WO2020191401A1

WO2020191401A1 - System magnitude response adjustment via use of a bass shelf filter

Info

Publication number: WO2020191401A1
Application number: PCT/US2020/024232
Authority: WO
Inventors: Brad STAROBIN; Scott Orth
Original assignee: Polk Audio, Llc
Priority date: 2019-03-21
Filing date: 2020-03-23
Publication date: 2020-09-24
Also published as: WO2020191401A9

Abstract

A full range loudspeaker system (300, 400) with a subwoofer section and a main (i.e., mid-bass tweeter) section has a user adjustable bass level control (350, 450) and includes a crossover network which is configured to provide user-adjustable (boost or cut) bass levels while maintaining a smoother overall response (i.e., without creating chesty or bloated mid-bass). The loudspeaker system intelligently adjusts spectral balance via a bass level control signal responsive shelf filter (370, 470) to generate a dynamically adjusted bass shelf filtered signal (377, 472).

Description

PCT PATENT APPLICATION

Inventor: Bradley STAROBIN and Scott ORTH

For: System Magnitude Response Adjustment via use of a Bass Shelf Filter

BACKGROUND OF THE INVENTION

Priority Claim and Reference to Related Applications:

[001] This application claims priority to related and commonly owned U.S. provisional patent application no. 62821805 filed March 21st, 2019, the entire disclosure of which is incorporated herein by reference. This application is also related to the following commonly owned patent applications: (a) Ser. No. 13/162,294, filed June 16, 2011 (now U.S. Pat. No. 8,995,697), and (b) Ser. No. 14/563,508, filed Dec. 8, 2014 (now U.S. Pat. No. 9,374,640), the entireties of which are also incorporated herein by reference for nomenclature and enablement purposes.

Field of the Invention:

[002] The present invention relates to signal processing methods used in full-range loudspeakers configured with subwoofer sections and their crossover networks.

Discussion of the Prior Art:

[003] Many full range loudspeaker systems consist of a low-frequency module or “subwoofer” section and a satellite or“main” section having (a) mid-bass drivers for which a passband is bounded by mid/upper-bass frequencies and (b) tweeters for treble extending into and beyond the upper frequency range of human hearing. [004] A conventional full range loudspeaker system can be configured as a“powered tower” system (e.g., 22, as illustrated in Figs 1A and 1 B) or as an active soundbar- subwoofer system (e.g., 100, as illustrated in Figs 1C and 1 D)). Both configurations have been plagued by poorly controlled acoustic magnitude response over the “subwoofer- satellite” passband, especially in systems where the user can adjust and control the amplitude or magnitude of the subwoofer or bass level signal separately. Simply increasing or attenuating the bass or subwoofer level evenly over its passband typically yields excessive or deficient subwoofer signal level through and above the crossover passband.

[005] When is use, any full range loudspeaker system (e.g., 22 or 100) must blend and balance the acoustic output of these sections and the lowest frequency bass level adjustment is often difficult to blend with the mid-bass level to achieve satisfactory spectral balance. Simply adjusting the subwoofer’s gain over its entire passband introduces unfavorable consequences in terms of system spectral balance, typically resulting in too much energy in the upper bass region (e.g., 90-300Hz.) such that listeners complain of“chesty” midrange and“bloated” or“muddy” sound. Excessive acoustic output in the frequency range above the subwoofer-satellite crossover - that frequency at which the subwoofer and its companion loudspeaker“hand-off’

responsibility for reproducing source material - is worsened when the bass level control is simply boosts the subwoofer amplifier’s gain (boosting the signal input solely to the subwoofer driver). Similarly, poorly controlled spectral balance characterized by insufficient output in the crossover range results when bass level attenuation is achieved via a full-range subwoofer gain control. [006] There is a need, therefore, for an accurate and effective system and method for more intelligently controlling spectral balance of a full range loudspeaker system as the user adjustable bass level is increased or decreased.

OBJECTS AND SUMMARY OF THE INVENTION

[007] Accordingly, it is an object of the present invention to overcome the above mentioned spectral balance difficulties by providing an effective and accurate system and method for intelligently adjusting spectral balance through the crossover range as the acoustic output of a subwoofer section is adjusted in amplitude.

[008] In accordance with the present invention, a loudspeaker system with a pleasing spectral balance throughout the entire range and at all bass levels consists of a low- frequency or“subwoofer” section and an upper bass-midrange“main” section characterized by its associated crossover network, passband and other attributes. The signal used to drive the subwoofer section and main section respond to a user’s“bass level” adjustment by dynamically adjusting a gain-adjustable bass-shelf filter which adjusts the magnitude response of the signals driving the subwoofer section and the main section through the crossover range to provide satisfyingly smooth spectral balance as the bass level is increased or attenuated by the user.

[009] The loudspeaker system and method of present invention preferably employs a bass level control signal responsive gain adjustable bass shelf filter as an alternative to a simple full-range gain control on the subwoofer’s output. The gain-adjustable bass shelf filter’s parameters are such that smooth adjustment (for positive gain and/or attenuation) over the selected bass passband is realized. [010] This full range loudspeaker system and method of this invention includes a user adjustable bass level control and the dynamically controllable low-shelf filter of this invention operates in response to the user’s adjustment of that bass level control.

