U.S. patent number 3,582,553 [Application Number 04/690,695] was granted by the patent office on 1971-06-01 for loudspeaker system.
This patent grant is currently assigned to Bose Corporation. Invention is credited to Amar G. Bose.
United States Patent |
3,582,553 |
Bose |
June 1, 1971 |
**Please see images for:
( Certificate of Correction ) ** |
LOUDSPEAKER SYSTEM
Abstract
A loudspeaker system comprises two angularly displaced rear
rectangular baffles each nearly filled with four closely spaced
full-range small loudspeakers and partially enclosing a
substantially fluid-tight volume also enclosed by a front baffle
containing a small asymmetrically located loudspeaker so that the
angularly inclined baffles typically face a wall to which the front
baffle is generally parallel. The small loudspeakers are connected
in phase and energized through means including a complementing
circuit so that the overall system is characterized by a
phase-frequency response characteristic that pleasingly reproduces
music.
Inventors: |
Bose; Amar G. (Chestnut Hill,
MA) |
Assignee: |
Bose Corporation (N/A)
|
Family
ID: |
24773540 |
Appl.
No.: |
04/690,695 |
Filed: |
December 4, 1967 |
Current U.S.
Class: |
381/89; 381/345;
181/147; 381/98; 381/111; 381/59; 381/103 |
Current CPC
Class: |
H04R
5/02 (20130101); H04R 1/323 (20130101); H04R
1/26 (20130101); H04R 2205/024 (20130101) |
Current International
Class: |
H04R
5/02 (20060101); H04R 1/26 (20060101); H04R
1/20 (20060101); H04R 1/22 (20060101); H04R
1/32 (20060101); H04r 001/28 () |
Field of
Search: |
;179/1E,1AT,1DIR
;181/31.1 ;333/28T |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Claffy; Kathleen H.
Assistant Examiner: Leaheey; Jon Bradford
Claims
I claim:
1. A loudspeaker system comprising, first means defining a front
panel arranged to be situated normally generally parallel to a
wall,
second means defining a rear baffle including means for supporting
at least one upper frequency radiating means,
means including said first means and said second mean for defining
a loudspeaker cabinet enclosing an internal volume,
said first and second means being relatively positioned so that
with said loudspeaker cabinet normally positioned with said front
panel generally parallel to a wall, a plurality of upper frequency
radiating means carried by said means for supporting are positioned
for emitting upper frequency sound in a beam that has a rearward
component directed away from said front panel toward said wall and
a sideward component directed generally parallel to said wall,
means including said upper frequency radiating mean and said
loudspeaker cabinet enclosing said internal volume substantially
fluidtight
and means associated with said upper frequency radiating means for
establishing the free field infinite baffle pressure frequency
response along the axis thereof higher relative to the response in
the middle range of audio frequencies while coacting with all the
elements in said loudspeaker system to provide an essentially
uniform radiated power density spectrum frequency response over
substantially the entire audible frequency range when said
loudspeaker system is normally positioned with said front panel
generally parallel to a wall.
2. A loudspeaker system in accordance with claim 1 and further
comprising,
third means defining another rear baffle including means for
supporting at least another upper frequency radiating means,
said third means being positioned relative to said first and second
means so that with said loudspeaker cabinet normally positioned
with said front panel generally parallel to a wall, an upper
frequency radiating means carried by said means for supporting of
said third means is positioned for emitting upper frequency sound
in a beam that has a rearward component directed away from said
front panel toward said wall and a sideward component directed
generally parallel to said wall opposite to said first-mentioned
sideward component.
