GB2620430A

GB2620430A - An enclosure for an electroacoustic transducer

Info

Publication number: GB2620430A
Application number: GB2210021.8A
Authority: GB
Inventors: Nisim Dahan Midbar
Original assignee: Individual
Current assignee: Individual
Priority date: 2022-07-08
Filing date: 2022-07-08
Publication date: 2024-01-10
Also published as: GB202210021D0

Abstract

The enclosure comprises several walls which define a spiral-shaped volume 8. A wall 4 of the enclosure has an aperture 5 configured to permit a loudspeaker 2 to be mounted in the aperture to form part of an external side of the walls, and a rear portion of the loudspeaker 2 forms part of an internal side of the walls defining the volume 8. The enclosure further comprises a formation 7, 11 that defines the spiral-shaped volume 8 to have a first end and a second narrower end, and wherein sound waves emitted from the rear portion of the loudspeaker 2 are transmitted into the spiral-shaped volume 8 at the first end and propagate along the spiral-shaped volume 8 from the first end towards the second end. The spiral shape may follow a Fibonacci spiral.

Description

An Enclosure for an Electroacoustic Transducer The invention relates to an enclosure for an electroacoustic transducer, and especially an enclosure for a loudspeaker.

The primary role of a loudspeaker enclosure is to prevent sound waves generated by the rearward-facing surface of the diaphragm of an open speaker driver interacting with sound waves generated at the front of the speaker driver. The forward-and rearward-generated sounds of a speaker driver appear out of phase lo from each other because they are generated through opposite motion of the diaphragm and because they travel different paths before converging at the listener's position. Since the rear of the loudspeaker radiates sound out of phase from the front, there can be constructive and destructive interference for loudspeakers without enclosures.

As the forward-and rearward-generated sounds are out of phase with each other, any interaction between the two in the listening space creates a distortion of the original signal as it was intended to be reproduced. This is because the forward-and rearward-generated sound waves travel different paths through the listening space and arrive at the listener's position at slightly different times, introducing echo and reverberation effects that are not part of the original sound.

Therefore, a loudspeaker driver cannot be used without installing it in an enclosure or cabinet of some type, or mounting it into a wall or ceiling.

However, even when a loudspeaker driver is mounted in an enclosure, there are still problems of out of phase unwanted sound waves that comes from the rear of the loudspeaker driver. These sound waves will generally reflect off the inside of the enclosure in which the loudspeaker driver is mounted before exiting the enclosure through the front of the driver. As these reflected sound waves travel a different and longer path than the primary (non-reflected) waves output directly from the front of the driver, the reflected waves interfere with the primary waves causing out of phase distortions to the sound coming from the loudspeaker and therefore, cause a distortion in the sound that the listener actually hears.

There have been numerous attempts to absorb and dissipate the reflected waves within the enclosure so that they do not exit the enclosure. However, these attempts have only had limited success.

In accordance with the present invention, there is provided an enclosure for an electroacoustic transducer, the enclosure comprising a number of walls which define a volume enclosed by the enclosure, a wall of the enclosure having an aperture configured to permit an electroacoustic transducer to be mounted in the aperture in use such that a front portion of the transducer forms part of an external side of the wall and a rear portion of the transducer forms part of an internal side of the wall defining the volume, and the enclosure further comprising a formation that defines a spiral-shaped volume having a first end and a second end that is narrower than first end; and wherein sound waves emitted from the rear portion of the transducer, in use, are transmitted into the spiral-shaped volume at the first end and propagate along the spiral-shaped volume from the first end towards the second end.

Preferably, the second end of the spiral-shaped volume is configured to reflect the sound waves back towards the opening so that, in use, the reflected sound waves destructively interfere with the sound waves propagating towards the second end.

In one example of the invention, the formation is configured such that the spiral-shaped volume lies in one plane. In other words, there exists one transverse plane (or cross-sectional plane) that intersects all of the spiral-shaped volume.

