Non-directional speaker system with point sound source

A speaker system is disclosed which is capable of supplying reproduced sounds vibrating in substantially the same manner as in the respiratory sphere to human's sense of hearing by using conventional unidirectional speaker units in combination in a contrived arrangement, and by applying real time digital signal processing by means of a digital signal processor to the speaker units to cancel a peak and a dip in frequency response and in phase response through inverse correction which cannot be canceled only by improving the arrangement of the speaker units, thereby forming a sound emitter capable of providing ideal reproduced sounds. The speaker system comprises an enclosure EC having a basic structure of a hollow 32-hedron composed of 12 pentagonal flat surfaces 1 and 20 hexagonal flat surfaces 2, speaker units 7, 8 or 78 mounted in all or 25-31 of the 32 surfaces, and a real time digital signal processing system inserted in a input line of each of the speaker units 7, 8 or 78. The digital signal processing system inverse-characteristically filtering driving signals of the speaker units to evenly correcting a peak 4 and a dip 5 caused in frequency response and in phase response of each of the speaker units 7, 8 or 78.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a non-directional speaker system with a 
point sound source which is capable of emitting a spherical sound wave 
whose focal point is clear to the surrounding space all around the speaker 
system. It relates to a speaker system which is capable of 
stereophonically reproducing presence of each sound emitter such as a 
person's voice or a musical instrument which is included in a sound 
source. 
2. Description of the Prior Art 
When a tuning fork is struck to vibrate, vibration of air whose sound 
emission source is the tuning fork spherically propagates over the 
surrounding space around the tuning fork. In other words, because the 
sound emitted from the tuning fork is heard at substantially the same 
sound pressure at any spatial positions equidistant from the tuning fork 
irrespective of directions, the sound wave emitted from the struck tuning 
fork is recognized to propagate as a spherical wave. When the sound of the 
tuning fork is collected and recorded through a microphone and reproduced 
by a conventional speaker system comprising a hexahedron (rectangular 
parallelepipedic enclosure) and a speaker unit disposed on one of the 
surfaces of the hexahedral enclosure, sound pressure level is high only in 
the front of the speaker unit but low outside the front. Accordingly, the 
spherical wave from the tuning fork cannot be reproduced. 
Heretofore, speaker systems have been used in reproduction of a music, 
amplification of a speech, reproduction of natural sounds and sound 
effects in a movie, and the like. However, many of sound emitters included 
in the sound source reproduced through a speaker unit, for example, 
percussion instruments and wood winds are non-directional and emit a 
spherical wave. Further, although stringed instruments have a sound 
emitting portion on one side thereof, they are roughly regarded as 
substantially non-directional sound emitters because of sound box-induced 
resonance acting as an influential tonal quality factor. Therefore, the 
majority of sound emitters may be considered to emit a non-directional 
spherical wave. 
On the other hand, it is considered that human's sense of hearing detects 
direction of a sound source through direct sounds coming from a musical 
instrument in the shortest course, and in parallel, compares information 
on indirect sounds from surrounding reflective objects such as a floor, a 
wall and a ceiling with experiential values, thereby realizing distance to 
the musical instrument, i.e., sound source, reality of the musical 
instrument, and vividness. 
Some of brass instruments such as a trumpet have their tones extremely 
different between the front and the rear thereof, that is, they are highly 
directional. In such highly directional instruments, frontal tones 
correspond generally to the sounds intrinsic to the instruments. This is 
similar to sound emitting mode of a nomodirectional speaker system. 
Accordingly, it tends to be considered that a non-directional speaker 
system with a point sound source is not suitable for reproducing sounds of 
brass instruments. However, with respect to sounds reproduced by a speaker 
system, in the absence of appearance of a player, a person who hears the 
reproduced sounds needs information on the sense of distance through 
indirect sounds so as to recognize existence of a musical instrument such 
as a trumpet or presence of sounds emitted therefrom. To reproduce with 
high fidelity any sounds from the above sound emitters, i.e., sound 
emitters which emit sounds in various mode, use of a non-directional 
spherical wave speaker system with a point sound source is preferred which 
is capable of exhibiting excellent characteristics in reproduction of 
sounds of unidirectional and highly directional musical instruments. The 
reasons for this are as follows. 
