A loudspeaker with a hybrid excitation-permanent magnet magnetic circuit and a dynamic BL compensation control method thereof

Abstract

This invention discloses a hybrid magnetic circuit loudspeaker with excitation and permanent magnet and its dynamic BL compensation control method. The loudspeaker includes a permanent magnet (providing 80%-95% of the main magnetic flux), an excitation coil (providing 5%-20% of the auxiliary magnetic flux), a temperature sensor, a controller, and an excitation power supply. The controller employs dual closed-loop control (temperature outer loop + BL inner loop), dynamically adjusting the excitation current through a BL-temperature compensation model to control BL fluctuations within ±2% in the 20-120°C range. The control method includes: initializing and establishing a BL-temperature reference database → real-time monitoring of temperature / current / speed → estimating BL using the back EMF method → ​​temperature compensation calculation → BL closed-loop fine-tuning → PWM output of the excitation current. This invention achieves a sound pressure level drop of <0.2dB (compared to 2.7dB for traditional permanent magnet circuits) at a continuous 500W input, a THD increase of only 2.3% from 2.0% (compared to 4.6% for traditional circuits), and excitation power consumption of only 1.4% of the rated power. It is suitable for large-diameter subwoofers and compression drivers.

Description

Technical Field

[0001] This invention relates to the field of electroacoustic transducer technology, and in particular to an excitation-permanent magnet hybrid magnetic circuit loudspeaker and its dynamic BL compensation control method, applicable to large-diameter subwoofers, compression drivers and full-range loudspeaker units. Background Technology

[0002] In an electroacoustic transducer, the magnetic circuit system provides the working magnetic field for the voice coil. When the voice coil is energized in the magnetic field, it generates a Lorentz force that drives the diaphragm. The performance of the magnetic circuit system directly determines the speaker's sensitivity, distortion, and power handling capability. Currently, mainstream magnetic circuit systems are divided into two categories: permanent magnet circuits and excitation circuits.

[0003] Permanent magnet circuits use neodymium iron boron (NdFeB) or ferrite permanent magnets to provide a constant magnetic field. They offer advantages such as simple structure, no need for external power supply, and low cost, making them the technology used in over 99% of loudspeakers. However, permanent magnet circuits have the following inherent drawbacks: the magnetic flux density of the permanent magnet decreases with increasing temperature (the remanence temperature coefficient of neodymium iron boron is approximately -0.12% / °C). When the voice coil heats up under high power input, the magnetic circuit temperature rises, leading to a decrease in the magnetic flux density B in the gap, which in turn reduces the force coefficient BL (B×L, where L is the effective length of the voice coil wire). This decrease in BL results in reduced loudspeaker sensitivity and increased low-frequency distortion (THD rises sharply with the nonlinear change of BL), a phenomenon known as power compression. For a 21-inch subwoofer, under continuous 500W input, the magnetic circuit temperature can rise from room temperature to 80-120°C, and the BL decreases by 8%-15%, causing audible sound quality degradation.

[0004] The field coil uses electromagnets instead of permanent magnets to generate a magnetic field through a DC excitation current. Its advantages include the ability to change the magnetic field strength in real time by adjusting the excitation current, and the absence of the high-temperature demagnetization problem associated with permanent magnets. However, the pure field coil requires continuous consumption of excitation power (typically 5%-15% of the voice coil's rated power), resulting in low efficiency; furthermore, the excitation coil has a relatively large inductance, leading to a slow magnetic field response and difficulty in keeping up with rapid changes in audio signals.

[0005] Prior art, US 5,761,317, discloses a LOUDSPEAKER AS VARIABLE GAIN DEVICE, whose structure includes a permanent magnet and an excitation coil. The excitation coil is driven by a frequency-rich signal source (fat generator) to modulate the permanent magnet magnetic field, generating modulation products to broaden the spectrum of the input signal. The core purpose of this patent is to use the loudspeaker as a variable gain device for audio effects processing (such as distortion, chorus, etc.), rather than improving the loudspeaker's linearity or compensating for power compression. Its excitation coil is driven by an audio frequency signal and interacts with the voice coil current to produce a modulation effect, essentially belonging to the field of signal processing, rather than thermal management or linearity optimization. Furthermore, this patent does not involve any temperature detection, BL monitoring, or closed-loop compensation control.

[0006] Prior art US 10,812,912 (Dinaburg) discloses a loudspeaker that includes a permanent magnet and an electromagnet, but the electromagnet is used to drive the relative motion of the inner and outer parts of the diaphragm to reduce acoustic distortion, and does not involve compensating for the temperature drift of the permanent magnet circuit through the excitation current.

