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The present invention relates to an acoustic wave guide.
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US-7068805-B2 describes an acoustic wave guide in the shape of an acoustic horn comprising an inner portion, which is a resonant cavity adapted to amplify an acoustic signal. Said acoustic signal is emitted by an acoustic transducer, such as for example a speaker placed at an input orifice of circular shape of said resonant cavity. Said input orifice of circular shape lies on a first geometric plane, which is parallel to a second geometric plane on which an output orifice of circular shape but of greater diameter lies. The resonant cavity is symmetric with respect to a symmetry axis which passes through circular geometric centers of the input orifice and of the output orifice. Disadvantageously, an acoustic pressure wave with spherical wave fronts and a symmetric acoustic beam is propagated towards the outside of the resonant cavity.
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Quantitatively, the acoustic beam may be described by means of an interference figure in the far field described by a function of the sound pressure level of the acoustic pressure wave normalized at the peak sound pressure, measured on logarithmic scale in decibel dB with respect to a direction angle measured in sexagesimal degrees. These are defined by a vertical plane and a horizontal plane, which are perpendicular to each other and with a reciprocal intersection, which is the symmetry axis of the wave guide. A first direction angle lies on the vertical plane, while a second direction angle lies on the horizontal plane. The sound pressure level of the acoustic pressure wave with respect to the first direction angle on the vertical plane shows the same values as the sound pressure level of the acoustic pressure wave with respect to the second direction on the horizontal plane. A main lobe of the acoustic beam is symmetric with respect to the symmetry axis. Secondary lobes of the acoustic beam have a high sound pressure level, to the extent that the acoustic pressure wave has a spherical wave front in all directions both on the vertical plane and on the horizontal plane in the far field.
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Disadvantageously, said wave guide of
US-7068805-B2 does not allow to modify the acoustic beam geometry so as to have a different acoustic beam shape on the vertical plane from the acoustic beam shape on the horizontal plane.
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There are other wave guides in the prior art which attempt to modify the geometric shape of the acoustic beam in order to obtain an acoustic beam which is as spherical as possible on the horizontal plane, while they attempt to increase the directionality of the acoustic beam on the vertical plane so as to limit the angular field in vertical direction and obtain an acoustic beam as flat as possible on the horizontal plane. These attempts are in vain because various unsolved technical problems take over; indeed, the sound is disadvantageously distorted and the acoustic pressure wave energy is dispersed along planes other than the horizontal plane, thus disadvantageously reducing the sound pressure level of the acoustic pressure wave.
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For example,
US4324313 describes an acoustic wave guide with a symmetric resonant cavity with respect to a symmetry axis which individuates a longitudinal axis. The length of the resonant cavity extends following the longitudinal axis from a circular transversal section input orifice to a quadrangular transversal section which is perpendicular to the longitudinal axis. Proceeding longitudinally along the symmetry axis, the shape and dimension of the resonant cavity gradually changes up to an output orifice with elliptical transversal section. Disadvantageously, part of the sound pressure wave is dispersed and a distorted sound is propagated from the output orifice in the portion of resonant cavity in which the transversal shape of the resonant changes.
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In
US4324313 , the function of the sound pressure level of the acoustic pressure wave describes an interference figure which is different on the horizontal plane from that on a vertical plane. The vertical plane passes through a shorter axis of a geometric ellipse corresponding to the elliptical section of the output orifice, while the horizontal plane passes through a longer axis of the geometric ellipse. The secondary lobes of the acoustic beam are also amplified on the vertical plane, thus the wave guide does not obtain a flat acoustic beam because an adequate portion of the sound pressure level of the acoustic pressure wave is also disadvantageously dispersed on the vertical plane.
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US-6059069 describes an acoustic horn wave guide with a transversal section input orifice of circular shape and a resonant cavity, the shape of which changes along a longitudinal axis to a transversal section output orifice of rectangular shape. The shorter sides of a geometric rectangle of the transversal section of the output orifice of rectangular shape are parallel to a shorter axis of a geometric ellipse of the input orifice. In this case, the wave front of the pressure wave outputted from the output orifice is disadvantageously spherical because a central portion of the wave front of the sound wave propagates faster than peripheral portions of the pressure wave front of the sound wave. The pressure wave front is not flat, because although most of the sound pressure level of the acoustic pressure wave remains on a horizontal plane parallel to the longer sides of the geometric rectangle, the secondary lobes remain high along a vertical plane parallel to the shorter sides of the geometric rectangle, thus disadvantageously causing a dispersion of pressure wave energy along the vertical plane and reducing the sound pressure level of the acoustic pressure wave along the horizontal plane. The acoustic signal is disadvantageously distorted and its sound pressure level is reduced.
