The invention relates to a loudspeaker device. Loudspeaker devices are known in many embodiments. It is generally known that the housing in which a woofer is arranged has a dominating influence on the fidelity of reproduction with which sound can be generated by the loudspeaker device.

It is an object of the invention to embody a loudspeaker device such that a quality of reproduction can be realized which meets the highest possible required standards.

In order to realize this objective the invention provides a loudspeaker device, comprising: a generally tubular housing having a cavity which is closed at a first end and open at a second end; and at least one woofer placed in an opening in the wall of this housing; which cavity comprises seven rotation- symmetrical mutually connecting spaces, which spaces have substantially the same shape and a common axis of symmetry; which spaces have corresponding linear dimensions from the first to the second end with substantially the following respective ratios: (1) 0.53

(2) 0.80

(3) 1.00

(4) 0.89

(5) 0.75 (6) 0.67

(7) 0.60; which spaces have smooth rounded shapes, are mutually connected via necks with smooth rounded shapes

and are at least substantially mutually tangential with imaginary basic contour surfaces; wherein a neck widening toward the outside connects onto the space adjacent to the second end. A specific embodiment has the special feature that each space has a generally spherical shape.

An alternative has the special feature that each space has the shape of a semi-ellipsoid of revolution directed toward the first end and a semi- spherical shape directed toward the second end, wherein the relative axial lengths of said two shapes are substantially in a ratio of 9:7.

A preferred embodiment is herein characterized in that the necks have diameters which are 0.5 to 0.8 times the largest diameter of the adjacent spaces.

An embodiment wherein the housing consists predominantly of concrete has the advantage that the housing has a great density and a correspondingly large mass and that there is no danger of unintended co- vibration of the housing.

It can nevertheless be advantageous to make use of an embodiment in which the cavity is lined with a layer consisting of a mixture of bitumen and rubber. In this manner damping is also obtained for very high frequencies. An embodiment is generally recommended in which the layer has a thickness of 1-6 mm.

A preferred embodiment has the special feature that the woofer is arranged in a hole in the wall of the third space. Other than most known devices, the loudspeaker device according to the invention requires no internal damping. The invention nevertheless also provides a variant in which the first and the second spaces are filled with porous damping material, such as mineral wool.

This variant is preferably characterized in that about ten times as much damping material is present in the first space as in the second space.

In order to also provide the loudspeaker device according to the invention with the advantages of a transmission line, the embodiment can serve in which the length of the cavity corresponds with the resonance frequency of the built-in woofer.

A very fine directivity pattern of substantially monopole character is obtained with an embodiment comprising two symmetrically placed woofers facing away from each other. Another embodiment is provided with a tweeter, for instance a dome tweeter, placed in the vicinity of the woofer.

It will be apparent that to each woofer an associated tweeter is preferably added. The use of radiation in two directions has the known advantage that a very attractive, spatial sound picture can be realized.

A specific embodiment has the special feature that the woofer and the tweeter are in phase linear arrangement. Such an embodiment is very simple to realize with a variant in which the woofer connects to the third space and the tweeter is situated in the region of the second space.

The invention will now be elucidated with reference to the annexed drawings. Herein:

Figure 1 shows a cross section through a loudspeaker device according to the invention in a first embodiment;

Figure 2 shows a perspective view of the device of figure 1;

Figure 3 shows a partial cross section, corresponding with figure 1, of a variant;

Figure 4 shows a cross section through yet another embodiment; Figure 5 shows a connection diagram for the loudspeakers; and

Figure 6 shows an alternative connection diagram for the loudspeakers.

Figure 1 shows a loudspeaker device 1. This comprises a generally tubular concrete housing 2 with a cavity 3 which is closed at the upper end and open at the lower end, in addition to two woofers 4, 5 placed in openings in the wall of this housing.