[0007] Prior art US 12,108,200 (Apple) discloses a flexible loudspeaker comprising a permanent magnet and an electromagnet for wearable displays. The magnet is formed from rubber or polymer doped with magnetic particles. This belongs to the field of micro loudspeakers and is unrelated to the high-power loudspeaker magnetic circuit compensation technology of this invention.

[0008] To address the aforementioned problems, this invention proposes a hybrid magnetic circuit loudspeaker with excitation and permanent magnet components and its dynamic thermal drift (BL) compensation control method. This hybrid magnetic circuit uses a permanent magnet to provide the main magnetic field (accounting for 80%-95% of the magnetic flux) and an excitation coil to provide the auxiliary magnetic field (accounting for 5%-20% of the magnetic flux). Through real-time temperature detection and a closed-loop control algorithm, the excitation current is dynamically adjusted to compensate for the BL decrease caused by temperature rise in the permanent magnet circuit, thus maintaining a constant BL over a wide temperature range. Unlike the audio modulation application in US 5,761,317, the excitation coil of this invention is driven by DC or low-frequency compensation current and does not participate in audio signal modulation; it is only used to compensate for thermal drift, falling within the field of thermal management / linearity optimization. Summary of the Invention

[0009] The purpose of this invention is to provide a hybrid magnetic circuit loudspeaker with excitation and permanent magnet and its dynamic BL compensation control method. By using a hybrid magnetic circuit with permanent magnet and excitation and closed-loop temperature compensation control, the BL fluctuation can be controlled within ±2% under high power input, which significantly reduces power compression and thermal distortion.

[0010] To achieve the above objectives, the present invention adopts the following technical solution: A hybrid magnetic circuit loudspeaker with excitation and permanent magnet components includes: a magnetic circuit system comprising a permanent magnet, an excitation coil, a magnetic guide plate, and a center post; the permanent magnet is a neodymium iron boron or ferrite permanent magnet, providing a main magnetic flux; the excitation coil is wound around the center post or the magnetic guide plate, providing an auxiliary magnetic flux; the main magnetic flux and the auxiliary magnetic flux are superimposed in the same direction in a magnetic gap; a voice coil is suspended in the magnetic gap and connected to a diaphragm; a temperature sensor is embedded in the magnetic circuit system for real-time detection of the magnetic circuit temperature T; a controller receives the signal from the temperature sensor and outputs an excitation current control signal according to a preset BL-temperature compensation model; and an excitation power supply provides a DC compensation current Ifc to the excitation coil according to the control signal from the controller.

[0011] Furthermore, the main magnetic flux provided by the permanent magnet accounts for 80%-95% of the total magnetic flux, and the auxiliary magnetic flux provided by the excitation coil accounts for 5%-20% of the total magnetic flux.

[0012] Furthermore, the excitation coil has 50-500 turns, a wire diameter of 0.3-1.2mm, a DC resistance of 0.5-10Ω, and a rated excitation current of 0.5-5A.

[0013] Furthermore, the temperature sensor is an NTC thermistor, a PT100 platinum resistance thermometer, or a thermocouple, embedded in the central post or magnetic plate, 1-5 mm away from the magnetic gap surface.

[0014] Furthermore, the controller is a DSP or MCU with a built-in BL-temperature compensation model, which is: Ifc(T)=Ifc0+k×(T-T0), where Ifc0 is the reference excitation current at room temperature T0, k is the temperature compensation coefficient, k=(αB×BL0) / (BLaux×Rfc)×(1+β), αB is the temperature coefficient of remanence of the permanent magnet, BL0 is the force coefficient at room temperature, BLaux is the force coefficient generated by the unit current of the excitation coil, Rfc is the resistance of the excitation coil, and β is the magnetic circuit thermal resistance correction factor.

[0015] Furthermore, it also includes a current sensor connected in series with the voice coil for real-time detection of the voice coil current I.

[0016] Furthermore, it also includes a real-time BL estimation module, which estimates the real-time force coefficient based on the voice coil current I and the voice coil back electromotive force ε using the formula BL=ε / v, where v is the voice coil vibration velocity, measured by a laser vibrometer or an accelerometer.

[0017] Furthermore, the controller employs dual closed-loop control: the outer loop is a temperature loop, which adjusts the excitation current based on feedback from the temperature sensor; the inner loop is a BL loop, which finely adjusts the excitation current based on the real-time estimated value of BL, so that BL is maintained within ±2% of the reference force coefficient BL0 at room temperature.

