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Claims  |
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What is claimed is:
1. A loudspeaker system comprising:
a plurality of loudspeaker drivers for producing sonic signals in response
to electrical driving signals, at least two of said loudspeaker drivers
each producing sonic signals substantially within the same frequency
range;
means for mounting said loudspeaker drivers in a predetermined spatial
array so that at least two of said drivers producing sonic signals
substantially within the same frequency range are angularly spaced with
respect to one another about a central axis; and
means for modifying the frequency and phase responses of at least two of
said loudspeaker drivers producing sonic signals substantially within the
same frequency range relative to one another so that said array of
loudspeaker drivers produces a combined predetermined radiation dispersion
pattern around said central axis in response to said electrical driving
signals.
2. A system according to claim 1, wherein said means for modifying the
frequency and phase responses of said loudspeaker drivers modifies said
frequency and phase responses of said loudspeaker drivers so that the
frequency response of said array is substantially independent of the
position of a listener within an enclosed space along a listening line
spaced from the system.
3. A system according to claim 1, wherein said means for modifying the
frequency and phase responses of said loudspeaker drivers modifies said
frequency and phase responses of said loudspeaker drivers so that the
frequency response of said array is substantially independent about said
central axis.
4. A system according to claim 3, wherein said frequency response is
substantially flat.
5. A system according to claim 3, wherein said loudspeaker drivers are
electromagnetic.
6. A system according to claim 5, wherein said means for mounting said
loudspeaker drivers includes support means for supporting said loudspeaker
drivers producing sonic signals substantially within the same frequency
range in substantially the same plane normal to said axis.
7. A system according to claim 6, wherein said support means supports said
loudspeaker drivers producing sonic signals substantially within the same
frequency range substantially equidistantly from said central axis.
8. A system according to claim 6, wherein said support means supports said
loudspeaker drivers producing sonic signals substantially within the same
frequency range in a substantially equiangularly spaced-apart relation
around said central axis.
9. A system according to claim 8, wherein said plurality of loudspeaker
drivers include at least two groups of drivers, each of the loudspeaker
drivers of one group producing sonic signals substantially within the same
first frequency range and each of the loudspeaker drivers of the other
group producing sonic signals substantially within the same second
frequency range, at least in part different from said first frequency
range, and said means for mounting said loudspeaker drivers includes
support means for supporting the loudspeaker drivers within each of said
groups in substantially the same plane normal to said axis.
10. A system according to claim 9, wherein said means for modifying the
frequency and phase responses includes a cross-over network for modifying,
as a function of frequency, the amplitude and phase of the electrical
driving signals applied to each of said drivers producing sonic signals
substantially within the same frequency range.
11. A system according to claim 9, wherein said loudspeaker drivers of one
of said groups is axially spaced along said central axis from said
loudspeaker drivers of said other group.
12. A system according to claim 11, wherein said first frequency range is
at least in part below said second frequency range.
13. A system according to claim 8, wherein said plurality of drivers
includes at least one group of woofers, at least one group of midrange
speakers and at least one group of tweeters, and said means for mounting
said drivers includes means for supporting said woofers each in a first
axial position equiangularly spaced about and equidistant from said axis
substantially within a first plane normal to said axis, means for
supporting said mid-range drivers each in a second axial position
equiangularly spaced about and equidistant from said axis substantially
within a second plane spaced from and parallel to said first plane, and
means for supporting said tweeters in a third axial position equiangularly
spaced about and equidistant from said axis substantially within a third
plane substantially parallel to said first and second planes, said second
plane being disposed between said first and third planes.
14. A system according to claim 13, wherein said plurality of drivers
includes four woofers, four midrange drivers and six tweeters.