(a) In a unidirectional speaker system of the most ordinary type, which 
comprises a hexahedral enclosure and a speaker unit mounted to one of the 
surfaces of the enclosure, right sounds of musical instruments are emitted 
only in the direction of the front of the speaker system, and other sounds 
corresponding to indirect sounds of the sound source are emitted in other 
directions than the front direction. It follows then that two different 
musical instruments respectively emitting the direct sounds and the 
indirect sounds are virtually existent at the position of the sound 
emitter. This causes a delicate gap between acoustic images, and as a 
result, prevents person's sense of hearing from forming an acoustic image 
with reality. 
(b) In view of this problem, speaker systems have been proposed in, for 
recent example, Japanese Patent Unexamined Publication No. 205490/1994 
which comprise a polyhedral or spherical enclosure and speaker units 
uniformly mounted on the surface(s) of the enclosure, and some of them 
have been practically used. Further, a report on "non-directional speaker" 
has been published in "JAS JOURNAL, September, 1993". 
However, with respect to such a conventional spherical wave emitting type 
speaker system comprising a polyhedron or sphere and speaker units mounted 
thereon, it has been known that a peak and a dip are observed in frequency 
response. Such a conventional speaker system has a drawback that it cannot 
be driven as a high fidelity speaker system unless the peak and the dip 
are corrected. 
(c) On the other hand, it has been known in conventional analog technique 
that when the defect in frequency response is corrected, phase distortion 
is concomitanly caused. There have been experimental reports on correction 
effected by means of an analog equalizer with a view to elucidating 
relationship between the phase distortion and auditory feeling. As an 
example of those reports, there may be mentioned "Phase and tonal quality" 
reported in "pre-lecture publication for AES Tokyo Convention, 1995". 
It is, however, difficult to effect correction by analog treatment at 
strict sound pressure level. Further, phase response is affected by 
correction of frequency response. Accordingly, it has been said that a 
clear acoustic image cannot be obtained by a conventional non-directional 
speaker system using analog technique. 
(d) Further, a speaker system which generates a quasi-spherical wave using 
a round reflector has hereto fore been proposed as one type of 
non-directional speaker systems. 
In the speaker system, however, frequency response and phase response are 
affected due to the reflector. In spite of the fact that cancel treatment 
is required to cope with the undesired influence, the speaker system is 
not constructed taking this point into consideration. Accordingly, 
reproduction of a point sound emitter, which is a basic performance of a 
non-directional speaker system, is not realized. 
(e) Recently, it has been attempted to evenly correct frequency response 
and phase response of a speaker system using a hexahedral enclosure by 
real time digital signal processing by means of a digital signal 
processor. However, this attempt has been made with a view only to 
applying digital signal processing to a multiway speaker unit mounted to a 
conventional hexahedral enclosure. Accordingly, the attempt is not 
development of a speaker system which, per se, is capable of realizing a 
non-directional spherical sound wave with a point sound source which is 
sound emission mechanism of a natural sound. 
(f) Such a real time digital signal processing unit using a digital signal 
processor as mentioned above has been commercially available as a digital 
equalizer which is unitary. When a speaker system with a digital equalizer 
is constructed using such a digital equalizer, it is as shown in the block 
diagram in FIG. 6. When the speaker system in FIG. 6 is used in, for 
example, a public address system or the like, the following problems are 
caused. 
Generally, in a public address system, an analog attenuator 13 is provided 
in a monitor output portion of a mixing console which is operated by a 
mixing engineer, and sound volume is controlled by operating the 
attenuator 13. When the speaker system in FIG. 6 is used in a high 
fidelity audio system, the attenuator 13 is provided in a control 
amplifier which is operated by a listener, and sound volume is controlled 
by operating the attenuator as described above. 
