Loudspeaker module and system

Abstract

There is provided a speaker module for generating a bass frequency sound, comprising: a speaker frame; a diaphragm suspended on the speaker frame; a driving unit for moving the diaphragm along a movement axis of the speaker module to generate sound from the first and second radiating surfaces of the diaphragm; the first radiating surface and the second radiating surface are arranged on opposite sides of the vibrating diaphragm; wherein the driving unit comprises a magnet unit used for generating magnetic flux across an air gap and a voice coil located in the air gap when the vibrating diaphragm is static; and a housing for receiving sound generated by the second radiating surface of the diaphragm; wherein when the vibrating diaphragm is static, the total quality factor Qtc of the loudspeaker module is at least 1.8; and wherein, when the diaphragm is stationary, a magnetic flux density at the first periphery of the voice coil is 50% or less of a magnetic flux density at the second periphery of the voice coil.

Description

Speaker modules and systems

[0001] This application claims priority to application number GB2314915.6, filed on September 28, 2023. Technical Field

[0002] The present invention relates to a speaker module for generating low-frequency sound and a speaker system including the speaker module. Background Technology

[0003] Traditional loudspeakers typically include a diaphragm that can be moved by an electrically driven unit. The drive unit consists of a magnet unit and a voice coil, which interact magnetically during use to move the diaphragm (which acts like a piston) to produce sound.

[0004] To produce optimal sound quality, loudspeakers are carefully designed to meet certain design parameters, including damping of diaphragm movement. This damping is caused by the back electromotive force generated by the mechanically suspended acoustic elements and the electrically driven unit. Furthermore, for loudspeakers housed in an enclosure, the airtight acoustic suspension behind the diaphragm also affects damping and thus the loudspeaker's response.

[0005] The damping of a loudspeaker within its cabinet can be quantified using the so-called total quality factor (Qtc). The Qtc of a loudspeaker within its cabinet is a dimensionless parameter defined as the ratio of initial energy to energy lost per cycle. Therefore, greater energy dissipation during movement implies a lower Qtc, while less energy dissipation implies a higher Qtc. The consensus in the art is that a Qtc value between 0.5 and 1.2 is generally acceptable, with at least some in the art considering a value of 0.707 particularly ideal, as it produces the flattest roll-off. In contrast, a Qtc exceeding the 0.5 to 1.2 range is considered undesirable. It is noteworthy that values ​​greater than 1.2 can lead to "ringing" at resonance, meaning that the duration of continuous diaphragm movement is quite long. In low-frequency reproduction, "ringing" is referred to as "booming" bass.

[0006] Increasing the signal level, i.e., driving the speaker at a higher output volume (corresponding to a larger displacement of the driver unit), will lead to an increase in the overall quality factor (Qtc). Therefore, for large signals, it is important to consider the Qtc to avoid a decrease in audio reproduction quality at high output volumes, such as the "ringing" effect mentioned earlier during resonance. A typical goal is to provide "tight" bass reproduction.

[0007] This invention is designed based on the above considerations. Summary of the Invention

[0008] The inventors observed that as long as the magnetic flux density in the air gap decreases relatively sharply across the voice coil, the loudspeaker module with the electric drive unit can be operated to compensate for a relatively large total quality factor Qtc.

[0009] According to the present invention, a loudspeaker module for generating low-frequency sound is provided, the loudspeaker module comprising: a loudspeaker frame; a diaphragm suspended on the loudspeaker frame; a drive unit configured to move the diaphragm along a movement axis of the loudspeaker module to generate sound from a first radiating surface and a second radiating surface of the diaphragm, wherein the first radiating surface and the second radiating surface are on opposite sides of the diaphragm; wherein the drive unit includes a magnet unit for generating magnetic flux across an air gap and a voice coil configured to be located in the air gap when the diaphragm is stationary; and a housing arranged to receive sound generated by the second radiating surface of the diaphragm; wherein, when the diaphragm is stationary, the total quality factor Qtc of the loudspeaker module is at least 1.8; and wherein, when the diaphragm is stationary, the magnetic flux density at a first periphery of the voice coil is 50% or less of the magnetic flux density at a second periphery of the voice coil.

[0010] In this combination, a large overall quality factor (Qtc) and a significant decrease in flux density across the voice coil (at least 50%) provide a speaker module operable to conveniently control at least some sonic characteristics, such as achieving tighter or warmer bass (e.g., according to user preference) by appropriately adjusting the input signal fed to the driver unit of the speaker module (e.g., by using suitable feedforward filtering). Furthermore, the relatively large Qtc means the speaker module is "underdamped," thus requiring less resistance to operate compared to conventional speakers. Consequently, for a given output volume, less power is needed to move the diaphragm compared to a lower Qtc.

[0011] The speaker module is operable to energize the drive unit, causing the diaphragm to move relative to the speaker frame along the moving axis of the speaker module to produce sound.

[0012] The diaphragm can be moved along the axis of motion to its nominal maximum displacement position. This nominal maximum displacement corresponds to the expected maximum output volume. In some examples, the nominal maximum displacement can be a position along the axis of motion where the force factor BL is half that when the diaphragm is stationary in the air gap. The force factor BL is defined as the product of the magnetic flux density B through the voice coil and the total length L of the voice coil winding, and quantifies the strength of the magnetic interaction between the magnet unit and the voice coil.

[0013] The drive unit may include a movable part connected to the diaphragm and a stationary part connected to the speaker frame. The speaker module is operable such that the movable part and the stationary part interact magnetically, allowing the movable part to move along a movement axis. Therefore, the movable assembly (which may include the movable part of the drive unit and the diaphragm) can move along the movement axis of the speaker module to generate sound. The movable assembly may also be referred to as a "moving" assembly.

[0014] The terms "stationary" and "movable" are relative terms, depending in principle on the specific reference frame. In this context, the terms "stationary" and "movable" refer to a conventional reference frame in which the diaphragm is considered movable and, in use, moves, while other components of the loudspeaker module are considered stationary. Therefore, those components in the loudspeaker module that move with the diaphragm during use, such as the movable parts of the driver unit, are called movable parts; while those components in the loudspeaker module that do not move with the diaphragm during use (and may be stationary relative to external devices attached to the loudspeaker module) are called stationary parts, such as the stationary parts of the driver unit. The movable parts in the loudspeaker module, i.e., the diaphragm and the parts that move with the diaphragm during use, can be collectively referred to as movable components.

[0015] The magnet unit of the drive unit may be included in one of the stationary part and the movable part, while the voice coil may be included in the other of the stationary part and the movable part. When the drive unit is energized (e.g., by providing a time-varying current to the voice coil), the movable part and the stationary part of the drive unit may interact magnetically, causing the movable part to move relative to the stationary part.

[0016] In some examples (referred to herein as "movable voice coil" examples), the movable part of the drive unit can be a voice coil, and the stationary part of the drive unit can be a magnet unit. In these examples, when the drive unit is energized, the magnetic flux generated by the current flow in the (movable) voice coil may interact with the magnetic flux generated by the (fixed) magnet unit of the drive unit, causing the movable part (i.e., the voice coil) to move relative to the stationary part (i.e., the magnet unit).

[0017] In other examples (referred to herein as the "movable magnet unit" example), the movable part of the drive unit can be a magnet unit, and the stationary part of the drive unit can be a voice coil. In these examples, when the drive unit is energized, the magnetic flux generated by the current flowing in the (fixed) voice coil may interact with the magnetic flux generated by the (movable) magnet unit of the drive unit, causing the movable part (i.e., the magnet unit) to move relative to the stationary part (i.e., the voice coil).

[0018] Magnetic flux density can be radial magnetic flux density. Radial magnetic flux density can be measured along the radial direction, which is perpendicular to the axis of movement.

[0019] The distance between the inner and outer circumferences of the voice coil, measured radially, can be used as the winding thickness of the voice coil. Therefore, the magnetic flux density passing through the voice coil may decrease by at least 50% with respect to the winding thickness.

[0020] If the voice coil is roughly circular, then the inner circumference of the voice coil can be called the inner diameter of the voice coil, and the outer circumference of the voice coil can be called the outer diameter of the voice coil.

[0021] As mentioned above, the overall quality factor (Qtc) is a parameter known to those skilled in the art; therefore, the Qtc value of the loudspeaker module when the diaphragm is at rest can be determined by those skilled in the art using known methods. For example, the overall quality factor Qtc can be determined by computer simulation of the loudspeaker module or based on physical measurements of the loudspeaker module (see, for example, RH Small, “Closed-Box Loudspeaker Systems, Part I: Analysis”, J. Audio Eng. Soc., Vol. 20, pp. 798-808 (December 1972)). Physical measurements of the overall quality factor Qtc may involve, for example, a distortion analyzer or optical devices used to measure the position of the diaphragm along the axis of movement when the loudspeaker module is in operation. For example, see W. Klippel and U. Seidel, “Fast and Accurate Measurement of Linear Transducer Parameters,” presented at the 110th Convention of the Audio Engineering Society, Amsterdam, May 12–15, 2001, preprint 5308; or W. Klippel, “Distortion Analyzer - a New Tool for Assessing and Improving Electrodynamic Transducers,” presented at the 108th Convention of the Audio Engineering Society, Paris, February 19–22, 2000, preprint 5109.

[0022] The total quality factor Qtc when the diaphragm is at rest is a small-signal parameter. Small-signal parameters are a concept known in the art, describing operating parameters under small input signals (e.g., see V. Dickason, Loudspeaker Design Cookbook, 7th edition, KCP Media Corp., 2006; RH Small, “Closed-Box Loudspeaker Systems, Part I: Analysis,” J. Audio Eng. Soc., Vol. 20, pp. 798–808 (December 1972)). Therefore, a physical measurement of the total quality factor Qtc when the diaphragm is at rest can be performed when the loudspeaker module is operating at a small voltage, causing a small displacement of the diaphragm, or by any other suitable method known to those skilled in the art.

[0023] When the diaphragm is at rest, the overall quality factor Qtc of the speaker module can be at least 2.0, and optionally at least 2.5.