The cavity 3 comprises seven rotation- symmetrical, mutually connecting, substantially spherical spaces 6, 7, 8, 9, 10, 11, 12 respectively. These spaces 6-12 have a common axis of symmetry which corresponds with the longitudinal axis of cavity 3. The spaces 6-12 have diameters with substantially the following respective ratios: 0.53 - 0.80 - 1.00 - 0.89 - 0.75 - 0.67 - 0.60. As shown in figure 1, adjacent spaces mutually connect via necks, respectively 13, 14, 15, 16, 17, 18 with smooth rounded shapes. The space 12 debouches into the outside space via a neck 19 with a shape widening toward the outside.

The cavity 3 is lined with a layer 20 consisting of bitumen mixed with rubber granules. Damping material is arranged in the spaces 6 and 7. The quantity of damping material in space 6 amounts to about ten times the quantity in space 7. The damping material can for instance be natural or mineral wool.

As shown in figure 2, the internal form of the device 1 is also reflected in the external design. The spaces 6-12 are enclosed by a wall having approximately the same thickness everywhere. Thus created is the form shown in figure 2, which has the general appearance of a column consisting of spheres stacked one on top of anoth- er.

The loudspeakers 4 and 5 are directed away from each other and are connected in phase, so that loudspeaker device 1 has a substantially monopole character, at least up to a frequency determined by the dimensions of the loudspeakers. The woofers 4, 5 are arranged in the region of the space 8. Placed in the region of the space 7 above the loudspeakers 4, 5 are tweeters respectively 21, 22. This placing is embodied

such that the arrangement is phase linear relative to the woofers 4, 5. It must be understood in this respect that it may be desirable to give the radiation front of the loudspeaker a certain incline. The housing 2 further comprises a foot flange

21 which can rest by means of legs 22 on the floor or on a board. It will be apparent that this also ensures that sound radiated via cavity 3 and neck 19 can reach the outside space. Also ensured in this manner is that the loudspeaker device 1 is of the so-called "open* ¹ type, which is desirable for reasons of quality.

Figure 4 shows a variant wherein a loudspeaker device 23 has a housing 24 which on the outside does not follow the internal contours but has a more or less flat outer form. The drawback of this embodiment is that it is comparatively heavy. The properties of such a device 23 are otherwise in principle the same as those according to figures 1 and 2. The housing 24 can also have a rotation- symmetrical outer appearance. Attention is drawn to the fact that the basic shapes of the spaces 6-12 are imaginary spheres which substantially mutually tangential in the region of said necks 13-18.

The necks have diameters which are 0.5 - 0.8 times the largest diameter of the adjacent spaces.

Figure 3 shows a variant 25 wherein a housing 26 is embodied such that the spaces 27, 28 do not have a spherical shape but each have a general egg shape. The relevant contours are drawn schematically in full lines in figure 3. In accordance with the teaching of the invention each of the spaces 27, 28 is rotation- symmetrical. Each space has the shape of a semi-ellipsoid of revolution directed toward the closed end and a semi- spherical shape directed toward the open end. The axial lengths of said two shapes are substantially in a ratio of 9:7.

Figures 5 and 6 show possible connection diagrams for the loudspeakers.

In order to prevent phase effects and to embody a cross-over filter as simply as possible, use is made according to the invention of a direct connection of the woofers 4, 5. The loudspeakers 4, 5 are of the type which have a natural attenuation for the higher frequencies, for instance because the cone is covered with a neoprene rubber layer. The dome tweeters 21, 22 take over the sound-radiating function from the natural cross-over frequency of the woofers. The relevant take-over frequen- cy is determined by the impedance of loudspeakers 21, 22 and a series capacitor 29.

The difference between the wiring diagrams according to figures 5 and 6 lies in the fact that in figure 5 the woofers respectively the tweeters are connected in series, while according to figure 6 these loudspeakers are connected in parallel. It will be apparent that this will affect the terminal impedance and the value of capacitor 29. It is not however necessary to discuss this further within the scope of the invention as this relates to generally known techniques.

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