Energy limiter for loudspeaker protection

One embodiment provides a method comprising determining a potential energy in a loudspeaker, a kinetic energy in the loudspeaker, and an electrical energy in the loudspeaker based on a physical model of the loudspeaker. The method further comprises determining a total energy stored in the loudspeaker based on the potential energy, the kinetic energy, and the electrical energy. The method further comprises determining a maximum potential displacement of a diaphragm of a speaker driver of the loudspeaker based on the total energy, and limiting the total energy stored in the loudspeaker by attenuating a source signal for reproduction via the loudspeaker. An actual displacement of the diaphragm during the reproduction of the source signal is controlled based on the attenuated source signal.

TECHNICAL FIELD

One or more embodiments relate generally to loudspeakers, and in particular, a method and system for limiting energy stored in a loudspeaker.

BACKGROUND

A loudspeaker produces sound when connected to an integrated amplifier, a television (TV) set, a radio, a music player, an electronic sound producing device (e.g., a smartphone, a computer), a video player, etc.

SUMMARY

One embodiment provides a method comprising determining a potential energy in a loudspeaker, a kinetic energy in the loudspeaker, and an electrical energy in the loudspeaker based on a physical model of the loudspeaker. The method further comprises determining a total energy stored in the loudspeaker based on the potential energy, the kinetic energy, and the electrical energy. The method further comprises determining a maximum potential displacement of a diaphragm of a speaker driver of the loudspeaker based on the total energy, and limiting the total energy stored in the loudspeaker by attenuating a source signal for reproduction via the loudspeaker. An actual displacement of the diaphragm during the reproduction of the source signal is controlled based on the attenuated source signal.

Another embodiment provides a system for limiting energy in a loudspeaker. The system comprises a voltage source amplifier connected to the loudspeaker and a limiter connected to the voltage source amplifier. The limiter is configured to determine a potential energy in the loudspeaker, a kinetic energy in the loudspeaker, and an electrical energy in the loudspeaker based on a physical model of the loudspeaker. The limiter is further configured to determine a total energy stored in the loudspeaker based on the potential energy, the kinetic energy, and the electrical energy. The limiter is further configured to determine a maximum potential displacement of a diaphragm of a speaker driver of the loudspeaker based on the total energy, and limit the total energy stored in the loudspeaker by attenuating a voltage of a source signal for reproduction via the loudspeaker. The voltage source amplifier outputs the attenuated voltage to drive the speaker driver. An actual displacement of the diaphragm during the reproduction of the source signal is controlled based on the attenuated voltage.

One embodiment provides a loudspeaker device comprising a speaker driver including a diaphragm, a voltage source amplifier connected to the speaker driver, and a limiter connected to the voltage source amplifier. The limiter is configured to determine a potential energy in the loudspeaker, a kinetic energy in the loudspeaker, and an electrical energy in the loudspeaker based on a physical model of the loudspeaker. The limiter is further configured to determine a total energy stored in the loudspeaker based on the potential energy, the kinetic energy, and the electrical energy. The limiter is further configured to determine a maximum potential displacement of a diaphragm of a speaker driver of the loudspeaker based on the total energy, and limit the total energy stored in the loudspeaker by attenuating a voltage of a source signal for reproduction via the loudspeaker. The voltage source amplifier outputs the attenuated voltage to drive the speaker driver. An actual displacement of the diaphragm during the reproduction of the source signal is controlled based on the attenuated voltage.

These and other features, aspects and advantages of the one or more embodiments will become understood with reference to the following description, appended claims, and accompanying figures.

DETAILED DESCRIPTION

One or more embodiments relate generally to loudspeakers, and in particular, a method and system for limiting energy stored in a loudspeaker. One embodiment provides a method comprising determining a potential energy in a loudspeaker, a kinetic energy in the loudspeaker, and an electrical energy in the loudspeaker based on a physical model of the loudspeaker. The method further comprises determining a total energy stored in the loudspeaker based on the potential energy, the kinetic energy, and the electrical energy. The method further comprises determining a maximum potential displacement of a diaphragm of a speaker driver of the loudspeaker based on the total energy, and limiting the total energy stored in the loudspeaker by attenuating a source signal for reproduction via the loudspeaker. An actual displacement of the diaphragm during the reproduction of the source signal is controlled based on the attenuated source signal.

Another embodiment provides a system for limiting energy in a loudspeaker. The system comprises a voltage source amplifier connected to the loudspeaker and a limiter connected to the voltage source amplifier. The limiter is configured to determine a potential energy in the loudspeaker, a kinetic energy in the loudspeaker, and an electrical energy in the loudspeaker based on a physical model of the loudspeaker. The limiter is further configured to determine a total energy stored in the loudspeaker based on the potential energy, the kinetic energy, and the electrical energy. The limiter is further configured to determine a maximum potential displacement of a diaphragm of a speaker driver of the loudspeaker based on the total energy, and limit the total energy stored in the loudspeaker by attenuating a voltage of a source signal for reproduction via the loudspeaker. The voltage source amplifier outputs the attenuated voltage to drive the speaker driver. An actual displacement of the diaphragm during the reproduction of the source signal is controlled based on the attenuated voltage.

