WO1999045742A1

WO1999045742A1 - A loudspeaker featuring acoustic friction to damp resonance

Info

Publication number: WO1999045742A1
Application number: PCT/IB1999/000242
Authority: WO
Inventors: Erich Klein
Original assignee: Koninklijke Philips Electronics NV; Philips AB; Philips Svenska AB
Current assignee: Koninklijke Philips NV; Philips AB; Philips Svenska AB
Priority date: 1998-03-03
Filing date: 1999-02-11
Publication date: 1999-09-10
Anticipated expiration: 2000-09-03

Abstract

In a loudspeaker configuration (1) comprising an electrodynamic loudspeaker (3), a housing (4), and damping means (30) for damping the sound pressure rise, caused by the housing (4), at the basic loudspeaker resonant frequency (f2) which has been shifted by the housing (4), the damping means (30) are formed by at least one duct (31, 32) which provides an acoustic friction, each duct (31, 32) being realized with the aid of a part (21) of the housing (4) and an associated part (33) of the loudspeaker configuration (1), which associated (33) part adjoins the part (21) of the housing (4).

Description

A LOUDSPEAKER FEATURING ACOUSTIC FRICTION TO DAMP RESONANCE

The invention relates to a loudspeaker configuration for radiating sound into an acoustic free space, comprising an electrodynamic loudspeaker and a housing which accommodates the loudspeaker and which isolates the loudspeaker at its back in an acoustically impermeable manner with respect to the free space, and damping means accommodated in the housing and providing an acoustic friction, by which damping means the sound pressure rise, caused by the housing, at the basic loudspeaker resonant frequency which has been shifted by the housing is damped.

Such a loudspeaker configuration of the type defined in the opening paragraph is commercially available in different versions and is consequently known. The known loudspeaker configuration uses for example wadding, cellular plastics or similar damping materials as damping means inside the housing. Such damping means must be fitted separately in the housing of such a loudspeaker configuration during the manufacture of the loudspeaker configuration, which is an additional operation and, moreover, such damping means lead to additional costs, which make the loudspeaker configuration more expensive. Moreover, such damping means are merely capable of damping the sound pressure rise caused by the housing at the basic loudspeaker resonant frequency which is shifted by the housing.

It is an object of the invention to eliminate the afore-mentioned problems and restrictions and to provide an improved loudspeaker configuration. According to the invention, in order to achieve this object with a loudspeaker configuration of the type defined in the opening paragraph, the damping means are formed by at least one duct which provides an acoustic friction, and the at least one duct is realized with the aid of a part of the housing and an associated part of the loudspeaker configuration, which associated part adjoins the part of the housing.

By taking the measures in accordance with the invention it is achieved in a simple manner that no separate means are required in order to realize an acoustic friction for damping the sound pressure rise caused by the housing at the basic loudspeaker resonant frequency which is shifted by the housing but that the damping means for damping the afore- 2 mentioned sound pressure rise are realized substantially without any additional expenditure, using elements of a loudspeaker configuration in accordance with the invention which are required anyway for realizing this loudspeaker configuration, which is favorable in view of a construction which is as simple and cheap as possible. Moreover, it is achieved by means of the measures in accordance with the invention that by a suitable shape and dimensioning of the at least one duct forming an acoustic friction and provided as damping means slightly different acoustic friction values are attainable and that in this way it is possible not only to damp the sound pressure rise caused by the housing at the basic loudspeaker resonant frequency which is shifted by the housing but that, in addition, the frequency response of the loudspeaker configuration can be influenced, as desired, which has also proved to be advantageous.

