RU2237981C2 - Method and device for radiating audio signals into environment - Google Patents

Abstract

FIELD: sound amplification in manufacturing electrodynamic-type acoustic make-up.

SUBSTANCE: acoustic system has at least one loudspeaker mounted on front wall of housing. Inner space of the latter forms main waveguide with aperture. System also has additional waveguide connected to main waveguide aperture and provided with its respective output port to environment inclined through 60 to 120 deg. relative to longitudinal axis of loudspeaker. Cross-sectional area of each waveguide is equal to or greater than active surface area of loudspeaker cone. During system operation sound energy developed by rear surface of cone is conveyed by means of additional waveguide to space being sonicated in addition to main front flow of sound vibrations.

EFFECT: enhanced electroacoustic efficiency, reduced nonlinear sound distortions.

5 cl, 14 dwg

Description

The device relates to sound reinforcement systems and, in particular, to structural elements of the acoustic design of electrodynamic-type loudspeakers.

A known acoustic system containing an electrodynamic loudspeaker mounted on one of the walls open from the back of the housing [1].

The disadvantage of this speaker system is the small electro-acoustic efficiency K _ea - less than 50% is emitted into the sound space, and the rest of the acoustic power is not emitted due to the acoustic short circuit between the oscillations of the front and back surfaces of the speaker cone.

A known acoustic system comprising a closed housing, on one of the walls of which an electrodynamic loudspeaker is installed [2].

A disadvantage of the known acoustic system is the small electro-acoustic efficiency K _ea due to the conversion of the vibrational power generated by the back surface of the speaker cone into heat - more than 50%.

A known acoustic system containing a closed housing, on one of the walls of which an electrodynamic loudspeaker is installed and a waveguide is made - a phase inverter for the output of the vibrational power developed by the back surface of the loudspeaker diffuser into the voiced space [3].

For most reasons, this device can be taken as a prototype.

The prototype device has the following disadvantages:

- a small electro-acoustic efficiency K _ea due to the small area of the outlet of the waveguide, which is the main one, and the appearance of residual elasticity in it, which reduces the oscillation amplitude of the loudspeaker diffuser, and also because the sound vibrations at the output of the waveguide have a maximum phase shift equal to only 90 °, although a complete phase shift of 180 ° is required for the complete phasing of the oscillations; the maximum possible shift of the output oscillations of the waveguide, equal to 180 °, is obtained only at one frequency equal to the resonant frequency of the Heimgoltz resonator, which is the prototype device;

- significant non-linear distortions arising near the resonant frequency of the speaker system, as a result of which the bass register musical instruments sound unnatural, similar and distorted, according to acoustic measurements, the value of non-linear distortions reaches 5-7%; at higher frequencies, the bass reflex is useless.

The technical problem to which the invention is directed is to increase the electro-acoustic efficiency and to reduce non-linear sound distortions.

The specified technical problem is solved in that the known acoustic system containing at least one loudspeaker mounted on one of the walls of the housing, the morning volume of which forms a main waveguide having an outlet in the outer space, according to the invention is made with at least one additional waveguide, connected to the outlet of the main waveguide and having its own exit into the external space directed at an angle from 60 ° to 120 ° with respect to the longitudinal axis govoritelya, wherein the cross-sectional area of each waveguide is equal to or greater than the area of the active surface of the speaker cone, the speaker mounted on the front wall of the housing.

In a variant of the device, an additional waveguide is combined with the rear wall of the housing and has an acoustically rigid screen.

In another embodiment of the device, the additional waveguide is aligned with the front wall of the casing, installed at an angle with an inclination into the internal volume of the main waveguide and shorter in height than the rear wall of the casing by t = s / b, where s is the cross-sectional area of the additional waveguide, ab is the width of the front or back walls of the casing, while the passage section of the additional waveguide is formed by parts of the side walls of the casing, the front wall and an acoustically rigid screen that overlaps the output tverstie main waveguide by an amount not less than L = (1-2t).

In the next embodiment, the system is made in the form of interconnected identical acoustic systems with open-type housings, the rear walls of which are convex in shape, with an additional waveguide formed by the convex walls of the housings facing each other and spaced apart from each other by a distance h = r _a , where r _a is the radius of the active surface of the diffuser.

