FR2893213A1 - ANTI-VIBRATION PROTECTION DEVICES FOR MICROPHONE. - Google Patents

Abstract

The invention relates to a main microphone suspension device and an additional joint suspension device adapted to wind shields for microphone, both intended for vibration protection of microphone capsule. The main device comprises a bar (1c) for fixing four insulators (2a) consisting of portions of spring wire, each partially surrounding the microphone (3a), and intersecting in pairs without touching each other. The additional device comprises an armature (1g) for fixing four insulators (2c), also consisting of portions of spring wire, and provided for suspending a windshield (3h). The vibratory systems of each of the devices are damped by their respective damping elements (2b) (2d).

Description

DESCRIPTION The present invention relates to the general field of

  microphones and more particularly that of their anti-vibration protection.

  At first approach, a mobile mass isolated from the vibrations of its support by a suspension is a mechanical problem called vibratory transmissibility whose scientific formulation will not be explained. A rigid support (1) is a source of vibrations; a suspension (2) has essentially stiffness (2a) and damping (2b) characteristics; and a moving mass (3) has three degrees of freedom in translation and three in rotation. In the case of a microphone, its vibratory sensitivity is different for each degree of freedom and the suspension must provide the system with a set of resonance frequencies as low as possible, in relation to this sensitivity and the risk of excitation of each of modes, in order to guarantee a good compromise between a correct microphone hold and sufficient filtering.

  So that there is no confusion of vocabulary, the spring elements having essentially stiffness characteristics will be called "insulators". Similarly, for the sake of editorial clarity, the term "microphone" denotes an entity or group of entities rigidly linked to each other, each having one or more capsules sensitive to acoustic and mechanical vibrations.

  The first microphone suspensions appeared in the years 1925-1930. The insulators were then made of true helicoidal metal springs as is clearly stated in US1653109 and US1805362. By their helical nature, these springs can maintain a microphone only to the extent that each of them works only in extension in its main axis. Since the years 1930-1940, all inventions for microphones suspensions incorporate insulators based on rubber or elastomeric materials, as described for example in patents US2235505, US2628289, US2920150, US3155780, US3653625, US4194096, DE3220643, JP57171898. , US4396807, US4514598, US4791674 or US6459802.

  The use of these nonmetallic materials offers certain advantages (simplicity, plasticity, intrinsic damping), but it is difficult to control and especially to lower sufficiently certain fundamental frequencies of the mass-spring system, which is detrimental to the quality of the insulation. vibratory, taking into account the need to ensure sufficient firmness to hold the microphone, especially when it is placed at the end of a pole held by hand. In conjunction with this approach, in the frequent case of outdoor sound recording, the addition of a windshield completely surrounding the microphone and its suspension, may lead to an indirect degradation of the anti-vibration quality of this suspension. . This degradation is due to an acoustic recovery of the vibration of the envelope of this cap rigidly fixed to the support, by the capsule or the microphone capsules. As is clearly visible in the patent figures GB375246, US2520706, GB2085263, GB2184916 or US4966252, the wind caps are rigidly attached to the vibrating support.

  The proposed solution to the problems emerging from this state of the art, consists of a main device for microphone suspension and an additional device for windshield hanger suspension, said devices being both intended for single vibratory isolation purposes. of microphone capsule. The quality of the result is obtained above all by a particular implementation of insulators made of spring wire, and associated dampers.

  The main device is a microphone suspension comprising: a bar rigidly connected to the vibrating support; a cradle rigidly connected to said microphone; two pairs of insulators each consisting of a portion of wire simply curved spring effect, with the exception of coil springs, the ends of said insulators of each of said pairs being embedded on one side at the same point in said bar and recessed on the other side at two distinct points of said cradle, said insulators of the same pair being arranged symmetrically so that they cross without touching. According to one embodiment, the main device is characterized in that the cradle is constituted of a single piece joining the pairs of insulators. According to one embodiment, the main device is characterized in that the cradle consists of a profiled piece and mounted so that it partially surrounds the microphone on a face opposite to the bar. According to one embodiment, the main device is equipped with four damping elements each having at least one contact point on the central parts of the insulators which are respectively associated with them, said elements being provided for combining the damping roles of the resonances. of said insulators and damping of the fundamental resonances of the complete modal system in its low frequency approximation. According to one embodiment, the main device is characterized in that the damping elements consist of elongated parallelepipedal blocks made of Ethylene Propylene Diene Monomer. According to one embodiment, the main device is characterized in that the electrical socket (3d) adapted to said microphone (3a) is integral with said cradle (3b). The additional joint device is a suspension adapted to the wind shields for microphone. This device is intended for vibration protection of microphone capsule. It comprises: a four-pointed star-shaped armature, considered as rigid and rigidly fixed to the support, possibly dismountably, said armature being situated inside said cap; - Four insulators consist of portions of simply curved wire spring effect, respectively embedded on one side in the ends of the branches of the frame, and the other at certain points of the cap. According to one embodiment, the additional device is characterized in that its insulators are each constituted by a complete loop of generally circular shape.