3. A loudspeaker system in accordance with claim 1 wherein said
front panel includes mans for supporting at least one front upper
frequency radiating means so that with said loudspeaker cabinet
normally positioned with said front panel generally parallel to a
wall, a front upper frequency radiating means carried by said means
for supporting is positioned for emitting upper frequency sound
without reflection in a direction away from said wall,
and further comprising said at least one front upper frequency
radiating means carried by said means for supporting,
and means including said upper frequency radiating means and said
loudspeaker cabinet enclosing said internal volume substantially
fluidtight
4. A loudspeaker system in accordance with claim 2 wherein said
front panel includes means for supporting at least one upper
frequency radiating means so that with said loudspeaker cabinet
normally positioned with said front panel generally parallel to a
wall, a front upper frequency radiating means carried by said means
for supporting is positioned for emitting upper frequency sound
directed away from said wall,
and further comprising said at least one front upper frequency
radiating means carried by said means for supporting,
and means including said upper frequency radiating means and said
loudspeaker cabinet enclosing said internal volume substantially
fluidtight
5. A loudspeaker system in accordance with claim 1 wherein said
first means and said second means are nonparallel to one
another.
6. A loudspeaker system in accordance with claim 2 wherein said
first means, said second means and said third means are nonparallel
to one another.
7. A loudspeaker system in accordance with claim 3 wherein said
first means and said second means are nonparallel to one
another.
8. A loudspeaker system in accordance with claim 4 wherein said
first means, said second means and said third means are nonparallel
to one another.
9. A loudspeaker system in accordance with claim 6 wherein small
loudspeakers comprising said upper frequency radiating means occupy
most of the area of each of said rear baffles.
10. A loudspeaker system in accordance with claim 9 wherein said
front panel includes means for supporting a number of small
loudspeakers that is less than the number of small loudspeakers
said means for supporting on said second and third means is
arranged to support.
11. A loudspeaker system in accordance with claim 10 wherein said
front panel means for supporting is asymmetrically located from the
bounding edges of said front panel.
12. A loudspeaker system in accordance with claim 9 wherein said
rear baffles are contiguous flat panels forming an angle,
and said loudspeaker cabinet comprises a pair of side panels each
interconnecting a respective normally vertical edge of said front
panel with a normally vertical edge of a respective rear baffle
flat panel to define said internal volume as of pentagonal cross
section and interconnecting generally parallel top and bottom
panels to coact therewith and define said internal volume.
13. A loudspeaker system in accordance with claim 12 wherein said
front panel includes means for supporting only a single small
loudspeaker.
14. A loudspeaker system in accordance with claim 13 wherein said
front panel means for supporting is asymmetrically located with
respect to the normally vertical and normally horizontal edges of
said front panel.
15. A loudspeaker system in accordance with claim 12 and further
comprising means for cophasally energizing all said small
loudspeakers with electrical energy over substantially the full
range of audio frequencies.
16. A loudspeaker system in accordance with claim 13 and further
comprising means for cophasally energizing all said small
loudspeakers with electrical energy over substantially the full
range of audio frequencies.
17. A loudspeaker system in accordance with claim 14 and further
comprising means for cophasally energizing all said small
loudspeakers with electrical energy over substantially the full
range of audio frequencies.
18. A loudspeaker system in accordance with claim 12 wherein each
of said rear baffle panels is substantially square.
19. A loudspeaker system in accordance with claim 16 and further
comprising,
means for delivering much less of high frequency electrical energy
for direct radiation from said front panel than is delivered for
radiation from said rear baffles in a ratio corresponding
substantially to the ratio of direct to reflected energy received
by a listener in a concert hall.
20. A loudspeaker system in accordance with claim 19 wherein said
ratio is of the order of 1:8.
21. A loudspeaker system in accordance with claim 20 wherein each
of said rear baffles supports four like small loudspeakers.
22. A loudspeaker system in accordance with claim 12 wherein said
angle is substantially 120.degree..
23. A loudspeaker system in accordance with claim 2 and further
comprising an internal panel inside said loudspeaker cabinet
extending between said front panel and the junction between said
rear baffles for dividing said internal volume into a pair of
acoustically isolated chambers.
24. A loudspeaker system in accordance with claim 12 and further
comprising an internal panel inside loudspeaker cabinet extending
between said front panel and the junction between said rear baffle
panels and between said top and bottom panels for dividing said
internal volume into a pair of acoustically isolated chambers.
25. A loudspeaker system in accordance with claim 23 wherein said
front panel includes means for supporting only a single small
loudspeaker.
