Compression Driver

Abstract

A compression driver (100) comprising: an acoustic outlet duct (101); a magnetic assembly (102, 103, 104) comprising a permanent magnet (103) and an air gap (106); a diaphragm (107) comprising a movable coil (108) adapted and configured to move within the air gap (106); wherein the diaphragm (107) comprises: a first front face (107a) facing a first chamber (107a) communicating with the outlet duct (101); 10a), wherein the first chamber (110a) is a compression chamber; a second front side (107b) is opposite to the first front side (107a) and faces a second chamber (110b) which is connected to the air gap (106) and is opposite to the first chamber (110a); characterized in that the compression driver (100) includes at least one acoustic connecting duct (111) which connects the second chamber (110b) with the acoustic outlet duct (101).

Description

Technical Field

[0001] The present invention relates to the technical field of audio reproduction systems, and in particular to compression drivers. Background Art

[0002] An electroacoustic transducer is an audio system device adapted to convert an electrical signal into sound waves. A particular type of known acoustic transducer comprises at least one sound source in the audio band (such as a compression driver, for example) and an acoustic waveguide (referred to as a horn).

[0003] The horn includes an inner hollow body extending between an inlet opening adapted to receive acoustic radiation and an outlet opening for diffusing the acoustic radiation to the exterior of the horn. The body has an inner wall defining a tapered conduit that allows the acoustic radiation to propagate between the inlet opening and the outlet opening. The inlet opening is often referred to as the throat of the horn, while the outlet opening is often referred to as the mouth of the horn.

[0004] In certain acoustic transducers, at least one compression driver may be fixed to the throat of the horn.An example of a compression driver of known art is described in patent EP 2 640 089 B1.

[0005] The compression driver generally comprises a housing that houses at least one diaphragm having two opposite faces. One of the two faces of the diaphragm faces a compression chamber that is in communication with at least one acoustic outlet duct. The at least one acoustic outlet duct conducts the sound waves generated by the movement of the diaphragm upward to the outlet port of the compression driver and thus up to the horn inlet (i.e., up to the throat of the horn).

[0006] A movable coil fed by an electrical signal is fixed to the diaphragm. The compression driver also includes a magnetic assembly having an air gap in which the movable coil is free to move. The other of the two faces of the diaphragm encloses another chamber opposite the compression chamber and in effect serving as a second compression chamber.

[0007] During operation, the air enclosed inside the second compression chamber is compressed and decompressed due to the movement of the diaphragm. Thus, the air contained in the second compression chamber resists the movement of the diaphragm with a certain resistance, which limits the low-frequency response of the compression driver. Conventionally, the stiffness of the suspension of the diaphragm is reduced to extend the low-frequency response in the compression driver. However, this may not be sufficient or may not be possible due to design constraints.

[0008] Document WO 2014 / 081092 A1 describes a driver that has a complex and bulky structure because it requires an outer cover (which has a front cover and a rear cover) and an inner cover. The acoustic connection duct extends at least partially between the inner cover and the outer cover. Document JP 2016 082369A also describes a driver that has a similarly complex and bulky structure. Summary of the invention

[0009] It is an object of the present invention to provide a compression driver which allows solving or at least partially reducing the disadvantages described above with reference to prior art compression drivers.

[0010] This object is achieved by a compression driver according to some embodiments of the invention. The invention also describes preferred and advantageous embodiments of the above compression driver.

[0011] The invention will be better understood from the following detailed description of specific embodiments, given by way of illustration and not limitation, with reference to the accompanying drawings briefly described in the following paragraphs. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 A three-dimensional top view of a non-limiting embodiment of an electro-acoustic transducer including a horn and a compression driver coupled to the horn is shown.

[0013] Figure 2 Show Figure 1 Side cross-sectional plan view of the speaker.

[0014] Figure 3 Show Figure 1 Side cross-sectional plan view of the compression driver in FIG.

[0015] Figure 4 Show Figure 3 Isometric top view of the compression drive.

[0016] Figure 5 Show Figure 3 Side cross-sectional plan view of a first possible embodiment variation of the compression driver in.

[0017] Figure 6 Show Figure 3 Side cross-sectional plan view of a second possible embodiment variation of the compression driver in.

[0018] Figure 7 Show Figure 3 Side cross-sectional plan view of a third possible embodiment variation of the compression driver in. DETAILED DESCRIPTION

[0019] Figure 1 A non-limiting embodiment of an electroacoustic transducer 1 is shown.

