Stereo loudspeaker system for a picture reproducing screen

A television system having a stereo loudspeaker system with a plurality of speakers and delay circuitry for successively delaying the left and right signals so that the speaker at the right end of the speaker arrangement receives the least delayed right signal and the most delayed left signal and the speaker at the left end of the speaker arrangement receives the least delayed left signal and the most delayed right signal.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to a television set being capable of receiving and 
reproducing stereo sound. 
More particularly, the invention relates to a television set comprising 
loudspeakers for reproducing a left channel sound signal and a right 
channel sound signal. 
2. The Prior Art 
Stereophonic listening to more than one sound reproducing source has been 
studied for many years (see: Jens Blauert: Raumliches Horen, Hirzel 
Verlag, Stuttgart, 1974, p. 161). A very important result of these 
researches was the finding that two sound sources are recognized as one 
sound source only, if the two sound signals were similar in phase and 
amplitude. This effect is called "Sum localisation". Another important 
finding was the so-called "Law of the first wave front" which means that 
only one out of two sound signals is recognized, if a time difference of 
about 1 Millisecond lies between two sound signals of similar levels or 
amplitudes. Differences in the transit time of more than one second will 
cause an echo-effect, if the amplitudes of two sound sources are similar. 
A variation of the level (H. D. Harwood "Stereophonic Image Sharpness", 
Wireless World, 1968, p. 207-210) as well as of the time difference of two 
sound signals has a mutual influence on the sound localisation or image 
position. In view of these experiments the best position for listening to 
two-channel stereo sound reproductions is between the two loudspeakers 
being capable of reproducing the left and right channel information, 
respectively. More specifically, the two loudspeakers and the listener 
should define the corners of an equilateral triangle (see: W. Baier: 
Rundum-Klang, radio-tv-electronic 1977, No. 12, p. 30,32, FIG. 1). If the 
distance from the listener to one of the two loudspeakers differs from the 
distance between the listener and the other loudspeaker, the stereo effect 
disappears in dependence upon the difference of the two distances. Thus, 
only a very small area in front of the two loudspeakers is suitable for a 
good stereo effect. This area is the smaller the smaller the so-called 
stereo basis is, i.e. the distance between the two loudspeakers. 
In a television set comprising two loudspeakers, one being located at the 
left side of the television tube and the other being located at the right 
side of said tube, the stereo basis is very small, since television sets 
have a tube diameter of 30 to 70 cm only. Therefore, it is desirous to 
broaden the stereo area of a television set. Many proposals have been made 
in the art of radio stereophony to enlarge the stereo basis. One of those 
proposals concerns an electrostatic loudspeaker in a rectangular room, the 
diaphragm of this loudspeaker covering one wall of the room (P. J. Walker, 
Wide Range Electrostatic Loudspeakers, part 3--Complete Systems, Wireless 
World, August 1955, FIG. 6). Sound intensity throughout the room is 
independent of position. The apparent sound source is always in a 
direction perpendicular to the diaphragm and, of course, moves a the 
listener moves. The same loudspeaker may be used for stereophony. With 
transmission line matching and feeding the signal at one end the wavefront 
will be tilted, due to the time delay. Separate signals may be fed from 
either end to produce two tilted wavefronts, one for each signal. Since 
each apparent origin is perpendicular to its wavefront, the aspect angle 
from the listener is a constant and entirely independent of the listener's 
position over a large triangular area. The relativ intensity of the two 
signals is also constant. A similar principle using a plurality of 
electrodynamic loudspeakers instead of an electrostatic loudspeaker has 
recently been proposed (see: Verbesserung des Raumeindrucks durch 
Holophonie, Funkschau 1980, No. 5, p. 74-76). In this latter system, 
however, it is also made use of the fact that only frequencies of more 
than 300 Hz are useful for stereo location (see: K.de Boer, Plastische 
Klangwiedergabe, Philips Technische Rundschau, 1940, No. 5, p. 108-115). 
Consequently, only the frequencies above 300 Hz are led to a plurality of 
tweeters and midrange loudspeakers, whereas the lower frequencies are led 
to common woofers. 
SUMMARY OF THE INVENTION 
It is a general object of the invention to improve the stereo effect of a 
stereo television set. 
More particularly, it is an object of the invention to broaden the area in 
which a good stereo effect can be achieved in view of the small stereo 
basis of a television set. 
Another object of the invention is to provide an improved housing of a 
television set which is capable of receiving a loudspeaker system 
comprising signal delay means. 
