CN104078037A - Low-frequency double-resonance sound-absorbing structure and design method thereof - Google Patents

Abstract

The invention provides a low-frequency double-resonance sound-absorbing structure and a design method thereof. The structure comprises a loudspeaker unit, a closed back cavity, a negative resistor, a capacitor and an inductor. The design method of the structure comprises the following steps that (1), TS parameters of the loudspeaker unit are measured; (2), the negative resistor and the capacitor are connected in series, and the position of a first sound-absorbing peak is adjusted; (3), the inductor is connected in series, and the position of a second sound-absorbing peak is adjusted; (4) the positions of the two sound-absorbing peaks are finely adjusted. The sound-absorbing structure based on a bypass loudspeaker can well absorb low-frequency noise with a plurality of specific frequencies.

Description

Low frequency double resonance sound absorption structure and method for designing thereof

One, technical field

The present invention relates to the method for designing of sound absorption structure, especially relate to a kind of double resonance sound absorption structure and method for designing thereof that is applicable to low frequency.

Two, background technology

Electric system (as transformer etc.) noise, rotation Reciprocatory machinery (as fan etc.) noise, its composition is taking low-frequency noise as main, and concentration of energy is at several characteristic frequency place, if transformer noise is taking 100Hz, 200Hz equifrequent composition as main.

Existing resistive acoustic absorbant, sound absorption structure, as sound-absorbing porous material, perforated plate etc., application cost simple in structure is low.But sound-absorbing porous material needs larger thickness could realize good acoustically effective at low frequency place.Perforated plate coordinates air back of the body chamber to use, and utilizes Resonance Mechanism sound absorption, the noise of certain bandwidth is had to good assimilation effect, but frequency is lower, and the thickness in air back of the body chamber is also larger.

China publication CN202093817 has described a kind of compound sound-absorption structural being made up of perforated plate, spring, resonant load plate, expanded the low frequency absorption ability of perforated plate, but the following acoustically effective of 200Hz is poor.CN102044239 has described the resonance sound-absorbing structure of a kind of perforated plate and resonant cavity composition, by adaptively changing cavity depth, changes low frequency absorption performance, but self-adaptation conditioning equipment is comparatively complicated.CN202268160 has described a kind of sound absorption structure being made up of perforated plate, piezoelectric membrane, Noise Acquisition device and adaptive control system, the assimilation effect to specific noise is improved in the aperture that changes microperforated panel by acquisition noise signal adaptive, but needs Noise Acquisition device and adaptive control system.

Piezoelectric, acoustic-electrical transducer etc. can change into electric energy by acoustic energy.It is combined with divided circuit, electric energy is converted in circuit to interior energy, thereby realize the absorption to acoustic energy.Because divided circuit takes up room littlely, the integral thickness of sound absorption structure depends on the thickness of transducer, and therefore the sound absorption method based on dividing technology can be improved preferably Low Frequency Sound Absorption in thinner size.

CN101929865 has described the sound absorption structure that a kind of metal sheet, piezoelectric ceramics and divided circuit form, and has improved the acoustical absorption coefficient at sheet metal fundamental frequency place, and has expanded low frequency absorption frequency band, but can not regulate the position of fundamental frequency.2007, Australia scholar has proposed to connect with loudspeaker unit the resonance sound-absorbing structure (Fleming that divided circuit forms, " Control of resonant acoustic sound fields by electrical shunting of a loudspeaker ", Control Systems Technology, IEEE Transactions.15 (4), 689-703,2007); Within 2014, Chinese scholar utilizes microperforated panel and shunting loudspeaker composition compound sound-absorption structural; But the research of the two only absorbs for wideband, does not have the research that the noise of multiple characteristic frequency is absorbed.

Large for above-mentioned sound absorption structure thickness, need adaptive control system, cannot be for shortcomings such as multiple characteristic frequency absorb, the invention provides a kind of simple in structure, sound absorption structure that can absorb for multiple characteristic frequency.