Accordingly, the bass level control signal responsive gain adjustable bass shelf filter and method for dynamically controlling spectral balance (as bass level is increased or decreased by a user) in the full range loudspeaker system of the present invention includes three novel characteristics:

(1st) Frequency: the nominal frequency in Hertz (or Hz) below which the bass level control signal responsive gain adjustable bass shelf filter (or low-shelf filter) operates is selected in a particular manner. For example, when a 200Hz bass-shelf filter is set to +5.0dB (gain), approximately 2.5dB occurs at 200Hz and progressively more gain is achieved at lower frequencies until the gain setting is fully achieved.

Depending on the“slope” setting for the low shelf filter, the set gain (e.g., 5.0dB) is achieved at about two octaves below (50Hz for this example).

(2nd) Gain or Attenuation: the maximum achieved gain (boost) or attenuation (cut) provided by the bass level control signal responsive low-shelf filter is substantially achieved at and below two octaves below the set filter frequency.

(3rd) Filter“slope”: the low-shelf filter’s shape is expressed by a dimensionless quantity that’s related to its Quality Factor or“Q”. A filter providing a slope (or Q) of 0.707, sometimes referred to as a Butterworth filter, yields a well behaved filter substantially free of any overshoot or ringing (excessive resonance). By comparison, setting Q = 1.0 (or larger values) gives rise to overshoot - gain or attenuation exceeding the nominal setting - over some portion of the bandwidth over which the filter operates.

[011] The bass level control signal responsive gain adjustable bass shelf filter (or low- shelf filter) frequency setting in conjunction with the companion“satellite” soundbar’s complex (i.e. , magnitude and phase) acoustic response are such that the resulting system acoustic magnitude response is well controlled through the low-shelf filter’s passband. For fully active systems, the frequency should be set so the bass-shelf filter operates on both the low-frequency portion of the“satellite” loudspeaker’s passband and the entire passband of its companion subwoofer. For example, for a soundbar- subwoofer system whose crossover frequency occurs at 120Hz, the bass level control signal responsive gain adjustable bass shelf filter (or bass-shelf filter) should be set to provide boost and cut over a passband that substantially covers ~200F1z and below.

The upper bound of the bass-shelf filter may vary with the host system - in part, where the crossover occurs -- and in accordance with the preferred system performance. In an active crossover network or DSP system programmed to operate in accordance with the present invention, digital signal preprocessing signal flow has a bass-shelf shelf filter upstream of both the subwoofer and soundbar in a fully active system. Constituent low- pass and high-pass filters are applied to the subwoofer and to mixed-monophonic signals which are reproduced by the soundbar.

[012] The above and still further objects, features and advantages of the present invention will become apparent upon consideration of the following detailed description of a specific embodiment thereof, particularly when taken in conjunction with the accompanying drawings, wherein like reference numerals in the various figures are utilized to designate like components. DESCRIPTION OF THE FIGURES

[013] Figs 1 A-1 B illustrate a full-range tower-shaped loudspeaker system with an integral subwoofer section, in accordance with the prior art.

[014] Figs 1C and 1 D illustrate a Soundbar/Subwoofer home theater loudspeaker system having a soundbar enclosure and a separate subwoofer system enclosure, in accordance with the prior art.

[015] Fig. 1 E is a frequency response plot (SPL v. Freq.) illustrating four traces, a first for the frequency response of the subwoofer, a second for the midrange, a third for the tweeter, and a fourth which integrates all of the drivers into a full range system response, illustrating that, using prior art subwoofer amplifier gain control and signal processing methods, the boosted sub signal results in an undesired increase in SPL in the upper bass and midrange regions (e.g., between 90 and 500Hz).

[016] Fig 2 is a Digital Signal Processing (“DSP”) system screenshot which diagrammatically illustrates a Bass or“LoShelf filter set to +5.0dB @ 200Hz, having a “slope” = 0.707 (Butterworth), for use in the bass level control signal responsive gain adjustable bass shelf filter and the method for dynamically controlling spectral balance as bass level is increased or decreased by the user in a full range loudspeaker of the present invention.

[017] Fig. 3 is a DSP system screenshot which diagrammatically illustrates a Bass or “LoShelf filter set to +5.0dB @ 200Hz,“slope” = 2.0; note overshoot (where gain exceeds 5.0dB) over the 30 to ~180Hz frequency range, wherein the filter actually provides cut over the -280 - 700Hz frequency range, in accordance with the present invention. [018] Fig. 4 is a plot illustrating magnitude vs time response for various filter classifications, wherein: (a) for a Bessel class filter (Q = 0.5), the response is well damped and characterized by lack of oscillation, (b) for a Butterworth class filter (Q = 0.707), the response is moderately damped and characterized by minimal oscillation, and (c) for a Chebyshev class filter (Q = 1.0), the response is lightly damped and hence prone to significant oscillation.

