CN106528907B - Ventilated vehicle-mounted bass loudspeaker system and design method thereof - Google Patents
Ventilated vehicle-mounted bass loudspeaker system and design method thereof Download PDFInfo
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- H—ELECTRICITY
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- H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
- H04R1/00—Details of transducers, loudspeakers or microphones
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- H—ELECTRICITY
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- H04R1/00—Details of transducers, loudspeakers or microphones
- H04R1/20—Arrangements for obtaining desired frequency or directional characteristics
- H04R1/22—Arrangements for obtaining desired frequency or directional characteristics for obtaining desired frequency characteristic only
- H04R1/28—Transducer mountings or enclosures modified by provision of mechanical or acoustic impedances, e.g. resonator, damping means
- H04R1/2807—Enclosures comprising vibrating or resonating arrangements
- H04R1/2838—Enclosures comprising vibrating or resonating arrangements of the bandpass type
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- H—ELECTRICITY
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- H04R1/34—Arrangements for obtaining desired frequency or directional characteristics for obtaining desired directional characteristic only by using a single transducer with sound reflecting, diffracting, directing or guiding means
- H04R1/345—Arrangements for obtaining desired frequency or directional characteristics for obtaining desired directional characteristic only by using a single transducer with sound reflecting, diffracting, directing or guiding means for loudspeakers
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- H—ELECTRICITY
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- H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
- H04R9/00—Transducers of moving-coil, moving-strip, or moving-wire type
- H04R9/06—Loudspeakers
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Abstract
The invention discloses a ventilation type vehicle-mounted bass loudspeaker system and a design method thereof. A design method of a vehicle-mounted ventilated type woofer system comprises the following steps: s1, calculating radiation impedance of a current waveguide tube of a loudspeaker system; s2, constructing a mathematical model of the loudspeaker system according to the waveguide radiation impedance obtained in the step S1; s3, calculating a radiation sound field of the loudspeaker system according to the mathematical model established in the step S2; s4, comparing the radiation sound field obtained in the step S3 with an expected radiation sound field, and if the expected radiation sound field is not met, adjusting the structure of the waveguide tube.
Description
Technical Field
The invention relates to the field of vehicle-mounted speakers, in particular to a ventilated vehicle-mounted bass speaker system and a design method thereof.
Background
With the rapid development of the automobile industry, automobile tools are increasingly popular, and the relationship between the vehicle-mounted sound equipment of the automobile and people is becoming more and more compact. The quality of sound quality in automobiles is a hot spot of current market attention. The automobile sound equipment relates to the design of physical devices, including speakers, cavities, optimization of the acoustic environment of the automobile, and the like; car audio also involves audio signal processing such as equalization, surround sound adjustment, etc. An excellent high quality car audio system, bass unit is particularly important. Currently, a common design solution is to design the woofer unit as a closed or open box placed in the trunk, and transmit low-frequency sound waves through the gap between the trunk and the carriage; there is also a second design, in which a hole is made in the partition sheet metal of the cabin and the trunk, to allow the bass unit to radiate directly. In the first scheme, the forward radiation of the loudspeaker is combined by the volume of the cavity of the trunk and the sound quality of the gap to form an acoustic filter, and the parameters of the acoustic filter are uncontrollable, so that the transmission of sound waves in certain frequency bands is most likely to be inhibited; in the second scheme, the size of the bass unit is usually larger, and the large holes are formed in the metal plate, so that the firmness of the metal plate can be influenced, and structural vibration damage is easy to occur along with the vibration of the loudspeaker unit. In addition, in the above two schemes, the speaker unit needs to be installed in the case, and the volume of the case itself is limited by the size of the trunk, thereby affecting the low frequency radiation of the woofer.
If the energy radiated by the forward or backward sound waves of the loudspeaker is guided into the carriage through a waveguide tube, the sheet metal behind the carriage only needs to be provided with a small-caliber hole, so that the firmness of the sheet metal is not affected; and the other side of the loudspeaker takes the whole trunk as a cavity. If the trunk is in communication with the outside air, the rear cavity of the woofer unit may be considered infinite. This structure is called a vented speaker, which will greatly increase the low frequency energy radiation of the speaker. This is also the core content in patent US8804991 and patent US 2013/0142380. Which directs the energy radiated rearward from the speaker into the cabin, mainly through a tube. The tube and the rear cavity of the loudspeaker are used as a Helmholtz resonator, and the low-frequency resonance frequency and the high-frequency cutoff frequency of the bass loudspeaker system can be adjusted by adjusting the size of the rear cavity and the length and thickness of the tube.
