A speaker enclosure

Abstract

The speaker enclosure 30 comprises a damped pathway 14, a drive unit mount 22 and a port 12. The port is fluidly connected to the damped pathway and the drive unit mount. The damped pathway comprises

Description

TECHNICAL FIELD The present disclosure relates to a speaker. Particularly, but not exclusively, the disclosure relates to a speaker enclosure. Aspects of the invention relate to a speaker enclosure, to a transmission line speaker, to a bass reflex speaker, a computer-implemented method for designing a speaker enclosure passageway geometry, a data processing apparatus, a computer program, a computer-readable medium. BACKGROUND Speakers come in a variety of arrangements and generally include a speaker enclosure and a drive unit (e.g. a loudspeaker, bass driver, mid-range driver, high range driver, tweeter, etc). The speaker enclosure is used to prevent soundwaves generated from the front and rear of the drive unit interfering with each other. Examples of speakers are closed-box speakers, transmission line speakers and bass reflex speakers. Closed-box speakers are substantially airtight speaker enclosures with the drive unit being mounted on the speaker enclosure. Closed-box speakers do not have a vent or port. A bass reflex system utilises a speaker enclosure which has an aperture in the wall of the speaker enclosure to enable air to move in-and-out of the speaker. A transmission line speaker features a drive unit mounted at some point along a long tube that is open at one end. At frequencies with wavelengths corresponding to multiples of the tube length, the tube resonates, giving very high acoustic pressure output at the open end of the tube and simultaneously reducing the excursion of the drive unit by means of the air inside the tube coupling to the driver and behaving like a mass attached to the cone of the speaker. Such prior art speaker designs with vents or ports can become susceptible to acoustic issues at certain frequencies and input levels. It is at least one aim of the present invention to provide a speaker enclosure that addresses one or more of the disadvantages associated with the prior art. SUMMARY OF THE INVENTION Aspects and embodiments of the invention provide a speaker enclosure, a speaker, a transmission line speaker, a bass reflex speaker, a computer-implemented method, a data processing apparatus, a computer program and a computer-readable medium as claimed in the appended claims. According to an aspect of the invention, there is provided a speaker enclosure comprising a damped pathway, a drive unit mount and a port fluidly connected to the damped pathway and the drive unit mount; wherein the damped pathway comprises a plurality of passageways extending a first distance between a first portion of the damped pathway and the port; wherein the first distance is equal to or greater than a length calculated in dependence upon a hydrodynamic entry length for fully developed flow in at least one of the plurality of passageways. The speaker enclosure provides a number of benefits, by relating the first distance to the hydrodynamic entry length a speaker comprising the speaker enclosure has reduced unwanted noise as compared to a speaker without such an arrangement due to the stabilisation of fluid flow being expelled out of the port in use. As a result of this stabilisation there is a decrease in turbulent air flow which may otherwise cause ‘chuffing’ at the port. Chuffing is noise caused by turbulence as air enters or exits a speaker port due to large movements of air within the port. Such chuffing can be exacerbated when using speaker systems at or near maximum sound intensity (volume) of the drive unit in a speaker. Without this unwanted chuffing, higher fidelity sound can be output from the speaker. The arrangement advantageously provides improved and higher fidelity sound (with reduced chuffing) without the need to employ more costly drive units. Likewise, where ‘top-of-the-range’ drive units are improved there is a noticeable improvement to sound fidelity. Moreover, by relating the length to the hydrodynamic entry length reduced chuffing in practice can be utilised in many different specific speaker enclosure geometries. For example, a desk speaker will typically have a smaller enclosure (e.g. having a footprint of 0.2 m by 0.2 m) than a free-standing speaker (e.g. having a footprint of 0.5 m by 1.5 m) for use in a music venue or event space however the invention may be utilised in either sized speaker and is not limited to use in a particular sized speaker. Optionally, the first distance may be from the first portion of the damped pathway to the port. 2 The speaker enclosure, wherein the length is calculated by: L = nl_h wherein: L is a length in m, n is a dimensionless value, and Lh is the hydrodynamic entry length in m. n = 0.1 to 10 and Re -2300 to 2700 (turbulent flow) or preferably -2500. By Optionally, wherein n is value between 0.1 and 10. Optionally, wherein the hydrodynamic entry length is calculated by: Lh = 1.359DhRe1 / 4 wherein: Lh is the hydrodynamic entry length in m, Re is the Reynolds number, dimensionless, and Dh is the hydraulic diameter of the fluid flow passageway in m. By taking into account the hydrodynamic entry length of the fluid flow passageway a speaker enclosure can be produced which can stabilise the flow conditions at or next to the port to reduce losses. Optionally, wherein the hydraulic diameter is calculated using the equation: Dh = (4A) / P wherein: A is the cross-sectional area, m2, and P is the perimeter of the wet part of the fluid flow passageway, m. The ‘wet part’ being the perimeter of the fluid flow passageway in contact with the fluid passing through the fluid flow passageway. Optionally, wherein the plurality of passageways are parallel with respect to each other. Providing the passageways parallel to each other reduces the likelihood of turbulence being introduced to a volume of fluid as it passes through the passageway. Optionally, wherein the number of passageways of the plurality of passageways is 2 to 50 channels. Preferably 5 to 25 channels. Optionally, wherein the speaker enclosure further comprises a body, the body comprising the plurality of passageways. By providing the passageways in or on a body, the speaker enclosure may be more easily assembled by attaching the body to the enclosure whilst is being manufactured. Optionally, wherein the body further comprises the port. By defining the port as part of the body there is a reduction in any surface disruptions as the port, body and passages may be unitary. As a result, there may not be any airgap between