Apparatus for redistributing acoustic energy

Abstract

An apparatus for re-distributing acoustic energy. The apparatus comprises a first concave surface defined as a surface of revolution of a line or curve. This curve of revolution is rotated beyond 230 degrees and thus defines a rather small opening, which has advantages in the frequency response output. Additionally or alternatively, edges of the concave surface may be rounded to provide advantageous effects in the sound output.

Claims

1. An apparatus for redistributing acoustic energy, the apparatus comprising a surface with: a first part having a shape of a first surface of revolution, within a first angular interval from a first angular position to a second angular position and around an axis, of a first line extending through a point, P, on the axis; a second part having a shape of a second surface of revolution, within a second angular interval from a fifth angular position to a sixth angular position and around the axis, of a second line extending through the point P, the first part being defined at longitudinal positions, along the axis, on one side of the point P and the second part being defined at longitudinal positions on an opposite side of the point P; and a back surface extending, within a third angular interval from a third angular position to a fourth angular position and around the axis, the back surface being positioned further away from the axis than the first part, wherein the first angular interval exceeds 230°.

2. An apparatus for redistributing acoustic energy, the apparatus comprising a surface with: a first part having a shape of a first surface of revolution, within a first angular interval from a first angular position to a second angular position and around an axis, of a first line extending through a point, P, on the axis, a back surface extending, within a third angular interval from a third angular position to a fourth angular position and around the axis, the back surface being positioned further away from the axis than the first part, and a first side portion extending from the first part at the first angular position and to the back surface at the third angular position, the first the side portion having, at the first angular position and at the first part, a shape approximating, in a first plane perpendicular to the axis and positioned at a first longitudinal position along the axis, a part of a circle having a first radius, and in a second plane perpendicular to the axis and positioned at a second longitudinal position along the axis, a part of a circle having a second radius, the second longitudinal position being closer to the point P than the first longitudinal position and the second radius being smaller than the first radius.

3. An apparatus according to claim 2, wherein the first side portion has, at the first part, a shape approximating a part of a circle, where the radius of the circle increases with increasing distance, along the axis, to the point P.

4. An apparatus according to claim 2, further comprising a second side portion extending from the first part at the second angular position and to the back surface at the fourth angular position, the second side portion, at the second angular position and at the first part, having a shape approximating, in the first plane and at the first longitudinal position along the axis, a part of a circle having a third radius, and in the second plane and at the second longitudinal position along the axis, a part of a circle having a fourth radius, the fourth radius being smaller than the third radius.

5. An apparatus according to claim 2, further comprising a second part having a shape of a second surface of revolution, within a second angular interval and around the axis, of a second curved line extending through the point P, the first part being defined at longitudinal positions, along the axis, on one side of the point P and the second part being defined at longitudinal positions on an opposite side of the point P.

6. An apparatus according to claim 5, wherein at least 60% of the second angular interval extends diametrically opposite, around the axis, to angles within the first angular interval.

7. An apparatus according to claim 5, wherein the second part has an outer edge shaped as at least substantially a part of a circle having a centre at the axis and a radius defined by a distance between the axis and a border between the back surface and the first side portion in a plane perpendicular to the axis and comprising the outer edge.

8. An apparatus according to claim 7, wherein the distance between the axis and the border, in the plane perpendicular to the axis, decreases with increasing distance to P, along the axis and on the opposite side of the point P.