However, it should be noted that the current research, including the above two patents, does not give a specific method for adjusting the low frequency resonance frequency of the speaker, nor does it give a size of the tube and a size design of the rear cavity what kind of frequency response curve will be obtained; moreover, from the design point of view of the Helmholtz resonator alone, the degree of freedom in adjustment is too small, and it is likely that the tube length satisfying the index requirements is not suitable for installation in an automobile.
In order to solve the problems, the invention provides a method for designing a ventilated vehicle-mounted woofer system based on waveguide theory, and simultaneously provides the ventilated vehicle-mounted woofer system.
Disclosure of Invention
The invention aims to provide a ventilated vehicle-mounted bass loudspeaker system and a design method thereof, wherein the design method is based on a waveguide tube, and the design method can adjust more parameters and has larger degree of freedom.
In order to achieve the purpose, the invention adopts the technical scheme that:
a design method of a vehicle-mounted ventilated type woofer system comprises the following steps:
s1, calculating radiation impedance of a current waveguide tube of a loudspeaker system;
s2, constructing a mathematical model of the loudspeaker system according to the waveguide radiation impedance obtained in the step S1;
s3, calculating a radiation sound field of the loudspeaker system according to the mathematical model established in the step S2;
s4, comparing the radiation sound field obtained in the step S3 with an expected radiation sound field, and if the expected radiation sound field is not met, adjusting the structure of the waveguide tube.
Preferably, step S1 comprises:
s1-1, calculating Z resistance of radiation group of waveguide tube end opening ar The opening at the end of the tube can be considered as piston radiation on an infinite baffle. The cross-sectional area of the end of the waveguide tube is S L Radius a, open radiation group Z resistance ar As described below,
Z ar ＝R ar +jωM ar
wherein the acoustic radiation resistance R ar As described below,
acoustic radiation resistance M ar As described below,
and j is an imaginary unit, defined as j 2 = -1, ω is angular frequency, ρ 0 For the density of the medium of the acoustic wave propagation, the invention is applied to the air medium, thus the density of the air, c 0 For the speed of propagation of sound waves in air, k is the beam, specifically defined as k=ω/c 0 ；
S1-2, calculating the distributed impedance of the waveguide, wherein the waveguide is not necessarily a tube with a constant section, and the section of the waveguide is changed along with the length, so that the distributed parameters need to be considered in calculation. Dividing the waveguide tube into n sections according to the curvature change of the waveguide tube, wherein each section is a cylinder, and the sectional area is S i Length Deltal i Radiation sensation DeltaL of the ith section of waveguide i And radiation resistance delta C i As shown in the following formula respectively,
wherein i is more than or equal to 1 and less than or equal to n;
s1-3, obtaining the total radiation impedance of the waveguide tube through stepping calculation because the impedance of the waveguide tube belongs to a distributed parameter,
calculating the total impedance Z formed by the n-th section tube and the radiation of the opening n ，
Calculating the n-1 section of the section tube and Z n Total impedance Z between n-1 ，
And so on, the total radiation impedance Z to the waveguide and the radiation opening ao Is that
Preferably, the mathematical model of the speaker system in step S2 is used to describe the speaker unit and the waveguide, and the whole speaker system can be considered in three parts: a circuit portion, a vibration portion, and an acoustic portion.