In another example of the invention, the formation is configured such that the spiral-shaped volume also has a helical component. In this example, there is not a single transverse plane that intersects all of the spiral-shaped volume.

Typically, the spiral-shaped volume progressively decreases from the first end towards the second end.

Preferably, the spiral-shaped volume is at least partly defined by a portion of a Fibonacci spiral, and more preferably, all of the volume enclosed by the enclosure is defined by a portion of a Fibonacci spiral.

Preferably, the portion of the Fibonacci spiral is defined by a number of sequential terms in the Fibonacci series.

Typically, the sequential terms of the Fibonacci series that define the portion of the Fibonacci spiral comprise at least the first two terms in the Fibonacci series. Preferably, the sequential terms of the Fibonacci series that define the portion of the Fibonacci spiral comprise at least the first seven terms in the Fibonacci series.

is It is possible that the sequential terms of the Fibonacci series that define the portion of the Fibonacci spiral comprise at least the first twelve terms in the Fibonacci series The spiral-shaped volume may comprise a polynomial cross-section. In one example, the spiral-shaped volume may comprise a quadrilateral cross-section.

Alternatively or in addition, the spiral-shaped volume comprises a curved-shaped cross-section, such as at least one of: an oval cross-section; a circular cross-section; and an elliptical cross-section.

Preferably, the formation comprises a spiral-shaped component. The formation may further comprise a helical component.

In one example of the invention, the first end of the spiral-shaped volume is displaced from the second end of the spiral-shaped volume in a direction transverse to a transverse plane through the spiral-shaped volume.

Typically, the first end of the spiral-shaped volume is displaced from the second end of the spiral-shaped volume in a direction substantially perpendicular to the transverse plane. Preferably, the displacement is in accordance with the Fibonacci number sequence. More preferably, the displacement from the second end to the first end increases every 90 degree rotation in accordance with the next term in the Fibonacci number sequence. Even more preferably, the displacement of the first end relative to the second end increases from the second end to the first end in accordance with a sequential number of terms of the Fibonacci number sequence.

Typically, a curve defined by the radially outermost points of the spiral volume has a constant gradient relative to the transverse plane.

Preferably, the enclosure further comprises a first connector to permit an audio signal to be input to the enclosure and to the transducer. More preferably, the enclosure further comprises a second connector to permit an audio signal to be output from the enclosure. Typically the second connector is electrically coupled to the first connector to permit a signal input to the first connector to be output from the second connector.

In use of the enclosure of the present invention, sound waves propagate along the enclosure and are emitted at the open end. It is preferred that the enclosure is configured to have the sound waves propagate with little to no turbulence in the air flow, more preferably in a laminar flow regime. It has been found that the quality of the sound waves emitted by the enclosure when propagating in laminar flow through and out of the enclosure is increased and that the quality is maintained over a greater distance from the enclosure. This is particularly advantageous when listening to audio material, such as music. In addition, it has been found that having the sound waves move within and be emitted from the enclosure in laminar flow results in a sound wave that maintains its power and amplitude over a greater distance. In particular, it has been found that having the sound waves propagate in laminar flow increases the dB level of the wave at a given distance from the enclosure.

