AN ISOBARIC SOUND EMITTING SYSTEM

The present invention relates to a sound emitting system, comprising a first housing part with a first sound emitting device having a first central sound emitting axis. Loudspeakers generally comprise a housing and devices for emitting sound waves. In addition to these wanted primary sound waves, an undesired side effect arises from the connection between the sound emitters and the housing of a loudspeaker as mechanical vibrations spread to the housing of the loudspeaker and contribute to the generation of secondary, unwanted, sound waves, deteriorating the sound quality when mixed with the main sound waves.

Known prior art discloses different embodiments of loudspeakers. A well known embodiment comprises bass, midrange and tweeter elements arranged with their front portions in the loudspeaker front plane. This configura- tion is commonly referred to as a 3-way loudspeaker. Another known embodiment comprises only a bass element and a tweeter element arranged with their front portions in the loudspeaker front plane. This configuration is commonly referred to as a 2-way loudspeaker. One disadvantage of these common solutions is that the vibrations generated by the moving parts of the system cause vibrations in the loudspeaker cabinet as a whole and especially in the loudspeaker front board. The above mentioned vibrations distort the sound emitted by the system as a whole.

Further on, strong vibrations from the sound emitting system propagate through the cabinet structure to the floor, creating secondary noise emitting sources there. These secondary sources can seriously affect the quality of the reproduced sound.

Furthermore, due to the inherent properties of the bass unit, a relatively large bass element volume box is required. One way to address this problem is to introduce two bass elements arranged in isobaric configuration, lsobaric configuration is described in US5701358B. In isobaric configuration, two bass elements are mounted in pair, in an air-tight room of constant pressure. The

trapped air acts like a stiff connection between the bass elements. A system arranged in this way can produce the same frequency response in half the box volume compared to what a single bass unit of the same type would require. In this way, the size of the bass unit box volume may be reduced by a half. However, the isobaric configuration does not address the other problems described above.

One way of improving the sound quality by dealing with unwanted secondary sound waves is to provide an active solution involving components, such as for instance electronic devices. Such solutions are however ac- quainted with problems, such as complexity and introduction of new side effects.

Hence, a problem with current sound generating systems is the generation and spread of unwanted sound waves arising from mechanical vibrations in the housing. The object of the present invention is to provide a sound emitting system with improved sound emitting properties. To achieve this, the sound emitting system further comprises a second housing part with a second sound emitting device having a second central sound emitting axis, the first and the second sound emitting axes being substantially coincident, and a connecting part that connects the first and second housing parts, the connecting part being adapted to at least partially counteract generation of undesired mechanical vibrations in the first and second housing parts and the sound emitting system being adapted to distribute substantially the same electrical signal to the first and second sound emitting devices. Hence, as an advantage, im- proved control and reduction of the generation and spread of unwanted sound waves arising from mechanical vibrations in the housing is achieved. Hence, simultaneous mechanical vibrations of the two housings may cancel each other out, whereby a reduction of the mechanical vibrations of the entire sound emitting system is achieved. The reduction of mechanical vibrations will have a direct positive impact on the quality of the emitted sound. In more detail, it is achieved by coupling the sound emitting devices to generate essentially identical sound waves, such as by feeding the same signal to the devices, and by connecting the devices mechanically rigidly, unwanted vibra-

tions to the housing are cancelled out, partially due to balancing of forces arising from the sound emitting devices and acting on the housings. As an advantage with this passive solution, there is no need for active cancellation of unwanted secondary sound waves. Advantageously, the cut-off frequen- cies for the respective sound emitting devices are essentially the same, ensuring reduction of unwanted mechanical vibration production over essentially the entire range of frequencies generated by the sound emitting devices. In an embodiment, at least one of the sound emitting devices comprises two sound emitting elements arranged in isobaric configuration. In this way, non- linearities in the movement of the moving parts of the sound emitting elements are reduced since movement errors for sound reproduction in an isobaric pair normally are of opposite direction, the two sound emitting elements correct each other.

In another embodiment, the distance between the first and the second housing parts is smaller than 1/3, preferably smaller than 1/4, and more preferred smaller than 1/5, of the length of the sound wave corresponding to the maximum frequency value in the sound signal that may be emitted by the first and the second sound emitting devices. In this way, generation of unwanted resonance frequencies may be reduced, thus avoiding the risk of degrading the sound quality. Hereby, an advantageous balance between size and sound quality is achieved.