26. A loudspeaker system in accordance with claim 23 and further
comprising a plurality of small loudspeaker comprising said upper
frequency radiating means,
means including said small loudspeakers and said loudspeaker
cabinet enclosing said internal volume substantially fluidtight
with each of said pair of acoustically isolated chambers being
substantially fluidtight,
first coupling means for energizing each small loudspeaker carried
by said second means with first channel energy,
and second coupling means for energizing each small loudspeaker
carried by said third means with second channel energy that may be
different from said first channel energy.
27. A loudspeaker system in accordance with claim 26 wherein said
front panel also includes means for supporting, and at least one of
said small loudspeakers, and further comprising,
means for coupling both first channel energy and second channel
energy to the last-mentioned at least one small loudspeaker.
28. A loudspeaker system in accordance with claim 26 wherein each
of said coupling means includes means for energizing each small
loudspeaker coupled thereto with electrical energy over
substantially the full range of audio frequencies.
29. A reflecting loudspeaker system having at least a rear panel
for facing an adjacent wall and a front panel for facing the normal
listening area when normally positioned in a room comprising,
upper frequency radiating means,
means for supporting said upper frequency radiating means so that
most upper frequency sound energy is directed across the plane of
said rear panel and reaches a listener after a first reflection
from said adjacent wall when normally positioned in a room,
and means associated with said upper frequency radiating means for
establishing a radiation characteristic of said upper frequency
radiating means so that the free field infinite baffle pressure
response along the axis thereof is higher relative to the response
in the middle range of audio frequencies while coacting with all
the elements in said reflecting loudspeaker system to provide an
essentially uniform radiated power density spectrum frequency
response over substantially the entire audible frequency range when
said loudspeaker system is in a normal room listening position.
30. A loudspeaker system having at least a rear panel for facing an
adjacent wall and a front panel for facing the normal listening
area when normally positioned in a room comprising,
sound radiating means for first directing most of the sound energy
therefrom across the plane of said rear panel upon said adjacent
wall and then to a listener when said sound radiating means is
normally positioned in a room,
and complementing means coacting with said sound radiating means
for establishing an essentially uniform radiated power density
spectrum frequency response over substantially the entire audible
frequency range for said loudspeaker system when said sound
radiating means is normally positioned in a room.
31. A first loudspeaker system in accordance with claim 1,
a second loudspeaker system in accordance with claim 1,
said wall,
the first and second loudspeaker system cabinets being spaced along
said wall with the front panel of each generally parallel to said
wall and said second means of each facing said wall so that upper
frequency sound beams directed from each second means are reflected
from said wall through the region between said cabinets.
32. A loudspeaker system having at least a rear panel for facing an
adjacent wall and a front panel for facing the normal listening
area when normally positioned in a room comprising,
a plurality of upper frequency radiating means intercoupled for
cophasal excitation,
means for supporting said upper frequency radiating means so that
some of the energy radiated therefrom reaches a listener over a
first direct path and the remainder of said energy reaches said
listener over other indirect paths which are longer than said first
direct path and first crosses the plane of said rear panel,
means for establishing said some of the energy less than said
remainder,
and complementing means associated with said system and coacting
therewith for establishing an essentially uniform radiated power
density spectrum frequency response for said system over at least
the audible frequency range of energy radiated by said upper
frequency radiating means.
33. A loudspeaker system having at least a rear panel for facing an
adjacent wall and a front panel for facing the normal listening
area when normally positioned in a room comprising,
radiating means for directing most of the sound energy therefrom
first across the plane of said rear panel, then said adjacent wall
and then to a listener when said sound radiating means is normally
positioned in a room while directing at least some of said sound
energy directly to a listener when said sound radiating means is
normally positioned in a room without reflection,
and complementing means coacting with said sound radiating means
for establishing an essentially uniform radiated power density
spectral frequency response over substantially the entire audible
frequency range for said loudspeaker system when said sound
radiating means is normally positioned in a room.
34. A loudspeaker system in accordance with claim 2 and further
comprising a plurality of small loudspeakers comprising said upper
frequency radiating means,
means including said small loudspeakers and said loudspeaker
cabinet enclosing said internal volume substantially
fluidtight,
first coupling means for energizing each small loudspeaker carried
by said second means with first channel energy,
and second coupling means for energizing each small loudspeaker
carried by said third means with second channel energy that may be
different than said first channel energy.
