Nonlinear Port Parameters for Bass Reflex Enclosure Modeling of Loudspeakers

Abstract

A loudspeaker parameter system for inverting box driver drift modeling may include a loudspeaker driver having a conductor, a magnet, and a diaphragm. The system may also include a processor for drift modeling, the processor being configured to receive an input signal, determine a voltage level of the input signal, a housing having a resonant port, estimate port parameters, the port parameters including at least one of acoustic resistance or acoustic mass, and apply a voltage limit based on an inverting box drift model utilizing the port parameters.

Description

Technical Field

[0001] This disclosure provides non-linear port parameters for vented enclosure modeling of loudspeakers. Background Art

[0002] A variety of methods and systems have been developed to protect loudspeakers with digital signal processing (DSP), including vented enclosure loudspeakers. A variety of models have been developed to characterize the non-linearity of loudspeakers. The main sources of such non-linearity may include force factor, stiffness, inductance, and acoustic resistance and acoustic mass. Existing loudspeaker limiters can limit peak or RMS voltage, but lack appropriate information, including a complete thermal model and drift model. These loudspeaker limiters may be overly conservative in their limiting and thereby prevent the loudspeaker from performing at its supported maximum output. Summary of the Invention

[0003] A loudspeaker parameter system for vented enclosure driver drift modeling may include a loudspeaker driver having a conductor, a magnet, and a diaphragm. The system may further include a processor for drift modeling, the processor being configured to receive an input signal, determine a voltage level of the input signal, a housing having a resonant port, estimate port parameters, the port parameters including at least one of acoustic resistance or acoustic mass, and apply a voltage limit based on a vented enclosure drift model utilizing the port parameters.

[0004] A method for modeling parameters of a vented enclosure loudspeaker may include receiving an input signal, determining a voltage level of the input signal, interpolating port parameters, the port parameters including at least one of acoustic resistance and acoustic mass, and applying a voltage limit based on the port parameters.

[0005] A loudspeaker parameter system may include a loudspeaker having a transducer and a diaphragm, and a processor for drift modeling. The processor may be configured to receive an input signal, determine a voltage level of the input signal, estimate acoustic resistance, wherein the acoustic resistance and acoustic mass are voltage-dependent, and apply a voltage limit based on the port parameters to limit drift.

[0006] A loudspeaker parameter system for vented enclosure driver drift modeling may include a loudspeaker driver having a coil, a magnet, and a diaphragm. The system may further include a processor for drift modeling, the processor being configured to receive an input signal, determine a voltage input of the input signal, estimate port parameters, the port parameters including acoustic resistance and acoustic mass, and apply a voltage limit based on a vented enclosure drift model utilizing non-linear port parameters. Description of the Drawings

[0007] The embodiments of the present disclosure are particularly pointed out in the appended claims. However, other features of the various embodiments will become more apparent and best understood by reference to the following detailed description when considered in conjunction with the accompanying drawings, in which:

[0008] Figure 1 An example loudspeaker system is shown;

[0009] Figure 2 An example drift modeling system for a reflex enclosure system is shown;

[0010] Figure 3 An example input voltage test signal for characterizing loudspeaker and port parameters is shown;

[0011] Figure 4A An example graph of acoustic resistance versus peak input voltage is shown;

[0012] Figure 4B An example graph of acoustic quality versus peak input voltage is shown;

[0013] Figure 5A A graph of estimated reflex enclosure parameters for medium-level voltage is shown;

[0014] Figure 5B A graph of estimated reflex enclosure parameters for high-level voltage is shown;

[0015] Figure 5C An enlarged graph of linear matching is shown, with the error displayed as superimposed waveforms. Blue is the modeled displacement; orange is the measured displacement; and

[0016] Figure 6 Shows Figure 2 An example process of an example drift modeling system. DETAILED DESCRIPTION

[0017] As needed, detailed embodiments of the present invention are disclosed herein; however, it should be understood that the disclosed embodiments are merely examples of the invention that may be embodied in various and alternative forms. The drawings are not necessarily to scale; some features may be enlarged or minimized to show details of particular components. Accordingly, the specific structural and functional details disclosed herein should not be construed as limiting, but merely as a representative basis for teaching one skilled in the art to variously employ the present invention.