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Furthermore, the prior art indicates that the input orifice and the output orifice must lie on respective geometric planes which are parallel to each other, otherwise in the known acoustic wave guides the wave front of the acoustic pressure wave would undergo a geometric distortion and the secondary lobes of the acoustic beam would disadvantageously increase the sound pressure level of the acoustic pressure wave also along the vertical plane, thus contributing to creating a distorted acoustic beam, and thus distorting the sound.
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Indeed, the prior art indicates wave guides which modify the shape of the resonant cavity, for example such as
US-5163167 , in which on a horizontal plane parallel to a long side of a rectangular geometric section of an output orifice of rectangular shape, the transversal section of the resonant cavity gradually increases along a longitudinal axis, while on a vertical plane parallel to a short side of the rectangular geometric section of the output orifice of rectangular shape, the section of the resonant cavity increases to a maximum corresponding to a transversal geometric section at half the length of the resonant cavity, to then decrease to the output orifice of rectangular shape. Also in this case, the acoustic beam has very intense secondary lobes also on the vertical plane, thus disadvantageously making the acoustic pressure wave lose energy on the horizontal plane and reducing the sound pressure level of the acoustic pressure wave on the horizontal plane.
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Furthermore, the rhomboidal shape of the resonant cavity on the vertical plane generates multiple reflections of secondary harmonic components of the acoustic beam which distort the sound and make the acoustic pressure wave lose further energy.
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A further unsolved issue of the prior art is the impossibility of directing the wave guide differently from the perpendicular direction to the geometric plane on which the input orifice lies without dispersing too much energy and disadvantageously preventing the positioning of the output orifices according to different directions, thus disadvantageously limiting the angular diffusion field of the sound on the horizontal plane.
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The prior art has attempted in vain to solve the problem of directionality by reflecting the sound in different directions by means of reflecting wall, such as for example
US-6585077-B2 , which has a wave guide with a resonant cavity with an input orifice having a circular transversal section and an output orifice having a circumference crown-shaped transversal section. The resonant cavity extends along a linear longitudinal axis and the two geometric planes on which the input orifice and the output orifice respectively lie are parallel. The output orifice fits a reflecting portion, which has the enormous disadvantage of creating multiple reflections of lower order harmonics, thus creating sound distortion, which disadvantageously disperse the sound pressure level of the acoustic pressure wave and create higher level secondary lobes, and the main lobe is even reflected, causing a disadvantageous loss of the sound pressure level of the acoustic pressure wave and disadvantageously creating an extremely asymmetric acoustic beam with extremely low sound pressure level of the acoustic pressure wave.
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It is the object of the present invention to provide an acoustic wave guide comprising a resonant cavity adapted to amplify an acoustic pressure wave emitted by an acoustic transducer, so that the acoustic pressure wave has high directionality on a vertical plane parallel to shorter sides of a transversal geometric section of an output orifice of rectangular shape of the acoustic wave guide and a broad angular diffusion field on a horizontal plane parallel to long sides of the rectangular transversal geometric section of rectangular shape, thus considerably decreasing the loss of energy of the acoustic pressure wave on the vertical plane and optimizing the sound pressure level of the acoustic pressure wave along the horizontal plane, thus obtaining a flat acoustic wave front, obtaining an acoustic beam with high directionality along a vertical plane, with secondary side lobes of low sound pressure level of the acoustic pressure wave and instead obtaining an angular diffusion field on the horizontal plane with a main lobe and secondary side lobes of high sound pressure level of the acoustic pressure wave, thus diffusing a harmonious distortion-free sound also at higher acoustic frequencies, so that a multiplicity of acoustic wave guides made in this manner can be coupled in an acoustic wave guide array to obtain an extremely amplified, extremely directed acoustic diffusion of high sound pressure level, so that a multiplicity of acoustic wave guides may be coupled to obtain an extremely amplified acoustic diffusion in multiple directions, thus maintaining a high sound pressure level and diffusing a harmonious, distortion-free sound also at high frequencies of the acoustic pressure wave.