15. A loudspeaker system for reproducing a stereophonic image within a
predefined space, said loudspeaker system comprising:
at least two loudspeakers, each of said loudspeakers including (1) a
plurality of loudspeaker drivers for producing sonic signals in response
to electrical driving signals, at least two of said loudspeaker drivers
each producing sonic signals substantially within the same frequency
range, (2) means for mounting said loudspeaker drivers in a predetermined
spatial array so that at least two of said loudspeaker drivers producing
sonic signals substantially within the same frequency range are angularly
spaced with respect to one another about a central axis, and (3) means for
modifying the frequency and phase responses of at least two of said
loudspeaker drivers producing sonic signals substantially within the same
frequency range relative to one another so that said array of loudspeaker
drivers produces a combined predetermined radiation pattern around said
central axis in response to said electrical driving signals;
wherein the radiation dispersion pattern of said two loudspeakers
complement one another so that when said loudspeakers are positioned
within said predefined space in a preselected orientation, said
loudspeakers reproduce said stereophonic image within said predefined
space in response to said driving signals substantially independent of the
listener's position within said predefined space along a listening line
spaced from the loudspeakers and nonintersecting a line extending between
said loudspeakers.
16. A system according to claim 15, wherein said means for modifying the
frequency and phase responses of said loudspeaker drivers of each of said
loudspeakers modifies said frequency and phase responses of said drivers
so that the frequency response of said array of each loudspeaker is
substantially independent of the position of a listener within said
predefined space along said listening line.
17. A system according to claim 15, wherein said means for modifying the
frequency and phase responses of said loudspeaker drivers of each said
loudspeaker modifies said frequency and phase responses of said
loudspeaker drivers so that the frequency response of said array of each
loudspeaker is substantially independent about the corresponding central
axis.
18. A system according to claim 17, wherein said frequency response is
substantially flat.
19. A system according to claim 15, wherein each of said loudspeakers
includes a prime axis along which more energy is propagated than in any
other direction, and said loudspeakers are in said mutually preselected
orientation when said prime axes are aligned and directed toward one
another.
20. A system according to claim 19, wherein said loudspeaker drivers are
electromagnetic.
21. A system according to claim 20, wherein said means for mounting said
loudspeaker drivers includes support means for supporting said drivers
producing sonic signals substantially within the same frequency range in
substantially the same plane normal to said central axis.
22. A system according to claim 21, wherein said support means of each of
said loudspeakers supports said loudspeaker drivers producing sonic
signals substantially within the same frequency range substantially
equidistantly from the corresponding central axis.
23. A system according to claim 22, wherein said support means of each said
loudspeaker supports said loudspeaker drivers producing sonic signals
substantially within the same frequency range in a substantially
equiangularly spaced-apart relation around the corresponding central axis.
24. A system according to claim 23, wherein said plurality of loudspeaker
drivers of each of said loudspeakers include at least two groups of
drivers, each of the loudspeaker drivers of one group producing sonic
signals substantially within the same first frequency range and each of
the loudspeaker drivers of the other group producing sonic signals
substantially within the same second frequency range at least in part
different from said first frequency range, and said means for mounting
said loudspeaker drivers includes support means for supporting the
loudspeaker drivers within each of said groups of each said loudspeaker in
substantially the same plane normal to the corresponding central axis of
said loudspeaker.
25. A system according to claim 24, wherein said means for modifying the
frequency and phase responses includes a cross-over network for modifying
as a function of frequency, the amplitude and phase of the electrical
driving signals applied to each of said drivers of each of said
loudspeakers.
26. A system according to claim 24, wherein said loudspeaker drivers of one
of said groups of each loudspeaker is axially spaced along the
corresponding central axis from said loudspeaker drivers of said other
group of that loudspeaker.
27. A system according to claim 26, wherein said first frequency range is
below said second frequency range.
28. A system according to claim 23, wherein said plurality of loudspeaker
drivers of each of said loudspeakers includes at least one group of
woofers, at least one group of mid-range speakers and at least one group
of tweeters, and said means for mounting said drivers of each of said
loudspeakers includes means for supporting said woofers of each said
loudspeaker each in a first axial position equiangularly spaced about and
equidistant from said central axis substantially within a first plane
normal to said axis, means for supporting said mid-range drivers of each
said loudspeaker each in a second axial position equiangularly spaced
about and equidistant from said axis substantially within a second plane
spaced from and parallel to said first plane, and means for supporting
said tweeters of each said loudspeaker in a third axial position
equiangularly spaced about and equidistant from said central axis
substantially within a third plane substantially parallel to and spaced
from said first and second planes, said second plane being disposed
between said first and third planes.
