GB2176370A - Loudspeaker, preferably sound column or horn loudspeaker - Google Patents

Abstract

The box of the loudspeaker consists of one or more parts which form a cavity or a horn and are made of at least two layers. Both layers are of the same synthetic two-component foam material. The inner layer (2) is softer, more elastic, the outer layer (1) is harder and stiffer. The two layers are produced in one single phase of work: after having cast the first layer, prior to complete hardening the second layer is cast directly on the first. The factor of sound absorption of the inner layer is at least 0.6, while the factor of absorption of the outer layer is 0.2 at most. The cavity is either closed or it is provided with openings leading to the atmosphere. The openings are either uncovered or they are covered with a material serving as acoustic impedance. Drivers (7), transformers (8) are fixed by means of the undercut lugs (5) formed in the inner layer (2). <IMAGE>

Description

SPECIFICATION Loudspeaker, preferably sound column or horn loudspeaker The invention relates to a loudspeaker, preferably sound column or horn loudspeaker with an enclosure box formed at least parly of two layers and both layers are formed of a synthetic foam of the same basic material so that the inner layer is softer and more elastic, while the outer layer is harder and stiffer.

It is a well known fact that beside the driver, the enclosure of the loudspeaker forms the most important part of the loudspeaker. So the design of the box is not at all indifferent, it defines fundamentally circumstances of sound emission and function of the loudspeaker. Under design not only the shape of the box, the openings thereon or other acoustic elements are meant, but the stiffness of the box wall, sound absorbing and sound reflecting abilities are also to be considered. With known equipments, due to the multipurpose function the box is made mostly of wood. From the point of view of internal attenuation of the enclosure wood does not meet the requirements, accordingly, an absorbing layer of a sound absorbing material, so e.g. cotton-wool, rockwool or glasswool used to be fixed onto the inner surface.Due to its internal attenuation vibration properties of wood are most advantageous. It has been a well-proved material in producing musical instruments, so it became the basic material for transducers. Wood can be processed relatively easily, however, it cannot be used expediently outdoors due to climatic influences.

As a consequence, outdoor i.e. the boxes of sound columns are made mostly of metal, sometimes of a synthetic material. In this case internal sound absorption is of utmost importance. Due to the undamped vibrations of the sheets special formation and materials are required for loudspeaker of high level. Due to climatic influences and multifold requirements selection of proper materials does not represent a simple task.

The aim of the invention is to solve the above problems in the most economical and simple manner, simultaneously to facilitate production and to meet complex acoustic and mechanical requirements on a high level.

The invention is based on the recognition that the task set usually has been solved by using a diversity of materials involving different technologies and processes and a plurality ofworking phases. In accordance with the invention a solution is at disposal, with which by using one single material and one work process the box of the loudspeaker can be formed, simultaneously meeting all the requirements.

Accordingly, the invention relates to a loudspeaker, preferably sound column or horn loudspeaker, having a box (enclosure) for the desired improvement of transmission characteristics; the box consists of one or more parts and one or more drivers are arranged therein: behind and/or before the driver(s) the enclosure forms one or more cavities or/and horns, while the cavity is either closed or provided with openings leading into the atmosphere through the box wall, the openings are either uncovered or covered with a material forming an acoustic impedance.

The essential characteristic of the invention lies in that at least a part of the box is formed with at least two layers and both layers are made of a synthetic foam of the same two-component basic material, e.g. of polyurethane base. The inner layer is softer and more elastic, while the outer layer is harder and stiffer, the two layers are interconnected by a chemical bond and/or they are glued to one another so that the second layer is cast onto the first layer and the materials of the two layers differ only in respect of the mixing proportion of the components of the synthetic material on polyurethane basis.

With a preferred embodiment of the invention, factor of absorption of the soft inner layer measured at 1000 Hz-- amounts to at least 0.6, while the factor of the outer harder layer is less, than 0.2.

It is considered as advantageous, if the material of the acoustic impedance covering the openings of the box leading to the atmosphere is arranged between the two layers of the box, that is after having cast the first layer and prior to casting the second one, said material is placed inbetween.

With a further preferred embodiment of the invention the softer inner layer and/or the harder outer layer are applied as acoustic impedances in such a manner that the closing layer of the foam is removed at the openings leading to the atmosphere.

