Prior art Loudspeaker systems usually represent an active speaker consisting of a diaphragm connected to an actuator. Radiation is improved usually by enlarging the diaphragm area. This results in increasing the pressure of the radiated sound waves. However, in order to avoid radiation distortion at medium and high frequencies, it is necessary to increase the diaphragm rigidity. Even higher rigidity cannot help fully avoid the radiation distortion in large diaphragms. Thus the frequency radiated gets restricted.

Radiation may also be improved by the use of a phase inverter /bass reflex/. The purpose of using a phase inverter is to utilise the sound energy emitted from the back side of the active diaphragm, thus raising the low frequency radiation efficiency. In terms of construction, the phase inverter represents a closed box with two openings on the front side thereof, in which there are disposed an acoustic speaker and a radiating tube. Similar constructions are described in patents DE 2 911 849 and DE 2 854 899.

Where the phase inverter is correctly sized for a particular frequency domain around the resonant frequency of the inverter, phase inversion occurs of the vibrations emitted from the back side of the diaphragm. Thus the air in the tube effects vibrations whose phase coincides with the phase of those emitted from the front side of the diaphragm, this increasing the sound pressure within the low frequencies domain. However, a disadvantage of this construction is that it causes variation in the frequency response due to phase non-coincidence of the sound waves emitted by the diaphragm and the tube at frequencies differing from the frequency of their own resonance, as a result of which the radiated sound becomes unnatural, this being easily caught by the ear. The phase inverter has a narrow frequency range disposed close to its resonance frequency domain.

In order to improve radiation it is possible to use also a passive diaphragm. The construction of the loudspeaker system with a passive diaphragm is similar to the phase inverter, but for the fact that, instead of a radiating tube, it has a diaphragm vibrating with regard to its suspension, the diaphragm being passive for it has no actuator of its own. The sound waves radiated from the back side of the active speaker diaphragm actuate the passive diaphragm. There is a similar construction described in Patent RU 1 838 895. It makes it possible to increase the sound pressure, and has the same drawbacks as the phase inverter. In addition, the passive diaphragm inertness causes an increase of the phase difference between the sound waves radiated from the active speaker diaphragm and the passive diaphragm. This leads to distortions in the phase frequency response of the loudspeaker system within the low frequency domain.

A loudspeaker system is known, which represents an enclosure with an inner reflecting wall. The latter divides the enclosure interior into two chambers/Patent US 4 076 097/. In openings on the front wall of the first chamber there is disposed an active speaker and the front side of a passive diaphragm, the back side of the latter being disposed in an opening on the inner reflecting wall.

The above loudspeaker system has the same drawbacks as those described in Patent RU 1 838 895. However, it is more efficient, for the air displaced by the passive diaphragm is more than the air displaced by the active speaker diaphragm. Thus the sound wave gets sufficiently amplified, but its phase frequency response is disturbed.

Still another loudspeaker system is known, which uses a twin passive diaphragm consisting of a pair of passive diaphragms. The two diaphragms have different dimensions. The small bases of the diaphragms are fixed to each other by means of a joint. Sound is transmitted from the active speaker diaphragm through an air medium to one of the passive diaphragms of the pair, usually having smaller dimensions, and then through the joint to the second diaphragm, which radiates the sound through its external surface into the outer space. The construction of a loudspeaker system using a twin passive diaphragm is described in Patent US 4 301 332. It has an elongated box with an inner reflecting wall disposed crosswise therein. The wall separates the box interior into two closed chambers. There is an active speaker disposed in an opening on one of the externat walls of the first chamber. The larger base of the small diaphragm of the twin passive diaphragm is situated in an opening on the reflecting wall. The large base of the large cone of the twin diaphragm is attached to the outer wall of the second chamber. That outer wall faces the reflecting wall. The joint is disposed in the second chamber.

A disadvantage of the above construction is that the joint is long for the purpose of ensuring large volume of the second chamber, this rendering the construction heavy and bulky. The joint is not rigid enough, this causing distortion of the sound. Besides, the radiation from the active speaker and that of the large diaphragm of the twin passive diaphragm are in phase opposition, therefore the resultant radiation of the loudspeaker system has a sound pressure that is smaller than the sum of the sound pressures individually determined by the active speaker and the twin passive diaphragm. The phase difference between the active speaker radiation and the twin passive diaphragm brings about a phase difference between the input electric signal fed to the actuating system of the active speaker and the output acoustic signal from the loudspeaker system, this affecting its phase frequency response, In other words, the twin passive diaphragm distorts the phase frequency response of the loudspeaker system.

