U.S. patent application number 10/685034 was filed with the patent office on 2004-03-25 for system and method for adjusting the low-frequency response of a crossover that supplies signal to subwoofers in response to main-speaker low-frequency characteristics.
Invention is credited to Thiel, James.
Application Number | 20040057587 10/685034 |
Document ID | / |
Family ID | 30444460 |
Filed Date | 2004-03-25 |
United States Patent
Application |
20040057587 |
Kind Code |
A1 |
Thiel, James |
March 25, 2004 |
System and method for adjusting the low-frequency response of a
crossover that supplies signal to subwoofers in response to
main-speaker low-frequency characteristics
Abstract
A system and method for adjusting a subwoofer sonic output in
response to known main speaker characteristics in order to produce
a desirable blending of sound from the combined subwoofer-main
speaker output.
Inventors: |
Thiel, James; (Lexington,
KY) |
Correspondence
Address: |
THOMAS, KAYDEN, HORSTEMEYER & RISLEY, LLP
100 GALLERIA PARKWAY, NW
STE 1750
ATLANTA
GA
30339-5948
US
|
Family ID: |
30444460 |
Appl. No.: |
10/685034 |
Filed: |
October 14, 2003 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10685034 |
Oct 14, 2003 |
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09849633 |
May 4, 2001 |
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6687379 |
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60207790 |
May 30, 2000 |
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Current U.S.
Class: |
381/98 ;
381/59 |
Current CPC
Class: |
H04R 3/14 20130101 |
Class at
Publication: |
381/098 ;
381/059 |
International
Class: |
H03G 005/00; H04R
029/00 |
Claims
I claim:
1. A system for adjusting the frequency response of subwoofer
systems comprising: a user interface configured to receive
user-adjustable variables indicative of main speaker
characteristics; and a compensation circuit configured to produce a
desired low-frequency signal from an input signal in response to
the user-adjustable variables.
2. The system of claim 1, wherein the main speaker characteristics
comprise low-frequency characteristics of the main speaker.
3. The system of 1, wherein the user adjustable variables comprise
a low-frequency cutoff frequency.
4. The system of 1, wherein the user adjustable variables comprise
a low-frequency damping factor.
5. The system of 1, wherein the user adjustable variables comprise
a speaker sensitivity factor.
6. The system of 1, wherein the user adjustable variables comprise
an enclosure type.
7. The system of 1, wherein the user adjustable variables comprise
a gain factor.
8. A method for adjusting the frequency response of subwoofer
systems, comprising the steps of: inputting user adjustable
settings indicative of main speaker characteristics; and producing
a desired low-frequency signal in response to the user adjustable
settings.
9. The method of claim 8, wherein main speaker characteristics
comprise low-frequency characteristics of the main speaker.
10. The method of claim 8, wherein the main speaker characteristics
comprise a low-frequency cutoff frequency.
11. The method of claim 8, wherein the main speaker characteristics
comprise a low-frequency damping factor.
12. The method of claim 8, wherein the main speaker characteristics
comprise a speaker sensitivity factor.
13. The method of claim 8, wherein the main speaker characteristics
comprise an enclosure type.
14. The method of claim 8, wherein the main speaker characteristics
comprise a gain factor.
15. A system for adjusting the frequency response of subwoofer
systems, comprising: means for inputting a plurality of user
adjustable setting indicative of main-speaker characteristics;
means for receiving an input signal; and means for producing a
desired low-frequency signal from the input signal in response to
the plurality of user adjustable setting.
16. The system of claim 15, wherein the main speaker
characteristics comprise low-frequency characteristics of the main
speaker.
17. The system of claim 15, wherein the means for producing the
desired low-frequency signal further comprises means for setting a
low-frequency cutoff-frequency of the main speaker.
18. The system of claim 15, wherein the means for producing the
desired low-frequency signal further comprises means for setting a
low-frequency damping factor of the main speaker.
19. The system of claim 15, wherein the means for producing the
desired low-frequency signal further comprises means for setting a
gain of the main speaker.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of U.S. patent
application Ser. No. 09/849,633, filed on May 4, 2001, which claims
the benefit of U.S. Provisional Patent Application No. 60/207,790,
filed May 30, 2000. These applications are incorporated herein by
reference in their entireties.