In an embodiment, the distance between the central planes of the first and the second sound emitting devices arranged in isobaric, face-to-face configuration, is smaller than 20 cm, preferably smaller than 15 cm, and more preferred smaller than 10 cm and a cross-over frequency of the first and second sound emitting devices is between 250 and 350 Hz. Hereby, an advantageous balance between size and sound quality is achieved.

In a particular embodiment, the connecting part comprises at least one substantially mechanically rigid element, such as a rod or a tube, extending between the first and second housing parts. The rigid connection contributes to at least partially counteract generation of undesired mechanical vibrations in the housings. Preferably, the rigid element, when placed in the sound ra-

diation direction, is rod-shaped or tube-shaped and relatively thin, thus exerting a minimal influence on the propagating emitted sound waves.

In an embodiment, at least one sound wave directing element is provided in the area between the first and second housing parts. Thereby, as an advantage, better control of the direction, including off-axis characteristics, of the emitted sound may be achieved.

In a structurally advantageous embodiment, the connecting part may comprise a robust framework structure, such as to form a wall or barrier, partially surrounding the space between the first and second sound emitting de- vices. In this way, the emitted sound waves may be guided in the desired direction.

In a further embodiment, the wall may comprise an inner and an outer surface and the inner surface may be arc- or curve-like in its shape, such as defining a partial circle, and the outer surface may resemble the housing of the first and second parts to create a continuous wholeness appearance.

In yet another embodiment, the sound wave directing element may advantageously be formed by substantially rigid material, and it may preferably be arranged to block sound travelling in a backward direction, that is being different from the preferred sound emitting direction. It is thus prevented for the sound waves to travel behind any of the housing parts and return to the front with a time-delay, thereby preventing the occurrence of a comb-filter effect. Furthermore, the sound wave directing element allows for appropriate amount of sound waves to propagate laterally. As a further advantage, improved structural stability of the sound wave directing element is achieved. In an advantageous embodiment, the sound wave directing element is a part of the connecting part, preferably constituting the connecting part, having the combined effect of connecting the housing parts and directing sound emitted from the first and second sound emitting devices.

Preferably, the sound wave directing element comprises a sound ab- sorbing material, such as mineral wool. Thereby, better control of the quality of the emitted sound may be achieved and unwanted reflections in the sound wave directing element are avoided. Typical sound absorbing, or damping materials are natural wool, synthetic. wool, rock wool, glass wool, damping

foam with appropriate cell structure or any other material suited for sound wave absorption in the sound emitting system. As an additional advantage, the off-axis response of the sound emitting system may be even more closely regulated. In a particular embodiment, the sound absorbing material at least partially fills the space between the first and second sound emitting devices. In this way, unwanted resonance frequencies may be reduced.

In a structurally advantageous embodiment, the first housing part, the connecting part and the second housing part are comprised by one enclo- sure. In this way, an improved, simpler form of design of the sound system is achieved.

In a further embodiment, at least one of the housing parts comprises at least one supplementary sound emitting device, and wherein a central sound emitting axis of the supplementary sound emitting device is essentially per- pendicular to the common substantially central sound emitting axis of the first and second sound emitting devices. Hence, by arranging the sound emitting devices perpendicular in respect to each other, mechanical vibrations from the first and second sound emitting devices are not generated and transmitted in the same plane as the sound emitted from the supplementary sound devices. The movement caused by mechanical vibrations is thus in a plane different from that of the supplementary sound emitting devices, and hence, instead of moving the supplementary sound emitting devices in the direction of the emitted sound, the movement induced by the mechanical vibrations are acting on the supplementary sound emitting devices perpendicularly to the sound emitting direction. In addition, in a situation where the first and second sound emitting devices are arranged to emit sound waves in a direction coincidental with the direction of field of gravity, the mechanical vibrations are reduced more efficiently due to the inertia of the housing and entire sound emitting system. Hence, instead of causing a tilting or rocking motion of the sound emitting system arranged on a horizontal surface, the mechanical vibrations are restricted to move the arrangement vertically, perpendicular to the direction of emitted sound waves. For instance, in the case where the first and second sound emitting devices comprise bass units and the supplementary

sound emitting devices comprise tweeter and midrange units. Furthermore, the vibrations induced by the sound emitting devices do not impact on the sound waves emitted by the supplementary sound emitting device and hence, interference between the sound emitting devices and the supplementary sound emitting device may be avoided. _.