Three, summary of the invention

1, goal of the invention: the object of the present invention is to provide a kind of low frequency double resonance sound absorption structure and method for designing thereof.

2, technical scheme: for achieving the above object, 1. low frequency double resonance sound absorption structure of the present invention carries on the back chamber, negative resistance-R by loudspeaker unit and sealing _e2., capacitor C _pand inductance L 3. _p4. form; 2., 4. 3. electric capacity be connected in parallel on 1. two ends of loudspeaker unit after divided circuit in series with inductance to described negative resistance, as shown in Figure 1.

The method for designing of low frequency double resonance sound absorption structure of the present invention, is characterized in that comprising the following steps:

(1) measure loudspeaker unit TS parameter 1..

(2) diaphragm of loudspeaker be connected to coil on vibrating diaphragm etc. and formed a vibrational system, have certain acoustic impedance at diaphragm of loudspeaker place, sound wave is had to certain assimilation effect.

By the electricity part of coil-moving speaker and mechanics part convert to analogy wiring diagram after acoustics part as shown in Figure 2, the equivalent acoustic impedance at diaphragm of loudspeaker place is:

$Z_L=R_{\mathrm{ms}}{S}^2+\mathrm{j\ω}{M}_{\mathrm{ms}}{S}^2+\frac{C_{\mathrm{ms}}+C_{\mathrm{ac}}S}{\mathrm{j\ω}{C}_{\mathrm{ms}}{C}_{\mathrm{ac}}}S+\frac{B^2{l}^2}{S(R_E+\mathrm{j\ω}{L}_E)}---\left(1\right)$

R in formula _msfor the mechanical resistance of vibrational system, M _msfor the mechanical quality of loudspeaker and air load, C _msfor the mechanical compliance of vibrational system, S is diaphragm of loudspeaker area, and ω is angular frequency, and j is complex symbol, and V is loudspeaker back of the body cavity volume, C _ac=V/ ρ ₀c ₀ ²s ²for loudspeaker back of the body chamber acoustic capacitance, ρ ₀, c ₀be respectively the velocity of sound in atmospheric density and air, B is the magnetic density in loudspeaker magnetic gap, and l is voice coil loudspeaker voice coil conductor length in magnetic field, R _efor voice coil loudspeaker voice coil direct current resistance, L _efor voice coil loudspeaker voice coil inductance.

Open-circuit condition low-resonance frequency f _l, acoustical absorption coefficient α is as follows:

$f_L=\frac{1}{2\mathrm{\π}}{\left(\frac{C_{\mathrm{ms}}+C_{\mathrm{ac}}S}{M_{\mathrm{ms}}{C}_{\mathrm{ms}}{C}_{\mathrm{ac}}S}\right)}^{1/2}---\left(2\right)$

$\mathrm{\α}=\frac{4\mathrm{Re}\left(Z_L\right)}{{[{\mathrm{\ρ}}_0{c}_0+\mathrm{Re}\left(Z_L\right)]}^2+{\left[\mathrm{Im}\left(Z_L\right)\right]}^2}---\left(3\right)$

In formula, α is acoustical absorption coefficient, Z _lfor diaphragm of loudspeaker place equivalent acoustic impedance, Re (Z _l), Im (Z _l) be respectively Z _lreal part and imaginary part.System is at resonant frequency f _lplace's acoustical absorption coefficient reaches maximal value.

On loudspeaker, series connection is by negative resistance-R _e(realization of negative resistance can with reference to Analog Circuit Design textbook, as " Fundamentals of Electronic Technology simulation part " the 5th edition, Higher Education Publishing House, 2005), capacitor element C _pafter the divided circuit forming, the equivalent acoustic impedance at diaphragm of loudspeaker place is:

$Z_L=R_{\mathrm{ms}}{S}^2+\mathrm{j\ω}{M}_{\mathrm{ms}}{S}^2+\frac{C_{\mathrm{ms}}+C_{\mathrm{ac}}S}{\mathrm{j\ω}{C}_{\mathrm{ms}}{C}_{\mathrm{ac}}}S+\frac{B^2{l}^2}{S(\mathrm{j\ω}{L}_E+\frac{1}{\mathrm{j\ω}{C}_p})}---\left(4\right)$

Resonant frequency is as follows, and acoustical absorption coefficient has a peak value herein.