[0018] Furthermore, the magnetic circuit system also includes a short-circuit ring, which is a copper or aluminum ring conductor embedded in the magnetic plate to suppress high-frequency eddy current losses caused by magnetic flux modulation.

[0019] Furthermore, the permanent magnet is a radially magnetized annular permanent magnet, and the excitation coil is an annular coil, coaxially sleeved on the central column.

[0020] The present invention also provides a method for dynamic black-light compensation control of loudspeakers, comprising the following steps: S1: Initialization: At room temperature T0 (20±2°C), measure the reference force coefficient BL0 and reference excitation current Ifc0 of the loudspeaker to establish a BL-temperature reference database; the method for establishing the BL-temperature reference database is as follows: in a constant temperature chamber, the temperature is increased from 20°C to 120°C in 5°C increments. After stabilizing at each temperature point for 30 minutes, the BL value and the corresponding compensation excitation current are measured, and the BL(T) curve and Ifc(T) curve are obtained by fitting.

[0021] S2: Real-time monitoring: The magnetic circuit temperature T is collected in real time by a temperature sensor, the voice coil current I is collected in real time by a current sensor, and the voice coil vibration velocity v is collected in real time by a laser vibrometer or an accelerometer.

[0022] S3: BL estimation: The real-time force coefficient BLreal=ε / v is estimated according to the back electromotive force method, where ε is the back electromotive force of the voice coil, which is obtained by subtracting the voltage drop across the resistance from the voltage at the voice coil terminals; the calculation method of the back electromotive force ε is: ε=UI×Re, where U is the voltage at the voice coil terminals and Re is the DC resistance of the voice coil (real-time correction: Re(T)=Re0×[1+αCu×(T-T0)], where αCu is the temperature coefficient of copper 0.0039 / °C).

[0023] S4: Temperature compensation: Calculate the target excitation current Ifc(T) = Ifc0 + k × (T - T0) according to the BL-temperature compensation model.

[0024] S5: BL closed-loop fine-tuning: Compare BLreal with the target value BLtarget. If the deviation exceeds ±2%, fine-tune the excitation current ΔIfc=(BLtarget-BLreal) / BLaux, where BLaux is the force coefficient generated by the unit current of the excitation coil. The response bandwidth of the BL closed-loop fine-tuning is lower than the audio operating frequency band of the voice coil (20Hz-20kHz) to avoid mutual interference with the audio signal.

[0025] S6: Output control: Ifc(T)+ΔIfc is used as the final excitation current command, and the excitation power supply is driven by PWM or a linear amplifier, with an update cycle of ≤1ms; the switching frequency of the PWM-driven excitation power supply is 20-100kHz, and the bandwidth of the linear amplifier is 0-50kHz.

[0026] Beneficial effects 1. Significantly reduced power compression: Through dynamic BL compensation, BL fluctuations are controlled within ±2% as the magnetic circuit temperature rises from 20°C to 120°C, while the BL of traditional permanent magnet circuits drops by 12%-18%. Under continuous 500W input, the sound pressure level of traditional loudspeakers drops by about 2-3dB, while the sound pressure level of this invention drops by <0.2dB.

[0027] 2. Significantly reduced thermal distortion: Nonlinear changes in BL are one of the main sources of low-frequency distortion. This invention reduces THD below 10kHz by 30%-50% by maintaining a constant BL (at 500W input, the THD of a conventional loudspeaker increases from 2.5% to 4.8%, while the THD of this invention only increases from 2.0% to 2.3%).

[0028] 3. Efficiency optimization: The permanent magnet provides 80%-95% of the main magnetic flux, while the excitation coil provides only 5%-20% of the auxiliary magnetic flux. The excitation power consumption is only 1%-3% of the rated power of the voice coil, which is much lower than that of the pure excitation magnetic circuit (5%-15%).

[0029] 4. Fast response speed: It adopts dual closed-loop control (temperature outer loop + BL inner loop), with an update cycle of ≤1ms, which can track the temperature change of the magnetic circuit in real time and compensate for the delay of <5ms.

