Subwoofer phase alignment control system and method

Abstract

A multi-speaker (e.g., home theater or stereo) audio system with one or more subwoofers includes an improved phase adjustable subwoofer 222, and an improved subwoofer phase adjustment method allows a user to quickly and accurately select the most satisfactory subwoofer phase adjustment value for blending the output of the subwoofer with the rest of the system's speaker outputs.

Description

[Technical field]

[0001] REFERENCE TO RELATED APPLICATIONS For purposes of background and nomenclature, this application is related to the following commonly owned patent applications, which are also incorporated by reference in their entireties: (a) U.S. Patent Application Serial No. 12 / 153,623, filed May 21, 2008 (now U.S. Patent No. 8,194,874); (b) U.S. Patent Application No. 13 / 162,294, filed June 16, 2011 (now U.S. Patent No. 8,995,697); (c) U.S. Patent Application No. 14 / 563,508, filed December 8, 2014 (now U.S. Patent No. 9,374,640); and (d) PCT / US20 / 24232, filed March 23, 2020 (now WIPO publication no. WO2020 / 191401). This application claims priority to U.S. Provisional Patent Application No. 63 / 127,073, filed December 17, 2020 ("Subwoofer Phase Alignment Control Method and System"), the entire contents of which are incorporated herein by reference.

[0002] The present invention relates to a method and circuit configured for use in a subwoofer speaker system and its crossover network. [Background technology]

[0003] Consumer audio systems often include one or more main or satellite speakers and one or more subwoofers that are positioned together in a listener's room, as shown in Figures 1A and 1B, which show perspective and top views of a typical prior art surround sound system, generally shown at 10, positioned in a media space or room 12. The illustrated system is a conventional Dolby® digital configuration having a home theater or other audio / video (AV) source 14, and optionally including an audio-video receiver ("AVR") 15. System 10 also includes a left channel speaker 16, a right channel speaker 18, and a center channel speaker 20, used in conjunction with a subwoofer 22, all positioned in front of the listener's main seating area at a listening position or listening station 24, such as a sofa or chair. Systems often include a pair of left and right surround speakers spaced apart from each side of the listening station to provide a sense of spaciousness to the sound radiated by the speakers and to provide ambient sound for AV programs such as movies and concerts. A typical home theater system 10 also includes left and right back speakers 30 and 32 generally positioned behind and on either side of the listening location to provide a more powerful surround sound. The speakers are preferably centered about a centerline 34 passing through the AV unit 14 and the listening location 24. The subwoofer 22 is typically an "active" subwoofer system, i.e., includes within a single enclosure an electrodynamic "woofer" or low frequency driver connected to an amplifier assembly having a line level "SW" input (typically a single RCA female connector) and an array of input connections and user accessible controls (e.g., a cutoff frequency dial, a "+ / - polarity" or "0 degree or 180 degree" phase switch, and an "auto on / off" enable switch).Older "passive" subwoofers (often used in two-channel "stereo" systems) had no built-in amplifier and contained a passive crossover circuit which distributed signals below a selected cutoff frequency (e.g. 80Hz) to a dual voice coil woofer driver and passed higher frequency signals to the left and right "main" speakers (e.g. 16 and 18).

[0004] Referring to FIG. 1C, a full-range speaker system 50 may be used as the main left and right speakers (16, 18), typically consisting of a low frequency module or "subwoofer" section 58, a satellite section 52 with mid-bass drivers 60, 62 (with passbands bounded by mid-bass / high-bass frequencies), and a tweeter 64 for ultra-high frequencies, for example extending beyond the high human hearing range. Conventional "subwoofer-satellite" systems (whether realized by a "powered tower", i.e., a powered subwoofer together with a passive speaker co-located in a single enclosure (e.g., 50 shown in FIG. 1C), or an active sound bar subwoofer system (e.g., system 100 with a sound bar 110 and a separate subwoofer 130, as shown in FIG. 1D)) suffer from poor acoustic magnitude response control over the subwoofer-"satellite" passband. Simply increasing or decreasing the subwoofer signal level evenly across the entire passband would result in excessive or insufficient subwoofer levels passing through and beyond the crossover passband (see typical ideal or theoretical frequency response plot in FIG. 1E, showing the receiver crossover set at 80 Hz and a 2nd order Butterworth filter that models the inherent high-pass characteristic of the associated main LCR speakers (e.g., 16, 18 and 20) or soundbar 110).

[0005] Any stereo or home theater sound system (e.g., 10) that includes a full-range speaker system (e.g., 50 or 100) preferably requires that the outputs of each of these parts be blended and balanced for use in listening space 12, and the bass signal of the subwoofer is often difficult to adjust for a satisfactory blend with the bass-mid levels of the other speakers to achieve a satisfactory spectral balance. Simply adjusting the gain or polarity of the subwoofer signal across its entire passband produces undesirable results in terms of system spectral balance, with listeners complaining of "chest-rattling" midrange and a "full" or "dull" sound.

[0006] In a typical modern home theater system, an audio / video source (AV) 14 (optionally an audio / video receiver AVR 15) includes built-in crossover circuitry that (a) provides high-pass filtered or full-band signals to "main" LCR speakers (e.g., left 16, center 20 and right 18 speakers) or to a soundbar (e.g., 110) and (b) provides low-pass filtered signals to one or more subwoofers or subwoofer sections (e.g., 22, 58 or 130). A typical prior art stand-alone subwoofer (e.g., 22 or 130) typically has a built-in crossover and at least one amplifier with an LFE input (i.e., for low frequency effects) that allows the user to adjust the low-pass filter cutoff frequency, amplitude, or amplifier gain level and "polarity" once the subwoofer is placed in the room. These subwoofer adjustment controls have been found to be inadequate, i.e., to real users in real rooms, the overall system is often perceived as sounding "muddy" or weak, especially at the lower frequencies in the octave around the subwoofer cutoff frequency.

[0007] Blending the acoustic outputs of the subwoofers (e.g., from 22 or 130) in the system 10 in the room 12 is an extremely complex problem. Important factors include: 1) Room acoustics (for example, in Room 12), 2) the distance to the speakers (e.g., between the subwoofer 22 and the LCR speakers 16, 18 and 22); 3) Number of other speakers (other than the subwoofer), 4) The low-frequency design of all speakers involved; 5) Amplifier / receiver frequency response and phase response (e.g. AVR15), 6) Amplifier / receiver filter slope and frequency (e.g. in the AVR15), and 7) Other DSP (digital signal processing) adjustment means or room EQ (equalization) routines (for example, whether the AVR15 includes a room correction feature such as the Audyssey(TM) MultiEQ(TM) DSP system)

[0008] Adding more adjustments to the subwoofer (e.g. 22, 58 or 130) can confuse the user or installer when combined with all of the above factors. The law of entropy dictates that increasing these variables will do more harm than good. The problem with the prior art's crude subwoofer control is that it does not allow the user to adjust the subwoofer output to smoothly blend with the output of the other speakers while listening from the listening position 24. Other examples of the prior art include U.S. Patent No. 9,524,098 and U.S. Patent No. 10,681,481.

[0009] Therefore, there is a need for an easy-to-use, accurate and effective system and method for more intelligently controlling the phase and amplitude of a subwoofer such that the subwoofer section (e.g., 22, 58 or 130) can be easily adjusted by the user in the user's room (e.g., 12) using a method that reduces the likelihood of erroneous user input. Summary of the Invention

[0010] Accordingly, the present invention seeks to alleviate at least some of the above-mentioned difficulties by providing an effective and accurate system and method for controlling the phase angle of a subwoofer and integrating the sound reproduced by a subwoofer with the sound produced by other speakers in a home theater or stereo system by providing a user-adjustable phase alignment control input and method.

