplying to said first speaker a first channel signal which corresponds to a sound emanating from the front and left of the listener;

e. first phase-shifting means mounted in said left headphone body casing for shifting in phase a signal which is applied to said first phase-shifting means;

f. second means for supplying through said first phase-shifting means to said second speaker a second channel signal which corresponds to a sound emanating from the rear and left of the listener;

g. third means for supplying to said third speaker a third channel signal which corresponds to a sound emanating from the front and right of the listener;

h. second phase-shifting means mounted in said right headphone body casing for shifting in phase a signal which is applied to said second phase-shifting means;

i. fourth means for supplying through said second phase-shifting means to said fourth speaker a fourth channel signal which corresponds to a sound

5. The four-channel headphone as defined in claim 4, wherein each of the first and second phase-shifting means comprises a transformer, a series combination of a variable resistor and a capacitor, which series combination is connected across the secondary winding of said transformer, said secondary winding having an intermediate tap, said second speaker and said fourth speaker being respectively connected between said intermediate tap and the connecting point of said variable resistor and said capacitor, and wherein the second and fourth means supply respectively said second channel signal and said fourth channel signal to the primary winding of

6. The four-channel headphone as defined in claim 5 wherein the resistance adjusting knobs of the variable resistors in the first and second phase-shifting means are exposed respectively outside of the left and

7. The four-channel headphone as defined in claim 6 which further comprises two spaced partitions provided in said left headphone body casing for separating in space said first speaker from said second speaker, said first phase-shifting means being provided between said two spaced partitions, and two spaced partitions provided in said right headphone body casing for separating in space said third speaker from said fourth speaker, said second phaseshifting means being provided between said two spaced partitions.