Voice Coil Temperature Research Articles

Numerical study on magneto-acoustic thermal characteristics of micro-speaker for mobile phones

The numerical study was conducted on 1.2 W micro-speaker module of yoke thickness 0.40 mm without center air hole used in mobile phones and experimentally validated for sound pressure level and temperature distribution within ± 5.9% and ± 3.6%, respectively for frequency ranging from 100 Hz to 20 kHz. The sound pressure level, magnetic flux density, magnetic excitation force and temperature distribution of three different micro-speaker designs were evaluated. The micro-speaker module design with yoke thickness of 0.45 mm without center air hole showed superior acoustic, magnetic and thermal performance as compared to other module designs with the lowest voice coil temperature of 126.02 °C and the maximum sound pressure level of 118.6 dB around resonant frequency of 1100 Hz. The proposed nonlinear thermal model predicted the voice coil temperature accurately. In addition, the present study demonstrated the complete 3-dimensional thermal distribution of micro-speaker components and the detailed heat flow pattern.

Measurement Method for Wire Resistance Temperature Coefficient Based on Heat Transfer Model

The voice coil temperature coefficient is a crucial parameter in the field of voice coil temperature measurement technology, speaker thermal effect, and others. A measurement method for wire resistance temperature coefficient based on heat transfer model is presented in this paper. Measure the voltage at both ends of the coil and the current through the coil before and after the temperature rise by simply energizing the coil in the heat resistance box under the condition of stable ambient temperature. The temperature coefficient of the coil can be obtained according to Ohm’s law and heat transfer model in the method.

Heat Transfer Characteristics of a Speaker Using Nano-Sized Ferrofluid

The purpose of this article is to study the heat transfer characteristics of a voice-coil and permanent magnet for a speaker using nano-sized ferrofluid. In order to investigate the temperature characteristics of the speaker, the speaker power ratings, ambient temperatures of the test chamber, chamber sizes and input signals were tested. As a result, the temperatures of the voice-coil and magnet for the speaker increased with time due to the thermal linearity. The temperature of the voice-coil increased with the decrease of the input signals, but with the increase of the nominal power rating. The voice-coil temperature of Speaker 1 using ferrofluid of an amount of 650 μL at an elapsed time of 10,000 s was 24.5% lower than that of general Speaker 1. In addition, the proper size selection of the enclosure is an important design factor to ensure the sound quality and effective heat transfer of the speaker.

A 4Ω 2.65W Class-D Audio Amplifier With Embedded DC-DC Boost Converter, Current Sensing ADC and DSP for Adaptive Speaker Protection

In this paper a class-D smart speaker driver is presented that can deliver 2.65 W at 1% THD into a 4Ω load. Maximal output power is maintained at low battery voltage by supplying the class-D amplifier from a DC-DC boost converter. Speaker damage is avoided by a speaker protection algorithm that runs on an embedded DSP. The protection algorithm estimates the membrane excursion and voice coil temperature using a speaker model that tracks the speaker impedance which is determined by measuring the speaker current with less than 2% relative error. A sample & hold technique is presented that rejects the load current ripple by sampling at the moments where the instantaneous load current equals the average current. At full output power the combined efficiency of the class-D amplifier and DC-DC boost converter is higher than 80%. The complete system is implemented on a single chip that measures 6.6 mm2 and is fabricated in a 0.14 μm CMOS technology with a 5 V gate-oxide option.

자성유체를 이용한 우퍼 스피커의 보이스 코일 온도 특성에 관한 수치적 연구

본 연구는 자성유체 우퍼 스피커 내부에 위치한 보이스 코일의 입력전류에 따른 열전달 특성을 수치 해석적으로 고찰하는 것이다. 이를 위하여 일반 우퍼 스피커 및 자성유체 우퍼 스피커에 대하여 입력전류를 10W에서 50W로 10W씩 변화시켜가면서 입력전류에 따른 보이스 코일 발열 및 각 부품으로 전달되는 열전달 및 온도 특성 변화를 고찰하였다. 그 결과 우퍼 스피커에 공급되는 입력전류가 증가함에 따라 보이스 코일 온도가 선형적으로 증가하였고 자성유체 우퍼 스피커의 보이스 코일 온도가 일반 우퍼 스피커에 비하여 동일 입력 전류 40 W 기준에서 51.0 % 감소하였고, 동일 보이스 코일 발생 온도 490 K 기준에서 필요 입력전류는 42.5 % 감소하였다. 또한 보이스 코일에서 주변 부품으로 열전달은 자성유체 우퍼 스피커가 일반 우퍼 스피커에 비하여 51.7 % 증가하였다. This article is to numerically investigate the temperature and heat transfer characteristics of the voice coil in the woofer speaker using ferrofluid with the input currents. The temperature and heat transfer of the major components of the woofer speakers with and without ferrofluid are calculated and analyzed with the increase of the input currents from 10 W to 50 W at an interval of 10W. As results, the temperature of voice coil is linearly increased with an increase of input currents. The temperature of the woofer speaker with ferrofluid is lower 51.0 % than that of the woofer speaker without ferrofluid at the condition of input current 40W and the required input current of the woofer speaker with ferrofluid is lower 42.5 % than that of the woofer speaker without ferrofluid at the condition of voice coil temperature 490 K. In addition, the heat transfer from voice coil to other components for woofer speaker with ferrofluid is higher 51.7 % than that for woofer speaker without ferrofluid.