35. A loudspeaker system comprising,
sound radiating means,
and means for supporting said sound radiating means for directing
of the order of 87 percent of the sound energy therefrom upon a
reflecting surface and then to a listener when said sound radiating
means is normally positioned in a room while directing of the order
of 13 percent of the sound energy therefrom directly to a listener
when said sound radiating means is normally positioned in a room.
Description
The present invention relates in general to loudspeaker systems and
more particularly concerns a novel compact loudspeaker system that
is compact and relatively easy and inexpensive to manufacture and
provides realistic reproduction of sound with negligible
distortion.
The standard of loudspeaker systems is the commercially available
Bose 2201 spherical radiating system comprising 22 closely spaced
small loudspeakers substantially filling a spherical triangle
baffle of about 25-inch radius and comprising means for enclosing a
substantially fluidtight volume preferably situated in the corner
of a room. This loudspeaker system takes advantage of Bose known
property that in a concert hall most of the sound reaches the
listener by reflection. In addition, the Bose 2201 is characterized
by the advantages enumerated in Bose U.S. Pat. Nos. 2,915,588 and
3,038,964. These advantages include low distortion arising from
sing a number of small closely spaced loudspeakers coacting in
reproducing low frequencies to provide large vibrating area so that
the deflection of each speaker diaphragm is slight and distortion
low. In addition the disadvantages associated with crossover
networks are eliminated.
The Bose 2201 represents a practical approximation to an ideal
vibrating spherical surface that is so nearly perfect that it is
believed listeners are unable to distinguish between music
reproduction provided by the Bose 2201 and that which would be
provided by an ideal pulsating sphere. This result was established
by separating the room transfer characteristics from the
loudspeaker system characteristics in the following manner. A spark
source situated in the corner of a room was compared with a Bose
loudspeaker situated in the same corner. A high speed digital
computer determined the Green's function of the room and produced
samples of music that would be produced by an ideal pulsating
sphere in the room for comparison with the same sample of music
that would be provided by a Bose loudspeaker. The complementing
circuitry of the latter was adjusted until listeners were unable to
distinguish between the reproduction afforded by an ideal pulsating
sphere and the Bose loudspeaker. The commercially available Bose
2201 is an absolute standard that can be used to compare in an
actual listening room the performance between an existing
loudspeaker system and the Bose 2201.
It is well known that loudspeakers perform differently in different
rooms and perform in a room differently from the performance in an
anechoic chamber (a special suspended compartment surrounded by
sound absorbing wedges of material so that the compartment is
essentially free of sound echoes). Nevertheless, not infrequently
it is thought that anechoic chamber measurements of loudspeakers
represent meaningful indicia of loudspeaker performance. In fact,
recent work shows that anechoic chamber measurements provide less
meaningful information for evaluating the performance of a
loudspeaker in a listening room than previously thought.
The reason for this conclusion is that the hard surfaces provided
by walls represent a portion of the loudspeaker sound radiating
system whereas an anechoic chamber does not have such hard
surfaces. Those acquainted with the antenna field and the
determination of magnetic and electric fields will readily
recognize the analogy between establishing pressure and velocity
fields by a loudspeaker system transducer and establishing magnetic
and electric fields by an antenna transducer. Antenna engineers are
well aware that the proper design of an antenna involves either
isolating the antenna from nearby structures or taking into account
the surrounding structure. Thus, technical publications commonly
display properties of an antenna system, such as radiation patterns
and impedance plots, measured with the antenna situated in its
operating environment, such as on an aircraft or satellite. Field
strength measurements are usually made many wavelengths from the
antenna to provide meaningful information on the properties because
normally antenna systems are used for communication with other
systems many wavelengths away.