One embodiment provides a loudspeaker device comprising a speaker driver including a diaphragm, a voltage source amplifier connected to the speaker driver, and a limiter connected to the voltage source amplifier. The limiter is configured to determine a potential energy in the loudspeaker, a kinetic energy in the loudspeaker, and an electrical energy in the loudspeaker based on a physical model of the loudspeaker. The limiter is further configured to determine a total energy stored in the loudspeaker based on the potential energy, the kinetic energy, and the electrical energy. The limiter is further configured to determine a maximum potential displacement of a diaphragm of a speaker driver of the loudspeaker based on the total energy, and limit the total energy stored in the loudspeaker by attenuating a voltage of a source signal for reproduction via the loudspeaker. The voltage source amplifier outputs the attenuated voltage to drive the speaker driver. An actual displacement of the diaphragm during the reproduction of the source signal is controlled based on the attenuated voltage.

For expository purposes, the terms “loudspeaker”, “loudspeaker device” and “loudspeaker system” may be used interchangeably in this specification.

For expository purposes, the terms “displacement” and “excursion” may be used interchangeably in this specification.

A conventional loudspeaker is nonlinear by design and produces harmonics, intermodulation components, and modulation noise. Nonlinear audio distortion (i.e., audible distortion) impairs sound quality of audio produced by the loudspeaker (e.g., audio quality and speech intelligibility). In recent times, industrial design constraints often require loudspeaker systems to be smaller-sized for portability and compactness. Such design constraints, however, trade size and portability for sound quality, resulting in increased audio distortion. As such, an anti-distortion system for reducing/removing audio distortion is needed, in particular for obtaining a more pronounced/bigger bass sound from smaller-sized loudspeaker systems.

A loudspeaker device includes at least one speaker driver for reproducing sound.FIG. 1illustrates a cross section of an example speaker driver55. The speaker driver55comprises one or more moving components, such as a diaphragm56(e.g., a cone-shaped diaphragm), a driver voice coil57, a former64, and a protective cap68(e.g., a dome-shaped dust cap). The speaker driver55further comprises one or more of the following components: (1) a surround roll58(e.g., suspension roll), (2) a basket59, (3) a top plate61, (4) a magnet62, (5) a bottom plate63, (6) a pole piece66, and (7) a spider67.

FIG. 2illustrates an example loudspeaker system100, in accordance with an embodiment. The loudspeaker system100comprises a loudspeaker device60including a speaker driver65for reproducing sound. The loudspeaker device60may be any type of loudspeaker device such as, but not limited to, a sealed-box loudspeaker, a vented-box loudspeaker, a passive-radiator loudspeaker, a loudspeaker array, etc. The speaker driver65may be any type of speaker driver such as, but not limited to, a forward-facing speaker driver, an upward-facing speaker driver, a downward-facing speaker driver, etc. In one embodiment, the speaker driver55inFIG. 1is an example implementation of the speaker driver65. The speaker driver65comprises one or more moving components, such as a diaphragm56(FIG. 1) and a driver voice coil57(FIG. 1).

The loudspeaker system100comprises an energy limiter system200configured to monitor and control energy stored in the loudspeaker device60to predict and limit and/or compress displacement of the one or more moving components during audio reproduction. In one embodiment, the system200is configured to receive a source signal (e.g., an input signal such as an input audio signal) from an input source10for audio reproduction via the loudspeaker device60. In one embodiment, the energy limiter system200is configured to receive a source signal from different types of input sources10. Examples of different types of input sources10include, but are not limited to, a mobile electronic device (e.g., a smartphone, a laptop, a tablet, etc.), a content playback device (e.g., a television, a radio, a computer, a music player such as a CD player, a video player such as a DVD player, a turntable, etc.), or an audio receiver, etc.

Let u generally denote an input voltage of the source signal. As described in detail later herein, the energy limiter system200is configured to: (1) based on a physical model of the loudspeaker device60, determine a total energy E stored in the loudspeaker device60, (2) determine a maximum potential displacement (e.g., predicted maximum cone displacement) x of the one or more moving components, and (3) determine, in real-time, an amount of attenuation to apply to the input voltage u to produce an energy and displacement limiting voltage (“limiting voltage”) ulimthat limits and/or compresses the total energy E stored in the loudspeaker device60and in turn limits and/or compresses an actual displacement (e.g., actual cone displacement) of the one or more moving components within a predetermined range of safe displacement.

A physical model of the loudspeaker device60may be based on one or more loudspeaker parameters for the loudspeaker device60. In one embodiment, a physical model of the loudspeaker device60utilized by the energy limiter system200is a linear model (e.g., a linear state-space model as shown inFIG. 4A). In another embodiment, a physical model of the loudspeaker device60utilized by the energy limiter system200is a nonlinear model (e.g., a nonlinear state-space model as shown inFIG. 4B).

In one embodiment, the loudspeaker system100comprises a voltage source amplifier71connected to the loudspeaker device60and the energy limiter system200. The voltage source amplifier71is a power amplifier configured to output (i.e., apply or produce), for each sampling time t, an actual voltage (i.e., applied voltage) u* based on a limiting voltage ulimdetermined by the energy limiter system200at the sampling time t. The limiting voltage ulimcontrols the voltage source amplifier71, directing the voltage source amplifier71to output an amount of voltage that is substantially the same as the limiting voltage ulim. The speaker driver65is driven by the actual voltage u* output by the voltage source amplifier71, thereby amplifying the source signal for audio reproduction via the loudspeaker device60. Therefore, the loudspeaker system100controls actual displacement of the one or more moving components (i.e., cone displacement/motion of the one or more moving components) during the audio reproduction of the source signal by performing voltage correction based on the limiting voltage ulim.