29. A system according to claim 28, wherein said plurality of loudspeaker
drivers of each of said loudspeakers includes four woofers, four mid-range
drivers and six tweeters. |
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Claims |
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Description |
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The present invention relates generally to audio reproduction systems, and
more particularly, to an improved audio reproduction system having one or
more of the following features: (1) a loudspeaker having (a) a flat
frequency response (unless described otherwise, the term "frequency
response" shall be used hereinafter to refer to the frequency response of
a loudspeaker in one direction) and (b) a power response (unless described
otherwise, the terms "power response" shall refer to the amplitude
response of a loudspeaker averaged 360.degree. around the vertical axis of
the loudspeaker in an anechoic chamber); (2) two loudspeakers adapted to
be positioned relative to one another so that they reproduce a
stereophonic image substantially independent of the listener's position in
the listening area; (3) an improved cross-over network having a
substantially constant input impedance as a function of frequency; (4) a
power sensor for sensing the power applied to a transducer so that audio
signals are transmitted over a first signal path through the system when
the sensed power is above a predetermined minimum level, and over a second
path when the sensed power falls below the minimum level; (5) a power
monitoring circuit to prevent a loudspeaker driver from being overdriven;
and (6) a circuit for substantially balancing the signal energy levels
between two audio channels over a long period of time.
Conventional loudspeakers typically have a low frequency speaker driver (a
"woofer"), a mid-frequency speaker driver and a high frequency speaker
driver (a "tweeter") all mounted on a front panel of a speaker cabinet so
as to radiate in the direction of a major or prime axis, the latter being
adapted to be directional when oriented in the direction of the listening
area. These conventional loudspeakers typically exhibit radiation
dispersion patterns (unless otherwise described, the term "radiation
dispersion pattern" as used herein shall mean the power radiated by a
speaker as a function of the angle about the vertical axis of the speaker)
and frequency responses which are strongly variable functions of the
horizontal angular position of the listener relative to the speaker
cabinet of each loudspeaker. Generally, the lower the frequency of a sonic
signal generated by the loudspeaker, the longer the wavelength and the
greater angular dispersion of the sonic signal.
These conventional loudspeaker systems generally are designed so that
radiation generated along the prime or major axis of radiation propagation
of the loudspeaker, i.e., typically in the direction in which the speaker
drivers face, oriented typically towards the listener, will be such that
the on-axis frequency response is flat. However, off angle responses,
i.e., positions other than on the front axis of the speaker, have an
uneven frequency response. As a gross generalization it can be said that
signals below about 500-600 Hz will be substantially omnidirectional
becoming less so as the frequencies increase from about 20 Hz to the
500-600 Hz limit. The signals generated by the midrange drivers are
substantially half omnidirectional at the lower frequency limit of about
500-600 Hz of the mid-range frequencies, while becoming less so with
increasing frequencies to the upper limit of 8 Khz. The signals of the
tweeter become more closely unidirectional as the frequency of the signal
increases from 8 KHz to the 20 KHz.
Another approach in speaker design is to provide a power response in which
the average power propagated into the listening area over all directions
is substantially constant as a function of frequency. Signal attenuation
averaged over all horizontal directions is therefore frequency
independent. However, when the actual power radiated is measured in any
one direction the power propagated can vary substantially as a function of
angular position about the vertical axis of the loudspeaker.
Thus, in conventional loudspeaker designs, there is a trade-off between a
flat on-axis frequency response and a flat average power response into the
listening area. More recent loudspeaker designs have attempted to provide
both in a single design. These designs, however, utilize relatively
expensive, unusual speaker drivers (such as Walsh drivers) to make a flat
on-axis frequency and flat power response simultaneously possible.
It is an object of the present invention to provide an improved loudspeaker
having a substantially flat frequency response 360.degree. around the
vertical axis of the loudspeaker (which insures both a substantially flat
on-axis frequency response and a substantially flat power response) and a
preselected radiation dispersion pattern, without the need of utilizing
unusual and costly speaker drivers.