9. An apparatus for redistributing acoustic energy, the apparatus comprising a surface with: a first part having a shape of a first surface of revolution, within a first angular interval from a first angular position to a second angular position and around an axis, of a first line extending through a point, P, on the axis, a first border being defined by the first part at the first angular position and a second border being defined by the first part at the second angular position; a second part having a shape of a second surface of revolution, within a second angular interval from a fifth angular position to a sixth angular position and around the axis, of a second line extending through the point P, the first part being defined at longitudinal positions, along the axis, on one side of the point P and the second part being defined at longitudinal positions on an opposite side of the point P, a fifth border being defined by the second part at the fifth angular position and a sixth border being defined by the second part at the sixth angular position; a back surface positioned, within a third angular interval from a third angular position to a fourth angular position and around the axis, a third border being defined by the back surface at the third angular position, a fourth border being defined by the back surface at the fourth angular position, the back surface being positioned further away from the axis than the first part; a first side portion extending from the first border to the fifth border and to the third border; and a second side portion extending from second border to the sixth border and to the fourth border, wherein the second part has an outer edge portion shaped as a polygon all parts of which are positioned at or within a circle having a centre at the axis and a diameter defined by a distance between second part at the fifth and sixth angular positions, respectively, in a plane perpendicular to the axis and comprising the outer edge, wherein a distance between the axis and the third and fourth borders, respectively, in the plane perpendicular to the axis, decreases with increasing distance, along the axis, to P.

10. An apparatus according to claim 9, wherein a sum of the first and third angular intervals is less than 360 degrees.

11. An apparatus according to claim 9, wherein: the first side portion has, at the first border, a shape approximating at a first longitudinal position along the axis, a part of a circle having a first radius, and at a second longitudinal position along the axis, a part of a circle having a second radius, the second longitudinal position being closer to the point P than the first longitudinal position and the second radius being smaller than the first radius; and the second side portion has, at the second border, a shape approximating, at the first longitudinal position along the axis, a part of a circle having a third radius, and at the second longitudinal position along the axis, a part of a circle having a fourth radius, the fourth radius being smaller than the third radius.

12. An apparatus according to claim 11, wherein the first side portion has, at the first part, a shape approximating a part of a circle, where the radius of the circle increases with increasing distance, along the axis, to the point P.

13. An apparatus according to claim 9, wherein at least 60% of the second angular interval extends diametrically opposite, around the axis, to angles within the first angular interval.

14. An apparatus for redistributing acoustic energy, the apparatus comprising a surface with: a first part having a shape of a first surface of revolution, within a first angular interval from a first angular position to a second angular position and around an axis, of a first line extending through a point, P, on the axis, a first border being defined by the first part at the first angular position and a second border being defined by the first part at the second angular position; a first side portion extending from the first border and in a direction away from the first and second borders; and a second side portion extending from second border and in a direction away from the first and second borders, wherein, in a cross section perpendicular to the axis, the first part and the first and second side portions define a curve, no parts of which deviates from a circle, having a diameter exceeding a predetermined minimum diameter and being fitted to the part, by more than 10% of the diameter of the circle.

15. An apparatus according to claim 1, further comprising a third area comprising an opening through which a first curved line, within the first angular interval, and the axis extend.

16. A loudspeaker comprising an apparatus according to claim 1 and a sound generator positioned so as to emit sound along the axis and onto a first area.

17. An apparatus according to claim 1, wherein the first angular interval is 240-270°.

18. An apparatus according to claim 1, wherein the first angular interval is 260-280°.

Description

(1) In the following, preferred embodiments of the invention will be described with reference to the drawing, wherein: FIG. 1 illustrates a first embodiment of an apparatus according to the invention seen along the axis, FIG. 2 illustrates the first embodiment seen from the side, FIG. 3 illustrates a cross section of a loudspeaker comprising a membrane and the first embodiment of FIG. 1, FIG. 4 illustrates another embodiment of an apparatus according to the invention seen from the front, FIG. 5 illustrates horizontal directivity and absolute frequency response at selected frequencies for the apparatus of FIGS. 2 and 4, FIG. 6 illustrates a third embodiment with a differently shaped second part and FIG. 7 illustrates a cross section perpendicular to the axis A.

(2) In FIGS. 1 and 2, a first embodiment 10 according to the invention is seen having a first part 12 shaped as a surface of revolution around an axis A directed perpendicularly out of and into the drawing at the point P. The first part 12 extends from a first border 14 to a second border 16 along the direction of rotation around the axis A. In this embodiment, the angular extent of the first part 12, in all planes perpendicular to the axis A and wherein a portion of the first part 12 exists, is the same. The borders 14 and 16 are illustrated by lines but preferably are identifiable as the transition from the surface of revolution and the side portions.

