Note: Descriptions are shown in the official language in which they were submitted.
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BACKGROUND OF TH~: I~7ENTION
The present invention relates in general to loudspeaker
systems and more particularly concerns novel apparatus and
techniques for providing an inexpensive bookshelf loudspeaker
with few placement constraints that is relatively inexpensive
to manufacture while offering unique spatial properties.
The internationally known BO~E 901 loudspeaker system
embodies principles for simulating in the home sound of the
character heard in the concert hall. For optimum results the
sOSE 901 loudspeaker is located about a foot from a wall
facing angled speaker panels to provide a good balance of
reflected and direct sound with a substantially uniform
radiated power response in cooperation with an electronic
active equalization network~ While performance of this system
is excellent, there are a number of home listening locations
where placement for optimum performance is difficult.
Accordingly, it is an important object of this inven-
tion to provide a bookshelf loudspeaker having few placement
constraints offering unique spatial properties while being
relatively inexpensive to manufacture.
It is another object of the invention to achieve the
preceding objects with a relatively compact system.
It is still a further object of the invention to achieve
one or more of the preceding objects while providing a good
balance of direct and reflected sound and presenting a broad
acoustical image source that is interesting to the listener.
SUMMARY OF THE I~VENTION
According to the invention, there is a loudspeaker
cabinet having a first panel for supporting a first driver
means, and at least a second panel for supporting second
driver means that faces to the front and side, first driver
means mounted on the first panel for radiating acoustical
energy in a first frequency
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range, second driver means supported on the second panel for
radiating energy ln a second frequency range tha-t includes
portions higher than the flrs-t frequency range and a common
frequency range that overlaps the first frequency range for at
least a half octave and crossover network means for coupling
electrical energy from an input terminal pair to the first
driver means and the second driver means so that the first
driver means radiates energy over said first frequency range
and the second driver means radiates energy over said second
frequency range.
Accordiny to another aspect of the invention there
is adjustable deflector means intercepting the energy radia~ed
by the second driver means for directing the high frequency
energy radiated therefrom in a predetermined direction.
According to a specific aspect of the invention there is at
least a third panel for supporting third driver means between
the first and second panels, and third driver means supported -
on the third panel.
According to a still further broad aspect of the
present invention there is provided a loudspeaker system
which comprises cabinet means for supporting loudspeaker
drivers. First loudspeaker drivermeans is supported by the
cabinet for radiating sound energy to the front over a first
frequency range and having a first polar response~ Second
loudspeaker driver means i~ supported by the cabinet for
radiating sound energy to the front and side over a ~econd
frequency range mostly higher than the first frequency range
and having a second directional polar response different from
the first polar response. The angle between the axes of the
first and second loudspeaker driver means is an acute angle.
Also provided is an input terminal pair. Means is further
provided for intercoupling the input terminal and the first
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and second lougspeaker driver means for providiny spectral com-
ponents in a common frequency range to the first and second
loudspeaker driver means. The second means for intercoupling
includes means for attenuating spectral cornponents applied to
the first and second driver means above and below respectively
first and second frequencies respectively at the high and low
ends respectively of the common frequency range relative to
spectral components applied thereto in the common frequency
range so that the difference between output frequency response
of the first driver means and output frequency response of the
second driver means is substantially the same over the common
frequency range. This means for intercoupling coacts with the
first and second loudspeaker driver means to comprise means for
dissimilarly radiating from first and second locations defined
by the first and second loudspeaker driver means,respectively, -
~spectral components over the common frequency range to provide
a spatially diffuse source. m e common frequency range is at
least half an octave,
Numerous other features, objects and advantages of the
invention will become apparent from the following specification
when read in connection with the accompanying drawing in which:
FI~. 1 i a top view of an embodiment of the invention
in a room,
FIG~ 2 is a front view of the embodiment of FIG. 1,
FIG. 3 is a perspective view of an embodiment of the
invention using only two drivers for each loudspeaker cabinet,
FIG. 4 is a plan view of a pair of loud~peakers accord-
ing to the invention in a room arranged for stereo;
FIG. 5 is a plan view of a preferred form of a
deflector panel accordin~ to the invention,
FIG, 6 illustrates the frequenc~ ranges of the woofer,
midrange driver and tweeter in the embodiment of E'IGS. 1 and 2,
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FIG. 7 illustrates the frequency ranges of the woofer
and tweeter in the embodiment of FIG. 3; and
FIG. 8 is a schematic circuit diagram of a loudspeaker
system for the embodiment of FIG. 3.