In an acoustic system made in accordance with the proposed technical solution, the losses of the oscillatory system are reduced due to the fact that the energy developed by the back surface of the loudspeaker diffuser, through the attached waveguide, additional to the main one, is directed to the sound space in addition to the sound stream from the front surface . Moreover, in accordance with the theory of oscillations [see 4] excludes the possibility of an acoustic short circuit between the oscillations of the front and back surfaces of the speaker cone characterized by a phase shift of 180 °. In the proposed speaker system, an acoustic short circuit is completely absent if the directivity angle α between the frontal vibrations and the vibrations at the output of the additional waveguide is 90 °. Technically permissible acoustic power equal to 50% of the maximum possible is emitted if the angle α is 60 ° or 120 °. The boundary values of 60 ° and 120 ° correspond to the value of half power, i.e. with a partial manifestation of the acoustic short circuit phenomenon between frontal and rear vibrations, the value of the total vibrational energy will be at the level of 3 dB. These oscillations have circular or elliptical polarization, because their amplitudes are equal or almost equal, but directed in relation to each other at an angle ranging from 60 ° to 120 °. Due to the fact that these vibrations do not affect each other [see 4], theoretically, all the acoustic power developed by the loudspeaker is transferred to the voiced space, which leads to an increase in the electro-acoustic efficiency K _ea = P _a / R _e , where P _a is the acoustic power developed by the loudspeaker, and P _e is the electric power supplied to the electrodynamic loudspeaker power in watts

Nonlinear distortions during the operation of the system are reduced by eliminating the harmful effects of the internal environment - air, and various sound absorbers in the system case on the movements of the speaker cone when excited with a voice coil connected to the output of the low-frequency amplifier, as well as by eliminating the deformation of the walls of the diffuser and increasing oscillation amplitudes, especially at low frequencies with a significant decrease in air elasticity inside the housing.

The invention is illustrated by drawings, where Fig. 1 shows an embodiment of a speaker system with a primary and secondary waveguides, where the latter is attached to the rear wall of the housing; figure 2 shows a view of figure 1; figure 3 is a diagram explaining the interaction of the vector characteristics of the directivity of the oscillatory sound streams from the front and rear surfaces of the diffuser; figure 4 shows a variant of the speaker system with frontal alignment of an additional waveguide; in Fig.5 shows a view of D in Fig.5; figure 6 shows a variant of the design of the speaker system in the form of two identical speakers combined with each other; in FIG. 7 shows the experimentally recorded directivity of the speaker system shown in figure 1; on Fig - frequency response of the same speaker system at a frequency of 100 Hz; figure 9 shows the frequency response of the frontal radiation of the speaker system (vector A) shown in figures 4 and 5; figure 10 presents the frequency response of the rear radiation of the same speaker system (vector B); figure 11 shows the directivity of the speaker system shown in figure 6; in Fig.12 shows the frequency response of the frontal radiation (vector A), and Fig.13 - frequency response of the rear radiation (vector B) of the same speaker system; in Fig.14 shows the frequency response of the speaker system shown in Fig.1.

The frequency characteristics in Figs. 8 and 14 were taken using loudspeakers of type 10 GDSH-1, in Figs. 9 and 10 - using loudspeakers of type 4A32, in Fig. 11 - using loudspeakers of type 3GD-38E.

In the drawings, the following notation:

A and B are vectors characterizing the direction of propagation of acoustic vibrations corresponding to the work of the front and back surfaces of the speaker cone, respectively;

α is the angle between the directions of propagation of acoustic vibrations characterized by vectors A and B;

b is the linear size of the speaker housing;

t is the linear dimension, by the value of which the front wall of the housing is shortened in the embodiment of the speaker system;

β is the angle of inclination of the front wall of the housing in the embodiment of the speaker system;

h is the distance between the convex rear walls of the housing in an embodiment of a dual speaker system;

r _a is the radius of the active surface of the speaker cone;

r is the radius of the outlet at the output of the main waveguide.