Preferably, step S2 includes:
s2-1, the circuit part generates dynamic electromotive force for cutting magnetic force lines by direct current resistance in the voice coil, inductance of the voice coil and voice coil movement. The loop equation for the speaker system circuit is as follows,
wherein U (t) is the voltage output by the front-end power amplifier of the loudspeaker unit, R e Is the DC resistance of the voice coil, i (t) is the current in the voice coil, L e Is the inductance of the voice coil, bl is the electromagnetic force inductance, v (t) is the motion speed of the voice coil, and t is the time;
s2-2, the vibration part means that the cone connected with the voice coil and the voice coil is subjected to the combined action of electromagnetic driving force and elastic restoring force of the folding ring and the centering support piece to generate reciprocating vibration, the vibration loop equation of the loudspeaker system is as follows,
wherein M is m Is the mass of the vibrating diaphragm and the voice coil, R m Is the vibration impedance, K m The elastic force coefficient of elastic components such as a bending ring and the like, and x (t) is the relationship of the vibration displacement of the voice coil and the vibrating diaphragm along with the change of time;
s2-3, the acoustic part is that the cone of the loudspeaker vibrates to act on air, so that the air moves to radiate sound waves outwards, and the action force generated by the cone is considered by the acoustic vibration. This includes, inter alia, the free radiation impedance of the loudspeaker facing air on one side and the radiation impedance of the waveguide on the other side. The influence of the radiation impedance of the waveguide on the acoustic vibration is added as an acoustic load of the vibration circuit to the vibration circuit equation
R ao Is a radiation resistance, comprises air direct action and waveguide action, M ao Is the radiation mass, and includes the direct effect of air on one side, and the radiation effect of the waveguide, also called the resonant mass. Although this formula does not appear to give an effect on the radiation resistance, it is true that the radiation resistance is contained in the radiation resistance R ao And radiation mass M ao Therefore, the radiation resistance and the radiation mass actually also comprise the frequency,should be a function of frequency variation and cannot be considered as constant.
The vibration loop equation is rewritten as,
wherein, the liquid crystal display device comprises a liquid crystal display device,
K ms ＝K m ，S D is the equivalent area of the speaker cone;
s2-4, taking into account all loops of the loudspeaker system, said mathematical model being shown in the following set of differential equations,
preferably, in step S3, the mathematical model is solved to obtain sound pressures at different frequency points of the speaker system, and sound pressure levels at different frequency points are calculated according to the sound pressures to obtain a sound pressure level curve of the speaker system.
More preferably, according to the sound pressure level curve obtained in step S3, comparing whether the curve satisfies a desired radiated sound field; if not, setting new waveguide tube structural parameters, returning to the step S1, and re-solving to obtain a new sound pressure level curve according to the steps S2 and S3, and comparing with the expected radiation sound field; and (5) repeating the steps until a sound pressure level curve meeting the expected radiation sound field is obtained, and storing corresponding waveguide tube structure parameters.
Further, the structural parameters of the waveguide tube include sectional area, changing curvature and length.
Further, only one of the parameters is changed while resetting the structural parameters of the waveguide, and the other parameters remain unchanged. That is, in step S4, whether the curve satisfies the required performance index is compared according to the sound pressure level curve obtained in step S3; if not, returning to the step S1, setting a new waveguide structure including parameters such as the size of the sectional area, the changing curvature, the length of the waveguide and the like. According to the step S2 and the step S3, a new sound pressure level curve is obtained through recalculation and solving, and is compared with the performance index; and (3) repeating the steps circularly until a sound pressure level curve meeting the performance index is obtained, and storing the parameters of the corresponding waveguide tube. In the resetting process of the waveguide parameters, most of the parameters can be kept unchanged, only one of the parameters is changed, the parameter is enlarged or reduced, the sound pressure level is recalculated, the sound pressure level is compared with a target curve, an error is obtained, the adjustment is carried out according to the change of the error, for example, the error is enlarged, and the parameter needs to be adjusted in the opposite direction.
More preferably, step S3 includes:
s3-1, initializing the differential equation set, setting parameters of a loudspeaker unit, and substituting the parameters into the differential equation set by combining the waveguide radiation impedance obtained in the step S1;
s3-2, solving a differential equation set by adopting a forward Euler method,
the input and output of the speaker system is shown in the following equation,
y＝Ax
wherein a= [ 01 0]，X T ＝[x 1 x 2 x 3 ]＝[i(t) x(t) dx/dt]The method comprises the steps of carrying out a first treatment on the surface of the The vector X satisfies the following relation
Wherein, the liquid crystal display device comprises a liquid crystal display device,
writing differential forms as first-order forward differential forms in discrete time domains, e.g.