Technical substance A loudspeaker system is disclosed herein having two coaxial passive diaphragms fixed to each other, said diaphragms having different dimensions and being disposed within a loudspeaker enclosure together with an active speaker, the latter being placed together with the smaller passive diaphragm in the same acoustic chamber. According to the invention applied for, both diaphragms are isolated from each other in terms of acoustics by means of a mechanical partition. The coaxial diaphragms may radiate in opposite directions, the mechanical partition being disposed externally to the diaphragms. In another embodiment of the invention, the coaxial diaphragms radiate in the same direction, the mechanical ! partition being disposed internally to the diaphragms.

The external partition disposed extematty to the passive diaphragms shapes the bottom of an inner chamber, whereat the small passive diaphragm is placed within the inner chamber so that the outer opening of the small passive diaphragm lies on the top wall of the inner chamber, while the outer opening of the large passive diaphragm lies on the bottom of the outer chamber shaped as a loudspeaker enclosure, the inner chamber lying within the outer chamber, and there is a plug placed inside the two passive diaphragms and connected therewith, the two diaphragms being connected to the chambers through flexible suspensions.

One of the vertical walls of the inner chamber may lie on one of the vertical walls of the outer chamber, the active speaker being mounted on that vertical wall of the inner chamber so that the front side of its diaphragm radiates into the outer space, while the rear side of the diaphragm of the active speaker radiates into the inner chamber.

In another embodiment of the invention, a part of the inner chamber is situated outside the outer chamber, the active speaker being mounted on that external part of the inner chamber so that the front side of its diaphragm radiates into the outer space, while the rear side of the diaphragm of the active speaker radiates towards the inner chamber.

In the case of a sub-woofer construction, one or several active speakers are mounted on a partition so that one side of the diaphragms of the active speakers is directed to the inner chamber, while the other side of the diaphragms of the active speakers is directed to a second inner chamber, whose bottom is shaped by a bottom partition, the latter being connected to the large passive diaphragm by means of a flexible joint. The bottom partition may coincide with the bottom of the outer chamber.

According to another embodiment of the loudspeaker system, the latter consists of an outer chamber and an inner chamber placed one inside the other and isolated one from the other in terms of acoustics by means of an intemal mechanical partition placed within them, the inner chamber comprising also the intemal space of the small passive diaphragm, whereat the small open end of the small passive diaphragm is mounted at the bottom of the inner chamber, while the large open end of the large diaphragm is mounted at the bottom of an outer chamber shaped as a loudspeaker enclosure, the passive diaphragms being connected to the chambers through flexible joints. The intemal mechanical partition situated intemally to the two passive diaphragms is connected to the chambers by means of stands.

In the case of using an internal partition placed inside the diaphragms it is possible also that one of the vertical walls of the outer chamber lies on one of the vertical walls of the outer chamber, the active speaker being mounted on that vertical wall of the inner chamber so that the front side of its diaphragm radiates into the outer space, while the rear side of the diaphragm of the active speaker radiates towards the inner chamber. In another embodiment of the invention, a part of the inner chamber is disposed outside the outer chamber, the active speaker being mounted on that extemal part of the inner chamber so that the front side of its diaphragm radiates into the outer space, while the rear side of the diaphragm of the active speaker radiates towards the inner chamber.

In the case of a sub-woofer construction, one or several active speakers are mounted on the bottom wall of the inner chamber so that one side of the diaphragms of the active speakers is directed to the inner chamber, while the other side of the diaphragms of the active speakers is directed to a second inner chamber, whose bottom is shaped by a bottom partition, the latter being connected to one of the two passive diaphragms by means of flexible joint. The bottom partition may coincide with the bottom of the outer chamber.

Description of the figures enclosed The invention is disclosed in the enclose figures. Figure 1 represents a loudspeaker construction according to a first embodiment of the invention, and Figure 2 is a construction according to a second embodiment of the invention. Figures 3 and 4 represent further two embodiments of the invention.

Embodiments of the invention Figure 1 illustrates the construction of a loudspeaker according to a first embodiment of the invention applied for. it consists of two passive coaxial diaphragms 1 and 2 fixed to each other and making a passive speaker. The diaphragms radiate in opposite directions and have different dimensions. A mechanical partition 3 isolates in terms of acoustics the space extemal to the diaphragm 1, shaped as an outer chamber 4, from the space external to the diaphragm 2, shaped as an inner chamber 5. The partition 3, further called extemal, is situated outside the passive diaphragms 1 and 2. The inner chamber 5 is placed within the outer chamber 4, the latter being formed external as a loudspeaker enclosure. One of the vertical walls of the inner chamber 5 may lie on one of the vertical walls of the outer chamber 4. The active speaker may be mounted on that vertical wall of the inner chamber 5.

According to another embodiment of the invention, the inner chamber 5 may cross one of the vertical walls of the outer chamber 4 and a part of the inner chamber 5 may stick out of the outer chamber. In this case, the active speaker is mounted on that protruding part of the inner chamber 5 and lies outside the outer chamber 4.