Another object of the present invention is to provide an improved
loudspeaker utilizing state of the art electromagnetic loudspeaker drivers
and having a substantially flat frequency response 360.degree. around the
vertical axis of the loudspeaker and a preselected radiation dispersion
pattern.
These and other objects of the present invention are achieved by a
loudspeaker system comprising a plurality of loudspeaker drivers for
producing sonic signals in response to electrical driving signals. Means
are provided for mounting the loudspeaker drivers in a predetermined
three-dimensional array with at least some of the drivers being angularly
spaced with respect to one another about the vertical axis of the
loudspeaker. The system also comprises means for modifying the frequency
and phase responses of at least some of the loudspeaker drivers of the
array so that the array of loudspeaker drivers produces in response to the
electrical driving signals a combined predetermined radiation dispersion
pattern and a substantially flat frequency response 360.degree. around the
vertical axis.
By modifying the frequency and phase responses of at least some of the
speaker drivers of a loudspeaker so that the loudspeaker has a
predetermined radiation dispersion pattern in response to electrical
driving signals, it is possible to design two loudspeakers each having a
predetermined radiation dispersion pattern so that when properly oriented
with respect to one another the speakers can produce a stereophonic image
which is substantially independent of listener position along a listening
line spaced from both loudspeakers and non-intersecting with a line
extending between both loudspeakers.
Accordingly, another object of the present invention is to provide a
loudspeaker system comprising at least two loudspeakers each having a
predetermined radiation dispersion pattern such that when properly
oriented with respect to one another they can produce a stereophonic image
substantially independent of listener position along a listening line
spaced from both loudspeakers and non-intersecting with a line extending
between the two loudspeakers.
This and other objects of the present invention are achieved by a
loudspeaker system for reproducing a stereophonic image within a
predefined space such that the perception of the image by the listener is
substantially independent of the listener's position along a listening
line spaced from the two loudspeakers and non-intersecting with a line
extending between the two loudspeakers. The loudspeaker system comprises
at least two loudspeakers. Each loudspeaker includes (1) a plurality of
loudspeaker drivers for producing sonic signals in response to electrical
driving signals, (2) means for mounting the loudspeaker drivers in a
predetermined three-dimensional array with at least some of the
loudspeaker drivers of the array being angularly spaced with respect to
one another about the vertical axis of the loudspeaker and (3) means for
modifying the frequency and phase responses of at least some of the
loudspeaker drivers of the array so that the array of loudspeaker drivers
produces a combined predetermined power dispersion pattern and a
substantially flat frequency response at all positions around the vertical
axis in response to the electrical driving signals. The radiation
dispersion patterns of the two loudspeakers complement one another when
the loudspeakers are in a mutually preselected orientation with respect to
one another so that the loudspeakers reproduce the stereophonic image in
response to the electrical driving signals substantially independent of
the listener's position within the predefined space along a listening line
spaced from the loudspeakers and non-intersecting a line extending between
the two loudspeakers.
Another problem encountered in loudspeaker systems, is that the systems
typically exhibit relatively large variations in input impedance as a
function of frequency which many claim can adversely affect power
amplifier performance. Some manufacturers of the more expensive power
amplifiers have therefore claimed that their amplifiers are adapted to
deal with these non-ideal loads, and thus are usable with any loudspeaker
system.
Accordingly, it is another object of the present invention to provide an
improved loudspeaker system that can be utilized with substantially any
amplifier of sufficient power.
It is yet another object of the present invention to provide an improved
cross-over network for use in a loudspeaker system and having a
substantially flat input impedance as a function of frequency.
These and other objects of the present invention are provided by an
improved loudspeaker system comprising an input terminal for receiving an
electrical input signal; at least two transducer means, the first of the
transducer means for producing sonic signals within a relatively low
frequency range in response to electrical driving signals within that
range, and the second of the transducer means for producing sonic signals
within a relatively high frequency range in response to electrical driving
signals within that range; and cross-over network means connected between
the input terminal and each of the first and second transducer means for
respectively providing to the first and second transducer means the
electrical driving signals within the low frequency range and high
frequency range in response to the electrical input signal. The input
impedance of the cross-over network means when coupled to the first and
second transducer means is substantially constant throughout the low and
high frequency ranges.