[0024] When the diaphragm is at rest, the overall quality factor (Qtc) of the speaker module can be up to 10, with an optional maximum of 5.

[0025] The total quality factor Qtc may have a first value when the diaphragm is at rest and a second value when the diaphragm is at its nominal maximum displacement. The second value may be up to 3 times the first value; alternatively, it may be up to 2.5 times the first value; alternatively, it may be up to 2 times the first value; alternatively, it may be up to 1.5 times the first value; and alternatively, it may be up to 1.25 times the first value. The second value is at least 1.00 times the first value.

[0026] At nominal maximum displacement, the overall quality factor (Qtc) can be up to three times that at rest, potentially reducing distortion across the entire output volume range, especially at high output volumes, compared to conventional speaker modules. For conventional speaker modules, the overall quality factor (Qtc) can increase significantly with increasing output volume. For example, the overall quality factor (Qtc) of a conventional speaker at nominal maximum displacement might be seven times that at rest. Therefore, for conventional speakers, significant distortion in sound reproduction can occur across the entire output volume range, especially at high output volumes.

[0027] Qts is used to indicate the overall quality factor of a loudspeaker without a cabinet (as opposed to Qtc, which is used to indicate the overall quality factor of a loudspeaker with a cabinet).

[0028] It is known that the overall quality factor Qtc of the speaker module is proportional to the overall quality factor Qts of the speaker, i.e. The overall quality factor Qts of a loudspeaker is known to depend on the electrical quality factor Qes (associated with the driver unit) and the mechanical quality factor Qms (associated with the suspension elements). More specifically, Qts is equal to the product of Qes and Qms divided by the sum of Qes and Qms, i.e. .

[0029] When the diaphragm is stationary in the air gap, the electrical quality factor Qms of the drive unit can be at least 3, and optionally at least 4.

[0030] When the diaphragm is stationary in the air gap, the electrical quality factor Qms of the drive unit can be up to 8, and optionally up to 6.

[0031] When the diaphragm is stationary in the air gap, the electric quality factor Qes of the drive unit can be at least 1.2, and optionally at least 2.0.

[0032] When the diaphragm is stationary in the air gap, the electric quality factor Qes of the drive unit can be up to 2.5, and optionally up to 2.0.

[0033] The loudspeaker module may have a free-air resonant frequency fs, which has a first resonant frequency value when the diaphragm is stationary and a second resonant frequency value when the diaphragm is at its nominal maximum displacement. The second resonant frequency value may be 1.20 times the first resonant frequency value; optionally, it may be up to 1.10 times the first resonant frequency value. The second resonant frequency value may be at least 1.00 times the first resonant frequency value.

[0034] The free-air resonant frequency fs of a loudspeaker module can be considered as the resonant frequency of the loudspeaker module when the cabinet is omitted / removed.

[0035] It is well known that the free-air resonant frequency fs of a loudspeaker may not remain constant across the output volume range, but rather may be higher at higher output volumes. When the diaphragm is at rest, its free-air resonant frequency fs is a small-signal parameter. As mentioned above, small-signal parameters are a known concept in the art, and can be measured when the loudspeaker is operated with a small voltage (i.e., a small output volume). For more information, see, for example, V. Dickason, Loudspeaker Design Cookbook, 7th Edition, KCP Media Corp., 2006.

[0036] Therefore, at nominal maximum displacement, the free-air resonant frequency fs can be up to 20% higher than the resonant frequency fs at rest (for measurements of the free-air resonant frequency at nominal maximum displacement, see, for example, W. Klippel, “Nonlinear Large-Signal Behavior of Electrodynamic Loudspeakers at LowFrequencies,” J. Audio Eng. Soc., Vol. 40, pp. 483–496 (1992). In contrast, for conventional loudspeakers, the free-air resonant frequency fs can increase by up to 50%. Thus, current loudspeakers can provide a free-air resonant frequency fs that is relatively constant within the loudspeaker's normal operating range and the corresponding loudspeaker module's normal operating range. A relatively constant free-air resonant frequency fs within the loudspeaker's normal operating range helps improve audio reproduction across output volumes and can potentially provide reduced power consumption because the resonant frequency fs of current loudspeaker modules can more closely match the spectral power density of the audio content across output volumes.

[0037] Those skilled in the art will understand that the choice of suspension may affect the degree to which the resonant frequency fs of the speaker varies within the speaker's normal operating range. Furthermore, those skilled in the art will be able to select a suitable suspension without significantly altering the resonant frequency fs. Examples of suitable suspensions can be found in GB2212935.7 and PCT / EP2023 / 073013.

[0038] The speaker's free-air resonant frequency fs may be in the range of 20Hz to 100Hz (Hz), and optionally 40Hz to 80Hz when the diaphragm is at rest.

[0039] The resonant frequency fc of the loudspeaker module, also known as the resonant frequency within the enclosure (because it is the resonant frequency when the enclosure is present), is known to be proportional to the loudspeaker's free-air resonant frequency fs, i.e. The resonant frequency fc of the loudspeaker module is higher than the free air resonant frequency fs.

[0040] The resonant frequency fc of the loudspeaker module may have a first resonant frequency value when the diaphragm is at rest, and a second resonant frequency value when the diaphragm is at its nominal maximum displacement. The second resonant frequency value may be up to 1.20 times the first resonant frequency value; optionally, up to 1.10 times the first resonant frequency value. The second resonant frequency value may be at least 1.00 times the first resonant frequency value.

[0041] The resonant frequency fc of the speaker module can be in the range of 28Hz to 160Hz, optionally in the range of 30Hz to 100Hz, and optionally in the range of 40Hz to 80Hz.

[0042] A speaker module (potentially a subwoofer) is configured to produce bass-frequency sound. The bass frequency can be within a bass frequency range that can include 60 Hz to 80 Hz, more preferably 40 Hz to 100 Hz. By way of example, the bass frequency range could be 20 Hz to 100 Hz.

[0043] The loudspeaker module may have a force factor BL, which has a first BL value when the diaphragm is at rest and a second BL value when the diaphragm is at its nominal maximum displacement. The second BL value may be at least 0.5 times the first BL value.

[0044] The force factor BL at maximum nominal displacement is at least 0.5 times the force factor BL at rest, which means that the motor force drops to at least 50% of the value at rest. Therefore, even at the nominal maximum displacement, the drive unit can be ensured to have full control over the diaphragm movement, whereas in traditional speaker modules, the diaphragm may move to a position that the drive unit cannot fully control, in which case control is mainly performed by the suspension.

[0045] Furthermore, a force factor BL dropping to at least 50% of its resting value implies a relatively uniform magnetic flux density, as in conventional loudspeakers, the force factor BL might drop to 15%. This relatively uniform magnetic flux density ensures a relatively constant electrical quality factor across the output volume compared to conventional loudspeakers.

[0046] The enclosure stiffness of the speaker module may be Kb. The enclosure stiffness Kb can be calculated as follows:

[0047]

[0048] in, It is air density; It is the speed of sound in the air; It is the effective radiating area of ​​the loudspeaker; and It is the acoustic volume enclosed by the enclosure.

[0049] The drive stiffness of a loudspeaker module may be Kms. The drive stiffness Kms is a known parameter that quantifies the mechanical stiffness of the loudspeaker suspension based on Thiele-Small parameter measurements, as described in RH Small, “Closed-Box Loudspeaker Systems, Part I: Analysis,” J. Audio Eng. Soc., Vol. 20, pp. 798–808 (December 1972). The drive stiffness Kms can be measured using a distortion analyzer (see, for example, W. Klippel, “Distortion Analyzer - a New Tool for Assessing and Improving Electrodynamic Transducers,” published at the 108th Convention of the Audio Engineering Society, Paris, February 19–22, 2000, preprint 5109). The ratio of the drive stiffness Kms to the housing stiffness Kb is known and used to quantify the stiffness acting on the moving component. When the stiffness of the housing Kb is greater than the stiffness of the actuator Kms, that is, the ratio of the stiffness of the actuator Kms to the stiffness of the housing Kb is less than 0.5, the stiffness of the housing Kb is considered to be dominant.

[0050] The ratio of the actuator stiffness Kms to the housing stiffness Kb can be at least 0.25, and can be up to 0.75, and optionally up to 0.5. Therefore, the actuator stiffness Kms may be one-quarter to three-quarters (optionally one-half) of the housing stiffness Kb provided by the air volume Sd acting on the diaphragm.

[0051] The mass of the movable part of the drive unit is at least 60%, more preferably 70%, of the mass of the movable component. That is, the movable part of the drive unit may have a first mass, the movable component may have a second mass, and the first mass may be at least 60% (preferably 70%) of the second mass.

[0052] In this context, the movable component of the drive unit can be understood as including only the component that magnetically interacts with the stationary component of the drive unit when the drive unit is energized. Therefore, in the "movable voice coil" example (see above), the movable component of the drive unit may consist only of the voice coil (in some examples, it may be considered as consisting only of the metal wire of the voice coil). Similarly, in the "movable magnet unit" example (see above), the movable component of the drive unit may consist only of the magnet unit (e.g., only the permanent magnet and flux guiding element of the magnet unit).

[0053] The mass of the movable part of the drive unit is at least 60%, more preferably 70%, of the mass of the movable component, which may mean that an unusually large proportion of the mass of the movable component is due to the movable part of the drive unit.

[0054] The inventors have observed that by mounting the speaker modules onto a heavy object (e.g., 100 kg or more), the force caused by the relatively large mass of the movable components can be absorbed; or, when a pair of speaker modules are mounted back-to-back, this force can be counteracted, thereby achieving good sound performance. The ratio of the mass of the movable components to the effective radiating area Sd of the diaphragm can be at least 5 kg per square meter, and optionally at least 7 kg per square meter. The ratio of the mass of the movable components to the effective radiating area Sd of the diaphragm can be at most 20 kg per square meter, optionally at most 15 kg per square meter, and optionally at most 12 kg per square meter.