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According to the invention, these objects are achieved by a wave guide according to claim 1.
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These and other features of the present invention will become more apparent from the following detailed description of a practical embodiment thereof, shown by way of non-limitative example in the accompanying drawings, in which:
- Figure 1 shows a bottom perspective view of an acoustic wave guide according to the present invention;
- Figure 2 shows a front plan view of the acoustic wave guide;
- Figure 3 shows a rear plan view of the acoustic wave guide;
- Figure 4 shows a side plan view of the acoustic wave guide;
- Figure 5 shows a section view of a vertical plan of the acoustic wave guide according to line V-V in Figure 2;
- Figure 6 shows a section view of a horizontal plan of the acoustic wave guide according to line VI-VI in Figure 2;
- Figure 7 shows a top perspective view of the acoustic wave guide;
- Figure 8 shows a graph into the far field of sound pressure level of an acoustic pressure wave measured in decibel (dB) at a maximum of a main lobe of an acoustic beam of the acoustic pressure wave as a function of a multiplicity of input frequencies in the acoustic wave guide having the same amplitude and measured in Hertz (Hz);
- Figure 9 shows a graph into the far field of a sound pressure level of the acoustic pressure wave measured in dB in a multiplicity of different frequencies on the horizontal plane, as a function of an orientation angle measured in sexagesimal degrees on the horizontal plane;
- Figure 10 shows a graph into the far field of the sound pressure level of the acoustic pressure wave measured in dB in a multiplicity of different frequencies on the horizontal plane, as a function of an orientation angle measured in sexagesimal degrees on the vertical plane;
- Figure 11 shows a graphic representation of small air volumes with wave fronts of an acoustic pressure wave at 8000 Hz in a section of an acoustic cavity of the acoustic wave guide;
- Figure 12 shows a graphic representation of small air volumes with wave fronts of an acoustic pressure wave at 15000 Hz inside a section of the acoustic cavity of the acoustic wave guide;
- Figure 13 shows a perspective view of the multiplicity of acoustic guides with output orifices orientated in multiple directions with respect to one another so as to cover a broader solid angle and form a wave guide array;
- Figure 14 shows a front perspective view of a multiplicity of wave guides with output orifices arranged parallel to one another so as to form a linear array of wave guides;
- Figure 15 shows a top perspective view of a multiplicity of wave guides with output orifices arranged parallel to one another so as to form the linear array of wave guides;
- Figure 16 shows a rear perspective view of a multiplicity of wave guides with output orifices arranged parallel to one another so as to form the linear array of wave guides.
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The above-listed figures, and in particular Figures 1-3 and 7, show an acoustic wave guide 1 comprising a hollow inner portion which forms a resonant cavity 2.
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Said resonant cavity 2 is adapted to amplify an acoustic pressure wave emitted by an acoustic transducer 5, such as for example a speaker positionable at an input orifice 3 of said acoustic wave guide 1 (Figures 13-16).
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Said acoustic transducer 5 may emit, for example, in a range of frequencies from about 1000 Hz to about 20000 Hz so as to test the response of the acoustic wave guide 1.
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As shown in Figure 4, the longitudinal dimension of the resonant cavity 2 extends along a curved longitudinal axis L extending from the input orifice 3 of the acoustic wave guide 1 to an output orifice 4 of rectangular shape of the acoustic wave guide 1.
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As shown in Figure 3, said input orifice 3 has a transversal section 30 geometrically elliptical in shape and lies on a first transversal geometric plane A perpendicular to the longitudinal axis L (Figure 4). The first transversal geometric plane A is individuated in Figures 4-6 by a first section line G.
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As shown in Figures 1-3, 7 said output orifice 4 of rectangular shape has a transversal section 40 geometrically rectangular in shape and lies on a second transversal geometric plane B perpendicular to the longitudinal axis L (Figure 4). The second transversal geometric plane B is individuated in Figures 4-6 by a first section line W.