  According to one embodiment, the additional device is characterized in that the interface zone between the support and said cap is filled by a flexible material provided to ensure sufficient freedom of relative movement between the cap and the support, while by maintaining the anti-wind properties normally offered by the cap. According to one embodiment, the additional device is characterized in that said material is a silicone molded diaphragm forming a bellows.

  Figure 1 is a symbolic representation of the notion of suspended mobile mass. Figure 2 is a simplified representation of a helical spring and a spring consisting of a portion of simply curved wire. It illustrates the differences in behavior between the two models. Figure 3 is a symbolic representation of the vibratory problem posed by the addition of a windshield completely surrounding the microphone and its suspension. Figure 4 is a symbolic representation of the solution provided to the problem in Figure 3, by detaching the windshield. Figure 5 is a perspective view of a simplified embodiment of the main device, in the case of a single body microphone of generally elongated cylindrical shape. Figure 6 is a perspective view of a simplified embodiment of the main device, in the case of a microphone composed of two parallel entities, rigidly interconnected, of generally elongated cylindrical shapes. Figure 7 is a perspective view of a simplified embodiment of the main device, in the case of a microphone composed of two parallel entities, rigidly interconnected, of generally short cylindrical shapes. Figure 8 is a perspective view of a detail of an embodiment of the main device, relating to the dampers and the stop system.

  Figure 9 is a top view of a detail of an embodiment of the main device, relating to the dampers. Figure 10 is a perspective view of a detail of an embodiment of the main device, relating to an electrical socket secured to the cradle.

  Fig. 11 is a perspective view of an embodiment of the main device, in the case of a body and capsule microphone of elongated cylindrical shape. Figure 12 is a perspective view of an embodiment of the additional joint suspension device adapted to the wind shields for microphone, presented alone. Figure 13 is a perspective view of an embodiment of the main device and the additional device jointly presented.

  The common point of the two devices is the particular implementation of mobile mass suspension. FIG. 1 illustrates the general principle of mobile mass (3) suspended and isolated from the vibrations of the support (1) by insulators (2a) and dampers (2b). The relationship between the vibration amplitudes of the moving mass and those of the support is called transmissibility. In a simplified theoretical model with a degree of freedom, there are curves whose profile as a function of the excitation frequency is known. These curves are very useful reference points to appreciate the quality of a suspension.

  As illustrated in Figure 2, a spiral spring (4) provides its characteristic of stiffness in its axis, which is also the case of a simple rubber elastic or a flexible elastomeric material tape. On the other hand, a simply formed wire with a spring effect (5) offers more complex stiffness characteristics depending on its profile and on the forces (F) to which it is subjected. It is this anisotropy of behavior that makes it possible to play more finely on the distribution of the frequencies of resonances according to the modes in a suspension.

  On the other hand, compared with other spring-like materials, natural or synthetic, metal such as steel has a much more constant Young's modulus even for large elongations, which ensures a good quality of vibratory filtering regardless of the static position of the moving mass, due to the gravitational effect.

  Figures 3 and 4 justify the need for the additional device, in the case where the microphone and its suspension are surrounded by a windshield protection (3h). In the absence of a cap, a good suspension guarantees good vibratory isolation of the microphone capsule. In the presence of a cap rigidly connected to the support, as illustrated in FIG. 3, the envelope behaves like a drum skin which transmits the vibrations of the support and vibrates the microphone capsule (s) acoustically. Indirect degradation of the quality of the suspension is therefore all the more important as this quality is great. FIG. 4 thus illustrates the principle of vibratory decoupling of the cap, by the use of insulators (2c) and dampers (2d), thus limiting the transmission of the vibration acoustically.