A concomitant object of the invention is to adapt prior art stereo 
improvements, e.g. the ambience-stereophony as described in German 
Offenlegungsschrift No. 28 06 914 or the pickup-room evaluating devices as 
described in German accepted Patent Application No. 23 55 943. 
Still a further object of the invention is to mechanically broaden the 
stereo basis by an enlargement of the distance between loudspeaker means.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring now to FIG. 1, the television set 1 depicted therein comprises a 
television tube 2, a mono loudspeaker housing 3 and a stereo loudspeaker 
housing 4. Above the mono loudspeaker housing 3 a remote control device 5 
is provided which can be removed from the television set 1 and control the 
different functions by means of infrared or ultrasonic radiation. Two 
optical displays 6,7 are provided for the indication of the numbers of the 
selected tv channels as well as of the receipt of a stereo program. The 
loudspeaker arrangement housing 4 comprises a plurality of loudspeaker 
units being arranged from the left side 8 to the right side 9 of the 
housing 4. The loudspeaker arrangement housing 4 also includes delay means 
being capable of delaying the left channel audio signal as well as the 
right channel audio signal successively from one loudspeaker unit to 
another. The loudspeaker units can either be electrodynamic loudspeakers 
as described in Funkschau 1980, No. 5, p. 74-76 or an electrostatic 
loudspeaker as described in Wireless World, August 1955. Each loudspeaker 
unit is co-ordinated to a delay element, and it is also known in the art 
to co-ordinate an amplifier or an attenuator to each loudspeaker unit so 
as to control the loudness of each loudspeaker element individually. 
Assuming now that a television program with stereo sound is being 
received, the loudspeaker in the housing 3 reproduces a sum signal of the 
right and left stereo channel, i.e. a mono audio signal. This mono signal 
may either comprise all frequencies received by the tuner of the 
television set 1 or the lower frequencies only. "Lower frequencies" in the 
sense of the present invention means those frequencies which are not of 
importance with respect to the stereo effect. The stereo sound being 
emitted from the loudspeaker arrangement in the housing 4 is a combination 
of two wavefronts being inclined to each other. The wavefronts may have 
either a straight or an arcuated from. Thus, the area in which stereo 
sound can be received by a listener is broadened. By locating the housing 
4 of the loudspeaker arrangement above or below the television tube 2, 
what is very essential in view of the present invention, the sound will 
always correspond exactly to the picture displayed on the tube 2. 
Moreover, if a multi-channel stereo system having more than two channels 
were introduced, the loudspeaker arrangement of the housing 4 could be 
used, too, by co-ordinating each loudspeaker to a separate channel. Still, 
the separation of high and low frequencies makes it possible to use either 
tweeters or electrostatic louspeakers for the loudspeaker arrangement 
being incorporated into the housing 4. Since those loudspeakers are much 
smaller than woofers or multi-band loudspeakers, the housing 4 can be very 
small so as to keep the size of the television set 1 small. In principal, 
however, the loudspeaker arrangement od the housing 4 can either be 
suplied with signals including all frequencies of the signal received by 
the tuner of the television set 1 or by the medium and high frequencies 
only. It is advantageous to supply the loudspeaker arrangement of housing 
4 with those frequencies which are responsible for the stereo effect, 
whereas the loudspeaker in the housing 3 is supplied with lower 
frequencies which are not relevant with respect to the stereo effect. 
Consequently, the loudspeaker of the housing 3 should be a woofer and a 
medium-range loudspeaker only. 
FIG. 2 depicts another television set 10 comprising two lateral 
loudspeakers housing 11,12 and one to loudspeaker arrangement housing 13. 
The television set 10 also comprises the remote control device 5 and a 
video tape recorder 14 including a drawer 15 as it is known in the Hifi 
audio cassette recorder art. The housing 13 of the loudspeaker arrangement 
is located symmetrically above the television tube 2 and rests with its 
ends on the housings 11,12, respectively. The two loudspeakers of the 
housings 11,12 may be supplied conventionally with left and right channel 
stereo signals. It is also possible, however, to supply these loudspeakers 
with mono audio signals. The loudspeaker arrangement of the housing 13 is 
connected to the left and right channel stereo signals as described in 
connection with FIG. 1. The loudspeakers of the housings 11,12 as well as 
the loudspeaker arrangement of the housing 13 may be either supplied with 
all frequencies of the audio band or with a limited frequency band only. 