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As shown in Figure 2, said transversal section 40 of the output orifice 4 of rectangular shape comprises longer sides 420 parallel to a horizontal section line H and shorter sides 410 parallel to a vertical section line V. In Figures 2, 5, a horizontal plane C is individuated by the horizontal section line H. In Figures 2, 6, a vertical plane D is individuated by the vertical section line D. The horizontal plane C is perpendicular to the vertical plane D.
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As shown in Figures 4-5, the curved longitudinal axis L describes a curve on the vertical plane D so that the first transversal geometric plane A forms an acute angle α on the vertical plane D with the second transversal geometric plane B.
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A third section line S, which is perpendicular to the longitudinal axis L, is individuated at a maximum curvature point 15 of the longitudinal axis L. Said third section line S individuates a third transversal geometric plane E. The maximum curvature point 15 is positioned at 1/3 of the longitudinal length of the resonant cavity 2, in which said longitudinal length of the resonant cavity 2 is measured on the longitudinal axis L starting from the input orifice 3 and proceeding longitudinally towards the output orifice 4 of the acoustic wave guide 1.
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The resonant cavity 2 is asymmetric, indeed, as shown in Figure 6, a horizontal section 21 of the resonant cavity 2 is acoustic horn-shaped on the horizontal plane C, while as shown in Figure 5 a vertical section 22 of the resonant cavity 2 is shaped as a curved hollow tube on the vertical plane D, extending its longitudinal dimension along the curved longitudinal axis L.
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As shown in Figure 5, a linear dimension 401 on the vertical plane D of the transversal section 40 of the output orifice 4 of rectangular shape corresponds to the shorter side 410 of the geometric rectangle of the transversal section 40 (Figure 1-2).
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As shown in Figure 6, a linear dimension 302 on the horizontal plane C of the transversal section 30 of the input orifice 3 corresponds to a longer axis 302 of the geometric ellipse of the transversal section 30 of the input orifice 3, instead as shown in Figure 5 a linear dimension 301 on the vertical plane D of the transversal section 30 of the input orifice 3 corresponds to a shorter axis 301 of the geometric ellipse of the transversal section 30 of the input orifice 3 (Figure 3).
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With particular reference to Figure 6, said horizontal section 21 of the resonant cavity 2 provides that on the horizontal plane C walls 10 of the acoustic wave guide 1 gradually broaden the linear dimension of the horizontal plane C of the transversal section of the resonant cavity 2 from the shorter linear dimension 302 on the horizontal plane C of the transversal section 30 of the input orifice 3 to the longer linear dimension 402 on the horizontal plane C of the transversal section 40 of the output orifice 4 of rectangular shape.
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The broadening of the linear dimension on the horizontal plane C of the transversal section of the resonant cavity 2 occurs according to a linear function so that longitudinal sections of the walls 10 are straight on the horizontal plane C, as shown in Figure 6.
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The linear dimension on the horizontal plane C of any transversal section of the resonant cavity 2 is shown in Figure 6, instead the linear dimension on the vertical plane D of any transversal section of the resonant cavity 2 is shown in Figure 5.
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With particular reference to Figure 5, said vertical section 22 of the resonant cavity 2 comprises a narrowed transversal section 20 of the resonant cavity 2 lying on the third transversal geometric plane E.
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Said narrowed transversal section 20 has a linear dimension 201 on the vertical plane D which is shorter than the linear dimension 301 on the vertical plane D of the transversal section 30 of the input orifice 3 and which is shorter than the linear dimension 402 on the vertical plane D of the transversal section 40 of the output orifice 4 of rectangular shape.
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As shown in Figure 5 on the vertical plane D the vertical section 22 of the resonant cavity 2 provides that the walls 10 of the acoustic wave guide 1 gradually narrow the linear dimension on the vertical plane D of the transversal section of the resonant cavity 2 from the linear dimension 301 on the vertical plane D of the transversal section 30 of the input orifice 3 to the linear dimension 201 on the vertical plane D of the narrowed transversal section 20 of the resonant cavity 2.
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Proceeding along the curved longitudinal axis L, on the vertical plane D the walls 10 of the acoustic wave guide 1 gradually broaden the linear dimension on the vertical plane D of the transversal section of the resonant cavity 2 from the shorter linear dimension 201 on the vertical plane D of the narrowed transversal section 20 of the resonant cavity 2 to a longer linear dimension 401 on the vertical plane D of the transversal section 40 of the output orifice 4 of rectangular shape.