FIELD OF INVENTION
[0002] This invention relates generally to loudspeakers, and more
particularly to a crossover or a frequency response shaping system
for adjusting the frequency response of a subwoofer that, in
conjunction with a main speaker, produces the sonic output.
BACKGROUND
[0003] As is well known, a loudspeaker receives an electrical
signal representing an audio sound, and converts the electrical
signal to an audio sound wave via a loudspeaker driver unit. The
driver unit comprises, in part, a motor that responds to the
electrical signal to move a diaphragm. The movement of the
diaphragm perturbs the surrounding air, which causes the audio
wave.
[0004] Due to inadequate low-frequency characteristics, many
loudspeakers do not respond well to input signals of very low
frequencies (i.e., the bass or lower register). Thus, a high
quality audio system may include a separate, specialized speaker,
termed a subwoofer, which is designed to more accurately reproduce
the lower frequencies of the full sound spectrum. This subwoofer
may be used to reproduce the low-frequency portion of the same
signal that is provided to the main speakers. In these
applications, it is usually desirable to restrict the frequency
range reproduced by the subwoofer to a range that is not reproduced
by the main speakers. Further, it is desirable that the frequency
and phase response characteristics of the subwoofer be adjustable
so that the outputs of the subwoofer and the main speaker will
combine in a desirable way (e.g. to produce a uniform frequency
response). Thus, the response characteristics of the subwoofer is
intended to complement the response characteristics of the main
speaker, hence, achieving a desirable blending of the sonic output
(i.e., sound) of the main speaker and the subwoofer. Unfortunately,
subwoofer controls normally lack the capacity to properly adjust
the output to achieve a subwoofer response that will complement the
main speaker response.
[0005] In light of these problems, there is a need in the art for a
subwoofer response determining system (commonly referred to as a
crossover) that produces a proper blending of the subwoofer sonic
output and the main speaker sonic output.
SUMMARY
[0006] The present invention provides a system and method for
accurately reproducing audio sounds by adjusting the response
characteristics of a subwoofer to produce a proper blending of
sound from a subwoofer and a main speaker in a sound reproduction
system.
[0007] In architecture, the system comprises a compensation circuit
configured to produce a desired low-frequency signal from an input
signal in response to user adjustable settings that are indicative
of main speaker response characteristics. The desired low-frequency
signal, when cascaded through the subwoofer amplifier and the
subwoofer, produces a subwoofer sonic output that, when combined
with the main speaker sonic output, produces a more desirable
blending of high-frequency and low-frequency sounds (i.e., a higher
quality sound).
[0008] In accordance with another aspect of the present invention,
a method is provided for accurately producing audio sounds by
adjusting the low-frequency sonic output of a subwoofer. In the
method, a desired low-frequency signal is produced in response to
user adjustable settings that are indicative of main speaker
characteristics. The desired low-frequency signal is produced by
subtracting a signal indicative of the main speaker response from a
signal indicative of the desired combined subwoofer-main speaker
response.
[0009] Other systems, methods, features, and advantages of the
invention will be or become apparent to one with skill in the art
upon examination of the following figures and detailed description.
It is intended that all such additional systems, methods, features,
and advantages be included within the scope of the invention, and
be protected by the accompanying claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] The above and further features, advantages, and benefits of
the present invention will be apparent upon consideration of the
following detailed description, taken in conjunction with the
accompanying drawings, in which like reference characters refer to
like parts throughout.
[0011] FIG. 1 is a frequency response plot showing a combined
subwoofer-main speaker frequency response.
[0012] FIG. 2 is a simplified block diagram showing a crossover in
relation to components of a typical audio system.
[0013] FIG. 3 is a diagram of a front panel of the preferred
crossover, configured to receive user adjustable settings.
[0014] FIG. 4A is a block diagram showing a simplified architecture
of a compensation circuit having a desired transfer function
circuit, a main-speaker equivalent circuit, and a summing
circuit.