An active speaker/not shown in the figure/is situated in the chamber 5 together with the small diaphragm 2 so that the rear side of its diaphragm radiates towards the inner chamber 5, while the front side of its diaphragm radiates into the outer space. The two diaphragms 1 and 2 are mechanically connected at their junction point to the external partition 3 /Fig. 1/or to a bearing basket 12 by means of a flexible suspension 6.

Within the same region, inside the diaphragms there is placed an additional rigid partition/"plug"/, which isolates from each other the acoustic radiations, created by the two diaphragms 1 and 2. If the gap between the external partition 3 and the passive diaphragms 1 and 2 at their junction point is narrow, acoustic resistance is created therein which isolates the radiation of the small diaphragm 2 from the radiation of the large diaphragm 1. In the region of the outer openings 8 and 9 of the diaphragms 1 and 2 respectively, the latter are mechanically connected through flexible suspensions 10 and 11 to the walls of the chambers 4 and 5 or to the bearing basket 12.

Figure 2 illustrates the second embodiment of the loudspeaker system according to the invention. The diaphragms 13 and 14 have different dimensions, and they are disposed coaxially and are fixed to each other, thus making a passive speaker. They radiate in the same direction. The two diaphragms are constructively separated by a mechanical rigid partition 15, whose transverse cross-section has the same form as the inside cross-sections of the diaphragms 13 and 14 at their junction point. The internal mechanical partition 15 isolates in terms of acoustics a space, shaped as an inner chamber 16 and associated with the volume delimited by the inner surface of the small diaphragm 14, from the radiation of the diaphragm 13. The active speaker/not shown in the figure/is disposed within the chamber 16.

The extemal surfaces of the diaphragms 13 and 14, together with the walls of the inner chamber 16, shape a space closed as an outer chamber 17. The diaphragms 13 and 14 are isolated in terms of acoustics by the internal partition 15.

The inner chamber 16 is placed within the outer chamber 17, the latter being formed externally as a loudspeaker enclosure. One of the vertical walls of the inner chamber 16 may lie on one of the vertical watts of the outer chamber 17. The active speaker may be mounted on that vertical wall of the inner chamber 16. In another embodiment, the inner chamber 16 may cross one of the vertical walls of the outer chamber 17 and a part of the inner chamber 16 may stick out of the outer chamber. In such case, the active speaker is mounted on that external part of the inner chamber 16 and lies outside the outer chamber 17.

The mechanical internal partition 15 is fixed to the ends of bearing stands 18, which may represent rods or bars. The stands 18 may be situated within the small diaphragm, as shown with continuous lines, as well as within the large diaphragm, as illustrated with dotted lines. The stands may be connected to the inner chamber as well as to the outer chamber, or to the basket. The diaphragms 13 and 14 are connected through flexible suspensions 20,21 and 22 to the partition 15 and the chambers.

The diaphragms/usually cones/may be made in a known manner.

They may be conical, flat, or executed in some other familiar way. Each pair of the diaphragms 1 and 2, respectively 13 and 14, may be executed in terms of construction as an integral unit, forming one diaphragm.

The principe of low-frequency amplification used in the constructions according to Figs. 1 and 2 may by applied also in the construction of su-woofer devices, intended for the reproduction of frequencies below 100-150 Hz.

Figure 3 depicts a loudspeaker system used as a sub-woofer. It is made by perfecting the construction according to Fig. 1. The same reference numerals are used as those in Fig. 1. In this construction, the active speaker 27 is mounted on an external partition 3. It is possible to use more than one speaker mounted on that partition 3. The radiation 23 from the rear side of the diaphragm of the active speaker 27 is propagated in the inner chamber 5 and influences the small diaphragm of the passive speaker. The radiation 28 from the front side of the active speaker 27 is propagated in a second inner chamber 29 and influences the whole diaphragm 1 or only a part thereof. The second inner chamber 29 is formed between the external partition 3 and a bottom partition 30. When the radiation 28 influences a part of the diaphragm 1, the bottom partition 30 is connected through a flexible suspension 31 to the diaphragm 1.

Where the radiation 28 influences the whole diaphragm 1, the bottom partition 30 coincides with the bottom of the inner chamber 4. Due to the mounting of the active speaker on the external partition 3 and due also to the presence of the two inner chambers 5 and 29, the radiations from both sides of the diaphragm of the active speaker 27 get superposed on the passive diaphragm.