On the other hand, in the speaker system in FIG. 6, an analog attenuator 14 
inserted in advance of a power amplifier 17 is usually preset for 
presetting input gain of the power amplifier 17. Accordingly, if the 
analog attenuator 14 is set so as not to cause distortion of output sounds 
of a speaker unit 18 at the maximum power, in usual conditions operated at 
lower volume levels, sound volume is controlled by the analog attenuator 
13 located at the upper stream of the input system. This leads to a low 
level of signals inputted to an A/D converter 15, thereby preventing the 
A/D converter 15 from performing highly precise analog-digital conversion. 
As a result, low levels of input signals are processed by a digital 
equalizer 16, and computing errors are accumulated in the course of signal 
processing. Consequently, there is a problem in that disadvantages such as 
increase of noise and aggravation of distortion ratio are caused. 
To solve the above-mentioned problem, a speaker system has been proposed 
and practically used which comprises a master attenuator 20 placed within 
reach of a mixing engineer and a special signal line 21 for level 
controlling signals besides a sound signal line to control the analog 
attenuator 14. When this system is applied to, for example, a system using 
a number of speaker units in parallel, such as a public address system, 
the resulting system has a construction as shown in the block diagram in 
FIG. 7. However, in such a large-sized speaker system, for example, an 
incident is likely to be caused that even if reduction of sound volume is 
required at the end of a tune, sound volume is out of control in only one 
channel and the sound volume of the speaker unit 18 of the channel cannot 
be reduced due to a cause such as contact failure of a connector. 
As described above, in terms of sound emission mechanism of sound emitters, 
such as musical instruments and natural sound emitters, whose sounds are 
to be reproduced by a speaker system, there are many non-directional sound 
emitters, and listener's sense of hearing recognizes existence of a sound 
emitter more clearly by indirect sounds. In view of these facts, a 
non-directional speaker system with a point sound source is considered to 
be an ideal sound emitter for reproducing sounds emitted by a sound 
emitter with high fidelity. 
Further, conception of "respiratory sphere" has heretofore been known. If 
sounds can be reproduced by a speaker system in such a manner that entire 
surface of a sphere is uniformly expanded and contracted to transmit 
vibrations of sound wave to air, it is possible to listen reproduced 
sounds in the same mode as sound emission mechanism of musical instruments 
or natural sound emitter, i.e., in such a mode that sound at the same 
sound pressure can be heard at positions equidistant from the speaker 
system. However, a non-directional speaker system with a point sound 
source has not been provided which is capable of reproducing sounds in a 
wide range of about 20 Hz to about 20 KHz in the same manner as that of 
the respiratory sphere. 
SUMMARY OF THE INVENTION 
It is, therefore, an object of the present invention to provide a speaker 
system which is capable of supplying reproduced sounds vibrating in 
substantially the same manner as in the respiratory sphere to human's 
sense of hearing by using conventional unidirectional speaker units in 
combination in a contrived arrangement, and by applying real time digital 
signal processing by means of a digital signal processor to the speaker 
units to cancel a peak and a dip in frequency response and in phase 
response through inverse correction which cannot be canceled only by 
improving the arrangement of the speaker units, thereby forming a sound 
emitter capable of providing ideal reproduced sounds. It is another object 
of the present invention to effect real time digital signal processing in 
optimum conditions without additionally providing a special signal line 
for controlling signals of the attenuator, by inserting an analog level 
controller practically required such as an analog attenuator downstream 
from a D/A converter in an input signal line. 
The present invention has been made with a view to solving the 
above-mentioned problems. 