[0011] According to one aspect of the invention, there is provided a phase alignment control system for a subwoofer configured for use in a multi-speaker home theater system. The phase alignment control system includes a first-order all-pass filter having a selectable tuning frequency and a polarity selection stage. The system allows one of at least four different user-selectable phase correction settings to be selected at a time. The phase alignment control system is configured to generate an output signal by applying a phase change to an input signal based on which one of the different user-selectable phase correction settings is selected by a user. The phase alignment control system is configured to apply a phase change to the input signal by a combination of (a) the first-order all-pass filter causing a phase change as a result of a selected all-pass filter tuning frequency f0 and (b) the polarity selection stage selectively applying or not applying a polarity reversal. The phase alignment control system may be configured to apply a phase change to an input signal by a combination of (a) a first-order all-pass filter that causes a phase change, and (b) only a polarity selection stage that selectively applies or does not apply a polarity inversion. For example, there may be no need to provide another filter stage for phase correction or to correct the signal change caused by the filter implemented for phase correction. For example, the phase alignment control system may include only one first-order all-pass filter, i.e., a single first-order all-pass filter.

[0012] The phase alignment control system may be configured to be responsive to a first user-selectable phase correction setting corresponding to a first desired change in phase angle, i.e., X1 degrees, where the first desired change in phase angle is realized by (a) the first order all-pass filter causing a phase change of Y degrees, and (b) the polarity selection stage applying a polarity reversal, thereby adding a phase change of 180 degrees, where the magnitude of the difference between X1 and Y is 180 degrees. The phase alignment control system may additionally or alternatively be configured to be responsive to a second user-selectable phase correction setting corresponding to a second desired change in phase angle, i.e., X2 degrees, where the second desired change in phase angle is realized by (a) the first order all-pass filter causing a phase change of X2 degrees, and (b) the polarity selection stage applying no polarity reversal. The phase alignment control system may additionally or alternatively be configured such that in response to a third user-selectable phase correction setting corresponding to a third desired change in phase angle, i.e., 180 degrees, the third desired change in phase angle is realized by (a) the first order all-pass filter causing no phase change and (b) the polarity selection stage applying a polarity inversion. The phase alignment control system may additionally or alternatively be configured such that in response to a fourth user-selectable phase correction setting corresponding to a fourth desired change in phase angle, the fourth desired change in phase angle is realized by (a) the first order all-pass filter causing no phase change and (b) the polarity selection stage applying a polarity inversion. The phase alignment control system may be configured as described above with respect to the first through fourth user selectable phase correction settings, and further configured such that in response to a fifth desired change in phase angle, i.e., a fifth user selectable phase correction setting corresponding to X5 degrees, the fifth desired change in phase angle is achieved by (a) the first order all pass filter causing a phase change of Y degrees, and (b) the polarity selection stage applying a polarity reversal, thereby adding a phase change of 180 degrees. None of 0°, 180°, X1°, X2° and X5° may be equal.

[0013] At least one, preferably at least two (and possibly only two) user selectable phase correction settings may be in the range of -10 degrees to +100 degrees. At least one, preferably at least two (and possibly only two) user selectable phase correction settings may be in the range of +80 degrees to +190 degrees. At least one, preferably at least two (and possibly only two) user selectable phase correction settings may be in the range of +10 degrees to -100 degrees. At least one, preferably at least two (and possibly only two) user selectable phase correction settings may be in the range of -80 degrees to -190 degrees. There may be eight or more user selectable phase correction settings. There may be up to 24 user selectable phase correction settings. The user selectable phase correction settings are preferably equally spaced phase increments.

[0014] In an embodiment further described and illustrated below, the phase alignment control system is configured such that the selected tuning frequency of the first-order all-pass filter is selected at least in part in response to the subwoofer crossover frequency. There may be embodiments of the invention that are advantageous where the subwoofer crossover frequency is preselected, e.g., pre-set in a manner that is not user-alterable. The subwoofer crossover frequency may be a user-selectable value. The phase alignment control system may select the selected tuning frequency of the first-order all-pass filter in response to the subwoofer crossover frequency and which of the different user-selectable phase correction settings is selected. For a first subset of the different user-selectable phase correction settings, the selected tuning frequency may be lower than the subwoofer crossover frequency, and for a second subset of the different user-selectable phase correction settings, the selected tuning frequency may be higher than the subwoofer crossover frequency. In certain cases (e.g., when the user-selectable phase correction settings are -90 degrees or +90 degrees), the selected tuning frequency is selected to be equal to the subwoofer crossover frequency. It should be understood that in an embodiment, the selection of the tuning frequency of the first-order all-pass filter is automatically selected, for example by a digital signal processor, executable software, computer, control circuitry or other electronic means. The phase alignment control system may include, for example, such electronic means. The phase alignment control system may include a polarity inverter. The phase alignment control system may include an adjustable amplifier gain stage. For example, the polarity selection stage (e.g., a polarity inverter) may optionally include an adjustable amplifier gain stage.

[0015] The phase alignment control system may be entirely incorporated within or on the subwoofer. The phase alignment control system may be partially incorporated within or on the subwoofer. The phase alignment control system may be partially incorporated within or on a device, e.g., an AVR, that outputs an audio signal received by the subwoofer. The phase alignment control system may be entirely incorporated within or on such a device.

[0016] Further, a user display device may be provided for use with the phase alignment control system. The user display device may be configured, for example, to display which of the different user-selectable phase correction settings has been selected. The user display device may be configured to allow a user to select a desired user-selectable phase correction setting. The user display device may form part of the subwoofer. The user display device may form part of the subwoofer. The user display device may form part of a device that outputs an audio signal received by the subwoofer, for example an AVR. The user display device may be a remote device (for example a remote control unit, preferably a wireless remote control unit).

[0017] According to another aspect of the invention there is provided a subwoofer including an integrated phase alignment control system according to any aspect of the invention claimed or described herein.

[0018] According to yet another aspect of the present invention there is provided a multi-speaker home theatre system which may include a subwoofer and a phase alignment control system according to any aspect of the present invention claimed or described herein, the subwoofer being driven based on an output signal from the phase alignment control system.

[0019] The multi-speaker home theater system may include at least one subwoofer speaker driver having a low frequency operating range and a number of other speaker drivers each having a higher frequency operating range, the speaker drivers being arranged to provide a surround sound system. The multi-speaker home theater system may include an audio signal source, for example an AVR. The system is preferably configured to allow a user of the system to select a cut-off frequency, optionally from one of a set of different values, that determines how the audio signal is distributed between the subwoofer speaker driver and one or more of the other speaker drivers. The system is additionally or alternatively configured to allow a subwoofer phase correction value to be used by the system to perform subwoofer phase correction. Preferably, the subwoofer phase correction value is optionally selectable from one of a set of different values ​​by the user of the system. The multi-speaker home theater system includes a phase-changing digital signal processor (preferably in the form of a first-order all-pass filter) and a polarity inverter. The digital signal processor and polarity inverter are both configured to modify the phase of an audio signal from (including derived from) an audio signal source before the signal is passed to a subwoofer speaker driver. In use, the phase of the signal is modified (e.g., by a first order all-pass filter operating at a tuning frequency that is automatically selected based on a selected subwoofer phase correction value and a selected cutoff frequency), thereby enabling a user to, for example, reduce (e.g., correct) a subwoofer signal phase error that might otherwise be present. The phase of the signal is selectively modified by the polarity inverter, which produces a phase change of 0 degrees or 180 degrees based on a selected subwoofer phase correction value.