[0015] FIG. 4B is a block diagram showing an example system of FIG.
4A having an all-pass filter as a desired transfer function circuit
and a 2.sup.nd-order high-pass filter as an analog of the main
speaker high-pass function.
[0016] FIG. 5A is a circuit diagram showing the all-pass filter of
FIG. 4B in more detail.
[0017] FIG. 5B is a circuit diagram showing the high-pass filter of
FIG. 4B in more detail.
[0018] FIG. 5C is a circuit diagram showing the summing circuit of
FIG. 4B in more detail.
[0019] FIG. 6A is a circuit diagram showing an
equivalent-resistance circuit that can be used for the first
resistor (R1) in FIG. 5A.
[0020] FIG. 6B is a circuit diagram showing an
equivalent-resistance circuit that can be used for the third
resistor (R3) in FIG. 5B.
[0021] FIG. 6C is a circuit diagram showing an
equivalent-resistance circuit that can be used for the fourth
resistor (R) in FIG. 5B.
[0022] FIG. 6D is a block diagram showing a microcontroller circuit
for providing a control voltage to the equivalent resistances of
FIGS. 6A, 6B, and 6C.
[0023] FIG. 7A is a flow chart showing the operation of the
compensation circuit of FIG. 4A.
[0024] FIG. 7B is a flow chart showing the production of the
low-frequency signal of FIG. 7A in more detail.
DETAILED DESCRIPTION OF DRAWINGS
[0025] Having summarized various aspects of the present invention,
reference will now be made in detail to the description of the
invention as illustrated in the drawings. While the invention will
be described in connection with these drawings, there is no intent
to limit it to the embodiment or embodiments disclosed therein. On
the contrary, the intent is to cover all alternatives,
modifications, and equivalents included within the spirit and scope
of the invention as defined by the appended claims.
[0026] Theory
[0027] The normal audible sound spectrum consists of a frequency
range from approximately 20 Hz up to approximately 20 kHz. Since
speakers in a typical stereo system do not have a uniform frequency
response to the lowest parts of the audible sound range, the
low-frequency components of the sound range may be reproduced by
different speakers having a superior low-frequency response. An
example of this is given in FIG. 1, which is a frequency response
plot showing the high-frequency and low-frequency components of a
signal. Ideally, a crossover alters a uniform input signal 150 into
a low-frequency signal 130 having frequencies below the given
frequency 105. The input signal 150 is amplified through a main
speaker amplifier while the low-frequency signal 130 is amplified
through a subwoofer amplifier. The signal from the main speaker
amplifier is then channeled through a main speaker which provides
the high-frequency signal 140, determined by its low-frequency
characteristics. Similarly, the signal from the subwoofer amplifier
is channeled through a subwoofer which provides the low frequency
sounds.
[0028] Since the combined output 150 of the subwoofer and the main
speaker is the sum of the high-frequency component 140 and the
low-frequency component 130, if a desired combined output 150 is
known and the actual high-frequency output 140 of the main speaker
is also known, then an appropriate low-frequency signal 130 having
the desired low-frequency characteristics may be produced by
subtracting the high-frequency output 140 from the desired combined
output 150.
[0029] The present invention provides such a system and method for
producing such a desired low-frequency signal from a crossover. The
details of the invention, discussed below, are not to be taken in a
limiting sense but are made merely for the purpose of describing
the general principles of the invention. The scope of the invention
should be ascertained with reference to the issued claims.