[019] Fig. 5 is a DSP signal flow graphic (screenshot) exemplifying the network and method of the present invention, where“ToneControl 1” (the improved bass level control) operates on both subwoofer and soundbar (of system 300); also shown are high and lowpass filter settings associated with both subwoofer and soundbar, in accordance with the present invention.

[020] Fig. 6 is a signal flow diagram illustrating the method for dynamically controlling spectral balance as bass level is increased or decreased by the user in a full range loudspeaker and intelligent bass signal processing method as implemented for use in a Soundbar - Subwoofer full range loudspeaker system 300 (e.g., as in Fig. 5), in accordance with the present invention.

[021] Fig. 7 is a signal flow diagram illustrating the method for dynamically controlling spectral balance as bass level is increased or decreased by the user in a full range loudspeaker and intelligent bass signal processing method as implemented for use in a Powered Tower full range loudspeaker system 400, in accordance with the present invention.

[022] Fig. 8A is a crossover diagram and partial signal flow diagram illustrating the system crossover and intelligent bass signal processing method implemented for use in a Powered Tower full range loudspeaker system 400, in accordance with the present invention.

[023] Fig. 8B is another signal flow diagram continuing that shown in Fig. 8A and illustrating the intelligent bass signal processing method as implemented for use in a Powered Tower full range loudspeaker system 400, in accordance with the present invention.

[024] Fig. 9A is a frequency response plot (SPL v. Freq.) with two traces, a first for the frequency response of the system with the user-adjustable bass level control set to maximum (for maximum bass level) and a second for the frequency response of the system with the user-adjustable bass level control set to minimum (for minimum bass level), illustrating that, using the dynamic control and signal processing method of the present invention, the intelligently boosted (or attenuated) bass signal results in a more satisfactory adjustment increase in SPL in the lower bass without the problems previously seen in the upper bass, lower midrange region (e.g., between 90 and 500Hz).

[025] Fig. 9B is a screenshot diagram used in developing an embodiment of the dynamic control and signal processing method of the present invention with a frequency response plot (SPL v. Freq.) having thirty one (31) traces illustrating thirty one index- selectable bass shelf filter responses, where the upper trace corresponds to the upper (maximum bass level) trace in Fig. 9A and the lowest trace corresponds to the lower (minimum bass level) trace in Fig. 9A.

[026] Fig. 9C is a table of the bass shelf filter parameters for the 32 bass shelf filters which are indexed and dynamically selectable in response to the user-adjustable bass level control to provide the frequency responses shown in Fig. 9B.

[027] Fig. 9D is a frequency response plot (SPL v. Freq.) for the system of Figs 8A-9C, illustrating four traces, a first for the frequency response of the subwoofer, a second for the midrange, a third for the tweeter, and a fourth which integrates all of the drivers into a full range system response, illustrating that, using the control and signal processing method of the present invention, the intelligently boosted sub signal results in a more satisfactory increase in SPL in the lower bass without the problems previously seen in the upper bass, lower midrange region (e.g., between 90 and 500Flz).

[028] Fig. 10 is a frequency response plot (SPL v. Freq.) illustrating two traces, a first for the frequency response of the prior art full range system and a second for the dynamically controlled system driven in accordance with the gain-adjustable bass shelf method of the present invention, illustrating the difference in the SPL in the upper bass, lower midrange region (e.g., between 90 and 500Hz).

DESCRIPTION OF THE PREFERRED EMBODIMENT

[029] Turning initially to Figs 1A and 1 B, a multi-driver powered tower loudspeaker system or assembly 22 has midrange or mid-bass drivers 30, 32 and 36 mounted to project sound into a listening space from the upper portions of the front and rear walls 24 and 26 of a generally rectangular tower-shaped speaker enclosure 28. Towershaped speaker enclosure 28 defines a box-shaped enclosure with a first sub-enclosure or chamber for a front-facing driver array 40, a second sub-enclosure or chamber for a rear-facing driver array 42 and a third sub-enclosure for a Subwoofer section driver array 50, 52. [030] The exemplary tower shaped full range loudspeaker system 22 in the illustrated embodiment includes front-facing midrange or mid-bass loudspeakers 30 and 32 with a tweeter 34 forming front-facing or forward speaker array, and rear-facing midrange or mid-bass loudspeaker 36 with a tweeter 38 forming a rear speaker array. The loudspeaker drivers in the front and rear arrays may be conventional electro-acoustic drivers, also referred to as acoustic transducers, mounted in a known manner on suitable baffles in the enclosure 28, it being understood that herein the term“drivers” refers to acoustic transducers or loudspeakers mounted to produce a selected range of output frequencies (bandwidth) as is usual and intended for such midrange speakers and tweeters. As illustrated, the front speaker assembly or array is mounted in a front chamber 40 of the enclosure 28, while the rear speaker assembly or array is mounted in a rear chamber 42 of the enclosure, and a volume of enclosed air is disposed there between comprising part of the Subwoofer section’s enclosure volume Cabinet or enclosure 28 also includes one or more side-facing sub-woofer drivers 50, 52; these are conventional active drivers and passive radiators and may be mounted via suitable baffles in one or both of the side walls 56 and 58 of the enclosure 28 in known manner.