In one embodiment, the system100comprises an optional controller110for linear or nonlinear control of the loudspeaker device60. For example, in one embodiment, the controller110is a nonlinear control system configured to provide correction of nonlinear audio distortion by pre-distorting voltage to the speaker driver65. The controller110is configured to receive, as input, a limiting voltage ulimat a sampling time t (e.g., from the system200), and generate and transmit a control voltage signal s specifying a target voltage that produces a target displacement at the sampling time t. The control voltage signal s can be any type of signal such as, but not limited to, a current, a voltage, a digital signal, an analog signal, etc. In one embodiment, the voltage source amplifier71is configured to output an actual voltage u* at a sampling time t based on a control voltage signal s from the controller110, wherein the control voltage signal s directs the voltage source amplifier71to output an amount of voltage that is substantially the same as a target voltage included in the control voltage signal s for the sampling time t.

The energy limiter system200facilitates a higher level of audio reproduction, with improved sound quality, and additional control and protection of the loudspeaker device60. The energy limiter system200maximizes bass output and sound loudness. The energy limiter system200facilitates smooth control of energy stored in the loudspeaker device60to preserve audio quality. The energy limiter system200utilizes a time-domain algorithm without any change in frequency content or spectral balance (i.e., frequency filtering).

As described in detail later herein, the energy limiter system200is configured to counter audio distortion during the reproduction of the source signal via the speaker driver65by calculating a limiting voltage ulimat each instant/sampling time t based on an instantaneous position of the one or more moving components, wherein an actual voltage output by the voltage source amplifier71is substantially equal to the limiting voltage ulim.

Reproducing bass via the loudspeaker device60requires larger excursions of the one or more moving components to achieve the same loudness. However, excessive excursion of the one or more moving components can cause damage to the speaker driver65. The energy limiter system200allows the one or more moving components to achieve the largest possible excursion without exceeding safe limits (i.e., the predetermined range of safe displacement), thus maximizing bass output.

In one embodiment, the loudspeaker system100may be integrated in different types of electrodynamic transducers with a broad range of applications such as, but not limited to, the following: computers, televisions (TVs), smart devices (e.g., smart TVs, smart phones, etc.), soundbars, subwoofers, wireless and portable speakers, mobile phones, car speakers, etc.

FIG. 3illustrates an example electroacoustic model70for a loudspeaker device60(FIG. 2) driven by a voltage source amplifier71. One or more loudspeaker parameters (i.e., loudspeaker characteristics) for the loudspeaker device60may be classified into one of the following domains: an electrical domain or a mechanical domain. In the electrical domain, examples of different loudspeaker parameters include, but are not limited to, the following: (1) an applied voltage u* from the voltage source amplifier71for driving a speaker driver65of the loudspeaker device60, (2) an electrical resistance Reof a driver voice coil57of the speaker driver65, (3) a current i* flowing through the driver voice coil57as a result of the applied voltage u*, (4) an inductance Leof the driver voice coil57, and (5) a back electromagnetic force (back EMF) Bl·{dot over (x)} resulting from the motion of the driver voice coil57in the magnetic field of the motor structure (i.e., driver voice coil57, top plate61, magnet62, bottom plate63, and pole piece66) of the speaker driver65, wherein the back-EMF Bl·{dot over (x)} represents a product of a force factor Bl of the motor structure and a velocity {dot over (x)} of one or more moving components of the speaker driver65(e.g., a diaphragm56, the driver voice coil57, and/or the former64).

In the mechanical domain, examples of different loudspeaker parameters include, but are not limited to, the following: (1) the velocity {dot over (x)} of the one or more moving components of the speaker driver65, (2) a mechanical mass Mmsof the one or more moving components (i.e., moving mass) and air load, (3) a mechanical resistance Rmsrepresenting the mechanical losses of the speaker driver65, (4) a stiffness factor Kmsof the suspension (i.e., surround roll58, spider67, plus air load) of the speaker driver65, and (5) a mechanical force Bl·i* applied on the one or more moving components, wherein the mechanical force Bl·i* represents a product of the force factor Bl of the motor structure and the current i* flowing through the driver voice coil57.

The state of a loudspeaker device60at each instant may be described using each of the following: (1) a displacement x of the one or more moving components of the speaker driver65, (2) a velocity {dot over (x)} of the one or more moving components of the speaker driver65, and (3) a current i flowing through the driver voice coil57. Let X1(t) generally denote a vector representing a state (“state vector representation”) of the loudspeaker device60at a sampling time t. The state vector representation X1(t) may be defined in accordance with equation (1) provided below:
X1(t)=[x,{dot over (x)},i]T(1).
For expository purposes, the terms X1(t) and X1are used interchangeably in this specification.

As described in detail later herein below, the system200determines, at each sampling time t, an estimated displacement x of the one or more moving components at the sampling time t, an estimated velocity {dot over (x)} of the one or more moving components at the sampling time t, and an estimated current i flowing through the driver voice coil57at a sampling time t based on a physical model of the loudspeaker device60, such as a linear model (e.g., a linear state-space model as shown inFIG. 4A) or a nonlinear model (e.g., a nonlinear state-space model as shown inFIG. 4B). The physical model may be based on one or more loudspeaker parameters for the loudspeaker device60.