[0018] An electromagnetic loudspeaker can use a magnet to generate magnetic flux in an air gap. A voice coil can be placed in the air gap. The voice coil can have a cylindrically wound conductor. An audio amplifier is electrically connected to the voice coil to provide an electrical signal corresponding to a specific current to the voice coil. The electrical signal and magnetic field generated by the magnet cause the voice coil to oscillate, and in turn drive the diaphragm to produce sound.

[0019] However, the performance of a loudspeaker is limited. Typically, as more power is applied to the loudspeaker, the voice coil will heat up and eventually fail. This is due to the resistance of the conductor that generates heat. Since the DC resistance (DCR) of the voice coil constitutes the major part of the impedance of the driver, most of the input power is converted into heat rather than sound. Therefore, as the temperature of the coil increases, the DCR of the coil will increase. The power handling capacity of the driver is limited by its ability to tolerate heat. Additionally, as the temperature of the voice coil increases, the resistance and impedance of the loudspeaker also increase. This can lead to power compression, i.e., a frequency-dependent loss of the expected output due to the increase in the temperature and DCR of the voice coil. As the DCR increases, the linear and non-linear behavior of the system changes. As more low frequencies are applied to the driver, a greater cone drift can be identified. The loudspeaker has a limited amount of drift capacity before extreme distortion occurs at the output. To compensate for these changes, adjustments such as limiting the voltage input may be necessary. To apply the appropriate adjustments, it may be necessary to accurately predict the voice coil temperature and the non-linear behavior of the cone drift in real-time or near real-time. With appropriate mitigation actions or voltage limiting, this prediction can enable the cone to reach the safe maximum drift and appropriately control over-drift without generating cancellation distortion.

[0020] To obtain an accurate model of the voice coil temperature and the non-linear behavior of the cone drift, the system includes a non-linear port parameter system. The system can accurately predict various port parameters, such as the acoustic resistance R a and the sound quality M a . For the purpose of modeling a bass-reflex loudspeaker, these parameters have historically been assumed to be linear. The system supports accurately predicting the voice coil drift of the loudspeaker, improving the health and safety of the loudspeaker, and enhancing the sound quality at higher sound levels. The drift limiter can limit the peak of the drift, enabling the loudspeaker to play safely at maximum loudness with minimum distortion. When only the peak of the sound is limited, very little distortion is caused.

[0021] Boost measurements can be used to determine the port parameters. The port parameters can be used to apply a real-time model. When the system is in operation, the input voltage of the loudspeaker can be used to calculate the voltage envelope. The voltage envelope can be used to find the instantaneous acoustic resistance R a and the sound quality M a values at a specific voltage level. Different from traditional modeling, the acoustic resistance R a and the sound quality M a can vary and are voltage-dependent. Then, the port parameter values can be sent through a lumped element model to predict the drift of the voice coil. Then, the drift envelope is used to limit the loudspeaker in the best way that only limits the peak and generates minimum distortion, where it is possible to obtain the maximum sound output without damaging the loudspeaker.

[0022] Therefore, the acoustic resistance R a and the acoustic quality M a can be used to accurately predict the voice coil displacement, current, and velocity for a vented box loudspeaker having a port. The system can be applicable to both the low-level linear range of the port and the high-level non-linear range of the port. The system may not require measurements at the port via a hot-wire sensor or other means to obtain the acoustic resistance R a and the acoustic quality M a . The port parameters can be mapped as a function of the input voltage level.