Greater difficulties are encountered in attempting to measure the
characteristics of a loudspeaker system that radiates energy for
use in a room a few wavelengths, or a fraction of a wavelength,
from the transducer system itself. That is to say, it is difficult
to separate the room characteristics from those of the loudspeaker
system to facilitate establishing a meaningful objective evaluation
of the performance of the loudspeaker system itself in the room
environment. Since the Bose 2201 represents a nearly perfect
transducing system itself, a comparison of the field intensity at a
point in the room between a Bose 2201 and an unknown loudspeaker
system represents a meaningful objective determination of the
performance of the unknown relative to that of the standard Bose
2201. When the measured performance of the unknown is essentially
undistinguishable from that of the Bose 2201, then the unknown is
known to be performing as well as it can as a loudspeaker system
transducer.
Accordingly, it is an important object of this invention to provide
a high performance loudspeaker system.
It is another object of the invention to provide a loudspeaker
system that performs nearly as good as the ideal pulsating
sphere.
It is another object of the invention to achieve the preceding
objects with a compact structure that is relatively low in
cost.
It is another object of the invention to achieve the preceding
objects with a structure that may be situated in a convenient
location in a room.
It is still a further object of the invention to achieve the
preceding objects with a loudspeaker system having the property of
spreading the apparent source of sound to the listener to simulate
a performance by a large group, such as an orchestra or chorus.
It is a further object of the invention to achieve the preceding
objects with a loudspeaker system that provides both direct and
reflected sound to the listener so as to more nearly simulate the
character of the sound heard in the concert hall.
It is still a further object of the invention to achieve the
preceding objects with a system that may be used for stereo
reproduction in a manner that avoids the "hole-in-the-center"
effect and provides good stereo reproduction in all portions of the
room.
It is still another object of the invention to achieve the
preceding objects with a loudspeaker system that is relatively
efficient and free of distortion so that it defines the individual
instruments with great clarity, even when reproducing passages of
music involving simultaneous playing by a large number of
instruments.
SUMMARY OF THE INVENTION
According to the invention, there are means defining a front panel
arranged to be situated normally parallel to a wall and means
associated with a loudspeaker cabinet having the front panel for
supporting upper frequency radiating means to that the radiating
means normally faces out the back of the loudspeaker cabinet with
its axis oriented at an angle to the front panel so that with the
loudspeaker cabinet normally positioned with the front panel
generally parallel to a wall, the upper frequency radiating means
emits at least upper frequency sound; that is, sound having
spectral components above 200 Hz., in a beam that has both
component directed away from the front panel toward the wall and to
the side of the cabinet.
Preferably the loudspeaker system comprises at least two normally
rear baffles forming an angle with each other and at an angle to
the front panel and comprising the loudspeaker cabinet with each
baffle having at least one small loudspeaker thereon with each
small loudspeaker normally directing upper frequency sound in a
beam having both a rearward and sideward component of the sound
beam radiated by the speaker associated with the other baffle, the
loudspeaker preferably being cophasally excited.
Preferably the normally rear baffles contain a number of closely
spaced loudspeaker connected in phase and nearly filling the
baffle. Preferably the front panel comprises a baffle containing at
least one small loudspeaker cophasally excited with the other small
loudspeakers for providing direct sound to the listener.
Preferably, the small loudspeaker are essentially full-range high
compliance loudspeakers coupled to a signal source by means
including a complementing circuit to establish a system
phase-frequency response characteristic that results in
exceptionally pleasing reproduction of sound.
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;
FIG. 1 is a diagrammatic representation to illustrate how a
listener in a concert hall receives mostly reflected sound
energy;
FIG. 2 is a diagrammatic representation of a stereo loudspeaker
system according to the invention illustrating how the invention
tends to simulate the ratio of reflected to direct sound for the
listener in a room of the sound received by the listener in a
concert hall of FIG. 1;
FIG. 3 is a perspective view of a preferred embodiment of a
loudspeaker system according to the invention;
FIG. 4 is a front view of the system of FIG. 3;
FIG. 5 is a block diagram illustrating the logical arrangement for
incorporating the complementing circuit for coaction with the
speaker system according to the invention with a commercially
available receiver or integrated preamplifier-amplifier;
FIG. 6 is a schematic circuit diagram of an exemplary complementing
circuit;
FIG. 7 is a block diagram illustrating the logical arrangement for
using a single one of the speaker systems of FIGS. 3 and 4 to
achieve stereo reproduction;
FIG. 8 shows a typical frequency response characteristics of the
circuit of FIG. 6; and
FIG. 9 is a diagrammatic representation of a single unit stereo
reproducer in a room.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
With reference now to the drawing and more particularly FIG. 1
thereof, there is shown a representation of a listener 11 in a
concert hall 12 facing the stage 13 receiving sound from point 15
on the left side of that stage and 16 on the right side of the
stage directly over the paths 17 and 18, respectively, and
indirectly over paths such as 21 and 22 from the left side, and 23
and 24 from the right side. It is believed that of the order of 87
percent of the sound which reaches a listener in the concert hall
is through reflection.