FIG. 4Aillustrates an example linear system500representing a linear state-space model of the loudspeaker device60. The linear system500may be utilized to determine an estimated displacement x of one or more moving components (e.g., a diaphragm56and/or a driver voice coil57) of the speaker driver65based on a state vector representation X1of the loudspeaker device60and an input voltage u of a source signal for reproduction via the loudspeaker device60.

Let {dot over (X)}1generally denote a time derivative (i.e., rate of change) of the state vector representation X1of the loudspeaker device60(“state vector rate of change”). The state vector rate of change {dot over (X)}1may be defined in accordance with a differential equation (2) provided below:
{dot over (X)}1=A1X1+B1u(2).

Let A1, B1, and C1denote constant parameter matrices. The constant parameter matrices A1, B1, and C1may be represented in accordance with equations (3)-(5) provided below:

An estimated displacement x of the one or more moving components of the speaker driver65may be computed in accordance with equation (6) provided below:
x=C1X1(6).

Determining an estimated displacement x of the one or more moving components utilizing the linear system500involves performing a set of computations that are based on equations (2)-(6) provided above. The linear system500may utilize one or more of the following components to perform the set of computations: (1) a first multiplication unit501configured to determine a product term A1X1by multiplying the constant parameter matrix A1with the state vector representation X1, (2) a second multiplication unit502configured to determine a product term B1u by multiplying the constant parameter matrix B1with the input voltage u, (3) an addition unit503configured to determine the state vector rate of change {dot over (X)}1by adding the product terms A1X1and Bu in accordance with equation (2) provided above, (4) an integration unit504configured to determine the state vector representation X1by integrating the state vector rate of change {dot over (X)}1in the time domain, and (5) a third multiplication unit505configured to determine the estimated displacement x by multiplying the constant parameter matrix C1with the state vector representation X1in accordance with equation (6) provided above.

The system representation500inFIG. 4Ais a linear system that receives an input voltage u as an input and provides an estimated displacement x as an output.

FIG. 4Billustrates an example nonlinear system550representing a nonlinear state-space physical model of the loudspeaker device60. The nonlinear system550may be utilized to determine an estimated displacement x of one or more moving components (e.g., a diaphragm56and/or a driver voice coil57) of the speaker driver65based on a state vector representation X1of the loudspeaker device60and an input voltage u of a source signal for reproduction via the loudspeaker device60.

Let g1(X1, u) and ƒ1(X1) generally denote nonlinear functions that are based on the state vector representation X1of the loudspeaker device60and one or more large signal loudspeaker parameters for the loudspeaker device60. The nonlinear functions g1(X1, u) and ƒ1(X1) may be represented in accordance with equations (7)-(8) provided below:

Let C1generally denote a constant parameter matrix. The constant parameter matrix C1may be represented in accordance with equation (9) provided below:

Let {dot over (X)}1generally denote a time derivative (i.e., rate of change) of the state vector representation X1of the loudspeaker device60(“state vector rate of change”). The state vector rate of change {dot over (X)}1may be defined in accordance with a differential equation (10) provided below:
{dot over (X)}1=g1(X1,u)+ƒ1(X1)  (10).

An estimated displacement x of the one or more moving components of the speaker driver65may be computed in accordance with equation (11) provided below:
x=C1X1(11).

Determining an estimated displacement x of the one or more moving components utilizing the nonlinear system550involves performing a set of computations that are based on equations (7)-(11) provided above. The nonlinear system550may utilize one or more of the following components to perform the set of computations: (1) a first computation unit551configured to compute the nonlinear function ƒ1(X1) in accordance with equation (8) provided above, (2) a second computation unit552configured to compute the nonlinear function g1(X1, u) in accordance with equation (7) provided above, (3) an addition unit553configured to determine the state vector rate of change {dot over (X)}1by adding the nonlinear functions g1(X1, u) and ƒ1(X1) in accordance with equation (10) provided above, (4) an integration unit554configured to determine the state vector representation X1by integrating the state vector rate of change {dot over (X)}1in the time-domain, and (5) a multiplication unit555configured to determine the estimated displacement x by multiplying the constant parameter matrix C1with the state vector representation X1in accordance with equation (11) provided above.

The system representation550inFIG. 4Bis a nonlinear system that receives an input voltage u as an input and provides an estimated displacement x as an output.

Let E generally denote total energy stored in the loudspeaker device60. At any sampling time t, total energy E stored in the loudspeaker device60may be represented as a sum of potential energy, kinetic energy, and electrical energy in the loudspeaker device60, as expressed by equation (12) provided below:
E=½Kmsx2+½Mms{dot over (x)}2+½Lei2(12),
wherein ½Kmsx2denotes the potential energy in the loudspeaker device60, ½Mms{dot over (x)}2denotes the kinetic energy in the loudspeaker device60, and ½Lei2denotes the electrical energy in the loudspeaker device60.

Let xsupgenerally denote a maximum potential displacement (e.g., predicted maximum cone displacement) of the one or more moving components of the speaker driver65, wherein the maximum potential displacement xsupcan be either a positive value (+xsup) or a negative value (−xsup). The maximum potential displacement xsupresults when all the energy E stored in the loudspeaker device60is concentrated in the suspension, i.e., the total energy E stored in the loudspeaker device60is equal to the potential energy in the loudspeaker device60, as represented by equation (13) provided below:
E=½Kmsxsup2(13)

Based on equation (13) provided above, the maximum potential displacement xsupmay be represented in accordance with equation (14) provided below:

xsup=2⁢⁢EKms,(14)
wherein |xsup| denotes an absolute value of the maximum potential displacement xsupand represents a maximum potential displacement envelope (i.e., a predetermined range of maximum potential displacement [−xsup, xsup] of the one or more moving components of the speaker driver65).