Examples of an enclosure for an electroacoustic transducer will now be described with reference to the accompanying drawings, in which: Fig. 1 is a perspective view from the front of a first example of an enclosure for a loudspeaker with a loudspeaker driver mounted on the enclosure; Fig. 2 is a left side view of the enclosure shown in Fig. 1; Fig. 3 is a cross-sectional view through the enclosure shown in Fig. 1; Fig. 4 is a cross-sectional view similar to Fig. 3 including a diagrammatic representation of sound travelling within the enclosure; Fig. 5 is a perspective cross-sectional view of a second example of an enclosure for a loudspeaker with a loudspeaker driver mounted on the enclosure; Fig. 6 is a cross-sectional view of the second example of the enclosure including a diagrammatic representation of sound travelling within the enclosure; Fig. 7 is a front view of a third example of an enclosure for a loudspeaker without a loudspeaker driver; Fig. 8 is a top view of the third example of the enclosure; Fig. 9 is a perspective cross-sectional view from the right side of the third example with a loudspeaker driver mounted on the enclosure; Fig. 10 is a perspective cross-sectional view from the left side of the third example with a loudspeaker driver mounted on the enclosure; Fig. 11 is a perspective view from the left side of a fourth example of an enclosure for a loudspeaker with a loudspeaker driver mounted on the enclosure; Fig. 12 is a front view of the fourth example of the enclosure; Fig. 13 is a top view of the fourth example of the enclosure; Fig. 14 is a perspective view from the right side of the fourth example of the enclosure; Fig. 15 is a perspective view from below of the fourth example of the enclosure; and Fig. 16 is a cross-sectional view through a transverse plane of the fourth example of the enclosure.

Figs. 1 to 3 show a first example of a loudspeaker enclosure 1 with a loudspeaker driver 2 mounted on the enclosure. The loudspeaker enclosure 1 includes a top side wall 3 and an identical bottom side wall 6. Located between the top side wall 3 and the bottom side wall 6 is a front side wall 4 and a curved side wall 7 that extends from a left end 9 of the front side wall 4, around the rear of the driver 2 and to a right end 10 of the front wall 4. The front wall 4 has a circular aperture 5 on which the loudspeaker driver 2 is mounted. Hence, the side walls 3, 6, 4, 7 together with the driver 2 define an internal volume 8 within the enclosure 1. Although the aperture 5 is shown as circular in this first example of the loudspeaker enclosure, the aperture could be any appropriate shape that corresponds to the shape of the loudspeaker driver to be mounted on the enclosure 1. For example, the aperture could be oval shaped.

The enclosure 1 also has two speakon sockets 15, 16 (or other speaker twist connector) mounted on the curved side wall 7 adjacent to the end 9 of the front side wall, one of these is an input socket 15 and the other is an output scoket 16.

These permit the loudspeaker enclosure 1 to be connected to an audio input and/or to output audio signals to another device, such as another loudspeaker enclosure. The input socket 15 is connected to the driver 2 and enables an audio signal from another device, such as an amplifier, to be fed to the driver 2 to drive the driver 2. The input socket 15 is also connected to the output socket 16 to enable the output socket 16 to pass the audio signal received at the input socket 15 to another device.

As shown in Fig. 3, the curved wall 7, after completing the enclosure by meeting with the right end 10 of the front side wall 4, continues to curve inwards into the internal volume 8. The curved wall 7 curves inwards to define a spiral shape 11 within the internal volume 8. In this first example of the loudspeaker enclosure 1, the spiral shape is a spiral defined by the Fibonacci number series and is commonly referred to as a Fibonacci spiral. In the example shown in Figs. 1 to 3, the entire length of the curved wall 7 forms a spiral that is defined by adjacent terms of the Fibonacci number sequence. In this first example of the loudspeaker enclosure 1, the curved side wall 7 is in the form of a spiral defined by the first twelve terms, the 15t to 12th term of the Fibonacci number sequence..

The Fibonacci number sequence is a number sequence where the nth term is given by the formula: xn = x(n-1) + x(n-2). Therefore, the first few terms of the Fibonacci number sequence are as follows: 1, 1, 2, 3, 5, 8, 13, 21, 34, 55,...