Preferably, the supplementary sound emitting device or devices are configured to emit sound waves having frequencies essentially higher than that of the first and second sound emitting devices.

Advantageously, the first and second sound emitting devices are lar- ger, heavier and more powerful than the supplementary sound emitting devices.

In another embodiment, the sound emitting system comprises a plurality of arrangements wherein each arrangement comprises a first housing part, a connecting part and a second housing part. Hence, with a plurality of ar- rangements of sound emitting devices, the generation of sound waves is divided and the load distributed between these. As an advantage, the system can administer a greater load. In addition, due to mounting deviations and inherent irregularities in sound emitting devices, an increased number of arrangements enable improved overall-linearity. In an embodiment, four sound emitting devices are arranged symmetrically diagonal to each other, preferably slightly tilted towards each other, having a collective central sound emitting axis essentially perpendicular to a sound emitting axis of supplementary sound emitting device or devices in connection with the same housing. Other objects, features and advantages of the present invention will appear from the following detailed disclosure, from the attached dependent claims as well as from the drawings.

Generally, all terms used in the claims are to be interpreted according to their ordinary meaning in the technical field, unless explicitly defined other- wise herein. All references to "a/an/the [element, device, component, means, step, etc]" are to be interpreted openly as referring to at least one instance of said element, device, component, means, step, etc., unless explicitly stated otherwise.

The above, as well as additional objects, features and advantages of the present invention, will be better understood through the following illustrative and non-limiting detailed description of preferred embodiments of the present invention, with reference to the appended drawings, where the same reference numerals will be used for similar elements, wherein:

Fig. 1 is a front view of a sound ^' emitting system according to the present invention;

Fig. 2 is a cross-sectional side view along the line I - I of Fig .1 of one embodiment according to the invention; Fig. 3 is a cross-sectional side view along the line I - I of Fig .1 of another embodiment according to the invention;

Fig. 4 is a cross-sectional side view of another embodiment of the sound emitting system according to the present invention;

Fig. 5 is a cross sectional top view along the line Il - Il of Fig. 1 of an embodiment according to the invention;

Fig. 6 is a cross sectional top view along the line Il - Il of Fig. 1 of yet another embodiment according to the invention;

Fig. 7 is a close-up side view of a section of Fig. 3;

Fig. 8 is a schematical cross sectional front view of a quadruple system according to one embodiment of the present invention;

Fig. 9 is a cross-sectional side view of yet another embodiment of the sound emitting system according to the present invention.

Figure 1 shows a front view of a sound emitting system 101 according to one embodiment of the present invention. It shows a 3-way loudspeaker comprising two housings, a first 102 and a second 103, mounted on top of each other and configured preferably for vertical positioning, with the first housing 102 on top. The housings 102 and 103 have side walls 104, 105 and front walls 106 and 107. The first and second housings 102, 103 are separated by a connecting part 108 having side walls 109, 110 and a back wall 111. At the bottom 112 of the first housing 102 and the top 113 of the second housing 103 are a first and a second sound emitting device (not shown). Additionally, the first housing 102 is seen with first 114 , second 115 and third 116 supplementary sound emitting devices mounted vertically in respect of

each other. In this 3-way configuration, the first 1 14 and third 116 sound emitting devices are midrange elements, and the second sound emitting device 115 is a tweeter. Other configurations of sound emitting devices are possible. Dashed lines indicate vertical (I - I) 117 and horizontal (Il - II) 118 cross sec- tions.

Figure 2 shows a cross sectional side view of one embodiment of a sound emitting system 201 as depicted in figure 1. It shows a first 202 and a second 203 housing, front walls 204, 205, back walls 206, 207, a connecting part 208 having a back wall 209, a first and second sound emitting device 210, 211 , a first 212, a second 213 and a third 214 supplementary sound emitting device. Dashed lines indicate the direction 215 of the substantially coincident first and second sound emitting axes of sound emitting devices 210, 21 1 and the direction 216 of the central sound emitting axis of the supplementary sound emitting device 212. It is seen that the sound emission di- rections are essentially perpendicular. It is furthermore seen that the first housing 202 encloses a first volume 217, the second housing 203 a second volume 218. In addition, internal structures 219, 220 together with the first housing 202 encloses a third 221 and a fourth 222 volume respectively. Each of the first 210 and second 21 1 sound emitting devices are shown to com- prise a first 223, 224 and a second 225) 226 sound emitting element, here arranged in an isobaric face-to-face configurations. The enclosures may furthermore comprise additional internal structures for stiffening and other components for various purposes, such as electrical wiring and connections, although not shown for simplicity. Also shown are rods 227 and 228 providing a rigid connection between the first 202 and second 203 housings, and supporting the weight of housing 203.