[0023] Figure 1 FIG. 1 shows an exemplary loudspeaker system 10 including an audio source 12 configured to transmit an audio signal to an amplifier 14 and a loudspeaker 18. One or more controllers (referred to hereinafter as "controller 16") may communicate with the amplifier 14. The controller 16 may generally be coupled to a memory for operating instructions to execute the equations and methods described herein. Generally, the controller 16 is programmed to perform the various methods described herein. The controller 16 may include the models described herein. The controller 16 may modify the audio signal based on the temperature and non-linearity of the loudspeaker. The loudspeaker 18 may include one or more drivers, the one or more drivers including a horn driver (or high-frequency (HF) driver) and / or a woofer to reproduce the audio signal. The drivers included and described herein are exemplary and not intended to be limiting. Other drivers having various frequency ranges may be included. The loudspeaker 18 may include a cone and a voice coil.

[0024] The loudspeaker 18 may include a magnet, a back plate, a top plate, a pole piece, and a voice coil. The voice coil may include a wire such as insulated copper wire wound around a bobbin (i.e., the voice coil or coil). The voice coil may be centered in the magnetic gap. The voice coil may be configured to receive a signal from the amplifier 14. This signal may create a current in the voice coil. The magnetic field in the magnetic gap may interact with the current-carrying voice coil, thereby generating a force. The resulting force may cause the voice coil to move back and forth, and thereby displace the cone from its rest position. The movement of the loudspeaker cone will move the air in front of the cone to create sound waves, thereby acoustically reproducing the electrical signal.

[0025] The loudspeaker 18 includes a loudspeaker cone (or diaphragm) that extends radially outward from the coil to produce a conical or dome-shaped form. The center of the cone near the voice coil can be fixed in place by the spider. The spider and the surround generally jointly allow only axial movement of the loudspeaker cone. During operation, and when current is driven through the coil, the coil may move axially, resulting in movement of the cone (i.e., cone drift). Generally, the cone drift or displacement x is the distance the cone moves from the rest position. As the amplitude of the electrical signal supplied to the coil changes, the distance from the rest position changes. For example, when the coil receives an electrical signal with a large voltage, the coil can move out of or further into the magnetic gap. When the coil moves into and out of the magnetic gap, the cone can be displaced from the rest position of the cone. A large voltage may produce a large cone drift, which in turn may cause the inherent non-linearity of the transducer to become apparent.

[0026] As the cone drift or displacement x increases, the surround and the spider may gradually stiffen. Due to the increased stiffness K ms , then more force may be required, and thus a greater input power may be needed to further increase the cone drift. Additionally, when the cone moves into the enclosure, the air inside the enclosure can be compressed and can act as a spring, thereby increasing the overall stiffness K ms (x). The inductance L of the coil e may also be affected by the electrical signal. The change in the inductance L of the voice coil e represents the displacement-dependent non-linear behavior of the inductance L e (x).

[0027] Figure 2 FIG. shows an example drift modeling system 100 for a bass reflex enclosure system. The system 100 can be executed by a Figure 1 controller 116. The system 100 can include a voltage envelope detector block 105 that is configured to receive an input audio signal. The input audio signal can be a test signal or a multi-level test signal. The input audio signal can be used to record displacement, AC voltage, DC voltage, AC current, and DC current. Based on these parameters, R driver, R_dc, and R_residual can be calculated. Subsequently, Δ temperature, as well as R e , impedance, and power compression can be calculated.

[0028] Figure 3 FIG. shows an example input voltage test signal used to characterize loudspeaker and port parameters. The signal consists of 4 seconds of pink noise followed by 4 swept sine waves (from 20 Hz to 1000 Hz), and these signals are repeated 15 times at increasing levels until the maximum available range of the loudspeaker to be modeled is reached.

[0029] Return Figure 2, the voltage envelope detector block 105 can determine the voltage envelope of the input audio and provide the voltage envelope of the input audio to the lookup function block 110.

[0030] The lookup function block 110 can include a lookup function for port parameters such as acoustic resistance R a and sound quality Ma. The voltage envelope can be used by the model 120 (as Figure 2 shown) to determine the instantaneous acoustic resistance R a and sound quality M a values at a specific voltage level. The port parameters can be interpolated from the voltage envelope via a lookup table and / or a smoothing function (curve fitting of measured R a and M a values that vary with the voltage level).