A Fibonacci spiral can be created by drawing adjoining squares each having a side length equal to the corresponding term of the Fibonacci series. Hence, the first square has side = 1, the second square has side = 1, the third square has side = 2, the fourth square has a side length = 3, the fifth square has a side length = 5, etc. A Fibonacci spiral is then created by drawing circular arcs connecting the diagonally opposite corners of the squares in the Fibonacci tiling. Different numbers of squares based on the Fibonacci number sequence with the corresponding Fibonacci spiral drawn are shown in Figs. 17 to 19. Fig. 17 shows a Fibonacci spiral 50 for the first eight terms of the Fibonacci series, Fig. 18 shows a Fibonacci spiral 60 for the first nine terms of the Fibonacci series and Fig. 19 shows a Fibonacci spiral 70 for the first ten terms in the Fibonacci series. In each case the numbers inside each square indicate the value of the corresponding term of the Fibonacci series for that square and the side length of that square.

Although any form of spiral could be used, the inventor has found that spirals defined by the Fibonacci number sequence (that is, Fibonacci spirals) are particularly useful for loudspeaker enclosures, such as the loudspeaker enclosure 1, as will be explained below.

As explained above, even when a loudspeaker driver, such as the driver 2, is mounted in a conventional loudspeaker enclosure, there can be problems with out of phase unwanted sound waves that come from the rear of the loudspeaker driver. These sound waves will generally reflect off the inside of the enclosure in which the loudspeaker driver is mounted before exiting the enclosure through the front of the driver. As these reflected sound waves travel a different and longer path than the primary (non-reflected) waves output directly from the front of the driver, the reflected waves interfere with the primary waves causing out of phase distortions to the sound coming from the loudspeaker and therefore, cause a distortion in the sound that the listener actually hears.

Fig. 4 shows diagrammatically how sound waves emitted from the rear of the loudspeaker driver 2 behaves within the enclosure 1. In Fig. 4 the sound waves are represented by arrows 12. As shown in Fig. 4 by the arrows 12, sound waves emitted from the rear of the loudspeaker driver propagate around the inside of the enclosure 1 by the curved side wall 7 away from the driver 2 towards the spiral shape 11 section of the curved side wall 7 by reflections from the inside of the curved side wall 7. When the sound reaches the inner end 13 of the curved wall 7, it is reflected by the end of the spiral shape 11 back on itself, causing the reflected sound waves to be cancelled out or reduced by the sound propagating towards the inner end 13 by destructive interference between the sound waves propagating towards the inner end 13 and the sound waves reflected from end of the spiral shape 11. This reduction or cancelling of sound waves from the rear of the speaker driver 2 reduces the out of phase unwanted sound waves that are emitted from the enclosure 1.

Although other spirals can be used, the inventor has found that Fibonacci spirals exhibit superior sound cancelling characteristics compared to other spirals.

Therefore, the loudspeaker enclosure 1 has the advantage of reducing the emission from the loudspeaker enclosure 1 of out of phase unwanted sound waves that come from the rear of the loudspeaker driver 2 by causing them to cancelled out by destructive interference by use of the spiral shape 11 within the loudspeaker enclosure 1 Figs. 5 and 6 show a second example of a loudspeaker enclosure 20 with the loudspeaker driver 2 mounted on it. The enclosure 20 is similar to the enclosure 1 and parts of the enclosure 20 that are the same as the enclosure 1 are indicated with the same reference numerals.

The main difference between the enclosure 1 and the enclosure 20, is that the enclosure 20 has a curved side wall 21 that replaces the curved side wall 7. The curved side wall 21 has the same shape as the curved wall 7 between the ends 9, 10 of the front side wall 4 but the continuation of the curved wall 7 into internal volume 22 of the enclosure 20 is different so that the curved wall 21 defines a spiral shape 23 that is different from the spiral shape 11.

The spiral shape 23 is still a spiral defined by terms of the Fibonacci number sequence, so is still a Fibonacci spiral. However, the number of terms of the Fibonacci series used to define the spiral shape 23 and the curved wall 21 is less than the number of terms used to define the spiral shape 11 and the curved wall 7.

