EA000858B1 - Inertial vibration transducers - Google Patents

Abstract

1. An inertial vibration transducer (9) for exciting bending waves in an acoustic radiator, characterized in that comprising a plate-like piezo-electric bender and a mass arranged along the periphery of the bender and secured to the bender centrally for rigid fixing the bender to the acoustic radiator of a distributed mode, the arrangement being such that a substantial part of the bender is spaced from the acoustic radiator for movement relative thereto. 2. A transducer according to claim 1, characterized in that the mounting means for rigid fixing the piezo-electric bender to the acoustic radiator is a lightweight rigid member. 3. A transducer according to claim 1 or 2, characterized in that comprises a dome-like housing arranged above the piazi-electric bender and rigidy fixed to the acoustic radiator. 4. A loudspeaker having an acoustic radiator, characterized in that comprises a transducer according to any one of the preceding claims.

Description

Technical field

The invention relates to transducers, and more specifically to oscillation transducers for loudspeakers containing panel-shaped acoustic emitting elements.

State of the art

GB-A-2262861 proposes a panel-shaped loudspeaker comprising:

a resonant multi-mode radiating element, which is a single multilayer panel formed of two surface layers of material with an intermediate core in the form of a transverse cellular structure, the panel being such that it has a bending stiffness ratio (B) in all directions to the cubic degree of the panel mass per unit a surface area (μ) of at least 10;

mounting hardware that holds the panel or loosely mounts it to the chassis without damping; electromechanical excitation means connected to the panel, which serves to excite multi-mode resonance in the radiating panel in response to an electromagnetic input signal within the operating frequency band of the speaker.

French patent FP-A-2569931 in the name SAWAFUJI discloses a piezoelectric vibrator and loudspeaker comprising a piezoelectric plate loaded with a mass located close to its center of gravity and connected to the diaphragm of the loudspeaker subjected to vibrations through the periphery of the piezo-plate.

Disclosure of invention

Embodiments of the present invention utilize elements of this type and with such construction and configuration that can be generally and / or specifically obtained by embodying the ideas of our simultaneously pending international application PCT No. WO 97/09842 with the same filing date. Moreover, such elements have the ability to withstand and distribute the input vibrational energy through the bending of waves in the working area (s), which is transverse to the thickness, often, but not necessarily, to the edges of the element (s); they are configured with anisotropy or without anisotropy of bending stiffness so that the vibration components in the resonance mode are distributed over said zone (s) for favorable acoustic coupling with ambient air, while said zone has predetermined preferred locations or locations of the conversion means, in particular , its operationally active or moving part (s), effective with respect to acoustic vibrational activity in said zone (s), and signals, usually electric physical, corresponding to the acoustic content of such vibrational activity. In the simultaneously considered international publication No. WO 97/09842 with the same filing date, it is said about the use of such elements in “passive” acoustic devices without converting means, for example, for reverb or for acoustic filtration, or for acoustic “expression” in space or in a room , and in “active” acoustic devices with converting means, for example, in an unusually wide range of sound sources or loudspeakers, when the input signals are input, converted to sound, or in microphones when exposed to sound that is converted to other signals.

This invention, in particular, relates to active acoustic devices in the form of speakers.

The above-mentioned elements are called acoustic emitters with a distributed type of oscillation and differ in the same way as in the aforementioned PCT application and / or otherwise, if in this case it is specifically provided.

The invention is an inertial vibration transducer for exciting an element having the ability to withstand and propagate the input vibrational energy by bending waves in at least one working zone extending transversely to the thickness so that the vibration components in the resonance mode are distributed over said at least one zone , in the presence of predetermined peripheral placements or locations within the said zone for the conversion means, and the presence of the converter, mounted on the said element in one of the mentioned locations or locations to cause oscillations of the element to ensure its resonance, with the formation of an acoustic emitter, which in resonance mode produces an acoustic output signal, the transducer has a plate piezoelectric means of bending, the tool located in the center plate bending means for mounting bending means on the element subjected to vibrations, and the device is such that itelnaya portion bending means is spaced from the member for movement relative thereto, and the periphery of the bending means attached mass. The mounting means may be a lightweight rigid element. The piezoelectric bending agent may have a crystalline shape. According to another aspect of the invention, it can be a loudspeaker characterized by the presence of an element capable of withstanding and distributing the input vibrational energy by means of bending waves in at least one working zone extending transversely to the thickness so that the vibrational components in the resonance mode are distributed according to at least one zone, in the presence of predetermined peripheral locations or locations within the said zone for the conversion means, and when Ichii above described transducer mounted on said member at one of said locations or placements for the oscillation element to ensure its resonance to form acoustic radiator, which creates the acoustic resonance mode output signal.

Brief Description of the Figures

The invention is illustrated by way of example, schematically represented in the accompanying drawings, in which in FIG. 1 is a diagram showing a loudspeaker with a distributed type of oscillation, which is described and claimed in our simultaneously considered international publication WO 97/09842;

in FIG. 2a is a partial sectional view taken along line AA in FIG. one;

in FIG. 2b is an enlarged cross-sectional view of a distributed-mode emitter, of the kind shown in FIG. 2a, with two alternative designs being presented;

in FIG. 3 is a diagram of an embodiment of a converter.