[0055] For example, the ratio of the mass of the movable component to the effective radiation area Sd of the diaphragm can be in the range of 5 to 20 kg per square meter, optionally in the range of 5 to 15 kg per square meter, or optionally in the range of 7 to 12 kg per square meter.

[0056] This proportion, especially when combined with the fact that the mass of the movable part of the drive unit is at least 60% (more preferably 70%) of the mass of the movable assembly, can represent a compact yet heavy movable assembly. Such a movable assembly may generate a large force during use, but as mentioned above, the inventors have observed that this force can be absorbed by mounting the speaker module onto a heavy object (e.g., more than 100 kg); or, when a pair of speaker modules are mounted back-to-back, this force can be counteracted, thereby achieving good sound performance (despite the presence of a large force).

[0057] The effective radiating area Sd is a concept known in the art. For a circular diaphragm, the effective radiating area Sd is quantified using the half-roll-to-half-roll diameter, and therefore the suspension contributes to the effective radiating area Sd. Especially for loudspeakers with relatively small diaphragms, the contribution of the suspension to the effective radiating area Sd may be non-negligible. For a diaphragm with a circular perimeter, suspended from the loudspeaker frame by a roll-shaped suspension with an outer diameter of do ("d_o") and an inner diameter of di ("d_i"), the effective radiating area of ​​this diaphragm can be estimated as Sd. ("Sd equals pi multiplied by the square of d divided by the square of 2"), where d is half the diameter of the coiled suspension, (d o + d i ) / 2 ("d_o d_i divided by 2").

[0058] In other examples, the effective radiating area Sd of the diaphragm can be measured using known techniques, for example, see Klippel GmbH's "Dynamical Measurement of the Effective Radiating Area SD" (…). https: / / www.klippel.de / fileadmin / klippel / Files / Know_How / Application_Notes / AN_32_ Effective_Radiation_Area.pdf ).

[0059] The ratio of the mass of the movable part of the drive unit to the indicated effective radiation area Sd of the diaphragm can provide a relatively heavy movable part compared to the effective sound radiation area Sd, and thus provide a relatively powerful drive unit and a relatively low resonant frequency.

[0060] The loudspeaker module is operable to displace the volume VD of the diaphragm. The volume VD of diaphragm displacement can be defined as the volume of air displaced when the diaphragm moves from its rest position in the air gap to its nominal maximum displacement position. Therefore, when the diaphragm moves from the nominal maximum displacement inward to the nominal maximum displacement outward or vice versa, the diaphragm is displaced by twice the volume VD, i.e., the peak-to-peak travel.

[0061] A loudspeaker module, particularly its enclosure, encloses an acoustically effective volume VB. The acoustically effective volume VB (hereinafter referred to as volume VB) is a concept known in the art (see, for example, LL Beranek, Acoustics, McGraw-Hill, 1954). It is known that the volume VB is not the purely structural volume enclosed by the enclosure, but rather a volume VB that can be increased by filling the structural volume (e.g., by stuffing with wool), typically by up to 20%, and in some cases by up to 40%.

[0062] The volume VD of diaphragm displacement can be at least 0.05 times (5% of the volume VB) of the enclosure, meaning the ratio of VD to VB is greater than 0.05. This can result in a speaker module with a relatively large diaphragm and a relatively small volume.

[0063] When a loudspeaker module includes multiple loudspeakers sharing the same volume VB, the air volume VD displaced by the multiple loudspeakers can be at least 5% of the volume VB.

[0064] The ratio of the enclosure volume VB to the effective radiation Sd can range from 0.01 m to 0.5 m. This ratio of VB to Sd can provide an alternative parameter variable for a relatively large diaphragm and a relatively small volume.

[0065] According to a second aspect, a loudspeaker system is provided, including the loudspeaker module as described above. The loudspeaker system also includes a signal processor, such as an infinite impulse response filter, configured to adjust the electrical signal to be supplied to the voice coil of the loudspeaker module. For example, the signal processor can be configured to perform frequency-dependent adjustment of the electrical signal, thereby providing feedforward filtering of the electrical signal; for example, the signal processor can apply different gains at different frequencies.

[0066] Feedforward filtering for modifying the frequency response of loudspeaker modules is well known and has been discussed, for example in “Active control of loudspeakers: An investigation of practical applications” (Bright et al, 2002, Chapter 3, https: / / core.ac.uk / download / pdf / 13746312.pdf).

[0067] The inventors have discovered that combining a speaker module according to the first aspect with a signal processor configured to provide feedforward filtering of the electrical signal supplied to the voice coil of the speaker module can provide remarkably good subjective sound quality (e.g., tight bass or warm bass according to user preference), despite the speaker module's relatively high overall quality factor (Qtc) (which is generally considered to lead to worse sound quality). Without wishing to be bound by theory, it is believed that this useful result is achieved because the speaker module's high Qtc provides a flatter Qtc curve, making it easier to apply feedforward filtering, as will be discussed in more detail below with reference to the figures.

[0068] It can be observed here that the relatively large overall quality factor (Qtc) of the loudspeaker module according to the first aspect of the invention affects the time response of the loudspeaker module. Given that the time response of a loudspeaker module with a large Qtc is generally considered undesirable, the inventors have discovered that appropriate frequency-dependent adjustments to the electrical signal can be made to compensate for this undesirable time response.

[0069] The signal processor can be configured to reduce group delay at and near the resonant frequency of the speaker module.

[0070] The signal processor can be user-configurable between performing a first frequency-dependent adjustment and a second frequency-dependent adjustment on the electrical signal. The first and second frequency-dependent adjustments can correspond to different user preferences, such as "tighter" bass and "warmer" bass, respectively.

[0071] A loudspeaker module may include one or more suspension elements, wherein the diaphragm is suspended from the loudspeaker frame by one or more suspension elements. Preferably, the loudspeaker module includes at least two suspension elements.

[0072] One or more suspension elements may include a first suspension element (e.g., a surround element (also known as a roll-up suspension)) attached to a first landing surface of the speaker frame. The first suspension element may be attached directly or indirectly to the diaphragm. In some examples, the first suspension element may be (directly) attached to the outer edge of the diaphragm. In other examples, the first suspension element may be attached to another element of the movable assembly.

[0073] One or more suspension elements may include a second suspension element (e.g., a damper) attached to the speaker frame at a second landing surface of the speaker frame. The second suspension element may be attached directly or indirectly to the diaphragm. In some examples, the second suspension element may be (directly) attached to the diaphragm at a location inside the outer edge of the diaphragm. In other examples, the second suspension element may be attached to another element of a movable assembly (e.g., a movable part of a drive unit, particularly when the movable part is a magnet unit).

[0074] The center of gravity of the movable part of the drive unit may be located between the first and second landing surfaces along the axis of movement.

[0075] By positioning the center of gravity of the magnet unit between the first and second landing surfaces, the swaying of the movable components can be suppressed. More specifically, the swaying pattern of the speaker module may exceed the operating frequency range of the speaker module.

[0076] The magnet unit may include a permanent magnet and one or more flux guiding elements for guiding the magnetic flux generated by the permanent magnet in the magnetic circuit and through the air gap, wherein the voice coil is configured to be located in the air gap when the movable part of the drive unit is stationary.

[0077] Here, the mention of the movable parts of the drive unit being stationary, or the diaphragm being stationary, can be considered as corresponding to a state in which the drive unit is not energized (e.g., no current is supplied to the voice coil of the drive unit), where the movable parts of the drive unit and the diaphragm have time to reach a stationary state.

[0078] The magnet unit may include at least two flux guiding elements. The at least two flux guiding elements may be configured to guide the magnetic flux generated by the permanent magnet through an air gap. The air gap may be formed between the at least two flux guiding elements.

[0079] At least two flux guiding elements may include a washer and a yoke. A permanent magnet may be located between the washer and the yoke. The washer and the yoke may be arranged to define an air gap between them.

[0080] The yoke may include a base and a vertical portion extending from the base. In some examples, the yoke may be a U-shaped yoke, where the vertical portion is an annular sidewall. In some examples, the yoke may be a T-shaped yoke, where the vertical portion is a central post.

[0081] Magnetic units can form magnetic circuits. A magnetic circuit provides a essentially closed loop (or circuit) for magnetic flux. Magnetic circuits may have relatively high reluctance. For example, the reluctance of a magnetic circuit may be at least 2.5 x 10^6 [1 / H] or even 3 x 10^6 [1 / H], where "H" represents the physical unit "henry". A large portion of the reluctance of a magnetic circuit can be attributed to the air gap. For example, the reluctance of an air gap may be at least 2 x 10^6 [1 / H].

[0082] Further details regarding the high reluctance magnetic circuit in the loudspeaker background are described in GB2209544.2 and PCT / EP2023 / 067426.

[0083] The voice coil may have a first periphery and a second periphery. The first periphery can be the outer or inner periphery of the voice coil, and the second periphery can be the inner or outer periphery of the voice coil, respectively.

[0084] The distance between the first and second circumferences can be called the winding thickness of the voice coil. Therefore, as mentioned above, the magnetic flux density passing through the voice coil may decrease with the winding thickness of the voice coil.

[0085] If the voice coil is roughly circular, then the inner periphery of the voice coil can be called the inner diameter of the voice coil, and the outer periphery of the voice coil can be called the outer diameter of the voice coil.

[0086] When the voice coil is in the air gap, i.e., when the movable part of the drive unit is stationary, the magnetic flux density at the first periphery of the voice coil may be only 50% or less of the magnetic flux density at the second periphery of the voice coil.

[0087] In an arrangement of at least two flux guiding elements including a U-shaped yoke, the flux density at the outer periphery of the voice coil can be 50% or less of the flux density at the inner periphery of the voice coil.

[0088] In an arrangement of at least two flux guiding elements including a T-shaped yoke, the flux density at the inner periphery of the voice coil can be 50% or less of the flux density at the outer periphery of the voice coil.

[0089] According to a third aspect of the invention, a vehicle is provided, the vehicle including a speaker module according to the first aspect or a speaker system according to the second aspect.