(3) The first part 12 extends from a first angle at the border 14 to a second angle at the border 16 and thus over a first angular interval illustrated by the bent double arrow.

(4) A back portion 30 is provided, the shape of which is not particularly important. The back portion 30 is the other side of the element or material of which the concavity forming the first part is provided. Preferably, the back surface extends, around the axis, from a third border or angle 32 to a fourth border or angle 34 substantially within a third angular interval, which preferably has a large overlap with the first angular interval. One of the first and third angular interval preferably is comprised within the other of the first and third angular intervals.

(5) Two side portions 18 and 19 are provided between the first/second borders 14/16 and the third/fourth borders 32/34 of the back surface 30. The transition between the side portions 18/19 and the back portion 30 need not be particularly important, especially if no sound impinges on this transition.

(6) Provided is also a second part 20 is illustrated which is also defined as a surface of revolution of the same line as that of the first part 12 or another line/curve. Also the line/curve defining the second surface 20 intersects the axis A at the point P. Along the axis, the first part 12 extends, along the axis, to one side of the point P and the second part extends to the other side of the point P.

(7) The second part and the side portions engage or meet at the fifth/sixth borders, respectively, 22 and 24. The second part is limited, at an outermost part, by an edge 26 shaped as a part of a circle having its centre at the axis A. The diameter of this circle is defined by the distance between the axis A and the borders 32 and 34, respectively, at the same longitudinal position along the axis.

(8) Especially in FIG. 1, the shape of the side portions is visible. This shape may be provided in order that the cavity formed by 12 does not become closed to an extent where the opening has an area smaller than the radiating area of the diaphragm of the sound source. This is especially interesting when the first angular interval of the part 12 exceeds 180 degrees, such as when it exceeds 200, 220 or 230 degrees.

(9) Another reason is to avoid sharp edges causing negative interference in the sound. The shape is provided by the portion 17 of the side portions the closest to the first/second borders 14/16 having been rounded so as to form a smooth transition from the shape of the first part 12 and to the more radial shape of a main portion 17′ of the side portions. The exact shape of this rounded portion 17 may be selected in many manners. In one embodiment, the shape is that of a part of a circle, as indicated in hatched lines, but also other shapes may be defined.

(10) It is seen that the closer to the point P, the smaller is the diameter of the circle of the shape of the part 17.

(11) It is desired that from the border 16/14 the shape of the part 17 of the side portion 18/19 is rounded and conforms to a circle for at least an angle of 40°, such as at least 75°, where the “conforms” means that the side portion 18/19 deviates from the circle by no more than 10%, such as no more than 5% of the length of the radius of the circle, where the deviation from a point on the side portion to the circle is determined along a radius of the circle.

(12) Alternatively, the side portions may simply be flat and extend outwardly from the borders 14/16. In that situation, the parts 17 are not rounded but may be desired sharp. Then, the rotation angle of the first part 12 in FIG. 1 is 270 degrees. This rotation angle may be from 230-300 degrees, for example.

(13) At the bottom of the apparatus 10, an opening O is positioned which is defined at a lower edge of the first part 12. This opening may (see FIG. 3) be used for receiving the sound or acoustic energy to be redistributed. Naturally, the opposite direction of the sound may be used, if desired, such as if using the apparatus 10 as a collector of sound for e.g. a microphone.

(14) In FIG. 3, a cross section is seen wherein also a tweeter T is positioned in the opening O. Sound output of this tweeter T, when positioned with the diaphragm plane perpendicular to the axis and with the axis intersecting the tweeter diaphragm at its center, will be directed more or less along the axis and will impinge on the first part 12 and the second part 20 and on the part 16 and will be re-directed thereby and toward the surroundings.

