CN101394688A - Non-thermal resistance prediction method for power compression of coil driven loudspeaker - Google Patents

Abstract

The invention relates to a prediction method for power compression of a coil driven loudspeaker without thermal resistance. For arbitrary coil driven loudspeaker, the impedance curve and the temperature variation of a voice coil are measured, the power compression value of a characteristic frequency point is calculated through the computing formula of the power compression without thermal resistance, then a modified coefficient is calculated through the modified formula, and finally power compression curves under different input power conditions are obtained. Based on the measured impedance curve and the temperature variation of the voice coil, the computing formula of the power compression without thermal resistance is adopted for calculating, and the computing formula is as follows: PC is equal to 10log10<ZTa plus kRe DeltaT (1 plus k DeltaT)/ZTa>, wherein, the power compression indicates the relative reducing of the frequency response amplitude of the coil driven loudspeaker under different input power conditions.

Description

Moving-coil speaker power compression without thermal resistance Forecasting Methodology

Technical field

The present invention relates to the Forecasting Methodology of moving-coil speaker power compression, is a kind of non-thermal resistance prediction method based on moving-coil speaker cell impedance curved measurement and temperature rise curve measurement of novelty.

Background technology

Loud speaker is the electroacoustic transducer that converts the electrical signal to acoustical signal and medium radiation towards periphery.Loud speaker can be divided into moving-coil type, electromagnetic type, electrostatic, piezoelectric type, ionic formula etc. by the transducing mode, and wherein moving-coil speaker is widely used, and plays a significant role in life, engineering application.

Moving-coil speaker has different temperature rise situations when working under the different capacity initial conditions, the reason that temperature raises is the voice coil loudspeaker voice coil heating.According to the temperature characterisitic of voice coil loudspeaker voice coil material, its direct current resistance meeting raises along with voice coil temperature and increases, and direct current resistance increase can cause reducing of input electric power, finally causes the reduction of sound output.The relative decrease of the frequency response of moving-coil speaker under the different capacity initial conditions is exactly the power compression value.

In order to measure the power compression value, someone has proposed to calculate entire thermal resistance based on the quadratic equation that the hot equivalent model of linearity is found the solution about Δ T under the constant voltage initial conditions, and utilization and entire thermal resistance, temperature rise then, the power compression computing formula that input power is relevant are calculated the power compression value.But calculate so several drawbacks are arranged, the one, linear hot equivalent model lost efficacy in low-frequency range, and just there is very mistake in the thermal resistance of calculating with this method itself, and the power compression that calculates must be forbidden; The 2nd, this method thinks that voice coil loudspeaker voice coil is in same steady temperature at full frequency band, thereby the value that calculates and actual result deviation are very big.

The relevant method of having published at present:

1, based on the power compression computational methods of the hot equivalent model thermal resistance of linearity.

(1992) have proposed the computing formula of moving-coil speaker power compression,

$\mathrm{PC}=10{\log }_{10}\left[\frac{P_e{R}_0(1+\mathrm{k\&Delta;T})}{\mathrm{\&Delta;T}}\right],$ R ₀Be entire thermal resistance, P _eBe input electric power.

Calculate R ₀Then need to obtain by separating following two formulas:

k ₂ΔT ²R _e+k1ReΔT-V ²＝0

$V^2=\frac{\mathrm{\&Delta;}{\mathrm{Tk}}_1{R}_e}{R_0}+\frac{k_2\mathrm{\&Delta;}{T}^2{R}_e}{R_0}$

K wherein ₁Be the ratio of loud speaker minimum impedance and the resistance of voice coil loudspeaker voice coil direct current, k ₂Be temperature coefficient, R ₀Be entire thermal resistance.This method based on hot equivalent model lost efficacy at low frequency it be restricted.

Referring to DOUGLAS J.BUTTON.Heat dissipation and power compression in loudspeakers[J] .J.AudioEng.Soc., 1992,40 (1/2): 32-41.