[031] In the improved exemplary powered tower loudspeaker system of the present invention 400 (including crossover and signal processing elements illustrated in Figs 7- 10), the physical configuration of full range powered tower system 22 is retained, but the signals input to the driver elements or transducers are changed to overcome the problems discussed above, so, in the embodiment described below, the“subwoofer section” includes subwoofer drivers 50 and 52 and the“main section” includes midrange or mid-bass drivers 30, 32, 34 and tweeters 34 and 38. [032] Fig. 1C is a perspective view illustrating a subwoofer-soundbar home theater loudspeaker system 100 with single enclosure multi-element loudspeaker line array 110, configured for use with a separate subwoofer 130. Fig 1 B illustrates the front of the single enclosure multi-element loudspeaker line array 110 of Fig. 1C, where, in a traditional home theater listening space, the single soundbar enclosure 110 is configured to be placed near a video display (not shown), generally in front of the video display and enclosure 110 is positioned such that line array 120 is aligned in a substantially horizontal orientation which is preferably proximate to and substantially parallel with the bottom or top edge of the display’s surface. In the exemplary embodiment, a plurality (e.g., eight) loudspeaker drivers or elements are aligned along a central axis and the signal for each loudspeaker driver is appropriately band limited to provide an acoustically summed (or superposed) collective acoustic output of the array within the seating space which is highly intelligible, natural sounding and localized to the center of the loudspeaker array 110, regardless of the listener’s location relative to the loudspeaker enclosure 110 within listening space.

[033] In the improved subwoofer-soundbar system 300 of the present invention, the physical configuration of the subwoofer-soundbar loudspeaker system 100 is retained, but the signals which drive the driver elements are changed to overcome the problems discussed above. In accordance with the present invention, a single enclosure loudspeaker array (e.g., like 120) is configured to provide superior spectral balance at all amplitude or volume levels while playing all 5.1 audio channels from DTS™ or Dolby Digital™ sources augmented by signal processing designed to create a broad, deep and tall sound field that extends along the side walls and overhead with a high degree of specificity. The exemplary array (like 120) consists of a 44 5/8" amplified“main” soundbar enclosure 110 which supports five (5) 2 1/2" midrange or midbass drivers 210, 212, 214, 216 and 218 and three 1/2" tweeters 220, 222 and 224. The“subwoofer section” of improved subwoofer-soundbar system 300 comprises a powered wireless subwoofer section (like 130) which has a cabinet with a down-firing (e.g., 8" long throw composite cone with rubber surround) woofer driver. Each of the five mid-bass drivers 210, 212, 214, 216 and 218 and three tweeters 220, 222 and 224 in the“main” or soundbar section is driven by a dedicated amplifier channel.

[034] The system and method of the present invention are applicable for loudspeaker systems configured as standalone full range tower speakers (e.g., 22 as shown in Figs 1A and 1 B) or as a full range soundbar loudspeaker system (e.g., 100 as shown in Figs 1 C and 1 D). Other full range loudspeaker system configurations are possible, and the illustrated embodiments are exemplary.

[035] Turning next to Figs 2-10, in accordance with the present invention, a full-range loudspeaker system with a pleasing spectral balance (e.g., 300 or 400) consists of a low-frequency module or“subwoofer” section and a bass-midrange or“main” section characterized by a crossover network with a particular passband. The phase and amplitude of the signal used to drive the subwoofer section drivers or transducers is controlled in response to a user-adjustable“bass level” control or adjustment (e.g., 350 or 450) which achieves a satisfactory spectral balance by employing a specially configured bass level control signal responsive gain adjustable bass shelf filter (or low- shelf filter, e.g., 370 or 470) so that the magnitude response through the crossover range remains smooth as bass level is increased or attenuated by the user. [036] As illustrated in Figs. 2-10, the loudspeaker system (e.g., 300 or 400) and method of present invention preferably includes crossover and amplification networks including an adjustable bass shelf filter (e.g., 370 or 470) as an alternative to simple full- range gain control of the subwoofer’s output. The parameters of bass shelf filter (370 or 470) are such that smooth adjustment (positive gain and attenuation) over the selected bass passband is realized. Referring specifically to Figs 2 and 3, the bass-shelf filter of the present invention preferably is configured with three principal characteristics.

[037] First, the nominal frequency (in Hertz or Hz) below which shelf filter (370 or 470) operates is selected to achieve a particular result. The bass-shelf’s“knee” frequency is that at which the filter provides approximately half of the gain or attenuation setting. For example, when a 200Hz bass-shelf filter is set to +5.0dB (gain), approximately 2.5dB occurs at 200Hz and progressively more gain is achieved at lower frequencies until the gain setting is fully achieved. Depending on the“slope” setting selected for bass-shelf filter (370 or 470), the set gain of 5.0dB is substantially achieved at approximately two octaves below (50Hz for this example). Similarly, for a bass-shelf filter (370 or 470) set to attenuation at xx Hz (or negative gain) the set cut (i.e. gain = -y.z dB) would be substantially achieved at and below two octaves from the nominal filter frequency ( f = xx/4 Hz) and approximately one-half of the set attenuation (y.z/2 dB) would occur at the nominal filter frequency of xx Hz.

