Patent Publication Number: US-6707919-B2

Title: Driver control circuit

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to driver control circuits for controlling audio speakers. More particularly, the invention relates to a driver control circuit that optimally controls the frequencies of audio signals delivered to one or more speakers using a minimum number of components. 
     2. Description of the Prior Art 
     Driver control circuits divide audio signals into different frequency bands or ranges for controlling two or more speakers or “drivers” in a speaker system. Driver control circuits apportion the frequency spectrum in such a way that each speaker operates in its optimum frequency range and the entire speaker system reproduces sound with a minimum of distortion. 
     The frequency at which a driver control circuit separates one frequency band from an adjacent band is called the crossover frequency. A driver control circuit passes a selected frequency range or band of signals to each speaker and attenuates frequencies that are beyond the speakers&#39; crossover frequency. In this way, each speaker reproduces audio signals only in its optimum frequency range and then “rolls off” beyond the crossover frequency. 
     The rate at which a driver control circuit attenuates frequencies delivered to a speaker beyond the crossover frequency is called the crossover slope. Crossover slopes are measured in dB of attenuation per octave and are categorized by their magnitude or “steepness”. 
     Driver control circuits with steep crossover slopes are desirable because they attenuate frequencies that are beyond a speaker&#39;s effective operating range more rapidly so that the speaker audibly reproduces only audio signals in its optimum frequency range, reducing distortion from signals outside the range. Steep crossover slopes are also desirable because they allow the operating ranges of the speakers to be extended and reduce or eliminate interference between speakers operating at adjacent frequency ranges. 
     In addition to constructing driver control circuits with steep crossover slopes, it is also often desirable to select or shape the frequency response of a driver control circuit above or below its crossover frequency. Such frequency shaping or selecting is especially desirable for audio speakers used in home theater systems where sound is reproduced by a plurality of different types of speakers including, for example, left and right main speakers, a center channel speaker, left and right surround speakers, and a low-frequency effects sub-woofer speaker. Because each speaker or speaker pair in a home theater system should optimally reproduce only certain frequencies of audio signals, it is important to carefully select the crossover frequencies of all of the speakers and to shape the frequency response of the speakers using the driver control circuits. It is often even desirable to adjust the frequency response of each type of speaker using the driver control circuits so that the sound from the different types of speakers match as perfectly as possible. 
     Applicant has discovered that home theater speaker operation can often be optimized if the frequency response of the driver control circuits for the speakers can be selectively shaped or adjusted above and below the speakers&#39; crossover frequencies to match all the speakers. Such selective adjustment of the frequency response allows home theater system designers and installers to custom-configure home theater systems to achieve extremely high-quality sound. 
     Many solutions exist in the prior art to shape or select the frequency responses and crossover frequencies of driver control circuits. However, prior art solutions require the addition of a plurality of inductors, capacitors, and other electronic components to existing filter networks, thus significantly increasing the size and cost of the driver control circuits. In addition, in-wall units required in many home theater applications do not have space for such components. 
     SUMMARY OF THE INVENTION 
     The present invention solves the above-described problems and provides a distinct advance in the art of driver control circuits. More particularly, the present invention provides a driver control circuit that enhances a steep crossover slope while permitting selective shaping or adjusting of its in-band frequency response near its crossover frequency with a minimum number of components. 
     One embodiment of the driver control circuit of the present invention broadly includes a signal connector for connecting with a source of audio signals; a speaker connector for connecting with a speaker; and a frequency passing circuit coupled between the signal connector and the speaker connector for passing a selected range of frequencies of the audio signals to the speaker and for attenuating other frequencies. The frequency passing circuit includes components forming a traditional low-pass and/or high-pass filter network and a resistive component connected in parallel across the second series mounted component of the low-pass and/or high-pass filter network. 
     The resistive component increases the crossover slope of the driver control circuit and shapes its in-band frequency response near the crossover frequency. By selectively adjusting the resistance value of the resistive component, the frequency response and crossover frequencies of the driver control circuit can be optimally selected or adjusted for use in home theater systems and other applications requiring precise frequency shaping between multiple types of speakers. 
