Underwater acoustic projector

Abstract

The present invention relates to an acoustic projector intended to operate at moderate depths of up to 3 m without the need for subsequent compensation and efficiently reproduce signals below 100 Hz. The acoustic projector consists of a sealed container comprising at least one speaker, said speaker being characterised in that it is based on a magnetic motor with a permanent magnet, a moving coil and a cylindrical coil holder; a diaphragm that radiates the sound though the water and is connected to a flat rubber suspension attached to the cover of the container by means of a support; and an exciter cylinder secured at one end to the coil holder and at the other end to the diaphragm. The coil holder is in contact with a membrane, which can be secured by suspensions.

Description

[0001] DESCRIPTION

[0002] UNDERWATER ACOUSTIC PROJECTOR

[0003] Object of the invention

[0004] The present invention relates to a new type of underwater acoustic projector, specifically configured for use in underwater environments up to 3 meters deep.

[0005] The invention falls within the industrial sector related to electrodynamic acoustic projectors and, specifically, to projectors intended for underwater applications.

[0006] Background of the invention

[0007] It is well known that electrodynamic acoustic projectors for underwater applications are scarce, and this scarcity is attributed to their lower performance and power capabilities compared to other technologies such as piezoelectric or magnetostrictive. However, unlike the latter, which, due to their physical properties, are deficient in low-frequency performance, electrodynamic projectors allow access to the lower part of the audible spectrum with high linearity and high sound pressure.

[0008] In this regard, two types of electrodynamic acoustic projectors are known for underwater applications: those that require internal pressure compensation when submerged in water; and those that, due to their construction, do not. Both types have a considerable radiation surface, resulting in a force originating from hydrostatic pressure that depends on the depth.

[0009] In the first type, compensation for inward displacement due to pressure exerted by the medium, which increases with working depth, is achieved by applying pneumatic pressure inside the enclosure housing the loudspeaker. An example of this type of projector is the one disclosed in document FR2764160. In the second type, the enclosure itself, or part of it, is used as a diaphragm, which gives an idea of ​​its high rigidity when acting as a diaphragm, severely limiting its low-frequency response. An example of this type of projector is the one disclosed in document US3670299.

[0010] The large diaphragm size required in both cases means that, since the imaginary part of the low-frequency radiation impedance is inductive, the mass of water to be moved during the displacement of the moving assembly is considerable. For this reason, extremely rigid suspensions are used in the first case, while in the second, the suspension and diaphragm are replaced by part of the chassis. This significantly hinders movement at low frequencies, resulting in a reduction of the audio level in the low frequencies and a poor response below 100 Hz.

[0011] This limitation considerably compromises its application in situations that require the reproduction of low-frequency sounds, between 60 Hz and 120 Hz, such as those generated by boat engines, or windmills in marine environments.

[0012] It should be noted that these well-known projectors contain a source of non-linearity due to the inclusion of elements that rub against each other during operation, in order to keep the coil centered in the air gap. This causes high harmonic distortion, reducing the fidelity of the reproduced signal.

[0013] Given these known problems, it is necessary to improve the efficiency, quality, and low-frequency response of electrodynamic acoustic projectors to broaden their applicability in scenarios that demand accurate reproduction of specific sounds, thus overcoming the current limitations of this type of technology.

[0014] The present invention described below consists of a new type of acoustic projector that solves two fundamental aspects of the problem previously indicated; firstly, it allows operation at moderate depths of up to 3 m without requiring subsequent compensation; and secondly, it efficiently reproduces signals below 100 Hz.

[0015] The applicant is unaware of any type of underwater acoustic projector that is similar or as advantageous as the one described and claimed below.

[0016] Explanation of the invention

[0017] The invention is intended for use in an underwater environment and, as previously mentioned, this new type of acoustic projector addresses two fundamental aspects to overcome the limitations of the state of the art. Firstly, it allows operation underwater at moderate depths of up to 3 m without requiring subsequent compensation; and secondly, it efficiently reproduces signals below 100 Hz.

[0018] To overcome the existing and known limitations, and to achieve this objective, the underwater acoustic projector that is the subject of the present invention comprises at least one electrodynamic loudspeaker with a magnetic motor based on a permanent magnet, a moving coil, whose wire is wound on a cylindrical support, attached to a membrane, which, at its lower part, is attached to a flexible suspension and, at its upper part, to another suspension located on the periphery of the membrane.

[0019] The loudspeaker is mounted inside a watertight enclosure and serves as an exciter for a smaller diaphragm, which is in turn attached to a flat rubber suspension. This suspension radiates the sound delivered to the loudspeaker via an electrical cable connected to an amplifier located on the surface. The cable is inserted into the enclosure using a cable gland or threaded tightening piece to ensure its watertightness.