[0030] Crossover for Producing a Desired Low-Frequency Signal
[0031] Turning now to the system of the invention, FIG. 2 shows a
high-level diagram of a sound system utilizing the present
invention. The sound system includes the crossover 200 designed to
incorporate information about the frequency response of a main
speaker 280 (i.e., to implement the compensation technique
discussed above). The crossover 200 comprises a user interface 205
that allows a user to input various parameters related to the main
speaker 280. These parameters reflect the degree of adjustment
needed to compensate for actual frequency response characteristics
of the main speaker 280 as described in FIG. 1. The crossover 200
receives an input signal 210 and produces the desired low-frequency
signal 230. The input signal 210 is also sent to a main speaker
amplifier 240, which amplifies the input signal 220 to produce an
amplified input signal 260. The amplified input signal 260 is then
sent to a main speaker 280 for the production of sound. The desired
low-frequency signal 230 is cascaded through a subwoofer amplifier
250 configured to amplify the desired low-frequency signal 230, and
the resulting amplified low-frequency signal 270 is then sent to a
subwoofer 290 configured to produce the low-frequency sounds. The
desired low-frequency signal 230 produced by the crossover 200
takes into account the low-frequency range that is produced by the
main speaker 280. Hence, the blending of the subwoofer's sonic
output with the main speaker's sonic output produces the desired
combined sonic output.
[0032] Although the crossover 200 is shown as a separate component,
it may be integrated with other components of the speaker system.
For example, the crossover 200 and subwoofer amplifier 250 may be
integrated into a single unit or, alternatively, the crossover 200
and main-speaker amplifier 240 may be integrated into a single
unit. Moreover, although the current embodiment only shows a
low-frequency output, it will be clear to one of ordinary skill in
the art that a high-frequency component may also be produced by the
crossover. It will also be clear to one of ordinary skill in the
art that the inventive nature does not depend on the possible
permutations by which the crossover may be combined with other
sound system components.
[0033] FIG. 3 shows a front panel, or user interface 205, of a
crossover 200 (FIG. 2) in the sound system of FIG. 2. The user
interface 205 allows the user to control many parameters associated
with the sound reproduction system such as configuration parameters
315, system parameters 325, or main speaker characteristics 335.
The configuration parameters 315 typically include mode (e.g.,
augment or crossover), channel (e.g., stereo or mono), number of
subwoofers, and main amplifier gain. System parameters 325 may
include low frequency extension, low frequency level, and crossover
frequency. Main speaker characteristics 335 may include type (e.g.,
sealed or reflex), low frequency limit, sensitivity, and damping
factor. These parameters are adjusted using selection buttons 345
configured to select the parameter to be adjusted, and adjust
buttons 355 configured to adjust those selected features. A display
385 on the user interface 205 apprises the user of the changing
parameters. Once the system parameters are set using the selection
buttons 345 and the adjust buttons 355, the user may store the
parameters using a store button 365. Alternatively, once certain
parameters have been stored, the user may recall the stored
parameters using a recall button 375.
[0034] Although several parameters and options are shown in the
example user interface 205, it will be clear to one of ordinary
skill in the art that the user interface 205 may be more or less
complex depending on the options available for such a system. For
purposes of this discussion, the parameters of interest are
configuration mode (specifically, augment mode) and the main
speaker characteristics 335. Upon selection of augment mode
(configuration parameter 315), the user may enter main speaker
characteristics 335 (e.g., type, low frequency limit, sensitivity,
damping factor, etc.) related to known characteristics of the main
speaker 280 (FIG. 2). Responsive to the user's input of the main
speaker characteristics 335, the crossover 200 adjusts the
low-frequency response of the crossover 200 (FIG. 2) in response to
these main speaker characteristics so that the crossover 200 (FIG.
2) produces a desired low-frequency component 230 (FIG. 2) of the
signal. The desired low-frequency component 230 (FIG. 2), when
cascaded through the subwoofer amplifier 250 (FIG. 2) and the
subwoofer 290 (FIG. 2), produces a response that, when combined
with the main speaker response, produces an ideal combined response
(i.e., a desirable blending of sound). Although the front panel (or
user interface) is shown in the present embodiment as having
configuration parameters, system parameters, and main speaker
characteristics, it will be clear to one of ordinary skill in the
art that additional user options may be implemented through the
user interface. These user options may include, but are not limited
to, acoustics of the room, temperature, number of speakers, etc.
Similarly, it will be clear to one of ordinary skill in the art
that several options may be removed from the user interface in
order to reduce the complexity of the system for the user. Although
only certain options are shown in the user interface, it is not
intended to limit the invention to only those options. On the
contrary, the intent is to cover all alternatives, modifications,
and equivalents included within the spirit and scope of the
invention as defined by the appended claims.