[0031] In an example of a lookup table, the lookup table can use the voltage level of the audio input to determine the instantaneous acoustic resistance R a and sound quality M a .

[0032] Figure 4A And Figure 4B shows an example of a smoothing function for acoustic resistance and sound quality. Figure 4A Shows an example graph of acoustic resistance versus peak input voltage. The optimal value for R a is seen at each of the 15 levels in the input test signal shown in Figure 3 . Then, a second-order polynomial is used to curve fit the 15 optimal values. The acoustic resistance R a can be determined for the voltage level either by interpolation or via the polynomial function of the curve fit.

[0033] Figure 4B Shows an example graph of sound quality versus peak input voltage. The graph can be modeled using some type of general function such as a polynomial or sigmoid. Similarly, the optimal value for M a is seen at each of the 15 voltage levels in the input test signal shown in Figure 3 . Then, in this case, a generalized sigmoid function is used to curve fit the 15 optimal values. The sound quality M a can be determined for the voltage level based on interpolation or via the sigmoid function of the curve fit.

[0034] Return Figure 2 , the lumped element model 120 can use the port parameters determined in the lookup function block 110 to determine the voice coil drift. The model 120 can receive the resistance Re from the thermal model block 115. The thermal model block 115 can update the drift model with the updated resistance R e .

[0035] A simplified recursive model for a reflex enclosure may include 'voltage' lumped element equations and is described below. This is only an example, and other forms and configurations are possible. Additionally, Le and its derivative can be removed from these equations.

[0036] And

[0037] 'Force' lumped element equations:

[0038]

[0039] The volume velocity can be expressed as:

[0040] M a q′ = -R a q + p;

[0041] Sound pressure:

[0042] C b p′ = -q + S d x′;

[0043] Current:

[0044]

[0045] Volume velocity:

[0046]

[0047] Sound pressure:

[0048]

[0049] Force of displacement:

[0050]

[0051]

[0052] where Bl(x), Kms(x), Le(x), are the force, stiffness, inductance, and the derivative of inductance, all of which are functions of the displacement x, and dt = 1 / audio sampling rate;

[0053] R ms is the mechanical resistance;

[0054] M ms is the voice coil diaphragm mass;

[0055] R e is the DC resistance of the voice coil;

[0056] Sd is the area of the transducer;

[0057] C b is the acoustic compliance. Additionally or alternatively, the mutual acoustic stiffness K b ;

[0058] M a (U pk ) is the acoustic mass assumed to be a function of the input voltage level; and

[0059] R a (U pk ) is the acoustic resistance assumed to be a function of the input voltage level. Compared with traditional methods, the simplified recursive form can use fewer computational resources.

[0060] The state - space model for the reflex box can be represented by a 5 - state column state vector X, where the 5 states include displacement x, velocity x′, current i, volume velocity q, and pressure p.

[0061] u(n) is the input voltage, where:

[0062]

[0063] and

[0064]

[0065] The state vector is updated as follows:

[0066] X(n + 1)=F*X(n)+G*u(n)

[0067] i = X(3,n).

[0068] Here, Bl(x),K ms (x),L e (x), are the force, stiffness, inductance, and derivative of the inductance, all of which are functions of the displacement x.

[0069] dt = 1 / audio sampling rate.

[0070] U pk - The peak voltage envelope detected from the input voltage.

[0071] M a (U pk ) is the acoustic mass in kg / m 4 and is a function of the input voltage level; and

[0072] R a (U pk ) is the acoustic resistance in N·s / m 5The calculated acoustic resistance, which is a function of the input voltage level.

[0073] State - space modeling may require matrix multiplication.

[0074] The non - linear parameters from the lumped - element model 120 can be used at block 130 to limit the voltage based on the drift envelope. This limitation can protect the voice coil of the speaker from having large displacements that could cause permanent damage to the speaker.

[0075] In general, the model can use the average DC resistance (DCR) on a test signal to first find the linear parameters. The linear parameters can include Bl, K ms , L e , M ms , R ms , M a , R a and C b . Then, the model can estimate the non - linear parameters, including DCR, fixed S d , M ms , K ms , C b , L e and Bl. The non - linear parameters can also include, but are not limited to, adaptive Bl, K ms and L e parameters. In a reflex box, the acoustic resistance R a and the acoustic mass M a can be adjusted according to the above method.