Utilizing such a cross-over network coupled to two transducer means,
however, will result in a frequency response which is non-flat.
Accordingly, it is preferable to utilize means, such as an equalizer
circuit in front of the power amplifier to complement the cross-over
network to provide a flat frequency response. However, should it be
desirable to listen to the program signal through other means, such as
headphones, the equalizer circuit will no longer be necessary.
It therefore is another object of the present invention to provide an
improved audio signal processing system in which the signal path through
the compensating means, such as a compensating equalization circuit, is
automatically by-passed and the audio signal transmitted over another
signal path when the power applied to any device for receiving audio
signals from the processing system drops below a predetermined level, as
for example, when the device is disconnected.
These and other objects of the present invention are achieved by an audio
signal processing system for use with at least one device for receiving
audio signals. The system comprises an input terminal for receiving an
input signal, an output terminal for coupling the system to the input of
the device, a first signal path, and a second signal path. Means are
connected in the first signal path for processing said audio signal. The
system also comprises means for sensing the signal energy within at least
one predetermined frequency range at the input of the device and for
coupling the first signal path to the input and output terminals when the
signal energy is above a predetermined level and for coupling the second
signal path to the input and output terminals when the signal energy is
below the predetermined level.
Another problem associated with loudspeaker systems relates to the power
limitations of most speaker drivers, particularly mid-range drivers and
tweeters, which tend to be more fragile than woofers of the same quality
level. Overdriving such speakers can result in permanent damage.
Accordingly, another object of the present invention is to provide a
circuit for use in a loudspeaker system for monitoring the power
transmitted to a an audio device for processing audio signals, such as a
loudspeaker.
Yet another object of the present invention is to provide a power
monitoring circuit for preventing speaker drivers of a loudspeaker system
from being overdriven.
Still another object of the present invention is to provide a power
monitoring circuit for monitoring mid and high frequency signal energy
used for normally driving mid-range and tweeter speaker drivers and for
reducing the power transmitted to the speaker drivers of the loudspeaker
system when the signal energy exceeds a predetermined level.
And yet another object of the present invention is to provide a power
monitoring circuit for monitoring the average signal energy in each of two
audio channels adapted to be respectively coupled to at least two
loudspeakers so that the power transmitted to either loudspeaker will not
exceed a predetermined level and the loudspeaker drivers will not be
overdriven.
These and other objects are achieved by a circuit for monitoring the power
at least within a predetermined frequency range of an electrical
information signal applied to the input of a transducer of an audio
reproduction system in response to a audio input signal transmitted over a
signal path of the circuit. The circuit comprises the signal path, the
signal path having an input terminal for receiving the input signal and an
output terminal for coupling the circuit to the transducer; means capable
of being coupled to the input of the transducer for detecting the level of
the power of the information signal within the predetermined frequency
range and for varying the gain impressed on the input signal in response
to and as a function of the detected power level.
Yet another problem associated with loudspeaker systems, and in particular,
stereophonic systems, relates to the long term power balance between
stereophonic signals transmitted over two stereophonic channels. For
example, differential gain between the two channels may vary from
recording to recording, or along the length of an audio recording tape.
This can be particularly critical when one considers that a precondition
of producing a stereophonic image is that two loudspeakers should produce
substantially balanced power outputs, i.e. the power responses of the
speakers should be substantially the same.
Accordingly, another object of the present invention is to provide a signal
processing system of the type for use with a loudspeaker system for
creating stereophonic sound in which the signal energy transmitted over
the two stereophonic channels is substantially balanced over relatively
long periods of time.
Another object of the present invention is to provide a signal processing
system for comparing the average power levels in each of two stereophonic
channels of a stereophonic audio reproduction system and for adjusting the
power levels so they are balanced over long periods of time.