[0090] The vehicle according to the third aspect may include any one or more features described in the first aspect of the invention or the second aspect of the invention.

[0091] The present invention includes combinations of the described aspects and preferred features, except for such combinations that are expressly not permitted or expressly avoided. Attached Figure Description

[0092] Embodiments and experiments illustrating the principles of the invention will now be discussed with reference to the accompanying drawings, in which:

[0093] Figure 1 is a cross-sectional view of a speaker module including the speaker and the enclosure.

[0094] Figure 2 is an enlarged view of a portion of the speaker.

[0095] Figure 3 is a cross-sectional view of the loudspeaker, in which some components are not shown.

[0096] Figure 4 is a diagram of the magnetic flux lines of the speaker.

[0097] Figure 5 is a graph illustrating the magnetic flux density of the loudspeaker.

[0098] Figure 6 is a graph showing the total quality factors Qts and Qtc of the speaker.

[0099] Figure 7 is a graph illustrating the total quality factor Qts of a conventional loudspeaker.

[0100] Figure 8 is a graph showing the resonant frequencies fs and fc of the speaker.

[0101] Figure 9 is a graph illustrating the resonant frequency fs of a conventional loudspeaker.

[0102] Figure 10 is a graph illustrating the step response of the speaker module under the original signal input.

[0103] Figure 11 is a graph illustrating the step response of the speaker module under a filtered signal input.

[0104] Figure 12 is a graph showing the measured amplitude-frequency response of the loudspeaker module's transfer function under the original signal input.

[0105] Figure 13 is a graph illustrating the measured amplitude-frequency response of the loudspeaker module's transfer function under filtered signal input.

[0106] Figure 14 is a graph illustrating the measured amplitude-frequency response of the loudspeaker module's transfer function under the original signal input.

[0107] Figure 15 is a graph illustrating the measured amplitude-frequency response of the loudspeaker module's transfer function under filtered signal input.

[0108] Figure 16 is a schematic diagram of a speaker system including a speaker module.

[0109] Figure 17 is a graph illustrating the actual power input of a speaker module and a conventional speaker module.

[0110] Figure 18 is a flowchart illustrating the method used in manufacturing a speaker module.

[0111] Figure 19 is a graph showing the mass Mms of the movable component of the speaker module, the volume VB enclosed by the speaker module, and the resonant frequency fc of the speaker module.

[0112] Figure 20 is a cross-sectional view of another speaker module, which includes two speakers arranged back-to-back with force cancellation as shown in Figure 1.

[0113] Figure 21 is a cross-sectional view of yet another speaker module, which includes two speakers in a force-canceling back-to-back configuration.

[0114] Figure 22 shows a vehicle including the speaker module shown in Figure 1. Detailed Implementation

[0115] Various aspects and embodiments of the invention will now be discussed with reference to the accompanying drawings. Further aspects and embodiments will be apparent to those skilled in the art. All documents mentioned herein are incorporated by reference.

[0116] Figure 1 is a cross-sectional view of an exemplary speaker module 20. The speaker module 20 includes a speaker 200 and a housing 300.

[0117] The loudspeaker 200 includes a loudspeaker frame 210, a diaphragm 220, and a drive unit 230. The drive unit 230 includes a movable part 240 (attached to the diaphragm 220) and a stationary part 250 (attached to the frame 210).

[0118] The speaker module 20 is operable to power the drive unit 230, thereby moving the movable part 240 relative to the stationary part 250. Appropriately, the movable part 240 and the stationary part 250 magnetically interact with each other, thus affecting the movement of the movable part 240. The diaphragm 220 and the movable part 240 of the drive unit 230 are connected together to define a movable assembly 260 such that when the movable part 240 is moved, they move together "as a whole" along the axis of movement 202. When the movable assembly 260 is moved, the diaphragm 220 acts as a piston and produces sound.

[0119] The movable component 260 is suspended from the frame 210 by at least a first suspension element 262 and a second suspension element 264. The first suspension element 262 is attached to the frame 210 at a first landing surface 211, and the second suspension element 264 is attached to the frame 210 at a second landing surface 212. The first suspension element 262 and the second suspension element 264 are fixed to the movable component 260 such that when the movable component 260 is stationary, the center of gravity of the movable part 240 of the drive unit 230 is located between the first landing surface 211 and the second landing surface 212. More specifically, the center of gravity of the movable part 240 has a position between the first landing surface 211 and the second landing surface 212 along the axis of movement 202.

[0120] The diaphragm 220 has a first radiating surface 221 and a second radiating surface 222. The first radiating surface 221 faces forward (away from the frame 210) and is used to generate sound. The second radiating surface 222 faces backward (toward the frame 210). The forward and backward directions are opposite directions parallel to the axis of movement 202.

[0121] The enclosure 300 is arranged to receive sound generated by the second radiating surface 222 of the diaphragm 220. When the speaker module 20 is operating, the enclosure 300 isolates the sound generated by the second radiating surface 222 from the sound generated by the first radiating surface 221 to prevent the sound generated by the first radiating surface 221 from being canceled out. Suitablely, a sealed volume 310 is formed in the speaker module 20, and the sound generated by the second radiating surface 222 is received in this volume.

[0122] In some examples, the enclosure 300 is separate from the speaker frame 210. In other examples, part or all of the enclosure 300 is integrally formed with the speaker frame 210; or part or all of the speaker frame 210 is integrally formed with the enclosure 300.

[0123] As shown in Figure 1, the movable part 240 of the drive unit 230 is the voice coil 242, while the stationary part 250 is the magnet unit 252.

[0124] Magnet unit 252 is configured to generate magnetic flux and guide the magnetic flux through air gap 253. Suitablely, magnet unit 252 includes a permanent magnet 254 to generate the magnetic flux, and at least two flux guiding elements 255, 256 to guide the magnetic flux through air gap 253. The permanent magnet 254 is a rare-earth magnet and may include more than one structural element. Flux guiding elements 255, 256 are provided as a (magnetic) yoke 255 and a (magnetic) washer 256. In Figure 1, the yoke 255 is a U-shaped yoke with a base and a wall extending from the base and arranged around a movement axis 202. In some examples, the permanent magnet 254 and the flux guiding elements 255, 256 are axially symmetrical about the movement axis 202, although other arrangements are also possible.

[0125] The magnet unit 252 and the air gap 253 constitute a magnetic circuit. The magnetic circuit provides a closed loop for the magnetic flux generated by the permanent magnet 254 and guided through the air gap 253 by the two flux guiding elements 255 and 256. In some examples, the magnetic reluctance of the air gap 253 is 5.3 x 10^6 [1 / Henry], and the total magnetic reluctance of the magnetic circuit is slightly greater than that of the air gap 253.

[0126] The loudspeaker module 20 employs a relatively large voice coil 242 with multiple layers in its magnetic circuit. In some examples, the mass of the voice coil 242 is 60% or more of the total mass of the movable component 260. Given the large mass of the voice coil 242, the connection between the voice coil 242 and the diaphragm 220 is improved, for example, as described with reference to Figures 2 and 3, to prevent forces acting on the movable component during operation from damaging the movable component 260.

[0127] Figures 2 and 3 are views of the loudspeaker 200. Figure 2 is an enlarged view of a specific portion of Figure 1 (indicated by a dashed circle in Figure 1). Figure 3 shows the loudspeaker 200 with the movable part 240 of the drive unit 230 removed.

[0128] The voice coil 242 has a first periphery 243 and a second periphery 244. The distance between the first periphery 243 and the second periphery 244 is the winding thickness 245 of the voice coil 242. Here, the voice coil 242 is a generally circular ring, such that the first periphery 243 is the inner diameter boundary of the voice coil 242 and the second periphery 244 is the outer diameter boundary of the voice coil 242.

[0129] The diaphragm 220 includes a neck portion 223 forming a diaphragm aperture 224 (as shown in Figure 3). The neck portion 223 (in cross-section) is a straight segment of the diaphragm 220. The diaphragm 220 also includes an inner diaphragm portion 225 and a curved portion 226 (or "curved segment"). The inner diaphragm portion 225 is another segment of the diaphragm 220, and its (cross-section) is straight. The curved portion 226 is located between the neck portion 223 and the inner diaphragm portion 225, connecting the two portions, and its (cross-section) is curved.

[0130] The movable component 260 also includes a voice coil former 290 that carries the voice coil 242. The voice coil former 290 extends through the diaphragm aperture 224, thereby forming a first gap 266 between the voice coil former 290 and the neck portion 223 of the diaphragm 220. Furthermore, a second gap 268 is formed between the neck portion 223 and the voice coil 242. An adhesive body 269 of a hardened adhesive occupies the first gap 266 between the voice coil former 290 and the neck portion 223 of the diaphragm 220, and the second gap 268 between the neck portion 223 and the voice coil 242, thereby attaching the neck portion 223 of the diaphragm 220 to the voice coil former 290. The adhesive body 269 may occupy the entire first gap 266 and / or the entire second gap 268, i.e., fill one or both of gaps 256 and 258. In some examples, the adhesive body 269 may not be bonded to the voice coil 242, and the voice coil 242 may become very hot during use, causing damage to the bond between the adhesive body 269 and the voice coil 242. Nevertheless, the bond between the diaphragm 220 and the voice coil frame 290 may be improved compared to conventional loudspeakers.

[0131] The adhesive body 269 of the hardening adhesive, such as the integral body of the hardening / curing adhesive, occupies the space above and below the neck portion 223. More specifically, the adhesive body 269 of the hardening adhesive extends all the way to the voice coil 242 (even when not bonded to the voice coil 242 during use). Therefore, an adhesive with a larger volume than that possibly present in a conventional loudspeaker is provided. Furthermore, the volume of the adhesive exists above and below the neck portion 223, whereas in the case of a conventional loudspeaker, the adhesive may only be present on the diaphragm.

[0132] Figures 4 and 5 illustrate the magnetic flux generated by magnet unit 252. Specifically, Figure 4 shows a cross-sectional view of drive unit 230 and illustrates the magnetic flux lines generated by magnet unit 252, while Figure 5 is a graph showing the magnetic flux density across voice coil 242 (“COIL ID” to “COIL OD”, i.e., inner diameter / periphery 243 to outer diameter / periphery 244).