[0076] Figures 5A to 5B Examples of modeled displacements using the methods disclosed herein are shown. These are graphs of modeled displacements versus measured displacements. Figure 5A A diagram of an estimated reflex - box model for low voltage levels is shown. The diagram shows the modeled drift 505 and the measured drift 510. As shown, the modeled drift 505 is within a small degree of error of the measured drift. The normalized root - mean - square error is reported for the difference between the modeled and the measured. A low error means a good match.

[0077] In Figure 5A the example shown, the linear starting parameters are:

[0078] Blexp = 11.13 N / A (Newtons per Ampere);

[0079] K ms = 3531.9 N / m;

[0080] L e = 4.2e - 16, or a zero value;

[0081] R ms= 3.50978 N·s / m;

[0082] M ms = 0.049865 kg; and

[0083] R e = 5.3 ohms.

[0084] The parameters of the bass reflex enclosure are:

[0085] R a = 615 N·s / m 5 ;

[0086] M a = 13.54 kg / m 2 ;

[0087] S d = 0.055155 m 2 ; and

[0088] C b = 8.92e-7 m 5 / N.

[0089] Figure 5B A graph showing the estimated parameters of the bass reflex enclosure for a high-level voltage (e.g., 28V RMS) is shown. The graph shows the modeled drift 525 and the measured drift 530. As shown, the modeled drift 525 is within a small degree of error of the measured drift 530. In the example shown in Figure %B, the linear starting parameters can be the same as those in Figure 5A , except for R e , which can be 5.9. The parameters of the bass reflex enclosure can be:

[0090] R a = 3010 N·s / m 5 ;

[0091] M a = 11.12 kg / m 2 ;

[0092] S d = 0.055155 m 2 ;

[0093] C b = 8.92e-7 m 5 / N;

[0094] Figure 5C A graph showing the amplified linear match is shown, with the error shown as an overlaying waveform. Blue is the modeled displacement; orange is the measured displacement.

[0095] The acoustic resistance R aVary from 615 to 2197 to 3000 N s / m at 4Vp, 20Vp, and 40Vp respectively 5 The sound quality M a Vary from 13.54 to 11.12 to 11.12 kg / m at 4Vp, 20p, and 40Vp respectively 2 and can reach the maximum at 20V

[0096] As Figures 5A to 5C shown, a generalized model with the same or similar input parameters can be used. The acoustic resistance R a and the sound quality M a affect the swept - frequency signal because the shape of the curve changes with the acoustic resistance R a and the sound quality M a changing. As the voltage increases, the nulling at port tuning (0.6 on the X - axis) decreases. Figure 5A 、 Figure 5B and Figure 5C The swept - frequency signals of

[0097] Figure 6 reach nominal errors of 4.19%, 4.48%, and 6.425% respectively. Figure 2 shows an example process 600 of an example drift modeling system 100 for

[0098] At block 605, the process 600 can start, where the controller 116 can receive an input audio signal.

[0099] At block 610, the controller 116 can determine the voltage envelope of the input audio signal. a At block 615, the controller 116 can determine or interpolate port parameters, which include the acoustic resistance R a for a specific voltage level and the sound quality M. This can be achieved by using a look - up table and / or a smoothing function (curve fitting of the peak input voltage level of the audio input signal).

[0100] At block 620, the controller 116 can use the port parameters to determine the voice - coil drift. The controller 116 can also determine other linear and non - linear speaker parameters.

[0101] At block 625, the controller 116 can limit the voltage based on the drift envelope to protect the speaker from large displacements that may cause speaker damage or excessive distortion. The process 660 can then end.

[0102] Therefore, by monitoring the input level in the model, the acoustic resistance R a and the sound quality M aAssumed value. The compliance Cb can be fixed to a single value. The bass reflex enclosure model can use the input voltage tracking and the acoustic resistance R a and the sound quality M a mapping with the input voltage to generate the bass reflex enclosure parameters. R e can be a characterization function of temperature for achieving model accuracy.