2, come the rated output compression based on direct current resistive reckoning temperature rise

(2002) have proposed to be similar to the temperature rise of reckoning voice coil loudspeaker voice coil based on the linear hot equivalent model in three rank, calculate the power compression value again.

$\mathrm{\&Delta;T}\&ap;\frac{Z_{\min }\left(T_a\right)}{2\mathrm{\&delta;}{R}_e\left(T_a\right)}(1+\frac{4u^2{R}_t\mathrm{\&delta;}{R}_e\left(T_a\right)}{Z_{\min }^2\left(T_a\right)-1})$

$\mathrm{PC}=10\log \left[\frac{R_t(1+\mathrm{\&delta;\&Delta;T})}{\mathrm{\&Delta;T}}\right]$

Wherein Δ T is the front and back temperature difference, and δ is a temperature coefficient, R _tBe entire thermal resistance.

This method is based on the power compression calculating of thermal resistance equally, because itself is not based on the temperature data of actual measurement, last resultant error is very big, has method 1 restricted condition equally simultaneously.Referring to WOLFGANG KLIPPEL.Nonlinear modeling ofthe heat transfer in loudspeakers[J] .J.AudioEng.Soc., 2004,52 (1/2): 3-21.

Situation to sum up, existing technical method is measured the calculating power compression based on thermal resistance, and is not only loaded down with trivial details but also can not get accurate result.

The power compression computational methods that propose no thermal resistance are not also arranged so far.More and more universal at current high-power high-fidelity loudspeaker, moving-coil speaker power compression situation is more and more by the epoch that people paid close attention to, and a simple and easy quick power compression Forecasting Methodology all benefits for research and development, production.

Summary of the invention

The objective of the invention is: a kind of moving-coil speaker power compression without thermal resistance Forecasting Methodology is provided.For any moving-coil speaker, as long as change, utilize the criterion of no thermal resistance power compression directly to extrapolate the power compression value by impedance curve and the voice coil temperature of measuring moving-coil speaker, dope the power compression curve.

The object of the present invention is achieved like this: the impedance curve of at first measuring moving-coil speaker, the variation of respective frequencies point measurement voice coil temperature then, utilize the power compression without thermal resistance computing formula, obtain the power compression value of characteristic frequency point, revise by correction formula again, dope the power compression curve under the different capacity condition at last.

Moving-coil speaker power compression without thermal resistance Forecasting Methodology: for any moving-coil speaker, at first measure the impedance curve and the temperature curve of loud speaker, extract the modulus of impedance value of needed Frequency point then, utilize the power compression without thermal resistance computing formula directly to calculate the power compression value again, as needs frequency range is predicted, directly made the power compression curve with the frequency range algorithm.The curve of making reduces curve for the relative amplitude of the frequency response before and after the rising of moving-coil speaker voice coil temperature.

The present invention chooses two characteristic frequency points and measures: valley point behind resonant frequency point and the impedance curve peak.Measuring system is simple, and the measuring equipment cost is low, can express delivery dope power compression, and the inventive method also can guarantee certain relative accuracy.The present invention also aims to carry out the single-point prediction for the characteristic frequency point, the power compression value of characteristic frequency point can characterize the quality of the heat dispersion of moving-coil speaker to a certain extent.Do not adopt the thermal resistance calculation power compression, need not linear or nonlinear hot equivalent model, be not subjected to the material of moving-coil speaker basin frame, vibrating diaphragm etc. and the influence of structure.

The inventive method also is included on the basis of the variations in temperature of measuring impedance curve and voice coil loudspeaker voice coil, utilizes the power compression without thermal resistance computing formula to calculate, and this calculating formula is: $\mathrm{PC}=10{\log }_{10}\left[\frac{(Z_{\mathrm{Ta}}+k{R}_e\mathrm{\&Delta;T})(1+\mathrm{k\&Delta;T})}{Z_{\mathrm{Ta}}}\right].$

Improvement of the present invention also comprises: moving-coil speaker power compression without thermal resistance Forecasting Methodology, correction formula is

Correction factor a, b, c are all based on the measurement of impedance curve and variations in temperature.