[0133] In Figure 4, the magnetic flux diffuses along a curved path through the air gap 253 of the voice coil 242. Accordingly, the magnetic flux density across the voice coil 242 decreases. Figure 5 shows the radial magnetic flux density Br over the winding thickness of the voice coil 242, illustrating a significant drop that is generally undesirable in loudspeaker design. In a typical loudspeaker, the magnetic flux density may be nearly constant and can drop to approximately 85% to 90% (percentage) of its initial value. In contrast, the radial magnetic flux density of the loudspeaker module 20 can drop by at least 50% over the winding thickness of the voice coil 242. For example, the magnetic flux density at the outer periphery 244 of the voice coil 242 is approximately 37% of the magnetic flux density at the inner periphery 243 of the voice coil 242. In other words, the magnetic flux density from the inner periphery 243 to the outer periphery 244 of the voice coil 242 can drop by approximately 63%.

[0134] The relatively large decrease in magnetic flux density is related to the relatively high magnetoresistance of the magnet unit 252 of the speaker module 20. The magnetoresistance can be estimated by calculations derived from simulations, for example, using the finite element method for static magnetic circuits.

[0135] It has been found that a magnetic reluctance greater than 2.5 x 10^6 [1 / H] (or "2.5E6 [1 / H]"), preferably greater than 3 x 10^6 [1 / H] (or "3E6 [1 / H]"), can result in lightweight and highly efficient loudspeakers. In contrast, the same calculations for the magnet systems of conventional loudspeakers show that their magnetic reluctance may not exceed 1.5 x 10^6 [1 / H] (or "1.5E6 1 / H").

[0136] When the relative permeability of flux guiding elements 255 and 256 When >>1, for example for a flux guide element made of steel, the magnetic reluctance of the flux guide element can be ignored, and all magnetic reluctance can be allocated to the air gap 253.

[0137] Figures 6 and 7 illustrate the overall quality factor Qts of loudspeaker 200 and conventional loudspeaker, respectively. Figure 6 further shows the overall quality factor Qtc of loudspeaker module 20.

[0138] In Figure 6, the solid line at the bottom represents the total quality factor Qts of the loudspeaker 200, physically measured at displacements of up to ±10 mm. The dashed line below represents the quadratic fitting curve 0.015x^2 + 0.0052x + 0.894, which approximates the total quality factor Qts; where x represents the displacement of the movable part 240 of the drive unit 230 (voice coil 242 in this example), in millimeters, ranging from -10 mm to +10 mm, i.e., the nominal maximum displacement of 10 mm.

[0139] The overall quality factor Qts of speaker 200 (at rest) is relatively large, with a value of approximately 0.9. Furthermore, at a nominal maximum displacement of ±10 mm, the overall quality factor Qts is approximately 2.7 times the value of Qts at rest. Therefore, compared to the overall quality factor Qts of a conventional speaker shown in Figure 7, the overall quality factor Qts across speaker 200 is more uniform within its normal operating range.

[0140] The normal operating range of speaker 200 should be understood as operating speaker 200 at the expected output volume, causing the movable component 260 to displace along the movement axis 202. When speaker 200 is operated at the maximum output volume for speaker 200, the nominal maximum displacement of movable component 260 along the movement axis 202 is caused. As shown in Figure 6, for speaker 200, the maximum output volume corresponds to a nominal maximum displacement of ±10mm.

[0141] In Figure 6, the solid line at the top represents the total quality factor Qtc of the speaker module 20, physically measured when the displacement is up to ±10 mm. The dashed line at the top represents the quadratic fitting curve 0.0183x^2 + 0.0262x + 1.9172, which approximates the total quality factor Qtc.

[0142] The overall quality factor Qtc of speaker module 20 (at rest) is approximately 1.9, which is even larger than the overall quality factor Qts (at rest). At the nominal maximum displacement, the overall quality factor Qtc is approximately twice the Qtc value at rest. Therefore, the overall quality factor Qtc is more uniform than that of speaker modules that include conventional speakers.

[0143] In Figure 7, the solid line represents the total quality factor Qts of a conventional loudspeaker obtained by physical measurement. The dashed line represents the quadratic fitting curve 0.0555x^2-0.0117x+0.8628, which approximates the total quality factor Qts.

[0144] The overall quality factor (Qts) of a conventional loudspeaker when stationary is approximately 0.86. However, the value of Qts varies more significantly across the normal operating range of a conventional loudspeaker, especially increasing sharply with increasing coil displacement. At the nominal maximum displacement, the overall quality factor of a conventional loudspeaker is more than seven times greater than the overall quality factor (Qts) of a conventional loudspeaker when stationary.

[0145] Figure 7 does not show the overall quality factor Qtc of the speaker module, including conventional loudspeakers. It is worth noting that the overall quality factor Qtc can be represented by a curve that is substantially the same as the overall quality factor Qts but shifted upwards. The magnitude of this shift depends on the specific cabinet selection. As explained in the background above, specific cabinet selection (sometimes referred to as "alignment") is typically made to achieve the desired loudspeaker response, which generally involves an overall quality factor Qtc in the range of 0.5 to 1.2. It should be noted that an overall quality factor Qtc exceeding 1.2 is generally considered undesirable. Therefore, those skilled in the art who implement these conventional teachings will wish to avoid an overall quality factor Qtc as large as 1.9, as shown in Figure 6.

[0146] The total quality factor Qtc is a dimensionless parameter that quantifies the movement damping of the movable component 260 in the speaker module 20. The total quality factor Qtc is defined as the initial energy divided by the energy lost per cycle; therefore, a lower total quality factor Qtc is associated with higher damping, and vice versa.

[0147] The overall quality factor Qtc of speaker module 20 can be calculated based on the overall quality factor Qts of speaker 200 (i.e., excluding cabinet 300), the equivalent air volume Vas of speaker 200, and the volume VB of speaker module 20:

[0148] (Qtc equals Qts multiplied by the square root of the sum of Vas / VB and unit 1)

[0149] The equivalent air volume Vas and the volume VB are parameters known to those skilled in the art.

[0150] Connecting Qts and the scaling factor of Qts, i.e., the square root, is strictly greater than unit 1, therefore Qtc is greater than Qts. Thus, when a loudspeaker with a large overall quality factor Qts is installed in a cabinet, the resulting loudspeaker module will have a larger overall quality factor Qtc. In reality, Qms is usually not constant but varies with displacement, and this variation becomes particularly pronounced when the cabinet stiffness Kb becomes (significantly) greater than the driver stiffness Kms. With increasing displacement, the change in Qms is primarily attributed to losses caused by the suspension. In free air, i.e., considering loudspeaker 200, that's only Kms. When used in a cabinet, i.e., considering loudspeaker module 20, the suspension is mainly dominated by Kb, and its losses are typically much lower than mechanical suspension Kms, thus Qms increases. The small losses in air remain essentially constant with displacement, while this is not necessarily the case for mechanical suspension components. Therefore, Qtc typically differs from the Qts curve by a factor of sqrt(Vas / Vb+1). However, even if approximated, the relationship indicated between the total quality factors Qtc and Qts is still considered useful.

[0151] The total quality factor Qts can be calculated from the speaker's electrical quality factor Qes and mechanical quality factor Qms. The relationship is:

[0152] (Qts equals the product of Qes and Qms divided by the sum of Qes and Qms)

[0153] The mechanical quality factor Qms is associated with the mechanical suspension of the movable component 260 and is determined by the suspension elements (e.g., first suspension element 262 and second suspension element 264). Typically, the suspension elements are carefully designed to ensure that the mechanical quality factor Qms remains substantially constant across the speaker's expected operating range, i.e., to provide linear suspension, meaning that the restoring force exerted by the suspension elements on the movable component is linearly proportional to the displacement of the movable component along its axis of movement.

[0154] The electrical quality factor Qes is associated with the electric drive unit 230. When the voice coil 242 is moved relative to the magnet unit 252, the magnetic flux density through the voice coil 242 changes, generating a back electromotive force (EMF) that opposes the change in magnetic flux density. Therefore, since the motor force factor BL decreases with relative displacement, Qes typically increases with relative displacement. However, the air gap 252 of the speaker module 20 has relatively high magnetic reluctance (or correspondingly, the magnetic flux density across the voice coil 242 decreases relatively sharply when the voice coil 242 is stationary in the air gap 253), which leads to an increase in stray magnetic flux density outside the air gap 252. Therefore, for the speaker 200, the magnetic flux density has increased uniformity, and thus the back EMF is reduced, providing a substantially constant electrical quality factor Qes and a more linear suspension.

[0155] The combination of a substantially constant mechanical factor Qms and an electrical quality factor Qes means that the overall quality factor Qts of the loudspeaker 200 is relatively uniform, i.e., less dependent on the relative displacement of the voice coil 242 and the magnet unit 252. In contrast, the electrical quality factor Qes of a conventional loudspeaker can be highly dependent on the relative displacement of the voice coil and the magnet unit, and therefore, the overall quality factor Qts of a conventional loudspeaker is also highly dependent. It is a general consensus in the art that the magnetic reluctance of the air gap should be as low as possible to ensure efficient use of the magnetic circuit. Therefore, the radial magnetic flux density across the air gap in a conventional loudspeaker is kept as constant as possible; while the magnetic flux density of the voice coil across the air gap typically decreases from an initial 100% to 90% of its value, or possibly as low as 85%. Thus, in a conventional loudspeaker module, the magnetic flux density within the air gap is relatively high, while the stray magnetic flux density outside the air gap is relatively low. Consequently, the voice coil experiences a sharp drop when moving out of the air gap, generating a correspondingly large back electromotive force. Figure 7 illustrates the strong displacement dependence of the electrical quality factor Qes of a conventional loudspeaker. At rest, and for small signals, the overall quality factor Qts is approximately 0.8, which is generally considered an acceptable value. However, once a conventional loudspeaker produces sound at a higher output volume, causing the movable components to shift by ±5mm or even more than ±10mm at their nominal maximum displacement, the overall quality factor Qts increases, reaching values ​​of 1.5 or even 2. Figures 8 and 9 illustrate the resonant frequencies fs of loudspeaker 200 and conventional loudspeakers, respectively. Figure 8 further shows the resonant frequency fc of loudspeaker module 20.