[0020] In the particular embodiment shown, the electroacoustic transducer 1 comprises a compression driver 100 and a speaker 2, which are operatively connected to each other, for example, by a mechanical coupling system. Figure 1 In the particular example shown, the horn 2 is mechanically coupled to the compression driver 100 via a coupling flange 5 and an associated screw system 6 .

[0021] The speaker 2 has an internally hollow body extending between an inlet opening 3 adapted to receive acoustic radiation in the audio band emitted by the compression driver 100 and an opposite outlet opening 4 adapted to diffuse the acoustic radiation to the exterior of the speaker 2. The inlet opening 3 is often referred to as the throat of the speaker 2, while the outlet opening 4 is often referred to as the mouth of the speaker 2.

[0022] The body of the horn 2 has walls defining a tapered duct that allows the emitted acoustic radiation to propagate between the inlet opening 3 and the outlet opening 4 (i.e. between the throat and the mouth). In the non-limiting example shown in the figures, the outlet opening 4 is quadrilateral in shape (rectangular in the example).

[0023] The body of the speaker 2 may be made of plastic or metal material (eg, aluminum).

[0024] Reference Figure 3 and Figure 4 , a first embodiment of the compression driver 100 is now described.

[0025] The compression driver 100 comprises an acoustic outlet duct 101 adapted and configured to be coupled to the throat 3 of the horn 2. The acoustic duct 101 is preferably a tapered duct, in particular a duct whose cross section gradually widens in a direction approaching the throat 3 of the horn 2. The acoustic outlet duct 101 is preferably delimited by a side wall 115.

[0026] The compression driver 100 further comprises a magnetic assembly 102, 103, 104 or a magnetic motor, comprising a permanent magnet 103 and an air gap 106. For example, the permanent magnet 103 has a ring shape and is thus provided with a central through hole.

[0027] The magnetic assembly 102, 103, 104 comprises a ferromagnetic structure 102, 104 in addition to the permanent magnet 103. Conveniently, the compression driver 100 comprises a cap 105 fixed to the magnetic assembly 102, 103, 104. The cap 105 is preferably made of a plastic or metal material, for example, it is made of hard plastic or aluminum.

[0028] The compression driver 100 also includes a diaphragm 107 including a movable coil 108 adapted and configured to move inside the air gap 106. The movable coil 108 has a coil axis ZZ. When the movable coil 108 is fed with an electrical signal, it is configured to move axially (i.e., along the coil axis ZZ) relative to the magnetic assembly 102, 103, 104 and cause the diaphragm 107 to vibrate. The axis ZZ shown in the figures is also the axis of the acoustic outlet duct 101.

[0029] exist Figure 3 and Figure 4 In the embodiment of FIG. 1 , the diaphragm 107 is an annular diaphragm and is fixed to a radially outer support ring 112 and a radially inner support ring 113 .

[0030] The compression driver 100 is preferably a driver for mid-high frequencies and has, for example (but without introducing any limitation), a frequency response equal to 1 kHz to 20 kHz.

[0031] The diaphragm 107 includes a first face 107a facing a first chamber 110a communicating with the outlet duct 101. The first chamber 110a is a compression chamber. The diaphragm 107 also includes a second face 107b opposite to the first face 107a and facing a second chamber 110b communicating with the air gap 106 and opposite to the first chamber 110a.

[0032] For convenience, the first chamber 110a and the second chamber 110b are arranged so that: if the volume of one of the two chambers expands due to the vibration of the membrane 107, the volume of the other chamber contracts, and vice versa. This clarifies the meaning of the term "relative" used in the previous paragraph with respect to the first chamber 110a and the second chamber 110b.

[0033] The compression driver 100 comprises at least one acoustic connection duct 111 which connects the second chamber 110b with the acoustic outlet duct 101. It has been noted that the presence of the above-mentioned acoustic connection duct 111 actually allows to extend the low-frequency response of the compression driver. Preferably, the acoustic connection duct 111 extends between an inlet opening to the second chamber 110b and an outlet opening to the acoustic outlet duct 101. More preferably, the acoustic duct 111 is a completely straight duct in order to increase the manufacturing convenience.

[0034] According to an advantageous embodiment, the outlet opening of the acoustic connection duct 111 is defined on a side wall 115 of the acoustic outlet duct 101 .

