FIELD OF THE INVENTION

The present invention generally refers to an acoustic box equipped with at least one sound transducer for low frequencies reproduction. More specifically, the present invention refers to an acoustic box equipped with at least one sound transducer, said acoustic box having a reduced size, particularly a reduced width, in comparison prior art with acoustic boxes without however impairing the efficiency or quality of the sound reproduced. BACKGROUND OF THE INVENTION

Electro-acoustic transducers assembled in acoustic boxes or sub- woofers are common assemblies of the state of the art. These assemblies have the purpose of reproduction of low frequencies, particularly frequencies of about 200 Hz or lower. The frequency response of the acoustic box typically follows the relation of the resultant of the parameters known as Small and Thiele, particularly regarding the resonance frequency (Fo), cavity volume, quality factor of the entire system (Qts), and the equivalent air volume (Vas).

Prior art reveals several types of constructions for sub-woofers that use one or more transducers assembled in acoustic boxes, such as, for example, US patents 6,801 ,633; 5,771 ,302; 5,475,764; 5,147,986; and 4,903,300. These documents reveal acoustic boxes that use one or more transducer assembled directly inside the acoustic box. Said one or more transducers can be completely assembled inside the acoustic box, forming a second compartment usually sealed, or then assembled with the magnet assembly inside the acoustic box and the diaphragm facing outwards the acoustic box and closing-cut to a wall of said acoustic box.

However, all the sub-woofers found in prior art, those using transducers completely assembled inside the acoustic box as well as those

using transducers assembled with the magnet inside the acoustic box, necessarily imply that the transducer should be completely covered by the acoustic box, i.e. there is a limitation in the shape of the acoustic box with consequent increase in its size and volume. Currently, there is an increasing tendency to reduce the size, particularly the thickness, of sound and video equipments, such as, for example, the advent of plasma televisions and liquid crystal monitors. Consumers are increasingly appreciating such sound and video equipments of reduced size and thickness, since they occupy less space in the environment, giving a modern look and technology status, and providing greater comfort and the possibility of adaptation of said equipments in a room.

Thus, it is one object of the present invention to provide an acoustic box equipped with at least one sound transducer that promotes a significant reduction in the volume and size of the acoustic box, particularly its dimension extending along the longitudinal axis of the transducer.

Still another object of the present invention is to provide an acoustic box equipped with at least one acoustic transducer that promotes a reduction in the volume and size of the acoustic box without, however, impairing the quality of the reproduced sound. DESCRIPTION OF THE INVENTION

The abovementioned objects, among others, are accomplished with the present invention, which comprises an acoustic box equipped with at least one electro-acoustic transducer wherein said transducer is assembled in one of the walls of said acoustic box in a median position taken along the longitudinal axis of the transducer in relation to said wall on which it is assembled, being that the diaphragm of said transducer faces the inner side of said acoustic box, and faces the opposite wall in relation to which it is assembled.

Particularly, without limitation to any other embodiment, the

transducer is assembled on any of the side, front or rear walls of the acoustic box. Still according to the present invention, the transducer, instead of being completely assembled inside the acoustic box or with the magnet assembly facing the inner part of the acoustic box, it is assembled on one wall of the acoustic box in a median position taken along the longitudinal axis of the transducer. Therefore, the transducer does not have to be inside the acoustic box, thus enabling the reduction of the volume and size of the acoustic box, particularly its width.

The transducer diaphragm should face the inner part of the acoustic box, such that said diaphragm faces an opposite wall. This characteristic reduces and dampens the reproduction of relative high range of frequencies, i.e. frequencies of above about 200 Hz, and on the other hand emphasizes the reproduction of low frequencies, i.e. frequencies of below about 200 Hz. Said median position should be understood as the one that follows the relation between (1 ) the distance of the diaphragm and said opposite wall; and (2) the inner width of the acoustic box. This is of about 0.2 to about 0.6; particularly between about 0.3 and about 0.5; more particularly about 0.4. Furthermore, the ratio between (1 ) the area (Si) of the virtual wall formed around the diaphragm, between the diaphragm and the opposite wall of the acoustic box along the longitudinal axis of the transducer, and (2) the effective area (S ₂ ) of the diaphragm shall be greater than or equal to one, i.e. (SySgJ ≥ L The effective area of the diaphragm must also be understood as that comprising the area of the diaphragm plus 1/3 of the area of the transducer's edge.