In a loudspeaker configuration in accordance with the invention having the characteristic features defined in the independent Claim 1 , the at least one duct provided as damping means can be formed between a part of the housing and an associated part of a magnet system of the electrodynamic loudspeaker. However, in a loudspeaker configuration in accordance with the invention having the characteristic features defined in the independent Claim 1 , it has proved to be particularly advantageous if, in addition, the measures defined in the dependent Claim 2 are taken. Such a construction has the advantage that it can be manufactured easily. Moreover, such a construction has the advantage that each duct serving as a damping means can be manufactured with a high accuracy, as a result of which the friction realized by means of such a duct is within comparatively narrow tolerance limits and, consequently, a highly controlled damping of the sound pressure rise caused by the housing at the basic loudspeaker resonant frequency which is shifted by the housing can be achieved. In a loudspeaker configuration in accordance with the invention having the characteristic features defined in the dependent Claim 1 it has further proved to be very advantageous if, in addition, the measures defined in the dependent Claim 3 are taken. This is advantageous for simple production, particularly if the housing, i.e. the two housing sections, are made of a plastic and are manufactured in an injection-molding process.

It is to be noted that the housing may alternatively comprise more than two housing sections, in which case at least one duct, which acts as a damping means for the sound pressure rise caused by the housing at the basic loudspeaker resonant frequency which is shifted by the housing, can be provided between every two housing sections.

The above-mentioned as well as further aspects of the invention will become apparent from the example of an embodiment described hereinafter and will be elucidated with reference to this example. The invention will now be described in more detail with reference to the drawings, which show an example of an embodiment to which the invention is not limited.

Figure 1 shows, partly in diagrammatic form, a loudspeaker configuration having a housing comprising two housing sections by means of which ducts acting as damping means have been realized.

Figure 2 is a diagram which represents the sound pressure that can be generated by the loudspeaker of the loudspeaker configuration of Figure 1 in dependence on the frequency under different conditions.

Figure 1 shows a loudspeaker configuration 1. The loudspeaker configuration 1 serves for the emission of sound into a acoustic free space 2. The loudspeaker configuration 1 includes an electrodynamic loudspeaker 3 and has a housing 4.

The electrodynamic loudspeaker 3 has a plastic supporting member 5 which is constructed to support a magnet system 6 and to support a diaphragm 7 and a centering ring 8. The magnetic system 6 comprises a permanent magnet 9, which is disposed between a discshaped yoke member 10 and an annular yoke member 11. A cylindrical yoke member 12 is integral with the disc-shaped yoke member 10 and its end portion 13 is surrounded by the annular yoke member 11 , an annular air gap being formed between the cylindrical yoke member 12 and the annular yoke member 11. A moving coil 14 is arranged in the air gap and is connected to the diaphragm 7 of the loudspeaker 3 in a manner not shown in Figure 1. The connection between the moving coil 14 and the diaphragm 7 can be made, for example, by means of an adhesive joint and, moreover, in the area of the connection between the moving coil 14 and the diaphragm 7 a connection to the centering ring 8 is formed, which is realized by ultrasonic spot-welding and the additional application of an adhesive. At its periphery the diaphragm 7 is connected to the supporting member 5 by means of an adhesive joint. At its periphery 16 the centering ring 8 is also connected to the supporting member 5 by means of an adhesive joint.

It is to be noted that the moving coil 14 is connected to two contact terminals, of which only one contact terminal 18 is visible in Figure 1, via two connecting wires which extend behind the diaphragm 7, of which also only one connecting wire 17 is visible in Figure 1.

In the present case, the housing 4 of the loudspeaker configuration 1 comprises two housing sections 19 and 20. The first housing section 19 is substantially pot-shaped and 4 thus has a bottom wall 21 and a hollow cylindrical circumferential wall 22, while in addition an annular end wall 23 is connected to the hollow cylindrical circumferential wall 22. In the transitional area between the circumferential wall 22 and the end wall 23 the first housing section 19 has a stepped portion 24 in which the supporting member 5 is fitted, the supporting member 5 being fixed in the stepped portion 24 by means of an adhesive joint.

The second housing section 20 is also substantially pot-shaped and thus has a bottom wall 25 and a circumferential wall 26. In the area of the end 27 of the circumferential wall 26, which end is remote from the bottom wall 25, the first housing section 19 is placed onto the second housing section 20 with its end wall 23. The bounding wall 23 may be connected to the circumferential wall 26 in the area of the free end 27 of the circumferential wall 26.