the passageways and the port which may provide an acoustic boundary introducing turbulence. Optionally, wherein the plurality of passageways extends the first distance from the first portion of the damped pathway to a second distance from the port. Optionally, wherein each passageway of the plurality of passageways are separated from each other by a wall or walls that extend along the length of the passageways. Optionally, wherein the wall or at least one of the walls has a cutaway portion, the cutaway portion being disposed at a first end of the wall, the first end of the wall being closer to the port than a second end of the wall. Optionally wherein the speaker enclosure further comprises an insert and wherein the plurality of passageways are defined by the insert. Optionally wherein the speaker enclosure further comprises a plinth and wherein the plurality of passageways are defined by the plinth, the plinth being located at the base of the speaker enclosure. Optionally, wherein the insert or plinth are separable from a body of the speaker enclosure. According to a further aspect of the invention there is provided a speaker comprising the speaker enclosure according to any embodiment of the previous aspect and a drive unit, wherein the drive unit is mounted in the drive unit mount and a rear portion of the drive unit is fluidly connected to the damped pathway and the port. According to an even further aspect of the invention there is provided a transmission line speaker comprising the speaker enclosure according to any embodiment of the aspect describing a speaker enclosure and a drive unit, wherein the drive unit is mounted in the drive unit mount and a rear portion of the drive unit is fluidly connected to the damped pathway and the port. Optionally, wherein the damped pathway has at least one bend along the length of the damped pathway, preferably wherein the damped pathway is tortuous and / or preferably wherein the damped pathway has one or more partially closed chambers. According to an even further aspect of the invention there is provided a bass reflex speaker comprising the speaker enclosure according to any embodiment of the aspect describing a speaker enclosure and a drive unit, wherein the drive unit is mounted in the drive unit mount and a rear portion of the drive unit is fluidly connected to the damped pathway and the port. According to a yet further aspect of the invention there is provided a computer-implemented method for designing a speaker enclosure passageway geometry, the method comprising the steps of receiving a first speaker enclosure geometry data, the speaker enclosure geometry data describing a damped pathway, a drive unit mount and a port fluidly connected to the damped pathway and the drive unit mount, and the damped pathway includes a plurality of passageways extending a first distance between a first portion of the damped pathway and the port; calculating a minimum length (L) of the first distance in dependence upon a hydrodynamic entry length (Lh) for fully developing flow in at least one of the plurality of passageways; and outputting the minimum length to a user for designing a first speaker enclosure with a plurality of passageways extending the first distance, where the first distance is equal to or greater than the minimum length such that there is a reduction in unwanted noise at the port due to a change in a first fluid characteristic at or adjacent the port. The computer-implemented method for designing a speaker enclosure passageway geometry provides a more effective method to design and produce a speaker enclosure which has reduced chuffing and vent compression at high output levels as compared to 5 speaker enclosures without a plurality of passageways with a length dependent upon the hydrodynamic entry length. The computer implemented method takes into consideration the geometry and calculated hydrodynamic length in order to change the first fluid characteristic. Optionally, the method may comprise an additional step of calculating the change in the first fluid characteristic. Calculating the change in the first fluid characteristic may enable more intuitive analysis of the output by the user and enable the user to tailor the characteristics of the fluid flow at the port for enabling superior sound fidelity in use. Optionally, the change in the first fluid characteristic is: compared to a second speaker enclosure geometry identical to the first speaker enclosure except it is without a plurality of passageways, or compared to a second speaker enclosure geometry identical to the first speaker enclosure but with a plurality of passageways having a first distance smaller than the minimum length. By undertaking such a comparison, a quick and efficient means to compare different speaker enclosure geometries can be made without the need to produce real world models in when undertaking testing. Optionally, the step of receiving the speaker geometry data comprises retrieving the first speaker geometry data from a computer readable medium or memory, or the step of receiving the speaker geometry data from a user input. By retrieving the first speaker geometry data it enables quick and efficient data input. Optionally, the speaker enclosure geometry data describing one or more of: type of speaker, speaker enclosure geometry, drive unit mount geometry, port geometry, geometry of the plurality of passageways, damped pathway geometry, location and geometry of a dampening material, data relating to the materials properties of a dampening material. By incorporating such data into the method a more intuitive analysis of fluid flow through the speaker enclosure can be obtained. Optionally, the method further comprises the step of simulating the fluid flow conditions in the first speaker geometry determined from the first speaker enclosure data and having a plurality of passageways extending the first distance to calculate the fluid characteristic at or 6 adjacent the port and determining the first fluid characteristic. By undertaking such a comparison, a quick and efficient means to compare different speaker enclosure geometries can be made without the need to produce real world models when undertaking testing. Optionally, the first fluid characteristic is one or more of: vorticity, pressure, velocity, noise level, harmonic distortion, sound pressure. By calculating the vorticity, pressure, velocity, noise level, harmonic distortion and / or sound pressure more intuitive analysis can be undertaken by the user to produce higher fidelity speakers. Optionally, the method further comprises the step of: determine a second speaker enclosure in