[0035] Turning now to the details of a system for generating the
desired low-frequency signal in response to the user inputs
indicative of main-speaker low-frequency characteristics, FIG. 4A
shows an embodiment of the invention as a compensation circuit 400a
configured to produce the desired low-frequency signal 230 (FIG.
2). In this embodiment, an input signal 210 is passed through a
desired transfer function circuit 410a, which produces a desired
system signal 415 having the characteristics of a desired combined
subwoofer-main speaker signal 150 (FIG. 1). The desired system
signal 415 is then transmitted to a summing circuit 430.
[0036] The input signal 210 is also passed through a main-speaker
equivalent circuit 420a, which produces a main-speaker equivalent
signal 425 having the low-frequency characteristics of a signal
produced by a main speaker (e.g., 140 of FIG. 1). This main-speaker
equivalent signal 425 is also transmitted to the summing circuit
430. The summing circuit 430 receives both the desired system
signal 415 and the main-speaker equivalent signal 425, and
subtracts the main-speaker equivalent signal 425 from the desired
system signal 415 to produce a subtracted signal 430. The amplitude
of the subtracted signal 430 is adjusted by a gain adjusting
circuit 440, which is typically a variable resistor, to produce a
desired low-frequency signal 230. As seen from FIG. 4A, rather than
directly setting the characteristics for the low-frequency signal
(e.g., directly setting a high-frequency roll-off or directly
setting low-pass characteristics) as is done in typical subwoofer
systems, this invention generates the desired low-frequency signal
230 from known characteristics of the main speaker so as to better
compensate for main-speaker low-frequency characteristics and,
therefore, producing a better blend of sound from the main speaker
and the subwoofer.
[0037] The compensation circuit 400a of this invention can be best
demonstrated by using a specific example. FIGS. 4B, 5A, 5B, 5C, 6A,
6B, 6C, and 6D provide the specific example illustrating the
construction and operation of the compensation circuit 400a
illustrated in FIG. 4A. This example is not provided to limit the
invention to the specific details but, rather, to more clearly
illustrate the operation of certain aspects of the invention.
[0038] FIG. 4B is a specific example of the compensation circuit
400a of FIG. 4A. In this example, the main speaker response is
represented as a 2.sup.nd-order high-pass filter 420b having a
cutoff frequency of F.sub.sp and a damping factor of Q.sub.sp. In a
preferred embodiment, a desired combined subwoofer-main speaker
response 150 (FIG. 1) would be represented by a 2.sup.nd-order
all-pass filter having a characteristic frequency, F.sub.ap, of: 1
F ap = F sp 2 Q sp [ Eq . 1 ]
[0039] Once the cutoff frequencies and damping factors of the main
speaker response and the desired combined response are known, these
factors are used to create the compensation circuit 400a (FIG. 4A)
configured to produce the desired low-frequency signal 230 in
response to the main-speaker low-frequency characteristics.