[0156] The free-air resonant frequency fs is the fundamental mechanical resonant frequency of the moving components of a loudspeaker. As shown in Figure 9, a conventional loudspeaker has a resonant frequency fs that is relative to the displacement. In contrast, Figure 8 shows that loudspeaker 200 has a substantially constant resonant frequency fs across the nominal range of coil displacement (i.e., across the output volume).

[0157] In some examples, the loudspeaker 200 may include suspension elements, particularly a second suspension element 264, which is selected by those skilled in the art to provide a linear response, i.e., the stiffness of the suspension element(s) is described by a substantially flat KMS curve within the normal operating range of the loudspeaker 200. Using conventional suspension elements, those skilled in the art will be able to design a suspension in which the KMS value at the nominal maximum displacement may, for example, not exceed 1.3 times the value at the rest position.

[0158] The resonant frequency fc of speaker module 20 is the fundamental mechanical resonant frequency of the moving component 260 of speaker module 20. The resonant frequency fc of speaker module 20 can be calculated based on the free-air resonant frequency fs of speaker 200 (i.e., excluding the enclosure 300), the equivalent air volume Vas of speaker 200, and the volume VB of speaker module 20.

[0159]

[0160] As before, the scaling factor is greater than 1, therefore fc is greater than fs. Thus, when a loudspeaker 200 with a resonant frequency of fs is installed in the enclosure 300, the resulting loudspeaker module 20 has a resonant frequency fc greater than the loudspeaker resonant frequency fs.

[0161] As shown in Figure 8, the resonant frequency fs of the loudspeaker 200 is less than 40Hz, and furthermore, the normal operating range of the loudspeaker 200 is essentially constant, i.e., the nominal maximum displacement from negative to positive is 10mm. Similarly, the resonant frequency fc of the loudspeaker module 20 is less than 70Hz, and furthermore, the normal operating range of the loudspeaker module 20 is essentially constant.

[0162] In contrast, Figure 9 shows the relative shift of the resonant frequency fs of a conventional loudspeaker across its normal operating range. The resonant frequency of a conventional loudspeaker has a minimum of approximately 50 Hz and rises above 70 Hz for high output volumes. The resonant frequency of a loudspeaker module incorporating a conventional loudspeaker exhibits a similar curve for the resonant frequency of the loudspeaker module, but is shifted upwards depending on the cabinet selection.

[0163] The overall quality factor Qtc and resonant frequency fc of speaker module 20 are less dependent on the displacement of the movable components than those of speaker modules including conventional speakers. Furthermore, the inventors have found that the overall quality factor Qtc and resonant frequency fc are sufficiently constant so that speaker module 20 provides a linear time-invariant system under a first approximation, thus allowing for appropriate use of linear signal processing to uniformly adjust the sound produced by speaker module 20 across different output volumes. In contrast, the overall quality factor Qtc and resonant frequency fc of conventional speaker modules are highly dependent on the displacement of the movable components, and therefore cannot be easily approximated as linear systems across the normal operating range of conventional speaker modules.

[0164] Many modern audio systems allow digital signal processing before the signal is amplified for playback through speakers. However, many speakers are designed independently of the signal processing stage, assuming that the electronics have a constant voltage-frequency transfer function.

[0165] There are two main types of signal processing. In feedforward designs, the signal to the loudspeaker is modified based on parameters selected by the loudspeaker system designer during the development phase. In feedback systems, the loudspeaker's state parameters (such as the acceleration or position of the loudspeaker diaphragm or the current flowing through the voice coil) are fed back to the control electronics, and the signal processing is dynamically adjusted to achieve a specific loudspeaker response. Despite considerable effort in this field, feedback systems have not been widely adopted due to their complexity. Examples of feedback systems are described, for instance, in US3334184A (DEKONING) and DE4332804C2 (KLIPPEL).

[0166] For economic reasons, a balance must be struck between controlling the cost of electronics and speakers. Ideally, speakers used to produce bass-frequency sound should be designed to perform well at low signal levels, including a tight bass response, while also handling higher signal levels with the same quality, resulting in greater diaphragm displacement and louder bass. However, this can be difficult to achieve with traditional speaker designs and can lead to high speaker design costs. For feedback systems, the linearity requirement can be slightly relaxed because the amplifier can compensate for speaker performance by appropriately increasing the voltage output to the speaker based on feedback parameters. However, this increased voltage output may not be ideal, and maintaining such a voltage output may be impractical for typical amplifiers and speakers.

[0167] The speaker module 20 employs a low-cost speaker design and allows for low-cost feedforward signal processing, such as using a conventional amplifier with a standard voltage output, while still providing tight and loud bass reproduction across the normal operating range of the speaker module 20. To illustrate the effectiveness of this approach, the step response of the speaker module 20 was measured using the original input signal and after signal processing of the input signal. This can be described with reference to Figures 10 and 11.

[0168] Figures 10 and 11 illustrate the step response of speaker module 20. The step response is the output pressure generated over time after a continuous DC pulse (i.e., a step function) is supplied to speaker module 20.

[0169] Figure 10 shows the step response of speaker module 20. Multiple noticeable oscillations up to approximately 50 milliseconds indicate “ringing” in the time domain. This ringing is associated with poor transient behavior of speaker modules with a total quality factor exceeding 1.2.

[0170] Figure 11 shows the step response of loudspeaker module 20, but unlike Figure 10, it has undergone appropriate signal processing to adjust the step response. Notably, due to the signal processing, the ringing seen in Figure 10 disappears in Figure 11. The step response shown in Figure 11 is essentially the same as the step response of a loudspeaker module with a total quality factor Qtc equal to 1, as described by RH Small in his seminal paper “Closed-Box Loudspeaker Systems – Part 1: Analysis” (J.Eng. Soc. (December 1972)).

[0171] The use of signal processing, particularly linear filtering, to eliminate ringing during resonance might seem surprising, given the existing notion that ringing during speaker resonance cannot be equalized. Specifically, for speaker module 20, ringing during resonance is eliminated across the output volume (e.g., the nominal operating range of speaker module 20). In contrast, for conventional speakers, linear filtering can eliminate ringing for small signals, but the same linear filtering cannot eliminate ringing for larger signals.

[0172] In contrast, existing technology teaches that, in the context of low-frequency reproduction, only alignment (i.e., choosing a suitable enclosure to house the speaker) ultimately determines the overall quality factor. For example, Vance Dickason writes in his popular textbook, Loudspeaker Design Cookbook (7th edition, KCP Media Corp., 2006): “The wholepoint of fitting a woofer to a particular box volume is to control the response characteristic of the combination. The objective method is to measure and align the Q-factor. [...] Qtc greater than 1.2 or so, however, should be regarded as undesirable.” Following the main text's repetition section are several pages of alignment tables guiding loudspeaker designers on how to perfectly mount loudspeakers into enclosed enclosures to avoid "misalignment," as a large overall quality factor degrades audio performance and results in "muddy" bass reproduction instead of the desired "tight" bass. Therefore, it might be considered surprising that loudspeaker module 20 and the signal processing used to achieve a step response essentially identical to that of a loudspeaker module with an overall quality factor Qtc equal to 1.

[0173] Figures 12 and 13 illustrate the measured amplitude frequency response of the transfer function, showing the roll-off behavior (solid line) of speaker module 20 (i.e., speaker 200 mounted in a 1.5-liter enclosure 300) at low frequencies from approximately 30 Hz to approximately 300 Hz. The dashed line shows a typical ideal low-frequency roll-off target, corresponding to a second-order Butterworth target with a total quality factor Qtc of 1. In Figure 12, speaker module 20 overshoots approximately 12 dB at 70 Hz when the raw signal is fed.

[0174] The loudspeaker module 20 responds more strongly to the original input signal around its resonant frequency fc. Therefore, the amplitude-frequency response shown in Figure 12 relates to the resonant behavior shown in Figure 10. As before, the addition of signal processing aligns the measured amplitude-frequency response of the loudspeaker module 20. This is shown in Figure 13, where the signal processing has aligned the measured amplitude-frequency response of the loudspeaker module 20 with a second-order Butterworth target. The measured amplitude-frequency response shown in Figure 13 is substantially consistent with the second-order Butterworth target across the measured frequency range.

[0175] Figures 14 and 15 illustrate the group delay of speaker 200 over frequencies from approximately 30 Hz to approximately 300 Hz. Group delay is a measure of the time delay between signal input and signal output. Group delay can be understood as frequency-dependent lag, resulting in “slow” and inaccurate bass reproduction. While the upper limit of acceptable group delay may be controversial in the art, a consensus seems to be reached regarding a limit of one cycle; that is, at any given frequency, the group delay should be less than one cycle time, and for “tight” bass reproduction, the group delay should be as small as possible.

[0176] Figure 14 plots the measured group delay of the original input signal. Around 70 Hz, the local maximum of the group delay is approximately 14 ms. The cycle time at 70 Hz is 1 / 70 s = 14 ms, therefore the graph in Figure 14 will be considered to represent a speaker unsuitable for high-quality reproduction. This is consistent with Figure 10 (showing resonant behavior) and Figure 12 (showing overshoot in the amplitude frequency response at 70 Hz). As before, signal processing techniques can be applied to address this issue. In Figure 15, the application of signal processing reduces the group delay at and near the resonant frequency fc of speaker module 20. More specifically, signal processing reduces the group delay at 70 Hz to 4.5 ms. The resulting group delay increases with frequency, reaching 10 ms at 40 Hz, which is less than half the limit of one cycle.