[0030] 5. Fundamental Difference from Existing Technologies: The excitation coil in US 5,761,317 is driven by an audio frequency signal to modulate the permanent magnet magnetic field and produce audio effects (distortion / chorus), which falls under signal processing; the excitation coil of this invention is driven by a DC / low-frequency compensation current to compensate for temperature drift in the permanent magnet circuit, which falls under thermal management / linearity optimization. The driving signal frequencies, control objectives, and technical fields of the two are completely different. In Comparative Example 2 (pure permanent magnet circuit), the BL decreases by 12.5% ​​with temperature; in Comparative Example 3 (pure excitation circuit), there is no power compression but low efficiency (excitation power consumption accounts for 8.4%). This invention achieves constant BL while maintaining high efficiency. Attached Figure Description

[0031] Figure 1 This is a half-sectional schematic diagram of the excitation-permanent magnet hybrid magnetic circuit loudspeaker of the present invention; Figure 2 for Figure 1 An enlarged cross-sectional view of the central magnetic circuit system (AA section) shows the magnetic flux distribution of the permanent magnet, excitation coil, and magnetic gap. Figure 3 This is a block diagram illustrating the principle of the control system. Figure 4 This is a comparison graph of the BL-temperature curves of the examples and the comparative examples; Figure 5 The sound pressure level-time curves for the examples and comparative examples are shown at a continuous input of 500W. Figure 6 A comparison graph of THD-temperature curves for the example and the comparative example (500W input). Figure 7 The flowchart is for the dual closed-loop control algorithm; Figure 8 The curves showing the relationship between different permanent magnet ratios (80% / 90% / 95%) and excitation power consumption; Figure 9 A comparison of the effects of short-circuit rings in suppressing eddy current losses; Figure 10 This is a comparison diagram of the drive signal spectrum of the embodiment and that of US 5,761,317; Figure 11 Temperature distribution cloud map for magnetic circuit thermal simulation (showing the temperature difference between the central column and the magnetic plate) (ANSYS Fluent, 500W steady state). Figure 12 Comparison chart for verifying the accuracy of BL estimation using the back electromotive force method (Klippel measured value vs. estimated value); Figure 13 Bode plot for stability analysis of a dual-closed-loop control system; Figure 14 This is the temperature step response curve (BL recovery process from 20°C to 100°C). Figure 15 The power step response curve (BL instantaneous fluctuation when 100W→500W). Detailed Implementation

[0032] The specific embodiments of the present invention will be further described in detail below with reference to the accompanying drawings.

[0033] Example 1: Hybrid magnetic circuit of excitation-permanent magnet for 21-inch subwoofer This embodiment designs a hybrid magnetic circuit of excitation and permanent magnet for the Hermit Audio SW21-PRO 21-inch subwoofer unit.

[0034] Magnetic circuit system structure: An external magnetic circuit is adopted, with neodymium iron boron (N52) toroidal permanent magnets (outer diameter Φ180mm, inner diameter Φ140mm, thickness 20mm, axially magnetized) providing the main magnetic flux. The magnetic guide plates are made of low-carbon steel (DT4C), with an upper magnetic guide plate (outer diameter Φ200mm, thickness 15mm) and a lower magnetic guide plate (outer diameter Φ200mm, thickness 15mm). The central column is a DT4C cylinder (diameter Φ60mm, height 80mm). The magnetic gap width is 12mm, and the magnetic flux density Bgap = 2.0T (at room temperature 20°C).

[0035] Excitation coil: Utilizing high-temperature resistant enameled copper wire (QZY-2 / 180, temperature resistant 180°C), 0.8mm in diameter, wound on the central column (located below the permanent magnet, not occupying the magnetic gap space), with 200 turns and 4 layers. DC resistance is 3.5Ω, and inductance is 85mH. Rated excitation current is 1.5A, maximum excitation current is 3.0A. The auxiliary magnetic flux generated by the excitation coil enters the magnetic gap through the central column and the magnetic guide plate, superimposing in the same direction as the main magnetic flux of the permanent magnet. Actual measurements show that the main magnetic flux provided by the permanent magnet accounts for 90% of the total magnetic flux, while the auxiliary magnetic flux provided by the excitation coil accounts for 10%.

[0036] Temperature sensor: A PT100 platinum resistance thermometer (Class B accuracy, ±0.3°C) is embedded in the lower magnetic plate, 3mm from the magnetic gap surface, and is in close contact with the magnetic plate via thermal grease. The response time constant τ = 2.5s. Magnetic circuit thermal simulation (ANSYS Fluent, steady-state analysis, voice coil heating 500W, ambient temperature 20°C) shows: the highest temperature of the center column reaches 118°C, the magnetic plate temperature is 105°C, the magnetic gap surface temperature is 112°C, and the temperature at the temperature sensor installation position (3mm from the magnetic gap surface) is 110°C, with a deviation of only 2°C from the actual magnetic gap temperature, meeting the compensation accuracy requirements. If the temperature sensor embedding depth is 10mm, the temperature reading is 98°C, with a deviation of 14°C from the actual magnetic gap temperature, resulting in an open-loop compensation error of approximately 5.6%. Therefore, an embedding depth of 1-5mm is the optimal range that balances measurement response speed and temperature representativeness.

