SK25598A3 - Inertial vibration transducers - Google Patents

Abstract

An inertial vibration transducer (9) characterised by a plate-like piezo-electric bender (27) and means (20, 93) adapted to mount the bender on a member (2) to be vibrated, the arrangement being such that a substantial part of the bender is spaced from the member for movement relative thereto.

Description

Technical field

The invention relates to a transducer, in particular a vibration transducer of loudspeakers comprising panel acoustic radiating elements.

BACKGROUND OF THE INVENTION

GB-A-2262861 discloses a panel loudspeaker comprising a resonant multi-mode radiator consisting of a uniform composite plate comprising a core having a transverse chamber structure surrounding the two shells, the plate having a bending strength ratio (b) in all directions to a cubic power of a panel weight per unit area (μ) of at least 10, a fastener carrying or supporting said plate to the support body in a free, non-damped manner, and an electromechanical excitation means designed to drive multi-mode resonance in the radiating an electrical input board within the working frequency range of the speakers.

FR-A-2,596,931 discloses a piezoelectric vibrator and a loudspeaker comprising a mass loaded piezoelectric plate located near its center of gravity and coupled to the loudspeaker diaphragm to vibrate over the edge of the piezoelectric plate.

SUMMARY OF THE INVENTION

Individual embodiments of the invention use elements having properties, e.g. the structure and configuration generally and / or specifically described in WO 97/09842 relating to this application. Thus, these elements have the ability not to dampen and propagate the input vibration energy by bending waves in the functional surface or functional surfaces that extend transversely to the thickness of the element, often but not necessarily at the edge of the element or elements. They have a configuration with or without anisotropy of flexural strength such that resonant modes of flexural wave vibration distributed over the entire surface of the element favorably affect the acoustic connection with the ambient air, and have predetermined preferred positions or locations for the transducer means, in particular its functional active or moving parts effective depending on the acoustic vibration activity in the area and on signals, usually electrical, corresponding to the acoustic level of such vibration activity. In co-pending international patent application WO 97/09842, which has the same priority, elements for passive acoustic devices without converter means, such as e.g. reverberation or acoustic filtering or acoustic sounding equipment for a room or room, as well as active acoustic devices with converter means, including sound sources or loudspeakers with a remarkably wide frequency range, where the input signals are applied to sound or microphones, that are exposed to the sound they transmit to other signals.

In particular, the invention relates to active acoustic devices in the form of loudspeakers. The elements in these devices are called distributed mode acoustic radiators and have the characteristics described in patent application WO 97/09842 or other characteristics described in this patent application.

SUMMARY OF THE INVENTION The present invention provides an inertial vibration transducer for driving an element having the ability to dampen and propagate input vibration energy by bending waves in at least one functional area extending transversely to its thickness such that resonant bending vibration modes are distributed over at least one area and predetermined preferred positions. within the surface for the transducer means, and the transducer mounted on the element in one position to vibrate the element to achieve resonance of the acoustic radiator element which provides acoustic output during its resonance. The transducer has a plate acoustic output during its resonance. The transducer has a plate piezoelectric bending member and means for attaching the bending member to the element to be vibrated (the attachment means) located at the center of the plate bending member. The plate member is disposed relative to the member to be vibrated such that a substantial portion of the bending member is spaced from the member to move the bending member relative to the member, the transducer further comprising a mass attached to the edge of the bending member. The fastening means may be a lightweight rigid element. The piezoelectric bending member may be in crystal form. According to another aspect, the present invention provides a loudspeaker comprising an element having the ability to not dampen and propagate vibration energy by bending waves in at least one functional surface extending transversely to its thickness so as to have resonant bending vibration modes distributed over at least one surface and predetermined positions for the transducer means. , and a transducer mounted on the element in one of the vibration positions of the element to achieve resonance of the element constituting the acoustic radiator that provides the acoustic output during its resonance.