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Said narrowed transversal section 20 of the resonant cavity is thus advantageously positioned at 1/3 of the longitudinal length of the resonant cavity 2 being at a maximum curvature point 15 of the longitudinal axis L to respond to physical reasons related to considerations on the position of standing wave nodes present inside the resonant cavity 2.
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Indeed, the energy propagation of the acoustic pressure wave may be described by means of the propagation of vibrational energy among air molecules contained in small air volumes 25 inside the resonant cavity 2, as shown in Figures 11-12. Each of said air molecules acquires and loses part of vibrational energy alternatively over time, to the extent that the energy of the acoustic pressure wave can be described by means of standing waves.
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The position of the narrowed transversal section 20 at 1/3 of the length of the resonant cavity is dictated by considerations related to the fact of advantageously wanting to create an acoustic wave guide for a broad spectrum of high frequencies, because the standing wave node present at 1/3 of the wave length of the standing wave is advantageous for a wide spectrum of high frequency harmonics of the acoustic beam of the acoustic wave pressure.
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With regards to the creation of the acoustic wave guide 1, a first step is provided which comprises measuring of a time delay Dt between a central portion 27 of a wave front 26 of the acoustic pressure wave outputted from the output orifice 4 with respect to peripheral side portions 28 of the wave front 26 of the acoustic pressure wave outputted from the output orifice 4. It is indeed important to consider that the wave front 26 of the acoustic pressure wave would exit from the output orifice 4 of the acoustic wave guide 1 as a wave front 26 with a curvature due to the amplification of the resonant cavity 2 and the result would be an acoustic diffraction figure on a detector placed in front of the output orifice 4.
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The peripheral side portion 28 of a same wave front 26 of the acoustic pressure wave would reach the detector after a time interval Dt with respect to the central portion 27 of the same acoustic pressure wave front 26.
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In order to solve this technical problem, a second step comprises asymmetrically modifying the resonant cavity so that it has different shape and dimensions on the horizontal plane C compared to those on the vertical plane D.
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Firstly, the second step provides that on the horizontal plane C to maintain the resonant cavity 2 in the shape of an acoustic horn so that the acoustic pressure wave emitted by the acoustic transducer 5 being amplified, as shown in Figure 6.
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Secondly and to avoid amplifying also the curved shape of the wave front 26 of the acoustic wave, on the vertical plane D it is provided that the longitudinal axis L is curved in such that the first transversal geometric plane A forms the acute angle α on the vertical plane D with the second transversal geometric plane B and the third transversal geometric plane E perpendicular to the longitudinal axis L is at the maximum curvature point 15 of the longitudinal axis L and on the vertical plane D the vertical section 22 of the resonant cavity 2 extends its longitudinal dimension along the curved longitudinal axis L.
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It must be ensured that inside the resonant cavity 2, a central path of the central portion 27 of the wave front 26 of the wave front 26 of the acoustic pressure wave 26 is equal to a side path of one of the side peripheral portions 28 of the wave front 26 of the acoustic pressure wave so that the detector does not measure any time delay Dt between the two portions 27-28 of the wave front 26 of the acoustic pressure wave.
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The longitudinal axis L must be gradually curved, gradually changing direction along the longitudinal axis L, advantageously so as to avoid reflections of the acoustic pressure wave inside the resonant cavity 2 which would cause loss of energy with consequent loss of sound pressure level of the acoustic pressure wave.
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However, leaving only the curvature of the resonant cavity 2 on the vertical plane D, the sound would be distorted if the application of the creating method of the acoustic wave guide 1 according to the present invention were not prosecuted.
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Indeed, the resonant cavity 2 of the acoustic wave guide 1 may be described as it were divided by a multiplicity of small air volumes 25 comprising an equal number of air molecules by means of which the energy of the acoustic pressure wave is propagated. For example we will consider a small volume of air 23 which has a lower energy density with respect to a second consecutive small air volume 24 with greater energy density. The energy density in the small air volumes 23-25 corresponding to a sinusoidal function of sound pressure level of the acoustic wave which varies over the functioning time t of the acoustic wave guide 1 as a standing wave.