DETAILED DESCRIPTIO~ OF PREFERRED EMBODIME~TS
With reference now to the drawing and more particularly
FIG. 1 thereof, there is shown a top view of a loudspeaker
system according to the invention in a room~ The loudspeaker
cabinet 11 includes a top 12, a front panel 13 supporting a
woofer 14, side panels 16 and 17, a corner panel 18 facing
the side wall 21 and carrying a tweeter 22 and a corner panel
23 facing toward the center of the room and carrying a mid- : .
range driver 24. FIG. 2 is a front view of loudspea~er
system 11. The listener 25 receives some direct sound from
midrange driver 24 and reflected sound from tweeter 22.
In this embodiment -Iow frequency woofer 14 -typically
radiates between 40 Hz and a first crossover frequency by
itself and between the first crossover frequency and a second
crossover frequency with midrange driver 24. Midrange driver
24 radiates between the first crossover frequency and a third
crossover frequency. Tweeter 22 radiates between the second
crossover frequency and 18 kHz. Drivers 22 and 24 have an
overlapping range between 3 kHz and ~ kHz. The first cross-
over frequency is typically within the range of 500 to 1000
Hz; the second, between 2 kHz and 3 kHz, and the third
between 6 kHz and 9 kHz. A loudspeaker thus arranged produces
a very wide diffused acoustical spatial image, especially : -
noticeable in stereo with both tweeters 22 facing the adja- :
cent sidewall. By arranging loudspeaker system 11 as shown,
the embodimenk in FIG. 2 may be flipped over so that the top ~.
12 is on the bottom and thereby tweeter 22 will be to the
right of woofer 14 as seen by listener 25.
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The invention is believed to produce this widely
diffused spatial image by taking advantage of some known
factors. It is known that humans receive much auditory
localization information from the high frequency components of
sound having spectral components above 1 kHz. The invention
takes advantage of this characteristic in a number of ways.
The very high frequency components radiate toward the sidewall
away from the listener, and the reflections from the ~ide wall
create a virtual image of the tweeter on the other side of
the wall spaced from the sidewall by the same distance
between the sidewall and the tweeter 22. To create a reason-
ably well localized virtual image, tweeter 22 is reasonably
directional as distinguished from the omnidirectional tweeters
usually used in conventional loudspeaker systems. A small
amount of high frequency components are radiated directly at
the liste~er 25 by the midrange driver 24. It was discovered
that failing to provide this direct high frequency component
would cause an instrument to tend to sound far away and
smeared whereas providing this direct component maintained a
proper crispness to instruments.
It is known in psycoacoustics (Gardner, JOurnal of the
Acoustical Society of America, Vol. 46, ~o. 2 1969) that
several things can be done to effect the fusion of a sonic
image. By having two sources that are physically separated
and radiate overlapping portions of the spectrum, it is
possible to produce the impression of a single broad source
located between them. It i9 also known that by taking two
separated loudspeakers and arranging to radiate signals from
them in phase opposition while adjusting the amplitude of one
of the loudspeakers, it is possible to create phantom sources
that lie outside of the region between the two sources.