[0020] According to yet another aspect of the present invention, there is provided a method of operating a subwoofer, for example, a method of controlling the phase alignment of the subwoofer by modifying the phase of the input signal with a first order all-pass filter ("APF") and modifying or not modifying the polarity of the signal. The method may include one or more, preferably all of the following steps: (a) it may include receiving an audio signal input (e.g., from an AVR or the like) through a low pass filter configured to operate based on a selected low pass filter control frequency; (b) there may be a step of sensing or determining a low pass filter control frequency and a desired phase control setting selected by a user from a plurality of different user selectable phase correction settings; (c) there may be a step of calculating or selecting a desired tuning frequency and a desired polarity (e.g., inverting "-" and not inverting "+") in response to the low pass filter control frequency and the desired phase control setting so sensed or determined. (d) there may be a step of modifying the phase of the input signal by a first order all-pass filter ("APF") set to the desired tuning frequency so calculated or selected, and there may be a step of modifying or not modifying the polarity in response to the desired polarity so calculated or selected. (e) there may be a step of driving a subwoofer with the resulting signal of the audio signal input so modified, the signal optionally being amplified (or further amplified) before being supplied to the subwoofer driver. Preferably, after the APF has modified the phase and the polarity has been changed (or not) there are no other digital signal processing or filtering stages before the signal is passed to the subwoofer driver.

[0021] The signal processing steps are preferably performed by digital signal processing, although it will be appreciated that some or all aspects of the embodiments described herein may be partly performed by corresponding analog circuitry or other electronic means.

[0022] Thus, embodiments of the method of the present invention allow for altering the phase of an input signal to provide or most closely provide a desired phase corrected signal output for a subwoofer driver, and therefore certain embodiments may take the form of a phase alignment control method.

[0023] The step of calculating or selecting the desired tuning frequency (and optionally calculating or selecting the desired polarity) may include referencing a look-up table stored in a memory device. Such a look-up table may provide the desired tuning frequency values ​​for different combinations of values ​​of the low pass filter control frequency and the desired phase control setting value. Such a look-up table may provide the desired tuning frequency values ​​for each possible combination of a plurality (e.g., at least 10) values ​​of the low pass filter control frequency and a plurality (e.g., between 4 and 24, inclusive) of desired phase control setting values. The phase control setting values ​​may be at equally spaced phase increments. The step of calculating or selecting the desired tuning frequency (and optionally calculating or selecting the desired polarity) may additionally or alternatively include calculations or determinations that do not require a look-up table.

[0024] Of course, it will be understood that features described with respect to one aspect of the invention may be incorporated in other aspects of the invention, for example a method of the invention may incorporate any of the features described with reference to an apparatus of the invention, and vice versa.

[0025] The above and further objects, features and advantages of the present invention will become apparent from the following detailed description of specific embodiments thereof, particularly when considered in conjunction with the accompanying drawings, in which like reference numerals are used in different drawings to indicate similar elements.

[0026] Illustrative examples of the prior art and embodiments of the present invention will now be described, by way of example only, with reference to the accompanying schematic drawings in which: [Brief description of the drawings]

[0027] [Figure 1A] FIG. 1 shows an example of a typical home theater system in a listener's room according to the prior art. [Figure 1B] FIG. 1 shows an example of a typical home theater system in a listener's room according to the prior art. [Figure 1C] FIG. 1 is a front elevation view of a large tower-type multi-driver speaker system typically employed as main speakers in a home stereo or home theater system according to the prior art. [Figure 1D] FIG. 1 is a perspective view of a typical home theater soundbar / subwoofer system according to the prior art. [Figure 1E] FIG. 1 includes a pair of diagrams illustrating the modeled behavior of crossover elements in a typical home theater system, according to Applicant's analysis of prior art systems. [Figure 2A] FIG. 1 illustrates an improved multi-speaker home theater system including an improved subwoofer system disposed in a listener's room and a phase alignment control system and method for the subwoofer in accordance with an embodiment of the present invention. [Figure 2B] FIG. 1 illustrates an improved multi-speaker home theater system including an improved subwoofer system disposed in a listener's room and a phase alignment control system and method for the subwoofer in accordance with an embodiment of the present invention. [Figure 2A-5] FIG. 1 illustrates an improved multi-speaker home theater system including an improved subwoofer system and a phase alignment control system and method for the subwoofer in accordance with an embodiment of the present invention. [Figure 3A]FIG. 1 illustrates Applicant's modeling and analysis work used to develop an improved multi-speaker home theater system including an improved subwoofer system and phase alignment control systems and methods for the subwoofers, in accordance with embodiments of the present invention. [Figure 3B] FIG. 1 illustrates Applicant's modeling and analysis work used to develop an improved multi-speaker home theater system including an improved subwoofer system and phase alignment control systems and methods for the subwoofers, in accordance with embodiments of the present invention. [Figure 4] FIG. 2 is a signal flow diagram showing elements of an improved multi-speaker home theater system including an improved subwoofer system and a phase alignment control system and method for the subwoofer in accordance with an embodiment of the present invention. [Diagram 5] 5A-5C show the contents of a look-up table or matrix that may be incorporated as programming into digital signal processing or stored in memory as a matrix to generate an improved phase-aligned subwoofer drive signal for use in the improved subwoofer system and phase alignment control method of FIGS. 2A-4 in accordance with an embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0028] Hereinafter, an embodiment of the present invention will be generally described, including some variations not specifically shown. As detailed below, the subwoofer phase alignment control system and method of the embodiment of the present invention provides an easy and intuitive way for an installer, user or listener to control the phase angle of the signal provided to one or more low frequency speakers (e.g., an improved standalone subwoofer). The signal processing device or circuit used to achieve this includes an all-pass filter input to a stage that applies or omits polarity inversion. The frequency tuning of the all-pass filter (i.e., the "f0" of the filter stage) and the state (on / off) of polarity inversion are directly related to the desired high frequency cutoff frequency, sometimes called the crossover frequency, and the desired amount of phase shift at that frequency.

[0029] The embodiments of the present invention provide a selected amount of desired phase shift with a minimal (and least detrimental) amount of filtering. Phase shift is often necessary in systems consisting of one or more subwoofers and additional higher frequency speakers (such as in consumer home theater systems). The phase shift between the high and low frequency systems at the crossover frequency is rarely properly aligned for an equal total frequency response. By shifting the phase of the subwoofer, the response can be flattened, which results in a more natural sound. Doing this with a minimal amount of filtering ensures less group delay, which also results in a more natural sound.

[0030] This control is most easily implemented in digital signal processing ("DSP") and is the preferred embodiment. The required inputs from the user are the crossover frequency and the amount of phase shift desired. The parameters for the all-pass filters and polarity inversion can be calculated or read from simple tables.