The above relation is rewritten as
X(n+1)＝(ΔT·F+I)X(n)+ΔT·GU
Wherein X (n) T ＝[x 1 (n) x 2 (n) x 3 (n)]I is a unitVector, Δt is the sampling interval time;
s3-3, solving the radiation sound pressure,
obtaining vibration velocity of loudspeaker unit diaphragm according to step S3-2, i.e. x 3 (n) then obtaining the volume velocity x of the whole radiation surface of the loudspeaker 3 (n)S D Is denoted as U 0 ；
Then examine the acoustic wave passing through the waveguide, since the waveguide is distributed, each section needs to be analyzed, first, after passing through the first section of waveguide, the volume velocity U 1 Is that
With this rule, the volume velocity after passing through each section of waveguide is calculated gradually until the last section, namely the volume velocity U after the nth-order waveguide n Is that
Finally, calculating the radiation sound pressure p of different frequency points of the whole loudspeaker system r
And obtaining sound pressures at different frequency points, and further calculating the sound pressure level to obtain a sound pressure level curve.
The utility model provides a ventilation formula on-vehicle woofer system that obtains by design method, includes basin frame, magnetic circuit, setting are in have front and the cone on the basin frame, set up be annular centering piece support and the centering piece of setting on the centering piece support on the basin frame, centering piece inner wall of centering piece support and constitute the content chamber between the basin frame, magnetic circuit sets up in the content intracavity, the cone back, centering piece support's outer wall and constitute outer appearance chamber between the basin frame, its characterized in that, ventilation formula on-vehicle woofer still includes at least one waveguide tube that is used for wearing sound to the carriage, the waveguide tube includes at least one be located the guide part in outer appearance intracavity and with the exit portion that is used for wearing to the carriage from the vapour car trunk intercommunication of guide part.
The invention also provides a design system of the ventilation type vehicle-mounted bass loudspeaker system, which comprises:
the waveguide radiation impedance calculation module is used for introducing a transmission line theoretical model and calculating the acoustic impedance of the variable-section waveguide in a discretized mode by adopting distributed parameters;
a mathematical model of the speaker system is established, taking into account the influence of the radiation impedance of the waveguide, which would influence the vibration characteristics of the speaker unit and also the radiation sound field characteristics of the speaker system;
the solving module of the loudspeaker system adopts a time domain state space model to solve a differential equation of the loudspeaker system, constructs a coefficient matrix, and introduces a first-order differential equivalent formula to obtain a progressive solving expression;
and the optimization module of the loudspeaker system compares the calculated error between the sound pressure level curve and the target curve, and adjusts the structural parameters of the waveguide tube according to the change of the error. In the process of resetting parameters, most of the parameters can be kept unchanged, only one of the parameters is changed, the parameter is enlarged or reduced, and if the error is enlarged, the parameter needs to be adjusted in the opposite direction.
Compared with the prior art, the invention has the following advantages:
1. the design concept of the waveguide tube is introduced into the ventilated vehicle-mounted bass loudspeaker system, so that the design method has higher design freedom degree and more parameters for adjusting and controlling compared with the existing design scheme based on the Helmholtz resonator;
2. the analytical calculation method of the waveguide radiation impedance based on the transmission line theory is provided, can be suitable for various variable-section waveguides, and has good guiding significance for actual engineering operation;
3. giving a small signal parameter mathematical model of the loudspeaker system considering the radiation impedance of the waveguide, and calculating the influence of the radiation impedance of the waveguide on the vibration characteristic of the loudspeaker unit;
4. the invention provides a method for iteratively calculating the wave guide radiation sound field by adopting a state space equation, which is beneficial to engineering calculation and has practical value;
5. the optimization design method of the ventilation type vehicle-mounted bass loudspeaker system is provided, the structural parameters of the waveguide tube are adjusted by combining the minimum error iteration criterion through the change of the error, and the optimization design method has practical engineering significance and is very beneficial to practical operation.
Drawings
Fig. 1 is a schematic diagram of a waveguide-based woofer system in accordance with the present invention;
FIG. 2 is a schematic sectional view of a variable cross-section waveguide of a frame structure of a one-dimensional Volterra filter;
fig. 3 (a), 3 (b), 3 (c), 3 (d) and 3 (e) are schematic views of different structural forms of the variable cross-section waveguide tube;
fig. 4 is a schematic structural view of a ventilated vehicle-mounted woofer system of the present invention;
FIG. 5 is a schematic waveguide structure of the vehicle-mounted woofer system of FIG. 1;
FIG. 6 is an internal schematic diagram of an in-vehicle woofer system;
fig. 7 and 8 are internal schematic views of two different perspectives of an in-vehicle woofer system, with the cone omitted.