The invention takes advantage of these characteristics
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by having the crossover between the two drivers 22 and 24 of
gentle slope as shown in FIG. 6 with considerable overlap in
the crossover region where both drivers radiate spectral
components in this common region. By proper selection of the
midrange driver 24 and the tweeter 22, it is possible to
achieve two 180 phase shifts at relatively narrow bands of
frequencies in the common fre~uency range where drivers 22
and 24 radiate in phase opposition in the regions about the
fundamental resonances of the drivers. Drivers 22 and 24
each typically have a fundamental reson~nce in the common
frequency range, that of tweeter 22 being higher than that of
midrange driver 24 to effect these phase shifts. Although
these phase shi~ts may produce a desirable effect, there is
presently insufficient evidence to positively confirm it.
By having spatially separate sound sources radiating,
the apparent location of the sound source moves from one side
to the other with spectrum of the radiated signal. Since
music generally contains a broadband signal, the apparent
source is constantly apparently in motion to the listener,
and the listener is unable to localize the sound as coming
from any one point but perceives the sound as coming from a
broad source. The combination of these effects produces a
loudspeaker with a wide spatial imageO
Referring to FIG. 3, there is shown a perspective view
of another embodiment of the invention that uses only two
drivers while being relatively easy to locate, having
superior spatial properties relative to a conventional
loudspeaker and being adjustable to the taste of the listener
for room and source characteristics. FIG. 3 shows a right-
cornered loudspeaker system 31 having rectangular top andbottom panels 32 and 33, a rectangular front panel 34 side
panels 35 and 36, a rear rectangular panel (not visible in
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FIG. 3) and an angled corner panel 37 formed with a port
38. WooEer 45 is mounted in front panel 34. A vertical
shaft 41 split at the bottom depends from the corner o-E
top panel 32 and carries a sound deflecting panel or
vane 42 Eacing tweeter
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43 mounted in corner panel 37. A knob 44 attached to vertical
shaft 41 controls the orientation of sound panel 42 for adjust-
ment to control the energy radiated directly to the listener.
Deflecting panel 42 pivots about an axis near its front edge so
that movement of the rear edge toward andfrom the woofer deflects
less and more energy, respectively, toward the center of the room.
"Velcro" registered trade mark, tabs, such as 39, are
attached to the front and side panels for mating engagement with
"Velcro" tabs on grill cloth assemblies (not shown)~ One nearly
square grill cloth assembly covers woofer 45, A two-panel hinged
assembly bears against corner plate 40 and covers the tweeter
corner and side. A finished vertical wooden slat 46 sepaxates
the two assemblies.
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Referring ~o FIG. 4, there is shown a plan view of
right loudspeaker system 31 and a left loudspeaker system 51
that is the mirror image of right loudspeaker system 31. A
feature of the invention is that each woofer typically operates
over the frequency range from 30 ~Iz to 3.0 kHz while each tweeter
typically operates over a range of 1.2 to 1~ kHz so khat the
overlapping or cornmon frequency range is of the order of 1.8 kHz
and preferably an octave or more but no less than a half octave.
It was discovered that a cornmon frequency range as low as 1/3
octave resulted in sounds from the same instrument appearing to
come from different locations while a common frequency range
preferably at least an octave avoided the problem. A commmon
frequency range of a half octave may be acceptable but a greater
range is preferred.
Another feature of the invention is that tweeter 43 is
highly directional, unlika conventional loudspeaker sy,stems which
feature omnidirectional tweeter~. The directional tweeter
facilitates exercising good control over where the energy from
the tweeter is directed with the deflecting panel 42. FIG. 4
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shows the normal position of deflecting panels ~2 and 42'
with the plane of each along the tweeter axis. In this
position the listener perceives a reasonably wide image
extending somewhat into the center region between the loud-
speaker systems when used in stereo. By moving the rear edges
of deflecting panels 42 and 42' further away from the woofer
more high frequency energy is deflected toward the center of
the room to enhance the center image. The image perceived is
then less spacious than in the normal position and sounds more
intimate. This position may be advantageous when listening
to a vocalist or single instrument.