[0020] As for the airtight enclosure, which, as mentioned, houses the loudspeakers, it consists of a highly rigid polymer body, such as PVC, and end caps. The loudspeakers are mounted to the inner caps, and the flat suspensions are supported on the outer caps by supports made of polymer materials, such as nylon or any other material that can be extruded and machined. These enclosures are small. The loudspeakers are attached to the chassis caps with screws, while the exposed parts, such as the diaphragm and suspension, are bonded with adhesive. The fact that the parts exposed to the corrosive effects of the marine environment are made of non-metallic materials ensures long-lasting and reliable use in such an aggressive environment. To transmit the signal to the diaphragm, an exciter cylinder is used, attached at one end to the voice coil support and at the other end to the diaphragm.In one embodiment of the invention, this cylinder is made of a resin-based material, also known as a composite, and the fastenings are made, in one embodiment of the invention, using a structural epoxy resin adhesive. This exciter cylinder is designed to provide significant contact surfaces between the two parts, in order to ensure a strong and durable bond.

[0021] In current projectors, the large diaphragm area places considerable stress on it due to the hydrostatic pressure of the fluid when the transducer is submerged. To prevent inward displacement that would impede proper operation, pressure compensation is required at the rear of the transducer, which is often difficult to implement correctly. A system is also needed to keep the coil centered in the air gap by sliding a shaft through the motor. This is a source of nonlinearities that cause significant distortion of the reproduced signal. The advantage of the present invention lies in the significantly smaller diaphragm size compared to current models, which greatly reduces the force exerted on it by the water pressure.The force is proportional to the surface area, and if the diaphragm is circular, it is proportional to the square of the radius. This explains why no further compensation is needed to prevent the coil's resting point from shifting, as the reduced pressure force is counteracted by the additional rigidity provided by the diaphragm's flat suspension, plus that provided by the speaker's own suspensions.

[0022] In this regard, it should be noted that, in the present invention, the actual part of the radiation impedance, R MR , depends on the density of the medium, p0, the propagation speed, c, the frequency and the radius of the diaphragm according to the expression [1]: where K is the propagation constant (k=2*pi*f / c), a is the piston radius and J^x) is the so-called Bessel function of order 1.

[0023] For ka values ​​less than one, approximate expressions are usually used. Considering the previous equation, reducing the diaphragm size, unlike what happens in air where its radiated acoustic impedance is considerably lower than that of the membrane and must be compensated for by increasing the membrane's diameter to the maximum allowed, is the opposite in water. In water, the acoustic impedance is much higher and does not require a large piston diameter. Therefore, reducing the size of the piston does not affect its response and the acoustic pressure it delivers as significantly as it does in air.

[0024] Even so, to improve response in this range and increase power handling, the invention achieves better results when using more than one loudspeaker, that is, with the simultaneous use of at least two transducers based on this same system. This approach seeks to leverage the mutual coupling of the diaphragms to increase sound pressure in the useful operating range, as well as increase the permissible power handling, while reducing the risk of damaging the voice coil due to overheating. When the invention comprises at least two loudspeakers, each is equipped with an additional diaphragm and its own suspension, and each diaphragm is driven by the voice coil. Despite the small size of these diaphragms, good low- and mid-frequency response is achieved due to the high acoustic impedance of water compared to air.This approach eliminates the need for large loudspeakers to generate significant low-frequency sound pressure levels underwater, thus achieving a significant improvement in low-frequency response with this type of electrodynamic transducer. The electrical connection between the loudspeakers is preferably in parallel, provided the resulting impedance is suitable for the amplifier output.

[0025] Furthermore, by using two loudspeakers, the possibility arises that the entire device can be of variable directivity simply by introducing a small time lag between the two radiating systems or, alternatively, an electrical power control that allows varying the ratio between the voltage reaching each of the loudspeakers.

[0026] It should be noted that, throughout the description and claims, the term "comprises" and its variants are not intended to exclude other technical features or additional elements. Brief description of the figures

[0027] In order to complete the description and to aid in a better understanding of the characteristics of the invention, a set of figures and drawings is presented which, for illustrative and non-limiting purposes, represent the following:

[0028] Figure 1: Shows a schematic view of an acoustic projector with a loudspeaker.

[0029] Figure 2: Shows an exterior perspective view of an acoustic project with a loudspeaker.

[0030] Figure 3: Shows an internal section of a loudspeaker and its connection to the sealed enclosure.

[0031] Figure 4: Shows an internal section of the actuating part, the diaphragm and its suspension.

[0032] Figure 5: Shows a schematic view of a dual acoustic projector, i.e., with two speakers.

[0033] Figure 6: Shows a graph with the frequency response of the projector with a speaker submerged in water at a depth of 0.5 m.