According to the present invention, there is provided a non-directional 
speaker system with a point sound source comprising: 
an enclosure having a basic structure of a hollow 32-hedron composed of 12 
pentagonal flat surfaces and 20 hexagonal flat surfaces, 
speaker units mounted in all or 25-31 of the 32 surfaces, and 
a real time digital signal processing system inserted in a input line of 
each of the speaker units, the real time digital signal processing system 
inverse-characteristically filtering driving signals of the speaker units 
to evenly correcting a peak and a dip caused in frequency response and in 
phase response of each of the speaker units. 
In the above speaker system of the present invention, the enclosure has a 
basic structure of a hollow 32-hedron composed of 12 pentagonal flat 
surfaces and 20 hexagonal flat surfaces, and a speaker unit for a low 
range or low-mid range is mounted in each of 9-12 pentagonal surfaces and 
a speaker unit for a mid-high range or high range is mounted in each of 
15-20 hexagonal surfaces. The speaker units are thereby mounted to the 
sphere or polyhedron or sphere in such a well-balanced arrangement that a 
plurality of the speaker units for a mid-high range or high range are 
disposed around each of the speaker units for a low range or low-mid 
range. Accordingly, it is to provide a further widened range of reproduced 
sounds all around the speaker body. 
Further, in the above speaker system of the present invention, controlling 
data for sound volume control are multiplexed into SPDIF or AES/EBU 
signals which are digital audio interface standard signals and transmitted 
to a D/A converter block, and level of analog signals resulting from D/A 
conversion is controlled, thereby always maintaining arithmetic accuracy 
of the real time digital signal processing system at the best condition. 
Accordingly, arithmetic accuracy of the real time digital signal 
processing system can be maintained at the best condition, and sounds are 
reproduced from the speaker systems without any distortion of information 
on sound emitters.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Now, embodiments of the present invention will be described. 
As a well-balanced polyhedron preferably used in the speaker system of the 
present invention, there may be mentioned regular dodecahedron, regular 
icosahedron, 32-hedron composed of pentagonal surfaces and hexagonal 
surfaces, 180-hedron and the like. In the present invention, however, the 
speaker enclosure is preferably a hollow about 32- or more-hedron so as to 
provide a person with substantially the same auditory feeling as that 
caused by spherical wave due to a respiratory sphere. In the speaker 
system of the present invention, positional relationship between a woofer 
designed to handle a low range and a tweeter designed to handle a mid-high 
range and optimum location of the arrangement incorporating the positional 
relationship are experimentally determined using a 32-hedron (which is the 
polyhedron having minimum surfaces among the above-described preferred 
polyhedrons) from a practical viewpoint to realize the speaker system of 
the present invention. In terms of a sound receiving point, in the speaker 
system of the present invention which uses a hollow 32-hedron as an 
enclosure, the enclosure is preferably placed in such a manner that the 
top and bottom surfaces thereof are pentagonal surfaces. The same applies 
to the case where a sphere whose surface are supposed to be composed of 
pentagonal surfaces and hexagonal surfaces is used as an enclosure. 
In the next place, mode for operation of the speaker system of the present 
invention will be described with reference to the accompanying drawings. 
In the speaker system of the present invention, a hollow 32-hedron whose 
external surface is composed of 12 pentagonal surfaces 1 and 20 hexagonal 
surfaces 2 is the basic structure of an enclosure EC (which is also 
referred to as a speaker cabinet or speaker box). All of the 12 pentagonal 
surfaces 1 or, from practical viewpoint, 9 to 11 of the 12 pentagonal 
surfaces 1 are each provided with a speaker unit for a low range (woofer) 
7, and all of the 20 hexagonal surfaces 2 or, from practical viewpoint, 15 
to 19 of the 20 hexagonal surfaces 2 are each provided with a speaker unit 
for a mid-high range (tweeter) 8 to form a speaker body. Illustrated in 
FIGS. 1 and 2 are another embodiments of the speaker body, each of which 
has its pentagonal and hexagonal surfaces 1 and 2 each provided with a 
full-range type speaker unit 78. 