[0040] Continuing with this example, FIG. 5A shows a 2.sup.nd-order
all-pass filter 410b that may be used to produce the desired
all-pass response of FIG. 4B. The all-pass filter 410b comprises an
operational amplifier 525, a variable resistor 522 with a
resistance of R.sub.1, a capacitor with a capacitance of C.sub.1,
and two fixed resistors 524, 528 with a resistance of R.sub.2,
configured to achieve the desired 2.sup.nd-order all-pass
characteristics. The characteristic frequency of the all pass
filter is given by Eq. 2 as: 2 F ap = 1 2 C 1 R 1 . [ Eq . 2 ]
[0041] And, since in this example it is desired that the all-pass
frequency be set according to Eq. 1, the variable resistance,
R.sub.1, may be represented as: 3 R 1 = Q sp C 1 F sp . [ Eq . 3
]
[0042] FIG. 5B shows a 2.sup.nd-order high-pass filter 420b that
may be used to produce the equivalent main-speaker response 425
(FIG. 4B) of FIG. 4B. The example 2.sup.nd-order high-pass filter
420b comprises two RC circuits 530, 540 serially connected to the
input of the operational amplifier 545 to produce the desired
2.sup.nd-order characteristics. If identical capacitors 533, 543
are used in each of the RC circuits 530, 540, and the capacitor
value and resistor values are C.sub.2, R.sub.3, and R.sub.4,
respectively, then the characteristic frequency, F.sub.sp, and the
damping factor, Q.sub.sp, are given by Eq. 4 and Eq. 5,
respectively, as: 4 F sp = 1 2 C 2 R 3 R 4 and [ Eq . 4 ] Q sp = R
4 R 3 2 . [ Eq . 5 ]
[0043] Thus, the values of R.sub.3 (536 of FIG. 5B) and R.sub.4
(546 of FIG. 5B) in terms of F.sub.sp and Q.sub.sp would be: 5 R 3
= 1 4 C 2 Q sp F sp and [ Eq . 6 ] R 4 = Q sp C 2 F sp . [ Eq . 7
]
[0044] FIG. 5C shows a summing circuit 430 that may be used to
subtract the equivalent main-speaker signal 425 from the desired
system signal 415. The summing circuit 430 comprises an operational
amplifier 555 configured as an adder circuit with four fixed
resistors 552, 554, 556, 558. Since adder circuits are well known
in the art, details of adder circuits will not be further
discussed.
[0045] A convenient way to achieve adjustable values of R.sub.1
(522 of FIG. 5A), R.sub.3 (536 of FIG. 5B), and R.sub.4 (546 of
FIG. 5B) is to realize them with voltage controlled equivalent
resistances. This is shown in FIGS. 6A, 6B, 6C, and 6D.
[0046] FIGS. 6A, 6B, and 6C show the resistors R.sub.1 (522 of FIG.
5A), R.sub.3 (536 of FIG. 5B), and R.sub.4 (546 of FIG. 5B) as
voltage-controlled equivalent resistances, each implemented with
two operational transconductance amplifiers 620a, 640a, 620b, 640b,
620c, 640c. Details on the operation of transconductance amplifiers
are well known and understood by persons skilled in the art, and
need not be described herein. Given the circuit configurations of
FIGS. 6A, 6B, and 6C, the resistances R.sub.1, R.sub.3 and R.sub.4
are represented by: 6 R 1 = 2 R 7 R 8 gm R 6 V 1 , [ Eq . 8 ] R 3 =
2 R 7 R 9 gm R 6 V 3 , and [ Eq . 9 ] R 4 = 2 R 7 R 10 gm R 6 V 4 ,
[ Eq . 10 ]
[0047] where V.sub.1, V.sub.3, and V.sub.4 are the control voltages
and gm is the transconductance per current through the resistors
R.sub.8 (690 of FIG. 6A), R.sub.9 (693 of FIG. 6B) and R.sub.10
(696 of FIG. 6B). Thus, the required voltages V.sub.1, V.sub.3, and
V.sub.4, in terms of F.sub.sp and Q.sub.sp, would be: 7 V 1 = 2 R 7
R 8 C 1 F sp ( gm ) R 6 Q sp , [ Eq . 11 ] V 3 = 8 R 7 R 9 C 2 F sp
Q sp ( gm ) R 6 , and [ Eq . 12 ] V 4 = 2 R 7 R 10 C 2 F sp ( gm )
R 6 Q sp . [ Eq . 13 ]
[0048] FIG. 6D shows a microcontroller 605 that may be used in
conjunction with the equivalent resistance circuits of FIGS. 6A,
6B, and 6C. In practice, it is convenient to use a microcontroller
605 to perform the calculations so that user-adjustable controls
for F.sub.sp and Q.sub.sp can supply voltages to the
micro-controller 605, and the microcontroller 605 will supply
outputs V.sub.1 610, V.sub.3 615, and V.sub.4 620 according to Eqs.