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At the maximum curvature point 15 of the longitudinal axis L and thus of the maximum curvature of the resonant cavity 2 on the vertical plane D, if the linear dimension 201 on the vertical plane D of the narrowed transversal section 20 were not narrowed, then the small air volume 23-24 at the narrowed transversal section 20 would distort its shape in the linear dimension on the vertical plane D to avoid containing more molecules of air with respect to the other small air volumes 25, and thus would not be in phase with the other air volumes 25, thus dispersing the energy of the acoustic pressure wave, thus creating interferences and distorting the sound.
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Instead, by reducing the linear dimension 201 on the vertical plane D of the narrowed transversal section 20 on the vertical plane D, it is reduced the linear dimension on the vertical plane D of the air volume 23-24 at the narrowed transversal section 20 counterpart of a greater curvature of the resonant cavity 2 which would otherwise locally increase the small air volume 23-24. The narrowing makes the small air volume 23-24 at the narrowed transversal section 20 be equal to that of the small air volumes of the resonant cavity 2.
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Surprisingly, the narrowing of the linear dimension 201 on the vertical plane D of the narrowed transversal section 20 of the resonant cavity 2 further allows the air volume 23-24 at the narrowed transversal section 20 to have flat linear dimensions on the flat vertical plane D so as to contribute to making the wave front 26 of the acoustic pressure wave flat in synergistic, advantageous manner.
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A third step of the creation method of an acoustic wavelength 1 thus comprises narrowing the linear dimension 201 on the vertical plane D of the narrowed transversal section 20 of the resonant cavity 2 lying on the third transversal geometric plane E so that said narrowed transversal section 20 has linear dimension 201 on the vertical plane D which is shorter than the linear dimension 301 on the vertical plane D of the transversal section 30 of the input orifice 3 and which is shorter than the linear dimension 401 on the vertical plane D of the transversal section 40 of the output orifice 4 of rectangular shape.
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These three steps of the creation method must be repeated till to obtain the technical effect of this invention, indeed a fourth step of the creation method of the acoustic wave guide 1 comprises a cyclical repetition of the first step, of the second step and of the third step until it is verified that the time delay Dt between the central portion 27 of the wave front 26 of the acoustic pressure wave outputted by the output orifice 4 with respect to the side peripheral portions 27 of the wave front 26 of the acoustic pressure wave output from the output orifice 4 is zero.
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Furthermore, it is worth noting that another advantage of the present invention is due to the fact that the input orifice 3 and the output orifice 4 lie respectively on the first transversal geometric plane A which forms the acute angle α with the second transversal geometric plane B on the vertical plane D. Said gradual curvature of the curved longitudinal axis L further advantageously allows not to create interferences inside the resonant cavity 2, thus avoiding dangerous reflections inside the resonant cavity 2. The curvature of the resonant cavity 2 is related to the frequency of the acoustic pressure wave introduced by the acoustic pressure transducer 5 inside the resonant cavity 2. For high frequencies of the acoustic pressure wave, the acute angle α on the vertical plane D is advantageously comprised between 20 and 80 sexagesimal degrees so as to advantageously reduce internal reflections, and energy losses of the acoustic pressure wave.
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Figure 9 shows a graph into the far field of sound pressure level 9 of the acoustic pressure wave emitted by the acoustic wave guide 1 on the horizontal plane C. The graph measures the sound pressure level 9 of the pressure wave into the far field measured in dB in a multiplicity of different frequencies on the horizontal plane C, as a function of the orientation angle 61 measured in sexagesimal degrees on the horizontal plane C. The sound pressure level 9 of the acoustic pressure wave is a logarithmic measurement according to the standard techniques described in IEC 60268-1, IEC 60268-2 and ISO 3741. The sound pressure level 9 of the acoustic pressure wave on the horizontal plane C is measured in dB along a level axis of sound pressure. Said sound pressure level 9 is presented as a multiplicity of graphs 91-98 at different frequencies comprised between 8000 Hz and 19000 Hz.
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Said sound pressure level 9 is in function of the orientation angle 61 measured in sexagesimal degrees on the horizontal plane C.