Referring to FIG. 2 there is shown a diagrammatic representation of
loudspeakers according to the invention providing sound to a
listener 11' in room 12' by a left speaker 15' and a right speaker
16' providing direct sound over paths 17' and 18', respectively
from direct loudspeakers 21 and 22, respectively. The left speaker
system 15' provides indirect sound over paths including path 21'
and 22' from left rear panel 33 and right rear panel 34,
respectively. Similarly, right speaker 16' provides indirect sound
over paths including path 23' and path 24' from right rear panel 35
and left rear panel 36, respectively.
Referring to FIG. 3 there is shown a perspective view of
loudspeaker 15' and 16' showing left panels 33 and 36 and right
panels 34 and 35. The position of front loudspeaker 31 and 32 is
indicated by dotted lines in FIG. 3. Each of the rear panels
includes four loudspeakers 41, 42, 43 and 44 on the left, and 45,
46, 47 and 48 on the right. These loudspeakers are preferably
closely spaced and substantially fill each of the panels.
Typically, these loudspeaker are 4-inch speakers with the 41/8inch
circular opening with speakers separated from adjacent ones by
about three-sixteenth inch and from the baffle edges by about
one-half inch so that each rear panel is a 3/4inch piece of plywood
about 101/2inches by about 103/4inches forming an angle of
120.degree. so that the angle between each of the rear panels and
the wall upon which they direct sound for reflection is
substantially 30.degree..
FIG. 4 shows a front view of the loudspeaker system 15', 16'
showing front baffle 51. This baffle may be 3/4inch plywood about
17 inches by about 103/4inches. The essentially fluidtight
enclosure is completed by a pair of side panels, such as 52, a top
panel such as 53 and a like bottom panel (not shown). Side panel 52
is typically of 3/4inch plywood about 103/4inches high by about
51/2inches wide, and the top and bottom panels are dimensioned so
that they cover the opening defined by the rear baffle, front
baffle and side panels. The distance between side panels is about
161/4inches. The distance between the front baffle and the junction
of the rear baffles is about 9 9/16 inches. For decorative reasons,
the top and bottom panels may extend beyond the baffles and side
panels. For a pleasing decorative effect the baffles an both side
panels may be surrounded by suitable grille cloth.
In a specific embodiment of the invention the individual small
loudspeakers are all commercially available full range CTS 4 C 1077
high compliance ceramic magnet 4-inch loudspeakers having a nominal
impedance of 8 ohms with the speakers connected in series-parallel
so that the impedance to an amplifier of the series-parallel system
is 8 ohms. Typically speakers 42, 43 and 44 may be connected in
series to form one series group, speakers 45, 47 and 48 connected
in series to form a second series group and speakers 41, 46 and the
front speaker connected in series to form a third series group.
Each of these series groups presents an impedance of substantially
24 ohms. When the three groups are connected in parallel, the
effective impedance is then 8 ohms. The individual speakers are
cophasally excited so that all the speaker diaphrams move out
together and in together in response to the same input signal. The
inside volume may be filled with fiberglass if desired.
A feature of the invention resides in minimizing undesired
resonances. Thus, there are a number of baffles each containing at
least one loudspeaker, but none of these baffles are parallel to
another surface. Sharp resonances normally encountered when a
baffle is parallel to another surface at frequencies when the
separation between the baffle and such another surface is a
multiple of a quarter wavelength are thus minimized. And since the
individual resonances of each individual loudspeaker when the
loudspeakers are acoustically coupled are normally not exactly the
same as the other loudspeakers, sharp resonance effects normally
encountered when a single loudspeaker reproduces a given frequency
range embracing the speaker resonances, are believe to be
significantly reduced.