In such a loudspeaker configuration 1 there is always a sound pressure rise, caused by the housing 4, at the basic loudspeaker resonant frequency which is shifted by the housing 4, as a result of the fact that the electrodynamic loudspeaker 3 has been built into the housing 4, which isolates the loudspeaker 3 at its back from the acoustic free space 2 in an acoustically sealed manner. For this, reference is now made to Figure 2, which represents the sound pressure in dB which can be generated by the loudspeaker 3 of the loudspeaker configuration 1 of Figure 1 in dependence on the frequency in Hz under different conditions. The curve referenced 28 relates to the variation of the sound pressure produced by the loudspeaker 3 when the loudspeaker 3 without its housing 4 is mounted in an infinitely large baffle. This curve shows that the basic resonant frequency fi of the loudspeaker 3 lies at approximately 250 Hz and that a slight sound pressure rise of approximately 77 dB occurs at this basic loudspeaker resonant frequency fi .

The curve referenced 29 relates to the variation of the sound pressure produced by the loudspeaker 3 when the loudspeaker 3 is built into a housing which corresponds to the housing 4 of the loudspeaker configuration 1 but which does not have damping means for damping a resonance rise. This curve 29 shows that in this case the basic loudspeaker resonant frequency f₂ of the loudspeaker 3 lies at approximately 450 Hz and that a distinct sound pressure rise of approximately 83 dB occurs at this basic loudspeaker resonant frequency f₂. Thus, building the loudspeaker 3 into a housing without damping means results in a frequency shift of the basic loudspeaker resonant frequency from fi = 250 Hz to f₂ = 450 Hz as well as a distinct increase of the sound pressure rise from approximately 77 dB to 83 dB.

Therefore, the loudspeaker configuration 1 shown in Figure 1 has been provided with damping means 30 comprised in the housing 4 and providing an acoustic 5 friction, which damping means damp the sound pressure rise, caused by the housing 4, at the basic loudspeaker resonant frequency f shifted by the housing 4 during operation of the loudspeaker configuration 1.

In the loudspeaker configuration 1 the damping means 30 are advantageously formed by a plurality of ducts which each form an acoustic friction, two of said ducts 31 and 32 being shown in Figure 1, as will be described in detail hereinafter. Each of the ducts 31 and

32 is realized with the aid of a part of the housing 4 and an associated part of the loudspeaker configuration 1, which associated part adjoins the part of the housing 4. In the present case, the afore-mentioned part of the housing 4 is formed by the bottom wall 21 of the first housing section 19. The afore-mentioned associated part of the loudspeaker configuration 1 is formed by an annular and, consequently, hollow cylindrical intermediate wall 33 of the second housing section 20, which wall 33 projects from the bottom wall 25 of the second housing section 20 towards the loudspeaker 3. The bottom wall 21 of the first housing section 19 has an opening so that the bottom wall 21 of the first housing section 19 is, in fact, annular. The hollow cylindrical intermediate wall 33 of the second housing section 20 projects through the opening in the bottom wall 21. A press-fit is formed between the bottom wall 21 and the intermediate wall 33 and, consequently, the cylindrical bounding surface 34 of the annular bottom wall 21 fits snugly against the cylindrical bounding surface 35 of the intermediate wall

33 in an acoustically sealed manner. This means, in other words, that the two housing sections 19 and 20 of the housing 4 adjoin one another at the location of the two bounding surfaces 34 and 35, the two housing sections 19 and 20 being mechanically connected to one another by the press-fit and an inherently acoustically impermeable connection being obtained between the bottom wall 21 and the intermediate wall 33.

In the loudspeaker configuration 1 a plurality of grooves have been formed at the location of the bounding surface 35 of the intermediate wall 33 of the second housing section 20, of which only two grooves 36 and 37 are shown in bold lines in Figure 1. Each of these grooves 36 and 37 forms with the bounding surface 34 of the bottom wall 21 of the first housing section 19 a duct which acts as a damping means, i.e. also the two ducts 31 and 32 visible in Figure 1. The grooves 36 and 37, i.e. the ducts 31 and 32, locally interrupt the inherently acoustically impermeable connection between the bottom wall 21 and the intermediate wall 33, which is advantageously utilized for damping purposes.