“1” - experimental frequency response for various versions of the proposed speaker systems using the above types of standard speakers;

“2” - passport frequency characteristics of the above types of standard speakers.

The speaker system contains at least one loudspeaker 1 with two voice coils (not shown), but may also quantitatively contain two loudspeakers, as shown in FIG. Loudspeakers 1 are mounted on one of the walls, namely, on the front wall 2 of the casing 3, the internal volume of which forms the main waveguide 4. The latter has an outlet 5 in the external sound space made in the back wall 6 of the casing 3. At the same time, the speaker system is made at least with at least one additional waveguide 7 connected to the outlet 5 of the main waveguide 4. The waveguide 7 is made with its own output 8 into the outer space, in this case, a double-sided output 8 with left and right torons of the speaker system. Each output 8 of the additional waveguide 7 is directed at an angle of 60 ° ≤α≤120 ° with respect to the longitudinal axis of the speakers 1. In Fig. 1, the angle α is equally shown as the angle between the vectors A and B characterizing the directions of propagation of acoustic vibrations generated respectively by the front and the back of the active surfaces of the diffuser (not arbitrarily marked) loudspeakers 1 and are essentially in antiphase, i.e. having opposite signs for the same moment in time. In this case, the direction of the acoustic propagation vector B is formed by using an attached additional waveguide 7. Moreover, the cross-sectional area of each of the waveguides 8 — left and right — is equal to or greater than the active surface area of the speaker cone 1.

The speaker system shown in FIGS. 1 and 2 represents an embodiment of the system in that the additional waveguide 7 is aligned with the back wall 6 of the housing 3 and has an acoustically rigid flat screen 9.

As another option, the speaker system shown in FIGS. 4 and 5 (a variant with a broken deck) can be configured such that the additional waveguide 7 is aligned with the front wall 2 of the housing 3. At the same time, wall 2 is installed at an angle β with an inclination into the internal volume of the main waveguide 4 and is shorter in comparison with the back wall 6 of the housing 3 by a value of t = s / b, where s is the cross-sectional area of the additional waveguide; and b is the width of the front or back walls 2 or 6, respectively, of the casing 3. The passage section of the additional waveguide 7 is formed by parts of the side walls 10 of the casing 3, the front wall 2 and an acoustically rigid flat screen 11 that overlaps the outlet 5 of the main waveguide 4 by an amount not less than L = (1-2) t.

According to another embodiment, the speaker system can be made in the form of two, interconnected fastening elements 12, of the same speaker systems (reversed speaker version) with open-type housings 3, the back walls of which 6 have a convex shape (see FIG. 6). An additional waveguide 7 is formed by the convex rear walls 6 of the buildings 3, facing towards each other. The convex rear walls 6 are separated from each other at a distance h = r _a , where r _a is the radius of the active surface of the diffuser. A soundproof membrane 13 is provided to protect the system from contamination.

The acoustic system shown in figures 1 and 2, operates as follows.

When applying a sound frequency voltage to the sound coils of the loudspeaker 1, the diffuser of the latter moves in the longitudinal direction, which leads to the excitation of an air molecule exactly in accordance with the law of input voltage. The resulting acoustic vibrations associated with an increase and decrease in air pressure are directed both in the frontal direction — from the frontal surface of the diffuser, in the direction of vector A, and from the rear surface of the diffuser. Acoustic vibrations from the rear surface of the diffuser through the outlet 5 of the main waveguide 4 are directed into the volume of the attached additional waveguide 7 and then, reflected from the acoustically rigid flat screen 9, exit through their own outputs 8, propagating in the voiced space in the direction of vector B in addition to acoustic oscillations in the direction of vector A with a rotation through an angle α with respect to the longitudinal axis of loudspeaker 1, which is selected in the interval 60 ° ≤α≤120 ° and determines I, therefore, additional geometrical parameters of the waveguide 7. In FIG. 1 angle α = 90 °, as a special case, which is the optimal value from the proposed angular interval. In the proposed range of angles α, acoustic vibrations in the direction of vectors A and B, although they pass with a phase shift of 180 °, have a minimal effect on each other with respect to acoustic power losses, especially at α = 90 °, because these vectors mutually perpendicular and in accordance with [4] an acoustic short circuit between them does not occur. In contrast to acoustic closure in the voiced space, at least a doubling of acoustic energy occurs, i.e. doubles the value of the acoustic efficiency K _ea .