sy moving the rear edges of deflecting panels 42 and 42'
toward the woofer, more high frequency energy is directed
away from the listener and back toward the rear and sidewalls
to create a very spacious sound image with less center image
between the loudspeaker systems. This position may be useful
when the loudspeaker systems are positioned very close to
each other, such as in a small room. -
It is preferred that the deflecting panels 42 and 42'
be arranged so that as a deflecting panel is rotated, it is
possible to redirect as much energy from the tweeter as
possible, it should function at as low a fxequency as practi-
cal, it should not hornload the tweeter and rotation or the
deflecting panels should not change the radiated power fre-
quency response of the loudspea~er system, this response
being substantially constant. The deflecting panel should be
massive and stiff enough so that it reflects at the frequen-
cies of interest and its length, and width preferably are
larger than a wavelength at these frequencies. These frequen- -
cies are typically above 3 kHz, typically the second crossover
frequency. The rear edge preferably is very close to tweeter
43.
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Referring to FIG. 5, there is shown a plan view of
a preferred form of deflecting panel which meets these
criteria
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made of 0.~5" thick blac~ anodized or chromated high strength
aluminum. It may be advantageous to place sound absor~ing
material on the side of the deflecting panel that faces the
tweeter when the rear edge of the deflecting panel is pointed
away from the woofer because there is then less high frequency
absorption compared with other positions when there is sub-
stantial reflection from the walls allowing coverings and other
objects to absorb.
Referring to FIGS. 6 and 7, there are shown graphical
representations of typical crossover network responses with
the ~ystem according to the invention in the embodiments of
FIGS. 1 and 3, respectively, The crossover networks comprise
means for intercoupling the input terminal and the loudspeaker
driver means for providing spectral components in a common
frequency range to first and second ones of the loudspeaker
driver means, the means for intercoupling including means for
attenuating spectral components applied to the first and second
frequencies respectively at the high and low ends respectively
of the common frequency range relative to spectral components
applied thereto in the common frequency range. For the embodi-
ment of FIG. 3 this common frequency range is between 1 and 3
kHz with the first driver being woofer ~5 and the second driver
being tweeter 43 and the first and second frequencies being
substantially 3 and 1 kHz, respectively. For the embodiment of
FIGS. 1 and 2, there is a common frequency ranye and first and
second frequencies between the woofer and midrange driver,
between the midrange driver and the tweeter and between the
woofer and tweeter as ~een in FIG. 6. The crossover network
thus comprises means for establishing the crossover between
the first and second drivers of yentle slope in the common
frequency range so that the difference between the first driver
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output frequency response and second driver output frequency
reiSpOnSe i5 substantially the same over the common fre~uency
range.
Referring to FIG. 8 there is shown a schematic circuit
diagram of a preferred crossover network for use with the loud-
speaker system of FIG. 3 in which woofer ~5 is an 8" woofer
having a d-c impedance of 5.7 ohms, tweeter 43 is a three inch
electrodynamic spea~er having a d-c resistance of 6.5 ohms to
form a system that has a nominal ~ ohm impedance and radiates a
substantially uniform power response as a function of frequency.
This network coacts with the tweeter to produce an on-axis
free-field pressure response that rises as a function o-f increas-
ing frequency so that the system has a substantially uniform
radiated power response as a function of frequency.
It is within the principles of the invention to mount
one or more tweeters on gimbals to permit energy to be directed
upward or downward and to enable a loudspeaker system to be
oriented with its length horizontally or vertically whlle still ;
permitting energy to be reflected from sidewalls. While a
ported structure is shown and preferred for efficiency reasons,
it is within the principles of the invention to use 2L sealed
cabinet.