Figure 3 shows a cross sectional side view of an embodiment of a sound emitting system 301 as depicted in figure 1 and similar to that depicted in figure 2. The system 301 differs, however, from figure 2 in that the first 302 and second 303 sound emitting devices comprise a first 304, 305 and a second 306, 307 sound emitting element, arranged in isobaric back-to-back configuration.

Figure 4 shows a cross-sectional side view of a sound emitting system

401 according to another embodiment of the present invention. The system 401 comprises a single housing 402 enclosing a first 403 and a second 404 volume being separated by an internal plane 405. The system further com- prises front 406, back 407, top 408, and bottom 409 walls, first 410 and second 411 sound emitting devices, and first 412 and second 413 supplementary sound emitting devices mounted in the front wall 406. Each of the first 410 and second 411 sound emitting devices are shown to comprise a first 414 and a second 415 sound emitting element, here arranged in an isobaric face- to-face configuration. The isobaric sound emitting elements 414, 415 are mounted to the housing 402, which together with an adjacent vertical wall 416 defines a cavity 417 having an opening 418 through the front wall 406 to allow sound generated from the first 410 and second 411 sound emitting devices to be directed away from the housing 402 in a direction of a listener (not shown). The centre part of the housing 402, comprising the internal plane 405, the vertical wall 416, and housing parts 419, 420 in which the first 410 and second 411 sound emitting devices are mounted, together define a connecting part 421 between the first 403 and second 404 volumes.

Figure 5 shows a cross sectional top view along the line Il - Il of figure 1 of one embodiment of a connecting part 501 according to the present invention. It shows a front wall 502, side walls 503, 504, and a back wall 505 of the second housing, and a sound emitting devices 506 arranged in the top of said housing. Connecting means 507, such as rods or tubes, and a sound wave directing element 508 are also indicated. The connecting means 507 rigidly connects the first and second housings, and the sound wave directing element 508 blocks, or absorbs sound waves emitted in its direction, such as to improve the control and increase the directivity of emitted sound.

Figure 6 shows a cross sectional top view along the line Il - Il of figure 1 of another embodiment of a connecting part 601 according to the present invention. It shows a front wall 602, side walls 603, 604, and a back wall 605 of the second housing, and a sound emitting devices 606 arranged in the top of said housing. The connecting part comprises a U-shaped wall 607 surrounding essentially three of the four sides. The wall 607 also acts as a sound

directing element, in that sound is allowed to pass through the opening in the front wall 602. A sound absorbing member 608 is also shown.

Figure 7 is a close-up side view 700 of a section of figure 3. It shows the first 701 and second 702 housings and connecting part 703. It further shows the first 704 and second 705 sound emitting devices comprising a first 706 and a second 707 sound emitting element, arranged in isobaric back-to- back configuration. The sound emitting elements 706, 707 are connected to each other and each of the housings 701, 702 via internal structures 708, 709 of the respective housings. The internal structures 708, 709 each enclose a volume 710, 71 1 , such as to avoid short-circuiting the sound generated by the respective sound emitting elements 706, 707. Dashed lines indicate a first 712, direction of motion of the sound emitting devices, and a second 713 direction of the resulting sound output generated by the sound emitting devices 704, 705. Figure 8 shows schematically a cross sectional front view of a quadruple system 801 according to one embodiment of the present invention comprising four arrangements of isobaric sound emitting devices 802, 803, 804,

805 arranged symmetrically in respect of each other. Also depicted are a first

806 and a second 807 housing part, a connecting part 808, and internal walls 809, 810.

Figure 9 shows a more basic variation of the configuration of a sound emitting system 901 as shown in figure 4, wherein each sound emitting device comprises only one sound emitting element and the first 902 sound emitting element is arranged in a lower wall 903 of the upper part of the first vol- ume 904 and the second 905 sound emitting element is arranged in an upper wall 906 of the lower volume 907. Further indicated is a sound wave guiding element 908. Also indicated is a supplementary sound emitting device 909.