Naturally, the acoustic box may comprise more than one transducer. The number of transducers used is not relevant to the scope of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be described herein with relation to a particular embodiment represented in attached figures, included in this specification for illustrative purposes only. Such figures are schematic, and their dimensions and/or proportions may not correspond to the reality since they illustrate the present invention didactically, without imposing any limitations other than those contained in the attached claims, being that:

- Figure 1 is an isometric perspective view of the acoustic box according to an embodiment of the present invention; - Figure 2 is a front cross-section view of the acoustic box according to an embodiment of the present invention; and

- Figure 3 is a side cross-section view of the detail of figure 2, showing the transducer assembled in the acoustic box, according to an embodiment of the present invention. DESCRIPTION OF A PARTICULAR EMBODIMENT

Figures 1 , 2 and 3 show an acoustic box (10) equipped with a transducer (21) according to a particular embodiment of the present invention. The acoustic box has substantially the shape of a parallelepiped, and comprises two side walls (11 , 16), a front wall (12), a rear wall (13), an upper wall (15) and a lower wall (14). Obviously, the denomination used herein for the acoustic box (10) walls is for didactic purposes, to better describe the present invention.

The walls are fixed to each other by appropriate means, such as adhesives, pins, pegs, screws etc. The acoustic box walls may be made of adequate material, such as wood, fiberglass, carbon fiber, thermoplastic material, metal etc, and the thickness must be adequate or duly structured to prevent excess vibration when the transducer (21 ) is operating. The dimensions and proportions of the walls (11 , 12, 13, 14, 15, and 16) may also vary according to the total volume of the acoustic box.

The acoustic box additionally comprises an opening (20) in one of its walls (11) and, in its inner part, another wall (19) substantially surrounds said opening (20).

Inside the wall (19), a sound transducer (21) is fixed in a median position taken along the longitudinal axis (X) of the transducer in relation to the wall (11) on which it is assembled, in such a way that the magnet assembly (23) of said transducer faces the outer part of said acoustic box, and the diaphragm

(22) faces the inner part of the acoustic box (10), facing the opposite wall (16).

That enables a substantial reduction of the total volume of the acoustic box (10), particularly a reduction of its width (L). This is achieved because the transducer (21 ) is not completely assembled inside the acoustic box; much less does the magnet assembly face the inner portion of the acoustic box (10). Prior art solutions imply that the total volume of the acoustic box should also comprise the transducer volume. As previously mentioned, the proportions and dimensions of the acoustic box walls (11 , 12, 13, 14, 15, 16) may vary according to the volume of said acoustic box. For example, if the area of the side walls (11 , 16) increases, the area of the front (12), rear (13), lower (14) and upper (15) walls may decrease. Correspondingly, if the area of the front (12), rear (13), lower (14), and upper (15) walls increases, the area of the sidewalls (11 , 16) may equally decrease.

Therefore, the alternative between the proportions of the acoustic box (10) walls must be such that the transducer (21 ) is fixed at a median position in relation to the wall (11) on which it is assembled, this median position being taken along the longitudinal axis (X) of the transducer. The median position shall follows a relation between the distance (d) of the transducer (21) diaphragm (22) and the opposite wall (16), and the inner width (e) of the acoustic box (10). A ratio (d/e) of about 0.4 is particularly adequate.

Furthermore, the ratio between the virtual wall formed around the diaphragm (Si), between the diaphragm (22) and the opposite wall (16), and the effective area (S2) of the diaphragm (22) should be greater than or equal to 1 , i.e. (SyS ₂ ) > 1 . The ratios (d/e) and (S1/S2) are adequate for a good airflow generated by the diaphragm's displacement, in such a way that such airflow minimizes turbulences or noises in the acoustic box (10), contributing toward the transducer's sound quality. For example, if the inner width (e) of the acoustic box (10) is approximately 60 mm, the distance (d) between the diaphragm (22) and the opposite wall (16) should be of approximately 24 mm, for a diaphragm area of 66.48 cm ² , of a transducer having an effective diameter of 92 mm.

The transducer (21 ) used may be a conventional one for home applications. Depending on its size, the magnet assembly (23) may be close-cut to or inwards the sidewall (11 ) on which said transducer is assembled (21). On the other hand, the magnet assembly (23), if larger, may also be outwards said side wall (1 1 ), according to the embodiment shown in the figures. However, regardless the size of the magnet assembly used, according to the present invention, size reduction of the acoustic box is maintained, particularly of its width (L). Furthermore, since the magnet assembly (23) faces the outer part of the acoustic box (10), a secondary channel is also formed by the borders of the magnet assembly (23), the wall (19) and the opening (20). This secondary channel allows exit of sound waves produced by the rear part of the transducer (21 ), aiding in sound response. The acoustic box additionally comprises a channel (18) for air escape that working with the larger cavity helps for a good response of low frequencies, following the Small and ThIeIe parameters, as mentioned above. According to the embodiment shown herein, said channel is located on the front

wall (12) of the box (10). However, the location, length, and diameter of the channel is not relevant to the scope of the present invention, only requiring that the channel is adequate for a good response in low frequencies.

The present invention has been described in relation to a particular embodiment. Those skilled in the art may develop a wide variation of structural details without, however, deviating from the principles of the present invention. Therefore, the attached claims shall be interpreted as covering all equivalents that fit into the scope and character of the present invention.