[0177] Figure 16 illustrates an audio system 1000 for implementing the signal processing described with reference to Figures 11, 13, and 15. The audio system 1000 includes a speaker module 20, a signal processor 1100, a data storage medium 1200, and an amplifier 1300.

[0178] Signal processor 1100 is configured to perform signal processing to generate the graphs in Figures 11, 13, and 15. Specifically, signal processor 1100 is configured to perform feedforward filtering (without feedback).

[0179] Analog components, such as capacitors and inductors, can be used for signal processing and exhibit linear characteristics. In this example, signal processor 1100 is a digital signal processor using a set of infinite impulse response filters, which can be considered as the digital counterpart of the analog components. Signal processor 1100 can be, for example, the Analog Devices™ ADAU1701 and is configured to apply the following peak equalizer:

[0180]

[0181] The data storage medium 1200 stores the peak balancer value.

[0182] By applying signal processing through signal processor 1100, the frequency response is adjusted to become as smooth as desired; the group delay at 70Hz is adjusted to be less than 4.5ms; and both of these adjustments are uniform across the output volume, i.e., even at high input levels and large displacements, as expected from the speaker behavior shown in Figures 6 and 8.

[0183] It is important to note that the above diagram illustrates a set of possible filters, but different filter settings can also result in similar transfer functions. In some examples, good alignment can be achieved using fewer than five peak filters. Here, "alignment" refers to the so-called alignment process, which, as mentioned above, is typically performed by selecting a specific cabinet to align with the target response. Here, the target response is chosen as a 12dB Butterworth roll-off and is achieved through the signal processing described.

[0184] Figure 17 is a graph illustrating the actual input power of speaker module 20 and a conventional speaker module over a frequency range of 40Hz to 60Hz and at a target displacement of ±8mm. Note that the actual input power is independent of the speaker's voltage curve (DSP settings) and the speaker's RDC (DC resistance), and can be calculated for any set of parameters for a given target displacement, thus providing a useful and advantageous metric.

[0185] The parameters of these two speakers are as follows:

[0186]

[0187] The speaker module 20 consumes an average of 130W to achieve the required peak displacement. A conventional speaker module requires an average of 360W, approaching 450W at 40Hz. Such high input power is impractical because power handling becomes difficult and costly.

[0188] For speaker module 20, amplifier 130 does not require a high peak voltage, and the actual input power to voice coil 242 is relatively low for several reasons. Due to the relatively large mass of movable component 260, the resonant frequency fc is within the frequency range where the audio content to be reproduced (such as modern music) has the highest spectral components and therefore the highest power requirements. Around the resonant frequency fc, the impedance amplitude is high, and the voltage and current are out of phase. The actual input power is low. Furthermore, due to the large overall quality factor Qtc, the voltage efficiency around the resonant frequency fc is very high. Returning to Figure 12 and comparing the solid line with the dashed line in Figure 12, the overshoot at 70Hz corresponds to approximately 12dB. To achieve the desired smooth frequency roll-off, the voltage can be reduced by 10^(12 / 20) = 4 times, correspondingly providing a reduction in power.

[0189] Therefore, speaker module 20 is very effective in low-frequency radiation.

[0190] Figure 18 is a flowchart illustrating the method used in manufacturing a loudspeaker module, which will be discussed below using an example of loudspeaker module 20.

[0191] The method includes step S110: selecting the volume VB of the enclosure 300. For example, the volume VB can be selected based on the limitations of available space according to the intended application.

[0192] The method includes step S120: determining the mass Mms of the movable component 260.

[0193]

[0194] in, ρ is the density of air; c is the speed of sound in air. It is the effective radiating surface of the speaker module 20; resonant frequency It can be selected, for example, at the center of the expected passband. The mass Mms of the movable component 260 thus determined may be relatively large compared to conventional low-frequency systems.

[0195] The method includes step S130: determining the mass of the movable part 240 of the drive unit 230.

[0196] To allow for a relatively high moving mass Mms and a low-cost drive unit 230, the mass of the movable component 240 of the drive unit 230 is chosen to be a substantial portion of the mass constituting the movable component 260, for example, at least 60% of the moving mass Mms. For example, in Figure 1, when the movable component 240 of the drive unit 230 is a voice coil 242, the mass of the voice coil 242 is appropriately increased. Increasing the mass of the voice coil 242 can typically involve increasing the number of layers in the voice coil 242 and / or using wires with a large cross-section and / or a non-circular cross-section (e.g., rectangular or square). As for non-circular cross-sections, this can be particularly useful because a large number of layers are typically used, thus the advantages of non-circular cross-sections are similarly amplified (high fill factor, increased mass, reduced resistance RDC for a given coil size).

[0197] Conveniently, housing the voice coil 242 within the air gap 253 means that the air gap 253 will be relatively wide, and therefore have relatively high magnetic reluctance. This means that the total flux in the magnetic circuit is reduced, and the cross-sectional area of ​​the magnetic steel components can be reduced. The result is a powerful yet lightweight drive unit.

[0198] When the movable part 240 of the drive unit 230 includes the magnet unit 252 (see the discussion of FIG21 below), the mass of the magnet unit 252 can generally be large enough that no increase is necessary.

[0199] The method includes step S140: constructing a drive unit 230 such that Qts(x) as a function of displacement x remains substantially constant across the expected normal operating range of the loudspeaker module 20. Here, a high value of Qts(0) is acceptable, i.e., when stationary in the air gap 242.

[0200] As described above, the air gap 253 is relatively wide to accommodate the exceptionally large voice coil 242, which means a relatively high stray magnetic flux density. This results in a relatively smooth force factor BL(x) curve, thus providing a relatively flat Qts(x) curve. Therefore, the high quality assigned to the voice coil 242 (in the moving voice coil example) may already contribute to achieving a substantially constant Qts across the expected normal operating range of the loudspeaker module 20. For the moving magnet unit example, the air gap 253 can be widened to smooth the force factor BL(x) curve and compensated for, and the voice coil 242 can be widened to achieve the required mass for the moving part of the drive unit.

[0201] The method includes step S150: constructing a suspension for the movable component 260 such that it remains substantially constant fs across the expected normal operating range of the speaker module 20.

[0202] To improve axial movement along the movement axis 202 and suppress swaying, suspension elements 262 and 264 are positioned such that the center of gravity of the moving assembly 260 has a position along the movement axis 202 between the landing surfaces 211 and 212 of the suspension elements 262 and 264. This makes the suspension elements 262 and 264 compliant and linear as they move along the movement axis 202, resulting in a linear fs(x) curve and allowing air suspension to dominate across the nominal operating range of the speaker module.

[0203] The method may further include step S210: selecting a target total quality factor Qtc. The target total quality factor Qtc may be selected based on the intended application during the manufacturing process of the speaker module 20.

[0204] The method further includes step S220: applying a set of filters to the input signal of the speaker module 20 to change the speaker response, thereby producing a sound that matches the target total quality factor Qtc.

[0205] The method further includes step S310: obtaining a speaker module with a target total quality factor Qtc.

[0206] Figure 19 is a graph illustrating the range of parameters applicable to a speaker module (e.g., speaker module 20) according to this disclosure. Therefore, Figure 19 can be used to estimate parameters during the design process, for example, referring to Figure 18.

[0207] The horizontal axis represents the normalized moving mass Mms / Sd, which corresponds to the mass of the movable component Mms divided by the effective radiating surface Sd, ranging from 0 to 20 [kg / m2]. The vertical axis represents the normalized volume VB of the enclosure, which corresponds to the volume VB divided by the effective radiating surface Sd, ranging from 0 to 1 [m3 / m2]. Therefore, Figure 19 shows Sd normalized; and Kms / Kb equals 0.5.

[0208] A set of frequency curves (solid lines) correspond to different resonant frequencies within the enclosure: 20Hz, 30Hz, 40Hz, 50Hz, 60Hz, 70Hz, and 80Hz. Therefore, Figure 19 correlates the mass Mms of the movable component, the volume VB of the speaker module, and the resonant frequency fc.

[0209] The gray area indicates a preferred parameter range, with darker areas being more preferred. Therefore, Mms / Sd is preferably in the range of 5 to 15 [kg / m²], more preferably in the range of 7 to 12 [kg / m²]. VB / Sd is preferably greater than 0 and up to 0.5 [m], more preferably in the range of 0.03 to 0.3 [m]. The resonant frequency within the cell is preferably in the range of 30 Hz to 80 Hz, more preferably in the range of 40 Hz to 80 Hz.

[0210] The upper left corner of Figure 19 can be considered as representing a conventional speaker design, where either the moving mass is small or the volume VB is large, or both. The lower right corner is a preferred area, associated with a relatively high mass Mms (e.g., 180 grams) and a volume VB, for example, 6 liters. These parameters may not be preferred for music reproduction but may be preferred for cinematic applications.

[0211] As an example, when the volume VB is chosen to be 1.5 liters, in order to achieve the target intracellular resonant frequency fc of 60 Hz, according to Figure 19, the normalized mobile mass Mms / Sd is estimated to be approximately 8.5 Mms / Sd. For an effective radiating surface Sd of 110 cm², this would correspond to a mobile mass of approximately 93.5 g.

[0212] This estimation can provide a preliminary indication of approximate parameter values ​​during the design process. It is worth noting that the effect of the mechanical suspension contribution may not be negligible in practice and has been taken into account in Figure 19 (Kms / KB=0.5).

[0213] Figure 20 shows a cross-section of a speaker module 30 including two speakers 200 as described above. Suitablely, the speaker module 30 also includes a housing 400 configured to receive the two speakers 200. The housing 400 is arranged to receive sound generated by the second radiating surface 222 of the diaphragm 220 of each speaker 200. Suitablely, a volume VB 410 is formed in the speaker module 20, in which the sound generated by the second radiating surface 222 is received. The volume VB 410 is 3 liters. The surface area of ​​the diaphragm 220 of each speaker 200 is 110 cm². The moving mass of each speaker 200 is 160 g, resulting in an in-cabin resonant frequency fc of 51 Hz.