These and other objects are achieved by an improved signal processing
system of the type for use with an audio reproduction system including at
least two transducers for creating stereophonic sound in response to two
audio input signals. The signal processing system comprises a pair of
signal paths for respectively transmitting the two audio input signals to
the corresponding transducers, each of the signal paths including an input
terminal for receiving a respective one of the audio input signals and an
output terminal for coupling the signal path to a corresponding one of the
transducers. Means are coupled to each of the input terminals for
detecting the signal energy level of the corresponding audio input signal.
Means are provided for comparing the detected signal energy levels of the
audio input signals and for generating a difference signal in response to
and as a function of the comparison. The signal processing system also
comprises means responsive to the difference signal and coupled between
the input and output terminals of at least one of the signal paths for
varying the signal gain impressed on the audio input signal transmitted
over the one path as a function of the difference signal so that the
signal energy levels of the audio input signals for the paths are
substantially balanced over relatively long periods of time.
Other objects will in part be obvious and will in part appear hereinafter.
The invention accordingly comprises the apparatus possessing the
construction, combination of elements, and arrangement of parts which are
exemplified in the following detailed disclosure, and the scope of the
application of which will be indicated in the claims.
Since certain changes may be made in the above apparatus without departing
from the scope of the invention herein involved, it is intended that all
matter contained in the above description and shown in the accompanying
drawings shall be interpreted in an illustrative and not in a limiting
sense.
In the drawings the same numerals are used to refer to like parts.
FIG. 1 shows the front view of a typical prior art loudspeaker having a
woofer, a mid-range frequency speaker and a tweeter;
FIG. 2 shows a cross-sectional view taken along line 2--2 in FIG. 1;
FIGS. 3A and 3B respectively show a simplified radiation dispersion pattern
at two different frequencies for a typical woofer;
FIGS. 4A and 4B respectively show typical radiation dispersion patterns at
two different frequencies for a typical mid-range speaker and a typical
tweeter;
FIG. 5 graphically illustrates the power output of a typical prior art
loudspeaker, such as shown in FIGS. 1 and 2, as a function of frequency
wherein the on-axis frequency response is constant;
FIG. 6 graphically illustrates a simplified plot of the power output of a
loudspeaker as a function of frequency so that the power output is
substantially constant;
FIG. 7 shows a front view of a preferred embodiment of a loudspeaker made
in accordance with the present invention;
FIG. 8 is a cross-sectional view taken through the woofers taken along line
8--8 in FIG. 7;
FIG. 9 is a cross-sectional view taken through the mid-range speaker
drivers along line 9--9 in FIG. 7;
FIG. 10 is a cross-sectional view taken through the tweeters along line
10--10 in FIG. 7;
FIG. 11 is designed to show typical radiation dispersion pattern of the
tweeters of the preferred embodiment of the present invention at
relatively high frequencies;
FIG. 12 shows the radiation dispersion pattern of the tweeters of the
preferred embodiment of the present invention at relatively low
frequencies;
FIG. 13 shows a plan view of a stereophonic loudspeaker system of the prior
art to illustrate the concept of stereophonic imaging and the problems of
the prior art;
FIG. 14 is a plan view of a loudspeaker system including at least two
speakers for creating a stereophonic image substantially independent of
listener position along the listening line;
FIGS. 15A-15C is a schematic diagram of the preferred embodiment of the
cross-over network utilized in the present invention;
FIG. 16 shows a block diagram of the preferred embodiment of an audio
reproduction system incorporating many novel aspects of the present
invention; and
FIGS. 17A-17I are schematic diagrams of the prefered embodiment of the
system shown in FIG. 16.
Referring to the prior art loudspeaker of FIG. 1, the typical loudspeaker
includes a woofer 10 for generating sonic signals generally within a
low-frequency range, typically between about 20 Hz and 500 Hz; a mid-range
speaker for generating sonic signals generally within a mid-frequency
ranee, typically between about 300 Hz and 3 KHz; and a tweeter for
producing sonic signals within a range of about 2 KHz and 20 KHz. As shown
in FIG. 2, the three different types of speakers are typically vertically
mounted, one above the other on the front panel 18 of the speaker cabinet
so that the prime axis or direction of radiation propagation is in front
of the loudspeaker. As shown in FIG. 3A, the woofer typically produces
almost an omnidirectional radiation dispersion pattern for
low-frequencies, for example, between 0 and 100 Hz for a 12 inch woofer,
while a less omnidirectional radiation pattern at higher frequencies of
the output of the woofer, e.g., between about 200 and 500 Hz. Similarly,
the mid-range and tweeter speakers provide radiation dispersion patterns
as shown in FIGS. 4A and 4B, wherein FIG. 4A is the lower frequencies of
each of the speakers, while FIG. 4B illustrates the dispersion pattern of
the higher frequencies of the speaker. As shown, the dispersion pattern of
FIG. 4A is typical of a 4 inch mid-range speaker at 2-3 KHz, while the
radiation dispersion pattern of FIG. 4B is typical of such a tweeter
speaker at 10-20 KHz.