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As shown on the graph in Figure 9, the sound pressure level 9 of the acoustic pressure wave on the horizontal plane C is amplified and has a wide angular diffusion range, thus considerably decreasing the loss of energy of the acoustic pressure wave on the vertical plane D and optimizing the sound pressure level of the acoustic pressure wave along the horizontal plane C.
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The main lobe 900 of the acoustic beam at different frequencies f is comprised between 50 and 70 dB, while the secondary side lobes 910 are maintained sufficiently intense so as to be higher than at least 40 dB and to cover a sound angular diffusion range as wide as possible on the horizontal plane C.
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It is worth noting that the sound pressure level 9 of the acoustic pressure wave remains comprised between about 40 dB and 70 dB for an angular field y comprised between 90° and 160° about a direction individuated by an orientation direction X which is normal to the second transversal geometric plane B on which the transversal section 40 of the output orifice 4 of the acoustic wave guide 1 lies.
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Figure 10 shows a graph in the far field of sound pressure level 8 of the acoustic pressure wave emitted by the acoustic wave guide 1 on the vertical plane D.
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The graph measures the sound pressure level 8 of the acoustic pressure wave on the vertical plane D in the far field with the same standard technique used for the sound pressure level 9 of the acoustic pressure wave in the far field on the horizontal plane C.
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Said sound pressure level 8 of the acoustic pressure wave on the vertical plane D is measured along the sound pressure level axis 7 measured in dB. The sound pressure level 8 of the acoustic pressure wave on the vertical plane D is measured along the sound pressure level axis 7 in dB. Said sound pressure level 8 is presented as a multiplicity of graphs 81-88 at different frequencies comprised between 8000 Hz and 19000 Hz. The sound pressure level 8 is placed as a function of the orientation angle 62 measured in sexagesimal degrees on the vertical plane D.
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As shown in the graph in Figure 10, the sound pressure level 8 of the acoustic pressure wave on the horizontal plane D is expanded in extremely directional manner about the direction individuated by the orientation direction X.
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Disadvantageously, the main lobe on the vertical plane D is extremely pronounced and amplifies the acoustic pressure wave about 60 dB, while advantageously the secondary side lobes on the vertical plane D are extremely reduced and slightly exceed 30 dB, thus advantageously avoiding to disperse energy of the pressure wave on the vertical plane D and optimizing the sound pressure level 9 of the acoustic pressure wave along the horizontal plane C.
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It is worth noting that the sound pressure level 8 of the acoustic pressure wave on the vertical plane D for high frequencies comprises a main lobe 800 of the acoustic beam at different frequencies f is comprised between 50 and 70 dB, while the side secondary lobes 810 are maintained sufficiently low so as to be lower than 45 dB, to avoid dispersing acoustic pressure wave energy on the vertical plane D.
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It is worth noting that the sound pressure level 8 of the acoustic pressure wave remains extremely narrow and remains comprised between about 50 dB and 70 dB for a vertical angular range β comprised between 5° and 40° about the direction individuated by the orientation direction X.
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The acoustic beam is advantageously flat because it remains extremely flatten in the direction individuated by the orientation direction X. Figure 8 shows a graph in far field of sound pressure level 99 of an acoustic pressure wave measured in decibel (dB) at a maximum of a main lobe 800, 900 of an acoustic beam of the acoustic pressure wave as a function of a multiplicity of input frequencies in the acoustic wave guide having same amplitude and measured in Hertz (Hz) in the direction individuated by the orientation direction X. The sound pressure level 99 is measured in dB on the axis of the sound pressure level 7 with respect to a multiplicity of frequencies 90 comprised between 1000 and 20000 Hz. It is worth noting that the sound pressure level 99 is comprised between 50 dB and 70 dB at frequencies higher than about 3000 Hz. It is worth noting that the attenuation of the sound pressure level 99 of the main lobe 800, 900 increases in gradual and linear manner without major variations as the frequency increases with a gradient of 6dB/Oct, i.e. of 6dB for each harmonic octave.
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The fact that the acoustic wave guide 1 of the present invention provides an extremely flat acoustic beam allows to couple a multiplicity of said acoustic wave guides 1.
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As shown in Figures 13-16, said multiplicity of acoustic wave guides 1 thus created may be arranged in an array of said acoustic wave guides 1 so as to diffuse the sound according to predetermined directions by the user, having the considerable advantage of being able to arrange the acoustic wave guides 1 spatially one on the other without creating major interferences with the other acoustic wave guides 1 by virtue of the fact that the acoustic beam is extremely flat.