Fig. 9 is a graph comparing measurement results.
In the above figures of the drawings,
1. a basin stand; 11. a sound wave guide plate; 110. a first inclined surface; 12. a second sound guide plate; 120. a second inclined surface; 2. a cone; 3. a waveguide; 31. a guide part; 32. an outlet portion; 4. a shadow mask; 5. a centering support; 50. a sound-transmitting hole; 6. a content cavity; 7. an outer cavity.
Detailed Description
Preferred embodiments of the present invention will be described in detail below with reference to the attached drawings so that the advantages and features of the present invention can be more easily understood by those skilled in the art.
In this example, a woofer unit is used, with the following small signal parameters: straight flow resistance R e =3.53 Ohm, inductance L e =0.375 mH, resonance frequency f s =66.5 Hz, vibrating mass M ms Damping r=12.95 g ms Elastic coefficient K of centering struts and folds =0.994 kg/s ms =2.26N/mm, electromagnetic driving force coefficient bl=3.9N/a.
Obviously, if a closed box is selected, the resonance frequency of the whole bass loudspeaker system is higher, and the requirement of the bass system can not be met far; if the phase inversion hole type loudspeaker box is selected, low frequency can be expanded, but a larger box body is needed. If the existing bass loudspeaker system is designed based on the Helmholtz resonator, a cavity is needed, and meanwhile, a tube is needed to form the Helmholtz resonator, a resonance frequency is provided in a low frequency band, low frequency response is expanded, and in the example, a ventilation type low frequency loudspeaker system of the Helmholtz resonator is designed according to the existing design method for comparison.
In the design method of the ventilating vehicle-mounted bass loudspeaker designed in the waveguide mode in this example, as shown in fig. 1, the back sound wave of the loudspeaker radiates outwards along the direction indicated by the arrow through the waveguide, the forward sound wave of the loudspeaker radiates to free space or a larger box (closed or open), and an infinite baffle is arranged between the sound field radiated by the waveguide and the sound field radiated by the loudspeaker. In an actual application scene, the baffle can be a sealing metal plate between the trunk and the carriage, and a hole is formed in the metal plate and used as a radiation hole of the waveguide tube. In this example, the acoustic impedance of the waveguide is calculated after the length and cross-sectional area change characteristics of the waveguide are set. As shown in fig. 2, the division of the waveguide into segments may be non-uniform. The shape of the waveguide may be varied as desired. The parameters of the waveguide tube are set, acoustic impedance is obtained through calculation, the acoustic impedance can be substituted into a calculation equation provided by the invention to solve the radiation sound field of the waveguide tube, and the shape and the structure of the waveguide tube are adjusted and corrected. Fig. 3 (a) to 3 (e) show some conventional waveguide structure designs. The cross-section of the waveguide may be constant, as shown in fig. 3 (a); or the wave guide can be gradually increased, as shown in fig. 3 (b), the wave guide with gradually increased sectional area is similar to a horn, and the transmission loss of sound waves can be reduced; the horn is also a waveguide of special construction. Fig. 3 (c) is a waveguide having a gradually decreasing cross-sectional area, and such a waveguide has a disadvantage of restricting propagation of acoustic waves, resulting in a certain loss of acoustic energy, but the structure can effectively expand the low frequency response of the speaker. Fig. 3 (d) shows a waveguide having a gradually decreasing cross-sectional area and then gradually increasing cross-sectional area, and thus has both the advantages of expanding the low frequency response of the speaker system and reducing the propagation loss of acoustic energy, and the present invention adopts such a structure. Meanwhile, it should be noted that in the structure, the minimum sectional area is set and the position where the minimum sectional area is needed to be found out by repeatedly performing iterative operation according to the design method of the invention. Fig. 3 (e) shows a waveguide having a constant cross-sectional area, and the relative positions of the waveguide and the speaker unit are different from those of fig. 3 (a).
The structure of the vented vehicle-mounted woofer system will be described in detail with reference to fig. 4 to 8.