BEST MODES FOR CARRYING OUT THE INVENTION

Referring to FIG. 1, it shows a panel-shaped loudspeaker 81 of the type described and claimed in our simultaneously pending international publication WO 97/09842 with the same date, comprising a rectangular frame 1 supporting an elastic suspension 3 around its inner periphery that holds the panel 2 sound radiation with a distributed type of oscillation. A converter 9, for example, one that is described in detail in our simultaneously considered international publications WO 97/09859, WO 97/09861, WO 97/09858 with the same date, is completely and completely installed on panel 2 or in it in a given place, determined by the dimensions of X and Y, the position of this place being calculated as described in our simultaneously considered international publication WO 97/09842 with the same date, in order to excite bending waves in the panel, causing the panel to resonate to emit an acoustic output signal.

The transducer 9 is driven by an amplifier 0 0 0 signals, for example, an audio frequency amplifier connected to the transducer by means of conductors 28. The amplifier loading and power requirements can be quite normal, like usual diffuser-type speakers, with a sensitivity of about 86-88 dB / W under loading conditions indoors. The total load resistance of the amplifier is mainly 6 ohms, and the control power is 20-80 watts. If the core of the panel and / or its surface layers are made of metal, they can be made so as to act as a heat sink from the converter so as to remove heat from the motor winding of the converter and thereby improve power control.

In FIG. 2a and 2b show partial typical cross-sections of a speaker (81) according to FIG. 1. In FIG. 2 a shows that frame 1, suspension 3 and panel 2 are connected to each other by means of corresponding adhesive joints 20. Suitable materials for the frame include light edging, for example, edging for paintings made of extruded metal, for example, aluminum alloy or plastic . Acceptable suspension materials include resilient materials such as foam rubber or foam. Suitable adhesives for compounds 20 are epoxy, acrylic and cyanoacrylate, etc. adhesive materials.

In FIG. 2b shows on an enlarged scale that panel 2 is a rigid and lightweight panel having a core 22, for example of rigid foam 97, such as cross-linked polyvinyl chloride, or of a cellular matrix 98, i.e. a honeycomb matrix made of metal foil, plastic or the like, with cells extending transversely to the plane of the panel and covered by opposing surface layers 21, for example, of paper, cardboard, plastic or metal foil, or a metal sheet. If the surface layers are made of plastic, they can be reinforced with fibers, for example, carbon, glass, Kevlar (RTM) or a similar material in a manner that is well known per se in order to increase their elastic modulus.

Thus, the materials under consideration, the surface layer and the reinforcing materials include carbon, glass, Kevlar (RTM), Nomex (RTM), i.e. aramid, etc. fibers in various layers and fabrics, as well as paper, bound paper laminate, melamine and various synthetic plastic films with a high modulus of elasticity, such as Mylar (RTM), Kaptan (RTM), polycarbonate, phenolic, polyester or related plastics, reinforced with fiber, etc., and a metal sheet or foil. A study of the Vectra index of liquid crystal polymer thermoplastics shows that they may be suitable for molding by injection molding to obtain ultra-thin surface layers or shells of small size, say, up to about 30 cm in diameter. This material itself forms an oriented crystal structure in the direction of introduction , with a preferred orientation for a good distribution of triple energy from the point of excitation to the perimeter of the panel.

In addition, this molding of this and other thermoplastics allows the molding tool to convey the location and characteristics, for example, grooves and rings, for the precise placement of transducer parts, for example, motor windings and magnetic suspensions. It is estimated that with somewhat weaker core materials, it would be preferable to increase the thickness of the surface layer in places, for example, in a certain zone or annular space, up to 150% of the transducer diameter, in order to strengthen this zone and to relate vibration energy to the panel in a useful way. With these means, in the case of softer foams, the high-frequency response will be improved.

The core layer materials considered include fabricated meshes or corrugations of sheets or foils made of aluminum alloy or Kevlar (RTM), Nomex (RTM), smooth or document paper and various synthetic plastic films, as well as foamed plastics or foam or from cellulosic materials and even from airgel metals with an acceptably low density. Some acceptable core layer materials effectively demonstrate acceptable self-formation of the surface layer during their manufacture and / or, in other words, have sufficient inherent rigidity for use without a layered structure between the surface layers. Known for its high performance properties is a cellular core material having the trade name "Rohacell", which may be suitable as a radiation panel and which has no surface layers. In practical terms, the task is to provide the utmost lightness and rigidity acceptable to obtain a specific result, especially including optimization of favorable factors provided by the surface layers and the core, and the transitions between them.

In some of the preferred compositions for the panel, surface layers of metals and metal alloys are used, or, alternatively, carbon fiber hardening, both of them, as well as designs with an Airgel alloy or a core with a metal cellular structure, will have a significant property in regarding shielding of radio frequencies, which would be very important in some cases of use in electromagnetic compatibility. A conventional panel or loudspeaker of a diffuser type is not characterized by the ability of shielding with electromagnetic compatibility.