Z wherein _TaBe the loudspeaker impedance mould value before the temperature rising, Z _TcBe the loudspeaker impedance mould value after the temperature rising, f _S0Be valley point frequency behind the impedance curve of loudspeaker peak, f is the Frequency point of required correction, R _eBe the resistance of voice coil loudspeaker voice coil direct current, k is a voice coil loudspeaker voice coil material temperature coefficient, and Δ T is the temperature rise of voice coil loudspeaker voice coil, Q _TBe the total quality factor of loud speaker, P _rBe the rated power of loudspeaker, P is an input power.

Characteristics of the present invention are: the moving-coil speaker power compression computational methods that proposed not rely on thermal resistance calculation first.As long as the impedance curve and the variations in temperature of known loudspeaker, just can calculate the power compression value and dope compression curve under the different capacity initial conditions.

Description of drawings

Fig. 1 is the flow process of the inventive method,

Fig. 2 is the inventive method block diagram

Fig. 3 is corresponding for the impedance curve of loudspeaker of the present invention and compression curve

Fig. 4 is for measuring the circuit of voice coil temperature.

Fig. 5 has provided and has utilized correction back power compression not have theoretical sound pressure level curve and measured curve contrast that the thermal resistance calculation formula calculates.

Embodiment

Fig. 1,2 is a basic skills of the present invention.

Flow process of the present invention as shown in Figure 1.The resistance of voice coil loudspeaker voice coil direct current increases along with the increase of voice coil temperature, and relational expression is:

R _ETc=R _ETa(1+k Δ T) R _ETcBe the voice coil loudspeaker voice coil direct current resistance after heating up, R _ETaBe the resistance of the voice coil loudspeaker voice coil direct current before heating up, Δ T is the front and back temperature difference, and k is a voice coil loudspeaker voice coil material temperature coefficient, is the moving-coil speaker of copper for the voice coil loudspeaker voice coil material, is 0.00393K ^-1

The power compression effect is meant that the voice coil temperature rising makes the resistance of voice coil loudspeaker voice coil direct current increase when speaker operation, under loud speaker constant voltage input condition, according to P=U ²/ R, the power of the loud speaker of feeding can descend, and so just can finally cause the decline of sensitivity and radiation efficiency.It is generally acknowledged that the power compression effect is in particular in the variation of direct current resistance, electrical quality factor, acoustic radiation efficiency and BL, direct result is exactly to cause the amplitude of the frequency response of loud speaker to descend relatively.Loud speaker electric power sound system (H ₁And the hot (H of system (s)) ₂(s)) all regard nonlinear and time-varying system continuous time (Fig. 2) as, after signal of telecommunication X (s) feeds loud speaker, the thermal power of system output Y ₂(s) through the H of system ₂(s), output temperature difference Y ₃(s), negative feedback is to the H of system ₁(s), cause last acoustics output Y ₁(s) minimizing.

Before the calculating of power compression all had been based on the method for thermal resistance, owing to count thermal resistance, will certainly cause the last result who in different frequency range, calculates difference again, because the air forced convection that moving-coil speaker produces when low frequency, it is non-linear to make that thermal resistance occurs, and the power compression result who obtains is inaccurate.

The present invention obtains the more convenient quick very computational methods of pinpoint accuracy that have again from impedance curve.

Under the constant voltage initial conditions, the output sound pressure level before voice coil temperature raises:

SPL ₁＝SPL ₀+10log ₁₀η ₁P ₁＝SPL ₀+10log ₁₀η ₁+10log ₁₀P ₁

Output sound pressure level after temperature raises:

SPL ₂＝SPL ₀+10log ₁₀η ₂P ₂＝SPL ₀+10log ₁₀η ₂+10log ₁₀P ₂

η ₁, η ₂Be divided into for temperature raise before and the loudspeaker enclosure of temperature after raising.P ₁And P ₂Be respectively before the temperature rising and the loudspeaker enclosure after the temperature rising.SPL ₀Be the output sound pressure level under the 1W input power condition.