[0037] Current sensor: A Hall current sensor (ACS712, range ±5A, accuracy ±1.5%) is used, connected in series with the voice coil to detect the voice coil current in real time.

[0038] Laser vibration meter: Polytec PSV-500 is used to measure the vibration velocity v of the voice coil for real-time estimation of BL.

[0039] Controller: Employs a TI TMS320F28379D dual-core DSP with a clock frequency of 200MHz. Built-in BL-temperature compensation model: Ifc(T) = Ifc0 + k × (T - T0). Where, Ifc0 = 0.5A (reference excitation current at room temperature of 20°C), and k = 0.025A / °C (obtained through fitting from the BL-temperature reference database).

[0040] BL-Temperature Reference Database Establishment: The loudspeaker was placed in a constant temperature chamber, and the temperature was increased from 20°C to 120°C in 5°C increments. After stabilizing at each temperature point for 30 minutes, the BL value was measured using a Klippel analyzer, and the excitation current required to restore BL to BL0 was recorded. The fitted results were: BL(T) = BL0 × [1 - 0.0012 × (T - 20)] (the remanence temperature coefficient of NdFeB N52 is αB = -0.12% / °C), Ifc(T) = 0.5 + 0.025 × (T - 20).

[0041] Dual closed-loop control algorithm: Outer loop (temperature loop): Sampling period 10ms, temperature sensor reads magnetic circuit temperature T, target excitation current is calculated according to Ifc(T) model. Inner loop (BL loop): Sampling period 1ms, real-time BLreal is estimated by back electromotive force method: ε=UI×Re(T), BLreal=ε / v. Where Re(T)=Re0×[1+0.0039×(T-20)], Re0=6.5Ω (voice coil room temperature DC resistance). If |BLreal-BL0| / BL0>2%, then the fine adjustment ΔIfc=(BL0-BLreal) / BLaux is calculated, where BLaux=0.08T·m / A (force coefficient generated by unit current of excitation coil). Output control: Ifc(T)+ΔIfc is used as the final command, PWM drives MOSFET full bridge (IRFP260N, switching frequency 50kHz), and after LC filtering (L=2.2mH, C=470μF), a smooth DC excitation current is output. Current ripple <50mA.

[0042] Short-circuit ring: A copper short-circuit ring (outer diameter Φ160mm, inner diameter Φ130mm, thickness 2mm, T2 copper) is embedded in the lower magnetic plate to suppress eddy current losses caused by changes in magnetic flux at audio frequencies. Actual measurements show that without the short-circuit ring, the eddy current loss of the magnetic plate is approximately 8W; with the short-circuit ring, the eddy current loss is reduced to 1.5W.

[0043] Accuracy verification of BL estimation using the back electromotive force (EMF) method: At three temperature points—20°C, 60°C, and 100°C—the BL values ​​were directly measured using a Klippel analyzer (as the true values) and compared with the estimated values ​​using the back EMF method. The results are as follows: At 20°C, the Klippel measurement was 118.0 T·m, and the back EMF estimation was 117.6 T·m, with an error of -0.34%; at 60°C, the Klippel measurement was 114.2 T·m, and the back EMF estimation was 113.8 T·m, with an error of -0.35%; at 100°C, the Klippel measurement was 109.8 T·m, and the back EMF estimation was 109.2 T·m, with an error of -0.55%. Statistical analysis of 20 repeated measurements showed a mean error of -0.42%, a standard deviation of 0.18%, and a maximum absolute error of 0.78%, indicating sufficient margin (>1.5 times) to meet the ±2% control target.

[0044] Stability analysis of the dual-loop control: The outer temperature loop transfer function is G1(s) = Kp1 / (τs+1), where τ = 2.5s (temperature sensor time constant), and Kp1 = 0.025A / °C; the inner loop transfer function is G2(s) = Kp2 / (0.001s+1), where Kp2 = 12.5A / (T·m). Frequency domain analysis using MATLAB / Simulink shows that the open-loop transfer function has a phase margin of 68° and a gain margin of 12dB at the cutoff frequency fc = 0.8Hz. Under a step disturbance (temperature suddenly increasing from 20°C to 100°C), the BL overshoot is <3%, the settling time is <120ms, and the steady-state error is <0.5%. This demonstrates that the dual-loop control system is stable and reliable over a wide temperature range.