When this particular type of prior art speaker is designed to provide a
flat frequency response the amplitude of the power output of the speakers
along the prime axis of propagation is generally flat as a function of
frequency as shown in FIG. 5. However, as shown in FIG. 5, the radiation
dispersed in directions other than the prime axis will not be constant as
shown.
Accordingly, another approach in speaker design is to provide a flat power
response into the listening area. Specifically, the speaker is designed so
that the energy radiated into the listening area averaged overall
direction is flat with respect to the frequency range within which the
speaker radiates sound. The average power output of such a prior art
system is shown in FIG. 6 as having a flat response. However, as shown,
the power output in any one particular direction may not be flat such as
the on-axis radiation curve as well as the off-axis radiation curve.
Accordingly, in these conventional prior art loudspeaker systems there is
a trade-off. A loudspeaker system can be designed to have a flat on-axis
frequency response resulting in a power curve which is not flat as shown
in FIG. 5, or a system can be designed to have a power curve which is flat
resulting in an on-axis response which is not flat as shown in FIG. 6.
In accordance with the present invention, a loudspeaker system is designed
to provide both a flat frequency response and a radiation dispersion
pattern which can be easily predesigned without necessarily resorting to
the use of unusual speaker drivers. The preferred embodiment of the
present invention comprises ordinary electromagnetic loudspeakers,
angularly spaced relative to one another about the vertical axis of the
loudspeaker cabinet and includes means for modifying as a function of
frequency, the phase and amplitude of the driving signals fed to each
loudspeaker driver so as to obtain a substantially flat power and on-axis
frequency responses.
More particularly, as shown in FIG. 7, the preferred embodiment of the
loudspeaker system includes a loudspeaker cabinet 28, including suitable
baffle structure (not shown) for supporting four woofers 32A, 32B, 32C,
and 32D mounted substantially in the same horizontal positions,
equidistant from and at 90.degree. intervals about the vertical axis 26 of
the loudspeaker. Similarly, four mid-range speakers 34A, 34B, 34C, and 34D
are mounted substantially in the same horizontal positions, preferably
above the respective woofers 32, equidistant from and at 90.degree.
intervals about the vertical axis 26, as shown in FIG. 9. Finally, six
tweeters 36A, 36B, 36C, 36D, 36E and 36F are mounted substantially in the
same horizontal positions, preferably above the midrange speakers,
equidistant from and at 60.degree. intervals about the vertical axis 26,
as best shown in FIG. 10. The front of loudspeaker 28 is defined by the
positions of speakers 32A, 34A, and 36A. The front of the loudspeaker
defines the direction of propagation of the prime axis of the loudspeaker.
In accordance with the present invention each of the woofers 32, mid-range
speakers 34 and tweeters 36 each may be any type of speaker which is known
in the art. Preferably, each of the speakers is of the electromagnetic
type, each woofer being a conventional 10 inch speaker. By controlling the
frequency and phase responses of each woofer 32, mid-range speaker 34, and
tweeter 36, the desired frequency response and power dispersion pattern
are achieved. Specifically, the responses of the auxillary speakers,
woofers 32B-32D, mid-range speakers 34B-34D, and tweeters 36B-36F are used
to complement the responses of the main speakers 32A, 34A and 36A to
provide an overall flat frequency response and a preselected radiation
dispersion pattern. Thus, when the main speaker drivers 32A, 34A and 36A
are omnidirectional at a particular frequency, the response required from
the auxiliary speaker drivers may be such as to reduce the
omnidirectionality of the main driver (by radiating substantially
out-of-phase) then producing the preselected radiation dispersion pattern.