[038] Second, the maximum achieved gain (boost) or attenuation (cut) provided by the bass-shelf or low (lo) shelf filter (370 or 470) is selected such that the nominal gain or attenuation is substantially achieved at and below two octaves below the set bass-shelf filter (370 or 470) frequency. [039] And third, for filter“slope”, the bass-shelf filter’s shape is expressed by a dimensionless quantity that’s related to its Quality Factor or“Q”. Referring now to Fig.

4, a filter providing a slope (or Q) of 0.707, sometimes referred to as a Butterworth filter, yields a well-behaved filter substantially free of any overshoot or ringing (i.e., excessive resonance). By comparison, setting Q = 1.0 or to larger values gives rise to overshoot - gain or attenuation exceeding the nominal setting - over some portion of the bandwidth over which the filter operates. Related, as would be evident in the time domain, is excessive ringing or resonance due to insufficient damping. Smaller values of Q are well damped and hence are largely free of ringing and resonance issues.

[040] The frequency setting for bass-shelf filter (370 or 470) is preferably adjusted such that the resulting system acoustic magnitude response is well controlled through the filter’s passband. For fully active full range loudspeaker systems (where each

transducer is driven by a selected amplifier with a signal having a selected spectral band at a selected amplitude level), the frequency should be set so bass-shelf filter (370 or 470) operates on both the low-frequency portion of the main section or“satellite” loudspeaker’s passband and the entire passband of its companion subwoofer section. For example, for a soundbar-subwoofer system (300, similar to 100) whose crossover frequency occurs at 120Hz, bass-shelf filter 370 should be set to provide boost and cut over a passband that substantially covers ~200Flz and below (see, e.g., Figs 5 and 6). The upper bound of bass level control signal responsive low-shelf filter 370 may vary with the host system - in part, where the crossover occurs -- and in accordance with the preferred system performance. Fig. 5 illustrates a screenshot with a portion of an exemplary digital signal preprocessing signal flow in which the bass-shelf shelf filter 370 is upstream of both the subwoofer section and the soundbar or main section in a fully active system 300. Also shown are the constituent low-pass and high-pass filters applied to the subwoofer (filters 1 , 2) and the mixed-monophonic signal (filters 3,4) reproduced by the soundbar or main section.

[041] Fig. 5 illustrates one exemplary Digital Signal Processing signal flow graphic (screenshot) for the network and method of the present invention where the network includes bass level control signal responsive low-shelf filter 370 (in“ToneControl 1”) which operates on both the subwoofer and soundbar sections. Fig. 5 also shows high pass and lowpass filter settings associated with both subwoofer and soundbar. In the illustrated example of this embodiment, an active (e.g., DSP and solid state amplifier) network provides a smoother overall bass response without creating chesty or bloated mid-bass by adjusting System Magnitude Response with Bass Shelf Filter 370 having a selected passband (e.g., 180 or 200 Hz) used upstream of a subwoofer’s low pass filter (which has a crossover frequency of, e.g., 120Hz.) Bass Shelf Filter 370, used in this manner, is controlled to provide amplitude or volume level boost or cut over a shelf passband which includes a bottom portion of the host system’s soundbar (or satellite) speaker(s) operating frequency range and the entire operating frequency range of the subwoofer section, in accordance with the present invention.

[042] Fig. 6 is a signal flow diagram illustrating the intelligent bass signal processing method (e.g., as in Fig. 5) as implemented for use in Soundbar - Subwoofer full range loudspeaker system 300 (e.g., having a soundbar enclosure 110 and a separate subwoofer 130, similar to that shown in Figs 1C and 1 D, but with a different crossover and signal processing). In accordance with the method of the present invention, the spectral balance of soundbar-subwoofer full range loudspeaker system 300 is controlled or optimized as bass level is increased or decreased by the user. Soundbar-subwoofer full range loudspeaker system 300 includes a subwoofer section and a main

(soundbar/mid-woofer/tweeter) section as well as a crossover or signal processing network (see Figs 5 and 6) configured to receive a full range audio input signal and a user adjustable bass level control signal from bass level control 350. The full range audio input signal (see Fig. 6) is input to bass level control signal responsive low-shelf filter 370 that is responsive to the audio input signal and the user adjustable bass level control signal, and in response generates a dynamically adjusted bass shelf filtered signal 377 for the main section and the subwoofer section. The dynamically adjusted bass shelf filtered signal 377 is then processed in a subwoofer section band pass filter signal processing section 380 and amplified to generate a subwoofer section drive signal 352. The dynamically adjusted bass shelf filtered signal 377 is also processed in a main or soundbar section band pass filter signal processing section 388 and amplified to generate a main or soundbar section drive signal 330. By amplifying said

dynamically adjusted bass shelf filter signal 377 in this manner, complimentary bass driving signals for communication with both the subwoofer section and the main midwoofer/tweeter section are provided.