Brief description of the figures

The subject matter of the invention will become more apparent from the following description of exemplary embodiments of the invention, with reference to the accompanying drawings, in which FIG. 1 shows a distributed mode loudspeaker as described and claimed in WO 97/09842, which is related to this application, FIG. 2a shows a partial cross-section along line A-A shown in FIG. 1, FIG. 2b shows an enlarged cross-section of a distributed mode radiator of the same kind as shown in FIG. 2a, wherein this figure also shows two alternative structures of the emitter, FIG. 3 shows a cross-section of a first embodiment of a converter, FIG. 4 shows a cross-section of a second embodiment of the converter, FIG. 5a shows a cross-section of a third embodiment of the converter.

DETAILED DESCRIPTION OF THE INVENTION

In FIG. 1, there is shown a panel loudspeaker 81 of the same type as described and claimed in the related application WO 97/09842 with the same priority, the loudspeaker comprising a rectangular frame 1 carrying a flexible hinge 3 around an inner edge carrying a sound emitting panel 2 with distributed modes . Converter 9, e.g. the transducer described in detail in the related patent applications WO / 09859, WO97 / 09861, WO97 / 09858 with the same priority is mounted wholly and exclusively on panel 2 or panel 2 at a predetermined position defined by x and y coordinates, calculated as this is described in co-pending application WO97 / 09842 with the same priority to generate a waveform in the panel to cause resonance of the panel forming the radiator providing acoustic power during its resonance.

Said transducer 9 is driven by a signal amplifier 10, e.g. a low frequency amplifier coupled to the transducer by means of conductors 28. The amplifier load and power requirements can be quite normal, i. as with conventional conical loudspeakers, with a sensitivity of the order of 86 to 88 dB / W under ambient load conditions. The impedance load of the amplifier has a strong resistive character at 6 Ω and a load rating of 20 to 80 W. If the core of the panel and / or its sheath are made of metallic material, they serve as heat dissipation of the converter to dissipate heat from the converter's coil and improve performance.

In FIG. 2a and 2b show typical cross-sections of the loudspeaker 81 in FIG. 1. FIG. 2a, it is clear that the frame 1, the elastic hinge 3 and the panel 2 are connected to each other at the joints 20 by means of adhesive means. Said frame may be a lightweight frame, e.g. an image extruded frame of metallic material, e.g. aluminum alloy or plastic. Suitable materials for the flexible hinge may be flexible materials, e.g. foam rubber and foam plastic. Suitable adhesives for the joints 20 may be epoxy, acrylate and cyanoacrylate resins, or other adhesives.

It can be seen from Figure 2b that the panel 2 is formed by a rigid light panel having a core 22 made e.g. rigid plastic foam 97; such as e.g. cross-linked polyvinyl chloride, or a core structure 98 with a cellular structure such as e.g. a honeycomb-shaped core made of metal foil, plastic or other similar material, the chambers of the structure extending transversely to the panel surface and closed by opposing shells 21 made of a material such as e.g. paper, plastic or metal foil. If the sheaths are made of plastic, the sheaths can be reinforced in a known manner to increase their modules, e.g. carbon, glass, Kevlar fibers, and the like.

Thus, the envisaged sheathing materials and reinforcements include carbon, glass, Kevlar (RTM), Nomex (RTM), i.e., carbon, glass, and liner. aramid fibers in different layers and bonds, also paper, laminated paper, melamine and various synthetic plastic films with high modules, such as e.g. Mylar (RTM), Kaptan (RTM), polycarbonate, phenolic, polyester or related plastics, fiber reinforced plastics and metal foils. On the basis of the Vectra quality research of liquid thermoplastics, it has been found that polymer thermoplastics can be used to form very large polymer-based crystals of thin coatings of small size, i.e., in the case of thermoplastics. with a diameter of about 30 cm by injection. This material itself forms an oriented crystalline structure in the injection direction, which is an advantageous direction for good propagation of high sound frequencies from the drive point towards the edge of the panel.

The additional shaping of said or other thermoplastics allows the molding tools to have locating and registration features, such as grooves or rings, to precisely locate the parts of the transducer, e.g. excitation coil and / or magnet hinge. In addition, in the case of a weaker core material, it is preferable to locally increase the thickness of the sheath, e.g. in a surface or ring with a diameter of up to 150% of the sensor diameter, to amplify the surface and advantageously couple the vibration energy in the panel. In this way, the high-frequency response can be improved for some softer foam materials.

