Patent Grant
9374634
This disclosure generally relates to loudspeaker systems.
One cause of loudspeaker failures is a mechanical defect that arises when the loudspeaker diaphragm is displaced beyond a certain limit. Such limits are often specified by the loudspeaker manufacturer. Going beyond this displacement limit either damages the loudspeaker immediately, or can considerably reduce its expected lifespan. Some systems limit the displacement of the loudspeaker diaphragm, for example, by analyzing and adjusting an input audio signal with variable cutoff filters (high-pass or other), a gain stage, or a dynamic range compression module, based on various parameters of the audio signal. For instance, loudspeaker characteristics may be modeled to map displacement of a loudspeaker relative to amplitude of an input signal. The model predicts the displacement of the loudspeaker, also referred to as cone excursion, which can be linear or non-linear. The control system can be used for loudspeaker protection, as mentioned above, as well as linearization of the loudspeaker output. The input signal is typically pre-processed in such a way that the amplitude of an input audio signal is kept below a specified amplitude.
Various example embodiments are directed to circuits and methods for controlling displacement of a loudspeaker in an enclosure. In an example embodiment, an apparatus includes an enclosure having a loudspeaker mounted therein. The apparatus also includes an IC package mounted inside the enclosure. The IC package includes an amplifier configured to amplify an input audio signal, received at an input of the amplifier, to produce a drive signal. The amplifier is configured to drive the loudspeaker with the drive signal, via an output of the amplifier. The IC package also includes a pressure sensor configured to output a status signal, indicative of a sound pressure level inside the enclosure, from an output terminal of the pressure sensor. The apparatus also includes an audio processing circuit connected to the amplifier and configured to adjust the strength of the drive signal produced by the amplifier as a function of the sound pressure level indicated by the status signal.
A method is also disclosed for controlling displacement of a loudspeaker in an enclosure. An input audio signal is amplified, using an amplifier in an IC package mounted inside the enclosure, to generate a drive signal. The loudspeaker is driven with the drive signal. A pressure level inside the enclosure is measured using a pressure sensor in the IC. The strength of the drive signal is adjusted as a function of the measured pressure level.
The above discussion/summary is not intended to describe each embodiment or every implementation of the present disclosure. The figures and detailed description that follow also exemplify various embodiments.
Various example embodiments may be more completely understood in consideration of the following detailed description in connection with the accompanying drawings, in which:
While various embodiments discussed herein are amenable to modifications and alternative forms, aspects thereof have been shown by way of example in the drawings and will be described in detail. It should be understood, however, that the intention is not to limit the invention to the particular embodiments described. On the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the scope of the disclosure including aspects defined in the claims. In addition, the term “example” as used throughout this application is only by way of illustration, and not limitation.
Aspects of the present disclosure are believed to be applicable to a variety of different types of apparatuses, systems and methods for controlling a loudspeaker in an enclosure. While not necessarily so limited, various aspects may be appreciated through a discussion of examples using this context.
In some embodiments, an IC package and a loudspeaker are mounted in an enclosure. The IC package includes an amplifier configured to amplify an input audio signal, received at an input of the amplifier, to produce a drive signal. The amplifier is configured to drive the loudspeaker with the drive signal via an output of the amplifier. The IC package also includes a pressure sensor configured to output a status signal, indicative of a sound pressure level inside the enclosure, from an output terminal of the pressure sensor. The apparatus also includes an audio processing circuit, which is connected to the amplifier and configured to adjust strength of the drive signal produced by the amplifier as a function of the sound pressure level indicated by the status signal.
In some embodiments, the gain control signal is configured to adjust the strength of the drive signal, based on the sound pressure level, to prevent the displacement of the loudspeaker from exceeding a threshold displacement. For example, the audio processing circuit may determine a displacement of the loudspeaker from the measured sound pressure level and adjust the strength of the drive signal, based on the determined displacement of the loudspeaker, to prevent the displacement of the loudspeaker from exceeding a threshold displacement. The threshold displacement may be set, for example, to be equal to a maximum safe displacement specified by the manufacturer of the loudspeaker.