Let xlimgenerally denote a predetermined displacement limit (i.e., maximum desired displacement) for safe displacement of the one or more moving components of the speaker driver65, and let [−xlim, xlim] generally denote a predetermined range of safe displacement of the one or more moving components of the speaker driver65. The system200ensures that the maximum potential displacement xsupdoes not exceed the predetermined displacement limit xlim. To limit an actual displacement (e.g., actual cone displacement) of the one or more moving components of the speaker driver65within the predetermined range of safe displacement [−xlim, xlim], total energy E stored in the loudspeaker device60must be limited to satisfy a constraint represented by expression (15) provided below:
E≤½Kmsxlim2(15).

d⁢⁢Ed⁢⁢t
generally denote total power in the loudspeaker device60, wherein the total power

d⁢⁢Ed⁢⁢t
is a time derivative (i.e., rate of change) of total energy E stored in the loudspeaker device60. The total power

d⁢⁢Ed⁢⁢t
in the loudspeaker device60may be represented in accordance with a differential equation (16) provided below:

d⁢⁢Ed⁢⁢t=-Rms⁢x.2-Re⁢i2+iu.(16)
Without electrical input (i.e., input voltage u=0), the total power

d⁢⁢Ed⁢⁢t
in the loudspeaker device60is negative due to mechanical and electrical losses, and the total energy E stored in the loudspeaker device60decreases to zero (i.e., stability).

FIG. 5is an example graph300illustrating different loudspeaker parameters for a loudspeaker device60during audio reproduction. A horizontal axis of the graph300represents time in seconds (s). The graph300comprises each of the following: (1) a first curve301representing a current i flowing through a driver voice coil57of a speaker driver65of the loudspeaker device60in Amperes (A), (2) a second curve302representing velocity {dot over (x)} of one or more moving components (e.g., a diaphragm56and/or the driver voice coil57) of the speaker driver65in meters per second (m/s), (3) a third curve303representing a negative value of maximum potential displacement −xsupof the one or more moving components of the speaker driver65in millimeters (mm), (4) a fourth curve304representing a positive value of maximum potential displacement xsupof the one or more moving components of the speaker driver65in mm, and (5) a fifth curve305representing displacement x of the one or more moving components of the speaker driver65in mm. As shown inFIG. 5, the displacement x of the one or moving components of the speaker driver65reaches ±xsup(“maximum displacement envelope”) when the velocity {dot over (x)} of the one or more moving components of the speaker driver65crosses zero. When the velocity {dot over (x)} of the one or more moving components of the speaker driver65crosses zero, electrical energy in the loudspeaker device60is negligible compared to mechanical energies in the loudspeaker device60.

FIG. 6illustrates an example energy limiter system200, in accordance to an embodiment. As described in detail later herein, the system200provides a limiter and/or a compressor for limiting and/or compressing total energy stored in a loudspeaker device60, which in turn limits and/or compresses displacement x of one or more moving components of a speaker driver65(e.g., a diaphragm56, the driver voice coil57, and/or the former64) of the loudspeaker device60.

In one embodiment, the system200comprises a loudspeaker model unit310configured to receive, as inputs, an input voltage u at a sampling time t and one or more loudspeaker parameters for the loudspeaker device60(e.g., small-signal loudspeaker parameters for the loudspeaker device60, such as mechanical mass Mms, inductance Le, and stiffness factor Kms). Based on the inputs received and a physical model of the loudspeaker device60(e.g., a linear state-space model as shown inFIG. 4Aor a nonlinear state-space model as shown inFIG. 4B), the loudspeaker model unit310is configured to recursively determine each of the following: an estimated displacement x of the one or more moving components of the speaker driver65at the sampling time t, an estimated velocity {dot over (x)} of the one or more moving components of the speaker driver65at the sampling time t, and an estimated current i flowing through a driver voice coil57of the speaker driver65at the sampling time t.

In one embodiment, the system200comprises an energy computation unit320configured to receive, as inputs, an estimated displacement x of the one or more moving components of the speaker driver65at a sampling time t (e.g., from the loudspeaker model unit310), an estimated velocity {dot over (x)} of the one or more moving components of the speaker driver65at the sampling time t (e.g., from the loudspeaker model unit310), an estimated current i flowing through the driver voice coil57at the sampling time t (e.g., from the loudspeaker model unit310), and one or more loudspeaker parameters for the loudspeaker device60(e.g., small-signal loudspeaker parameters for the loudspeaker device60, such as mechanical mass Mms, inductance Le, and stiffness factor Kms). Based on the inputs received, the energy computation unit320is configured to determine total energy E stored in the loudspeaker device60at the sampling time t.

In one embodiment, the energy computation unit320is configured to determine total energy E stored in the loudspeaker device60by: (1) computing, based on the inputs received, potential energy in the loudspeaker device60, kinetic energy in the loudspeaker device60, and electrical energy in the loudspeaker device60, and (2) computing a sum of the potential energy, the kinetic energy, and the electrical energy, wherein the total energy E stored in the loudspeaker device60factors into account the sum computed.