[0034] Figure 7. Shows a graph with the frequency response of a commercial UW30 projector, also from Lubell (https: / / www.lubell.com / products / uw30pa / ) measured under the same conditions as the loudspeaker in the previous figure, where these values ​​can be observed in the document “Acoustics: Sound Fields and Transducers” Ed. London: Academic Press. 2019 by Beranek LL, Mellow, T.

[0035] Detailed explanation of some ways of carrying out the invention

[0036] As can be seen in the preceding set of figures, the invention consists of an underwater acoustic projector comprising a hermetically sealed enclosure (1) containing at least one loudspeaker (2), where the enclosure (1) is formed by a body (1a) of polymeric material with at least one outer cover (1b) to which the loudspeaker is attached. In one embodiment, see, for example, Fig. 1, the projector has one loudspeaker; while in another possible embodiment of the invention, see, for example, Fig. 5, the projector has two loudspeakers. Going into greater detail, internally the projector comprises at least one loudspeaker (2) with a magnetic motor based on a permanent magnet (3), a moving coil (4) whose wire is wound on a cylindrical support,

[0037] (5), and the support is in contact with a membrane (8), which, at its lower part, is attached to a flexible suspension (7) and, at its upper part, to another suspension (9), located on the periphery of the membrane (8) and in contact with the lid (1b).

[0038] As previously mentioned, each loudspeaker (2) is mounted inside a watertight enclosure (1), and the loudspeaker acts as an exciter for a diaphragm (11), which is in turn attached to a flat rubber suspension (10). The diaphragm is responsible for radiating the sound delivered to the loudspeaker via a connection to an amplifier (14) with an electrical cable (12), which is inserted into the enclosure (1) through a cable gland (13) to ensure its watertightness. The diaphragm (11) is responsible for radiating the sound in the water.

[0039] To transfer the signal from the loudspeaker (2) to the diaphragm (11), an exciter cylinder is used.

[0040] (6), attached at one end to the coil support (5) and at the other end to the diaphragm (11). These attachments are made using a structural epoxy resin adhesive. The exciter cylinder (6) has a contact surface between the two parts to ensure a strong and durable bond.

[0041] The speaker chassis (2) is attached to the enclosure covers using screws (T), while exposed parts such as the diaphragm (11) and suspension (10) are bonded with adhesive. Specifically, the flat suspensions (10) are attached to the enclosure covers externally using polymer supports (15).

[0042] The electrical connection between speakers (2), in an embodiment comprising at least two speakers, is preferably in parallel.

[0043] This projector configuration, compared to those known in the prior art, allows operation at moderate depths of up to 3 m without requiring subsequent compensation; and it efficiently reproduces signals below 100 Hz. As can be seen in Fig. 6, for a projector with a loudspeaker, a flat frequency response is achieved in the range between 70 Hz and 700 Hz. Specifically, when viewing Figs. 6 and 7, it can be observed that in the range between 70 Hz and 700 Hz, in Fig. 6 (the loudspeaker of the present invention) the response is practically flat, while in Fig. 7 (a conventional loudspeaker) this is not the case.

Claims

CLAIMS 1.- Underwater acoustic projector, comprising a hermetically sealed enclosure (1) and at least one loudspeaker (2), wherein the enclosure comprises at least one lid (1b) and the loudspeaker (2) is housed within the enclosure (1), and characterized in that the loudspeaker (2) is connected to an amplifier (14) with an electrical cable (12), and the loudspeaker comprises a permanent magnet (3) and a moving coil (4) whose wire is wound on a cylindrical coil support (5); a diaphragm (11), which is responsible for radiating the sound in the water, and which is attached to a flat rubber suspension (10) which is attached to the lid (1b) by means of a support (15); an exciter cylinder (6), attached at one end to the coil support (5) and, at the other end, to the diaphragm (11), wherein the coil support (5) is in contact with a membrane (8); and where the membrane (8) is attached at its lower part to a flexible suspension (7) and, at its upper part, to another suspension (9) in contact with the lid (1b). 2- A projector, according to claim 1, wherein the electrical cable (12) is introduced into the enclosure (1) by means of a cable gland (13). 3- A projector, according to claim 1, wherein the speaker chassis (2) is fixed by means of screws (T) to the cover (1b). 4- A projector, according to claim 1, wherein the diaphragm (11) and the suspension (10) are fixed by an adhesive bond. 5- A projector, according to claim 1, wherein the support (15) is joined to the cover (1 b) by an adhesive bond 6- A projector, according to claim 1, wherein the support (15) is made of a polymeric material. 7- A projector, according to claim 1, wherein the exciter cylinder (6) is attached to the reel support (5) and to the diaphragm (11) by an adhesive. 8- A projector, according to claim 7, wherein the adhesive is a structural adhesive in epoxy resin. 9- A projector, according to claim 1, wherein the enclosure (1) is made of polymeric material. 10.- Use of a projector as defined according to any of claims 1 to 9 for underwater environments up to 3 meters deep.

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