dependence upon the first speaker enclosure geometry data, the second speaker enclosure without a plurality of passageways or having a plurality of passageways having a first distance smaller than the minimum length; simulating fluid flow conditions in the second speaker enclosure to determine a second fluid characteristic at or adjacent the port of the second speaker enclosure, comparing the first fluid characteristic and second fluid characteristic; and outputting data relating to the first and second fluid characteristics to a user for designing a first speaker enclosure. By undertaking such a comparison, a quick and efficient means to compare different speaker enclosure geometries can be made without the need to produce real world models when undertaking testing. Optionally, the second fluid characteristic is one or more of: vorticity, pressure, velocity, noise level, harmonic distortion, sound pressure. By calculating the vorticity, pressure, velocity, noise level, harmonic distortion and / or sound pressure more intuitive analysis can be undertaken by the user to produce higher fidelity speakers. Optionally, the first fluid characteristic and second fluid characteristic are the same. Preferably, the same parameter or same set of parameters. Optionally, wherein the step of calculating the minimum length comprises the equation: L = nLh wherein: L is a length in m, n is a dimensionless value, and Lh is a length in m. Optionally, wherein n is value between 0.1 and 10. Optionally, wherein the hydrodynamic entry length is calculated by: Lh = 1.359DRe1 / 4 wherein: Lh is a length in m, Re is the Reynolds number, dimensionless, and D is the diameter of the fluid flow passageway, m2. Optionally, wherein D is calculated using the equation: D = (4A) / P wherein: A is the cross-sectional area, m2, and P is the perimeter of the wet part of the fluid flow passageway, m. According an additional aspect of the invention there is provided a data processing apparatus comprising means for carrying out the method. According to a further additional aspect of the invention there is provided a computer program comprising instructions which, when the program is executed by a computer, cause the computer to carry out the method. According to an even further additional aspect of the invention there is provided a computer-readable medium having stored thereon the computer program. BRIEF DESCRIPTION OF THE DRAWINGS One or more embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 is a schematic showing a speaker having a speaker enclosure with top, left side, right side, front walls and a port having a plurality of channels. The extent of the channels into the speaker enclosure is indicated by the dashed lines; Figure 2 is an isometric view of a speaker enclosure in accordance with an embodiment of the invention, the speaker enclosure having a cutaway portion to show some of the internal aspects of the enclosure; Figure 3 is a body comprising a plurality of passageways in accordance with an embodiment of the invention; Figure 4 is a free-standing speaker in accordance with an embodiment of the invention comprising the body of Figure 3, in this example, the body is a plinth having feet on which a portion of the speaker enclosure sits; Figure 5 is an insert in accordance with an embodiment of the invention; Figure 6 is a speaker comprising the insert which forms part of a port of the speaker in accordance with an embodiment of the invention; Figure 7 is a cross-sectional view through the speaker of Figure 6 comprising the insert of Figure 5 in accordance with an embodiment of the invention; Figure 8 is a schematic drawing of a computer configured to undertake a method in accordance with an embodiment of the invention; Figure 9 is a flowchart describing a method of designing a speaker geometry in accordance with an embodiment of the invention; Figure 10 is a 2D slice of a three-dimensional computerised fluid dynamics simulation of a speaker and a portion of a volume adjacent to an exit of a port of the speakerin accordance with an embodiment of the invention; and Figure 11 is a trace showing sound pressure against frequency for different speaker enclosure geometries including a speaker with no channels / fins in the port, a speaker with 6 channels / fins of 50 mm length in the port, a speaker with 20 channels / fins of 50 mm length in the port, a speaker with 6 channels / fins of 400 mm length in the port, and a speaker with 20 channels / fins of 400 mm length in the port. The x-axis is logarithmic. The x-axis intersects the y-axis at 400 Hz. DETAILED DESCRIPTION A speaker enclosure, a transmission line speaker, a bass reflex speaker, a computer-implemented method for designing a speaker enclosure passageway geometry, a data processing apparatus, a computer program, and a computer-readable medium will be described with the aid of Figures 1 to 11. A speaker 10 is shown in Figure 1. The speaker may be an active speaker or a passive speaker which may require external amplification. The speaker 10 may be a transmission line speaker 100, 110 (Figures 2 and 4) or a bass reflex speaker 200 (Figure 6 and 7). The speaker 10 has a speaker enclosure 3O.The speaker enclosure is unit defining an internal space. The speaker enclosure is a cuboid. A forward face, a left side face and a top face are visible in Figure 1, but for the purposes of explanation those faces are shown as see-through. The speaker enclosure also has a rear face and bottom face. The forward face has two apertures, a first aperture and a second aperture. The first aperture is provided above the second aperture. The speaker 10 has a drive unit 20. The drive unit 20 is mounted onto the speaker enclosure 30 in the first aperture. The drive unit is mounted via a drive unit mount 22 on the speaker enclosure 10. The drive unit has a front side and a rear side. The rear side faces the internal space provided the within the enclosure. The speaker enclosure 30 has a port 12, the port 12 is defined by the speaker enclosure 30. The port 12 is provided in the second aperture. The port 12 extends into the speaker enclosure 30 and defines a plurality of passageways 40, or alternatively (as will be described below) the plurality of passageways may be defined by an insert that is received in the port 12. The speaker enclosure 30 has a damped pathway that extends between the drive unit 20 and the port 12. The damped pathway provides acoustic dampening. The damped pathway may comprise one or more internal walls of the speaker enclosure 30 and / or internal surfaces of the speaker enclosure 30 or acoustic chambers 102 and / or an acoustically absorbent