Resonator absorber with adjustable acoustic characteristics

Abstract

A resonator absorber with adjustable acoustic characteristics made in the form of a cuboid with sidewalls and with an open upper face that is covered by two identical movable perforated plates to allow partial overlapping of the the plates. Each plate is equipped with bores forming a planar binary amplitude diffusor by using a maximum length pseudorandom binary sequence mapped to 2D space to determine the bore position. Bores are arranged in rows which do not overlap between plates. The resonator absorber has six cavities of different geometry situated below the perforated plates, where five cavities simultaneously change the volume with movement of the perforated plates. The resonator absorber is useful for tuning the acoustic characteristics of the environment.

Claims

1. A resonator absorber with adjustable acoustic characteristic comprising: a plane bottom surrounded by sidewalls forming a cuboid with an open upper face filled with cuboids of different geometry fixed to the bottom; two perforated plates entirely covered with absorptive layers on their side facing said bottom, where said perforated plates are fixed to the guides formed in opposite sidewalls allowing the movement of said perforated plates in their respective planes parallel to the bottom, where said planes are at different heights from the bottom to allow an upper perforated plate of the two perforated plates to slide over a lower perforated plate of the two perforated plates, partially overlapping one another; and where the combined area of two perforated plates is capable to entirely cover the cuboid open upper face; wherein each perforated plate has rows of bores forming a planar binary amplitude diffusor; where said rows belonging to the different perforated plates are arranged in the manner where perforated plates overlap, the bores belonging to the different perforated plates do not coincide in any position in order to prevent sound propagation through the overlapped region that serves as a reflective part of said resonator absorber; each perforated plate has mounted a corresponding wing that extends towards the bottom being in contact with the corresponding cuboids situated at the bottom; each wing sliding over the corresponding cuboids defines the volumes of the adjustable cavities, where a first portion of the cavities are open and serve as sound reflective surfaces, and where a second portion of the cavities covered by the corresponding perforated plates serve as absorptive and diffusive parts of said resonator absorber; a perforated plate end and a corresponding stopper form another adjustable cavity always covered by a first one of the perforated plates, where a volume of said cavity is defined by the position of the second one of the perforated plates and serve as absorptive and diffusive parts of said resonator absorber; where said resonator absorber has an additional cavity of constant volume, situated between the cuboids, which acoustic characteristics are changed by the overlapping of the said perforated plates above the said cavity, where the additional cavity serves as absorptive, diffusive and reflective parts of said resonator absorber; and where independent movement of each perforated plate in their respective planes change the acoustic properties of said resonator absorber.

2. The resonator absorber with adjustable acoustic characteristics according to the claim 1, wherein the bores forming a planar binary amplitude diffusors arranged in one or more two dimensional patterns having dimension NM, each two dimensional pattern is obtained as a maximum length of a pseudorandom binary sequence of the order K mapped in the said matrix NM by using Chinese remainder theorem in order to maximize the sound diffusion above the perforated plates.

3. The resonator absorber with adjustable acoustic characteristics according to the claim 2, wherein the maximum length pseudorandom binary sequence is selected to be K=10.

4. The resonator absorber with adjustable acoustic characteristics according to the claim 3, wherein 2D patterns with raster 3331 are selected.

5. The resonator absorber with adjustable acoustic characteristics according to the claim 4, wherein each perforated plate has two identical 2D patterns arranged mirror symmetrically over the longer plate side; the first perforated plate is mirror symmetrical to the second perforated plate when inserted into the resonator absorber.

6. The resonator absorber with adjustable acoustic characteristics according to the claim 5, wherein each perforated plate has a perforation area less than 6%.

7. The resonator absorber with adjustable acoustic characteristics according to claim 1, wherein the cuboids are further partially or completely filled with sound absorption material.

8. The resonator absorber with adjustable acoustic characteristics according to claim 1, wherein once the perforated plates are in a position to cover the upper cuboid open face, the resulting cavities are tuned to predefined resonant frequencies.

9. The resonator absorber with adjustable acoustic characteristics according to claim 1 used for tuning the acoustic characteristics of the environment.

10. Use of two or more resonator absorbers simultaneously, each with arbitrary adjustable acoustic characteristics according to claim 1, for tuning the acoustic characteristics of the environment.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) FIG. 1A shows the resonator absorber in isometric projection when perforated plates overlap partially;

(2) FIG. 1B shows the same situation from top view;

(3) FIG. 1C represents the cross-section A-A of the situation depicted in FIG. 1A.