[0031] In an embodiment, a stand-alone subwoofer (e.g., similar to 22 or 130) is configured with a novel control input and circuitry including a phase control adjustment knob or slider having a number (e.g., 4-24) of different phase adjustment steps. For example, an 8-step adjustment input includes 45° phase adjustment steps each resulting in a different phase adjustment. Preferably, the phase control settings have different steps identified by user-readable indicia, and illuminated (e.g., LED) indicators near each phase adjustment setting position provide the user with additional visual confirmation of operation of the intelligent phase control settings. In an embodiment, the subwoofer system (e.g., similar to 22, 58, or 130) is configured to communicate with and respond to a hand-held remote controller that can be used when the user is at the listening position 24. In the method of the present invention, a user can play selected program material through the user's sound system (e.g., 10), but with an improved subwoofer of the present invention, listen to the sound, and switch between a number of (e.g., eight) phase control settings, alternating between those settings and determining at each transition whether the system sounds "better or worse" than the previous adjustment setting.

[0032] The improved subwoofer of the described embodiment of the invention has controls to select from the following choices: subwoofer volume, subwoofer low pass frequency, subwoofer low pass slope (filter order), other subwoofer EQ settings, subwoofer "phase" adjustment, and subwoofer polarity (absolute or inverted polarity). In one embodiment, the phase adjustment is from 0 degrees to -135 degrees (8 45 degree increments) or 0 degrees to -165 degrees (24 15 degree increments) and is implemented by a sliding all-pass filter that can track the low pass filter control (referred to as "intelligent phase control").

[0033] Applicant's research and development work on whether to use delays or all-pass filters to provide intelligent phase control has shown that an all-pass filter implementation built into each standalone subwoofer is more likely to achieve good results when used to compensate for differences in low frequency systems (i.e., inherent roll-off of speakers (e.g., 22, 130)). Differences of this type exist in all systems. Delays are only effective if used to compensate for delay errors. It is now preferable to address the delay issue in the receiver (e.g., 15).

[0034] 2A-5, there is shown an improved multi-speaker home theater system (e.g., 200) that includes one or more improved subwoofer systems 222 incorporating phase alignment control systems and methods of certain embodiments described in more detail below.

[0035] 2A and 2B show exemplary perspective and top views of an improved surround sound system 200 disposed in a typical media space or room 12. The illustrated system may be a conventional Dolby® digital configuration with a home theater or other audio / video (AV) source 214 in an embodiment including a typical AVR 15 (as shown in FIGS. 1A and 1B) or an improved AVR 215 (as shown in FIGS. 2A and 2B). The system 200 may also include conventional left channel speaker 16, right channel speaker 18, and center channel speaker 20 used with an improved subwoofer 222, all positioned in front of a listener's main seating area at a listening position 24, such as a sofa or chair. In an embodiment, the system includes left and right surround speakers 26 and 28 spaced apart from either side of the listening position to provide a sense of spaciousness to the sound radiated by the speakers and to provide ambient sound for AV programs such as movies and concerts. In an embodiment, the home theater system 200 includes left and right back speakers 30 and 32 generally positioned behind and on either side of the listening location, the speakers preferably being centered about a centerline 34 passing through the AV unit 214 and the listening location or listening position 24.

[0036] The exemplary system 200 and method of the described embodiment effectively and accurately integrates the sound from the improved subwoofer 222 playback with the sound generated by other speakers in a home theater or stereo system by controlling the phase angle of the subwoofer and providing a user-adjustable phase alignment control input and method. The subwoofer phase alignment control system and method of the described embodiment provides an easy and intuitive way for an installer, user or listener to control or correct the phase angle of the signal provided to the low frequency speaker (e.g., driver D1 of the subwoofer 222). The signal processing device or circuit used to achieve this includes a single all-pass filter 260 that inputs to a stage that applies or omits polarity inversion depending on pre-programmed parameters in a matrix 250 (e.g., as shown in FIG. 5). The tuning frequency of the all-pass filter (i.e., the "f0" of the filter stage) and the state of polarity inversion (on / off) are directly related to the desired high frequency cutoff frequency, sometimes called the crossover frequency, and the desired amount of phase shift at that frequency.

[0037] An embodiment of the system 200 and signal processing method of the present invention is shown in the diagrams of Figures 3A, 3B and 4, and in the table or matrix of Figure 5. Figures 3A and 3B illustrate and describe an exemplary prototype embodiment of the system and method of the present invention using phase shift and polarity settings developed to correct an example of phase error. Figure 3A models the feeding of an audio signal from a source through various digital signal processing stages to a subwoofer D1 and a main speaker D2. In this example, the user has selected a crossover frequency of 80 Hz that is applied by the AVR 215 using a 4th order LR (Linkwitz-Riley) low-pass IIR ("infinite impulse response") filter for the signal received at the subwoofer driver D1 and a 2nd order high-pass IIR filter for the signal received at the main speaker driver D2. Figure 3A models the inherent high-pass characteristic of the main speaker using a 4th order Butterworth filter 252 (fc=50 Hz), i.e. "speaker LF alignment". Similarly, the inherent high-pass characteristic of the subwoofer 222 is modeled by a fourth order Butterworth filter 255 (fc=20Hz). It should be understood that the model filter blocks 252, 255 as shown in Figure 3A are schematic elements that model the behavior of a system, and thus the modeled filters 252, 255 are not elements in a physical embodiment of the inventive system, an example of which is shown in Figure 4.

[0038] When using the improved system 200, the listener or user (e.g., while at position 24) adjusts the phase correction with his ears and selects a selected phase correction (e.g., +40 degrees) from a finite selection of different phase correction values. As a result (of the crossover at 80 Hz and the user's selection of a phase correction of +40 degrees), the audio signal passes through a first-order all-pass filter tuned to about 30 Hz (which results in a phase shift of about -140 degrees at the cutoff frequency of 80 Hz) and a polarity inverter 270 (which results in a phase shift of substantially 180 degrees) to achieve the desired phase correction of 40 degrees at the cutoff frequency of 80 Hz. The subwoofer has a gain of +0.6 dB. In the schematic model shown in FIG. 3A, this combines the phase shift (minus 140 degrees) with the polarity inversion (effectively a phase shift of plus 180 degrees) to correct the phase error or minus 40 degrees (i.e., the correction is plus 40 degrees).

[0039] Figure 3B shows a (simulated) sound pressure level ("SPL") graph (top graph) and a group delay / phase graph (bottom graph) corresponding to the configuration shown in Figure 3A. From the SPL curve, it can be seen that the frequency response in the crossover region is very flat (close to ideal), with an error (difference between performance characteristics and ideal characteristics) of about + / - 0.2 dB. The excess group delay is about 5 ms, which is acceptable. Thus, the combination of polarity inversion and all-pass filters provides an accurate amplitude response, at the expense of a slightly increased but acceptable group delay.

[0040] The example circuit shown in FIG. 3A illustrates the type of experimental work that was employed to develop a working embodiment DSP configuration capable of providing phase correction given many different combinations of input parameters, such as those shown in the matrix settings in the embodiment illustrated by FIG.

[0041] The objective of the described embodiment is to provide a selected desired amount of phase shift (or phase error correction) with a minimum (and least detrimental) amount of filtering. Phase shift is often necessary in systems consisting of one or more subwoofers (e.g., 222 with subwoofer driver D1) and other speakers (e.g., 16, 18, 20 with main speaker driver D2), such as those found in consumer home theater systems. The phase shift between the high and low frequency systems at the crossover frequency is rarely properly aligned for an equal total frequency response. By shifting and correcting the phase of the signal input to the subwoofer driver D1, the response of the combined system can be made flatter, thereby sounding more natural. Without sufficient measures of phase alignment of the subwoofer at the crossover frequency so that the phase is aligned with the other speakers of the sound system (i.e., by using the described embodiment), the bass may sound muddy and dull at or near the crossover or cutoff frequency. Also, achieving the corrective phase shift with a minimal amount of filtering ensures less group delay, which also translates into a more natural sound.