Referring to FIG. 5 there is shown a block diagram generally
illustrating the logical arrangement of a system including a
conventional receiver 54, a complementing circuit 55 and a speaker
16' energized by the 8 ohm output terminals of receiver 54. A
typical receiver 54 has a tape monitor jack 55 which is coupled to
the input of complementing circuit 55' by input cable 56. A typical
receiver 54 also has a pair of tape recording jacks one jack 57
coupling the output of complementing circuit 55 by output cable 58
to the amplifier input when the receiver (or integrated
preamplifier-amplifier) selector switch is in the tape monitor
position. Jack 55 is coupled to the output of the preamplifier
section of the receiver. These normally available jacks are
especially convenient for using the invention with a receiver or
integrated preamplifier-amplifier. For separate preamplifier
components and amplifiers, input cable 56 may be couple to the
preamplifier output jack and output cable 58 may be coupled to the
amplifier jack.
Referring to FIG. 6, there is shown schematic circuit diagram of a
complementing circuit suitable to use with the specific system
described above. Since those skilled in the art will be able to
practice the invention by constructing the specific circuit with
the indicated parameters, the specific circuit will not be
discussed further other than to indicate the frequency response
characteristic in FIG. 8. Adjustment of resistor R.sub.A alters the
lift in low frequency end indicated while adjustment of the
resistance R.sub.B alters the lift in the high frequency end as
indicated with the intermediate range remaining substantially flat
as shown. For minimum deviation between reproduction of the system
according to this invention and the Bose 2201, the curve designated
2201 should be selected. However, for certain recordings it may be
more pleasing to the listener if other settings are chosen.
In addition to enhancing the amplitude frequency response
characteristic of the system, the complementing circuit is believed
to to also enhance the phase frequency response characteristic of
the system. The system phase response characteristic is believed to
be important toward the proper reproduction of low frequency
signals below 200 Hz. Thus, although the ear may not be able to
detect wide phase differences at high frequencies, it is believed
that the human ear can detect phase differences at the low
frequencies corresponding to delays in the order of a number of
milliseconds. Most conventional loudspeaker systems have an
uncompensated resonance in a low bass region which results in
considerable phase distortion. However undetectable this phase
distortion may be when reproducing single low tones, the distortion
becomes audible when reproducing a complex musical signal having a
number of spectral components in the bass region that are displaced
in time differently upon reproduction by a conventional loudspeaker
system to produce sound waveform that is audibly distorted.
Referrng to FIG. 7 there is shown a combined block-schematic
circuit diagram of a means for energizing but a single speaker
system to provide many of the advantages of the present invention
with but a single loudspeaker enclosure, thereby effecting a mark
reduction in the cost of a stereo system and eliminating the space
that would be required to accommodate two units. To this end a
stereo receiver 61 has its A channel coupled to an A complementing
circuit 62 and its B channel coupled to A complementing circuit 62
and its B channel to a B complementing circuit 63 in the same
manner as complementing circuit 55 in FIG. 5 is coupled to receiver
54. Speakers 41, 42, 43 and 44 on the left panel are coupled to the
output of the A channel. Speakers 45, 46, 47 and 48 on the right
panel are coupled in series, parallel as shown and coupled to the B
channel output 65. The front speaker 31, 32 is coupled to the
center channel output 66 of stereo receiver 61. Most stereo
receivers and stereo amplifiers have such a center channel
output.
Alternately, the center loudspeaker may be connected so that it
receives a signal current representative of the sum of the signals
in the left and right channels provided by an appropriate combining
circuit. For example, the winding of the center speaker may be
connected so that it is in series with at least one winding of a
speaker on the left baffle and at least one winding of a speaker on
the right baffle.