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To couple said multiplicity of acoustic wave guides 1 the output orifice 4 of each of said acoustic wave guides 1 of said multiplicity of acoustic wave guides 1 comprises a flat flange 45 about the edge thereof lying on the second transversal geometric plane B. Said flange 45 comprising shorter sides 41 parallel to the shorter sides 410 of the transversal section 40 of the output orifice 4 and shorter sides 42 parallel to the longer sides 420 of the transversal section 40 of the output orifice 4 of the acoustic wave guide 1.
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The acoustic wave guides 1 are arranged in the space so that at least one shorter side 41 of the flange 45 of one said acoustic wave guide 1 of said multiplicity of acoustic wave guides 1 is at least one shorter side 41 of the flange 45 of another acoustic wave guide 1 of said multiplicity of acoustic wave guides 1.
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The correspondence between the shorter sides 41 of the flange 45 of different acoustic wave guides 1 may be a correspondence of touch when at least one shorter side 41 of the flange 45 of said one acoustic wave guide 1 of said multiplicity of acoustic wave guides 1 is in touch with said other at least one shorter side 41 of the flange 45 of said other acoustic wave guide 1 of said multiplicity of acoustic wave guides 1.
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A space interval which separates the shorter borders 41 of the flange 45 of two or more acoustic wave guides 1 may be provided.
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In particular, the multiplicity of acoustic wave guides 1 may be directed according to different directions individuated by the direction of the transversal section 40 of the output orifice 4 of the acoustic wave guide 1, as shown in Figure 13.
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When the second transversal geometric plane B of each acoustic wave guide 1 of said multiplicity of acoustic wave guides 1 faces a direction different from the second transversal geometric planes B of all the other acoustic wave guides 1 of said multiplicity of acoustic wave guides 1, it is possible to cover an angular sound diffusion field which may reach the dimensions of an entire solid angle of 4π and thus cover all the possible directions.
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Alternatively, as shown in Figures 14-16, a linear array of a multiplicity of acoustic wave guides 1 may be provided when the second transversal geometric plane B of each single acoustic wave guide 1 of said multiplicity of acoustic wave guides 1 is coplanar with the second transversal geometric planes B of all the other acoustic wave guides 1 of said multiplicity of acoustic wave guides 1. In said alternative, the short sides 410 of the transversal sections 40 of the output orifices 4 of rectangular shape of the acoustic wave guides 1 are parallel to the others of every acoustic wave guide 1 of said multiplicity of acoustic wave guides 1, thus obtaining an extreme directionality of the acoustic beams of the single acoustic wave guides 1 and a very high sound pressure level of the acoustic pressure wave of the array of said multiplicity of acoustic wave guides 1.
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In yet another alternative, according to the emitted frequency of the acoustic transducer 5, the point of maximum curvature 15 of the longitudinal axis L may be provided at any one of a multiplicity of the harmonic standing wave nodes. The narrowed transversal section 20 is positioned at a fraction of a longitudinal length of the resonant cavity 2, said fraction corresponds to a n mode of harmonics of standing waves inside the resonant cavity 2. Said longitudinal length of the resonant cavity 2 is measured along the longitudinal axis L starting from the input orifice 3 and proceeding along the longitudinal axis L towards the output orifice 4 of the acoustic wave guide 1. The maximum curvature point 15 is positioned at any one of the nodes of higher harmonics, such as for example at half the length of the acoustic wave guide 1 for low frequencies, or at other nodes of other lower harmonics of the acoustic pressure wave, such as for example 1/4, 1/5, 1/6, 1/7 to 1/n of the length of the acoustic wave guide 1 for high and very high frequencies emitted by the acoustic transducer 5, where n is the mode of the harmonic of the acoustic pressure wave.
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A yet further alternative provides that the broadening of the linear dimension on the horizontal plane C of the transversal section of the resonant cavity 2 occurs according to a function of order higher than the first-order, e.g. an exponential function or parabolic or hyperbolic functions or functions of "Non Uniform Rational Basis-Splines" (NURBS) type so that, on the horizontal plane C, longitudinal sections of the walls 10 are curved.