[0042] The control system and method is preferably implemented with digital signal processing ("DSP"). Required inputs from the user are a low pass filter crossover frequency 230 and a desired amount of phase shift or phase control setting 240 (see, e.g., FIG. 4). The all pass filter and polarity inversion parameters can be calculated or read from a simple look up table ("LUT") or matrix 250 (see, e.g., FIG. 5). In the exemplary embodiment of FIGS. 2A-5, a standalone subwoofer (e.g., 222) is configured with novel control inputs and circuitry including a phase control adjustment knob or slider (which provides an input signal to the phase control setting input 240) having multiple (e.g., 4-24, but 8 in the exemplary embodiment of FIG. 5) different phase control adjustment steps. For example, the matrix 250 provides an 8-step adjustment input with 8 45 degree phase adjustment steps, each step providing a different user selectable phase adjustment. In an embodiment, the phase control settings have different stages identified by user-readable indicia, and illuminated (e.g., LED) indicators near each phase adjustment setting provide the user with additional visual confirmation of operation of the intelligent phase control settings. In an embodiment, the subwoofer system (e.g., 222) is configured to communicate with and respond to a hand-held remote control (not shown) that can be used when the user is at the listening position 24. In a method of the present invention, the user can play and listen to selected program material through the user's sound system (200), but with the improved subwoofer 222 of the present invention, and can switch between multiple (e.g., eight) phase control settings, alternating between those settings and determining at each transition whether the system sounds "better or worse" than the previous adjustment setting.

[0043] The improved subwoofer 222 of the described embodiment is an active subwoofer system having a dedicated amplifier system A1 and signal processing circuitry with user adjustable controls selected from the following options: subwoofer volume, subwoofer low pass frequency (e.g., 230), subwoofer low pass slope (filter order), other subwoofer EQ settings, subwoofer "phase" adjustment (e.g., 240), and subwoofer polarity (absolute or inverted polarity). The illustrated phase adjustment setting 240 allows the user to select any value from the group consisting of 0 degrees to + / - 135 degrees and 180 degrees (e.g., in 45 degree increments) (i.e., eight different settings). One embodiment not shown allows the user to select any of 24 phase correction settings selected from the group consisting of 0 degrees to + / - 165 degrees and 180 degrees in 15 degree increments. A further embodiment, not shown, allows the user to select from any of four different phase correction settings selected from 0 degrees, +90 degrees, -90 degrees, and +180 degrees. The phase correction is implemented by a sliding all-pass filter that can track a low-pass filter control (referred to herein as "intelligent phase control").

[0044] Applicant's research and development work on whether to use delays or all-pass filters to provide intelligent phase control has shown that an all-pass filter implementation built into each standalone subwoofer is more likely to achieve good results when used to compensate for differences in low frequency systems (i.e., the inherent roll-off of the speakers (e.g., 22, 130)). Differences of this type exist in all systems. In system 200, delays are used only to compensate for delay errors, with delay issues optionally being addressed in an improved AVR (e.g., 215).

[0045] 2A-5, and with particular reference to FIG. 4, in system 200 and improved subwoofer 222, an intelligent phase control system and method (e.g., DSP) uses polarity adjustment (i.e., inversion or no inversion) and all-pass filter signal processing in a manner responsive to inputs including a low-pass filter frequency (e.g., a user-selected crossover frequency) and a user-selected phase control setting (e.g., as shown in FIGS. 4 and 5). An audio input signal 215 is processed by a single first-order all-pass filter 260 and inverted or not inverted by a polarity inverter 270 stage to produce an output signal 275, which is then amplified by gain stage A1 before being passed to subwoofer driver D1. The all-pass filter 260 modification combines with the polarity adjustment (or no adjustment) to produce a desired phase shift at the crossover frequency of the low-pass filter 230. The tuning frequency f0 of all-pass filter 260 is determined using matrix 250 based on the desired phase shift (selected by the user using phase control setting 240) and the crossover frequency of low-pass filter 230 (also selected by the user). Polarity is used to augment the all-pass phase shift (by selectively adding an effective phase change of 0 or 180 degrees) without adding the extra group delay that would otherwise be introduced by cascaded all-pass filters required to cover the phase range 0° to 345°.

[0046] The matrix of the exemplary embodiment shown in Figure 5 can be understood as follows: Eight different phase correction settings are available to the user: (i) -135°, (ii) -90°, (iii) -45°, (iv) 0°, (v) +45°, (vi) +90°, (vii) +135° and (viii) +180°. There are also 18 different settings for the crossover frequency: (i) 40 Hz, (ii) 45 Hz, (iii) 50 Hz, (iv) 55 Hz, (v) 60 Hz, (vi) 65 Hz, (vii) 70 Hz, (viii) 75 Hz, (ix) 80 Hz, (x) 85 Hz, (xi) 90 Hz, (xii) 95 Hz, (xiii) 100 Hz, (xiv) 110 Hz, (xv) 120 Hz, (xvi) 130 Hz, (xvii) 140 Hz, and (xviii) 150 Hz. The matrix 250 provides a method using look-up tables stored in digital memory to determine the value of the tuning frequency f0 of the all-pass filter 260 and whether to apply inversion by the polarity inverter 270, which in combination provide the desired phase correction at the selected cutoff frequency of the crossover. For example, the user selectable phase correction setting may be a +45° change and the cutoff frequency may be selected by the user as 70Hz. Referencing the matrix 250 with these values ​​(+45° and 70Hz) results in a tuning frequency f0 of the all-pass filter 260 of 28.994Hz (causing a phase change of -135° at 70Hz) and a polarity inversion (causing a phase change of +180°), thus providing the desired correction at a phase angle of +45° with minimal group delay in the audio signal path. As another example, the user selectable phase correction setting may be a -135° change and the cutoff frequency may be selected as 70Hz. Referencing the matrix 250 with these values ​​(-135° and 70Hz) results in a tuning frequency f0 of the all-pass filter 260 of 28.994Hz (causing a phase change of -135° at 70Hz), but no polarity inversion, thus providing the desired correction in phase angle. As yet another example, the user selectable phase correction setting may be a change of +180 degrees and the cutoff frequency may be selected as 90 Hz.Referencing matrix 250 with these values ​​(+180° and 90 Hz, or indeed any cutoff frequency) results in a polarity inversion (which produces a phase change of +180°) and a bypass of all-pass filter 260 (i.e., the all-pass filter does not produce any additional phase change), thus producing the desired correction of the +180° phase angle.

[0047] As yet another example, if the user selectable phase correction setting corresponds to no change in phase angle, i.e., 0 degrees, then when looking at matrix 250, there is no polarity reversal (i.e., no phase change), bypassing all-pass filter 260, thus resulting in the desired result, i.e., no correction of the phase angle. It can also be seen from Figure 5 that when the user selectable phase correction is set to +90° or -90°, the required tuning frequency of the all-pass filter is simply the same as the selected cutoff frequency value.

