Patent Publication Number: US-2020296514-A1

Title: Device, system and method for servo-controlled audio speaker

Description:
CROSS-REFERENCE TO RELEATED APPLICATIONS 
     Not applicable. 
     BACKGROUND 
     1. Technical Field 
     This disclosure relates generally to audio speakers and more particularly, but not necessarily entirely, to servo-controlled audio speakers. 
     2. Description of the Related Art 
     Audio speakers produce sound by converting an electrical signal into mechanical energy. Referring to  FIG. 1 , there is shown a diagram of a conventional audio speaker assembly  100  with its constituent components. The speaker assembly  100  includes a back plate  102 , a pole  104 , a permanent magnet  106 , a top plate  108 , a basket or frame  110 , a voice coil  112 , a spider  114 , a diaphragm or cone  116 , and a dust cap  118 . 
     The voice coil  112  consists of a coil of wire that terminates at each end in a positive lead  120  and a negative lead  122 . In addition, the voice coil  112  is connected to the frame  110  by the spider  114 . The spider  114 , a ring of flexible material, holds the voice coil  112  in position and allows the voice coil  112  to slide back and forth over the pole  104 . The voice coil  112  is also connected to the narrow end of the diaphragm  116  such that when the voice coil  112  moves the diaphragm  116  will move as well. 
     In addition, there are other diaphragm moving technologies that include a piezoelectric substrate that deflects with respect to the incoming voltage signal. There are also electrostatic speakers that use a mylar sheet or diaphragm between two charged electrodes that varies position based on the incoming voltage signal. Such technologies may be utilized by the disclosure. 
     Referring to  FIG. 2 , there is shown a conventional audio system  200 . The audio system  200  includes an amplifier  202  connected to the audio speaker  100 . In particular, the amplifier  202  includes a first lead  204  that is connected to the positive lead  120  of the voice coil  112  and a second lead  206  that is connected to the negative lead  122  of the voice coil  112 . The amplifier  202  is connected to a sound source  208  that provides an input signal to the amplifier  202 . The input signal from the source may be a digital or an analog signal. 
     In operation, the amplifier  202  amplifies the input signal and provides a drive signal to the voice coil  112  through its positive lead  120 . Essentially, the amplifier  202  is constantly switching the electrical signal, fluctuating between a positive charge and a negative charge, on the positive lead  120 . The current going through the voice coil  112  moves one way and then reverses and flows the other way. This alternating current causes the polar orientation of the electromagnet formed by the voice coil  112  and pole  104  to reverse itself many times a second. That is, when the electrical current flowing through the voice coil  112  changes direction, the polar orientation of the voice coil  112  reverses. This changes the magnetic forces between the voice coil  112  and the permanent magnet  106  and moves the voice coil  112  and attached diaphragm  116  back and forth to produce sound. Stated another way, when the voice coil  112  moves, it pushes and pulls on the speaker diaphragm  116 . This movement vibrates the air in front of the speaker diaphragm  116  to create sound waves. 
     Because audio speakers use mechanical movement to generate sound, they are plagued with errors and distortions that corrupt the sound. There are many factors in the construction of the speakers that cause these errors. Voice coils, which are inductors, exhibit counter forces which hinder changing voltages and currents. Further, speakers are complex systems which exhibit mechanical and electrical resonances that favor certain frequencies. In addition, the diaphragm of a speaker is a mass which has momentum and takes time to change directions. Lastly, the speaker baffle, the surface to which on which the speaker is mounted, acts as a spring that applies non-linear forces on the diaphragm. 
     Attempts have been made to reduce errors and distortions in audio speakers. A servo-controlled speaker system uses a feedback loop to correct for performance errors and distortion introduced by the speaker. That is, in a servo-controlled system, if the diaphragm fails to move exactly in accordance with the drive signal, the error is measured, and the input signal is modified by the amplifier to correct the error. The feedback loop consists of a sensor that converts the position or movement of the diaphragm of the speaker into an electrical signal that is fed back into the amplifier. The amplifier may then apply corrections to the drive signal to the speaker voice coil. 
     The effectiveness of the servo-controlled loudspeaker system is highly dependent on the performance of the feedback sensor. Unfortunately, many sensors used in servo-controlled loudspeakers are also inherently non-linear and therefore introduce their own errors and distortions into the system. Additional signal conditioning circuitry is required to compensate for these errors. This additional circuitry can add delays in the feedback loop that reduce the effectiveness of the feedback system. 
     Another common feedback sensor technique is to use a secondary voice coil that is used to determine the position of the diaphragm. To generate the return signal in the secondary voice coil, the diaphragm must be moving. Essentially, the secondary voice coil measures the velocity of the diaphragm. To determine the actual diaphragm position, the signal must be integrated. However, this step also produces additional error and delay. 