[0035] According to an advantageous embodiment, the at least one acoustic connection duct 111 extends completely into the thickness of the magnetic assembly 102, 103, 104. In other words, in this embodiment, the at least one acoustic connection duct 111 extends along its entire length into the thickness of the magnetic assembly 102, 103, 104. Thus, with reference to e.g. Figure 3 , the acoustic connection duct 111 extends into a space not exceeding the axial volume H of the magnetic assembly. By virtue of the present invention, the compression driver 100 has a highly compact structure.

[0036] According to an advantageous embodiment, said at least one acoustic connection duct 111 is a hole defined in the magnetic assembly 102 , 103 , 104 , preferably having a circular cross section.

[0037] According to a particularly advantageous embodiment, the aforementioned acoustic connection duct 111 and the second compression chamber 110b act as (i.e., define) a Helmholtz resonator. Advantageously, the resonant frequency of the Helmholtz resonator is calculated to be consistent with the volume of the second chamber 110b, the force factor BL and the stiffness of the vibrating membrane 107, so that the entire system operates in coordination as a single system to avoid phase shifts between the sound waves coming from the first face 107a and the second face 107b of the vibrating membrane 107, respectively, that meet each other in the acoustic outlet duct 111.

[0038] For the purpose of Helmholtz resonator tuning, it should be noted that the diaphragm mounted in a closed structure, used to define the post-compression chamber in the case of a compression driver of the known art, has a frequency response with a high-pass filter behavior in the low frequencies. In the case of mounting in a closed structure, the introduction of at least one connecting duct 111 allows the lower frequencies of the frequency response to be extended or reduced at the expense of an increase in the filter order.

[0039] In any case the choice of the final shape of the frequency response is not univocal, i.e. it is possible to choose between different "alignments" or tunings. Simplifying the problem, the preselected tuning determines the combined specification of four parameters: the resonant frequency f of the mechanical part s (determined by the mechanical suspension and movable mass), the speaker volume V B (which is an additional pneumatic suspension and here is equal to the volume of the second chamber 110b), the loss ratio Q T (mechanical and electrical, thus also depending on the motor and the movable coil Bl 2 / R E ) and the additional resonant frequency f generated by the acoustic connection duct 111 H .

[0040] Specifically, the additional resonant frequency f HIt is a combined pneumatic suspension system (sound compliance C) given by the air in the speaker. B ) (wherein the loudspeaker is the second chamber 110b here) and the mass of the air in the connecting duct 111 (acoustic mass M H ) function:

[0041]

[0042] Compliance C B Simply by the volume V of the speaker B Determined as:

[0043]

[0044] where ρ is the density of air, c is the speed of sound, and the acoustic mass M H The air mass M in the acoustic connection duct 111 can be air And the cross section A of the conduit 111 is calculated as follows:

[0045]

[0046] Here, l is the length of the acoustic connecting duct 111 .

[0047] The above relationship gives the resonant frequency f for direct selection of the Helmholtz resonator according to the system size. H Or tuning frequency f H The following formula:

[0048]

[0049] Some of the most common alignments require f H ≤f B , where f B is the frequency of the system without the conduit 111 connected, which is set to be equal to f s separate, since the pneumatic suspension of the closed loudspeaker is also taken into account. This simple condition allows an approximate preliminary tuning of the system to be achieved without first referring to a specific alignment.

[0050] For the sake of completeness, it is pointed out that the described disclosure refers specifically to direct radiating loudspeakers, in which the loudspeaker and the system of connecting ducts 111 are substantially subject to the same external acoustic load. This is obviously not absolutely true in the case of a compression driver, considering that the diaphragm 107 faces the compression chamber. However, conceptually, the described strategy can be similarly applied to manipulate the low-frequency response of a compression driver.

[0051] According to an advantageous embodiment, the magnetic assembly 102, 103, 104 comprises a ferromagnetic structure having a first ferromagnetic plate 102 and a second ferromagnetic plate 104, between which the permanent magnet 103 is inserted, and the at least one acoustic connection duct 111 extends into the first ferromagnetic plate 102 or into the second ferromagnetic plate 104. However, this does not exclude an embodiment in which the acoustic connection duct 111 extends into the permanent magnet 103.