Under ka＜＜1 condition, $\mathrm{\&eta;}=\frac{B^2{l}^2}{R_e}\frac{{\mathrm{\&rho;}}_0}{2\mathrm{\&pi;}{c}_0}\frac{S_D^2}{{(M_{\mathrm{MS}}+M_{\mathrm{MR}})}^2}\frac{w^2/w_s^2}{\frac{1}{Q_T^2}+{(\frac{w}{w_s}-\frac{w_s}{w})}^2}$

After voice coil temperature raise, direct current resistive (1+k Δ T) greatly before times, then η became 1/ original (1+k Δ T), therefore

${\mathrm{\&eta;}}_2=\frac{1}{1+\mathrm{k\&Delta;T}}{\mathrm{\&eta;}}_1$

$\mathrm{PC}={\mathrm{SPL}}_1-{\mathrm{SPL}}_2=10{\log }_{10}\left(\frac{P_1}{P_2}\right)+10{\log }_{10}\left(\frac{{\mathrm{\&eta;}}_1}{{\mathrm{\&eta;}}_2}\right)=10{\log }_{10}\left(\frac{P_1}{P_2}\right)+10{\log }_{10}(1+\mathrm{k\&Delta;T})$

$=10{\log }_{10}\frac{(1+\mathrm{k\&Delta;T})P_1}{P_2}$

$P_1=\frac{V^2}{Z_{\mathrm{Ta}}}$

$P_2=\frac{V^2}{Z_{\mathrm{Tc}}}$

Z _Tc＝Z _Ta+kR _eΔT

$\mathrm{PC}=10{\log }_{10}\left[\frac{(Z_{\mathrm{Ta}}+k{R}_e\mathrm{\&Delta;T})(1+\mathrm{k\&Delta;T})}{Z_{\mathrm{Ta}}}\right]$

Z wherein _TaBe the loudspeaker impedance mould value before the temperature rising, Z _TcBe the loudspeaker impedance mould value after the temperature rising, R _eBe the resistance of voice coil loudspeaker voice coil direct current, k is a voice coil loudspeaker voice coil material temperature coefficient, and Δ T is the temperature rise of voice coil loudspeaker voice coil.

Can see that from following formula the voice coil loudspeaker voice coil temperature rise reaches under the situation of stable state, the PC value is at Z _TaReach maximum when reaching minimum.So the selected characteristic Frequency point, promptly there is good representativeness the valley point behind the peak of impedance curve, simultaneously since loud speaker at resonance frequency place frequency of occurrences peak value of response, choosing resonance frequency is another feature Frequency point.From Fig. 3, can obviously find out the corresponding relation of power compression peak value and impedance curve characteristic frequency point.

Fig. 4 is for measuring the circuit of voice coil temperature.The basic principle of circuit is to utilize precision resister and the moving-coil speaker dividing potential drop of 1K.Input is that signal is exported through power amplifier.C6, C7 are capacitance (2.2mF/35V), and the butt joint of bipolarity electric capacity can realize jumbo nonpolar electric capacity.R1 is the cement resistor of 0.22ohm/5W, is used to monitor the voice coil loudspeaker voice coil electric current, and R2 is that temperature coefficient is 25ppm/ ℃ a precision resistance, and C1, C2 are used to protect direct-flow voltage regulation source, measure direct voltage after the 3 rank low-pass filtering.Since added cement resistor, so calculating formula is:

$\frac{V_{\mathrm{measure}}}{5}=\frac{R_{\mathrm{eTc}}+0.22}{1000+R_{\mathrm{eTc}}+0.22}$

$R_{\mathrm{eTc}}=\frac{1000.22V_{\mathrm{measure}}}{5-V_{\mathrm{measure}}}-0.2$

$\mathrm{\&Delta;T}=\frac{R_{\mathrm{eTc}}-R_{\mathrm{eTa}}}{R_{\mathrm{eTa}}\mathrm{\&delta;}}$

According to the temperature-measuring results of voice coil loudspeaker voice coil temperature measurement circuit with from the modulus of impedance value that impedance curve obtains, directly calculate the power compression value with formula.