     Another common feedback sensor uses an accelerometer mounted on the diaphragm, usually under the dust cover. The accelerometer measures the acceleration of the diaphragm. This requires two-steps of integration to determine the diaphragm position. One integration step determines velocity and the other determines position. Unfortunately, this two-step process adds even more error and delay than the secondary voice coil method. Another disadvantage of currently available servo-controlled speakers is that they are too slow to operate with high frequency sounds. 
     Accordingly, it is an object of this disclosure to provide a servo-controlled speaker with a sensor that provides the actual position of the speaker diaphragm without the need for additional integration steps. 
     It is an object of this disclosure to provide a highly accurate sensor to give feedback information on a position of a speaker diaphragm at a speed well above the audible range. 
     It is an object of this disclosure to provide a servo-controlled speaker with a position feedback system for the diagram with reduced error and delay in the response. 
     SUMMARY 
     Disclosed herein is a device, system, and method for servo-controlled audio speakers. The audio speaker may include a diaphragm, a frame, and a flexible sensor. The flexible sensor may be connected to the diaphragm and the frame. 
     The audio system may include a speaker having a diaphragm and a frame; an amplifier configured to provide a drive signal to the speaker; and a feedback circuit coupled between the speaker and the amplifier. The feedback circuit may comprise a flexible sensor and the flexible sensor may be connected to the diaphragm and the frame of the speaker. The feedback circuit may be configured to provide a feedback signal to the amplifier. 
     The method of driving a speaker may include a speaker having a diaphragm and a frame. The method may include providing a drive signal to the speaker that causes movement of the diaphragm; monitoring the movement of the diaphragm using a feedback circuit, where the feedback circuit may comprise a flexible sensor connected to the diaphragm and the frame; wherein the flexible sensor varies a physical property responsive to a position of the diaphragm. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings illustrate various embodiments of the present disclosure. Non-limiting and non-exhaustive implementations of the disclosure are described with reference to the following figures, wherein like reference numerals refer to like parts throughout the various views unless otherwise specified. Advantages of the disclosure will become better understood with regard to the following description and accompanying drawings where: 
         FIG. 1  illustrates an exploded view of a conventional audio speaker; 
         FIG. 2  is a diagram of a conventional audio system with a source, amplifier and speaker; 
         FIG. 3  is a sideview of an audio speaker with a flexible sensor mounted between the outer side of the cone and the frame; 
         FIG. 4  is a diagram of a servo-controlled audio system which uses a feedback circuit for error correction according to an embodiment of the present disclosure; 
         FIG. 5  is a schematic showing a feedback circuit according to an embodiment of the present disclosure; and 
         FIG. 6  is a schematic showing a feedback circuit according to an embodiment of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     The disclosure extends to devices, systems, and methods for an audio system having servo-controlled audio speaker and an amplifier. Interposed between the audio speaker and the amplifier is a feedback circuit configured to provide a feedback signal to the amplifier regarding errors and distortions in the operation of the speaker. The feedback circuit includes a flexible sensor connected to the speaker diaphragm and the frame of the speaker. The flexible sensor changes its resistance responsive to changes in its shape. The feedback signal is used by the amplifier to apply corrections to the drive signal for the audio speaker. In the following description of the disclosure, reference is made to the accompanying drawings, which form a part hereof, and in which is shown by way of illustration specific implementations in which the disclosure is may be practiced. It is understood that other implementations may be utilized and structural changes may be made without departing from the scope of the disclosure. 
     Disclosed herein is a device, system, and method for servo-controlled audio speakers. The audio speaker may include a diaphragm, a frame, and a flexible sensor. The flexible sensor may be connected to the diaphragm and the frame. 
     The audio system may include a speaker having a diaphragm and a frame; an amplifier configured to provide a drive signal to the speaker; and a feedback circuit coupled between the speaker and the amplifier. The feedback circuit may comprise a flexible sensor and the flexible sensor may be connected to the diaphragm and the frame of the speaker. The feedback circuit may be configured to provide a feedback signal to the amplifier. 
     The method of driving a speaker may include a speaker having a diaphragm and a frame. The method may include providing a drive signal to the speaker that causes movement of the diaphragm; monitoring the movement of the diaphragm using a feedback circuit, where the feedback circuit may comprise a flexible sensor connected to the diaphragm and the frame; wherein the flexible sensor varies a physical property responsive to a position of the diaphragm. 
     Also disclosed herein is a feedback system for an audio speaker that reduces, and in some cases eliminates, errors and distortions in sound produced by the audio speaker. 