With the aid of the ducts 31 and 32 provided as damping means 30 and each constituting an acoustic friction the sound pressure rise, caused by the housing 4, at the basic loudspeaker resonant frequency f₂ which has been shifted by the housing 4, which frequency is 6 450 Hz in the present case, during operation of the loudspeaker configuration 1, is damped clearly, as is apparent from the curve 38 representing the variation of the sound pressure produced by the loudspeaker 3, when the loudspeaker 3 has been mounted in the housing 4 provided with the damping means 30, i.e. with the ducts 31 and 32. In an advantageous manner the damping thus obtained results in a sound pressure of substantially 77 dB at the shifted basic loudspeaker resonant frequency f₂.

In the loudspeaker configuration 1 shown in Figure 1 the provision of the damping means 30, i.e. of the ducts 31 and 32, in addition results in a rise in sound pressure in a frequency band around a frequency of 1500 Hz, which is advantageous for a correct sound reproduction.

The loudspeaker configuration 1 shown in Figure 1 has the advantage that it does not require any separate means for realizing an acoustic friction for damping the sound pressure rise, caused by the housing 4, at the basic loudspeaker resonant frequency f₂ which has been shifted by the housing 4. This is because the damping means 30 for damping said sound pressure rise have been realized by means of the two housing sections 19 and 20, which is advantageous for a very simple and low-cost construction. In addition, the provision of damping means 30 realized by means of the ducts 31 and 32 have the advantage that a rise in sound pressure at higher frequencies around 1500 Hz is obtained, which neither requires any separate means. The invention is not limited to the embodiment described hereinbefore by way of example. For example, in another embodiment of the invention a construction can be used in which similarly, but as a variant to the loudspeaker configuration 1 shown in Figure 1, the bottom wall 21 of the first housing section 19 cooperates with the supporting member 5, in which case the supporting member extends through an opening in the bottom wall 21 of the first housing section 19, which bottom wall is again annular, and is formed with grooves at the location of the bounding surface 34 of the bottom wall 21, which grooves in conjunction with the cylindrical bounding surface of the supporting member each form a duct which provides acoustic friction, so that all these ducts again act as damping means for damping the sound pressure rise, caused by the housing 4, at the basic loudspeaker resonant frequency f₂ which has been shifted by the housing 4.

Claims

CLAIMS:

1. A loudspeaker configuration (1) for radiating sound into an acoustic free space (2), comprising an electrodynamic loudspeaker (3) and a housing (4) which accommodates the loudspeaker (3) and which isolates the loudspeaker (3) at its back in an acoustically impermeable manner with respect to the free space (2), and damping means (30) accommodated in the housing (4) and providing an acoustic friction, by which damping means the sound pressure rise, caused by the housing (4), at the basic loudspeaker resonant frequency (f₂) which has been shifted by the housing (4) is damped, characterized in that the damping means (30) are formed by at least one duct (31 , 32) which provides an acoustic friction, and the at least one duct (31 , 32) is realized with the aid of a part (21 ) of the housing (4) and an associated part (33) of the loudspeaker configuration (1), which associated (33) part adjoins the part (21) of the housing (4).

2. A loudspeaker configuration (1) as claimed in Claim 1, characterized in that the housing (4) has two housing sections (19, 20) which adjoin one another at the location of two bounding surfaces (34, 35) and of which one housing section (20) is used for the formation of the associated part (33) of the loudspeaker configuration (1), and the at least one duct (31, 32) is formed at the location of the two bounding surfaces (34, 35) between the two housing sections (19, 20).

3. A loudspeaker configuration (1) as claimed in Claim 2, characterized in that at the location of the bounding surface (35) of one (20) of the two housing sections (19, 20) at least one groove (36, 37) is formed, which groove forms a duct (31, 32) in conjunction with the bounding surface (34) of the other housing section (19).