It is also considered as advantageous, if the driver(s) is (are) fixed by the pressing lugs formed by undercutting in the softer inner layer and a seat is formed from the inner layer in the rear part of the box for receiving the magnet of the loudspeaker; in this case the tensile force needed for fixing is assured by the elasticity of the softer inner layer.

With a further preferred embodiment of the invention the seat formed in the box receives the cross-filter, the matching transformer and other complementary elements are arranged in the cavities of the loudspeaker, while the pressing force needed for fixation is delivered by the inner layer acting as a spring.

An embodiment is also considered as advantageous, in which the cast part formed from the outer hard layer serves for the screwed connection, above which the inner softer layer is either thinned or fully removed; as a screw a plate screw may be used.

With a further preferred embodiment of the invention a pin protruding from the soft inner layer and formed from the outer harder layer fixes the loudspeakers, the transformer and other complementary elements, fixing the elements by thermic pressure.

It was found expedient, if a grid is arranged before the driver(s) and/orthe openings leading to the atmosphere, formed by the outer hard layer, simultaneously a water-drain channel is also formed between the two layers.

With a further advantageous embodiment of the invention the two halves of the box are interconnected buy a rail-elementwith an U-profile and/or screws in such a manner that the inner soft layer of at least one of the box halves is lying between the closing surfaces.

It is considered as advantageous, if two independent loudspeakers are fixed to one another by means of the cast parts (lugs) of the outer hard layer.

The advantage of the invention lies in that one single tool suffices for making the two box-halves performing a most complicated function. Within the same phase of work first one of the layers is cast, followed by the other. In such a manner a boxwith two layers of different hardness is obtained, thus meeting all the requirements in respect to the strength of the box, internal sound absorption and crackle-free operation. Simultaneous application of the two layers is of double advantage: intensity of standing waves arising in the box decreases, while mechanical self oscillation of the wall will also be less.

The hard foamed outer layer has a stiff structure, due to the air enclosed in the pores it has a certain self-atenuation which is promoted by the inner soft layer,which considerably reduced mechanical oscillations of the outer layer and simultaneously absorbs the sound-waves arising in the inside of the loudspeaker; as a consequence, standing waves are also reduced. The box-- having been made with one single tool - is able to fix the loudspeakers, to attach the two box-halves without oscillation and crack, the proper mechanical fixation ofthe crossover filter, the matching transformers becomes possible; different openings and acoustic elements improving sound reproduction can be prepared in one single phase of work.

In contrast to loudspeakers prepared with wood and different damping materials the loudspeaker according to the invention is well resistentto the different climatic influences of outdoor spaces (cold, heat, solar radiation, moisture, etc.), at the same time it can be produced more economically and has several advantages in respect to acoustics.

By the appiication of the invention loudspeakers for indoor and outdoor use can be manufactured in agood quality and relatively cheaply, so horn loudspeakers, loudspeakers with closed or open boxes, so-calied reflex orcardioid loudspeakers.

Accordingly, the invention relates to a loudspeaker, preferably sound column or horn loudspeaker, the preferred embodiments serving as an example will be described in details by the drawings enclosed, wherein: figure 1 is the cross-section of the sound column according to the invention, figure 2 gives the frontal view of the sound column according to the invention, figure 3 shows cross-sections of the sound column according tq the invention, figure 4 illustrates an angular loudspeaker with a folded horn, and figure 5 shows the schematical arrangement of the horn loudspeaker according to the invention.

Figure 1 is the cross-section of the sound column according to the invention. The sound column has a cardioide directional characteristic and comprises four loudspeakers 7. The box is composed of two halves, both halves are formed with two layers in sense of the invention. The inner layer 6 is soft, elastic and porous, closed by a skinlike layer on the outer surface. Factor of absorption is higher than 0.6, while the outer layer 1 is hard with a factor of absorption less than 0.2. The hard layer has also a porous structure.

In the inner layer 6 of the box the lugs formed therein by undercutting fix the loudspeakers 7. In addition to the undercut lugs 5, the seat 15 formed in the two inner soft layers also fixes the four loudspeakers 7. The built-in matching transformer 8 is similarly carried by the undercut lug and the pressing force of the seat 15. However, there is another possible way for fixing the transformer, in so far as the cast part 10 of the outer hard layer and the sheet screw 9 fix collectively the transformer 9.