     Further disclosed herein is a servo-controlled audio system that has an amplifier, a loudspeaker and a feedback circuit. The feedback circuit comprises a resistive flexible sensor that is mechanically secured to the diaphragm of the loudspeaker on one end and to the frame of the loudspeaker on the other end. The flexible sensor changes shape as the diaphragm deflects in both the positive and negative direction in response to a drive signal from the amplifier. As the flexible senor bends responsive to the deflection of the diaphragm, a physical property of the flexible sensor varies in a predictable manner to thereby generate a feedback signal with information regarding the position of the diaphragm. The variable physical property of the flexible sensor may be one of resistance, capacitance, electric charge or the ability to transmit light. The feedback signal is then fed back into the amplifier. The amplifier then corrects errors and distortions in the speaker by modifying the drive signal to the speaker. 
     Further disclosed herein is a feedback system for an audio speaker that incorporates a flexible sensor for determining the position of a speaker diaphragm during operation. 
     Further disclosed herein is a feedback circuit for an audio speaker that converts mechanical movement of the speaker diaphragm into an electrical signal using a flexible sensor. 
     Further disclosed herein is a feedback system for an audio speaker that reduces, and in some cases eliminates, errors and delays in the feedback signal with position information regarding the speaker diaphragm. 
     Further disclosed herein is a feedback system for an audio speaker may also be used on speakers that produce frequencies in the range of about 20 Hz to 20,000 Hz. Also disclosed herein is a feedback system for an audio speaker that is able to be used on speakers that produce high frequencies, such as tweeters, typically from around 2,000 Hz to 20,000 Hz. 
     In the following description, for purposes of explanation and not limitation, specific techniques and embodiments are set forth, such as particular techniques and configurations, in order to provide a thorough understanding of the device disclosed herein. While the techniques and embodiments will primarily be described in context with the accompanying drawings, those skilled in the art will further appreciate that the techniques and embodiments may also be practiced in other similar devices. 
     Reference will now be made in detail to the exemplary embodiments, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers are used throughout the drawings to refer to the same or like parts. It is further noted that elements disclosed with respect to particular embodiments are not restricted to only those embodiments in which they are described. For example, an element described in reference to one embodiment or figure, may be alternatively included in another embodiment or figure regardless of whether or not those elements are shown or described in another embodiment or figure. In other words, elements in the figures may be interchangeable between various embodiments disclosed herein, whether shown or not. 
     Referring to  FIG. 3 , an audio speaker  300  according to the present disclosure includes essentially the same components of the speaker  100 , only some of which are identified in the discussion below. The audio speaker  300  includes a frame  308  and a diaphragm  310 . Mounted to the frame  308  is a flexible sensor  302  having a first end and a second end. The first end of the flexible sensor  302  is attached to the frame  308  and the second end of the flexible sensor  302  is attached to an outer surface of the diaphragm  310 . When mounted, the flexible sensor  302  includes a slight curvature or bend in a neutral position. The flexible sensor  302  further includes a first lead  304  and a second lead  306  for incorporating the sensor  302  into a feedback circuit. 
     Due to its connection points and configuration, the flexible sensor  302  deflects as the diaphragm  310  moves in response to a drive signal from an amplifier. It will be appreciated that the flexible sensor  302  changes a physical property in a predictable manner when the flexible sensor  302  is deflected by the diaphragm  310 . The physical property of the flexible sensor  302  may include one of resistance, capacitance, electrical charge and the ability to transmit light. The physical property may vary dependent on a shape of the flexible sensor. 
     In an embodiment, the flexible sensor  302  comprises a flexible resistor that varies its electrical resistance in a predictable manner when the flexible sensor  302  is deflected or bent. That is, the flexible resistor changes its electrical resistance dependent upon its shape. Therefore, the flexible resistor converts mechanical movement of the diaphragm  310  into an electrical signal dependent on the shape of the flexible sensor  302 . The flexible resistor may include a conductive epoxy-based carbon ink material deposited or printed on a polyimide or polyester substrate. The substrate is also flexible, such that it can be deflected or bent. The flexible sensor is microscopically cracked so that as it bends or changes shape the microscopic cracks open up, thereby increasing the resistance. A suitable flexible sensor with a flexible resistor for use with the present disclosure is manufactured by Flexpoint Sensor Systems Inc. of Draper, Utah. 
     In an embodiment, the flexible sensor  302  comprises a flexible capacitor that varies its capacitance in a predictable manner as the flexible sensor  302  bends and changes shape. 
     In an embodiment, the flexible sensor  302  comprises a piezoelectric material that generates a current in response to mechanical stress. The piezoelectric material is connected to the diaphragm and the frame of a speaker such that movement of the diaphragm generates a current. 