  Figure 5 shows an example of a single body microphone (3a) of generally elongated cylindrical shape, suspended by a double pair of wire insulators (2a). The elements 35 are now specified and referenced as follows: - The support is a rigid assembly, consisting of a base, such as the end of a pole (la), a possible ball joint (lb) and a bar (1c) for fixing the insulators. - The total mobile mass is in fact made of the microphone (3a) and its cradle (3b) rigidly fixed thereto by any means. In this example, each isolator (2a) partially surrounds the microphone about three quarters of a turn. For each pair of insulators, the ends are embedded on one side at the same point (ld) of the support, and on the other side at two distinct points (3c) of the cradle (3b), so that the insulators cross each other without touching each other. This configuration is advantageous for the following reasons: - Increased control of the fundamental resonant frequencies of the complete modal system, in particular that which corresponds to a rotation of the microphone around its main axis. This rotation resonance frequency can thus be lowered with a good independence vis-à-vis other modes of resonance. - "Shield" and "seat belt" effect around the microphone. - Optimization of the overall size of the suspended microphone. We also note that the cradle (3b), rigidly connected to the microphone by any means, consists of a single profiled part partially surrounding the microphone. The fact that it consists of a single piece allows to bring together the two pairs of insulators to make them less vulnerable, especially when storing and transporting the suspension. In this configuration, the cradle (3b) is in contact with the microphone (3a) on a face opposite to the bar (1c), which gives a maximum guard between the microphone (3a) and the bar (1c). It should be noted that the microphone shown may, for example, have a sensitive capsule on one side and an electrical socket on the other. It can also have a sensitive capsule on each side in the case of a stereo microphone.

  Some characteristics of the insulators (lengths, sections, type of metal) must be adapted to the desired objectives (fundamental resonance frequencies of the modal system) according to the characteristics of the microphone (shape, size, mass, sensitivity to vibrations), or the constraints of the microphone. use (firmness of maintenance) and manufacturing (costs, simplicity). The setting parameters are numerous and quite interdependent, but the simplest rules to respect are the following: - The overall decrease of the resonant frequencies is directly correlated to the reduction of the sections of the wires used or to the increase of their lengths. The relative decrease of a translation resonance frequency is mainly correlated with an increase in the size of a loop or a curvature. - The relative decrease in the rotation resonance frequency of the microphone around its axis is mainly correlated to the spacing of the fixing points (3c) insulators of the same pair, along a circumference around the microphone. - The relative decrease in the resonance frequency of the two other possible rotations is directly correlated to the approximation of the two pairs of insulators.

  In order to illustrate the adaptability of the device to different microphone characteristics, Figures 6 and 7 show examples of suspensions provided for multi-body microphones. The precise and complete reasons that determine the characteristics of insulators depend on many factors and are not detailed. Figure 6 shows a double microphone (3a) composed of two elongated generally cylindrical bodies, rigidly connected by the double cradle (3b) and suspended from the support (1) by the insulators (2a). In this example, the fixing points (3c) of the insulators (2a), microphone side, are located on the part of the cradle farthest from the support (1). Figure 7 shows a double microphone (3a) composed of two short overall cylindrical bodies, suspended from the support (1) by the insulators (2a) and coupled by a specific cradle (3b) to sufficiently separate the two pairs of insulators (2a) between them. In this new example, the characteristics of each pair of insulators are different given the dissymmetry of the microphone. The masses being unequally distributed, the pair of insulators located at the back of the microphone (on the right in the figure) is appreciably softer than that at the front.

  Insulators made of wire have the disadvantage of own resonances, values much higher than those of the complete system, which depend essentially on their intrinsic characteristics (mass, stiffness). In the case of these particular resonances, the ends (attachment points) and the central parts of the son are respectively the nodes and the bellows of displacement of the vibration. In the absence of treatment, these resonances significantly degrade the quality of the filtering of the suspension. In a more general manner, the metal such as spring steel having a very low intrinsic damping, the fundamental resonances of the complete system can have very high amplitudes in the absence of additional damping, which can cause a "sloshing" "embarrassing microphone when handling its support (pole held by hand). These problems are solved by the use of dampers placed directly in contact with the son, by gluing or other method of attachment. FIG. 8 shows the detail of a pair of insulators, which takes up part of the configuration shown in FIG. 5. Two flexible dampers (2b) of elongated parallelepipedal shapes are arranged in such a way that they absorb as much as possible the vibration. A stop (the) damping material, visible at the bottom of the figure, is necessary in case of shock or excessive displacement of the microphone. The two dampers (2b) presented from above in Figure 9 show the bridge they form between the nodes (cradle) and the vibration bellies (central parts of the son). On the other hand, this figure makes it possible to visualize the way in which the threads cross without contact. These dampers also have the role of limiting the amplitudes of the fundamental resonance frequencies of the different modes of the complete system. The desired damping level is thus adjustable by the choice of the nature of the material, but also by the section of the dampers.