[0214] The loudspeakers 200 are provided in a force-canceling arrangement. The first loudspeaker 200 and the second loudspeaker 200 are arranged back-to-back such that the first loudspeaker 200 and the second loudspeaker 200 face opposite directions. The loudspeaker module 30 is operable to energize the voice coil 242 of the first loudspeaker 200 and the voice coil 242 of the second loudspeaker 200, thereby moving the voice coil 242 in opposite directions along the movement axis 202, thereby moving the diaphragm 220 of the first loudspeaker 200 and the diaphragm 220 of the second loudspeaker 200 to produce sound.

[0215] Figure 21 shows a cross-section of another speaker module 40 including two speakers 700 mounted within a housing 400 in a force-counterar arrangement. This arrangement is substantially the same as that in Figure 20, but Figure 20 illustrates an example of a "movable voice coil," while Figure 21 illustrates an example of a "movable magnet."

[0216] Each loudspeaker 700 includes a loudspeaker frame 710, a diaphragm 720 suspended on the loudspeaker frame 710, and a drive unit 730 configured to move the diaphragm 720 along a movement axis 702 of the loudspeaker module 40, so that a first radiating surface 721 and a second radiating surface 722 of the diaphragm 720 generate sound. A movable component 740 of the drive unit 730 includes a magnet unit 742. A stationary component 750 of the drive unit 730 includes a voice coil 752 of the drive unit 730.

[0217] Referring to Figure 20, the loudspeakers 700 are arranged back-to-back, facing opposite directions. The loudspeaker module 40 is operable to energize the voice coils 752 of the first loudspeaker 700 and the second loudspeaker 700, thereby moving the magnet units 742 of the first loudspeaker 700 and the second loudspeaker 700 in opposite directions along the movement axis 702, thereby moving the diaphragms 720 of the first loudspeaker 700 and the second loudspeaker 700 to produce sound.

[0218] The mass of the voice coil 752 is relatively large due to its numerous layers and high winding height, while the mass of the magnet unit 742 is relatively small due to the small cross-section required for its flux guiding element. A feasible loudspeaker solution can be provided by incorporating the magnet unit 742 into the movable part 740 of the drive unit 730 and the voice coil 752 into the stationary part 750 of the drive unit 730. In this example, the moving mass of each loudspeaker 700 is 100 grams, and the internal resonant frequency fc is 64 Hz.

[0219] Figure 22 is a schematic diagram of a car 2000. In this example, the car 2000 includes a speaker module 20, but more generally, any speaker 20, 30, 40 or speaker system 1000, or a combination thereof, as described above, may be installed in the car 2000. In this example, the speaker module 20 is disposed between the footwells 2100 of the car 2000. Other locations are also conceivable.

[0220] The features disclosed in the foregoing specification, appended claims or drawings, expressed in their specific form or as means of performing the disclosed functions or methods or processes for obtaining the disclosed results (as the case may be), may be used alone or in any such particular combination to implement the invention in its various forms.

[0221] While the present invention has been described in conjunction with the exemplary embodiments described above, many equivalent modifications and variations will become apparent to those skilled in the art upon reading this disclosure. Accordingly, the exemplary embodiments of the invention set forth above are to be considered exemplary and not restrictive. Various changes may be made to the described embodiments without departing from the spirit and scope of the invention.

[0222] To avoid any ambiguity, any theoretical explanations provided herein are for the purpose of enhancing the reader's understanding. The inventor does not wish to be bound by any such theoretical explanations.

[0223] Any chapter headings used in this document are for organizational purposes only and should not be construed as limiting the subject matter described.

[0224] Throughout this specification (including the appended claims), unless the context otherwise requires, the terms “comprising” and “including”, as well as variations such as “including,” “comprising,” and “containing,” shall be understood to include the whole or a group of whole or steps specified, but not to exclude any other whole or a group of whole or steps.

[0225] It must be noted that, unless the context explicitly specifies otherwise, the singular forms “a,” “an,” and “the” used in the specification and appended claims include plural references. Ranges in this document may be expressed as starting “about” of a particular value and / or ending “about” of another particular value. When such ranges are expressed, another embodiment includes a range from one particular value and / or to another. Similarly, when values ​​are expressed as approximations, the use of the preposition “about” allows it to be understood that the particular value forms another embodiment. The term “about” in numerical values ​​is optional, for example, indicating + / - 10%.

[0226] References

[0227] The foregoing references several publications to more fully describe and disclose the invention and the prior art to which it pertains. Full citation information for these references is provided below. The entirety of each of these references is incorporated herein by reference.

[0228] 1. US3334184A (DE KONING)

[0229] 2. DE4332804C2(KLIPPEL)

[0230] 3. RH Small, “Closed-Box Loudspeaker Systems, Part I: Analysis”, J.Audio Eng. Soc., Vol. 20, pp. 798-808 (December 1972)

[0231] 4. W. Klippel, U. Seidel, “Fast and Accurate Measurement of Linear Transducer Parameters”, presented at the 110th Convention of the Audio Engineering Society held in Amsterdam from May 12 to 15, 2001, preprint 5308.

[0232] 5. W. Klippel, “Distortion Analyzer - a New Tool for Assessing and Improving Electrodynamic Transducers,” presented at the 108th Convention of the Audio Engineering Society held in Paris from February 19 to 22, 2000, preprint 5109.

[0233] 6. V. Dickason, Loudspeaker Design Cookbook, 7th Edition, KCP Media Corp., 2006.

[0234] 7. PCT / EP2023 / 073013(VUINE)

[0235] 8. GB2212935.7 (VUINE)

[0236] 9. LL Beranek, Acoustics, McGraw-Hill, 1954

Claims

1. A speaker module for generating low-frequency sound, the speaker module comprising: Speaker frame; The diaphragm suspended on the speaker frame; A driving unit is configured to move the diaphragm along a movement axis of the loudspeaker module to generate sound from a first radiating surface and a second radiating surface of the diaphragm, wherein the first radiating surface and the second radiating surface are on opposite sides of the diaphragm; wherein the driving unit includes a magnet unit for generating magnetic flux across an air gap and a voice coil configured to be located in the air gap when the diaphragm is stationary; and a housing arranged to receive the sound generated by the second radiating surface of the diaphragm; wherein the overall quality factor (Qtc) of the loudspeaker module is at least 1.8 when the diaphragm is stationary; and wherein the magnetic flux density at a first periphery of the voice coil is 50% or less of the magnetic flux density at a second periphery of the voice coil when the diaphragm is stationary.

2. The speaker module according to any one of the preceding claims, wherein, When the diaphragm is stationary, the total quality factor Qtc of the speaker module is at least 2.5; optionally, when the diaphragm is stationary, the total quality factor Qtc is at least 3.

3. The speaker module according to any one of the preceding claims, wherein, When the diaphragm is stationary, the total quality factor Qtc of the drive unit is up to 10; optionally, when the diaphragm is stationary, the total quality factor Qtc is up to 5.

4. The speaker module according to any one of the preceding claims, wherein, When the diaphragm is stationary, the mechanical quality factor Qms of the drive unit is in the range of 3 to 8.

5. The speaker module according to any one of the preceding claims, wherein, When the diaphragm is stationary, the electric quality factor Qes of the drive unit is in the range of 1.2 to 2.

5.

6. The speaker module according to any one of the preceding claims, wherein, When the diaphragm is stationary, the total quality factor Qtc has a first Qtc value; when the diaphragm is at its nominal maximum displacement, the total quality factor Qtc has a second Qtc value; wherein the second Qtc value is in the range of 1.00 to 2 times the first Qtc value, and optionally, the second Qtc value is in the range of 1.00 to 1.25 times the first Qtc value.

7. The speaker module according to any one of the preceding claims, wherein, The speaker module has a resonant frequency fc. When the diaphragm is stationary, the resonant frequency has a first resonant frequency value. When the diaphragm is at its nominal maximum displacement, the resonant frequency has a second resonant frequency value. The second resonant frequency value is in the range of 1.00 to 1.10 times the first resonant frequency value.

8. The speaker module according to any one of the preceding claims, wherein, The speaker module has a force factor BL. When the diaphragm is stationary, the force factor has a first BL value, and when the diaphragm is at its nominal maximum displacement, the force factor has a second BL value. The second BL value is at least 0.5 times the first BL value.

9. The speaker module according to any one of the preceding claims, wherein, The ratio of actuator stiffness Kms to housing stiffness Kb is in the range of 0.25 to 0.

75.

10. The speaker module according to any one of the preceding claims, wherein, The speaker module includes a movable component, which includes the diaphragm and a movable part of the drive unit.

11. The speaker module according to claim 10, wherein, The loudspeaker module is operable to cause the movable part of the drive unit to magnetically cooperate with the stationary part, so that the movable part moves along the axis of movement to generate sound; and the ratio of the mass of the movable part of the drive unit to the effective acoustic radiation area Sd of the diaphragm is at least 5 kg per square meter, and optionally at least 7 kg per square meter.

12. The speaker module according to claim 9 or 10, wherein, The mass of the movable part of the drive unit can be at least 60% of the mass of the movable component.

13. The speaker module according to any one of the preceding claims, wherein, The loudspeaker module surrounds an acoustically effective volume VB; the ratio of the volume VB to the effective acoustic radiation area Sd of the diaphragm is in the range of 0.01 m to 0.5 m.

14. A loudspeaker system comprising a loudspeaker module according to any one of the preceding claims, wherein, The loudspeaker system further includes a signal processor configured to regulate an electrical signal to be supplied to the voice coil; wherein the signal processor is configured to perform frequency-dependent regulation of the electrical signal.

15. The speaker module according to claim 14, wherein, The signal processor is configured to perform frequency-dependent modulation of the electrical signal, thereby providing feedforward filtering of the electrical signal.

16. The speaker module according to claim 14 or 15, wherein, The signal processor is configured to reduce the group delay at and near the resonant frequency of the speaker module.

17. The loudspeaker module according to any one of claims 14 to 16, wherein, The signal processor is user-configurable between the first frequency-dependent adjustment and the second frequency-dependent adjustment.

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