In one embodiment, the energy computation unit320is configured to determine total energy E stored in the loudspeaker device60in accordance with equation (17) provided below:
E=10 log10[½Kmsx2+½Mms{dot over (x)}2+½Lei2]  (17).

In another embodiment, the energy computation unit320is configured to determine total energy E stored in the loudspeaker device60based on a predictive model trained to learn dynamics of energy.

In one embodiment, the system200comprises a static gain computation unit330configured to receive, as inputs, an estimated total energy E stored in the loudspeaker device60at a sampling time t (e.g., from the energy computation unit320) and a set of displacement parameters indicative of a desired displacement behavior of the one or more moving components of the speaker driver65. In one embodiment, the set of displacement parameters comprise, but is not limited to, one or more of the following displacement parameters: a predetermined displacement limit xlim, a predetermined displacement compression threshold xthr, a predetermined compression ratio R, or a predetermined soft knee width Wknee. Based on the inputs received, the static gain computation unit330is configured to determine an instantaneous gain Gstaticto apply at the sampling time t to limit and/or compress the displacement x of the one or more moving components of the speaker driver65at the sampling time t.

Let Elimgenerally denote a predetermined energy limit, and let Ethrgenerally denote a predetermined energy compression threshold. In one embodiment, the system200operates as a limiter (i.e., the limiter is enabled) to limit total energy E stored in the loudspeaker60based on a predetermined energy limit Elim. In one embodiment, the system200operates as a compressor (i.e., the compressor is enabled) to compress total energy E stored in the loudspeaker60based on a predetermined energy compression threshold Ethr. In one embodiment, the system200is operable as one of the following: a limiter only, a compressor only, or both a limiter and a compressor.

In one embodiment, the static gain computation unit330is configured to convert one or more displacement parameters to one or more corresponding energy parameters, such as a predetermined energy limit Elimand/or a predetermined energy compression threshold Ethr. For example, in one embodiment, if the limiter is enabled, the static gain computation unit330is configured to convert a predetermined displacement limit xlimreceived as an input to a predetermined energy limit Elimin accordance with equation (18) provided below:
Elim=10 log10[½Kmsxlim2]  (18).

As another example, in one embodiment, if the compressor is enabled, the static gain computation unit330is configured to convert a predetermined displacement compression threshold xthrreceived as an input to a predetermined energy compression threshold Ethrin accordance with equation (19) provided below:
Ethr=10 log10[½Kmsxthr2]  (19).

In one embodiment, if only the limiter is enabled, the static gain computation unit330determines an instantaneous gain Gstaticto apply at a sampling time t to limit a displacement x of the one or more moving components of the speaker driver65at the sampling time tin accordance with equations (20)-(21) provided below:
Gstatic=0 ifE≤Elim(20), and
Gstatic=Elim−EifElim<E(21).

In one embodiment, if both the limiter and the compressor are enabled, the static gain computation unit330determines an instantaneous gain Gstaticto apply at a sampling time t to limit and compress a displacement x of the one or more moving components of the speaker driver65at the sampling time tin accordance with equations (22)-(25) provided below:

In one embodiment, the system200comprises a temporal gain smoothing unit340configured to implement temporal gain smoothing (i.e., gain attenuation). Specifically, the temporal gain smoothing unit340is configured to: (1) receive, as inputs, an instantaneous gain Gstaticat a sampling time t (e.g., from the static gain computation unit330), an optional set of attack parameters for reducing the gain Gstatic(i.e., attack), and an optional set of release parameters for increasing the gain Gstatic(i.e., release), and (2) apply a smoothing algorithm to the gain Gstaticto reduce or prevent rapid changes in the gain Gstaticthat can adversely affect perceived sound quality, resulting in a smoothed gain Gsmoothed.

In one embodiment, the temporal gain smoothing unit340is configured to apply any type of smoothing algorithm. For example, as described in detail later herein, in one embodiment, the smoothing algorithm applied involves adjusting the gain Gstaticexponentially utilizing the set of attack parameters and/or the set of release parameters.

In one embodiment, the system200comprises an optional look-ahead delay unit350configured to: (1) receive an input voltage u at a sampling time t, and (2) implement a look-ahead delay by delaying the input voltage u for a predetermined amount of time (e.g., 20 ms) to allow for temporal gain smoothing (e.g., implemented by the temporal gain smoothing unit340). Delaying the input voltage u allows for gain attenuation before total energy E stored in the loudspeaker device60exceeds a predetermined energy compression threshold Ethr. In one embodiment, the system200minimizes or eliminates the look-ahead delay by estimating/predicting a state of the loudspeaker device60, thereby removing the need for the look-ahead delay unit350.

In one embodiment, the system200comprises a component360configured to receive, as inputs, a smoothed gain Gsmoothedto apply at a sampling time t (e.g., from the temporal gain smoothing unit340), and an input voltage u at the sampling time t (e.g., from the look-ahead delay unit350if look-ahead delay is implemented). The component360is configured to attenuate the input voltage u by applying the smoothed gain Gsmoothedto the input voltage u, resulting in a limiting voltage ulimat the sampling time t that limits and/or compresses total energy E stored in the loudspeaker device60at the sampling time t and in turn limits and/or compresses an actual displacement (e.g., actual cone displacement) of the one or more moving components of the speaker driver65to within a predetermined range of safe displacement [−xlim, xlim] at the sampling time t.