[0045] Analysis of the impact of excitation coil heating: In Example 1, the power consumption of the excitation coil at the maximum compensation current of 1.75A (at 105°C) is Ifc²×Rfc=1.75²×3.5≈10.7W. Magnetic circuit thermal simulation shows that this power consumption causes an additional temperature rise of approximately 3.2°C, which accounts for only 2.8% of the temperature rise caused by the voice coil heating (approximately 450W). Therefore, the impact of excitation coil heating on BL compensation accuracy is negligible (<0.4%).

[0046] Performance testing: (1) BL-Temperature characteristics: In a constant temperature chamber, the temperature was increased from 20°C to 120°C, and BL was measured every 10°C. The measured BL fluctuation in this embodiment was ±1.8% (BL=118T·m at 20°C, BL=116.5T·m at 120°C). In Comparative Example 1 (pure permanent magnet circuit, N52 magnet of the same specification), BL decreased from 118T·m to 102T·m (a decrease of 13.6%). In Comparative Example 2 (pure excitation circuit, no permanent magnet, excitation current 3.5A), BL remained constant at 115T·m (but the excitation power consumption was as high as 42W).

[0047] (2) Continuous power test: In an anechoic chamber, input 500W pink noise (IEC 60268-5, 6dB peak factor) for 180 minutes. In this embodiment, the measured magnetic circuit temperature increased from 20°C to 105°C, the sound pressure level (at 1m, 100Hz) decreased from 112.5dB to 112.3dB (a decrease of 0.2dB), and the THD increased from 2.0% to 2.2%. In Comparative Example 1, the magnetic circuit temperature increased from 20°C to 110°C, the sound pressure level decreased from 112.5dB to 109.8dB (a decrease of 2.7dB), and the THD increased from 2.5% to 4.6%. In Comparative Example 2, the magnetic circuit temperature increased from 20°C to 85°C, the sound pressure level decreased from 110.2dB to 110.0dB (a decrease of 0.2dB), and the THD increased from 2.1% to 2.3%, but the excitation power consumption remained constant at 42W.

[0048] (3) Efficiency Comparison: The excitation power consumption of this embodiment varies with temperature: 3.5W at 20°C (Ifc=0.5A), 10.7W at 105°C (Ifc=1.75A), with an average power consumption of approximately 7.1W, accounting for 1.4% of the rated power of the voice coil (500W). In contrast, the excitation power consumption of the second embodiment is constant at 42W, accounting for 8.4% of the rated power. The efficiency of this embodiment is significantly better than that of the pure excitation circuit.

[0049] (4) Transient Response: At a magnetic circuit temperature of 60°C, the input power was suddenly increased from 100W to 500W, and the time it took for the BL to recover to the target value was measured. In this embodiment, the BL recovery time (from deviation >2% to <2%) was 4.2ms. In the comparative example (without compensation), the BL continued to decrease without recovery. This proves that the dynamic compensation response speed of the present invention meets the real-time requirements.

[0050] (5) Comparison with US 5,761,317: The technical purpose of US 5,761,317 is completely different from that of this invention—its excitation coil is driven by an audio frequency signal (1kHz sine wave, amplitude 1A), aiming to produce an audio modulation effect (distortion / chorus), and the 3.2% increase in THD is the intended function of that patent rather than a defect; the excitation coil of this invention is driven by a DC compensation current (ripple <50mA), aiming to counteract the temperature drift of the permanent magnet circuit and maintain a constant BL, and the reduction in THD is the expected result. The two have completely different drive signal spectra, magnetic flux characteristics, and technical purposes.

[0051] Example 2: 1.4-inch compression driver excitation-permanent magnet hybrid magnetic circuit This embodiment targets the 1.4-inch throat compressor driver for the Hermit Audio system. The magnetic circuit system employs an internal magnet structure, with the permanent magnet being a neodymium iron boron (N48) toroidal magnet (outer diameter Φ50mm, inner diameter Φ35mm, thickness 8mm, radially magnetized). The excitation coil uses 0.5mm enameled wire with 120 turns, wound at the base of the central post, with a DC resistance of 2.8Ω. The permanent magnet accounts for 92%, and the excitation coil accounts for 8%. The temperature sensor is an NTC thermistor (10kΩ, B value 3950), embedded in the upper magnetic plate, 2mm from the magnetic gap surface. The controller uses an STM32F407, with the BL-temperature model: Ifc(T) = 0.3 + 0.018 × (T - 20). Actual measurements within the 20-100°C range show BL fluctuation ±1.5% and SPL fluctuation <0.15dB.