In this case, the terms used to define the spiral shape 23 and the curved wall 21 are 1st to the 7th terms of Fibonacci number sequence. The use of less terms of the Fibonacci series, results in the spiral shape 23 having less revolutions than the spiral shape 11. This has the advantage that the use of less terms in the spiral makes the spiral shape 23 and the curved wall 21 easier to manufacture.

However, as shown in Fig. 6, sound waves emitted from the rear of the driver 2, as represented by the arrows 12, are still propagated by the curved wall 21 away from the speaker driver 2 towards the spiral shape 23, in a similar manner to the way in which the sound waves are propagated towards the spiral shape 11 in the enclosure 1. It is believed that due to the reduced number of revolutions of the Fibonacci spiral in the spiral shape 23, while there is still destructive interference and reduction of out of phase unwanted sound waves, there is not the same level of destructive interference between the sound waves being propagated towards end 24 and the sound waves reflected from at the inner of the spiral shape 23.

In both the enclosure 1 and 20, the enclosures have a rectangular cross-sectional profile in a plane that is generally perpendicular to central axes 19, 29 of the enclosures 1, 20 that extends from the aperture 5 to the inner ends 13, 24.

Figs. 7 to 10 show a third example of a loudspeaker enclosure 30. In Figs. 7 and 8 contour grid lines are shown to aid in showing the shape of the enclosure 30. The loudspeaker enclosure 30 has a side wall 34 that is tubular and is in the general shape of a spiral horn having an open end 31 and a closed end 32. The cross-sectional area of a volume enclosed by the side wall 34 decreases from the open end 31 towards the closed end 32. The loudspeaker driver 2 is mounted at the open end 31 of the enclosure 30, as shown in Figs. 9 and 10. The loudspeaker enclosure 30 also has two speakon sockets 15 (only one shown).

The enclosure 30 has a circular cross-sectional profile. In particular, the cross-sectional profile is circular in a plane that is perpendicular to a central axis 33 of the enclosure 30 that extends from the open end 31 to the closed end 32.

The spiral shape of the enclosure 30 is defined by terms of the Fibonacci number sequence, so that the spiral shape of the enclosure 30 is a Fibonacci spiral. In this example the first seven terms of the Fibonacci sequence are used to define the spiral shape of the enclosure 30.

In use, sound waves emitted from the rear of the driver 2, are propagated by the side wall 34 away from the speaker driver 2 and the open end 31 towards the closed end 32 by reflection from the inside surface of the side wall 34, in a similar manner to the way in which the sound waves are propagated towards the spiral shape 11 in the enclosure 1. Similar to the enclosure 1, when the sound reaches the closed end 32, it is reflected back on itself, causing the reflected sound waves to be cancelled out or reduced by the sound propagating towards the closed end 32 by destructive interference between the sound waves propagating towards the closed end 32 and the sound waves reflected back from the closed end 32. This reduction or cancelling of sound waves from the rear of the speaker driver 2 reduces the out of phase unwanted sound waves that are emitted from the enclosure 30.

The inventor has found that by using a circular cross-sectional profile as in the enclosure 30, reduction of out of phase unwanted sound waves is improved compared to the rectangular cross-sectional profiles of the other enclosures 1, 20.

The enclosures 1, 20, 30 described above all have spirals that are located in one plane. In other words, the spiral shapes used are all two-dimensional.

Figs. 11 to 16 show a fourth example of a loudspeaker enclosure 40. In Figs. 11 contour grid lines are shown to aid in showing the shape of the enclosure 40. The loudspeaker enclosure 40 has a side wall 41 that is tubular and the cross-sectional area of a volume enclosed by the side wall 41 decreases from an open end 42 towards a closed end 43. The loudspeaker driver 2 is mounted at the open end 42 of the enclosure 40. The loudspeaker enclosure 40 also has two speakon sockets 15, 16.

The enclosure 40 has a circular cross-sectional profile. In particular, the cross-sectional profile is circular in a plane that is perpendicular to a central axis 44 of the enclosure 40 that extends from the open end 42 to the closed end 43.