Because under the actual measurement condition, the measured deviation of steady temperature can cause the prediction margin error.Need make correction to the result, correction term is Correction factor a, b, c obtains by the power compression data computation at characteristic frequency point place.Q wherein _TBe the total quality factor of loud speaker, f _S0Be valley point frequency behind the impedance curve of loudspeaker peak, P _rBe the rated power of loudspeaker, P is an input power.

The concrete calculated examples of measuring

Be example with 1 inch moving-coil speaker below, the process of utilizing non-thermal resistance prediction method to calculate the moving-coil speaker power compression is described.

According to measuring flow process, at first measure the impedance curve of moving-coil speaker, characteristic of correspondence Frequency point place is with the variations in temperature of circuit measuring voice coil loudspeaker voice coil shown in Figure 3 again, the power compression formula of the no thermal resistance of utilization calculates the power compression value of single-point then, revise, calculate the prediction curve that then can obtain power compression through frequency range again.The actual measurement parameter of this moving-coil speaker:

Re＝4.31Ω，f ₀＝212Hz，f _s0＝530Hz，Q _m＝9.30，Q _e＝4.35，Q _t＝2.96，Z _max＝13.53Ω。Under 212HZ and the 530HZ initial conditions, when the different input power situation, its temperature raises when being respectively 50 ℃ and 80 ℃, not having the thermal resistance calculation formula by power compression, to calculate the power compression theoretical value be 1.03dB/1.65dB (70%Pr/100%Pr), the compression measured value is 0.76dB/1.32dB (70%Pr/100%Pr), the valley point is 530Hz behind the impedance peak, its corresponding compression theory value is 1.08dB/2.26dB (70%Pr/100%Pr), and the compression measured value is 0.88dB/1.92dB (70%Pr/100%Pr).

By the theoretical power (horse-power) compressed value that the characteristic frequency point is calculated and the comparison of actual measured value, the correction term parameter is carried out at 2 ask average computation, obtain a=316*10 ^-4, b=0.09, so the c=0.51 correction term is:

$3.16\&times;{10}^{-4}\&times;\sqrt{\frac{P}{\mathrm{Pr}}}+0.09\&times;\frac{f-f_{s0}}{f_{s0}}+0.51\&times;\frac{1}{Q_T}.$

Fig. 5 has provided and has utilized correction back power compression not have theoretical sound pressure level curve and measured curve contrast that the thermal resistance calculation formula calculates.Can see that under low frequency condition (ka＜＜1) promptly below the 750HZ, the power compression curve and the theoretical curve that utilize Forecasting Methodology provided by the invention to obtain have the good goodness of fit.

Claims (4)

1, a kind of moving-coil speaker power compression without thermal resistance Forecasting Methodology, it is characterized in that for any moving-coil speaker, measure the variations in temperature of impedance curve and voice coil loudspeaker voice coil, calculate the power compression value of characteristic frequency point by the power compression without thermal resistance computing formula, calculate the correction formula correction factor then, obtain the power compression curve under the different input power condition at last.

2, moving-coil speaker power compression without thermal resistance Forecasting Methodology as claimed in claim 1 is characterized in that on the basis of the variations in temperature of measuring impedance curve and voice coil loudspeaker voice coil, utilizes the power compression without thermal resistance computing formula to calculate, and this calculating formula is: $\mathrm{PC}=10{\log }_{10}\left[\frac{(Z_{\mathrm{Ta}}+k{R}_e\mathrm{\&Delta;T})(1+\mathrm{k\&Delta;T})}{Z_{\mathrm{Ta}}}\right].$

3, moving-coil speaker power compression without thermal resistance Forecasting Methodology as claimed in claim 1 is characterized in that correction formula is Correction factor a, b, c are all based on the measurement of impedance curve and variations in temperature.

4, moving-coil speaker power compression without thermal resistance Forecasting Methodology as claimed in claim 1, it is characterized in that getting earlier resonant frequency point and impedance curve peak after two Frequency points in valley point measure.

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