The envisaged core layer has a honeycomb structure or a corrugated structure formed of aluminum alloy foil, Kevlar (RTM), Nomex (RTM), unpainted paper or paperboard and sheets of various synthetic plastics, also cellular or foamed plastic or fiber materials, even aerogel metals if they have a suitably low density. Some suitable core layer materials have a self-sheathing capability in manufacture and / or have sufficient strength to be sandwiched between the sheath layers without the use of lamination. The core-material with a high-performance cellular structure is known under the trade name Rohacell and is suitable for a radiant panel without having a jacket. In practical terms, the aim is to achieve overall lightness and strength suitable for specific purposes, which in particular involves optimizing the contributions from the core, the skin layers and the transitions between them.

In several preferred embodiments of the panel, sheaths of metal and metal alloys or, alternatively, carbon fiber reinforced materials have been used. These panel designs as well as panel designs in which the Aerogel alloy is used or in which the core has a honeycomb structure of metallic material have a high frequency shielding capability that is important for the compatibility of the electromagnetic energy emitting device. Conventional cone-type panels or loudspeakers do not have shielding capability.

In addition, preferred forms of piezoelectric transducers and electrodynamic transducers have negligible electromagnetic radiation or stray magnetic fields. Conventional loudspeakers have a large magnetic field, up to a distance of up to 1 m, unless specific compensatory countermeasures are taken.

Where it is important to provide or maintain shielding in a given application, the electrical connections may be made such that the conductive portions of a suitable DML panel, the electrically conductive foam, or similar interfaces can be used for attachment in the edge region.

The hinge 2 may damp the edges of the panel 2 to prevent excessive movement of the edges of the panel. In addition, additional buffering means, e.g. means in the form of patches associated with the panel at selected positions to damp the excessive movement of the panel to achieve a uniform resonance distribution across the panel surface. These patches may be made of bitumen-based material typically used in conventional loudspeaker enclosures or a flexible or rigid polymeric sheet material. Some materials, especially paper and board and some types of core materials, may be self-muting. If desired, damping can be enhanced in the construction of the panels using adhesives that are flexible and not only rigid when cured.

Said effective selective damping comprises specific panel applications comprising a sheet material of the composition permanently associated with the panel. The edges and corners may be particularly important for the dominant and in relation to the less dispersed low frequency modes of the bending vibration of the panel described in this application. The edge fastening of the damping means may advantageously lead to a panel with a completely framed sheet material, although at least its corners may often be relatively free for the necessary elongation of the panel in low frequency panel operation. The attachment can be carried out by means of adhesive or self-adhesive materials. Other forms of useful damping, particularly with respect to a number of minor effects and / or intermediate and higher frequencies, may be accomplished by means of a suitable mass or masses attached to the sheet material at predetermined effective center positions on the surface.

The above panel is indeed two-dimensional. The sound energy from the rear of the panel is not strongly phase related to the sound energy from the front of the panel. This brings the advantage of the total sum of space, frequency, sound energy limited by the effect of acoustic performance in a given with uniform distribution reflecting standing waves and good reproduction of natural space.

While the sound or radiation from the acoustic panel is largely non-directional, the percentage of phase-related information outside the speaker axis increases. To improve the focusing of artificial stereo listening, positioning the speaker at a height at which images are usually hung, i.e. at the usual height of a standing person, gives the normal seated listener optimal stereo listening even when in a position slightly deviated from the axis speaker. This triangular left / right geometry relative to the listener provides an additional angular component. This gives a good stereo effect.

This is another advantage for a group of listeners compared to conventional loudspeaker reproduction. Given the truly scattered nature of the acoustic panel of the acoustic panel, the acoustic panel provides an acoustic volume to which the rule of decrement with a square distance to the equivalent point source does not apply. As a result, for a listener sitting off the axis of the speakers, or at a location not very suitable for listening, the panel speaker field strength enhances a better stereo effect compared to conventional speakers. This is because the listener located outside the center of action of all speakers does not suffer from two drawbacks, which are usually applied near the speakers. The first of these is the excessively increased perceived loudness of the proximity loudspeaker, and as a result of what is the second one, the perceived loudness of the other loudspeakers.