$f_{L1}=\frac{1}{2\mathrm{\π}}{\left[\frac{C_{\mathrm{ms}}+C_{\mathrm{ac}}S}{(M_{\mathrm{ms}}S+B^2{l}^2{C}_p/S^2)C_{\mathrm{ms}}{C}_{\mathrm{ac}}}\right]}^{1/2}---\left(5\right)$

More than need design and regulate: negative resistance-R _emiddle R _efor loudspeaker unit voice coil loudspeaker voice coil direct current resistance; With reference to formula (5), control capacittance C _p, make first sound absorption peak value appear at first resonant frequency place of design.The frequency occurring when first sound absorption peak value during higher than the lower resonant frequency of frequency of design, increases capacitor C _p; The frequency occurring when first sound absorption peak value during lower than the lower resonant frequency of frequency of design, reduces capacitor C _p.

(3) in divided circuit, add inductance component L _p, the equivalent acoustic impedance at diaphragm of loudspeaker place is:

$Z_L=R_{\mathrm{ms}}{S}^2+\mathrm{j\ω}{M}_{\mathrm{ms}}{S}^2+\frac{C_{\mathrm{ms}}+C_{\mathrm{ac}}S}{\mathrm{j\ω}{C}_{\mathrm{ms}}{C}_{\mathrm{ac}}}S+\frac{B^2{l}^2}{S[\mathrm{j\ω}(L_E+L_p)+\frac{1}{\mathrm{j\ω}{C}_p}]}---\left(6\right)$

After the frequency occurring at first sound absorption peak value, occur second resonant frequency, acoustical absorption coefficient has a peak value herein.

More than need design and regulate: with reference to formula (7), regulating inductance L _pmake second sound absorption peak value appear at second resonant frequency place of design.The frequency occurring when second sound absorption peak value during higher than the higher resonant frequency of frequency of design, increases inductance L _p; The frequency occurring when second sound absorption peak value during lower than the higher resonant frequency of frequency of design, reduces inductance L _p.

(4) owing in formula (5) and formula (7), the calculating of resonant frequency having been adopted to approximate processing, work as capacitor C _p, inductance L _pwhile accessing divided circuit, two resonant frequencies and the calculated value deviation to some extent obtaining by formula (5) and formula (7) in practical operation, need to be to capacitor C simultaneously _pand inductance L _pfinely tune, to guarantee that two resonance peaks appear at the resonant frequency place of design.

To capacitor C _pand inductance L _pthe method of fine setting is: first adjust capacitor C according to the described method of step (2) _p, change the frequency that two sound absorption peak values occur simultaneously; Adjust inductance L according to the described method of step (3) again _p, change the frequency of second sound absorption peak value appearance and first sound absorption crest frequency finely tuned.

Four, brief description of the drawings

Fig. 1 is the schematic diagram of low frequency double resonance sound absorption structure.

Fig. 2 is that shunting impedance is Z _etime coil-moving speaker electromechanical-acoustic analogy wiring diagram.

Fig. 3 is the acoustical absorption coefficient that in embodiment, loudspeaker unit does not connect divided circuit.

Fig. 4 is the actual measurement acoustical absorption coefficient of dual resonance structure in embodiment.