Referring to FIG. 9, there is shown a diagrammatic representation
of a suitable arrangement in a room 12' of single unit 71 connected
as shown in FIG. 7. Preferably speaker system unit 71 is located
along the center line of the room as shown spaced from the front
wall of the room so that listener 11' receives A channel signal
through reflection from the left wall of the room and B channel
information from the right wall of the room and center channel
information from the front panel. Speaker system unit 71 is
preferably placed far enough from the wall (usually about a foot)
to achieve a desired degree of apparent spreading of the sound, but
not so far that effective reflection from the wall is not obtained.
It may be advantageous with a single system to have the angle
between left panel 72 and right panel 73 be substantially
90.degree. so that the unit may be placed not too far from the wall
and still provide a desired degree of separation between he
apparent source of A channel signal and B channel signal.
It may also be advantageous to include an isolating wall 76 that
divides the unit into left substantially fluidtight compartment 74
and a right substantially fluidtight compartment 75. Such an
isolating wall helps reduce undesired mixing of left and right
channels inside the enclosure and thereby enhances the stereo
performance maintaining a relatively high degree of effective
channel separation.
Turning now to the preferred method of determining the frequency
response characteristic of the complementing circuit, a Bose 2201
is located in the corner of a listening room. A good full-range
microphone is also located on a stand in a typical listening
position in the room. A suitable microphone for this purpose is the
B&K commercially available microphone and associated
preamplifier. The Bose 2201 is fed with a swept frequency signal
preferably narrow band noise, such as that provided by a
commercially available General Radio sound and vibration analyzer
energized with pink noise capable of being swept over the full
audio frequency range by a mechanical drive that may be
synchronized with a General Radio logarithmic graphical recorder.
The output of the microphone preamplifier is applied to the General
Radio graphical recorder as the analyzer is swept over the
frequency range to provide a frequency response characteristic at
that point in the room that is representative of the transmission
properties of the room.
The microphone remains in the same position and then the
loudspeaker system, such as that shown in FIG. 3, is energized
through a power amplifier having an essentially flat frequency
response with the signal provided by the sound and vibration
analyzer, the loudspeaker being located in a typical location for
reproduction about a foot from a wall oriented generally as shown
in FIG. 2. The sound and vibration analyzer is again swept over the
audio frequency range, and the output of the microphone
preamplifier applied to the graphical recorder to provide a
representation of the transfer characteristics of both the
loudspeaker system thus energized and the room to that same
listening point previously measured with respect to the Bose
2201.
The difference between the graphical representation of the Bose
2201 and that of the uncompensated unit of FIG. 3 is determined
graphically on a point-by-point basis over the frequency range to
yield the preferred frequency response characteristic of the
complementing circuit. If desired, means may be provided or
altering the degree of lift at the high and low ends to satisfy the
preference of an individual listener, especially since many
commercial recordings are overcompensated.
It has been discovered that the overall free field axial infinite
baffle pressure high frequency response provided by the
complementing circuit coacting with a one of the small loudspeakers
is higher relative to the response in the middle range of
frequencies. This rise in response typically commences at a
frequency above 2 kHz. and may be effected electrically,
mechanically, through acoustic attenuation, by combination thereof
or by other suitable means. Yet the overall system radiated power
density spectrum response (proportional to pressure response
squared) provide by the loudspeaker system according to the
invention including complementing circuit is essentially
uniform.
Numerous variations of the invention may now be practiced. For
example, the baffle may be tilted upward or downward for low and
high locations, respectively, of the system. Different numbers and
different kinds of speakers may be used and the ratio of direct to
reflected sound retained in nearly the same desired ratio by
radiating less high frequency energy from the speaker on the front
baffle as a result of electrical, mechanical or acoustical
attenuation. Thus, an especially compact and inexpensive embodiment
of the invention might include just one loudspeaker on each rear
baffle and one on the front baffle with the front loudspeaker
energized trough an attenuating network that delivers about
one-fourth the high frequency energy to the front loudspeaker than
is delivered to each of the rear loudspeakers.
There has been described a novel loudspeaker system characterized
by the ability to reproduce music pleasingly and with great clarity
while being relatively easy and inexpensive to fabricate and
occupying relatively little space in the listening area. The
specific embodiments described herein are by way of example only.
It is evident that those skilled in the art may now make numerous
uses and modifications of and departures 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.
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