[0052] Comparative Example 1: Pure permanent magnet circuit (21-inch subwoofer) The same permanent magnet, magnetic plate, and central column as in Example 1 were used, but without the excitation coil, temperature sensor, and controller. The measured BL decreased from 118 T·m at 20°C to 102 T·m at 120°C (a decrease of 13.6%), the sound pressure level decreased by 2.7 dB, and the THD increased from 2.5% to 4.6%.

[0053] Comparative Example 2: Pure Excitation Magnetic Circuit (21-inch Subwoofer) The same magnetic plate and center post as in Example 1 were used, but without permanent magnets. The excitation coil had 600 turns, a wire diameter of 1.0 mm, a DC resistance of 8.5 Ω, and a rated excitation current of 3.5 A. The measured BL was constant at 115 T·m, but the excitation power consumption was constant at 42 W (Ifc²×Rfc=3.5²×3.5=42.9 W), accounting for 8.6% of the voice coil's rated power, indicating low efficiency. The magnetic circuit temperature rose from 20°C to 85°C (due to the excitation coil's own heating).

[0054] Comparative Example 3: Open-loop temperature compensation (no BL feedback) The same hybrid magnetic circuit hardware as in Example 1 was used, but the controller only performed open-loop compensation based on the temperature sensor (without BL inner loop feedback). Due to the uneven distribution of thermal resistance in the magnetic circuit (the temperature of the central column is higher than that of the magnetic plate), there is a deviation between the temperature sensor reading and the actual temperature of the magnetic gap (approximately 5-8°C), resulting in residual error in BL compensation. The measured BL fluctuation was ±4.5%, and the sound pressure level fluctuation was approximately 0.5 dB. This demonstrates the necessity of dual closed-loop control (temperature outer loop + BL inner loop).

[0055] Comparative Example 4: Reproduced Structure of US 5,761,317 According to US 5,761,317 Figure 9The structure employs a permanent magnet (N52) + excitation coil (200 turns, 0.8mm wire diameter) + audio modulation signal source (1kHz sine wave, 1A amplitude). Measured magnetic flux density showed a 1kHz modulation component (±0.15T), voice coil force showed 1kHz intermodulation distortion, and THD increased by 3.2%. The technical purpose of this patent is completely different from that of this invention—it aims to produce audio modulation effects (distortion / chorus), while this invention aims to suppress thermal distortion (maintain constant BL). The driving signal frequencies (audio vs. DC / low frequency), control objectives (modulation vs. compensation), and technical fields (signal processing vs. thermal management) are entirely different.

[0056] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Any simple modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention should still fall within the scope of the present invention.

Claims

1. A loudspeaker with a hybrid magnetic circuit of excitation-permanent magnet, characterized in that, include: A magnetic circuit system, comprising a permanent magnet, an excitation coil, a magnetic guide plate, and a central column; The permanent magnet is a neodymium iron boron or ferrite permanent magnet, which provides the main magnetic flux; The excitation coil is wound around the central column or magnetic plate to provide auxiliary magnetic flux; The main magnetic flux and the auxiliary magnetic flux are superimposed in the same direction in the magnetic gap; A voice coil, which is suspended in the magnetic gap and connected to the diaphragm; A temperature sensor, embedded in the magnetic circuit system, is used to detect the magnetic circuit temperature T in real time; The controller receives the signal from the temperature sensor and outputs an excitation current control signal according to the preset BL-temperature compensation model. The excitation power supply provides a DC compensation current Ifc to the excitation coil according to the control signal of the controller.

2. The loudspeaker according to claim 1, characterized in that, The permanent magnet provides 80%-95% of the main magnetic flux, and the excitation coil provides 5%-20% of the auxiliary magnetic flux. The excitation coil has 50-500 turns, a wire diameter of 0.3-1.2mm, a DC resistance of 0.5-10Ω, and a rated excitation current of 0.5-5A.

3. The loudspeaker according to claim 1, characterized in that, The temperature sensor is an NTC thermistor, a PT100 platinum resistance thermometer, or a thermocouple, embedded in the central post or magnetic plate, 1-5 mm away from the magnetic gap surface; the controller is a DSP or MCU with a built-in BL-temperature compensation model, the model being: Ifc(T)=Ifc0+k×(T-T0), where Ifc0 is the reference excitation current at room temperature T0, and k is the temperature compensation coefficient.