The housing 13 of FIG. 2 is especially useful as an additional device for 
a conventional stereo television set. If, for instance, a television set 
comprising a television tube 2 and two stereo loudspeakers in the housings 
11 and 12 is bought by a person, this set--which is, for instance, 
standard in Japan--can be improved by buying an additional device 
comprising a loudspeaker arrangement together with a corresponding 
electronic circuit. This additional device may be incorporated in the 
housing 13 and this housing 13 can be laid upon the television set. Thus, 
the housing 13 may be bought as an isolated device and added to an 
existing conventional stereo television set. The same would, of course, be 
possible with respect to a television set as shown in FIG. 1. 
FIG. 3 depicts another television set 16 comprising one mono loudspeaker in 
the housing 17 and two stereo loudspeaker arrangements in the housings 18 
and 19, respectively. The housing 18 is located above the television tube 
2, whereas the housing 19 is located below the television tube 2. By using 
two stereo loudspeaker arrangements the acoustical wavefront is enlarged 
with respect to the vertical direction, thus creating a good stereo sound 
for the listener in a sitting as well as in a standing position. 
FIG. 4 illustrates another television set 20 comprising one more 
loudspeaker 21 and two stereo loudspeaker arrangements being incorporated 
in three housing sections 21,22,23 and 24,25,26, respectively. The left 
and right housing sections 21,23 and 24,26, respectively, can be displaced 
with regard to the middle sections 22,25, respectively. When in their 
initial position, the lateral sections 21,23 and 24,26 will cover the 
middle sections, respectively; i.e. the television set 20 will then have 
an outer appearance similar to that of the television set 16 shown in FIG. 
3. In their position shown in FIG. 4, the lateral sections 21,23 and 24,26 
are drawn from the sections 22,25, respectively. These lateral sections 
21,23;24,26 are slidingly connected to the upper part of the television 
set and located in front of the stationary sections 22,25 to which they 
may also be slidingly connected. Thus, they can easily be moved 
horizontally from a position shown in FIG. 3 to a position shown in FIG. 
4. Instead of a sliding connection a collapsible connection is also 
possible; i.e. the lateral sections 21,23,24,26 can be connected by pins 
or screws to the television set or to the middle sections 22,25 so that 
their outer ends may be tilted from their position shown in FIG. 4 
upwardly and then brought into a position in the middle of the sections 
22,25. 
FIG. 5 illustrates another television set 27 comprising a television tube 
2, a mono loudspeaker 28, a stereo loudspeaker arrangement housing 29, a 
video tape recorder 30 and a video disc recorder player 31. Moreover, the 
television set comprises several pushbuttons 32 for selecting programs, a 
display 33 for indicating the selected program and several touch sensor 
plates 34 for actuating the tape recorder 30 as well as the disc record 
player 31. The video tape recorder 30 may be of any kind known in the art. 
A display unit 35 indicates the exakt position of the tape in centimeters, 
inches or the like. A similar display unit 36 is provided for the video 
disc record player 31 which may be a player with mechanical, optical, 
electrical or magnetical disc scanning. Both displays 35, 36 are provided 
at the front of a drawer as described in connection with FIG. 2. 
The loudspeaker arrangement in the housing 29 is connected to left channel 
and right channel stereo signals as described in connection with FIGS. 1 
and 2. The signal being supplied to the mono loudspeaker in the housing 
28, however, is delayed as described in German Pat. No. 1,000,865 so as to 
achieve that the sound waves of the stereo loudspeaker arrangement in 
housing 29 arrive at an earlier moment at the ears of a listener than the 
corresponding sound waves being emitted by the mono loudspeaker in the 
housing 28. The delay time is such that the sound of the stereo 
loudspeaker arrives earlier at any point of the listening area without 
causing an echo-effect. 
FIG. 6 depicts a circuit being capable of supplying a television set as 
shown in FIG. 1 with stereo and mono signals. The left channel stereo 
signal L and the right channel signal R which may be derived from a tuner 
not shown are led to a low-pass filter 40 as well as to a high-pass filter 
41. Having passed the low-pass filter 40, both the L- and the R-signal are 
added by an adder 42. The resulting sum signal L'+R' which is a mono 
signal is supplied to a loudspeaker 43 which is, for instance, enclosed by 
the loudspeaker housing 3 of the television set in FIG. 1. 
When the L- and R-signals have passed the high-pass filter 41, the left 
channel signal L" is led to the one end 44 of the loudspeaker arrangement 
45, whereas the R-signal R"-signal is led to the other end 46 of the 
loudspeaker arrangement 45. The loudspeaker arrangement 45 comprises an 
electrostatic loudspeaker 47 being connected to a delay device 48 as 
described in "Wireless World, August 1955". 