FIG. 7Ais an example graph400comparing differences in voltage as result of enabling the limiter, in accordance with an embodiment. A horizontal axis of the graph400represents time in s. A vertical axis of the graph400represents voltage in V. The graph400comprises a first curve401representing an actual voltage driving the speaker driver65when the limiter is not enabled (i.e., actual voltage u* is substantially about input voltage u), and a second curve402representing an actual voltage driving the speaker driver65when the limiter is enabled (i.e., actual voltage u* is substantially about limiting voltage ulim).

FIG. 7Bis an example graph410illustrating total energy as result of enabling the limiter, in accordance with an embodiment. A horizontal axis of the graph410represents time in s. A vertical axis of the graph410represents energy in Joules (J). The graph410comprises a first curve411representing total energy stored in the loudspeaker device60when the limiter is not enabled, and a second curve412representing total energy stored in the loudspeaker device60when the limiter is enabled. If the limiter is enabled, the system200adjusts the limiting voltage ulimto keep the total energy E stored in the loudspeaker device60below a predetermined energy limit Elim, as shown inFIG. 7B.

FIG. 7Cis an example graph420comparing differences in displacement as result of enabling the limiter, in accordance with an embodiment. A horizontal axis of the graph420represents time in s. A vertical axis of the graph420represents displacement in mm. The graph420comprises a first curve421representing an actual displacement of the one or more moving components of the speaker driver65when the limiter is not enabled, and a second curve422representing an actual displacement of the one or more moving components of the speaker driver65when the limiter is enabled. If the limiter is enabled, the system200applies a gain that limits actual displacement of the one or more moving components of the speaker driver65to within a predetermined range of safe displacement [−xlim, xlim]. For example, if xlimis 5 mm, the system200with the limiter enabled applies a gain that limits the actual displacement x* of the one or more moving components of the speaker driver65to within a range [−5, 5], as shown inFIG. 7C.

FIG. 7Dis an example graph430comparing gain Gstaticwith smoothed gain Gsmoothed, in accordance with an embodiment. A horizontal axis of the graph430represents time in s. A vertical axis of the graph430represents gain in dB. The graph430comprises a first curve431representing static gain Gstatic, and a second curve432representing smoothed gain Gsmoothed. In one embodiment, the smoothing algorithm applied by the system200involves adjusting an instantaneous gain Gstaticexponentially utilizing a set of attack parameters and/or a set of release parameters. As shown inFIG. 7D, if there is a step change in the gain Gstaticfrom a high gain value Ghighto a low gain value Glow, the system200reduces the gain Gstatic(i.e., attack) exponentially utilizing the set of attack parameters, resulting in a smoothed gain Gsmoothedthat is represented in accordance with equation (26) provided below:
Gsmoothed=(Ghigh−Glow)e−t/τattack+Glow(26),
wherein τattackis a time constant representing an amount of time it takes for the gain Gstaticto get within 36.8% of the smoothed gain Gsmoothed.

As further shown inFIG. 7D, if there is a step change in the gain Gstaticfrom the low gain value Glowto the high gain value Ghigh, the system200increases the gain Gstatic(i.e., release) exponentially utilizing the set of release parameters, resulting in a smoothed gain Gsmoothedthat is represented in accordance with equation (27) provided below:
Gsmoothed=(Ghigh−Glow)(1−e−t/τrelease)+Glow(27),
wherein τreleaseis a time constant representing an amount of time it takes for the gain Gstaticto get within 36.8% of the smoothed gain Gsmoothed.

In one embodiment, τattackis 2 ms, τreleaseis 50 ms, and the look-ahead delay is 3 ms. In one embodiment, τattack, τrelease, and the look-ahead delay have different values for different implementations.

FIG. 8is an example graph440comparing displacement when only the limiter is enabled with displacement when the limiter is not enabled, in accordance with an embodiment. A horizontal axis of the graph440represents an estimated displacement of one or more moving components of a speaker driver65of a loudspeaker device60in dB mm. A vertical axis of the graph440represents an actual displacement of the one or more moving components of the speaker driver65in dB mm. The graph440comprises a first curve441representing the actual displacement of the one or more moving components of the speaker driver65when the limiter is not enabled, and a second curve442representing the actual displacement of the one or more moving components of the speaker driver65when only the limiter is enabled. If a predetermined displacement limit xlimis 16.9 dB mm (i.e., 7.0 mm), the system200with the limiter enabled applies an instantaneous gain that limits actual displacement of the one or more moving components of the speaker driver65to substantially about 16.9 dB mm, as shown inFIG. 8.

FIG. 9is an example graph450comparing displacement when both the limiter and the compressor are enabled with displacement when neither the limiter nor the compressor are enabled, in accordance with an embodiment. A horizontal axis of the graph450represents an estimated displacement of one or more moving components of a speaker driver65of a loudspeaker device60in dB mm. A vertical axis of the graph450represents an actual displacement of the one or more moving components of the speaker driver65in dB mm. The graph450comprises a first curve451representing the actual displacement of the one or more moving components of the speaker driver65when neither the limiter nor the compressor are enabled, and a second curve452representing the actual displacement of the one or more moving components of the speaker driver65when both the limiter and the compressor are enabled. If a predetermined displacement limit xlimis 16.9 dB mm (i.e., 7.0 mm), a predetermined displacement compression threshold xthris 12.0 dB mm (i.e., 4.0 mm), a predetermined compression ratio R is 2:1, and a predetermined soft knee width Wkneeis 6 dB, the system200with the limiter and the compressor enabled applies an instantaneous gain that compresses actual displacement of the one or more moving components of the speaker driver65, and then limits the actual displacement to substantially about 16.9 dB mm, as shown inFIG. 9.