(4) FIG. 2A shows the resonator absorber in isometric projection when perforated plates completely cover the upper cuboid open face of the said resonator absorber;

(5) FIG. 2B shows the same situation from top view;

(6) FIG. 2C represents the cross-section A-A of the situation depicted in FIG. 2A.

(7) FIG. 3A shows the resonator absorber in isometric projection when perforated plates overlap each other completely;

(8) FIG. 3B shows the same situation from top view;

(9) FIG. 3C represents the cross-section A-A of the situation depicted in FIG. 3A.

(10) FIG. 4A represent the upper perforated plate equipped with the bores forming planar binary diffusor,

(11) FIG. 4B represents side view of the same perforated plate.

(12) FIG. 5A represents the lower perforated plate equipped with the bores forming planar binary diffusor,

(13) FIG. 5B represents the side view of the same perforated plate.

(14) FIG. 6 represents mutual position of the rows belonging to the upper and lower perforated plates.

DETAILED DESCRIPTION

(15) An aspect of the present invention discloses a resonator absorber with adjustable acoustic characteristics; that is a stand-alone self-supporting structure whose purpose is to tune the acoustic characteristics of environment. It can be used alone or as a part of array of two or more resonator absorbers simultaneously, each with arbitrary adjustable acoustic characteristics.

(16) The preferred embodiment is depicted in FIGS. 1-6 which are used to explain the construction of the preferred embodiment of the invention and its use. The resonator absorber has a plane bottom (10) surrounded by sidewalls (11, 12, 13, 14) that are forming cuboid with the open upper face; see FIGS. 1A, 2A, and 3A. Preferably, the material used for manufacturing the bottom (10) and sidewalls (11, 12, 13, 14) are wooden material or wood-based composite material commonly used for said purpose, as known in the art. Other materials with similar acoustic properties can be equally used without restriction, as well as their combinations. Mutual connection of sidewalls (11, 12, 13, 14) and bottom (10) can be performed by any suitable technique, preferably by gluing the parts together positioned by pins; as already known in the furniture technology.

(17) The interior of said formed cuboid is filled with other cuboids (51, 52, 53) as depicted in FIGS. 1C, 2C and 3C. Mentioned cuboids (51, 52, 53) have different geometry and are fixed to the bottom (10) of said resonator absorber by any suitable technique, preferably by gluing or screwing the parts. In practice, the desired technical effect is to obtain four different plains situated above the bottom (10) at different heights, as depicted in FIG. 1C. The first plane is cuboid (51) with face oriented up, the 2nd plane is cuboid (52) with face oriented up, the 3rd plane is part of the bottom (10) oriented up and situated between the cuboid (52) and the cuboid (53), and 4th plane is cuboid (53) with face oriented up. Said cuboids (51, 52, 53) can be solid, hollow or partially filled with the sound absorption material. Preferably, cuboids (51, 52, 53) are manufactured from wooden material or wood-based composite material commonly used in the art. If filled, the standard fillers known in the art are used which are capable to absorb mechanical sound energy. Upper cuboid (51, 52, 53) faces are machined and finished to form reflective surfaces, as well as the part of the bottom (10) used as 3rd plane.

(18) Two perforated plates, i.e. upper perforated plate (30) and lower perforated plate (40), which we will describe later in more detail, are fixed to the guides formed in opposite sidewalls (13, 14). Guides should provide smooth movements of the said perforated plates (30, 40) one over another. Any suitable guides are equally well applicable. The essence is that said guides allow the movement of said perforated plates (30, 40) in their respective planes parallel to the bottom; FIGS. 1C, 2C and 3C. The perforated plates (30, 40) are situated at different heights from the bottom (10). Purpose of that is to allow upper perforated plate (30) to slide over lower perforated plate (40), practically without air gap, when upper perforated plate (30) overlaps lower perforated plate (40). The combined area of two perforated plates (30, 40) is capable to entirely cover cuboid open upper face as depicted in FIG. 2B.

(19) Few words should be said about the perforated plates (30, 40) construction. The technical roles of said perforated plates (30, 40) are to act as the planar binary amplitude diffusors in the manner already described in the prior art and as the upper perforated plate of the resonator absorber. Perforated plates (30, 40) are preferably manufactured from wooden material or wood-based composite material commonly used in the art. Each perforate plate (30, 40) has their respective set of rows (34, 44) of bores (33, 43) drilled in said plates (30, 40); FIGS. 4A, 5A. The rows (34, 34, 34, . . . , 44, 44, 44, . . . ) belonging to the different perforated plates (30, 40) are arranged in the manner where perforated plates (30, 40) overlapbores (33, 43) belonging to different perforated plates (30, 40) do not coincide in any position, once perforated plates (30, 40) are being inserted into their guides; FIG. 6. This technical feature is necessary for proper functioning of the present invention. Namely, the role is to prevent sound propagation through the overlapped region of the perforated plates (30, 40) that serves as the reflective part of said resonator absorber.