FIG. 7 depicts another circuit being capable of supplying the television 
set of FIG. 2 with audio signals. The left and right channel signals L and 
R are again treated by a low-pass filter as well as by a high-pass filter 
50 and 51. The left channel output L' of the low-pass filter 50 is led to 
a first loudspeaker 52 which may be located in the housing 11 (FIG. 2), 
and the right channel output R' is fed to a second loudspeaker 53 which 
may be located in the housing 12 (FIG. 2). The audio signals passing the 
high-pass filter 51 are led to a loudspeaker arrangement 54 comprising a 
plurality of dynamic loudspeaker elements 55 and electronic delay elements 
56" e.g. bucket chain delay elements. The details of the device 54 being 
located in the housing 13 are known in the art and will be more apparent 
from FIG. 9. 
FIG. 8 illustrates a circuit being capable of supplying the television set 
shown in FIG. 3 with mono and stereo signals. The difference between the 
circuit of FIG. 6 and the circuit of FIG. 8 is characterized by a second 
loudspeaker arrangement 60 being located in the housing 19 of the 
television set 16. The loudspeaker arrangements may either include 
electrostatic or electrodynamic loudspeaker elements. 
FIG. 9 depicts a circuit being capable of supplying the television set 20 
shown in FIG. 4 with mono and stereo audio signals. For an easier 
understanding the circuit for one loudspeaker arrangement only is shown, 
said arrangement comprising the sections 21,22,13 in FIG. 4. The 
loudspeakers 90,91 are located in the housing 21, and the loudspeakers 
92,93 are located in the housing 23, whereas the loudspeakers 94-97 are 
located in the housing 22. If the loudspeaker housings 21,23 are pushed 
together so as to form a television set shown in FIG. 3, only the 
loudspeakers 90-93 are operated. In this state switches 98-109 are in 
their position shown in FIG. 9. Thus, only the delay elements 110-115 and 
the sum amplifiers 116-119 are operated. Now, if the loudspeaker housings 
21,23 are brought into their position illustrated by FIG. 4, switches 
98-109 are switched into their second state. This can be effected by an 
mechanical, optical, electrical or magnetic sensing means being provided 
between the housing 22 and the housings 21,23 or the like, e.g. the 
housing 22 carries a reed contact at its ends whereas the ends of the 
housings 21,23 are provided with magnets being capable of switching the 
reed contact being co-ordinated to the respective magnet. In their second 
position the switches 98-109 will actuate the delay elements 120 through 
127 and the sum amplifiers 128-131, too. The sum amplifiers 116-119 are 
now connected to the loudspeakers 94-97. Thus, the loudspeakers 94-97 have 
the functions the loudspeakers 90-93 had before, i.e. they emit sound in a 
zone or area where the television tube 2 is located. 
FIG. 10 depicts another circuit being capable of providing the television 
set shown in FIG. 5 with mono and stereo signals. This circuit corresponds 
to the circuit of FIG. 6 in principle. There is, however, a delay circuit 
150 connected between the loudspeaker 43 and the adder 42, this delay 
circuit 150 being capable of delaying the audio signal with respect to the 
audio signals supplied to the loudspeaker arrangement 44. As a result, the 
sound of the loudspeaker arrangement 44 being responsible for the stereo 
effect will arrive earlier at the listener's ears than the sound of the 
loudspeaker 43 not causing a stereo sensation. 
FIG. 11 depicts a circuit 151 as shown in FIG. 4 of German Auslegeschrift 
No. 23 55 943 together with a loudspeaker arrangement 44. Thus, FIG. 11 
illustrates that the present invention can be combined with a prior art 
stereo improvement device. The L' and R' signals can, of course, be 
divided into high and low frequencies and then treated as shown in one of 
the predescribed embodiments. Therefore, the combination illustrated in 
FIG. 11 is not the only combination possible with respect to the circuit 
151, said circuit being capable of simulating the reflections of acoustic 
waves at walls. 
Another stereo sound improvement device 152 as disclosed in FIGS. 11 and 12 
of German Offenlegungsschrift No. 28 06 914 is shown in FIG. 12, this 
device 152 being connected to a low-pass filter 153 as well as to a 
high-pass filter 154, the low-pass filter supplying two loudspeakers 155 
and 156 with left and right channel signals L.sub.L ' and R.sub.L ', 
respectively, and the high-pass filter 154 supplying the loudspeaker 
arrangement 60 with left right channel stereo signals L.sub.H ' and 
R.sub.H ', respectively. 
While the invention has been illustrated and described as embodied in a 
television set, it is not intended to be limited to the details shown, 
since modifications and structural chenges may be made without departing 
from the spirit of the invention.