material (such as a speaker acoustic foam as known in the art). For reasons of clarity acoustically absorbent material is not shown in the Figures however it may be incorporated into the speaker enclosure 30 by means and methods known to the skilled person. Acoustic dampening may be provided by the internal walls of the speaker enclosure 30 which reduce acoustic bleed through the walls of the speaker 10 which may be heard by user when listening to audio output from the drive unit 20. The drive unit 20 is fluidly connected to the port 12 via the damped pathway 14. In use, pressurised air from the rear side of the drive unit 20 passes through the damped pathway 14 and out through the port 12 into the atmosphere surrounding the speaker 10. This side of the drive unit 20 is not normally visible in use. The front and rear of the drive unit 20 may be substantially fluidly isolated from each other to reduce the likelihood of interference between soundwaves being produced from the front of the drive unit 20 and the rear of the drive unit 20. The fluid isolation may be achieved by means and methods known in the art when mounting the drive unit 20 to the drive unit mount 22. The plurality of passageways 40 are provided in the internal space of the speaker enclosure 30 and port 12. The plurality of passageways 40 are fluidly connected to the port 12. The passageways 40 have a distance D1 greater than or equal to a length L dependent upon the hydrodynamic entry length Lh. By providing such passageways the speaker 10, in use (i.e. emitting sound from the drive unit), has a reduction of unwanted noise compared to a speaker without such an arrangement. This is due to the stabilisation of fluid flow being expelled out of the port in use which is fluidly connected to a rear side of a drive unit 20. The speaker 10 may further comprise electronics such as a crossover circuit such as an active or passive crossover circuit and / or other electronic circuits as known in the art. To aid explanation of the speaker 10, a partially cutaway view of a speaker enclosure 30 of a transmission line speaker 100 is shown in Figure 2. The speakers 10, 100 may comprise a similar arrangement of features. The drive unit 20 is not shown in Figure 2. The walls 42 may have a cutaway portion 44 located at one end of the wall 42 such as at the end of the wall 42 that is closest to the port 12 as is the case in Figure 2. The cutaway portion 44 may be located at a bottom side 43 of the wall 42. There may also be a second cutaway portion 44 located at an upper side 45 of the wall 42. The plurality of passageways 40 and walls 42 may be attached to the enclosure 30 either directly or indirectly. For example, in the embodiment depicted in Figure 1 and 2 the walls 42 11 may be attached to a portion of the speaker enclosure 30, for example the walls 42 may be glued in place or retained in grooves on the speaker enclosure 30, for example a groove on the speaker enclosure 30 configured to receive the bottom side 43 of the wall 42 and / or a groove on the speaker enclosure 30 configured to receive the upper side 45 of the wall 42. The speaker enclosure 30 may optionally compromise a body 50. The body 50 has the plurality of passageways 40 and walls 42. An example of a body 50 is shown in Figure 3. The body 50 may be additionally comprise the walls 42 as shown in Figure 3. The body 50 may be assembled separately to the rest of the speaker enclosure 50. For example, where the body 50 comprises a constant cross-section the body 50 (or a portion thereof) may be made by an extrusion process, for example a polymer extrusion process or a metal (or alloy) extrusion process. Such a manufacturing process reduces the complexity of assembly and manufacturing for the speaker 10 in practice. The body 50 may form a portion of the speaker enclosure 30 and may comprise the port 12. In such a case the body 50 may have one or more sidewalls 52, 54 which form a part of the speaker enclosure 30 sidewalls when the body and the rest of the speaker enclosure 30 are assembled together. Optionally, the body 50 may have a slot 56 on a rear portion of the body 50. The slot 50 is configured to receive a panel or sidewall of the speaker enclosure 30 to close off the rear of the body 50 in use. An example of the body forming part of the speaker enclosure 30 sidewalls is shown in Figure 4 which shows a speaker 110 with a body 150 which is a plinth 150. The plinth 150 has four feet 152, as will be clear to the skilled reader only three feet are visible with the fourth hidden by the plinth 150 in the view of Figure 4. In alternative configurations there may be no feet 152 or there may be one, two, three, four, five, six, or any range or subset of feet 152. The feet 152 may be vibrational dampening feet 152 as known in the art. In alternative configurations of the body 50 instead of feet 152 there may be fixture for attaching a stand or pole to the body 50 such that the body 50 and speaker enclosure 30, 110 may be attached to a stand or pole in use. The fixture may be a male or female threaded connection, a bracket, a bayonetted fitting or any other suitable connection known in the art. Optionally, both feet 152 and a fixture for attaching a stand or pole to the body 50, 150 may be provided such that the same speaker 10, 110 may be utilised in more than one configuration, e.g. free standing, stand mounted, pole mounted, etc. 12 As shown in Figures 2 and 3 the body 50, 150 has an optional concave upper surface 58 that is shaped to receive a concaved lower surface of the front panel 132 of the speaker enclosure 130. The upper surface 58 being defined by the walls 42 and sidewalls 52, 54 of the body 50, 150. The upper surface 58 being concave helps to seat the upper part of the speaker enclosure 130 onto the body 50, 150 during manufacture. In alternative configurations the upper surface 58 may be flat or convex, in both cases the bottom surface of the upper part of the speaker enclosure 130 is complementary in shape to the upper surface 58. Instead of a plinth 150, the speaker enclosure 30 may comprise an insert 250. An example of an insert 250 is shown in Figure 5. The insert 250 comprises a tube 252 that extends between a first opening 254 and a second opening 256. The second opening may have a flared end 258 as shown inn Figure 5 or may not be flared. As shown in Figure 5 the second opening 256 forms the whole or a part of the port 12. The insert 250 in the embodiment depicted in Figure 5 comprises a lattice 260, the lattice 260 comprising a plurality of passageways 240 separated by a plurality of walls 242. In the depicted embodiment the cross-sectional