(20) Each perforated plate (30, 40) has on one of its end a corresponding wing (31, 41) that extends towards the bottom (10); FIGS. 4B, 5B. Each perforated plate (30, 40) is equipped with absorptive layers (61, 62) on their side facing said bottom (10), forming an integral structure. Whenever perforated plates (30, 40) are mentioned, it should be understood that the perforated plates (30, 40) are covered with absorptive layers (61, 62). The technical role of mentioned absorptive layers (61, 62) is decreasing the sound energy of the sound waves hitting the perforated plate (30, 40). Absorptive layers (61, 62) cover entire bottom surface of perforated plate (30, 40), covering also the bores (33, 43). The type of material and the thickness of the absorptive layers (61, 62) should be carefully selected in a manner that the resonator absorber matches the acoustic impedance of air. This fact is very well known in related art. On the opposite side, each perforate plate (30, 40) has a standard plate end (32, 42). Upper perforated plate (30) can freely move from the position depicted in FIG. 2C where the wing (31) is in the contact with the stopping surface (17) of the sidewall (11) to the position depicted on the FIG. 3C where the wing (31) is stopped by the stopper (15) situated between the cuboids (51, 52). Lower perforated plate (40) can move freely from the position depicted in FIG. 2C where the wing (41) is in the contact with the stopping surface (18) of the sidewall (12) to the position depicted in FIG. 3C where the plate end (42) is stopped by the stopper (15) situated between the cuboids (51, 52), and the wing (41) is stopped by the stopper (16) situated on the cuboid (53).

(21) Each wing (31, 41) is in permanent contact with the corresponding cuboids (51, 53) across its entire length, i.e. from the sidewall (13) to the sidewall (14). The essential technical feature that is expected is that each wing (31, 41) is capable of sliding over corresponding cuboids (51, 53) in any moment. Wings (31, 41) sliding over said cuboids (51, 53) define the volumes of the adjustable cavities (21, 22, 25, 26); FIG. 1C. Cavities (21, 26) are, when exist, open and serve as sound reflective surfaces of the exchangeable geometry; FIGS. 1C and 3C.

(22) Cavities (22, 25) are covered by the corresponding perforated plates (30, 40) from the above and have the volume defined by the position of inner part of the wing (31, 41) against the wing stoppers (15, 16) and upper face positions of the corresponding cuboids (51, 53). Such cavities (22, 25) serve as absorptive and diffusive parts of said resonator absorber and have the cuboid shape. From the engineering point of view, mentioned cavities (22, 25) without air-gap on the contact surfaces, i.e. stopper (15, 16)perforated plate (30, 40) and wing (31, 41)cuboid (51, 53); are important for the reliable functioning of the said resonator absorber.

(23) The wings (31, 41) can be manufactured from wooden material or wood-based composite material commonly used in the art, and preferably glued or otherwise attached to their respective perforate plates (30, 40). It is worth to note that the wings (31, 41) are of different size that strongly depends of the used cuboids (51, 53) geometry. Upper contact surface of lower perforated plate (40) should be additionally polished and varnished. This feature will ensure that the absorptive layer (61) of upper perforated plate (30) will glide smoothly over perforated plate (40) without air-gaps.

(24) It is obvious that perforated plate (30, 40) movements adjust the volume of the cavities (21, 26) from zero to some maximum volume obtained when the perforated plates (30, 40) are pushed to the center of the resonator absorber. The opposite is valid for the cavities (22, 25) whose volumes are maximal when the perforated plates (30, 40) are maximally separated.

(25) Perforated plate (30, 40) movement also defines the properties of other cavity (23). Perforated plate end (42) and the corresponding stopper (15) form another adjustable cavity (23) that is always covered by the plate (30). The volume of said cavity (23) is only defined by the position of the perforated plate (40), (i.e. wing (41)), relative to the sidewall (12) and serves as absorptive and diffusive parts of said resonator absorber.

(26) The disclosed resonator absorber has an additional cavity (24) that has constant volume, situated between two cuboids (52, 53). Its acoustic characteristics are changed solely by the overlapping of the said perforated plates (30, 40) above the said cavity (24). That part of the disclosed resonator absorber serves as absorptive, diffusive and reflective parts.