Still another sub-woofer construction may be made by perfecting the construction according to Fig. 2. Such an improved construction is shown in Fig. 4, where the reference numerals of the repeated parts are the same as those in Fig. 2. The intemal partition 32 lies on the smaller base of the small diaphragm 14 and shapes the bottom of the inner chamber 16. The active speaker 33/one or several/is mounted on the internal partition 32 so that one of its sides lies within the inner chamber 16. The radiation 25 from that side of the diaphragm of the active speaker 33 influences the inner surface of the small diaphragm 14, while the radiation 34 from the other side of the diaphragm of the active speaker 33 influences the rear surfaces of the diaphragms 13 and 14 or parts thereof, separated by means of the flexible suspension 35. In this case, the radiation from the active speaker is directed to the two inner chambers 16 and 36. The inner chambers 16 and 36 are situated within the outer chamber 17, the latter being separated from the second inner chamber 36 by means of the bottom partition 37. A flexible suspension 35 may also be mounted on the bottom partition 37.

Where the radiation 34 influences the whole diaphragm 13, the bottom partition coincides with the bottom of the outer chamber 17.

In the loudspeaker system according to Fig. 1, the radiation 23 from the rear side of the active speaker diaphragm creates acoustic pressure in chamber 5. That pressure causes displacement of the diaphragm 2 in the direction of the arrow 24. This makes the diaphragm 1 get displaced in the direction of the arrow 24 too. As a result of this, the radiation of the diaphragm 1 into the outer space is in step with the radiation from the front side of the active speaker diaphragm.

In the loudspeaker system according to Fig. 2, the radiation in the direction of the arrow 25 from the rear side of the active speaker diaphragm creates acoustic pressure in the chamber 16, which is in antiphase with the radiation from its front side directed to the outer space.

The acoustic pressure in the chamber 16 is perceived by the small diaphragm 14, the latter getting displaced in the direction of the arrow 26.

The diaphragm 13 fixed thereto gets displaced in the same direction 26.

The phase of radiation of the diaphragm 13 into the outer space coincides with that of the radiation from the front side of the active speaker diaphragm.

The resultant radiation from the active speaker diaphragm and the diaphragm 1, respectively 13, depends on the ratio between the areas of the radiating surfaces Sr, S2 and S3, where Sr, S2 and S3 are respectively the areas of the radiation surfaces of the active diaphragm, the small diaphragm and the large diaphragm.

The relative effectiveness of the passive speaker under ideal conditions/without rendering an account of the mechanical losses/is determined by the ratio Si. 83 == §3 S2 Si S2 and shows how many times the passive diaphragm radiation will exceed the active diaphragm radiation.

The passive speaker diaphragms cannot radiate vibrations above a certain frequency limit fo. Below that frequency, their efficiency increases along with the frequency lowering. That is why the loudspeaker system efficiency gets higher in the low frequencies domain.

The frequency limit fo depends on the volume of the chambers, on the mechanical flexibility of the diaphragms suspension, and on their full mechanical masses, the latter being determined by the mass of the respective mobile system together with the mass of the respective air volumes stirred thereby. The frequency fa may be altered by making changes in the constructions of the two chambers, e. g. by mounting inner sound absorbing lagging, adding phase inverters, additional passive diaphragms, or any other appliances for altering of the acoustic response.

The frequency fo may be influenced also by the use in the chamber of tunnels, baffles, labyrinths, transmission lines and many other structural units for their interior acoustic arrangement.

The loudspeaker system applied for allows to coordinate in terms of phase the radiation from the front side of the active speaker diaphragm and the efficient radiation from the passive diaphragm. In the domain of frequencies below the frequency limit fo, amplification occurs of the active diaphragm radiation. The amplification factor may easily be changed within a wide range by altering the dimensions of the two active speaker diaphragms connected therebetween.

According to the invention, the active speaker diaphragm may be manufactured so as to have a relatively small area, thus enabling it to determine small radiation distortions in the medium frequency domain.

The phase coincidence of the active and the passive diaphragms radiation results in precise reproduction of the sound from the loudspeaker system without any phase frequency distortions, thus making the sound natural.

The influence of the parasitic vibrations, the inertia vibration in particular, of the passive speaker diaphragm on the active speaker diaphragm is immaterial, for the area of the diaphragm 2, respectively 14, is small enough.

The principes of operation of the construction according to Fig. 3 are based on the fact that the influence of the radiation 23 from the rear side of the diaphragm of the active speaker 27 is added to the influence of the radiation 28 from the front side of that diaphragm. That summed influence is applied to the passive speaker, and it is much higher than the influence in the construction according to Fig. 1. That causes an increase of the power of radiation from the passive speaker. The radiation is utilised from both sides of the diaphragm of the active speaker.

The power of radiation from the passive speaker according to the construction in Fig. 4 is raised in the same way. Here, the influences are summed of the radiations 25 and 34 from the rear and the front sides respectively of the diaphragm of the active speaker 33. The summed influence on the passive speaker causes an increase of the power of the radiation thereof.