(15) In FIG. 4, a slightly different embodiment 10′ is seen wherein the side borders 32′ and 34′ are converging both toward each other and the axis in the upward direction. This slightly alters the shape of the side portions 18/19 but primarily reduces the size of the second part 20 and the diameter of the upper edge 26′, which is still defined by the distance, at that longitudinal position along the axis, between the axis and one of or both the edges 32/34.

(16) In the embodiment of FIG. 4, compared to that in FIG. 2, a slightly narrowing horizontal directivity is obtained with increasing frequency and smoother absolute response, whereas in 10 the radiation widens slightly >10 kHz see plots 5A and 5B, and the absolute response is more even. It is noted that the double lines in FIG. 4, as at the front border 26 of the second part 20 and at the borders 32′ and 34′, are caused by these parts being curved.

(17) In FIGS. 5A and 5B illustrate the horizontal directivity (when oriented as in the figures) and the absolute frequency response at selected, discrete angles, for the apparatus illustrated in FIGS. 2 and 4, respectively.

(18) It is seen that the directionality in the horizontal plane is extremely flat and is slightly increasing with frequency. In FIG. 5A, the radiation widens slightly above 10 kHz. These plots illustrate that the frequency response at angles in the horizontal plane in front of the device is almost constant, it is only the volume level that changes—lowering at angles further to each side of the main radiation axis of the device. Thus, no lobes or ripples are seen. Also, the frequency response is smoother.

(19) It is noted that due to the smaller size of the second part 20, the frequency response of the apparatus of FIG. 4 has less sharp bends, which makes the filtering of an acoustic signal for the loudspeaker T simpler in order to feed this loudspeaker with a signal counteracting the non-linear response of the apparatus.

(20) In FIG. 6, an embodiment quite similar to that of FIG. 1 is seen but wherein the second part 20 has a different shape, as is illustrated in hatched lines. In this embodiment, the outer boundary 26″ of the second part is that of a part of a polygon all parts of which are positioned at or within the circular outline 26 also seen in FIG. 1.

(21) Generally, the shape of the second part 20 may be varied, but it is preferred maintained inside or at the circular outline defined by the distance from the axis A to one or both of the borders 32/34.

(22) FIG. 7 illustrates the combined shape of the first part 12 and the side portions 18/19 in a cross section perpendicular to the axis A and at one longitudinal position along the axis. The illustrated cross section is usually at the bottom of the apparatus and far from the point P.

(23) As explained further above, when the rotation angle of the revolution surface of the first part 12 becomes large, such as 200° or more, a rounding of the side portions 18/19 may be desired in order to ensure a sufficient output of sound.

(24) It is seen that the part 17′ of the side portions 18/19 may conform to a circle, a parabola or a number of other shapes.

(25) It is desired that the curve does not have sharp edges or bends. Thus, it is desired that the derivative thereof has no discontinuities. However, a sharp bend/edge may be acceptable, if its extent over e.g. a flat surface is limited.

(26) Thus, it is desired that at least the part 17′ but preferably also at least half of the curve between the border 14/16 and the border 32/34, starting from the border 14/16, is smooth and has a predetermined minimum bending angle or rate of change, such as when approximated by—or conforming to—a circle with a diameter exceeding a predetermined minimum diameter.

(27) Preferably, the approximation is required over a predetermined minimum part of the circle, and especially if the circle diameter is close to the predetermined minimum diameter. Naturally, this part may be defined as an angle of the circle, but for large circles, this may not be the best option.

(28) In one embodiment, it is required that for each part of the curve having a length of 1/10 or more, such as ⅛ or more, such as ⅙ or more, such as ¼ or more of the circumference of a circle with the predetermined minimum diameter, this part must conform to a circle

(29) When the approximation allows a small deviation from the circle shape, small, localized, sharp bends/edges are accepted.

(30) Thus, preferably the approximation means that no part of the part of the curve deviates from the circle by more than 10%, such as no more than 5% of the length of the radius of the circle, where the deviation from a point on the side portion to the circle is determined along a radius of the circle.

(31) Usually, the diameter of the first part 12 is larger than the minimum diameter of the circle, whereby the first part 12 automatically fulfils this requirement.