4. The loudspeaker according to claim 1, characterized in that, It also includes a current sensor connected in series with the voice coil for real-time detection of the voice coil current I; it also includes a real-time BL estimation module, which estimates the real-time force coefficient based on the voice coil current I and the voice coil back electromotive force ε using the formula BL=ε / v, where v is the voice coil vibration velocity, measured by a laser vibrometer or an accelerometer.

5. The loudspeaker according to claim 4, characterized in that, The controller employs a dual closed-loop control: the outer loop is a temperature loop, which adjusts the excitation current based on feedback from the temperature sensor; the inner loop is a BL loop, which finely adjusts the excitation current based on the real-time estimated value of BL, so that BL is kept within ±2% of the reference force coefficient BL0 at room temperature.

6. The loudspeaker according to claim 1, characterized in that, The magnetic circuit system also includes a short-circuit ring, which is a copper or aluminum ring conductor embedded in the magnetic plate; the permanent magnet is a radially magnetized ring permanent magnet, and the excitation coil is a ring coil coaxially sleeved on the central column.

7. A method for dynamic BL compensation control of a loudspeaker, employing the loudspeaker as described in any one of claims 1-6, characterized in that, Includes the following steps: S1: Initialization: At room temperature T0 (20±2°C), measure the reference force coefficient BL0 and reference excitation current Ifc0 of the loudspeaker to establish a BL-temperature reference database; the method for establishing the BL-temperature reference database is as follows: in a constant temperature chamber, the temperature is increased from 20°C to 120°C in 5°C increments. After stabilizing at each temperature point for 30 minutes, the BL value and the corresponding compensation excitation current are measured, and the BL(T) curve and Ifc(T) curve are fitted to obtain the BL(T) curve; S2: Real-time monitoring: The magnetic circuit temperature T is collected in real time by a temperature sensor, the voice coil current I is collected in real time by a current sensor, and the voice coil vibration velocity v is collected in real time by a laser vibration meter or an accelerometer. S3: BL estimation: The real-time force coefficient BLreal=ε / v is estimated according to the back electromotive force method, where ε is the voice coil back electromotive force, obtained by subtracting the voltage drop across the resistor from the voltage across the voice coil terminals; the calculation method for the back electromotive force ε is: ε=UI×Re, where U is the voltage across the voice coil terminals and Re is the DC resistance of the voice coil (real-time correction: Re(T)=Re0×[1+αCu×(T-T0)], αCu is the temperature coefficient of copper 0.0039 / °C); S4: Temperature compensation: Calculate the target excitation current Ifc(T) = Ifc0 + k × (T - T0) according to the BL-temperature compensation model; S5: BL Closed-Loop Fine-Tuning: Compare BLreal with the target value BLtarget. If the deviation exceeds ±2%, fine-tune the excitation current ΔIfc=(BLtarget-BLreal) / BLaux, where BLaux is the force coefficient generated by the unit current of the excitation coil. The response bandwidth of the BL closed-loop fine-tuning is lower than the audio operating frequency band of the voice coil (20Hz-20kHz) to avoid mutual interference with the audio signal. S6: Output control: Ifc(T)+ΔIfc is used as the final excitation current command, and the excitation power supply is driven by PWM or linear amplifier, with an update cycle of ≤1ms; the switching frequency of the PWM-driven excitation power supply is 20-100kHz.

8. The method according to claim 7, characterized in that, The measurement equipment for the BL-temperature reference database mentioned in S1 is a Klippel analyzer, the fitting method is the least squares method, and the goodness of fit R² ≥ 0.

995.

9. The method according to claim 7, characterized in that, The PID parameters for the BL closed-loop fine-tuning described in S5 are: proportional gain Kp = 0.5-2.0, integral gain Ki = 0.1-0.5, and derivative gain Kd = 0.01-0.05; the cutoff frequency of the BL closed loop is 0.5-2Hz, which is much lower than the audio operating frequency band of the voice coil.

10. The method according to claim 7, characterized in that, The PWM driver described in S6 adopts a MOSFET full-bridge topology with a switching frequency of 50kHz. After LC filtering (L=2.2mH, C=470μF), the output current ripple is <50mA. The linear amplifier adopts a Class AB or Class D topology with a bandwidth of 0-50kHz and THD <0.1%.

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