Another advantage of the flat, lightweight panel loudspeaker is its visual attractiveness, good sound quality, and the requirement for only one transducer, and this loudspeaker does not require a switch over the entire sound range per panel diagram.

Fig. 3 shows one embodiment of a piezoelectric transducer 9 in which a crystal disk piezoelectric bending member 27 is secured at its center at one end of a lightweight rigid cylinder 93 made of rigid foam plastic and fixed in an aperture 20 in a radiated panel 2 with distributed modes, e.g. using adhesives. One end of the cylinder 28 extends from the face of the panel 2 so that the edge 31 of the bending member 27 is loosely hinged at a location adjacent to the face of the panel 2. To add mass to the free edge of the piezoelectric bending member 27 plastic, e.g. mineral filled with polyvinyl chloride. When the transducer is excited by an acoustic signal, the piezoelectric bending member 27 vibrates and, as a result, its mass causes bending waves in the panel 2, causing the panel to resonate and produce an acoustic output. The transducer 9 may be covered by a dome 26 which is attached to the panel 2 to protect the transducer.

The piezoelectric transducer 9 in FIG. 4 comprises a disc-shaped piezoelectric bending member 27 secured by its edge 31 to the surface of the panel 2, e.g. by means of adhesives, the central portion of the bending member 27 being hinged freely through the cavity 29 formed in the panel 2 such that only the edge 31 of the bending member 27 is in contact with the panel. A mass 25 is attached to the center of the bending member 27, e.g. a plastics material, wherein a damping pad 30 of a resilient material such as e.g. elastic polymer.

The acoustic signal applied to the piezoelectric transducer 9 causes vibration of the bending member 27, which in turn bends in the panel 2. The excitation effect of this transducer is enhanced by loading the exciter 27 with a mass 25 to increase its inertia.

The embodiment of the converter 9 in FIG. 5 is the same as that of FIG. 4, except that in this embodiment, the transducer comprises a pair of piezoelectric bending members 27 which are mounted on opposite sides of the cavity 29 extending through the panel 2 to operate the transducer in a dual action mode. In this embodiment, the centers of the two bending members 27 are connected to each other by a common mass 25 provided with resilient damping pads 30 positioned between each bending member 27 and the mass 25.

Industrial usability

The converter according to the invention has a simple construction and is effective in various applications.

Claims (4)

An inertia vibration converter for driving an element having the ability to dampen and propagate input vibration energy by bending waves in at least one functional surface extending transversely to its thickness such that resonant bending vibration modes are distributed over at least one surface and predetermined positions within the surface for a transducer means, and a transducer mounted on the resonance gain element of the acoustic radiator element which provides an acoustic output during its resonance, characterized in that it has a plate piezoelectric bending member (27) and means (93) for attaching the bend member to the transducer. an element (2) to be vibrated disposed in the center of the plate bending member (27), wherein the arrangement of the plate bending member (27) and the means (93) is such that a substantial portion of the bending member (27) is offset from the element (2) for moving the bending member (27) relative to the member (2), the converter (9) further comprising a mass (25) attached to the edge of the bending member (27). An inertia vibratory transducer according to claim 1, characterized in that the means (93) for attaching the bending member (27) to the element (2) is a lightweight rigid element. An inertia vibratory transducer according to claim 1 or 2, characterized in that the piezoelectric bending member (27) is in the form of a crystal. A loudspeaker comprising an element (2) having the ability to dampen and propagate the input vibration energy by bending waves in at least one functional surface extending transversely to its thickness such that the resonant modes of bending vibration are distributed over at least one surface and a predetermined advantageous position within the surface for the transducer means, and a transducer (9) according to any one of the preceding claims disposed on the element (2) in one of the vibration positions of the resonance element of the acoustic radiator element providing acoustic output during its resonance.