When more energy is radiated by the main driver at another particular
frequency along the prime axis than radiated in off-axis directions, the
auxiliary drivers begin to fill in for the overall dispersion
characteristics. In this manner, one can tailor the amplitude and phase
response of each speaker so that the system frequency response is flat in
any direction, but the overall radiation dispersion pattern conforms to a
preselected pattern. This is illustrated by FIGS. 11 and 12, wherein FIG.
11 shows the response of each tweeter at a relatively high frequency,
while FIG. 12 shows the response of each tweeter at a relatively low
frequency.
More particularly, in FIG. 11 at the higher frequencies each tweeter will
generate its radiation substantially within an approximate 60.degree.
angle symmetrical about the direction of propagation of radiation from the
driver, indicated by the corresponding arrow 40 so that the radiation
dispersion pattern of each tweeter 36 is substantially the same as
indicated by the patterns 42 to produce an overall radiation dispersion
pattern 44. On the other hand, at the lower frequencies generated by the
tweeters as shown in FIG. 12 the main driver 36A will generate the
dispersion pattern indicated by the pattern 46A which is more
omnidirectional than the pattern 42A. Thus, the adjacent drivers 36B and
36F need to contribute less, and therefore would produce patterns similar
to 46B and 46F, respectively. In a similar manner, the dispersion patterns
produced by the drivers 36C, 36D, and 36E produce the varied dispersion
patterns 46C, 46D, and 46E which combine with the other dispersion
patterns 46A, 46B, and 46F to provide the overall dispersion
characteristics substantially similar to the dispersion pattern 48. Thus,
by varying as a function of frequency the amplitude and phase of the
driving signals provided to the tweeters, the overall radiation dispersion
pattern including patterns 44 and 48 can be determined in a similar manner
for all of the frequencies generated by the drivers 36. In a similar
manner by controlling as a function of frequency the amplitude and phase
of the driving signals to the mid-range speakers 34A-34D and the woofers
32A-32D the overall radiation dispersion patterns can be made
substantially similar to patterns 44 and 48 throughout the entire
frequency range of the loudspeaker, e.g., 20 Hz-20 KHz. Where it may be
desirable to radiate greater power from the loudspeaker in one direction
than, for example, another, the overall radiation dispersion pattern can
be easily modified by varying the particular phase and power responses of
each of the main and auxiliary speakers. Thus, a particular array of
loudspeaker drivers (a minimum of two) can be made directional by a
combination of their relative locations to one another, and by controlling
as a function of frequency, the phase and amplitude of the driving signals
used to drive the loudspeaker drivers.
In accordance with one aspect of the present invention, in the preferred
embodiment, the specific radiation dispersion patterns of each of a pair
of separate loudspeakers can be developed such that a stereophonic image
can be created between the loudspeaker systems substantially independently
of a listener's position within a listening area along a listening line
spaced from the loudspeaker systems and non-intersecting with a line
extending between the loudspeaker systems. This will be more evident by
the following description with respect to FIGS. 13 and 14.
Referring to FIG. 13, conventional prior art loudspeakers 10 can, for
example, produce constant average power outputs. If the power output of
each speaker 10 is approximately the same then a listener positioned
approximately equidistant from each speaker 10 along a listening line
L.sub.2, parallel to a line L.sub.1 extending between the two
loudspeakers, the listener will perceive an apparent stereophonic image
(the apparent location of the source of the sound as heard by the
listener) approximately in the center between the two speakers, as
indicated by the point I. With the conventional prior art system shown in
FIG. 13, the listener receives information from the speakers which
includes amplitude and phase. Various certain phase delays occur between
the left and right speakers. A small interaural phase delay occurs as one
moves closer to one speaker than the other. Thus, should the listener move
along the listening line L.sub.2 in a direction toward either one of the
loudspeakers 10, the stereophonic image will no longer be perceived and at
some point all of the sound will appear to come from one speake | | |