When choosing the values of the angle α outside the specified interval, i.e. for α <60 and α> 120 °, the losses of the total acoustic power directed towards the vectors A and B gradually increase due to their increasing mutual influence on each other due to interference. Therefore, from a technical point of view, the above inequalities for angles α <60 ° and α> 120 ° are not practical.

It should be noted that in reality, as shown by experimental data obtained in an anechoic chamber when testing prototypes similar to the described acoustic system (see frequency characteristics in Figs. 8, 9, 10, 12, and 13), an increase in the value of K _ea more than 2 times. This is because in case 3 there is no sound absorber, usually placed inside the case, which usually leads to the conversion of part of the acoustic power from the rear surface of the diffuser into heat, and there is no mechanical negative reaction from the actual mass of the sound absorber.

In addition, the described design of the acoustic system allows to reduce the loss of acoustic power received from the rear surface of the diffuser due to the condition that the cross-sectional area of each of the waveguides 4 and 7 is equal to or greater than the active surface area of the speaker cone, which is determined by the size of the outlet 5 - for the main waveguide 4, and output 8 for the additional waveguide 7. Due to the fulfillment of this important condition, it becomes possible to further reduce the loss of vibration th energy by eliminating the negative impact of increased resistance by the elastic mass of air inside the housing 3. In essence, the system operation is organized so as if the speaker would work without mechanical loss in free space. In this case, an increase in the value of K _{ea by} 6 times or more becomes real.

As for the nonlinear distortions of sound, they also decrease simultaneously with an increase in K _ea . This is again explained by the fact that all the acoustic power of each speaker created inside the housing 3 is radiated into the voiced space through the primary and secondary waveguides 4 and 7, respectively. This leads to the exclusion of the occurrence of standing waves and to a significant reduction in the probability of excitation of vibrations in all body elements of the speaker system. The latter circumstance is especially important for the lower part of the sound spectrum of vibrations. Using the invention, nonlinear distortion can be reduced on average 3-8 times.

In addition, when analyzing the frequency response shown in Fig. 7, corresponding to the speaker system in question, it follows that the sound is surround. That is, a similar speaker system can be used as stereo if it is rationally placed in a room or in a car.

A positive point in the operation of this speaker system can be considered the fact that the increased several times the electro-acoustic efficiency K _ea reduces the power used in acoustic systems of low-frequency amplifiers, which is especially important for stand-alone sound systems powered by batteries and accumulators.

The operation of the speaker system, made in accordance with the embodiment of FIGS. 4 and 5, proceeds similarly to the case described above. Due to the design feature having the front wall 2 inclined at an angle β and shortened by a height t by an amount t, as well as an additional waveguide 7 connected thereto, formed using an acoustically rigid flat screen 11, it becomes possible to direct the acoustic vibrations generated by the back surface of the speaker cone 1 , through the outlet 5 of the main waveguide 4 and further, by turning the flow of acoustic energy around the upper part of the frontal wall 2, direct it with mations additional volume of the waveguide 7 via the outlet 8 in the direction of the space voiced by the vector B as a supplement to acoustic vibrations from the front surface of the diffuser, propagating in the direction of the vector A at an angle α to the latter. In this case, the angle α = 90 °, as the most optimal. The specified parameters t = s / b and L = (1-2) t must be maintained since they provide free passage and output of acoustic energy from the back surface of the speaker cone 1. Acoustic vibrations propagating in the direction of vector B, repeatedly reflected from the floor and ceiling, will create a sense of surround sound in the room.