The tubular side wall 41 has both spiral and helical components. This means that that the spiral shape of the enclosure 40 is three-dimensional. As can be seen from Figs. 11 to 16, the tubular side wall 41 curves both inwardly as a spiral from the open end 42 to the closed end 43 (see Fig. 13) and upwards as a helix away from the open end 42 (see Figs. 12 and 14). A curve defined by outermost part 45 of the spiral component of the side wall 40 (see for example Fig. 13) appears similar to a conical helix but differs in some important respects.

In fact the curve defined by the outermost part 45 of the side wall 41 is created by drawing adjoining cubes each having a side length equal to the corresponding term of the Fibonacci series. Hence, the first cube has side = 1, the second cube has side = 1, the third cube has side = 2, the fourth cube has a side length = 3, the fifth cube has a side length = 5, etc. The cubes are placed such that a bottom edge of one cube is adjacent a top edge of the cube defined by the next term in the Fibonacci number sequence, so that when viewed from above it appears as the Fibonacci tiling, similar to the tiling shown in Figs. 17 to 19 but when viewed from the side it appears as if the cubes form an ascending curved staircase which expands radially outwardly. The curve of the outermost part 45 of the side wall 41 is then created by drawing circular arcs connecting the diagonally opposite corners of the cubes. Hence, the circular arc of each cube is a rotation of 90 degrees that extends upwardly from its starting point by the side length of the same cube. Therefore, the curve of the outermost part of the side wall 41 can be considered as a helix that is defined by the Fibonacci number sequence, or in other words a Fibonacci helix.

Therefore, the tubular side wall 41 defines an internal volume 46 that has a spiral component as it curves inwardly from the open end 42 to the closed end 43 but also extends in a direction that is perpendicular to a transverse plane of the tubular side wall 41, such as the transverse plane on which the cross-sectional view of Fig. 16 is based. Hence, the internal volume and the curve of the outermost part 45 of the tubular side wall 41 can be considered as a spiral (in this case a Fibonacci spiral) in which one end (eg the closed end 42) is displaced from the other end (eg the closed end 43) in a direction perpendicular to a transverse plane through the tubular side wall 41 and the displacement along the spiral from the closed end to the open end is in accordance with the Fibonacci number sequence.

In the enclosure 40, seven terms of the Fibonacci number sequence are used to define the displaced Fibonacci spiral (or Fibonacci helix) that is used to create the tubular side wall 41.

In use, sound waves emitted from the rear of the driver 2, are propagated by the side wall 41 away from the speaker driver 2 and the open end 42 towards the closed end 43 by reflection from the inside surface of the side wall 41, in a similar manner to the way in which the sound waves are propagated towards the spiral shape 11 in the enclosure 1. Similar to the enclosure 1, when the sound reaches the closed end 43, it is reflected back on itself, causing the reflected sound waves to be cancelled out or reduced by the sound propagating towards the closed end 43 by destructive interference between the sound waves propagating towards the closed end 43 and the sound waves reflected back from the closed end 43. This reduction or cancelling of sound waves from the rear of the speaker driver 2 reduces the out of phase unwanted sound waves that are emitted from the enclosure 40.

The inventor has found that by using a shape with combined spiral and helical components together with a circular cross-sectional profile (as in the enclosure 30), reduction of out of phase unwanted sound waves is improved compared to the rectangular cross-sectional profiles of the enclosures 1, 20 and compared to purely spiral enclosure 30.

Advantages of the invention include reducing the out of phase unwanted sound waves that come from the rear of the loudspeaker driver being emitted from the loudspeaker enclosures 1, 20, 30, 40.

Sound waves within the enclosure propagate in a laminar flow regime. This in turn increases the quality of the sound waves leaving the open end of the enclosure, resulting in increased quality at a distance from the enclosure. In addition, the laminar flow regime results in the sound waves propagating with an increased power and amplitude, as evidenced by an increased decibel (dB) level at a given distance from the open end of the enclosure.