As shown in fig. 4 to 8, a ventilated vehicle-mounted bass loudspeaker system comprises a basin frame 1, a magnetic circuit system (not shown in the drawings), a cone 2 with front and back surfaces arranged on the basin frame 1, a ring-shaped centering support 5 arranged on the basin frame 1 and a centering support (not shown in the drawings) arranged on the centering support 5, wherein a content cavity 6 is formed between the inner wall of the centering support 5 and the basin frame 1, the magnetic circuit system is arranged in the content cavity 6, and an outer accommodating cavity 7 is formed between the back surface of the cone 2, the outer wall of the centering support 5 and the basin frame 1. The vented vehicle-mounted woofer also comprises at least one waveguide 3 for transmitting sound into the vehicle compartment, the waveguide 3 comprising at least one guide 31 located in said outer chamber 7 and an outlet portion 32 communicating with said guide 31 for passing from the trunk into the vehicle compartment, the remainder of the speaker system being located in the trunk of the vehicle except for the end of the outlet portion 32 of the waveguide 3. The speaker unit is integral with the structure of the waveguide 3. The back of the cone 2 of the loudspeaker radiates sound outwards through the structure of the waveguide 3. The figure shows a baffle 4 (corresponding to a sheet metal part for connecting a trunk of an automobile with a carriage) of the woofer system, and in practical installation, an infinite or nearly infinite plate is provided with a port, and the outlets of the rest of the waveguides 3 and the baffle 4 are in seamless connection so as to ensure that the front radiation of the cone 2 of the loudspeaker is isolated from the radiation of the waveguides 3.
The guide 31 comprises a first sound guiding plate 11 and a second sound guiding plate 12 arranged in said outer chamber 7, the sound guiding plates 11, 12 having inclined surfaces 110, 120 for constituting a part of the inner wall of said waveguide 3 and guiding sound to said outlet portion 32. The acoustic wave guide plates 11, 12 are fixedly connected or integrally formed with the basin stand 1. Specifically, the first sound wave guide plate 11 has a first inclined surface 110 for guiding sound waves, and the second sound wave guide plate 12 has a second inclined surface 120 for redirecting sound waves into the outlet portion 32, the second inclined surface 120 being disposed opposite to the first inclined surface 110. The outer chamber 7 is divided by the first sound guide plate 11 and the second sound guide plate 12 to form a propagation path of sound waves in the outer chamber 7, that is, the guide portion 31 of the waveguide 3. The outlet portion 32 is hollow and has a rectangular tubular shape with both ends open, and the guide portion 31 is fixedly connected to or integrally formed with the basin frame 1. The waveguide 3 includes two guide portions 31 and one outlet portion 32, and the two guide portions 31 communicate with the outlet portion 32, respectively, and are symmetrical with respect to the central axis of the outlet portion 32. The centering support 5 is provided with a sound-transmitting hole 50 for communicating the inner cavity 6 with the waveguide 3 (specifically, the guide portion 31).
Specifically, the rear surface of the cone 2 has two waveguide 3 guide portions 31, and the two waveguide 3 guide portions 31 are finally converged into one square tubular outlet portion 32, and the sound wave is radiated to the outside (i.e., in the vehicle cabin), and the structure of the two waveguide 3 guide portions 31 is completely symmetrical. The advantage of this vehicle-mounted woofer is that the rear cavity of the speaker unit in the prior art is not needed at all, and therefore, in this example, the rear cavity is changed to the waveguide 3 guide 31, reducing the volume of the entire speaker system, making the structure relatively compact. In addition, the channel of the guide 31 of the waveguide 3 is not linear but is curved like a zigzag. When the cone 2 moves back, compressed air generates sound waves, which are directed through the first inclined surface 110, then through the second inclined surface 120, and radiated outward through the outlet portion 32 of a quasi-linear duct. In addition, it should be noted that the sound-transmitting hole 50 can be communicated with the air on the back of the centering support and the air between the centering support and the cone 2, so that the sound wave energy of the two cavities are added, and are radiated outwards through the waveguide tube 3, so that all the sound energy of the cone 2 facing away is fully utilized, and the sensitivity of the system is improved.
From fig. 2, a schematic view of the structure of the waveguide 3 is given, from which it can be seen more intuitively that the cross-sectional area of the entire waveguide 3 shows a tendency to decrease and then increase gradually. This structure is advantageous in expanding low frequencies and reducing transmission loss of acoustic energy as much as possible. It can be seen from fig. 4 and 5 that the structure of the speaker unit is integrated with the acoustic waveguide 3, and in addition, the centering support and the support of the centering support form a closed inner cavity 6, and air and sound energy in the inner cavity 6 are all communicated with the outside through the sound transmission hole 50, so that the sound pressure level of the system can be effectively improved, and nonlinear distortion of the system caused by air compression in the closed cavity is avoided.