THERMAL PROTECTION OF ELECTRO DYNAMIC TRANSDUCERS USED IN LOUDSPEAKER SYSTEMS

Electro dynamic transducers can fail due to either excessive voice coil excursion, causing mechanical clipping, or by overheating of the voice coil causing degradation of the materials. The disclosed invention relates to protection against excess voice coil temperature in such transducers. The current through the transducer voice coil and the voltage across its terminals, are measured. The resistive part of the impedance of the transducer is then estimated based on the measurements of current and voltage. When the resistive impedance for the given type of transducer is well known at one temperature it is then possible to calculate the temperature when the resistive impedance changes. The estimated voice coil temperature is then fed to a signal attenuator or controller, which attenuates the output signal to the transducer.

System for using digital signal processing to compensate for power compression of loudspeakers

This invention provides a compensation system capable of compensating for power loss due to the power compression effects of the voice coil as the temperature of the voice coil increases. To compensate for the power compression effect, the invention predicts or estimates the temperature of the voice coil using a thermal-model, and adjusts the estimated temperature according to the cooling effect as the voice coil moves back and forth in the air gap. The thermal-model may be an equivalent electrical circuit that models the thermal circuit of a loudspeaker. With the input signal equating to the voltage delivered to the loudspeaker, the thermal-model estimates a temperature of the voice coil. The estimated temperature is then used to modify equalization parameters. To account for the cooling effect of the moving voice coil, the thermal resistance values may be modified dynamically, but since this cooling effect changes with frequency, a cooling equalization filter may be used to spectrally shape the cooling signal, whose RMS level may be used to modify the thermal resistance values. The invention may include a thermal limiter that determines whether the estimated voice coil temperature is below a predetermined maximum temperature to prevent overheating and possible destruction of the voice coil.

Apparatus and method of limiting power applied to a loudspeaker

A method of limiting the power applied to a loudspeaker is disclosed, in which both the voltage and current applied to the loudspeaker are measured, and instantaneous power is directly calculated and used to control the level of the input signal that drives the amplifier powering the loudspeaker. When the power applied to the loudspeaker exceeds a prescribed threshold, the input level to the power amplifier is reduced until the measured power falls below the threshold. Also disclosed is a method for indirectly determining the voice coil temperature from the loudspeaker's voltage and current and reducing power to the loudspeaker when the temperature exceeds a prescribed threshold. The power level is actively controlled to prevent damage to the loudspeaker and to minimize audibly objectionable artifacts.

Moving magnet loudspeaker system with electronic compensation

In most cases, an increase in voice-coil temperature is the major cause of speaker failure. Several techniques have been developed to keep the voice coil at room temperature under high-power inputs. It is a known fact that a rise in temperature causes a rise in the total resistance of the voice coil, thus reducing the sensitivity. Many performance improvements have been implemented on sound quality and high power output. However, less importance has been placed on the end stage of the hi-fi, i.e. the loudspeaker. The main problem faced by high-power loudspeakers is that of power compression. A cost-effective moving magnet structure, where the coil is directly heat sinked, is the best economical solution to reduce power compression. An attempt is made to build such a moving magnet loudspeaker system with a stationary coil. The compensation for the increase in voice coil resistance is provided by predicting the temperature of the voice coil in real time at different temperatures. A computer controlled measuring method is developed to enable long-term measurements with constant input power. A very simple digital technique to provide the required negative output impedance to compensate for the increase in voice-coil resistance is also discussed.

Temperature prediction of the voice coil of a moving coil loudspeaker by computer simulation.

In most cases the increase in voice coil temperature is the major cause for speaker failure.Several techniques have been developed to keep voice coil at room temperature under high power inputs.It is a known fact that rise in temperature causes a rise in the total resistance of the voice coil.Providing negative impedance at the amplifier output to compensate for the increase in voice coil resistance is not a new technique.Here we have developed a thermal model to predict the voice coil temperature at different instants of time through computer simulation without actually measuring the voltage across the voice coil and hence calculate the negative impedance required to counteract the increase in voice coil resistance.

Measuring system for the derivation of thermal loudspeaker parameters

Loudspeakers used in high-power applications are stressed by mechanical and thermal load. Both can be the reason for damage and should be controlled. Whereas the mechanical situation can be derived from the input voltage and the total impedance, which can be measured easily, it is rather difficult to calculate for the actual voice coil (VC) temperature under working conditions. It is possible to derive the VC temperature from the input voltage using linear mathematics if the thermal equivalent circuitry of the loudspeaker including the cabinet is known. Former papers have discussed the thermal equivalent circuitry of the loudspeaker without taking the cabinet into account. In the presented paper an equivalent circuit is presented, which can be used for loudspeakers in different cabinets and a measuring method is shown, that enables long-term measurements on loudspeaker systems with constant input power using a PC-based regulator. The main problem is to calculate the voice coil temperature from the measured impedance data. The solution of this problem is presented. At least the thermal parameters of the equivalent circuit are calculated from the measured data using curve fitting. Different loudspeakers and setups have been tested. The results will be presented.

Protective circuit for electroacoustic transducer with Hall element and voice coil temperature rise time constant circuit

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