11, 12, and 13, respectively. Since the structure and operation of
microcontrollers are well known in the art, these devices will not
be discussed further. It is sufficient to say that careful
adjustment of voltages V.sub.1 (610 of FIGS. 6A and 6D), V.sub.3
(615 of FIGS. 6B and 6D) and V.sub.4 (620 of FIGS. 6C and 6D)
produces the desired resistances R.sub.1 (522 of FIG. 5A), R.sub.3
(536 of FIG. 5B), and R.sub.4 (546 of FIG. 5B), which, in turn, are
used to construct the 2.sup.nd-order all-pass filter 410b (FIG. 4B)
and the 2.sup.nd-order high-pass filter 420b (FIG. 4B) used in the
production of the desired low-frequency signal 230.
[0049] As shown from the above embodiment of the invention, the
user inputs indicative of the main speaker characteristics may be
translated to adjustable voltages V.sub.1, V.sub.3, and V.sub.4,
which determine the variable resistances in the above-described
circuits. These voltages are subsequently used to produce a desired
all-pass response circuit, which has, as an output, the desired
characteristics of the combined signal. Furthermore, these
adjustable voltages are used to produce the equivalent main-speaker
response circuit, which produces a main-speaker equivalent output.
The desired low-frequency output is produced as a function of the
main-speaker low-frequency characteristics and, therefore, will
produce a better blending of sound when finally combined with the
main-speaker sonic output.
[0050] Method Steps for Producing the Desired Low-Frequency
Signal
[0051] FIG. 7A shows the operation of the above-described
embodiment of the invention. As an initial matter, the main speaker
output characteristics are determined in step 710. User-adjustable
settings, which are indicative of main speaker characteristics, are
then defined in step 720. These user-adjustable settings may
include, but are not limited to, the cutoff frequency of the main
speaker, the damping factor of the main speaker, a sensitivity
factor, an enclosure type (e.g., sealed or reflex), a gain factor,
or any number of other factors as described above with reference to
FIG. 3. Once these user-adjustable settings have been defined 720,
these settings are input, in step 730, into the compensation
circuit via a user interface similar to that described with
reference to FIG. 3. The compensation circuit then produces, in
step 750, the desired low-frequency signal in response to the
user-adjustable settings, which are indicative of main-speaker
low-frequency characteristics. This method, unlike conventional
methods of adjusting a subwoofer response, takes into consideration
the main-speaker low-frequency characteristics in determining the
output of the subwoofer. Thus, this method results in a better
blending of sound from the subwoofer-main speaker combination.
[0052] FIG. 7B shows the step of producing 750 (FIG. 7A) the
desired low-frequency signal in more detail. Once the
user-adjustable settings that are indicative of main-speaker
low-frequency characteristics have been input 730 (FIG. 7A) into
the compensation circuit via the user interface, the compensation
circuit 400a (FIG. 4A) generates, in step 753, a desired combined
system signal (which reflects the desired output 415 (FIG. 4A) from
a subwoofer-main speaker combination) from the user-adjustable
settings. The compensation circuit 400a (FIG. 4A) further
generates, in step 756, an equivalent main-speaker signal 425 (FIG.
4A) from the user adjustable settings. Once these two signals have
been generated 753, 756, the compensation circuit subtracts, in
step 759, the equivalent main speaker signal 425 (FIG. 4A) from the
desired system signal 415 (FIG. 4A). This subtracted signal 430
(FIG. 4A) may be directly used as the desired low-frequency signal
230 (FIG. 4A) or, alternatively, may be adjusted using a gain
adjusting circuit 440 (FIG. 4A) prior to being used as the desired
low-frequency signal. In either case, the step of subtracting 759
produces a low-frequency signal having the desired characteristics
which will produce the appropriate low-frequency sonic output which
will in turn, when combined with the main-speaker sonic output,
produce the desired combined sonic output (i.e., the desired
blending of sound).
[0053] Although an exemplary embodiment of the present invention
has been shown and described, it will be apparent to those of
ordinary skill in the art that a number of changes, modifications,
or alterations to the invention as described may be made, none of
which depart from the spirit of the present invention. For example,
the compensation mechanism, although described as an analog
circuit, may be implemented by digital means, the order of the
filters may be adjusted depending on the response of the actual
system components, the method steps may be rearranged, etc. All
such changes, modifications, and alterations should therefore be
seen as within the scope of the present invention.
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