[0048] The signal processing method and system 222 of the described embodiment is surprisingly effective, in part due to the unique simultaneous combination of polarity adjustment and phase control to obtain a desired phase shift (see, for example, FIG. 5). By varying the all-pass frequency tuning frequency f0 based on the low pass filter frequency and the desired phase shift, the system is able to provide a more natural, less adversely affected output signal to the subwoofer driver D1 that integrates more naturally with the sound from the other speakers in the system 200. Other advantages gained by using the system 200 are: (a) adjustment of the phase control to correct for subwoofer signal phase error is more precise and intuitive (as typical prior art phase controls are only accurate at one frequency because they do not vary with the low pass filter setting 230) and is easier for the user to control (e.g., using a remote control from the user's listening position 24 while music or a test tone is being played) because the phase shift resulting from the phase control setting is displayed; (b) Less group delay. Less group delay results from using fewer filter stages to obtain the required phase shift. Less group delay results in more accurate, better sounding bass. As a result, the user should be able to better tune their subwoofer to blend with the rest of their audio system.

[0049] The following items form part of this disclosure: (Item 1) FIGS. 2A-5 illustrate features of an improved multi-speaker home theater system including an improved subwoofer system and a phase alignment control system for the subwoofer, the subwoofer system having an audio signal input (e.g., from an AVR 15 or 215) and a control input (e.g., by a handheld remote controller (not shown)) of a low pass filter frequency 230 and a desired phase control setting 240, the control input of the desired phase control setting 240 including a plurality (e.g., 4-24) different user selectable phase correction settings in equally spaced phase increments, the phase alignment control system including a single first order all-pass filter 260 having a selectable f0 tuning frequency and a polarity selection stage optionally including an adjustable amplifier gain stage A1. (Item 2) FIGS. 2A to 5 show a phase alignment control system, (a) more accurate and intuitive adjustment of the phase control to correct for subwoofer signal phase error (as typical prior art phase controls are only accurate at one frequency because they are not changed by the low pass filter setting 230) and more user control because the phase shift resulting from the phase control setting is displayed; (b) Less group delay. Less group delay results from using fewer filter stages to obtain the required phase shift. Less group delay results in more accurate, better sounding bass. As a result, a user should be able to better tune their subwoofer to blend with the rest of their audio system. (Item 3) An improved multi-speaker home theater system as in item 1 including an improved subwoofer system and a phase alignment control system for the subwoofer, wherein the control input for desired phase control setting 240 includes eight different user-selectable phase correction settings in equally spaced (45 degree) phase increments. (Item 4) An improved multi-speaker home theater system of item 1 including an improved subwoofer system and a phase alignment control system for the subwoofer, wherein the plurality (e.g., eight) different user-selectable phase correction settings in equally spaced (e.g., 45 degree) phase increments (and display indicators indicating which phase correction is selected) are indicated on a user-accessible surface of the improved subwoofer 222 or on the user's hand-held remote controller. (Item 5) FIGS. 2A to 5 and the accompanying description show that the phase alignment control method includes: (a) providing a subwoofer system having an audio signal input (e.g., from an AVR 15 or 222) and control inputs of a low pass filter frequency 230 and a desired phase control setting 240, the control input of the desired phase control setting 240 including a plurality of different user selectable phase correction settings from 4 to 24 in equally spaced phase increments, the phase alignment control system including a single first order all pass filter ("APF") having a selectable f0 tuning frequency, and a polarity selection stage optionally including an adjustable amplifier gain stage; (b) the user selected phase correction setting method steps of sensing or determining the current control inputs of the low pass filter frequency 230 and the desired phase control setting 240; (c) A user-selected phase correction setting method step of calculating or selecting a desired APF selectable f0 tuning frequency and polarity (+ or -) adjustment to most closely provide a desired phase corrected signal output of driver D1 of improved subwoofer 222. (Item 6) A phase alignment control method for a subwoofer of Item 5, wherein the step of selecting a desired APF selectable f0 tuning frequency and polarity (+ or -) adjustment to most closely provide a desired phase corrected signal output of driver D1 of the improved subwoofer 222 includes storing a lookup table or matrix 250 within or in a manner accessible by the improved subwoofer 222 having a plurality of different user selectable phase correction settings of 4 to 24 in equally spaced phase increments.

[0050] Those skilled in the art will recognize that the present invention offers several improvements over available active subwoofers. The following items also form part of this disclosure: (Item 7) An active subwoofer for use in a multi-speaker home theater system (e.g., 200) including an improved phase alignment control system for the subwoofer, (a) a subwoofer system (e.g., 222) having a housing supporting at least one amplifier stage A1 configured to drive at least one electrodynamic transducer D1 in response to an audio signal input 215 (e.g., from an AVR 15 or 215), a first user-adjustable control input 230 for a low pass filter cutoff frequency, and a second user-adjustable control input 240 for a desired phase control setting; (b) the second control input 240 provides a user selectable phase correction setting selected (e.g., by a hand-held remote control (not shown)) from a plurality of at least four different user selectable phase correction settings in equally spaced phase increments to the phase alignment control system 222, and the first control input 230 provides a user selectable low pass filter cutoff frequency signal to the phase alignment control system 222; (c) the phase alignment control system 222 includes a single all-pass filter 260 having an adjustable all-pass tuning frequency f0 that is adjustable and that is automatically set in use in response to the user selectable low pass filter cutoff frequency; and (ii) optionally a polarity selection stage 270 incorporated in the amplifier gain stage A1; (d) an active subwoofer, wherein the phase alignment control system 222 is responsive to both (i) the first control input 230 and the user selectable low pass filter cutoff frequency signal and (ii) the second control input 240 and the user selected phase correction setting, and in response generates a phase, polarity and amplitude adjusted audio signal for the subwoofer driver D1. (Item 8) The active subwoofer of Item 7, wherein the second control input 240 includes eight different user-selectable phase correction settings in equally spaced phase increments for the phase alignment control system 222, and the first user-adjustable control input 230 for a low pass filter cutoff frequency is configured to operate in a frequency range of 40 Hertz to 150 Hertz at a selected plurality of equally spaced frequencies. (Item 9) The active subwoofer of item 8, wherein the first control input 230 supplies the user selectable low pass filter cutoff frequency signal to the phase alignment control system 222 as one user selected cutoff frequency selected from equally spaced frequencies of 40 Hz, 45 Hz, 50 Hz, 55 Hz, 60 Hz, 65 Hz, 70 Hz, 75 Hz, 80 Hz, 85 Hz, 90 Hz, 95 Hz, 100 Hz, 105 Hz, 110 Hz, 115 Hz, 120 Hz, 125 Hz, 130 Hz, 135 Hz, 140 Hz, 145 Hz and 150 Hz, and the selectable tuning frequency f0 of the all pass filter is automatically adjusted in response to the user selected cutoff frequency and the user selected phase correction setting. (Item 10) An active subwoofer of Item 7, wherein the second control input 240 supplies one user-selected phase correction setting to the phase alignment control system 222 from equally spaced phase correction setting values ​​of -135 degrees, -90 degrees, -45 degrees, zero degrees, +45 degrees, +90 degrees, +135 degrees and +180 degrees. (Item 11) The active subwoofer of Item 7, wherein the phase alignment control system 222 is programmed to provide an adjustable all-pass tuning frequency f0 that is automatically set to a value equal to the user-selectable low-pass filter cutoff frequency when the user-selected phase correction setting value is -90 degrees or +90 degrees. (Item 12) The active subwoofer of Item 7, wherein the phase alignment control system 222 is programmed to automatically bypass the all-pass filter 260 when the user-selected phase correction setting value is zero degrees or 180 degrees. (Item 13) The active subwoofer of Item 7, wherein the phase alignment control system 222 is configured and programmed to respond to a user-selected phase correction setting value and a user-selected low pass filter cutoff frequency signal transmitted from a hand-held remote control when held by a user at a listening position 24 in the room while listening to a movie soundtrack, music or test tone audio signal.