In this example, a vented woofer designed based on the method of the present invention was tested for performance, while a vented woofer based on the prior art scheme, a helmholtz resonator type, was also tested for comparison. The experiment was carried out in a totally anechoic room, the loudspeaker system was mounted on a baffle whose dimensions were much larger than the wavelength of the sound waves in the frequency band studied, and square holes were reserved on the baffle, consistent with the outlet aperture of the waveguide tube in this example. A B & K microphone 4189 was placed 1m from the waveguide outlet for picking up the system output signal of the speaker. The speaker and microphone are at the same height, 1m from the ground (wire mesh surface, not the true reflective ground). In addition, other hardware devices are selected for the experiment, including a power amplifier and an R & D measuring system of Klippel company.
The measurement result is shown in fig. 9, wherein the dotted line is a frequency response curve of the speaker unit mounted on the baffle, the dotted line is a frequency response curve of the existing Helmholtz resonator type speaker system, and it can be seen that the structure can effectively expand the low frequency response of the speaker; the solid line in the figure is the frequency response curve of the waveguide tube type bass loudspeaker system designed based on the method of the invention, and compared with the curve, the system designed by the method of the invention has more obvious low frequency expansion, and meanwhile, because the waveguide tube structure is a multi-degree-of-freedom resonance system, more resonance frequency points can be introduced, so that formants can be formed at other frequency points while the low frequency is expanded, for example, the embodiment system forms obvious formants at 26Hz frequency, and stronger bass effect can be presented, which is the greatest advantage of the ventilation type vehicle-mounted bass loudspeaker system designed based on the waveguide tube theory.
The above-described embodiments are provided for illustrating the technical concept and features of the present invention, and are intended to be preferred embodiments for those skilled in the art to understand the present invention and implement the same according to the present invention, not to limit the scope of the present invention. All equivalent changes or modifications made according to the spirit of the present invention should be included in the scope of the present invention.
Claims (7)
1. The design method of the vehicle-mounted ventilated type woofer system is characterized by comprising the following steps of:
s1, calculating radiation impedance of a current waveguide tube of a loudspeaker system;
s2, constructing a mathematical model of the loudspeaker system according to the waveguide radiation impedance obtained in the step S1;
s3, calculating a radiation sound field of the loudspeaker system according to the mathematical model established in the step S2;
s4, comparing the radiation sound field obtained in the step S3 with an expected radiation sound field, and if the expected radiation sound field is not met, adjusting the structure of the waveguide tube;
the step S1 comprises the following steps:
s1-1, calculating Z resistance of radiation group of waveguide tube end opening ar The cross-sectional area of the end of the waveguide tube is S L Radius a, open radiation group Z resistance ar As described below,
Z ar ＝R ar +jωM ar
wherein the acoustic radiation resistance R ar As described below,
acoustic radiation resistance M ar As described below,
and j is an imaginary unit, defined as j 2 = -1, ω is angular frequency, ρ 0 The density of the medium for propagation of sound waves, c 0 For the speed of propagation of sound waves in air, k is the beam, specifically defined as k=ω/c 0 ；
S1-2, calculating distributed impedance of the waveguide tube, dividing the waveguide tube into n sections according to curvature change of the waveguide tube, wherein each section is a cylinder, and the sectional area is S i Length Deltal i Radiation sensation DeltaL of the ith section of waveguide i And radiation resistance delta C i As shown in the following formula respectively,
wherein i is more than or equal to 1 and less than or equal to n;
s1-3, obtaining the total radiation impedance of the waveguide tube through stepping calculation,
calculating the total impedance Z formed by the n-th section tube and the radiation of the opening n ，
Calculating the n-1 section of the section tube and Z n Total impedance Z between n-1 ，
And so on, the total radiation impedance Z of the waveguide and the radiation opening ao Is that
The step S2 comprises the following steps:
s2-1, a loop equation of the loudspeaker system circuit is as follows,
wherein U (t) is the voltage output by the front-end power amplifier of the loudspeaker unit, R e Is the DC resistance of the voice coil, i (t) is the current in the voice coil, L e Is the inductance of the voice coil, bl is the electromagnetic force inductance, v (t) is the motion speed of the voice coil, and t is the time;