Claims

CLAIMS1. An enclosure for an electroacoustic transducer, the enclosure comprising a number of walls which define a volume enclosed by the enclosure, a wall of the enclosure having an aperture configured to permit an electroacoustic transducer to be mounted in the aperture in use, and the enclosure further comprising a formation that defines a spiral-shaped volume having a first end and a second end that is narrower than first end; and wherein sound waves emitted from the rear portion of the transducer, in use, are transmitted into the spiral-shaped volume at the first end and propagate along the spiral-shaped volume from the first end towards the second end.
2. An enclosure according to claim 1, wherein the second end of the spiral-shaped volume is configured to reflect the sound waves back towards the opening is so that, in use, the reflected sound waves destructively interfere with the sound waves propagating towards the second end.
3. An enclosure according to claim 1 or claim 2, wherein the formation is configured such that the spiral-shaped volume lies in one plane.
4. An enclosure according to claim 1 or claim 2, wherein the formation is configured such that the spiral-shaped volume also has a helical component.
5. An enclosure according to any of the preceding claims, wherein the spiral-25 shaped volume progressively decreases from the first end towards the second end.
6. An enclosure according to any of the preceding claims, wherein the spiral-shaped volume is at least partly defined by a portion of a Fibonacci spiral.
7. An enclosure according to claim 6, wherein all of the volume enclosed by the enclosure is defined by a portion of a Fibonacci spiral.
8. An enclosure according to claim 6 or claim 7, wherein the portion of the Fibonacci spiral is defined by a number of sequential terms in the Fibonacci series.
9. An enclosure according to claim 8, wherein the sequential terms of the Fibonacci series that define the portion of the Fibonacci spiral comprise at least the first two terms in the Fibonacci series.
10. An enclosure according to claim 9, wherein the sequential terms of the Fibonacci series that define the portion of the Fibonacci spiral comprise at least the first seven terms in the Fibonacci series.
11. An enclosure according to any of the preceding claims, wherein the spiral-volume comprises a polynomial cross-section.
12. An enclosure according to claim 11, wherein the spiral-shaped volume comprises a quadrilateral cross-section.
13. An enclosure according to any of the preceding claims, wherein the spiral-shaped volume comprises a curved-shaped cross-section.
14. An enclosure according to claim 13, wherein the spiral-shaped volume comprises at least one of: an oval cross-section; a circular cross-section; and an elliptical cross-section.
15. An enclosure according to any of the preceding claims, wherein the formation comprises a spiral-shaped component.
16. An enclosure according to claim 15, wherein the formation further comprises a helical component.
17. An enclosure according to any of the preceding claims, wherein the first end of the spiral-shaped volume is displaced from the second end of the spiral-shaped volume in a direction transverse to a transverse plane through the spiral-shaped volume.
18. An enclosure according to claim 17, wherein the first end of the spiral-shaped volume is displaced from the second end of the spiral-shaped volume in a direction substantially perpendicular to the transverse plane in accordance with the Fibonacci number sequence.
19. An enclosure according to claim 18, wherein the displacement from the second end to the first end changes every 90 degree rotation in accordance with the next term in the Fibonacci number sequence.
20. An enclosure according to claim 19, wherein the displacement of the first end relative to the second end increases from the second end to the first end in accordance with a sequential number of terms of the Fibonacci number sequence.
21. An enclosure according to any of claims 17 to 20, wherein a curve defined by the radially outermost points of the spiral volume has a constant gradient relative to the transverse plane.
22. An enclosure according to any of the preceding claims, further comprising a connector to permit an audio signal to be input to the enclosure.
23. An enclosure according to claim 22, further comprising a second connector to permit an audio signal to be output from the enclosure.
24. An enclosure according to any preceding claim, wherein in use sound 30 waves propagate within the enclosure in a laminar flow regime.