[0051] Those skilled in the art will recognize that the present invention provides several improvements to the method of accurately selecting the optimum phase alignment according to the present invention for an available active subwoofer. The following items also form part of this disclosure: (Item 14) A subwoofer phase control method that allows a listener or user to quickly and accurately select the most satisfactory subwoofer phase adjustment or phase correction setting for blending the output of the subwoofer with the rest of the output of the multi-speaker system in the room 12, comprising: (14a) providing a subwoofer system (e.g. 222) configured to receive an audio signal input 215 (e.g. from an AVR 15 or 215) and having a first user adjustable control input 230 for a low pass filter cutoff frequency and a second user adjustable control input 240 for a desired phase control setting, said second control input 240 providing a user selected phase correction setting selected from a plurality of at least four different user selectable phase correction settings in equally spaced phase increments to a phase alignment control system 222, said first control input 230 providing a user selectable low pass filter cutoff frequency signal to said phase alignment control system 222, said phase alignment control system 222 including a single all pass filter 260 having an adjustable all pass tuning frequency f0 that is adjustable and is automatically set in use in response to said user selectable low pass filter cutoff frequency; (14b) placing said subwoofer system 222 in a room 12 having a listening position 24 for a listener or user; (14c) playing music, a motion picture soundtrack, a test audio signal, or other audio program material through all of the speakers in the stereo or home theater system so that a user or listener at location 24 may audibly evaluate the output of the subwoofer when played simultaneously with the remainder of the output of the multi-speaker system; and while (14d) detecting a user first adjustment of the second control input 240 of the user selected phase correction setting for setting the phase alignment control system 222 (e.g., by a hand-held remote controller (not shown)), the user first adjustment being a first selection from the at least four different user selectable phase correction settings; (14e) generating a first phase, polarity and amplitude adjusted audio signal 275 for the subwoofer, the audio signal 275 enabling the user at listening position 24 to evaluate the first blended subwoofer output with the rest of the system's speaker output in the room; (14f) detecting a user second adjustment of the second control input 240 of the user selected phase correction setting of the phase alignment control system 222, the user second adjustment being a second selection from the at least four different user selectable phase correction settings that is different from the user first adjustment; and in response thereto: (14g) generating a second phase, polarity and amplitude adjusted audio signal 275 for the subwoofer, which allows the user at listening position 24 to evaluate whether the output of the second blended subwoofer with the rest of the system's loudspeaker output in the room is preferred over the output from any previous adjustment of the second control input 240 of the user selected phase correction setting phase alignment control system 222; (14h) detecting a user third adjustment of the second control input 240 of the user selected phase correction setting of the phase alignment control system 222, the user third adjustment being a third selection from the at least four user selectable phase correction settings that is different from the user first and second adjustments; and in response thereto, then: (14i) generating a third phase, polarity and amplitude adjusted audio signal 275 for the subwoofer, wherein the user at listening position 24 can evaluate whether a third blended output of the subwoofer with the remainder of the output of the system's speakers in the room is preferred over an output from any previous adjustment of the second control input 240 of the user selected phase correction setting phase alignment control system 222.

[0052] Although the present invention has been described and illustrated with reference to specific embodiments, those skilled in the art will recognize that the invention applies to many different variations not specifically set forth herein. For purposes of example only, certain possible variations are described below.

[0053] Although the system 200 and method of the presently described embodiments have been described using the exemplary embodiments of FIGS. 2A-5, they may also be implemented (a) in conjunction with a full-range speaker (such as 50 in FIG. 1C) having a built-in active subwoofer, or (b) as part of an improved subwoofer soundbar system externally similar to the system of FIG. 1D, possibly with one or more additional improved subwoofers 222.

[0054] It should be understood that in certain embodiments, the lookup table of FIG. 5 may be simplified for certain input parameters and may not even be referenced in certain situations. For example, the need to apply polarity inversion may be determined by a binary test, where if the phase correction setting is positive, polarity is inverted, and otherwise (i.e., if the phase correction setting is zero or negative), polarity inversion is not required. Also, if the phase correction setting is −90° or +90°, the required tuning frequency of the all-pass filter is equal to the selected cutoff frequency value. Also, if the user-selectable phase correction setting is 0° or +180°, it may be determined that the all-pass filter can be bypassed without directly referencing the matrix.

[0055] It may be advantageous to provide an embodiment that applies phase correction by not giving the user control over the selection of the crossover frequency for the subwoofer, but rather by the user selecting a correction value from a selection range of different user-selectable phase correction settings. For example, the crossover frequency may be fixed so that it does not need to (or cannot) be changed by the user. Such an embodiment may use a greatly simplified version of the matrix shown in FIG. 5.

[0056] It may be advantageous to provide an embodiment in which the phase alignment control system provides phase correction by allowing the user to select a correction value from a selection range of different user-selectable phase correction settings without taking into account the crossover frequency selected by the user for the subwoofer. For example, there may be, say, 12 phase correction settings including 0 degrees and 180 degrees (bypassing the all-pass filter), another 10 stepping through five different (but carefully selected) tuning frequencies of the all-pass filter, covering, say, a range of 15Hz to 360Hz without polarity inversion, and another five covering a range of 15Hz to 360Hz with polarity inversion. This may provide the user with sufficient phase control possibilities to select a rough correction for most, but not all, crossover frequencies.

[0057] The phase alignment control system of the present invention as shown in Figures 2A-5 provides, among other advantages, a surprisingly effective combination of features and methods that allow a listener or user to blend or integrate the sound of the subwoofer 222 with the sound of the multi-speaker (e.g., home theater) system 200 in the user's room by focusing on efficient and effective digital signal processing to achieve extremely short group delay in the subwoofer signal output 250. A novel combination of simultaneous adjustment of phase control and polarity is employed to achieve the user's desired phase correction or phase shift in the listening room. Also novel is the alteration of the tuning frequency of a preferably single first order all-pass filter based in part on the user-adjusted low pass filter frequency of the subwoofer to derive the user's desired phase correction. These novel features are particularly well suited to allow a user to make phase correction adjustments at a location 24 in the user's room to minimize muddiness or other adverse effects in the overall system sound.

[0058] Although the embodiments of the new and improved method and system have been described above, other modifications, variations and changes will be suggested to those skilled in the art in light of the teachings set forth herein. It is therefore to be understood that all such modifications, variations and changes are deemed to be within the scope of the present invention. The reader will also appreciate that integers or features of the present invention described as being preferred, advantageous, convenient, etc. are optional and do not limit the scope of the independent claims. It is also to be understood that such optional integers or features may be advantageous in some embodiments of the present invention, but may not be desirable in other embodiments and therefore may not be present.

