Subwoofer phase alignment control system and method
A multi-speaker (e.g., home theater or stereo) audio system 200 with one or more subwoofers includes improved phase-adjustable subwoofers 222 and an improved subwoofer phase control method allows the user to quickly and accurately select the most satisfying subwoofer phase adjustments for blending the subwoofer's output with the remainder of the system's speakers' output.
1 . A phase alignment control system for a subwoofer, the phase alignment control system comprising:
at least four distinct user-selectable phase correction settings, the phase alignment control system configured to allow at least one of the distinct user-selectable phase correction settings to be selected at a time;
a single first-order all-pass filter having a selectable tuning frequency; and
a polarity selection stage,
wherein the phase alignment control system is configured such that selection of the selectable tuning frequency of the single first-order all-pass filter is at least partly in response to a subwoofer cross-over frequency and wherein the phase alignment control system is configured to:
generate an output signal by applying a phase change to an input signal in response to the at least one of the distinct user-selectable phase correction settings that has been selected, and
apply the phase change to the input signal by a combination of (a) the single first-order all-pass filter causing the phase change as a result of selection of the selectable tuning frequency and (b) the polarity selection stage selectively applying, or not applying, a polarity inversion.
2 . A phase alignment control system according to claim 1 , wherein the phase alignment control system is configured such that in response to selection of the at least one distinct user-selectable phase correction setting corresponding to a desired change in phase angle of X 1 degrees, wherein the desired change in the phase angle is achieved by (a) the single first-order all-pass filter causing a phase change of Y degrees, and (b) the polarity selection stage applying the polarity inversion thus adding a 180 degree phase change, wherein a magnitude of the difference between X 1 and Y is 180 degrees.
3 . A phase alignment control system according to claim 1 , wherein the phase alignment control system is configured such that in response to selection of the at least one distinct user-selectable phase correction setting corresponding to a desired change in phase angle of X 2 degrees, wherein the desired change in the phase angle is achieved by (a) the single first-order all-pass filter causing a phase change of X 2 degrees, and (b) the polarity selection stage not applying the polarity inversion.
4 . A phase alignment control system according to claim 1 , wherein the phase alignment control system is configured such that in response to selection of the at least one distinct user-selectable phase correction setting corresponding to a desired change in phase angle of 180 degrees, the desired change in the phase angle is achieved by (a) the single first-order all-pass filter not causing a phase change, and (b) the polarity selection stage applying the polarity inversion.
5 . A phase alignment control system according to claim 1 , wherein the phase alignment control system is configured such that in response to selection of the at least one distinct user-selectable phase correction setting corresponding to a desired change in phase angle of 0 degrees, the desired change in the phase angle is achieved by (a) the single first-order all-pass filter not causing a phase change, and (b) the polarity selection stage not applying the polarity inversion.
6 . A phase alignment control system according to claim 1 , wherein the phase alignment control system is configured such that in response to selection of:
(i) a first user-selectable phase correction setting of the at least four distinct user-selectable phase correction settings corresponding to a first desired change in phase angle of X 1 degrees, wherein the first desired change in the phase angle is achieved by (a) the single first-order all-pass filter causing a phase change of Y degrees, and (b) the polarity selection stage applying the polarity inversion thus adding a 180 degree phase change, wherein a magnitude of the difference between X 1 and Y is 180 degrees;
(ii) a second user-selectable phase correction setting of the at least four distinct user-selectable phase correction settings corresponding to a second desired change in phase angle of X 2 degrees, wherein the second desired change in the phase angle is achieved by (a) the single first-order all-pass filter causing a phase change of X 2 degrees, and (b) the polarity selection stage not applying the polarity inversion;
(iii) a third user-selectable phase correction setting of the at least four distinct user-selectable phase correction settings corresponding to a third desired change in phase angle, namely of 180 degrees, wherein the third desired change in the phase angle is achieved by (a) the single first-order all-pass filter not causing a phase change, and (b) the polarity selection stage applying the polarity inversion; and
(iv) a fourth user-selectable phase correction setting of the at least four distinct user-selectable phase correction settings corresponding to a fourth desired change in phase angle of 0 degrees, wherein the fourth desired change in the phase angle is achieved by (a) the single first-order all-pass filter not causing a phase change, and (b) the polarity selection stage not applying the polarity inversion.