  For practical reasons of use or in the case where it would be desirable to keep the pairs of insulators as far as possible, it may be useful to make the electrical socket integral with the cradle. Figure 10 shows a version of this variant of the main device where the plug (3d) is fixed to the cradle (3b) by lugs (3e) thus providing the opportunity for it to pivot slightly about the axis passing through these pins. A compression seal (not visible), concealed between the socket and the cradle, then makes it possible to firmly clamp the microphone and the socket against the cradle, after insertion of the microphone into the socket. For reasons of readability, the electric wire is not shown.

  Figure 11 shows a concrete case of cardioid monophonic microphone suspension (3a), having a maximum acoustic and vibratory sensitivity in its main Z-axis (see Cartesian reference). The microphone is: - equipped with an individual windshield (3g) directly coupled to its body, - fixed to the cradle (3b) by an integral electrical outlet 25 (3d) and by an elastic fastener (3f), - isolated of the support (1) by insulators (2a) and dampers (2b), - protected against shocks by the stops (1c). The support (1) is, in this case, consisting of a pole (la) 30 whose visible end is fixed to a ball (lb), itself fixed to the support bar (1c) equipped with holes (1f). ) to shift the microphone relative to the main axis of the pole. It should be noted that, in this case, the individual wind protection (3g) does not degrade the anti-vibration quality of the suspension. On the other hand, this wind protection element (3g) has a clean mass and therefore has an influence to take into account in the behavior of the system.

  Detailed characteristics of this example: Microphone (3a): Length 13 cm without plug or protection; Diameter 20 mm; Weight 120 g with plug, cradle and individual wind protection; Insulators (2a): 4 psrtions of wire of circular section in spring steel with 1% carbDne; Length 105 mm each; Diameter 0.8 mm; 35mm crossover for each pair. Shock absorbers (2b): 4 flexible parallelepipeds of 24 x 6 x 4 mm in EPDM (Ethylene Propylene Diene Monomer).

  Cradle (3b) and bar (lc): length 8.5 cm. For the purpose of maximizing the maintenance of the microphone when it oscillates in rotation in the XZ or YZ planes, without changing its behavior in the X, Y and Z translation modes, the two pairs of insulators before- back are distant from each other to the maximum. The cradle (3b) is so dimensioned that the plug (3d) is housed at the end thereof, without exceeding it. To facilitate the establishment and maintenance of the microphone, the socket is made integral with the cradle by two fixing lugs (3e). The elastic wire tie (3f) allows quick and efficient microphone placement. Translational resonances: 8 Hz in Z; 13 Hz in Y; 12 Hz in X. Resonances of rotation: 8 Hz in XZ; 9 Hz in YZ; 18 Hz in XY. It should be noted that the microphone described is not very sensitive in translation in the X, Y and rotation axes in the XY plane. This justifies that it is not necessary to control the corresponding modes too effectively, that is to say, to lower their resonance frequencies too much, compared with those of the other modes, Z in particular. Resonances of insulators: 200 and 500 Hz.

  Vibration attenuation (transmissibility) obtained in the main Z axis: -12 dB at 20 Hz, -40 dB at 100 Hz.

  Figure 12 provides a perspective of the additional joint device, represented alone. Although the purpose of this device is an indirect anti-vibratory protection of microphone capsule, the mobile mass to suspend is the windshield (3h) itself. The physical characteristics of this cap are not described, especially those that would have utility in its essential purpose of wind protection. Nevertheless, it is imperative that the main structure of this cap is considered rigid in view of the flexibility of the insulators used, so that they play their full role. In the figure, the cap is shown on one half of its volume, thus revealing the elements of the device, located inside this cap. A frame (1g) in the form of a four-pointed star is rigidly fixed to the support, possibly dismountably. The four insulators (2c) consist of spring-loaded wire loops respectively embedded on one side in the ends (1h) of the arms of the armature, and on the other in certain points (3i) of the cap. . The insulators (2c) are respectively associated with dampers (2d) fixed on one side to the central parts of the loops and on the other side at certain points of the cap (not referenced). These dampers attenuate the resonances of the insulators, as well as the fundamental resonances of the complete modal system (ballotings of the cap). For reasons of readability, the dampers associated with isolators shown at the bottom of the figure are not shown. Since the windshield is considered rigid, its relative freedom of movement can only be preserved by specifically treating the interface zone between the cap (3h) and the pole (1a) by providing continuity of the anti - wind protection. -vent normally brought by this cap, in an area where acoustic transparency is not a priority. In the example, this zone is filled with a silicone molded membrane (1i) forming a bellows.