(27) It is obvious that independent movement of each perforated plate (30, 40) in their respective planes significantly change the acoustic properties of the said resonator absorber which is clearly visible from the FIGS. 1C-3C and 1B-3B.

(28) Few words should be addressed towards the perforated plates (30, 40) used as the planar binary diffusors, already disclosed via the prior art, and depicted via FIGS. 4A, 5A. The corresponding bores (33, 43) are distributed to form one or more 2D patterns, i.e. matrix, having dimension NM. Each of said two dimensional pattern is obtained as a maximum length of the pseudorandom binary sequence of the order K mapped in the said matrix NM by using Chinese remainder theorem in order to maximize the sound diffusion above the perforated plates (30, 40), as already known in the art, e.g. J. A. S. Angus and P. D'Antonio, Two dimensional binary amplitude diffusers, Proc. Audio Eng. Soc., preprint 5061 (D-5) (1999), which is incorporated by reference.

(29) Experimental setups via wooden models and additional simulations calculated via Matlab packages empirically confirmed that the preferred design and characteristic are achieved when the maximum length pseudorandom binary sequence is selected to be K=10, and where the used raster, i.e. matrix, with 3331 are selected. The mentioned raster was chosen in order to give a raster with the most similar lengths of dimensions, e.g. if the length of pseudorandom binary sequence would be K=8, the raster would have to be 773, which doesn't meet the requirements for a part of element with square or almost square shape.

(30) Moreover, the calculation revealed another preferred design where each perforated plate (30, 40) has two identical 2D patterns arranged mirror symmetrically over the longer plate side; i.e. over the plane depicted in FIGS. 4A, 5A. Finally, the preferred design has the upper perforated plate (30) that is mirror symmetrical to the lower perforated plate (40), when both inserted into the resonator absorber; as depicted in FIG. 2B.

(31) Third party surveys performed by Vican I., Jambroi{grave over (c)} K., Horvat M., Comparison of acoustic resistance of a perforated plate absorber with a tightly and loosely placed thin porous layer, 6th Congress of Alps-Adria Acoustics Association, (2014), which is incorporated by reference; U. Ingard, On the theory and design of acoustic resonators, Journal of the Acoustical Society of America 25 1037-1061, (1953), which is incorporated by reference, indicate that the decrease of the porosity of the perforated plate can significantly improve the acoustic resistance, and thus the overall acoustic characteristics. The target value of porosities, just below 6%, is chosen in accordance to match the acoustic impedance of air.

(32) Once the resonator absorber with adjustable acoustic characteristics is manufactured according to the preferred embodiment, its characteristic can be simply labeled with the following parameters: (i) planar binary diffusors type used, and (ii) with the resonant frequencies corresponding to the cavities (22, 23, 24, 25) once perforated plates (30, 40) being in position to cover upper cuboid open face.

(33) For the environments having less than 100 cubic meters, probably one or two resonator absorber; each having 0.2-1 cubic meters volume, with resonant frequencies corresponding to the cavities (22, 23, 24, 25) tuned to different spectra are more than sufficient to improve the sound quality reception and eliminate unwanted effects. It is emphasized several times that disclosed resonator absorber can change/tune acoustic properties in a simple and reliable manner. Effectively it means that resonator absorbers, once positioned, can be in situ manually adjusted with or without the help of additional measuring sound processing equipment. Moreover, the mutual perforated plates (30, 40) positions within the resonator absorber sidewalls can be simply memorized by outer marks made on the sidewalls (13, 14). That fact enables the disclosed invention to be quickly used for different environments once calibration is performed and position within the environment defined. That feature is not rendered obvious for the technical solutions found in the prior art.

(34) For larger environments like churches, conference halls, half-open spaces it is natural to use whole arrays of resonator absorbers simultaneously, each with arbitrary adjustable acoustic characteristics.

INDUSTRIAL APPLICABILITY

(35) The present invention discloses resonator absorber with adjustable acoustic characteristics. Disclosed resonator absorber, formed as a standalone element, is useful for tuning the acoustic characteristics of environment with mechanically adjustable reflective, diffusive and absorptive parts. Therefore, the industrial applicability of the said invention is obvious.

REFERENCES

(36) 10bottom 11, 12, 13, 14sidewalls 15, 16stoppers 17, 18stopping surfaces 21, 22, 23, 24, 25, 26cavities 30, 40perforated plates 31, 41wings 32, 42plate ends 33, 43bore 34, 44rows of bores 51, 52, 53cuboids 61, 62absorptive layers