In addition to the preferred shape of the piezoelectrodynamic transducers, they have negligible electromagnetic radiation or magnetic scattering fields. Conventional loudspeakers have significant magnetic fields, the length of which reaches 1 m, unless special compensation countermeasures are taken.

If it is important to preserve the shielding in a particular case, then it can be connected to the electrically conductive parts of the corresponding panel (DML) of the speaker with distributed mode or electrically conductive foam, or a similar interface can be used to mount the edges.

Suspension 3 may dampen the edges of panel 2 to prevent excessive movement of its edges. In addition, or alternatively, additional damping can be applied, for example, in the form of overlays associated with the panel at selected locations to dampen excessive movement in order to ensure uniform distribution of resonance across the panel. The pads can be made of a material based on bitumen, which is usually used in conventional speaker housings, or it can be an elastic or rigid polymeric sheet material. Some materials, especially paper or cardboard, and some cores can be self-damping. If desired, the damping in the panel structures can be enhanced by the use of adhesive substances that, when cured, become resilient rather than rigid.

Mentioned effective selective damping involves a certain application to the panel, including sheet material of those means that are constantly associated with it. Edges and corners can be especially important for the prevailing and to a lesser extent propagated low-frequency modes of vibration of the panel. Fixing the damping means at the edges can be useful so that the panel together with its aforementioned sheet material is completely framed, although the corners can often be relatively free, say, in the case of a desired extension of the range for operation at lower frequencies. Fastening can be carried out by means of adhesive or self-adhesive materials. Other forms of useful damping / especially with respect to finer effects and / or mid and higher frequencies, can be provided by appropriate masses or masses attached to the sheet material at predetermined effective middle local locations of said zone.

The acoustic panel described above is a bi-directional panel. Sound energy from the rear side does not have a strong phase relationship with sound energy from the front side. Therefore, in this case, there are advantages in the total summation of the acoustic power in the room, a uniform distribution of sound energy over the frequency, reduced effects with respect to reflected and standing waves, as well as the advantage of excellent reproduction of natural space and the environment in reproduced recordings sound.

Although the radiation from the acoustic panel is largely non-directional, some of the information associated with the phase increases away from the axis. To improve the focus of the illusory stereo display, placing the speakers, like pictures, at the usual height of a standing person is comparable to the benefit of moderate off-axis placement for a normally sitting listener, while optimizing the stereo effect. Similarly, triangular left / right geometry with respect to the listener provides an additional angular component. This way you can get a good stereo effect.

Compared to playing a regular speaker, this provides an additional advantage for a group of listeners. The characteristic nature of the acoustic panel propagation of sound radiation provides a sound volume that does not obey the quadratic law of inversion for the distance touching the equivalent point source of radiation. Since the intensity drop at a distance is much smaller than that assumed by the quadratic inversion law, if the listeners are located outside the center or the listeners are unsuccessful, the sound intensity field of the panel speakers provides an excellent stereo effect compared to conventional speakers. This is due to the fact that the listener, who is not centered, does not experience inconvenience due to a dual problem due to being in the vicinity of the near speaker, firstly, due to an excessive increase in volume from a nearby speaker, and due to a corresponding decrease volume from the remote speaker.

The advantage also lies in obtaining a flat, lightweight, panel-shaped loudspeaker with a pleasant appearance and good sound quality, which requires only one transducer and in which there is no transition over the entire sound range for each panel aperture.

In FIG. 3 shows an embodiment of the construction of a piezoelectric transducer 9, in which a disk-shaped piezocrystalline bending means 27 is mounted centered on one end of a light and rigid cylindrical block 93 of rigid foam plastic, which is rigidly fixed in the hole 20 in a radiation panel 2 with a distributed type of oscillation, for example , by means of an adhesive, the said end of the block 93 protruding from the front surface of the panel 2, so that the periphery 31 of the bending means 27 is free but suspended adjacent a front surface of the panel 2. The ring 25 of plastic, for example of polyvinyl chloride with a mineral filling is rigidly fixed to the periphery of the piezoelectric bending means 27 in order to add mass to the free periphery of the piezo bending means. Thus, when the transducer is excited by an acoustic signal, the bending piezoelectric means 27 undergoes vibrations and, due to its mass, excites bending waves in the panel 2 to cause the panel to resonate and emit an acoustic output signal. The transducer 9 can be covered with a vaulted housing 26, which is rigidly attached to the panel 2, providing protection for the transducer.

Claims (4)

1. A transducer for exciting bending vibrations in an acoustic emitter, characterized in that it contains a plate piezoelectric bending element with a mass located at the edge of this element and attached to this element in its center means for rigidly attaching this element to a distributed acoustic emitter in such a way that the element does not directly come in contact with the acoustic emitter and has the ability to move relative to it. 2. The transducer according to claim 1, characterized in that the means for rigidly attaching the piezoelectric bending element to the acoustic emitter is a light, rigid element. 3. The Converter according to claim 1 or 2, characterized in that it contains a vaulted housing located on top of the piezoelectric bending element and rigidly attached to the acoustic emitter. 4. A loudspeaker with an acoustic emitter, characterized in that it comprises a transducer according to any one of paragraphs. 1-3.