[0103] Although the exemplary embodiments are described above, these embodiments are not intended to describe all possible forms of the invention. On the contrary, the words used in the specification are descriptive rather than restrictive words, and it should be understood that various changes can be made without departing from the spirit and scope of the invention. Additionally, the features of various implemented embodiments can be combined to form further embodiments of the invention.

Claims

1. A loudspeaker parameter system for bass reflex enclosure excursion modeling, the loudspeaker parameter system comprising: A loudspeaker having a housing with a resonant port, the loudspeaker including a driver and having a conductor, a magnet, and a diaphragm, wherein the conductor is a voice coil having voice coil excursion; A processor for excursion modeling, the processor being configured to: Receive an input signal, Determine a voltage level of the input signal, Estimate port parameters of the resonant port, the port parameters including at least one of acoustic resistance and acoustic mass, Apply a lumped element model to the input signal to determine a voice coil excursion envelope based at least on the port parameters, and Apply a voltage limit to the driver based on the voice coil excursion envelope to protect the loudspeaker from large displacements.

2. The system of claim 1, wherein the port parameters are estimated at a specific voltage level.

3. The system of claim 1, wherein a look-up table is used to estimate the port parameters.

4. The system of claim 1, wherein the port parameters are estimated by curve fitting a peak input voltage level of the input signal.

5. The system of claim 1, wherein the voltage limit is at least partially based on the voice coil excursion.

6. The system of claim 5, wherein the lumped element model is based on a DC resistance received from a thermal model.

7. A method for modeling parameters of a bass reflex loudspeaker having a housing with a resonant port, the bass reflex loudspeaker including a driver and having a conductor, a magnet, and a diaphragm, wherein the conductor is a voice coil having voice coil excursion, the method comprising: Receiving an input signal, Determining a voltage level of the input signal, Interpolating port parameters of the resonant port, the port parameters including at least one of acoustic resistance and acoustic mass, Applying a lumped element model to the input signal to determine a voice coil excursion envelope based at least on the port parameters, and Applying a voltage limit to the driver based on the voice coil excursion envelope to protect the bass reflex loudspeaker from large displacements.

8. The method of claim 7, wherein the voltage level is determined by an envelope detector.

9. The method of claim 7, wherein the port parameters are estimated at a specific voltage level and the port parameters are voltage-dependent.

10. The method of claim 7, wherein a look-up table is used to estimate the port parameters.

11. The method of claim 9, wherein the port parameters are estimated by curve fitting a peak input voltage level of the input signal.

12. The method of claim 9, the method further comprising applying a lumped element model to the input signal to determine the port parameters and the voice coil excursion, wherein the voltage limit is at least partially based on the voice coil excursion.

13. The method of claim 12, wherein the lumped element model is based on a DC resistance received from a thermal model.

14. The method according to claim 9, determining the driver resistance and Δ temperature based on at least one of the voltage level and current of the input signal.

15. A loudspeaker parameter system, the loudspeaker parameter system comprising: A loudspeaker having a housing with a resonant port, the loudspeaker including a driver and having a conductor, a magnet, and a diaphragm, wherein the conductor is a voice coil having a voice coil drift; A processor for drift modeling, the processor being configured to: Receive an input signal, Determine the voltage level of the input signal, Estimate the acoustic resistance, wherein the acoustic resistance and the acoustic quality are voltage-dependent, Interpolate the port parameters of the resonant port, the port parameters including at least one of the acoustic resistance and the acoustic quality, Apply a lumped element model to the input signal to determine a voice coil drift envelope based at least on the port parameters, and Apply a voltage limit to the driver based on the voice coil drift envelope to protect the loudspeaker from large displacements.

16. The system according to claim 1, wherein the voltage level is determined by an envelope detector.

17. The system according to claim 15, wherein the acoustic resistance and the acoustic quality are estimated at a specific voltage level.

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