area of each passageway 240 is square or rectangular, however any shape may be utilised for example, the shape may be any one of: circular, triangular, square, rectangular, pentagon, hexagon, septagon, octagon, nonagon, dodecagon, or any n-sided polygon (regular or irregular) where n = 3 to 12. Alternatively, the lattice 250 may be made be made up of a combination of repeating or tessellating shapes. For example, a herringbone pattern. Alternatively, the lattice 250 may be made up of a similar pattern as the embodiment depicted in Figure 3 and 3. As will be apparent the body 50 or plinth 150 may likewise have a lattice 250 instead of the depicted arrangement shown in the embodiment of Figures 2 and 3. Figure 6 shows a speaker 210 that incorporates the insert 250. In the depicted example the speaker 210 is a bass reflex speaker 210. Figure 7 shows a cross-sectional view of the speaker 210. As can be seen in Figure 7 insert 250 is located in a wall of the speaker enclosure 230. Whilst in the depicted embodiment of Figure 7 the insert 250 is located on a rearward face of the speaker enclosure 230 spaced apart from the drive unit 20 the insert 250 may be disposed on any face of the speaker enclosure. In alternative configurations the speaker 210 may instead be a transmission line speaker and may comprise one or more walls and all acoustic chambers 102 similar to the depicted embodiment of Figure 2. To facilitate cleaning of the speaker 10, 110 in use the body 50, plinth 150 or insert 250 may be removable from the speaker enclosure 30, 130, 230. This facilitates easy cleaning of the speaker 10, for example for removal of dust. As shown in Figure 1 the damped pathway 14 comprises a plurality of passageways 40 extending a first distance D1 between a first portion 32 of the damped pathway 14 and the port 12. In the depicted embodiment of Figure 1 the passageways extend up to the port 12. Optionally, the plurality of passageways 40 may be offset from the port 12. The plurality of passageways may extend the first distance D1 from the first portion 32 of the damped pathway 14 to a second distance D2 from the port 12 (for example as shown in Figure 7). In Figure 1 there are four passageways 40 which are separated by three walls 42. The walls 42 may extend the entire length of the passageways 40 and may equal D1. Whilst four passageways 40 and three walls 42 are depicted this is not intended to be limiting and is for the purpose of teaching the invention. There may be any number of passageways 40, for example 2 to 40, 2 to 30, 2 to 25, 5 to 30, 5 to 25 or any subset thereof. As will be apparent for x number of passageways the number of walls in such a configuration will equal x - 1. In Figure 1 the passageways 40 are parallel to each other, in alternative embodiments two or more of the passageways 40 may be parallel to each other, or only a portion of the two or more passageways 40 may be parallel to each other, preferably wherein only a portion of the two or more passageways are parallel to each other the portion is the portion which extends to the port or adjacent the port. Other passageway 40 arrangements, as discussed below, may be employed with the speaker 10 without departing from the scope of the invention. Whilst Figure 1 depicts an embodiment with a single port 12 and single set of passageways 40 in alternative embodiments more than one port 12 may be present with each port having 14 its own set of passageways 40 or only a sub-set of the number of ports 12 having its own set of passageways 40. The distance D1 is equal to or greater than a length L calculated in dependence upon a hydrodynamic entry length Lh for fully developing fluid flow in at least one of the plurality of passageways 40. A fully developed flow may be a fully developed velocity profile for fluid passing through one of the plurality of passageways 40. L is calculated using equation 1: L = nLh ...(1) wherein: L is a length in m, n is a dimensionless value, and Lh is the hydrodynamic entry length in m. The value of n may be 0.1 to 10, or 0.1 to 1. Preferably n = 1. The hydrodynamic entry length is calculated using equation 2: Lh = 1.359DhRe1 / 4 ...(2) wherein: Lh is the hydrodynamic entry length in m, Re is the Reynolds number, dimensionless, and Dh is the hydraulic diameter of the fluid flow passageway in m. By taking into account the hydrodynamic entry length Lh of the fluid flow passageway a speaker enclosure 30 can be produced which can stabilise the flow conditions at or next to or adjacent the port 12. This reduce losses due to excess turbulence which may affect audio quality when a user listens to an audio output of the speaker 10 comprising the speaker enclosure 30. The Reynolds number may be a value of approximately 1500 to 2700, or 2100 to 2700 (that is, partially to fully turbulent flow) or preferably a Re = 2500 or Re = 1575. Alternatively, the Reynolds number may be calculated using equation 3: Re = (WDh) / (pA) ...(3) Wherein: W is mass flowrate of fluid in kg / s, p is dynamic viscosity of fluid in Pa.s, A is Cross sectional area of the port in m2, Dh is the hydraulic diameter of the plurality of passageways in m. The mass flow rate may be an average mass flow rate in kg / s. Optionally, the mass flow rate may be 0.029kg / s. Optionally, the mass flow rate may be obtained by means and methods known in the art and may be suited for a particular speaker geometry. Dh is calculated using equation 4: Dh = (4A) / P ...(4) wherein: A is the cross-sectional area, m2, and P is the perimeter of the wet part of the fluid flow passageway, m. The ‘wet part’ of the fluid flow passageway being the perimeter of the fluid flow passageway in contact with the fluid passing through the fluid flow passageway. According to an additional aspect of the invention a computer-implemented method 400 for designing a speaker enclosure 30 passageway geometry is described with the aid of Figures 8 to 11. The method 400 is used to design any of the previously described speaker enclosures 30 and minimum lengths L in dependence upon the hydrodynamic entry length Lh for a speaker 10, 100, 200 which has reduced chuffing and vent compression at high output levels as compared to a speaker enclosure without the passageway geometry. The method 400 is implemented in a computer 310 as shown in Figure 8 and may be undertaken using a computational fluid dynamics software suit, for example Fluent TM, Ansys TM, or a proprietary modelling suit such as using COMSOL TM, MATLAB TM, C++ or FORTRAN or alternative computing language as known in the art. The method 400 may be undertaken either using a single computer or utilising a distributed