[043] Figs 7, 8A and 8B are signal flow diagrams illustrating the intelligent bass signal processing method of the present invention as implemented for use in a Powered Tower full range loudspeaker system (e.g., 400, with a physical configuration similar to that shown in Figs 1A and 1 B, but with different signal processing steps). In the method for dynamically controlling spectral balance as bass level is increased or decreased by the user in a full range loudspeaker system 400 (including a subwoofer section and a main mid-woofer/tweeter section) crossover network 420 is configured to receive a full range audio input signal and a user-adjustable bass level control signal (e.g., from bass level control 450). The full range audio input signal is input to a first subwoofer filter stage 460 having a selected first subwoofer filter stage order and a selected first subwoofer filter stage Q factor to generate a frequency shaped first subwoofer low-pass filtered signal 462. The frequency shaped first subwoofer low-pass filtered signal 462 is input to a second bass shelf filter stage 470 that is responsive to it and to the user adjustable bass level control signal from bass level control 450. Second bass shelf filter stage 470 includes a gain-adjustable low frequency shelf filter having a second bass shelf filter stage selected order, a second bass shelf filter stage selected corner frequency and a second bass shelf filter stage selected Q factor to generate a dynamically adjusted bass shelf filtered signal 470 which is amplified to generate a bass driving signal for communication with both the subwoofer section and the main mid-woofer/tweeter section (as illustrated and described in Figs 7, 8A, 8B and 9A).

[044] Referring next to Figs 9A, 9B, 9C and 10, Fig. 9A is a frequency response plot (SPL v. Freq.) with two traces, a first for the frequency response of the system (e.g.,

300 or 400) with the user-adjustable bass level control (e.g., 350 or 450) set to maximum (for maximum bass level) and a second for the frequency response of the system with the user-adjustable bass level control set to minimum (for minimum bass level), illustrating that, using the dynamic control and signal processing method of the present invention, the intelligently boosted (or attenuated) bass signal results in a more satisfactory adjustment increase in SPL in the lower bass without the problems previously seen in the upper bass, lower midrange region (e.g., between 90 and 500Hz).

[045] Referring to Figs 9B and 9C, a screenshot diagram used in developing an embodiment of the dynamic control and signal processing method of the present invention is shown with a frequency response plot (SPL v. Freq.) having thirty one (31) traces illustrating thirty one index-selectable bass shelf filter (e.g., 370 or 470) responses, where the upper trace corresponds to the upper (maximum bass level) trace in Fig. 9A and the lowest trace corresponds to the lower (minimum bass level) trace in Fig. 9A. In the control method embodiment illustrated in Fig. 9B, bass-shelf filter (370 or 470) is configured as an array of DSP program outputs which are indexed for selection depending on how the bass level control (e.g., 350 or 450) is adjusted by the user. In the illustrated embodiment, the output from the bass level control signal responsive gain adjustable bass shelf filter (or low-shelf filter 370 or 470) is configured for use with a bass level selection in the range of -24db (or a bass level cut of 24 dB, corresponding to filter“0”, in Fig. 9C) to +15dB (or a bass level boost of 15 dB, corresponding to filter “31”, in Fig. 9C), and the resulting bass-shelf filter (370 or 470) signal from that selection is illustrated in Fig. 9B. For +15db (filter“31” selection), the resulting bass-shelf filter signal (e.g., 377 or 472) is shown as the uppermost“max bass level” trace 520 in Fig.

9A. And for a 24 dB cut (filter“0” selection), the resulting bass-shelf filter signal (e.g.,

377 or 472) is shown as the lowermost“min bass level” trace 530 in Fig. 9A.

Fig. 9C is a table of the bass shelf filter parameters for the 32 selected bass shelf filter contours which are indexed and dynamically selectable in response to the user- adjustable bass level control (e.g., 350 or 450) to provide the corresponding frequency responses illustrated in Fig. 9B.

[046] Turning next to Fig. 9D, the frequency response plot (SPL v. Freq.) for the full range loudspeaker system of the present invention (e.g., 300 or 400) is shown with four traces, a first for the frequency response of the subwoofer section (when bass is boosted), a second for the midrange portion of the main section, a third for the tweeter portion of the main section, and a fourth which shows the combined output from all of the drivers into a full range system (e.g., 300 or 400) response, illustrating that, using the control and signal processing method of the present invention, the intelligently boosted bass signal results in a more satisfactory increase in SPL in the lower bass without the problems previously seen in the upper bass, lower midrange region (e.g., between 90 and 500Hz) as compared to that illustrated in the plots of Fig. 1 E. That comparison is ore easily seen in Fig. 10, which shows the frequency response plot 660 for the prior art full range system with undesired boost and“chestiness” and the desired boost plot 670 for the dynamically controlled system (e.g., 300 or 400) driven in accordance with the gain-adjustable bass shelf method of the present invention, illustrating the difference in the SPL in the upper bass, lower midrange region (e.g., between 90 and 500Flz).

[047] Having described preferred embodiments of a new and improved method, it is believed that other modifications, variations and changes will be suggested to those skilled in the art in view of the teachings set forth herein. It is therefore to be understood that all such variations, modifications and changes are believed to fall within the scope of the present invention.

Claims

What is Claimed is:

1. A method for dynamically controlling spectral balance as bass level is increased or decreased by the user in a full range loudspeaker system (e.g., 300, 400) including a subwoofer section and a main (mid-woofer/tweeter) section, comprising:

providing a crossover network configured to receive (a1) a full range audio input signal and (a2) a user adjustable bass level control signal; said crossover network including a gain-adjustable shelf filter (e.g., 370 or 470), said gain-adjustable shelf filter (e.g., 370 or 470), being configured to generate a dynamically adjusted shelf filtered signal in response to said full range audio input signal and said user adjustable bass level control signal;

shelf filtering and adjusting the magnitude of said full range audio input signal in response to said user adjustable bass level control signal to generate a dynamically adjusted shelf filtered subwoofer signal; and

amplifying said dynamically adjusted shelf filtered subwoofer signal to generate driving signals for communication with both the subwoofer section and the main midwoofer/tweeter section.

2. The method for dynamically controlling spectral balance as bass level is increased or decreased by the user in a full range loudspeaker system of claim 1 , said method further comprising:

(a) providing a crossover network configured to receive (a1) a full range audio input signal and (a2) a user adjustable bass level control signal;

(b) filtering the full range audio input signal in a first subwoofer filter stage having a selected first subwoofer filter stage order and a selected first subwoofer filter stage Q factor to generate a frequency shaped first subwoofer low-pass filtered signal;

(c) filtering said frequency shaped first subwoofer low-pass filtered signal in a second bass shelf filter stage that is responsive to (d) said frequency shaped first subwoofer low-pass filtered signal and (c2) said user adjustable bass level control signal; said second bass shelf filter stage comprising a gain-adjustable low frequency shelf filter (e.g., 370 or 470) having a second bass shelf filter stage selected order, a second bass shelf filter stage selected corner frequency and a second bass shelf filter stage selected Q factor to generate a dynamically adjusted bass shelf filtered subwoofer signal; and

(d) amplifying said dynamically adjusted bass shelf filtered subwoofer signal to generate a bass driving signal for communication with both the subwoofer section and the main mid-woofer/tweeter section.

3. The method for dynamically controlling spectral balance as bass level is increased or decreased by the user in a full range loudspeaker system of claim 3:

wherein said first subwoofer filter stage comprises a low pass filter configured to pass frequencies below a knee frequency selected from within the range of 80-110Hz.

4. The method for dynamically controlling spectral balance as bass level is increased or decreased by the user in a full range loudspeaker system of claim 3, wherein said first subwoofer filter stage comprises a 3^rd order low pass filter at 95Hz comprising a 2^nd order LPF with a Q of 0.707 cascaded with a 1^st order LPF.

5. The method for dynamically controlling spectral balance as bass level is increased or decreased by the user in a full range loudspeaker system of claim 2:

wherein said gain-adjustable low frequency shelf filter stage comprises a 1^st order shelf filter having a selected fixed corner frequency, said gain-adjustable low frequency shelf filter stage being configured to respond to a user adjustable gain control signal having a selected bass level adjustment range.

6. The method for dynamically controlling spectral balance as bass level is increased or decreased by the user in a full range loudspeaker system of claim 5:

wherein said gain-adjustable low frequency shelf filter stage comprises a 1^st order shelf filter having a selected fixed corner frequency of 80Hz configured to respond to a user adjustable gain control signal having a selected bass level adjustment range of

-24dB to +15 dB.

7. The method for dynamically controlling spectral balance as bass level is increased or decreased by the user in a full range loudspeaker system of claim 2:

wherein said gain-adjustable shelf filter (e.g., 370 or 470) is responsive to a user adjustable bass level control (e.g., 350, 450) to provide positive gain or attenuation over a selected bass passband.

8. The method for dynamically controlling spectral balance as bass level is increased or decreased by the user in a full range loudspeaker system of claim 7, said method further comprising:

(e) adjusting user adjustable bass gain control signal to control said second gain-adjustable low frequency shelf filter (e.g., 370 or 470) and thereby provide positive gain or attenuation over a selected bass passband without creating spectral balance problems in the crossover range passband (e.g., 80-500Hz), generating a subwoofer section drive signal and a mid-high frequency (main) section drive signal; wherein said subwoofer section drive signal and said mid-high frequency (main) section drive signal each include signals within the crossover range passband (e.g., 80-500Hz).

9. An active full range multi-driver loudspeaker system (e.g., 300, 400) including a subwoofer section and a mid-bass/tweeter section, comprising:

(a) a crossover network configured to receive full range audio input signals and divide the audio input signals into a first low-passed (or band-passed) signal filtered to generate a subwoofer section drive signal and a second high-passed (or band-passed) signal filtered to generate a mid-bass (or mid-high frequency) section drive signal;

(b) wherein the first low-passed (or band-passed) signal and the second high- passed (or band-passed) signal each include signals within a crossover range passband;

(c) wherein said loudspeaker system includes a crossover and amplification network including a bass level control signal responsive gain adjustable bass shelf filter (or low- shelf filter) (e.g., 370 or 470) which is responsive to a user adjustable bass level control (e.g., 350 or 450) and has selectable shelf filter parameters that provide smooth adjustment (positive gain and/or attenuation) over a selected bass passband.

10. The active full range loudspeaker system of claim 9, wherein said bass level control signal responsive gain adjustable bass shelf filter (or low-shelf filter) (e.g., 370 or 470) has a nominal knee frequency in the range of 80 to 200 Hz;

wherein said bass-shelf’s knee frequency is that at which the filter provides approximately half of the gain or attenuation setting; whereby, when a 200Hz knee frequency bass-shelf filter is set to +5.0dB (gain), approximately 2.5dB gain occurs at 200Hz and progressively more gain is achieved at lower frequencies until the gain setting is fully achieved.

11. The active full range loudspeaker system of claim 10, wherein set gain (e.g., of 5.0dB) is substantially achieved at approximately two octaves below (e.g., 50Hz).

12. The active full range loudspeaker system of claim 10, wherein the maximum achieved gain (boost) or attenuation (cut) provided by the bass-shelf filter (370 or 470) is substantially achieved at and below two octaves below the set filter frequency; and said bass-shelf filter (370 or 470) is configured as a Butterworth filter and provides a Q factor of 0.707, to yield a well-behaved response in dynamically adjusted bass shelf filtered signal (e.g., 377 or 472) which is substantially free of excessive resonance.

13. A full range loudspeaker system including a subwoofer section and a main (mid woofer/tweeter) section, comprising:

a crossover network configured to receive (a1) a full range audio input signal and (a2) a user adjustable bass level control signal; said crossover network including a gain- adjustable shelf filter (e.g., 370 or 470) having a shelf filter selected order, a shelf filter selected corner frequency and a shelf filter selected Q factor;

wherein said gain-adjustable shelf filter (e.g., 370 or 470), is configured to generate a dynamically adjusted bass shelf filtered signal (e.g., 377, 472) in response to said full range audio input signal and said user adjustable bass level control signal.

14. The full range loudspeaker system of claim 13, further comprising:

(a) a crossover network (e.g., 420) configured to receive (a1) a full range audio input signal and (a2) a user adjustable bass level control signal;

(b) a first subwoofer filter stage in said crossover network having a selected first subwoofer filter stage order and a selected first subwoofer filter stage Q factor to generate a frequency shaped first subwoofer low-pass filtered signal;

(c) a second bass shelf filter stage in said crossover network that is responsive to (d) said frequency shaped first subwoofer low-pass filtered signal and (c2) said user adjustable bass level control signal; said second bass shelf filter stage comprising a gain-adjustable low frequency shelf filter (e.g., 370 or 470) having a second bass shelf filter stage selected order, a second bass shelf filter stage selected corner frequency and a second bass shelf filter stage selected Q factor to generate a dynamically adjusted bass shelf filtered subwoofer signal; and

(d) amplifier means responsive to said dynamically adjusted bass shelf filtered subwoofer signal to generate a bass driving signal (e.g., 377 or 472) for communication with both the subwoofer section and the main mid-woofer/tweeter section.

15. The full range loudspeaker system of claim 14, wherein said first subwoofer filter stage comprises a low pass filter configured to pass frequencies below a knee frequency selected from within the range of 80-110Hz.

16. The full range loudspeaker system of claim 15, wherein said first subwoofer filter stage comprises a 3rd order low pass filter at 95Hz comprising a 2nd order LPF with a Q of 0.707 cascaded with a 1st order LPF.

17. The full range loudspeaker system of claim 16, wherein said gain-adjustable low frequency shelf filter stage (e.g., 370 or 470) comprises a 1st order shelf filter having a selected fixed corner frequency, said gain-adjustable low frequency shelf filter stage being configured to respond to a user adjustable gain control signal having a selected bass level adjustment range.

18. The full range loudspeaker system of claim 17, wherein said gain-adjustable low frequency shelf filter stage comprises a 1st order shelf filter having a selected fixed corner frequency of 80Flz configured to respond to a user adjustable gain control signal having a selected bass level adjustment range of -24dB to +15 dB.

19. The full range loudspeaker system of claim 14, wherein said gain-adjustable shelf filter (e.g., 370 or 470) is responsive to a user adjustable bass level control (e.g., 350, 450) to provide positive gain or attenuation over a selected bass passband.

20. The full range loudspeaker system of claim 19, wherein said subwoofer section drive signal and said mid-high frequency (main) section drive signal each include signals within the crossover range passband (e.g., 80-500Hz).