The pressure sensor may be implemented using various devices sensitive to variations in atmospheric pressure, such as microphones or piezo-resistive pressure sensors. For ease of explanation, the examples may be discussed primarily with reference to a pressure sensor implemented using a micro-electro-mechanical system (MEMS) microphone. In some embodiments, the pressure sensor may be implemented using lower sensitivity microphones, which are insensitive to a portion of the audible frequency range. In some embodiments, the pressure sensor may only be sensitive to frequencies at which extreme displacement may occur (e.g., around the resonant frequency of the loudspeaker). For example, the pressure sensor may only be sensitive to a relatively small frequency band, spanning approximately 4 kHz.
Similarly, in some implementations, the pressure sensor may only be sensitive to pressure levels at which extreme displacement may occur. In some applications, the pressure sensor may be insensitive to a range of sound pressure levels up to approximately 20 decibels below a sound pressure level corresponding to a maximum rated displacement of the loudspeaker (e.g., 150 decibels). For example, in one application the pressure sensor may be insensitive to sound pressure levels below 100 decibels.
Off the shelf microphones may not be capable of measuring pressures at which extreme displacement of the loudspeaker may occur. For example, a signal generated by an of the shelf microphone may become saturated before pressures characteristic of extreme displacement are reached. Moreover, off the shelf microphones may be damaged by pressures at which extreme displacement of the loudspeaker may occur. In some embodiments, the pressure sensor is implemented using a microphone, configured and arranged to operate at sound pressure levels greater than 120 decibels.
In some embodiments, the pressure sensor may be configured to measure one or both of an alternating current (AC) variation in the pressure and a DC offset of the pressure, relative to a resting state of the loudspeaker. In contrast, off the shelf microphones are not configured to measure DC offset of sound pressure. The audio processing circuit may be configured to adjust the drive signal, based on measured DC bias of the pressure, to remove a DC offset of the drive signal.
The audio processing circuit may adjust the drive signal using various control mechanisms. In some implementations, the audio processing circuit is configured to adjust strength of the drive signal produced by the amplifier by adjusting a gain setting of the amplifier via a control signal. Alternatively or additionally, the audio processing circuit is configured to adjust the strength of the drive signal by adjusting the strength of the audio signal that is input to the amplifier and used to derive the drive signal.
In various embodiments, the pressure sensor and the amplifier are included in the IC package mounted inside the enclosure. In some embodiments, the audio processing circuit is in a separate IC package mounted outside of the enclosure. In some other embodiments, the audio processing circuit, the pressure sensor, and the amplifier are all located in the IC package mounted inside the enclosure.
Turning now to the figures,
In a sealed speaker enclosure, acoustic pressure inside of the enclosure changes proportionally to changes in the volume of the enclosure, caused by displacement of the loudspeaker. Assuming acoustic pressure to be constant throughout the enclosure, acoustic pressure P(t) is determined by:
where V0 is the volume when the diaphragm is in its rest position, ρ is the density of air and c is the speed of sound. The volume change is caused by a displacement x(t) of the loudspeaker, with respect to a resting position (an outward displacement corresponds to a positive displacement), as determined by:
ΔV(t)=x(t)Sd
where Sd is the effective diaphragm radiating area. Accordingly,
When the loudspeaker 160 in
In some embodiments, the audio processing circuit 130 is configured to adjust amplitude of the drive signal 152, based on the indicated pressure level, to prevent displacement of the loudspeaker 160 from exceeding a threshold displacement. In some implementations, the audio processing circuit 130 may adjust the amplitude of the drive signal 152 by adjusting a gain of the amplifier 150 via a control signal 136. In some other implementations, audio processing circuit 130 may adjust the amplitude of the drive signal 152 by adjusting an amplitude of the audio signal 134 provided to the amplifier 1150. For example, the audio processing circuit 130 may amplify′ an input audio signal 132, with a gain setting selected as a function of the status signal 142, to produce the audio signal 134 provided to the amplifier 150 in the IC package. The audio processing circuit may adjust the drive signal using various signal processing functions including, for example, limiters, compressors, and/or band pass filters. In some other applications, the audio processing circuit 130 may adjust the drive signal based on the indicated pressure level, to reduce distortion exhibited by the system. For instance, for a smartphone application, the audio processing circuit 130 may be configured to use the status signal 142 for acoustic echo cancellation (AEC).