computing system. The computer 310 receives one or more inputs 300 including a speaker enclosure geometry data. The inputs 300 may be entered into memory of the computer 310 by manual means (e.g. data entry by the user) or they may be loaded from a stored memory device or computer readable medium or memory. For example, the inputs 300 may be stored in and retrieved from a database. Optionally, the inputs 300 may comprise additional information, for example the speaker enclosure geometry data may comprise data describing one or more of: type of speaker, speaker enclosure geometry, drive unit mount geometry, port geometry, geometry of the plurality of passageways, damped pathway geometry, location and geometry of a dampening material, data relating to the materials properties of a dampening material. These parameters, such as the material used to dampen the pathway 14 may have a measurable effect upon the fluid flow through the speaker enclosure 30. The geometry of the plurality of passageways may comprise any one or more of: the width of each passageway, the distance between each passageway, the cross-sectional area of each passageway, the cross-sectional shape of each passageway, the breadth of each passageway and the wall thickness of the wall separating each passageway. Whilst Figure 8 shows the computer 310 as a desktop computer this is purely for explaining the invention. Computer 310 may be a terminal, distributed computing device, a laptop, a server, or any other suitable computing device 310. The computer 310 then determines a value for the minimum length L dependent on the inputs received and outputs the minimum length L. The output 320 may be an output to a display of the computer or a printout or other means of displaying the value or a 3D model of the speaker enclosure pathway geometry comprising a passageway of a minimum length L. The output 320 is for use in designing and manufacturing a speaker according to the output. Preferably, the output 320 is for use in designing and manufacturing a speaker according to the output to reduce unwanted noise at or adjacent to the port. Flowchart 400 shown in Figure 8 describes a number of method steps for designing a speaker enclosure 30. At step 410 the first speaker enclosure geometry data is received by the computer 310. The first speaker enclosure geometry data may be stored on a transitory memory means in the computer 310. The speaker enclosure geometry data describes the damped pathway 14, a drive unit mount 22 and a port 12 fluidly connected to the damped pathway 14 and the drive unit mount 22. The damped pathway 14 includes a plurality of passageways 40 extending a first distance D1 between a first portion 32 of the damped pathway and the port 12. The speaker enclosure geometry may describe a bass reflex speaker 100 or a transmission line speaker 200. For example, the data may comprise data relating to one or more of: a length of the damped pathway, relative location, depth, location of acoustic insulation, location of acoustic chambers, material that the speaker enclosure is made from and other previously described features of either the bass reflex speaker 100 or transmission line speaker 200. Subsequently at step 420 the minimum length (L) of the first distance is calculated in dependence upon a hydrodynamic entry length (Lh) for fully developing flow in at least one of the plurality of passageways 40 The minimum length (L) of the first distance is calculated in response to receiving the input data. The minimum length L may be calculated using the equations 1 to 4 above. Subsequently at step 430 the computer 310 outputs 320 the minimum length to a user for use in designing a first speaker enclosure with a plurality of passageways 40 extending the first distance D1. The first distance D1 being equal to or greater than the minimum length L such that there is a reduction in unwanted noise at the port 12 due to a change in a first fluid characteristic at or adjacent the port 12. An example of the parameters which may be used in the method 400 are provided below in Table 1 which describe the simulated speaker geometry 500 of Figure 10 and associated parameters thereof. The parameters listed and the values thereof are not intended to be limiting but are for the purpose of teaching the invention. The speaker geometry 500 of Figure 10 is a simplified transmission line speaker which comprises a single damped pathway with air travelling in direction F at a mass flow rate W. The mass flow rate W in this simplified geometry may be constant or variable. Where the mass flow rate W is constant W may be an average (e.g. mean) value of mass flow rate as expected in a speaker system, for example W may be 0.01-0.1 Pa.s. For the purposes of simulation the drive unit 20 is not included but instead is a boundary condition with a fluid flow entering the simulated system at a constant mass flow rate W is utilised. The constant mass flow rate W may be an average of expected mass flowrates expected in a speaker system of a certain size. Symbol Name Value M Dynamic Viscosity of Air 1.8x10-5 Pa.s A Cross-sectional area of the port 141 cm2 (including area lost from geometry of plurality of passageways) b Breadth of the Port 15 cm D1 Length of Fins 40 cm Dh Hydraulic Diameter 138.17 cm2 H Height of Damped Pathway 10 cm N Number of Passageways 19 P Perimeter of the Wet Part of the Fluid Flow Passageway 408.2 cm Re Reynolds Number 1575 T Length of Damped Pathway 100 cm W Mass Flowrate 0.029 kg / s w Width of the Port 15 cm Lh Hydrodynamic Entry Length 11.83 cm Table 1 - Example parameters for use in method 400 An example of the output 320 is shown in Figure 10. The output shows a simulated speaker enclosure passageway 500 created utilising the method 400. As can be seen from the 5 computational fluid dynamic output the vorticity V in s-1 is in the region of 0.5 to 1 s-1 at the simulated port 512. This indicates a fully developed flow profile is obtained for this simulation. In this example the Figure 10 shows a 2D slice of a 3D simulation showing the vorticity or rotation rate of a passageway comprising twenty-one walls 542 with a D1 equal to 400 mm. A low level of vorticity in a simulated volume Vs at the region near or adjacent to 10 the port, as shown in Figure 10 indicates that there is a simulated reduction in chuffing and vent compression at the simulated port 512. This indicates that there is a measurable effect in the interaction between the acoustic boundary at the end of the walls which are adjacent to the simulated port 512 and thus improve performance. 