If the speaker body, which comprises a 32-hedron provided with speaker 
units 7 and 8 or speaker units 78 as described above, is actuated without 
pre-treatment, a peak 4 and a dip 5 are caused in frequency response as 
diagrammatically shown in FIG. 3. In the present invention, however, to 
correct the distortion appearing as the peak 4 and dip 5 to substantially 
even the frequency response, driving signals of the speaker units 78 or 
speaker units 7 and 8 are subjected to inverse characteristic filtering by 
means of a digital signal processor 6 (hereinafter referred to as DSP 6) 
as shown in FIG. 4. In FIG. 4, reference numeral 9 represents a digital 
input signal inputted to the DSP 6, reference numeral 10 a D/A converter 
block, reference numeral 11 a power amplifier, reference numeral 12 a 
controlling panel connected to the DSP 6, and reference numeral 100 an 
analog attenuator inserted in advance of the power amplifier 11. 
In the speaker system of the present invention, when each of the speaker 
units 7 and 8 or speaker units 78 of the speaker body is driven, a program 
of a finite impulse response filter (FIR filter) or a program of a 
combination filter of an FIR filter with an Infinite impulse response 
filter (IIR filter) is preliminarily loaded into a program memory of the 
DSP 6 for processing digital input signals which is shown in FIG. 4, and 
coefficient of inverse correction of speaker responses including 
distortion of frequency & phase response inherent in each of the speaker 
units is preliminarily loaded into a coefficient memory. 
As shown in the block diagram in FIG. 4, the input signals 9 are subjected 
to processing for inverse correction of frequency response and phase 
response by means of the DSP 6 in a real time digital signal processing 
system, and the digital signals are converted into analog signals by means 
of the D/A converter 10. 
In the present invention, the controlling panel 12 of the DSP 6 forming the 
real time digital signal processing system is provided with a controlling 
unit capable of changing output sound volume of each of the speaker units 
7 and 8 or speaker units 78. The analog attenuator 100 is controlled by 
the controlling unit to determine volume of reproduced sound, and a value 
corresponding to the determined sound volume is allotted to elements of 
user bit in subcode of AES/EBU, SPDIF or the like which is a serial 
transmission format for digital audio signals or elements of bit which is 
not required by the D/A converter in subcode to multiplex control data for 
controlling sound volume into signals for driving a speaker. The signals 
for driving a speaker are transferred to the D/A converter block 10. 
By virtue of this constitution, a signal line 21 for analog attenuators 14 
which is used to control sound volume in the conventional speaker system 
shown in FIG. 7 can be eliminated. Accordingly, disadvantage is not caused 
which is due to contact failure of the control line for the attenuators 14 
or the like. Further, signal processing by the DSP 6 and sound volume 
control can be performed using the same controlling panel 12. This enables 
sound volume to be determined arbitrarily as well as the DSP 6 to be 
operated at the optimum signal level to constantly maintain arithmetic 
accuracy at the highest condition. Therefore, no lowering of S/N ratio nor 
undesirably high distortion degree is caused in reproduced sound. This is 
because volume information is read out from a subcode in the D/A converter 
block 10 and converted into an analog audio signal by the D/A converter 
10, and level of the audio signal is controlled by the analog attenuator 
100. 
First Embodiment 
FIG. 1 shows an embodiment of a speaker body in the speaker system of the 
present invention, which comprises an enclosure EC in the form of a hollow 
32-hedral frame having stiffness and full-range (gamut) speaker units 78 
disposed in the hollow frame equidistantly from the center of the hollow 
frame. Each of the speaker units 78 of this system is driven by a power 
amplifier 11. 
Analog signals to be inputted to the power amplifier 11 are obtained by 
filtering input signals in real time by means of digital signal processing 
in a DSP 6 to correct characteristics of the speakers 78, and converting 
the resulting digital output signals into analog signals by a D/A 
converter 10. The analog signals are amplified by the power amplifier 11 
to drive speaker units 78. 