The pressure sensor 140 may be implemented using various sensors, such as microphones, which are sensitive to variations in air pressure. Microphone are generally manufactured as separate components that may be used in various applications. To increase the applications for which microphones may be used, they are generally designed to accurately sense sound without distortion within frequency and amplitude ranges audible by most people. However, such accuracy is not required for some embodiments. For instance, a loudspeaker may only be subject to damage from extreme displacement within a small range of frequencies and/or amplitudes. In some embodiments, the pressure sensor is implemented using a lower accuracy microphone that is only responsive to a sub-set of audible frequency and amplitude ranges. For example, in some implementations, the microphone is insensitive to sound pressure levels below 100 decibels. As another example, the microphone may only be sensitive to frequencies at which extreme displacement may occur. In some implementations, the microphone may only be sensitive to a relatively small frequency band spanning approximately 4 kHz. Some types of microphones may not be operable at pressure levels at which the loudspeaker may become damaged. In some embodiments, the pressure sensor is implemented using a high durability microphone configured to operate at sound pressure levels greater than 120 decibels.
By using microphone that are less sensitive and/or that have a smaller frequency range of operation, manufacturing costs for the pressure sensor and system may be reduced. Manufacturing costs are also reduced by implementing the pressure sensor 140 and amplifier 150 in the same IC package. Even though the pressure sensor is not connected to or used by the amplifier in the IC package, by placing these components in the same IC package both of these devices can be mounted in the speaker enclosure 110 at the same time.
During operation of the loudspeaker 160, a diaphragm of the loud speaker is displaced outward and inward according to the drive signal 152. The outward and inward displacement creates variation in the pressure inside the enclosure 110, which can be modeled as an AC signal that is proportional to the drive signal. However, outward displacement of the loudspeaker 160 is not necessarily the same as the inward displacement of the loudspeaker. For instance, a direct current (DC) bias in the drive signal 152 may cause outward and inward displacements to be unequal, which may produce audible distortion or result in damage to the loudspeaker. In some embodiments, the status signal 142 output by the pressure sensor 140 includes an AC component indicative of variation in pressure inside the enclosure and a DC component indicative of a bias of the pressure inside the enclosure relative to a pressure exhibited inside the enclosure when the loudspeaker is at rest. In some implementations, the audio processing circuit 130 is configured to adjust the drive signal 152 to remove a DC offset of the drive signal based on the direct current component of the status signal. In some implementations, the pressure sensor 140 includes a single sensor configured to provide both AC and DC components of the status signal 142. In some other implementations, pressure sensor 140 includes a first sensor (not shown) configured to provide the AC component and a second sensor (not shown) configured to provide the DC component.
In this example, the audio processing circuit 330, the pressure sensor 340, and the amplifier 350 are included in the same IC package 320, which is mounted inside the enclosure. Incorporating the audio processing circuit 330, the pressure sensor 340, and the amplifier 350 in the same IC package 320 may reduce the size of the system, which may be preferred for some compact applications.
The IC package may include various numbers of substrates upon which the audio processing circuit 330, the pressure sensor 340, and the amplifier 350 may be placed. In some implementations, the audio processing circuit 330, the pressure sensor 340, and the amplifier 350 are placed on respective substrates in the IC package. In some other implementations, the audio processing circuit 330, the pressure sensor 340, and the amplifier 350 are placed on the same substrate.
Various blocks, modules or other circuits may be implemented to carry out one or more of the operations and activities described herein and/or shown in the figures. In these contexts, a “block” (also sometimes “logic circuitry” or “module”) is a circuit that carries out one or more of these or related operations/activities (e.g., gain control or amplification). For example, in certain of the above-discussed embodiments, one or more modules are discrete logic circuits or programmable logic circuits configured and arranged for implementing these operations/activities, as in the circuit modules shown in
Certain embodiments are directed to a computer program product (e.g., nonvolatile memory device), which includes a machine or computer-readable medium having stored thereon instructions which may be executed by a computer (or other electronic device) to perform these operations/activities.
Based upon the above discussion and illustrations, those skilled in the art will readily recognize that various modifications and changes may be made to the various embodiments without strictly following the exemplary embodiments and applications illustrated and described herein. For example, though aspects and features may in some cases be described in individual figures, it will be appreciated that features from one figure can be combined with features of another figure even though the combination is not explicitly shown or explicitly described as a combination. Such modifications do not depart from the true spirit and scope of various aspects of the invention, including aspects set forth in the claims.
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