     In an embodiment, the flexible sensor  302  comprises an optical flex sensor and a photosensitive detector that changes its resistance in a predictable manner with light intensity. The optical flex sensor is connected to the diaphragm and the frame such that movement of the diaphragm changes the shape of the optical flex sensor and the transmission of light through the optical flex sensor. 
     Referring now to  FIG. 4 , an audio system  400  according to the present disclosure includes the speaker  300 , an amplifier  322 , and an audio source  328 . In addition, coupled between the speaker  300  and the amplifier  322  is a feedback circuit  320 . A first lead  324  of the amplifier  322  is connected to a positive lead  314  of a voice coil  312  of the speaker  300 . A second lead  326  of the amplifier  322  is connected to a negative lead  316  of the voice coil  312 . The source  328  provides a source signal to the amplifier  322  over a connection  330 . The connection  330  may be wired or wireless. 
     The amplifier  322  provides a drive signal to the voice coil  312  through the positive lead  314 . The drive signal may be an amplified version of the source signal provided by the source  328 . In response to the drive signal, the voice coil  312  causes the diaphragm  310  to move in order to generate sound from the speaker  300 . 
     The feedback circuit  320  provides a feedback signal to the amplifier  322  over a connection  332 . The feedback signal may include information regarding a position of the diaphragm  310  of the speaker  300 . The amplifier  322  uses the information in the feedback signal to correct for performance errors and distortion introduced by the physical limitations of the speaker  300 . In an embodiment, the amplifier  322  subtracts the feedback signal from the source signal to determine an error signal. The error signal is added to the source signal to generate a modified drive signal that compensates for the performance errors in the speaker  300 . 
     In addition to traditional speakers, the disclosure may be utilized with other diaphragm moving technologies. One such diaphragm moving technology comprises a piezoelectric substrate that deflects with respect to the incoming voltage signal. Another such diaphragm moving technology comprises an electrostatic speaker that has a mylar sheet or diaphragm between two charged electrodes that varies position based on the incoming voltage signal. These, and any other, diaphragm moving technology may be utilized by the disclosure. 
     Referring to  FIG. 5 , there is depicted a schematic of a circuit  500  suitable for use in the feedback circuit  320  shown in  FIG. 4 . The circuit  500  includes a current source  502  and a flexible sensor  504  that includes a flexible resistor. A current from the current source  502  generates a voltage across the flexible sensor  504  in accordance with Ohm&#39;s Law which states that V=IR, where V is the voltage, R is resistance and I is current. The flexible sensor  504  varies its resistance as it deflects responsive to movement of the diaphragm  310 . Thus, the voltage across the flexible sensor  504  varies responsive to movement of the diaphragm. 
     Referring to  FIG. 6 , there is depicted a schematic of a circuit  600  suitable for use in the feedback circuit  320  shown in  FIG. 4 . The circuit  600  includes a top resistor  602  in series with a bottom resistor  604 . The voltage divider equation is Vout=Vin(Rb)/(Rb+Rt). In this circuit  600 , the flexible sensor can be substituted in place of the top resistor  602  or the bottom resistor  604 . 
     It will be appreciated that a flexible sensor has distinct advantages over existing sensor technologies used in servo-controlled loudspeakers. The first major advantage is that it gives the actual position of the speaker diaphragm without the need for any integration steps. Therefore, there is no error in position and there is no delay in the response of the flexible sensor and the position of the diaphragm. The second major advantage of the flexible sensor is that it reacts very fast and can even track a diaphragm in the range of 2 kHz to 20 kHz or above 5 kHz, or above 8 kHz, or above 10 kHz, or above 12 kHz, or above 15 kHz, or even well above the audible range of 20 kHz. This allows servo control of speakers that produce higher frequencies like tweeters whereas previous sensor technologies can only keep up with subwoofer frequencies, typically 20-200 Hz. 
     The foregoing description has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the disclosure to the precise forms or embodiments disclosed. Many modifications, variations, and adaptations will be apparent to those skilled in the art from consideration of the above teachings, specification, and practice of the disclosed embodiments. For example, components described herein may be removed and other components added without departing from the scope or spirit of the embodiments disclosed herein or the appended claims. Further, it should be noted that any or all of the aforementioned alternate implementations may be used in any combination desired to form additional hybrid implementations of the disclosure. 
     Further, although specific implementations of the disclosure have been described and illustrated, the disclosure is not to be limited to the specific forms or arrangements of parts so described and illustrated. The scope of the disclosure is to be defined by the claims appended hereto, any future claims submitted here and in different applications, and their equivalents. 
     Other embodiments will be apparent to those skilled in the art from consideration of the specification and practice of the disclosure disclosed herein. It is intended that the specification and examples be considered as exemplary only, with a true scope and spirit of the invention being indicated by the following claims.