s2-2, a vibration loop equation of the loudspeaker system is as follows,
wherein M is m Is the mass of the vibrating diaphragm and the voice coil, R m Is the vibration impedance, K m Is the elastic force coefficient of elastic components such as a bending ring, and x (t) is the vibration displacement of the voice coil and the vibrating diaphragm along with timeA chemical relationship;
s2-3, adding the influence of the radiation impedance of the waveguide tube on the acoustic vibration as the acoustic load of the vibration loop into the vibration loop equation
R ao Is a radiation resistance, M ao Is the radiation mass, the vibration loop equation is rewritten as,
wherein, the liquid crystal display device comprises a liquid crystal display device,
K ms ＝K m ，S D is the equivalent area of the speaker cone;
s2-4, taking into account all loops of the loudspeaker system, said mathematical model being shown in the following set of differential equations,
the step S3 comprises the following steps:
s3-1, initializing the differential equation set, setting parameters of a loudspeaker unit, and substituting the parameters into the differential equation set by combining the waveguide radiation impedance obtained in the step S1;
s3-2, solving a differential equation set by adopting a forward Euler method,
the input and output of the speaker system is shown in the following equation,
y＝Ax
wherein a= [ 01 0]，X T ＝[x 1 x 2 x 3 ]＝[i(t) x(t) dx/dt]The method comprises the steps of carrying out a first treatment on the surface of the The vector X satisfies the following relation
Wherein, the liquid crystal display device comprises a liquid crystal display device,
writing the differential form into a first-order forward differential form in a discrete time domain, and rewriting the relationship into
X(n+1)＝(ΔT·F+I)X(n)+ΔT·GU
Wherein X (n) T ＝[x 1 (n) x 2 (n) x 3 (n)]I is a unit vector, and DeltaT is a sampling interval time;
s3-3, solving the radiation sound pressure,
obtaining vibration velocity of loudspeaker unit diaphragm according to step S3-2, i.e. x 3 (n) then obtaining the volume velocity x of the whole radiation surface of the loudspeaker 3 (n)S D Is denoted as U 0 ；
After passing through the first section of waveguide, the volume velocity U 1 Is that
With this rule, the volume velocity after passing through each section of waveguide is calculated gradually until the last section, namely the volume velocity U after the nth-order waveguide n Is that
Finally, calculating the radiation sound pressure p of different frequency points of the whole loudspeaker system r
And obtaining sound pressures at different frequency points, and further calculating the sound pressure level to obtain a sound pressure level curve.
2. The design method according to claim 1, wherein the mathematical model of the speaker system in step S2 is used to describe the speaker unit and the waveguide.
3. The design method according to claim 1, wherein in step S3, the mathematical model is solved to obtain sound pressures at different frequency points of the speaker system, and sound pressure levels at different frequency points are calculated according to the sound pressures to obtain a sound pressure level curve of the speaker system.
4. A design method according to claim 3, wherein, based on the sound pressure level curve obtained in step S3, whether the curve satisfies a desired radiation sound field is compared; if not, setting new waveguide tube structural parameters, returning to the step S1, and re-solving to obtain a new sound pressure level curve according to the steps S2 and S3, and comparing with the expected radiation sound field; and (5) repeating the steps until a sound pressure level curve meeting the expected radiation sound field is obtained, and storing corresponding waveguide tube structure parameters.
5. The design method according to claim 4, wherein: the structural parameters of the waveguide tube comprise sectional area, changing curvature and length.
6. The design method according to claim 4, wherein: when resetting the structural parameters of the waveguide, only one of the parameters is changed, and the other parameters remain unchanged.
7. A ventilated vehicle-mounted woofer system obtained by the design method of any one of claims 1 to 6, comprising a basin frame, a magnetic circuit system, a cone provided on the basin frame and having a front surface and a back surface, a ring-shaped centering support provided on the basin frame, and a centering support provided on the centering support, wherein a content cavity is formed between the centering support, an inner wall of the centering support and the basin frame, the magnetic circuit system is provided in the content cavity, and an outer cavity is formed between the back surface of the cone, an outer wall of the centering support and the basin frame.
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