  The detailed characteristics of this concrete example are as follows: Ovoidal headdress (3h): length 24 cm; maximum diameter 14 cm; mass about 150g.

  Star frame (1g): aluminum 3 mm thick; average size 10 x 8 cm.

  Insulators (2c): 4 portions of 12 cm steel wire spring 1% carbon, sectio: z circular 0.8 mm in diameter, circular loops of 3 cm in diameter. Shock absorbers (2d): 4 flexible parallelepipeds of 30 x 6 x 6 mm in 5 EPDM (Ethylene Propylene Diene Monomer). Interface (1i): 1mm thick silicone membrane forming a bellows symmetry of revolution ("wave" circular double alternation); outside diameter 5 cm; total thickness 2 cm. Thus constituted, the complete modal system offers 6 fundamental resonances (three translations and three rotations) of frequencies between 8 and 10 Hz, very well balanced and damped. The gain provided by the implementation of this additional additional device depends in particular on the frequency and characteristics of the microphone. The analysis of the transfer functions measured between the excitation force produced in the support and the electrical signal delivered by a cardioid microphone, correctly centered in the cap, made it possible to draw the following conclusions: The transfer function obtained in FIG. the absence of cap 20 is taken as a reference. The transfer function obtained in the presence of the unsprung cap shows a degradation of the order of 10 to 20 dB depending on the modes of excitation, between 20 and 200 Hz. The transfer function obtained after suspension of the cap limits this degradation to values between 0 and 10 dB.

  Figure 13 gives an overview of the two devices used together. They are capable of a large number of variants adapted to various shapes, sizes and characteristics of microphones and wind shields.

  The advantage of the invention resides in part in the simplicity of the means, described throughout the document, to implement 35 for an industrial application.

Claims (10)

  Microphone suspension comprising: a bar (1c) rigidly connected to the vibrating support; a cradle (3b) rigidly connected to said microphone (3a); two pairs of insulators (2a) each consisting of a portion of simply curved spring wire, with the exception of helical springs, the ends of said insulators of each of said pairs being embedded on one side at the same point; (ld) in said bar, and the other at two distinct points (3c) of said cradle, said insulators of the same pair being arranged symmetrically so that they cross without touching.   2. Suspension according to claim 1, characterized in that said cradle (3b) consists of a single piece joining said pairs.   3. Suspension according to claim 2, characterized in that said cradle (3b) consists of a shaped part and mounted such that it partially surrounds the microphone (3a) in contact with it on one side opposite said bar (1c).   4. Suspension according to any one of the preceding claims, equipped with four damping elements (2b) each having at least one contact point on the central parts of the insulators (2a) respectively associated with them respectively, said elements being provided to combine the damping roles of the resonances of said insulators and the damping of the fundamental resonances of the complete modal system in its low frequency approximation.   5. Suspension according to the preceding claim, wherein the damping elements (2b) consist of elongated parallelepipedal blocks of Ethylene Propylene Diene Monomer. 15   6. Suspension according to any one of the preceding claims, characterized in that the electrical outlet (3d) adapted to said microphone (3a) is integral with said cradle (3b). 7 A suspension device adapted to the wind shields for a microphone, said device being intended for the purpose of vibratory protection of a microphone capsule, said device being associated together with the suspension defined according to any one of the preceding claims, comprising: - An armature (1g) in the form of four-pointed star, considered rigid and rigidly fixed to the support possibly removable manner, said armature (1g) being located inside said cap (3h); - four insulators (2c) consisting of portions of simply curved wire spring effect, respectively recessed on one side in the ends (1h) of said branches, and the other at certain points (3i) of said cap (3h) . 8. Device according to the preceding claim, characterized in that the insulators (2c) are each constituted by a complete loop of generally circular shape. 9. Device according to one of the two preceding claims, characterized in that the interface area between the support (1) and said cap (3h) is filled by a flexible material provided to ensure sufficient freedom of relative movement between the cap (3h) and the support (1), and maintain the windproof properties normally offered by the cap. 10. Device according to claim 9, characterized in that said material is a silicone molded membrane (1i) forming a bellows.