Second Embodiment 
FIG. 2 shows another embodiment of a speaker body in the speaker system of 
the present invention, which comprises an enclosure EC in the form of a 
hollow spherical frame having stiffness and full-range speaker units 78 
disposed in the frame equidistantly from the center 0 of the sphere 
forming the enclosure EC. Each of the speaker units 78 in this system is 
driven also by a power amplifier 11. 
Signals to be inputted to the power amplifier 11 are pre-treated in the 
same manner as in the speaker system shown in FIG. 1. When input signals 
are digital signals, the digital signals per se are treated by a DSP 6 to 
correct speaker characteristics. When input signals are analog signals, 
the analog signals are A/D converted and then subjected to treatment by 
the DSP 6 to correct speaker characteristics. The resulting digital 
signals are D/A converted to obtain the signals to be inputted to the 
power amplifier 11. 
Third Embodiment 
FIG. 5 shows a still another embodiment of a speaker body of the speaker 
system of the present invention, which comprises an enclosure EC in the 
form of a hollow spherical frame having stiffness and 12 woofers 7 and 20 
tweeters 8, and which is constructed by dividing the outer surface of the 
spherical frame into 12 pentagonal portions 1 and 20 hexagonal, portions 2 
and disposing a woofer 7 and a tweeter 8 in each of the pentagonal 
portions 1 and in each of the hexagonal portions 2, respectively. 
Also in the speaker body of the speaker system of the present invention 
comprising the hollow 32-hedral enclosure and the woofers 7 and tweeters 8 
which are disposed on the enclosure in such an arrangement, a peak 4 and a 
dip 5 are caused in frequency response, as in the two preceding 
embodiments, when the speaker body as such is driven. To substantially 
even the peak 4 and dip 5 and poorness in a low frequency range, a real 
time digital signal processing system which comprises a DSP 6 as main 
means is inserted in advance of a power amplifier 11. 
In the present invention, to subject analog or digital input signals to 
digital signal processing, a program of an FIR filter or a program of a 
combination filter of an FIR filter with an IIR filter is preliminarily 
loaded into a program memory of the DSP 6, and coefficient of inverse 
correction of speaker responses including distortion of frequency & phase 
response inherent in each of the speaker units 7 and 8 is preliminarily 
loaded into a coefficient memory. 
By virtue of this, the input signals 9 are subjected to processing for 
inverse correction of frequency response and phase response by means of 
the real time digital signal processing system comprising the DSP 6 as 
main means, and the treated digital signals are converted into analog 
signals by means of the D/A converter 10. The analog signals are amplified 
by the power amplifier 11 to drive the speaker system of the present 
invention. 
In the above embodiments, -8 decibel(db) and +10 (dB) are set as correction 
of the peak 4 and correction of the dip 5 of the frequency response in the 
DSP 6, respectively. In this connection, the values change depending upon 
size (volume) of the enclosure EC, types of the speaker units 7, 8 or 78, 
and other factors. Further, in the third embodiment, the driving signals 
for the speaker units 8 as tweeters are delayed by about 60 microseconds 
(.mu.sec.) as compared with the driving signals for the speaker units 7 as 
woofers, taking it into consideration that the distance from the center O 
of the hollow 32-hedron to a diaphragm of each speaker unit 7 as a woofer 
is different from the distance from the center 0 to a diaphragm of each 
speaker unit 8 as a tweeter. Analog signals to be inputted to the power 
amplifier 11 are obtained by filtering input signals in real time by means 
of digital signal processing in the DSP 6 to correct characteristics of 
the speakers 7, 8 or 78, and converting the resulting digital output 
signals into analog signals by the D/A converter 10. 
In each of the embodiments of the present invention shown in FIGS. 1, 2 and 
5, each of legs for placing the speaker body or a hook (or eye) for 
suspending the speaker body is located at a vacant portion of the 
enclosure EC, on which no speaker unit is disposed or a portion on which a 
speaker unit is not disposed intendedly for this purpose. Further, an 
input cable for each speaker unit may be introduced in the same manner as 
above. 