15 The effect of the invention is not only measurable in computational fluid dynamic simulations, but it is also born out in rear-world models of a speaker manufactured utilising the method. The reduction of unwanted noise at the port 12 is a measurable effect as can be seen in Table 1 below for the same port 12 size but with different passageway geometries of speakers produced utilising the method 400. 20 No passageways 602 6 passageways D1 = 50mm 604 20 passageways D1 = 50mm 606 6 passageways D1 = 400mm 608 20 passageways D1 = 400mm 610 Average Level (dB) 14.27 12.81 12.47 9.23 6.62 Reduction from Empty (dB) 0 1.46 1.80 5.04 7.65 Table 2 -Average Sound Pressure of Port Spectrum between 2kHz and 8kHz The experiments used a fixed geometry for the port opening of 0.015 m2 and a passageway arrangement similar to Figure 1 and 2 with a plurality of vertical walls 42 separating the passageways 40. As can be observed from Table 1 increasing the length of the passageways (in dependence upon the hydrodynamic entry length) has a measurable effect to improve the performance of the concept by reducing the interaction between the acoustic boundaries at each end of the fins. The D1 = 50 mm in this example is a value which is below the hydrodynamic entry length Lh for the configuration of speaker 10 whereas the value D1 = 400 mm is above the value of Lh. As such, whilst there is a marked improvement in the reduction in dB level from a no passageway arrangement for the 6 or 20 passageway D1 = 50 mm arrangement there is an even greater reduction for the 6 or 20 passageway D1 = 200 mm arrangement. This is also confirmed from careful review of Figure 11 which shows a graph 600 with overlays of high frequency vent noise between 400 Hz to 9 kHz for the different arrangements: No passageways 602, 6 passageways D1 = 50mm 604, 20 passageways D1 = 50mm 606, 6 passageways D1 = 400mm 608 and 20 passageways D1 = 400mm 610. As can be generally observed there is an overall reduction in the peaks of each trace from the worst performing trace 602 for the no passageway arrangement to the best performing arrangement 610 with 20 passageways at 400 mm in length. Figure 11 has been obtained by experimental analysis of speaker geometries produced using the design method in order to validate said design method 400. As will be apparent, the graph 600 may be directly obtainable as a result of the simulation shown in Figure 10 by measuring the SPL (‘Sound Pressure Level’ in kPa) at a defined point in the volume Vs for various frequencies, e.g. between 400 Hz and 9 kHz. By directly obtaining the results from the simulation time, cost, and materials can be saved which would otherwise be wasted creating multiple models of a speaker enclosure to be tested with specific passageway / channel / fin geometries. Moreover, speaker testing is generally undertaken in anechoic chambers (a room designed to stop reflections or echoes of sound). Time in an anechoic chamber can be very costly to rent, as such by utilising the method the designer of a speaker can reduce time in such a chamber by either only utilising the most preferable result(s) of the simulation with a model designed to the specifications of the simulation, or not testing a model in an anechoic chamber at all. As will be apparent to the skilled reader, a speaker comprising the invention will have reduced levels of cuffing and / or distortion which may be noticeable and measurable change in fluid characteristic (e.g. vorticity, volume (dB), pressure, velocity, noise level, harmonic distortion, sound pressure, etc). This change may be particularly apparent when the speaker 10 is used at high power levels (i.e. high volume) especially for low frequency Hz audio. Optionally, the method 400 may further comprise the step of calculating the fluid characteristic. For example, this may comprise a step of simulating the fluid flow of the speaker geometry in use for example as shown in Figure 10. Optionally, after the calculation of the fluid characteristic subsequently, the calculated fluid characteristic may be compared to a second speaker enclosure geometry which is identical to the first speaker enclosure 500 which has been simulated but without the presence of the passageways 540 or walls 542. Or alternatively it may be compared to a second speaker enclosure geometry identical to the first speaker enclosure 500 but with a plurality of passageways having a first distance smaller than the minimum length L. Undertaking this comparison enables the user to tailor the audio response required for a particular speaker geometry quickly and efficiently. For example, criteria for the ‘best’ speaker enclosure design may be obtained from the results of the simulation 600 by comparing the average level (dB) of each second speaker geometry design created using the method 400 (e.g. for each of the example in Table 2). The method 400 may as a result comprise the step of selecting the speaker enclosure geometry with the greatest reduction in level (dB) from the speaker enclosure with an empty port 12 (i.e. without a plurality of passageways). Taking the results of Table 2 for example, the output of such a method would be the 20 passageways D1 = 400mm speaker geometry. Alternatively, or optionally, some additional criteria may be taken into consideration. Optionally, the method 400 may further comprise the step of calculating the fluid flow conditions in the speaker enclosure 500 during use or in the simulated volume Vs. The simulation may comprise additional simulation inputs such as an average fluid flow velocity ms-1 for fluid flow through the simulated speaker enclosure 500 being expelled from a simulated drive unit. FEATURE REFERENCE TABLE No. Feature M Dynamic Viscosity of a Fluid A Cross-sectional Area b Breadth of the Port Dh Hydraulic Diameter D1 Distance D2 Distance F Fluid Flow H Height of Damped Pathway L Length Lh Hydrodynamic Entry Length Re Reynolds number S Streamline T Length of Damped Pathway V Vorticity Vs Simulated Volume w Mass Flowrate w Width of the Port 10 Speaker 12 Port 14 Damped Pathway 16 Electronics Port 18 Internal Wall 20 Drive Unit 22 Drive Unit Mount 30 Speaker Enclosure 32 First Portion 40 Passageway 42 Wall 43 Bottom Side 44 Cutaway Portion 45 Upper Side 50 Body 52 Sidewall 54 Sidewall 56 Slot 58 Upper Surface 100 Transmission Line Speaker 102 Acoustic Chamber 110 Speaker 130 Speaker Enclosure 132 Front Panel 150 Plinth 152 Foot 210 Bass Reflex Speaker 230 Speaker Enclosure 240 Passageway 242 Wall 250 Insert 252 Tube 254 First Opening 256 Second Opening 258 Flared End 260 Latice 300 Input 310 Computer 320 Output 400 Flow Chart 410 Step 420 Step 430 Step 500 Speaker enclosure geometry 502 Volume 512 Port 540 Passageways