7 . A phase alignment control system according to claim 1 , wherein:
at least a first distinct user-selectable phase correction setting of the at least four distinct user-selectable phase correction settings is in the range of −10 to +100 degrees,
at least a second distinct user-selectable phase correction setting of the at least four distinct user-selectable phase correction settings is in the range of +80 to +190 degrees,
at least a third distinct user-selectable phase correction setting of the at least four distinct user-selectable phase correction settings is in the range of +10 to −100 degrees, and
at least a fourth distinct user-selectable phase correction setting of the at least four distinct user-selectable phase correction settings is in the range of −80 to −190 degrees.
8 . A phase alignment control system according to claim 1 , wherein there are (a) eight or more and (b) 24 or fewer of the distinct user-selectable phase correction settings.
9 . A phase alignment control system according to claim 1 , wherein the phase alignment control system is configured such that the selectable tuning frequency of the single first-order all-pass filter is selected in response to the subwoofer cross-over frequency and selection of the distinct user-selectable phase correction settings, and wherein for a first sub-set of the distinct user-selectable phase correction settings the tuning frequency selected is less than the subwoofer cross-over frequency and for a second sub-set of the distinct user-selectable phase correction settings the tuning frequency selected is more than the subwoofer cross-over frequency.
10 . A phase alignment control system according to claim 1 , further comprising an adjustable amplifier gain stage.
11 . A phase alignment control system according to claim 1 , wherein the phase alignment control system is integrated in or on a subwoofer.
12 . A phase alignment control system according to claim 1 , further comprising a user display device configured to display which of the distinct user-selectable phase correction settings is selected.
13 . A phase alignment control system according to claim 12 , wherein the user display device is also configured to allow the user to select a desired user-selectable phase correction setting.
14 . A phase alignment control system according to claim 12 , wherein the user display device is a remote device.
15 . A subwoofer comprising a phase alignment control system according to claim 1 integrated into the subwoofer.
16 . A multi-speaker home theater system comprising:
a phase alignment control system according to claim 1 ; and
a subwoofer driven in dependence on the output signal from the phase alignment control system.
17 . A phase alignment control system according to claim 1 , wherein the at least four distinct user-selectable phase correction settings include eight distinct user-selectable phase correction settings at evenly spaced phase increments.
18 . A phase alignment control system according to claim 17 , wherein the eight distinct user-selectable phase correction settings include −135 degrees, −90 degrees, −45 degrees, zero degrees, +45 degrees, +90 degrees, +135 degrees, and +180 degrees.
19 . A phase alignment control system for a subwoofer, the phase alignment control system comprising:
at least four distinct user-selectable phase correction settings, the phase alignment control system configured to allow at least one of the distinct user-selectable phase correction settings to be selected at a time;
a single first-order all-pass filter having a selectable tuning frequency; and
a polarity selection stage,
wherein the phase alignment control system is configured to:
automatically select the selectable tuning frequency of the single first-order all-pass filter in response to a user-selectable subwoofer cross-over frequency and the user-selectable phase correction settings,
generate an output signal by applying a phase change to an input signal in response to the at least one of the distinct user-selectable phase correction settings that has been selected, and
apply the phase change to the input signal by a combination of (a) the single first-order all-pass filter causing the phase change as a result of selection of the selectable tuning frequency and (b) the polarity selection stage selectively applying, or not applying, a polarity inversion.
20 . A phase alignment control system according to claim 19 , wherein the phase alignment control system is configured such that selection of the selectable tuning frequency of the single first-order all-pass filter includes interrogating a look-up table stored in a memory device, the look-up table providing tuning frequency values for different combinations of values of subwoofer cross-over frequencies and the distinct user-selectable phase correction settings.
21 . A phase alignment control system according to claim 19 , wherein the phase alignment control system is configured such that selection of the selectable tuning frequency of the single first-order all-pass filter is at least partly in response to the user-selectable subwoofer cross-over frequency in a frequency range from 40 Hertz to 150 Hertz in a selected plurality of evenly spaced frequencies.
22 . A phase alignment control system according to claim 21 , wherein the phase alignment control system is configured such that selection of the selectable tuning frequency of the single first-order all-pass filter is at least partly in response to the user-selectable subwoofer cross-over frequency selected from the following evenly spaced frequencies: 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.
23 . A phase alignment control system according to claim 19 , wherein the phase alignment control system is configured to select a tuning frequency f 0 that is automatically set to be equal to the user-selectable subwoofer cross-over frequency when the user-selectable phase correction setting is-90 degrees or +90 degrees.
24 . A phase alignment control system according to claim 19 , wherein the phase alignment control system is configured to automatically bypass the all-pass filter when the user-selectable phase correction setting is zero degrees or 180 degrees.
25 . A phase alignment control system according to claim 19 , wherein the at least four distinct user-selectable phase correction settings include eight distinct user-selectable phase correction settings at evenly spaced phase increments.