The rear openings 11 needed for the realization of the cardioide directional characteristic reformed in the other half of the box. The openings 11 pass both the outer hard layer 1 and the soft inner layer 2.

After having cast the outer layer 1 and prior to casting the inner soft layer 2 suitable textile material 14 (or a wire-gauze) is placed inbetween, functioning as an acoustic resistor. The acoustic resistor can be formed in a different way, also within the scope of the invention. The acoustic impedance is ensured by the porous structure of the soft inner layer 6 so, that the skin-like seating layer formed in course of casting is removed. The openings 11 are always directed downwards, thus yielding protection against rain.

The grid 3 is seen well in figure, the openings 4 therein serve simultaneouslyforwater drainage, being importantfor outdoor use. The two boxhalves are fixed to one another by means of the screws 17 and the nut 20 or simply by using a rail with U-profile. A crackle-free function represents an important requirement, accordingly, thetwo hard box-halves are separated by the proper formation of the tongue 6 of the inner soft layer 2, as can be well seen in the figure. Fixation of the sound column, and optionally interconnection of a plurality of sound columns is performed by means of the tugs 18 and the bores 19, respectively. In the figure the plane is indicated with A-A, in which the section according to figure 3 was taken.

Figure 2 shows the frontal view of the sound column according to figure 1. Reference numbers are the same as applied in figure 1. The hard outer layer 1 forms the outer wall ofthe box. The two halves of the box are connected by means of the rail with U-profile. In fig. 2 the plane in which the section according to figure 3 was taken is indicated with A-A.

Figure 3 illustrates the section of the sound column according to figs. 1 and 2. The references applied are identical with the previous ones. The figure illustrates well the function of the rail 21 with U-profile. To avoid crackle, a double-layer can be used here too. The two halves of the box are separated by the tongue 6 ofthe inner soft layer 2, as the tongue 6 is made of a soft material, crackle can be avoided, atthe same time a good sealing may be obtained, being a most important prerequisite of a proper acoustic function; the seat 15 encloses the magnic circuit of the loudspeaker 7, and simultaneously supports it.

The sound column described in connection with figures 1 to 3 is well resistant to ambient climatic loads. In contrast to the constructions made with metal sheets, the solution according to the invention excels in resonance-free transmission, crackle-free emission and complete elimination of conducted sounds.

In figure 4 a loudspeaker according to the invention can be seen, having an angularform and a folded horn. This formation can be successfully applied in a horn loudspeaker of large dimension.

The loudspeaker formed of two-layer orthree-layer sheets or profiles. Factor of absorption of the soft layers is higher than 0.6, while that of the hard layers is less than 0.2. Mode of folding of the horn is well known. It is also a well known fact that folding causes strong reflexions, resulting from the perpendicular walls. By the application of the soft layers reflexion of sound-waves arising in the horn can be considerably decreased, thus quality of sound emission can be improved. The box of the loudspeaker is formed by the outer hard layer, the lateral sheets are coated with the soft layer 2.

Formation of the horn or enclosure of the driver 7 are achieved by the profile 37 covered on both sides with the soft layer 38, 39 together with the sheet 34 made of the hard layer and coated on both sides with the soft layer 35 and 36. The lateral plates or the profile 37 are interconnected e.g. by means of the screws 30 and the metal-nuts 31 glued in and poured around. At the initial section of the horn gradual widening is ensured by the two inner lateral plates 29. With this embodiment the large-sized heavy loudspeaker 7 is fixed by flattening the head of the rivet 26 formed from the hard profile 37 by using a hot tool.The solution according to the inventionwhen compared to similar loudspeaker made of a traditional wood plate - is not only more economical but due to the reduced horn reflections and wall oscillations an expressively better sound quality can be obtained.

Figure 5 shows a schematic arrangement of the horn loudspeaker according to the invention. In contrast to the horn loudspeaker according to figure 4, this is a loudspeaker with symmetrical multifold folded horn. The outer horn of the loudspeaker and simultaneously the box are formed of the hard layer 1, being coated - in sense of the invention -with the soft inner layer 2. The seat 15 formed from the soft layer 2 encloses the magnetic circuit of the driver 7 and fixes it together with the inner horn 47.

Said inner horn 47 is formed from the hard layer and it is coated on both sides with the soft layer 48,49.