Claims

1. A speaker enclosure (10) comprising a damped pathway (14), a drive unit mount (22) and a port (12) fluidly connected to the damped pathway (14) and the drive unit mount (20);wherein the damped pathway (14) comprises a plurality of passageways (40) extending a first distance (D1) between a first portion (32) of the damped pathway (14) and the port (12); wherein the first distance is equal to or greater than a length (L) calculated in dependence upon a hydrodynamic entry length (Lh) for fully developed flow in at least one of the plurality of passageways (40).

2. The speaker enclosure (30) of claim 1, wherein the length is calculated by:L = nLhwherein:L is a length in m,n is a dimensionless value, andLh is the hydrodynamic entry length in m.

3. The speaker enclosure (30) of claim 2, wherein n is value between 0.1 and 10.

4. The speaker enclosure (30) of claim 1,2 or 3, wherein the hydrodynamic entry lengthis calculated by:Lh = 1.359DhRe1 / 4wherein:Lh is the hydrodynamic entry length in m,Re is the Reynolds number, dimensionless, and Dh is the hydraulic diameter of the fluid flow passageway in m.

5. The speaker enclosure (30) of claim 4, wherein the hydraulic diameter is calculated using the equation:Dh = (4A) / Pwherein:A is the cross-sectional area, m2, andP is the perimeter of the wet part of the fluid flow passageway, m.

6. The speaker enclosure (30) of any preceding claim, wherein the plurality ofpassageways (40) are parallel with respect to each other.

7. The speaker enclosure (30) of any preceding claim, wherein the number ofpassageways (40) of the plurality of passageways (40) is 2 to 50 channels.

8. The speaker enclosure (30) of any preceding claim, further comprising a body (50), the body (50) comprising the plurality of passageways (40).

9. The speaker enclosure (30) of claim 8, wherein the body (50) further comprises the port (12).

10. The speaker enclosure (30) of any preceding claim, wherein the plurality of passageways (40) extends the first distance from the first portion (32) of the damped pathway (14) to a second distance from the port (12).

11. The speaker enclosure (30) of any preceding claim, wherein each passageway (40) of the plurality of passageways (40) are separated from each other by a wall or walls (42) that extend along the length of the passageways (40).

12. The speaker enclosure (30) of claim 11, wherein the wall (42) or at least one of the walls (42) has a cutaway portion (44), the cutaway portion (44) being disposed at a first end of the wall (42), the first end of the wall (42) being closer to the port (12) than a second end of the wall (12).

13. The speaker enclosure (30) of any preceding claim further comprising an insert (250) and wherein the plurality of passageways (40) are defined by the insert (250).

14. The speaker enclosure (30) of any of claims 1 to 12 further comprising a plinth (150) and wherein the plurality of passageways (40) are defined by the plinth (150), the plinth (150) being located at the base of the speaker enclosure (30).

15. The speaker enclosure (30) of claim 13 or 14 wherein the insert (250) or plinth (150) are separable from a body (50) of the speaker enclosure (30).

16. A transmission line speaker (100) comprising the speaker enclosure (30) of any preceding claim and a drive unit (20), wherein the drive unit (20) is mounted in the drive unit 25(20) mount and a rear portion of the drive unit (20) is fluidly connected to the damped pathway (14) and the port (12).

17. The transmission line speaker (100) of claim 16, wherein the damped pathway (14) has at least one bend along the length of the damped pathway (14), preferably wherein the damped pathway (14) is tortuous and / or preferably wherein the damped pathway (14) has one or more partially closed chambers (102).

18. A bass reflex speaker (200) comprising the speaker enclosure (30) of any of claims 1 to 15 and a drive unit (20), wherein the drive unit (20) is mounted in the drive unit mount and a rear portion of the drive unit (20) is fluidly connected to the damped pathway (14) and the port (12).

19. A computer-implemented method (300) for designing a speaker enclosure passageway geometry, the method comprising the steps of:receiving a first speaker enclosure (30) geometry data, the speaker enclosure (30) geometry data describing a damped pathway (14), a drive unit (20) mount and a port (12) fluidly connected to the damped pathway (14) and the drive unit (20) mount, and the damped pathway (14) includes a plurality of passageways (40) extending a first distance between a first portion (32) of the damped pathway (14) and the port (12);calculating a minimum length (L) of the first distance in dependence upon a hydrodynamic entry length (Lh) for fully developing flow in at least one of the plurality of passageways (40); andoutputting the minimum length to a user for designing a first speaker enclosure (30) with a plurality of passageways (40) extending the first distance, where the first distance is equal to or greater than the minimum length such that there is a reduction in unwanted noise at the port (12) due to a change in a first fluid characteristic at or adjacent the port (12).

20. The method (400) of claim 19 wherein the step of calculating the minimum length comprises the equation:L = nl_hwherein:L is a length in m,n is a dimensionless value, andLh is a length in m.

21. The method of claim 19 or 20, wherein the hydrodynamic entry length is calculated by:Lh = 1.359DRe1 / 4wherein:Lh is a length in m,Re is the Reynolds number, dimensionless, andD is the diameter of the fluid flow passageway, m2.

22. The method (400) of claim 21, wherein D is calculated using the equation:D = (4A) / Pwherein:A is the cross-sectional area, m2, andP is the perimeter of the wet part of the fluid flow passageway, m.

23. A data processing apparatus comprising means for carrying out the method of any of claims 19 to 22.

24. A computer program comprising instructions which, when the program is executed by a computer (310), cause the computer (310) to carry out the method of any of claim 19 to 22.

25. A computer-readable medium having stored thereon the computer program of claim 24.

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