[0052] For example, if the first ferromagnetic plate 102 comprises a pole shoe 109, it is advantageous that the acoustic connection duct 111 preferably extends completely into the pole shoe 109. Here, the acoustic connection duct 111 can be conveniently made by perforating the pole shoe 109, for example by means of a cutter or a drill. According to a preferred embodiment, the permanent magnet 103 has a through hole, and the pole shoe 109 is shaped to be inserted into the through hole.

[0053] According to an advantageous embodiment, the pole shoe 109 has a central hole coaxial with the outlet duct 101 , and the acoustic connection duct 111 extends into the pole shoe 109 laterally (ie radially or transversely) relative to the central hole.

[0054] According to a preferred embodiment, the acoustic connection duct 111 extends radially relative to the axis ZZ of the movable coil 108 (which is also the axis of the acoustic outlet duct 101). Advantageously, the acoustic connection duct 111 extends only radially or transversely relative to the axis ZZ of the movable coil 108 (i.e. over its entire length).

[0055] exist Figure 3 and Figure 4 In the embodiment shown, the compression driver 100 comprises two acoustic connection ducts 111. However, the number of acoustic ducts may be equal to one or even greater than two.

[0056] According to an advantageous embodiment, the acoustic connection duct 111 has a circular cross section. This circular cross section may be constant along the entire acoustic connection duct 111 or may vary along at least one section of the acoustic connection duct 111 .

[0057] Refer again Figure 3 and Figure 4, it should be noted that a non-limiting embodiment is shown, in which the compression driver 100 includes a connecting conduit 119 operably inserted between the compression chamber 110a and the acoustic outlet conduit 101. The connecting conduit 119 is preferably also such that: the generated acoustic radiation outlet is deflected from the first compression chamber 110a by 180° or approximately 180°, in other words, the conduit is a U-shaped or substantially U-shaped connection. According to a preferred embodiment, the above-mentioned connecting conduit 119 has an increasing cross-section in the direction from the first chamber 110a to the acoustic outlet conduit 101. In other words, the conduit 119 is a communicating expansion conduit.

[0058] The above-mentioned connecting duct 119 is preferably defined inside the cap 105 and more preferably has circular symmetry about the axis ZZ of the movable coil 108 .

[0059] according to Figure 3 and Figure 4 In the illustrated embodiment, the compression driver 101 comprises an ogive 120 housed in the acoustic outlet duct 101. The ogive 120 is preferably a conical element having cylindrical symmetry and is, for example, fixed to the cap 105, for example, being made as a single piece with the latter. The acoustic outlet duct 101 is preferably defined radially in the outer wall of the ogive 120 and radially outside the side wall 115.

[0060] Figure 5 A second embodiment of a compression driver 100 is shown, which is Figure 3 and Figure 4 The embodiment in is substantially different in that the compression driver 100 therein has a dome-shaped diaphragm 107. In this embodiment, the compression driver 101 does not have a pointed top 120, but is instead provided with an acoustic equalizer 130. A first compression chamber 110a is defined between a first face 107a of the diaphragm 107 and an underside of the acoustic equalizer 130. A second chamber 110b is formed by two chamber portions, a first portion of which is defined between a second face 107b of the diaphragm 107 and a cap 105, and a second portion of which is defined in a ferromagnetic structure 102, 104 (particularly in the first ferromagnetic plate 102). The two chamber portions are fluidically connected to each other via an air gap 106.

[0061] exist Figure 5 In the embodiment, four acoustic connection ducts 111 are provided by way of example only.

[0062] Figure 6 A third embodiment of a compression driver 100 is shown, which is Figure 5The embodiment in differs substantially in that the compression driver 100 therein comprises an acoustic connection duct 111 having a variable (preferably circular) cross-section. Figure 6 In the non-limiting embodiment of , the cross section specifically decreases gradually in the direction from the second compression chamber 110b to the acoustic outlet duct 101. Figure 6 In the embodiment shown, two diametrically opposed acoustic connection ducts 111 are provided by way of example only.

[0063] Figure 7 A fourth embodiment of a compression driver 100 is shown, which is Figure 5 and Figure 6 The embodiment of is substantially different in that the compression driver 100 therein includes a plurality of acoustic connection conduits 111, each of which extends longitudinally along a respective axis that is inclined relative to the axis ZZ of the movable coil 108 (e.g., inclined by about 45° relative to the axis ZZ). Figures 3 to 6 In the embodiment of , the acoustic duct instead extends along a corresponding axis perpendicular to the axis ZZ of the movable coil 108. Figure 7 In the embodiment shown, two diametrically opposed acoustic connection ducts 111 are provided by way of example only.