The inner horn 47 is fixed to the box 1 by means of the feet 41 and the screws 42. Similarly, the middle horn 44 is fixed to the box 1 by means of the feet 50.

Both sides of the middle horn 44 are coated with the soft layer 45,46. The driver 7 is fixed to the inner horn 47 by-using any of the previously mentioned methods. Also with this embodiment the soft layers 2,45,46,48, 49 reduce the reflexions and improve the quality to the loudspeaker.

The two-layer or three-layer sheets or profiles used for the embodiments described are formed in one single phase of work. Prior to hardening of the hard layer the soft layer is cast directly to the hard layer. it goes without saying that the sequence of casting can be reversed and the hard layer may be poured onto the soft one. Between the two layers a chemical bond is established, as both layers are made of the same synthetic two-component material, e.g. on a polyurethane base, the only difference lies in the ratio of mixing in compliance with the required hardness.

The solution according to the invention enables the production of economical loudspeakers resistant to climatic influences; simultaneously, conducted resonances, reflexions, distortions, crackles can be reduced in comparison to known solutions.

Claims (12)

1. Loudspeaker, in particular sound column and horn loudspeaker, having an outer box (enclosure) for improving the transmission characteristics, the box consisting of one or more parts and having one or more drivers arranged therein, the box forming behind and/or in front of the driver(s) at least one or more cavity and/or one horn and the cavity is either closed or provided with openings leading into the atmosphere through the box, said openings being either covered with a material serving as an acoustic impedance or being uncovered, at least a part of the box and the cavity and/or horn consists of sheets or profiles of at least two layers which are each made of the same synthetic two-component foam, expediently a polyurethane-based foam, the inner layer being used to bound the cavity and/or horn being relatively softer and more elastic which the outer layer is relatively harder and stiffer, and wherein the two layers are interconnected by a chemical and/or adhesive bond so that the second layer is cast on the first finished layer and the materials of the two layers differe from each other only in the mixing ratio of the components of the synthetic material.

2. Loudspeaker as claimed in claim 1, wherein the inner layer is an acoustically soft layer having an absorption factor of at least 0.6 measured at 1000 Hz, while the absorption factor of the outer layer is less than 0.2.

3. Loudspeaker as claimed in claim 1 or 2, wherein the softer inner layer and/or the outer harder layer is/are used as (an) acoustic impedance(s) such that the closing surface skin layer is removed at the openings leading to the atmosphere.

4. Loudspeaker as claimed in claim 1 or 2, wherein the material forming the acoustic impedance and covering the openings leading to the atmosphere is placed between the outer layer and the inner layer of the box in such a manner that after casting the first layer and prior to casting the second layer, the said material is placed on the openings.

5. Loudspeaker as claimed in any preceding claim, wherein undercut lugs are provided in the softer inner layer for fixing the driver(s) and/or a seat formed in the rear part of the box for the driver magnet, the tensile force neededforfixing being provided by the elasticity of the softer inner layer and the seat formed therein.

6. Loudspeaker as claimed in any preceding claim, where a seat formed in the box holds a cross-over filter, a matching transformer and other complementary elements (if any) arranged in the or each cavity of the loudspeaker, the pressing force needed for fixing being provided by the elastic inner layer and the nest therein, acting as a spring.

7. Loudspeaker as claimed in any preceding claim, wherein a cast part is formed in the hard outer layer for a screw-connection for the driver(s), a cross-over filter and a matching transformer and above said cast part the soft inner layer is thinned or removed.

8. Loudspeaker as claimed in any preceding claim, wherein a pin is formed from the hard layer for fixing the loudspeaker or any other elements of the loudspeaker, e.g. a matching transformer, whereas the fixing of the elements is achieved by hot pressing.

9. Loudspeaker as claimed in preceding claim, wherein in front of the driver(s) and/orthe openings leading to the atmosphere a grid is formed from the hard layer.

10. Loudspeaker as claimed in any preceding claim, wherein the box is in two halves which are interconnected by means of a screw and/or by means of a rail of U-profile such that the soft layer of at least one of the box-halves lies as a tongue between the closing surfaces.

11. Loudspeaker as claimed in any preceding claim wherein the stiff layer of the box and/or other internal components, e.g. the inner horn is of three layers each of which is coated on both sides with a soft layer.

12. A loudspeaker substantially as herein decribed with reference to and as shown in the accompanying drawings.