Although the invention preferably uses reflections
from sidewalls when available, a system according to the inven-
tion may function as a spatially extended source without using
wall reflectio~s. ~he invention achieves this efect by
having at least two spaced dri~ers, such as a woofer and a
tweeter, that operate over a common frequency range, and exhibit
different transfer characteristics between the input terminal
pair of the loudspeaker and the room into which the system
radiates. A preferred way of achieving these dif~erences is
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to use transducers having different characteristics, such as a
woofer and a tweeter. The woofer such as ~5 may be regarded as
a first loudspeaker driver supported by the cabinet for radiat-
ing sound energy to the front over a first fxequency range and
having a first polar response, and the tweeter such as 43 may be
regarded as a second loudspeaker driver supported by the cabinet
for radiating sound energy to the front and side over a second
frequency range mostly higher than the first frequency range
and having a second directional polar response different from
the first polar response.
If two spaced drivers with identical characteristics
radiate the same sound, the ear perceives the sound as origin-
ating midway between the two. The brain is believed to act as
a cross correlator that correlates the signal perceived by the
left ear with the signal perceived by the right ear, producing
an effective cross correlation signal characterized by spikes
because of the coherence between the signals emitted by the like
drivers, By causing the drivers to have dissimilar character- -
istics over a substantial common frequency range, there is no
coherence between the signals emitted by the drivers with the
result that there is no spike in the effective cross correlation
response of the left and right ears. q'he sound perceived is
then more nearly like that perceived by a listener in the con-
cert hall because there is an absence of exact coherence between
the sounds provided by the spaced instruments.
An actual commercial embodiment of the invention is
the BOSE Model 301 loudspeaker system. q'he panels are typically
made of 1/2" thick particle board with a density of ~2-~5 pounds.
The top and bottom panels are typically 17" by 9 1/4". The front
panel is typically 12" by 10", and the side panel facing the
center of the room is typically 9 1/4" by 10". The angle
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between front panel 3~ and corner panel 37 is substantially 135
degrees, and the diameter of port 3~ is substantially 2 1/2".
Deflecting panel 42 is ~ubstantially 2 1/4" wide, 4 31/32" long
along the front edge and substantially 15/32" less along the
rear edge with its axis of rotation substantially 5/32" from
the front edge.
An embodiment of the invention corresponding substan-
tially to the embodiment of FIG. 1 includes a 10" woofer having
a d-c resistance of 6 ohms having a depressed shelf response
beginnlng at 700 Hz and tapering down to 3 k~Iz, a midrange
driver or middler having a d-c resistance of 6.5 ohms having a
response that begins at about 700 Hz to complement the woo~er
to about 3 kHz tapering down from 3 kHz to 10 k~Iz and a tweeter
having a d~c resistance of 6.5 ohms that complements the woofer
and middler from 1.2 kHz to 3 or 4 kHz and then extends to about
16 kHz, The woofer and middler thus overlap for more than two
octaves, the middler and tweeter overlap for more than three
octaves and the tweeter and woofer overlap for more than an
octave. A suitable crossover network for coaction with these
drivers comprises connecting the woofer directly across the in-
put terminals, connecting the series combination of a 13 ohm
resistor, 5 mfd capacitor and the driver across the input
terminals and a 2 mfd capacitor in series with the tweeter across
the input terminals. Respective adjustable deflecting panels
similar to panel 42 in FIG. 3 are adjacent to the middler and
tweeter.
There has been described novel apparatus and
techniques for reproducing sound with high quality perceived
as emanating from a relatively broad source and that per~orms
well in a wide variety o~ listening environments. ~et the
structure is compact and relatively easy and inexpensive to
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~abricate. It is evident that those s~illed in the art may now
make numerous uses and ~nodifications of and departures from
the specific embodiments described herein without departing
from the inventive concepts. Consequently, the invention is to
be construed as embracing each and every novel feature and novel
combination of features present in or possessed by the apparatus
and techniques herein disclosed and limited solely by the
spirit and scope of the appended claims.
This application is a division of Canadian Patent
Application Ser. ~o. 241,393 filed December 9, 1975.
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