FIG. 10is an example flowchart of a process700for limiting energy in a loudspeaker, in accordance with an embodiment. Process block701includes determining a state of a loudspeaker (e.g., loudspeaker device60) based on a physical model of the loudspeaker (e.g., a linear state-space model as shown inFIG. 4Aor a nonlinear state-space model as shown inFIG. 4B) and a source signal for reproduction via the loudspeaker. Process block702includes determining a potential energy in the loudspeaker, a kinetic energy in the loudspeaker, and an electrical energy in the loudspeaker based on the state of the loudspeaker. Process block703includes determining a total energy stored in the loudspeaker based on the potential energy, the kinetic energy, and the electrical energy. Process block704includes determining a maximum potential displacement of a diaphragm of a speaker driver of the loudspeaker based on the total energy. Process block705includes limiting the total energy stored in the loudspeaker by attenuating the source signal, wherein an actual displacement of the diaphragm during the reproduction of the source signal is controlled based on the attenuated source signal.

In one embodiment, one or more components of the energy limiter system200, such as the loudspeaker model unit310, the energy computation unit320, the static gain computation unit330, the temporal gain smoothing unit340, the look-ahead delay unit350, and/or the component360, are configured to perform process blocks701-705.

FIG. 11is a high-level block diagram showing an information processing system comprising a computer system600useful for implementing various disclosed embodiments. The computer system600includes one or more processors601, and can further include an electronic display device602(for displaying video, graphics, text, and other data), a main memory603(e.g., random access memory (RAM)), storage device604(e.g., hard disk drive), removable storage device605(e.g., removable storage drive, removable memory module, a magnetic tape drive, optical disk drive, computer readable medium having stored therein computer software and/or data), user interface device606(e.g., keyboard, touch screen, keypad, pointing device), and a communication interface607(e.g., modem, a network interface (such as an Ethernet card), a communications port, or a PCMCIA slot and card).

The communication interface607allows software and data to be transferred between the computer system600and external devices. The nonlinear controller600further includes a communications infrastructure608(e.g., a communications bus, cross-over bar, or network) to which the aforementioned devices/modules601through607are connected.

Information transferred via the communications interface607may be in the form of signals such as electronic, electromagnetic, optical, or other signals capable of being received by communications interface607, via a communication link that carries signals and may be implemented using wire or cable, fiber optics, a phone line, a cellular phone link, a radio frequency (RF) link, and/or other communication channels. Computer program instructions representing the block diagrams and/or flowcharts herein may be loaded onto a computer, programmable data processing apparatus, or processing devices to cause a series of operations performed thereon to produce a computer implemented process. In one embodiment, processing instructions for process700(FIG. 10) may be stored as program instructions on the memory603, storage device604, and/or the removable storage device605for execution by the processor601.

Embodiments have been described with reference to flowchart illustrations and/or block diagrams of methods, apparatus (systems), and computer program products. In some cases, each block of such illustrations/diagrams, or combinations thereof, can be implemented by computer program instructions. The computer program instructions when provided to a processor produce a machine, such that the instructions, which executed via the processor create means for implementing the functions/operations specified in the flowchart and/or block diagram. Each block in the flowchart/block diagrams may represent a hardware and/or software module or logic. In alternative implementations, the functions noted in the blocks may occur out of the order noted in the figures, concurrently, etc.

The terms “computer program medium,” “computer usable medium,” “computer readable medium,” and “computer program product,” are used to generally refer to media such as main memory, secondary memory, removable storage drive, a hard disk installed in hard disk drive, and signals. These computer program products are means for providing software to the computer system. The computer readable medium allows the computer system to read data, instructions, messages or message packets, and other computer readable information from the computer readable medium. The computer readable medium, for example, may include non-volatile memory, such as a floppy disk, ROM, flash memory, disk drive memory, a CD-ROM, and other permanent storage. It is useful, for example, for transporting information, such as data and computer instructions, between computer systems. Computer program instructions may be stored in a computer readable medium that can direct a computer, other programmable data processing apparatuses, or other devices to function in a particular manner, such that the instructions stored in the computer readable medium produce an article of manufacture including instructions which implement the function/act specified in the flowchart and/or block diagram block(s).

In some cases, aspects of one or more embodiments are described above with reference to flowchart illustrations and/or block diagrams of methods, apparatuses (systems), and computer program products. In some instances, it will be understood that each block of the flowchart illustrations and/or block diagrams, and combinations of blocks in the flowchart illustrations and/or block diagrams, can be implemented by computer program instructions. These computer program instructions may be provided to a special purpose computer, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means for implementing the functions/acts specified in the flowchart and/or block diagram block(s).

The corresponding structures, materials, acts, and equivalents of all means or step plus function elements in the claims below are intended to include any structure, material, or act for performing the function in combination with other claimed elements as specifically claimed. The description of the embodiments has been presented for purposes of illustration and description, but is not intended to be exhaustive or limited to the embodiments in the form disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the invention.