Ideally, a high fidelity speaker system for professional consumers, a loud 
speaker for a public address system or the like, or a speaker system used 
as a point sound source for measuring acoustic characteristics of a hall, 
i.e., a converter which converts electric signals into acoustic signals is 
required to have its sound emitting point at the center of a sphere or 
sphere-like polyhedron and to be capable of transmitting substantially 
uniform vibrational energy to the surrounding space all around. 
Heretofore, as one capable of exhibiting the above-mentioned performance, a 
wide-directional speaker system having a 12-hedral enclosure or the like 
has been provided. However, it has seldom been used in reproducing a 
music. The reason for this resides in that it is greatly different from 
the above-mentioned ideal shape because of the small number of its sound 
emitting surfaces. On the other hand, however, if a hollow sphere or 
sphere-like hedron is used as a speaker enclosure, correction of so-called 
"turbulence" of frequency response which is inherent in such an enclosure 
cannot be effected precisely and appropriately. 
As opposed to the above conventional technique, the speaker system of the 
present invention has such a structure that speaker units are disposed in 
the surfaces of an enclosure in the form of a hollow sphere or sphere-like 
polyhedron such as 32-hedron, which surfaces are located equidistantly 
from the center of the enclosure. By virtue of this, the speaker system of 
the present invention is capable of emitting substantially uniform 
vibrational energy and transmitting the vibrational energy to the 
surrounding space all around. Further, if the speaker system of the 
present invention is constructed as a multiway loudspeaker system which 
comprises (a) speaker units allotted to each of more than two specific 
sound ranges speaker units, input signals for each of the sound ranges are 
subjected to digital signal processing to correct frequency response. It 
is thereby possible to attain a wave front generated by sounds emitted 
from the speaker units, which is uniform and equidistant from the center 
of a sphere or sphere-like polyhedron such as 32-hedron. Therefore, if 
constructed as a multiway loudspeaker system, the speaker system of the 
present invention is capable of emitting substantially uniform vibrational 
energy to the surrounding space all around. 
Moreover, in the speaker system of the present invention, its digital 
signal processor (DSP) corrects decrease in a low range of frequency 
response, suppresses increase of frequency response at the frequency point 
from which the decrease is observed to the lower range, and corrects dip 
appearing in the higher range. Consequently, it is possible to effectively 
cancel phase distortion due to differences in distances from the center of 
the sphere to the speaker units and due to differences in response times 
of diaphragms of the speaker units. 
Furthermore, in the present invention, the enclosure to which the speaker 
units are mounted has a spherical or sphere-like polygonal structure 
having a curved surface or polyhedrally continuous surface. It is thereby 
possible to considerably suppress concomitant sound due to vibration of a 
hexahedral box (enclosure), which is likely to be caused in a conventional 
system comprising a hexahedral enclosure composed of flat surfaces to 
which speaker units are mounted. Further, in the present invention, the 
speaker units are well-balancedly distributed over the entire outer 
surface of the sphere or polyhedron in such a manner that a plurality of 
the speaker units for a high range are arranged around the speaker units 
for a low to mid-range whose sounds are easily diffused. Consequently, 
reproduced sounds in the full range are substantially uniformly diffused 
all around the enclosure, thereby greatly contributing to realization of 
non-directional reproduced sounds emitted from a point sound source in 
cooperation with the above-mentioned function. 
The present invention is as described above. It is, therefore, possible to 
provide a non-directional speaker system having a point sound source, 
which exhibits good localization of acoustic image and excellent 
reproducibility of propagation of a sound field. Accordingly, the speaker 
system of the present invention is extremely useful as a so-called high 
fidelity speaker system for professional or commercial use, a loud speaker 
for a public address system or the like, or a point sound source for 
measuring acoustic characteristics of a hall.