     These and other important aspects of the present invention are described more fully in the detailed description below. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING FIGURES 
     A preferred embodiment of the present invention is described in detail below with reference to the attached drawing figures, wherein: 
     FIG. 1 is a schematic diagram of a driver control circuit constructed in accordance with a first preferred embodiment of the present invention. 
     FIG. 2 is a graph illustrating the frequency response of the driver control circuit of FIG. 1 for several different resistive values. 
     FIG. 3 is a schematic diagram of a driver control circuit constructed in accordance with a second preferred embodiment of the present invention. 
     FIG. 4 is a graph illustrating the frequency response of the driver control circuit of FIG. 3 for several different resistive values. 
     The drawing figures do not limit the present invention to the specific embodiments disclosed and described herein. The graphs are not necessarily to scale, emphasis instead being placed upon clearly illustrating the principles of the invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Turning now to the drawing figures, and particularly FIG. 1, a driver control circuit  10  constructed in accordance with a first preferred embodiment of the invention is illustrated. The driver control circuit  10  is operable for receiving audio signals from an audio signal source  12  and for driving an audio speaker  14  or other driver with certain frequencies of the audio signals. The driver control circuit  10  broadly includes signal connectors  16  for connecting with the audio signal source  12 , speaker connectors  18  for connecting with the speaker  14 , and a frequency passing circuit  20  coupled between the signal connectors  16  and the speaker connectors  18 . 
     The audio signal source  12  may be any conventional source of audio signals such as a stereo receiver, DVD player, home theater processor, VCR, or other audio/visual component. The signal connectors  16  may be any conventional input terminals or connectors for connecting with the audio signal source  12 . 
     In the embodiment illustrated in FIG. 1, the speaker  14  is preferably a “woofer” or mid-range type speaker that reproduces low or mid-frequency audio signals. The speaker  14  is conventional and may be manufactured by any known speaker maker such as Induction Dynamics, Bose, Pioneer, Velodyne, or Sony. The speaker connectors  18  may be any conventional output terminals or connectors configured for coupling with the speaker  14 . 
     The frequency passing circuit  20  is electrically connected between the signal connectors  16  and the speaker connectors  18  and is provided for passing a selected range of frequencies of the audio signals from the audio signal source  12  to the speaker  14  and for attenuating other frequencies. In the embodiment illustrated in FIG. 1, the frequency passing circuit  20  preferably forms a low-pass filter network that passes low-frequency range audio signals to the speaker  14  and attenuates other frequencies. 
     The frequency passing circuit  20  preferably includes a first inductor L 1 , a second inductor L 2 , a first capacitor Cl, and a second capacitor C 2 . The inductors L 1  and L 2  are coupled in series between the signal connectors  16  and the speaker connectors  18 . Inductors L 1  and L 2  are preferably low resistance coils, and their values may be selected to achieve any desired low-pass frequency response. In one embodiment, the inductors L 1  and L 2  have values of 2.3 mH and 1.15 mH, respectively. 
     The capacitor C 1  is coupled in shunt or parallel between the junction of the inductors L 1  and L 2 , and the capacitor C 2  is coupled in shunt or parallel between the inductor L 2  and the speaker connectors  18 . As with the inductors L 1  and L 2 , the capacitors C 1  and C 2  may have any values to achieve any low-pass frequency response. In one embodiment, the capacitors C 1  and C 2  have values of approximately 31 uF and 6.5 uF, respectively. 
     The inductors L 1  and L 2  and the capacitors C 1  and C 2  cooperate for passing low range frequencies of the audio signals from the audio signal source  12  to the speaker  14  and for attenuating other frequencies at a rate of approximately 24 dB/octave. With the specific values described above, the frequency passing circuit  20  has a low-pass crossover frequency of approximately 1000 Hz. Those skilled in the art will appreciate that the crossover frequency can be varied by selecting different values for the inductors L 1  and L 2  and/or the capacitors C 1  and C 2 . 