Claims

1. 1. A phase alignment control system for a subwoofer configured for use in a multi-speaker home theater system, comprising: at least four different user selectable phase correction settings, the at least four different user selectable phase correction settings allowing the system to select one of the different user selectable phase correction settings at a time; a single first order all-pass filter (260) having a selectable tuning frequency; a polarity selection stage (270); the phase alignment control system is configured to generate an output signal by applying a phase change to an input signal in response to a selected one of the different user-selectable phase correction settings; the phase alignment control system being configured to apply the phase change to the input signal by a combination of (a) the first order all-pass filter (260) causing a phase change as a result of a selected tuning frequency, and (b) the polarity selection stage (270) selectively applying or not applying polarity inversion.

2. The phase alignment control system detects a first desired change in phase angle, i.e., X 1 and (b) the polarity selection stage is configured such that in response to a first user-selectable phase correction setting corresponding to Y degrees, the first desired change in phase angle is achieved by (a) the first order all-pass filter causing a phase change of Y degrees, and (b) the polarity selection stage applies a polarity reversal, thereby adding a phase change of 180 degrees. 1 2. The phase alignment control system of claim 1, wherein the magnitude of the difference between A and Y is 180 degrees.

3. The phase alignment control system controls a second desired change in phase angle, i.e., X 2 In response to a second user selectable phase correction setting corresponding to a first degree, the second desired change in phase angle is achieved by: (a) causing the first order all pass filter to change to a second desired phase angle of X 2 3. The phase alignment control system of claim 1, configured to be implemented by (a) applying a phase change of 1.5 degrees and (b) the polarity selection stage applying no polarity reversal.

4. 4. The phase alignment control system of claim 1, wherein the phase alignment control system is configured such that in response to a third desired change in phase angle, i.e. a third user-selectable phase correction setting corresponding to 180 degrees, the third desired change in phase angle is achieved by: (a) the first order all-pass filter causing no phase change; and (b) the polarity selection stage applying polarity reversal.

5. 5. The phase alignment control system of claim 1, wherein the phase alignment control system is configured such that in response to a fourth desired change in phase angle, i.e. a fourth user-selectable phase correction setting corresponding to 0 degrees, the fourth desired change in phase angle is achieved by (a) the first order all-pass filter causing no phase change, and (b) the polarity selection stage applying no polarity reversal.

6. at least one, and preferably at least two, different user selectable phase correction settings in the range of −10 degrees to +10 degrees; at least one, and preferably at least two, different user selectable phase correction settings in the range of +80 degrees to +190 degrees; at least one, and preferably at least two, different user selectable phase correction settings in the range of +10 degrees to -100 degrees; A phase alignment control system according to any preceding claim, wherein at least one, and preferably at least two, different user selectable phase correction settings are in the range -80 degrees to -190 degrees.

7. The phase alignment control system of any one of claims 1 to 6, wherein there are (a) eight or more user-selectable phase correction settings, and (b) twenty-four or less user-selectable phase correction settings.

8. the phase alignment control system is configured such that the selected tuning frequency of the first order all-pass filter (260) is selected at least in part in response to a subwoofer crossover frequency; and 8. The phase alignment control system of claim 1, wherein the selected tuning frequency of the first-order all-pass filter is selected in response to a subwoofer crossover frequency and which of the different user-selectable phase correction settings is selected, and wherein for a first subset of different user-selectable phase correction settings, the selected tuning frequency is lower than the subwoofer crossover frequency, and for a second subset of different user-selectable phase correction settings, the selected tuning frequency is higher than the subwoofer crossover frequency.

9. A phase alignment control system according to any preceding claim, wherein the phase alignment control system comprises an adjustable amplifier gain stage.

10. configured to indicate which of the different user-selectable phase correction settings is selected; and and optionally configured to allow the user to select a desired user-selectable phase correction setting; A phase alignment control system according to any preceding claim, wherein the user display device is a remote device.

11. and / or comprising an embedded phase alignment control system according to any one of claims 1 to 10; A subwoofer that is part of a multi-speaker home theatre system including a phase alignment control system according to any one of claims 1 to 10, wherein the subwoofer is driven based on an output signal from the phase alignment control system.

12. An active subwoofer for use in a multi-speaker home theater system (e.g., 200) including an improved phase alignment control system for the subwoofer, comprising: (a) a subwoofer system (222) having a housing supporting at least one amplifier stage (A1) configured to drive at least one electrodynamic transducer (D1) in response to an audio signal input 215 (e.g., from an AVR 15 or 215), a first user-adjustable control input (230) for a low pass filter cutoff frequency, and a second user-adjustable control input (240) for a desired phase control setting; (b) the second control input (240) provides a user selected phase correction setting selected from a plurality of at least four different user selectable phase correction settings in equally spaced increments to a phase alignment control system (222), and the first control input (230) provides a user selectable low pass filter cutoff frequency signal to the phase alignment control system (222); (c) the phase alignment control system (222) includes a single all-pass filter (260) having an adjustable all-pass tuning frequency (f 0 ) that is adjustable and that is automatically set in use in response to the user selectable low pass filter cutoff frequency; and (ii) a polarity selection stage (270) that may be incorporated into the amplifier gain stage (A1); (d) an active subwoofer, wherein the phase alignment control system (222) is responsive to both (i) the first control input (230) and the user selectable low pass filter cutoff frequency signal, and (ii) the second control input (240) and the user selected phase correction setting, and in response generates a phase, polarity and amplitude adjusted audio signal for the subwoofer driver (D1).

13. A multi-speaker home theater system, comprising: at least one subwoofer speaker driver having a low frequency operating range; a plurality of other speaker drivers, each having a higher frequency operating range and arranged to provide a surround sound system; an audio signal source (e.g., an AVR); The system further comprises: A user of the system a cutoff frequency that determines how an audio signal is distributed between the subwoofer speaker driver and one or more of the other speaker drivers; and a subwoofer phase correction value and a subwoofer phase correction value; the multi-speaker home theater system comprising a single first order all-pass filter and a polarity inverter configured in combination to modify the phase of the audio signal from the audio signal source before the audio signal is passed to the subwoofer speaker driver; the signal is modified by the first order all-pass filter operating at a tuning frequency that is automatically selected based on a selected subwoofer phase correction value and a selected cutoff frequency; the polarity inverter producing a phase change of 0 or 180 degrees based on the selected subwoofer phase correction value; A multi-speaker home theater system thereby allowing a user to reduce subwoofer signal phase errors that might otherwise be present.

14. 1. A method of operating a subwoofer, comprising: (a) receiving an audio signal input (e.g., from AVR 15 or 215) through a low pass filter configured to operate based on a selected low pass filter control frequency; (b) sensing or determining the low pass filter control frequency and a desired phase control setting (240) selected by a user from a plurality of different user selectable phase correction settings; (c) calculating or selecting a desired tuning frequency and a desired polarity (e.g., invert "-" or not invert "+") in response to the low pass filter control frequency and the desired phase control set point (240) sensed or determined as above; (d) modifying the phase of the input signal with a single first order all-pass filter ("APF") set to the desired tuning frequency calculated or selected as above, and modifying or not modifying the polarity in response to the desired polarity calculated or selected as above; (e) driving said subwoofer with a signal resulting from said audio signal having been so modified.

15. wherein the step of calculating or selecting the desired tuning frequency includes referencing a look-up table (e.g., matrix 250) stored in a memory device, the look-up table providing desired tuning frequency values ​​for different combinations of low pass filter control frequency values ​​and desired phase control setting values; and optionally 15. The method of claim 14, wherein the lookup table provides desired tuning frequency values ​​for each combination of a plurality of values ​​of low pass filter control frequency and between 4 and 24, inclusive, desired phase control setting values.

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