Five, embodiment

Taking certain loudspeaker unit as basic engineering divided circuit is as example.Through actual measurement, loudspeaker unit parameter is as follows: DC impedance R _e=31.1 Ω, voice coil loudspeaker voice coil inductance is L _e=9.84mH, in the magnetic density B in loudspeaker magnetic gap and magnetic field, the product of voice coil loudspeaker voice coil conductor length l is Bl=17.02Tm, the mechanical resistance R of vibrational system _msthe mechanical quality M of=2.14kg/s, loudspeaker and air load _ms=15.95 _g, vibrational system mechanical compliance C _ms=0.23mm/N, diaphragm of loudspeaker area S=1.5 × 10 ^-2m ², loudspeaker back of the body cavity volume V=5.53 × 10 ^-3m ³.

1, the DC impedance R of loudspeaker unit _e=31.1 Ω, therefore (realization of negative resistance can be with reference to Analog Circuit Design textbook, as " Fundamentals of Electronic Technology simulation part " the 5th edition, Higher Education Publishing House to select suitable element to build negative resistance circuit, 2005), make the equivalent resistance of negative resistance circuit be-R _e,-31.1 Ω.

2,, according to step in technical scheme (2), select capacitor C _p=23 μ F, are connected in series in divided circuit, make the peak value of acoustical absorption coefficient appear at 100Hz.

3,, according to step in technical scheme (3), select inductance L _p=31mH, is connected in series in divided circuit, and second peak value appears in acoustical absorption coefficient, adjusts inductance value, makes this peak value appear at 200Hz.

4, according to step in technical scheme (4), to capacitor C _p, inductance L _pfinely tune, concrete value is C _p=21 μ F, L _p=33mH, now two peak values appear at 100Hz and 200Hz place simultaneously, as shown in Figure 4.

Measurement result:

Adopt method for designing provided by the invention, the acoustical absorption coefficient at shunting diaphragm of loudspeaker place is at 100Hz, 200H _zplace's acoustical absorption coefficient is greater than 0.9.

Claims (5)

1. a sound absorption structure for low frequency double resonance, is characterized in that, carries on the back chamber 1., negative resistance-R by loudspeaker unit and sealing _e2., capacitor C _pand inductance L 3. _p4. form; 2., 4. 3. electric capacity be connected in parallel on 1. two ends of loudspeaker unit after divided circuit in series with inductance to described negative resistance.

2. the method for designing of structure described in claim 1, is characterized in that comprising the following steps:

(1) the TS parameter of measurement loudspeaker unit;

(2) at 1. two ends negative resistance-R in parallel of loudspeaker _eand capacitor C 2. _p3., R wherein _efor loudspeaker unit direct current resistance 1., control capacittance C _p3. value, makes first sound absorption peak value appear at the lower resonant frequency place of frequency of design;

(3) series inductance L in circuit _p4., regulate inductance L _p4. value, makes second sound absorption peak value appear at the higher resonant frequency place of frequency of design;

(4) trimming capacitor C repeatedly _pand inductance L 3. _p4., guarantee that two peak values of acoustical absorption coefficient appear at two resonant frequency places of design simultaneously.

3. the method that regulates as claimed in claim 2 the frequency that first sound absorption peak value occurs in method for designing, is characterized in that, the frequency occurring when first sound absorption peak value during higher than the lower resonant frequency of the frequency of design, increases capacitor C _p3.; The frequency occurring when first sound absorption peak value during lower than the lower resonant frequency of frequency of design, reduces capacitor C _p3..

4. the method that regulates as claimed in claim 2 the frequency that second sound absorption peak value occur in method for designing, is characterized in that, the frequency occurring when second sound absorption peak value during higher than the higher resonant frequency of the frequency of design, increases inductance L _p4.; The frequency occurring when second sound absorption peak value during lower than the higher resonant frequency of frequency of design, reduces inductance L _p4..

5. the method for finely tuning as claimed in claim 2 two sound absorption crest frequencies in method for designing, is characterized in that, first method is adjusted capacitor C according to claim 3 _p3., change the frequency that two sound absorption peak values occur simultaneously; According to claim 4, method is adjusted inductance L again _p4., change the frequency of second sound absorption peak value appearance and first sound absorption crest frequency is finely tuned.