     In accordance with one important aspect of the present invention, the frequency passing circuit  20  also includes a resistor R 1  that is coupled in parallel across the second series component, in this embodiment, the inductor L 2 . The resistor R 1  preferably has a value between 1-100 ohms. The resistor R 1  allows the frequency response and the crossover frequency of the frequency passing circuit  20  to be selectively adjusted to achieve optimal operating results. The resistor R 1  is especially useful for shaping the frequency response of the driver control circuit  10  below its crossover frequency as described in more detail below. 
     FIG. 2 illustrates the frequency response of the driver control circuit  10  for different resistive values for resistor R 1 . The approximate crossover frequency of the driver control circuit is identified by the letter “X”. The curve identified with the letter “A” represents the frequency response of the driver control circuit  10  when resistor R 1  has a resistive value approaching infinity. For typical circuit values, there is no noticeable effect on the driver control circuit  10  when R 1  has an infinite resistance. Curve A demonstrates that the driver control circuit  10  passes low-frequency audio signals to the speaker  14  and then rapidly attenuates all frequencies exceeding the crossover frequency. Curve A is therefore typical of the frequency response for a conventional low-pass filter. 
     The curve identified by the letter “B” represents the frequency response of the driver control circuit  10  when resistor R 1  has a value of approximately 40 ohms. Lowering the resistance of R 1  changes the frequency response of the driver control circuit  10  in three primary ways. First, the driver control circuit  10  begins attenuating higher frequency signals slightly earlier than it did when the resistor R 1  had infinite resistance as evidenced by the in-band dip of curve B before the crossover frequency. Second, the driver control circuit  10  continues to pass low-frequency audio signals up to the crossover frequency as evidenced by the fact that curve B momentarily intersects curve A just below the crossover frequency. Third, the driver control circuit  10  more rapidly attenuates the higher frequency out of band audio signals as evidenced by the fact that curve B is steeper than curve A at frequencies higher than the crossover frequency. The net effect of lowering the resistance of R 1  is therefore to increase the crossover slope of the driver control circuit  10  and to permit selective shaping of the in-band frequency response of the driver control circuit  10  near the crossover frequency. Applicant has discovered that such frequency response shaping is desirable in many home theater applications as well as any quality speaker system designs. 
     The curve identified by the letter “C” represents the frequency response of the driver control circuit  10  when resistor R 1  has a value of approximately 10 ohms. In general, the characteristics of curve C are merely exaggerations of the same characteristics of curve B. Specifically, lowering the resistance of R 1  causes the driver control circuit  10  to begin attenuating higher frequency signals slightly earlier and to achieve a steeper crossover slope. 
     Applicant has discovered that is it desirable in some home theater applications to vary the resistance of R 1  until the optimal frequency response for the driver control circuit  10  is obtained. 
     FIG. 3 illustrates a driver control circuit  10 A constructed in accordance with a second preferred embodiment of the present invention. The driver control circuit  10 A is similar to the driver control circuit  10  illustrated in FIG. 1; therefore, like components are identified with the same numbering scheme followed by the letter “a”. 
     The speaker  14   a  for the second embodiment is preferably a midrange or high-frequency tweeter-type speaker that reproduces mid or higher frequency audio signals. The speaker  14   a  is conventional and may be manufactured by any known speaker maker such as Induction Dynamics, Bose, Pioneer, Velodyne, or Sony. 
     The frequency passing circuit  20   a  is similar to the frequency passing circuit  20  illustrated in FIG. 1 except that the circuit  20   a  is configured to operate as a high-pass filter network that passes high-frequency range audio signals to the speaker  14   a  and attenuates other frequencies. 
     The frequency passing circuit  20   a  preferably includes a first capacitor C 1 , a second capacitor C 2 , a first inductor L 1 , and a second inductor L 2 . The capacitor C 1  and C 2  are coupled in series between the signal connector  16   a  and the speaker connector  18   a . The capacitors C 1  and C 2  may have any values to achieve any high-pass frequency response. In one embodiment, the capacitors C 1  and C 2  have values of approximately 10.5 uf and 21 uf, respectively. 
     The inductor L 1  is coupled in shunt or parallel between the junction of the capacitor C 1  and C 2 , and the inductor L 2  is coupled in shunt or parallel between the capacitor C 2  and the speaker connectors  18   a . The inductors L 1  and L 2  may have any values to achieve any high-pass frequency response. In one embodiment, the inductors L 1  and L 2  have values of approximately 0.8 mH and 3.6 mH, respectively. 