In the variant with two identical acoustic systems, the rear walls 6 of which have a convex shape, the acoustic power from the rear surfaces of the diffusers from two symmetrically installed loudspeakers 1, having passed the output openings 5 of the main waveguide 4, are summed up and deployed with the help of a common additional waveguide 7 and sent to voiced space in the directions of the vectors In addition to the two-way acoustic vibrations propagating in the direction of the vectors A from the front ones NOSTA diffusers two speakers 1. The rear wall 6 of the housings 3 are spaced apart by a distance h, which is defined by a radius r _and an active surface of each of the diffusers. In this case, it is necessary to fulfill the condition regarding the passage area of the main waveguide 4 in cross section with the outlet 5, providing free passage of acoustic energy into the volume of the additional waveguide 7. Based on this, the radius r of the outlet 5 should be selected not less than the radius r _{and the} active surface of the diffuser of each loudspeaker 1. Providing the above structural relationships for h and r, the process of transferring the total acoustic energy from the main waveguide 4 to additional waveguide 7 and further into the voiced space. Moreover, at the output of the additional waveguide 7, acoustic vibrations are generated in the direction of the vector B, which propagate in the volume circular sector, significantly supplementing the two acoustic flows propagating in the direction of the vectors A, creating a sensation of surround sound without loss of low-frequency sound power. Such a speaker system is highly preferred for use in a confined space, such as on city streets, stadiums, etc.

Thus, the invention allows to increase the electro-acoustic efficiency K _{ea of the} acoustic system due to the additional use of acoustic power generated by the back surface of the speaker cone. The acoustic power with the help of an attached additional waveguide is output at an optimum angle into the sound space and is sent as an addition to the main acoustic power from the front surface of the speaker cone. At the same time, the invention allows to reduce the nonlinear distortion of sound.

Sources of information

1. Shishkovsky Z. Fundamentals of electroacoustics, Poland, Warsaw, Scientific and Technical Publishing House, 1965, p. 491, Fig. 15.21a.

2. Shishkovsky Z. Fundamentals of electroacoustics, Poland, Warsaw, Scientific and Technical Publishing House, 1965, p. 491, Fig. 15.216.

3. US Patent No. 1869178, publ. 1932 (prototype).

4. Malov N.N. Fundamentals of the theory of oscillations. M .: Education, 1971, p. 62.

Claims (5)

1. The method of emitting sound signals into the external space using an acoustic system containing a loudspeaker, which consists in the fact that they form one sound stream from the front surface of the loudspeaker diffuser, coinciding in direction with its longitudinal axis, and the other from the back surface of the diffuser in the external space in addition to the first sound stream using the waveguides of the speaker system, characterized in that the sound stream from the rear surface of the diffuser is directed to exit from the acoustic system by means of waveguides, the cross-sectional area of each of which is not less than the active surface area of the diffuser, and at the exit from the acoustic system, at an angle of 60 ° ≤α≤120 ° with respect to the sound stream from the front surface of the speaker cone. 2. An acoustic system containing at least one loudspeaker mounted on one of the walls of the housing, the internal volume of which forms a main waveguide having an outlet in the outer space, characterized in that the system is made with at least one additional waveguide connected to the output the opening of the main waveguide and having its own exit into the external space directed at an angle α = 60 - 120 ° with respect to the longitudinal axis of the loudspeaker, and the cross-sectional area each waveguide is equal to or greater than the area of the active surface of the loudspeaker diffuser, while the loudspeaker is mounted on the front wall of the housing. 3. The system according to claim 1, characterized in that the additional waveguide is aligned with the back wall of the housing and has an acoustically rigid screen. 4. The system according to claim 1, characterized in that the additional waveguide is aligned with the front wall of the casing, installed at an angle with a slope in the internal volume of the main waveguide and is shorter in height compared to the back wall of the casing by t = s / b, where s is the cross-sectional area of the additional waveguide, and b is the width of the front or back wall of the casing, while the passage section of the additional waveguide is formed by parts of the side walls of the casing, the front wall and an acoustically rigid screen overlapping the output hole of the main waveguide by an amount not less than L = 1-2t. 5. The system according to claim 1, characterized in that the system is made in the form of interconnected identical acoustic systems with open housings, the rear walls of which are convex in shape, while the additional waveguide is formed by the convex walls of the housings facing each other and spaced apart from each other at a distance h = r, where r is the radius of the active surface of the diffuser.

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