[0064] Finally, it should be noted that while an embodiment has been shown in which the acoustic connection conduit 111 extends into the ferromagnetic structures 102, 104, such a design, while advantageous and preferred, is not necessary or limiting. As described above, embodiments in which the acoustic connection conduit 111 extends into the permanent magnet 103 are indeed possible. Furthermore, it should be noted that the acoustic connection conduit 111 does not necessarily have to be straight, as it can, for example, be curved or "L" shaped, etc.

[0065] From the above, it is clear that a compression driver 100 of the type described above allows the intended objectives to be fully achieved in terms of overcoming the drawbacks of the prior art. In fact, by virtue of having at least one acoustic connection duct 111, it has in fact been noted that excellent results have been obtained in terms of the low-frequency extension of the frequency response of the compression driver 100.

[0066] Without prejudice to the principle of the invention, the embodiments and the manufacturing details may vary widely with respect to the above description disclosed by way of non-limiting examples, without departing from the scope of the invention as defined in the appended claims.

Claims

1. A compression driver (100), comprising: - an acoustic outlet duct (101); - a magnetic assembly (102, 103, 104) comprising a permanent magnet (103) and an air gap (106); - a diaphragm (107) comprising a movable coil (108) adapted to be configured to move inside said air gap (106); Wherein, the vibration membrane (107) comprises: - a first face (107a) facing a first chamber (110a) communicating with the acoustic outlet duct (101), wherein the first chamber (110a) is a compression chamber; - a second face (107b) opposite to the first face (107a) and facing a second chamber (110b) communicating with the air gap (106) and opposite to the first chamber (110a); Characterized in that the compression driver (100) comprises at least one acoustic connection duct (111) which connects the second chamber (110b) with the acoustic outlet duct (101), The magnetic assembly (102, 103, 104) comprises a ferromagnetic structure, the ferromagnetic structure has a first ferromagnetic plate (102) and a second ferromagnetic plate (104), the permanent magnet (103) is inserted between the first ferromagnetic plate (102) and the second ferromagnetic plate (104), and the at least one acoustic connection duct (111) extends into the first ferromagnetic plate (102), into the second ferromagnetic plate (104), or into the permanent magnet (103). wherein the first ferromagnetic plate (102) comprises a pole shoe (109) having a central hole coaxial with the acoustic outlet duct (101), and wherein the acoustic connection duct (111) extends radially or transversely into the pole shoe (109) relative to the central hole.

2. The compression driver (100) of claim 1, wherein: The at least one acoustic connection duct (111) extends between an inlet opening to the second chamber (110b) and an outlet opening to the acoustic outlet duct (101).

3. The compression driver (100) of claim 1, wherein: The at least one acoustic connection duct (111) extends completely into the thickness of the magnetic assembly (102, 103, 104).

4. The compression driver (100) of claim 1, wherein: The permanent magnet (103) has a through hole, and wherein the pole shoe (109) is shaped to be inserted into the through hole.

5. The compression driver (100) of claim 1, wherein: The movable coil (108) has a coil axis (ZZ), and wherein the at least one acoustic connection duct (111) extends radially relative to the coil axis (ZZ).

6. The compression driver of claim 5, wherein: The at least one acoustic connection duct (111) extends only radially or transversely relative to the coil axis (ZZ).

7. The compression driver (100) of claim 1, wherein: The at least one acoustic connecting duct (111) comprises a plurality of acoustic connecting ducts.

8. The compression driver (100) of claim 1, wherein: The acoustic connection duct (111) has a circular cross section.

9. The compression driver (100) of claim 8, wherein: The circular cross-section varies along at least one section of the acoustic connection duct (111).

10. The compression driver (100) of claim 1, wherein: The acoustic connection duct (111) is completely straight.

11. The compression driver (100) of claim 1, wherein: The acoustic connection duct (111) and the second chamber (110b) define a Helmholtz resonator.

12. The compression driver (100) of claim 11, wherein: The Helmholtz resonator has a tuning frequency defined by the following formula: in: -c is the speed of sound; -l is the length of the acoustic connection duct (111); - A is the cross section of the acoustic connection duct (111); -V B is the volume of the second chamber (110b).

13. An electroacoustic transducer (1), comprising a speaker (2), and characterized in that: It comprises a compression driver (100) as claimed in claim 1 operatively coupled to the loudspeaker (2).

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