     The capacitors C 1  and C 2  and the inductors L 1  and L 2  cooperate to pass high-range frequencies of the audio signals from the audio signal source  12   a  to the speaker  14   a  and for attenuating other frequencies at a rate of approximately 24 db per octave. With the specific values described above, the frequency passing circuit  20   a  has a high-pass crossover frequency of approximately 1000 Hz. Those skilled in the art will appreciate that the crossover frequency can be varied by selecting different values for the capacitors C 1  and C 2  and/or the inductors L 1  and L 2 . 
     In accordance with one important aspect of the present invention, the frequency passing circuit  20   a  also includes a resistor R 1  that is coupled in parallel across the second series-mounted component, in this embodiment, the capacitor C 2 . The resistor R 1  preferably has a value between 1-100 ohms. The resistor R 1  allows the frequency response of the frequency passing circuit  20   a  to be selectively adjusted to achieve optimal operating results. The resistor R 1  is especially useful for shaping the frequency response of the driver control circuit  10  above its crossover frequency as described in more detail below. 
     FIG. 4 illustrates the frequency response of the driver control circuit  10   a  for different resistive values for resistor R 1 . The approximate crossover frequency of the driver control circuit  10   a  is identified by the letter “X”. The curve identified with the letter “A” represents the frequency response of the driver control circuit  10   a  when resistor R 1  has a resistive value approaching infinity. For typical circuit values, there is no noticeable effect on the driver control circuit  10   a  when R 1  has an infinite resistance. Curve A demonstrates that the driver control circuit  10   a  passes high-frequency audio signals to the speaker  14   a  and then rapidly attenuates all frequencies below the crossover frequency. Curve A is therefore typical of the frequency response for a conventional high-pass filter. 
     The curve identified by the letter “B” represents the frequency response of the driver control circuit  10   a  when resistor R 1  has a value of approximately 40 ohms. Lowering the resistance of R 1  changes the frequency response of the driver control circuit  10   a  in three primary ways. First, the driver control circuit  10   a  begins attenuating the lower frequency in-band signals slightly earlier than it did when the resistor R 1  had infinite resistance as evidenced by the in-band dip of curve B above the crossover frequency. Second, the driver control circuit  10   a  continues to pass high-frequency audio signals up to the crossover frequency as evidenced by the fact that curve B momentarily intersects curve A just above the crossover frequency. Third, the driver control circuit  10   a  more rapidly begins to attenuate lower frequency audio signals below the crossover frequency as evidenced by the fact that curve B is steeper than curve A below the crossover frequency. The net effect of lowering the resistance of R 1  is therefore to increase the crossover slope of the driver control circuit  10   a  and to permit selective shaping of the in-band frequency response of the driver control circuit  10   a  near the crossover frequency. Applicant has discovered that such frequency response shaping is desirable in many home theater applications as well as any quality speaker system designs. 
     The curve identified by the letter “C” represents the frequency response of the driver control circuit  10   a  when resistor R 1  has a value of approximately 10 ohms. In general, the characteristics of curve C are merely exaggerations of the same characteristics of curve B. Specifically, lowering the resistance of R 1  causes the driver control circuit  10  to begin attenuating lower frequency signals slightly earlier and to achieve a steeper crossover slope. 
     Applicant has discovered that is it desirable to vary the resistance of R 1  until the optimal frequency response for the driver circuit  10   a  is obtained. 
     Although the invention has been described with reference to the preferred embodiment illustrated in the attached drawing figures, it is noted that equivalents may be employed and substitutions made herein without departing from the scope of the invention as recited in the claims. For example, the driver control circuit  10  illustrated in FIG.  1  and the driver control circuit  10   a  illustrated in FIG. 3 may be combined and also supplemented with other frequency passing circuits in a single circuit or device for driving several speakers in a multi-speaker system. 
     Having thus described the preferred embodiment of the invention, what is claimed as new and desired to be protected by Letters Patent includes the following: