Patent Publication Number: US-9432771-B2

Title: Systems and methods for protecting a speaker from overexcursion

Description:
FIELD OF DISCLOSURE 
     The present disclosure relates in general to audio speakers, and more particularly, to modeling displacement of a speaker system in order to protect audio speakers from damage. 
     BACKGROUND 
     Audio speakers or loudspeakers are ubiquitous on many devices used by individuals, including televisions, stereo systems, computers, smart phones, and many other consumer devices. Generally speaking, an audio speaker is an electroacoustic transducer that produces sound in response to an electrical audio signal input. 
     Given its nature as a mechanical device, an audio speaker may be subject to damage caused by operation of the speaker, including overheating and/or overexcursion, in which physical components of the speaker are displaced too far a distance from a resting position. To prevent such damage from happening, speaker systems often include control systems capable of controlling audio gain, audio bandwidth, and/or other components of an audio signal to be communicated to an audio speaker. 
     However, existing approaches to speaker system control have disadvantages. For example, many such approaches model speaker operation based on measured operating characteristics, but employ linear models. Such linear models may adequately model small signal behavior, but may not sufficiently model nonlinear effects to a speaker caused by larger signals. As another example, some existing approaches model nonlinear behavior, but such models are often mathematically complex, often requiring additional design complexity, cost, and processing resources. 
     SUMMARY 
     In accordance with the teachings of the present disclosure, certain disadvantages and problems associated with protecting a speaker from damage have been reduced or eliminated. 
     In accordance with embodiments of the present disclosure, a system may include a controller configured to be coupled to an audio speaker. The controller may be configured to receive an audio input signal. The controller may also be configured to, based on a linear displacement transfer function associated with the audio speaker, process the audio input signal to generate a modeled linear displacement of the audio speaker, wherein the linear displacement transfer function has a response that models linear displacement of the audio speaker as a linear function of the audio input signal. The controller may further be configured to, based on an excursion linearity function associated with the audio speaker, process the modeled linear displacement to generate a predicted actual displacement of the audio speaker, wherein the excursion linearity function is a function of the modeled linear displacement and has a response modeling non-linearities of the displacement of the audio speaker as a function of the audio input signal. 
     In accordance with these and other embodiments of the present disclosure, a method may include receiving an audio input signal. The method may also include, based on a linear displacement transfer function associated with the audio speaker, processing the audio input signal to generate a modeled linear displacement of the audio speaker, wherein the linear displacement transfer function has a response that models linear displacement of the audio speaker as a linear function of the audio input signal. The method may further include, based on an excursion linearity function associated with the audio speaker, processing the modeled linear displacement to generate a predicted actual displacement of the audio speaker, wherein the excursion linearity function is a function of the modeled linear displacement and has a response modeling non-linearities of the displacement of the audio speaker as a function of the audio input signal. 
     Technical advantages of the present disclosure may be readily apparent to one having ordinary skill in the art from the figures, description and claims included herein. The objects and advantages of the embodiments will be realized and achieved at least by the elements, features, and combinations particularly pointed out in the claims. 
     It is to be understood that both the foregoing general description and the following detailed description are explanatory examples and are not restrictive of the claims set forth in this disclosure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A more complete understanding of the present embodiments and advantages thereof may be acquired by referring to the following description taken in conjunction with the accompanying drawings, in which like reference numbers indicate like features, and wherein: 
         FIG. 1  illustrates a block diagram of an example system that uses speaker modeling and tracking to control operation of an audio speaker, in accordance with embodiments of the present disclosure; 
         FIG. 2  illustrates a model for modeling and tracking displacement of an audio speaker, in accordance with embodiments of the present disclosure; and 
         FIG. 3  illustrates graphs depicting example responses of excursion linearity factors for two different models of audio speakers, in accordance with embodiments of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  illustrates a block diagram of an example system  100  that employs a controller  108  to control the operation of an audio speaker  102 , in accordance with embodiments of the present disclosure. Audio speaker  102  may comprise any suitable electroacoustic transducer that produces sound in response to an electrical audio signal input (e.g., a voltage or current signal). As shown in  FIG. 1 , controller  108  may generate such an electrical audio signal input, which may be further amplified by an amplifier  110 . In some embodiments, one or more components of system  100  may be integral to a single integrated circuit (IC). 
     Controller  108  may include any system, device, or apparatus configured to interpret and/or execute program instructions and/or process data, and may include, without limitation, a microprocessor, microcontroller, digital signal processor (DSP), application specific integrated circuit (ASIC), or any other digital or analog circuitry configured to interpret and/or execute program instructions and/or process data. In some embodiments, controller  108  may interpret and/or execute program instructions and/or process data stored in a memory (not explicitly shown) communicatively coupled to controller  108 . As shown in  FIG. 1 , controller  108  may be configured to perform speaker modeling and tracking  112 , speaker protection  114 , and/or audio processing  116 , as described in greater detail below. 
     Amplifier  110  may be any system, device, or apparatus configured to amplify a signal received from controller  108  and communicate the amplified signal (e.g., to speaker  102 ). In some embodiments, amplifier  110  may comprise a digital amplifier configured to also convert a digital signal output from controller  108  into an analog signal to be communicated to speaker  102 . 
     The audio signal communicated to speaker  102  may be sampled by each of an analog-to-digital converter  104  and an analog-to-digital converter  106 , configured to respectively detect an analog current and an analog voltage associated with the audio signal, and convert such analog current and analog voltage measurements into digital signals  126  and  128  to be processed by controller  108 . Based on digital current signal  126 , digital voltage signal  128 , and an audio input signal x(t), controller  108  may perform speaker modeling and tracking  112  in order to generate a modeled response  118 , including a predicted displacement y(t) for speaker  102 , as described in greater detail below. In some embodiments, speaker modeling and tracking  112  may provide a recursive, adaptive system to generate such modeled response  118 . Example embodiments of speaker modeling and tracking  112  are discussed in greater detail below with reference to  FIG. 2 . 
     Controller  108  may perform speaker protection  114  based on one or more operating characteristics of the audio speaker, including without limitation modeled response  118 . For example, speaker protection  114  may compare modeled response  118  (e.g., a predicted displacement y(t)) to one or more corresponding speaker protection thresholds (e.g., a speaker protection threshold displacement), and based on such comparison, generate one or more control signals for communication to audio processing  116 . Thus, by comparing a predicted displacement y(t) (as included within modeled response  118 ) to an associated speaker protection threshold displacement, speaker protection  114  may generate control signals for modifying one or more characteristics of audio input signal x(t) (e.g., amplitude, frequency, bandwidth, phase, etc.) while providing a psychoacoustically pleasing sound output (e.g., control of a virtual bass parameter). 
     Based on the one or more control signals  120 , controller  108  may perform audio processing  116 , whereby it applies the various control signals  120  to process audio input signal x(t) and generate an electrical audio signal input as a function of audio input signal x(t) and the various speaker protection control signals, which controller  108  communicates to amplifier  110 . 
       FIG. 2  illustrates a more detailed block diagram of a system for performing modeling and tracking  112  shown in  FIG. 1 , in accordance with embodiments of the present disclosure. Speaker modeling and tracking  112  may be used to generate modeled response  118  (e.g., predicted displacement y(t)) based on measured characteristics of speaker  102  (e.g., as indicated by digital current signal  126  and digital voltage signal  128 , respectively), and/or audio input signal x(t). In some embodiments, speaker modeling and tracking  112  may provide a recursive, adaptive system to generate such modeled response  118 . As shown in  FIG. 2 , speaker modeling and tracking  112  may include an adaptive filter  202  with a response h(t) and a nonlinear filter  204  with a response ELF(y l (t)). Response h(t) of filter  202  is a linear displacement transfer function associated with audio speaker  102  that models linear displacement y l (t) of the audio speaker as a linear function of audio input signal x(t). In some embodiments, linear displacement transfer function h(t) correlates an amplitude and a frequency of audio input signal x(t) to an expected displacement of audio speaker  102  in response to the amplitude and the frequency of audio input signal h(t). 
     Response ELF(y l (t)) is an excursion linearity function that is a function of the modeled linear displacement y l (t) and models non-linearities of the displacement of audio speaker  102  as a function of the audio input signal. Response ELF(y l (t)) may combine non-linearities (e.g., force factor, stiffness) of audio speaker  102  into a single scaling factor which is a function of modeled linear displacement y l (t). Accordingly, responsive to a linear displacement y l (t), filter  204  generates a predicted actual displacement y(t). An example of response ELF(y l (t)) for two different models of audio speakers is shown in  FIG. 3 . 
     In some embodiments, excursion linearity function ELF(y l (t)) may be characterized using offline testing of one or more audio speakers similar to the audio speaker. For example, in such embodiments, excursion linearity function ELF(y l (t)) may be determined by comparing the modeled linear displacement y l (t) in response to a particular audio input signal (e.g., a pink noise signal) and a measured displacement of audio speaker  102  (or one or more audio speakers similar or identical in design and/or functionality with audio speaker  102 ) in response to the particular audio input signal, and statistically minimizing an error between the modeled linear displacement y l (t) and the measured displacement. This comparison and statistical minimization of area may be repeated at various amplitudes of audio signal, so that response ELF(y l (t)) may be determined for a full displacement range of audio speaker  102 . In addition or alternatively, such testing may be applied to many audio speakers similar in identical in design to audio speaker  102  (e.g., the same model as audio speaker  102 ), such that response ELF(y l (t)) is based on an average of similar or identical audio speakers. In some embodiments, excursion linearity function ELF(y l (t)) may be independent of a frequency of the audio input signal. 
     In these and other embodiments, controller  108  may shape the response of the linear displacement transfer function h(t) in conformity with a measured characteristics of speaker  102  (e.g., as indicated by current signal  126  and/or voltage signal  128 ). Accordingly, speaker modeling and tracking  112  may provide a recursive, adaptive system which modifies the response of filter  202  based on comparison of actual measured values (e.g., current signal  126 , voltage signal  128 ) that may be indicative of a physical state of audio speaker  102  (e.g., speaker temperature and surroundings) with predictive characteristics of audio speaker  102  (e.g., expected temperature and surroundings). 
     This disclosure encompasses all changes, substitutions, variations, alterations, and modifications to the example embodiments herein that a person having ordinary skill in the art would comprehend. Similarly, where appropriate, the appended claims encompass all changes, substitutions, variations, alterations, and modifications to the example embodiments herein that a person having ordinary skill in the art would comprehend. Moreover, reference in the appended claims to an apparatus or system or a component of an apparatus or system being adapted to, arranged to, capable of, configured to, enabled to, operable to, or operative to perform a particular function encompasses that apparatus, system, or component, whether or not it or that particular function is activated, turned on, or unlocked, as long as that apparatus, system, or component is so adapted, arranged, capable, configured, enabled, operable, or operative. 
     All examples and conditional language recited herein are intended for pedagogical objects to aid the reader in understanding the disclosure and the concepts contributed by the inventor to furthering the art, and are construed as being without limitation to such specifically recited examples and conditions. Although embodiments of the present disclosure have been described in detail, it should be understood that various changes, substitutions, and alterations could be made hereto without departing from the spirit and scope of the disclosure.