Method of installing a loudspeaker module in a vehicle frame

Abstract

Described herein is a method of installing a loudspeaker module in a vehicle frame The loudspeaker module comprises a loudspeaker and a module housing. The loudspeaker comprises a diaphragm, a drive unit configured to move the diaphragm to produce sound, and a movable assembly that includes the diaphragm and a movable part of the drive unit. A mass of the movable part of the drive unit is at least 60% of a mass of the movable assembly. The diaphragm of the loudspeaker and the module housing together enclose and acoustic volume. The method comprises installing the loudspeaker module in a pillar of the vehicle frame such that the acoustic volume is contained within the pillar, and such that sound produced by the loudspeaker module propagates out from an aperture in the pillar when the loudspeaker module is in use. There is also described a vehicle frame comprising a loudspeaker module installed in a pillar of the vehicle frame, using any of the described methods.

Description

[0001] METHOD OF INSTALLING A LOUDSPEAKER MODULE IN A VEHICLE FRAME This application claims priority to GB2400378.2, filed 11 January 2024. Field of the InventionThe present invention relates to a method of installing a loudspeaker module in a frame of a vehicle.Background It is conventional to install loudspeaker modules configured to produce sound in a bass frequency range (e.g., woofer and / or sub-woofer loudspeaker modules) in the doors of vehicles. This approach is typically favoured because doors have a sufficiently large back volume to accommodate the loudspeaker module. This back volume is typically defined by the so-called “wet zone” part of the door assembly. By using the door assembly as the installation location for the loudspeaker module, it is possible to allow for an efficient loudspeaker module design (e.g., an efficient woofer design) with a sufficiently largeradiating surface and a sufficiently low resonance frequency to facilitate the efficient operation of theloudspeaker module in the bass frequency range. Moreover, doors in vehicles are usually spaced evenly and / or symmetrically around a cabin of the vehicle. In typical vehicle geometries, spatial differences in sound pressure levels are usually, relatively straightforwardly, equalised out by use of gains, filters and delays to realise an evenly distributed bass frequency sound amongst multiple listening positions within the cabin of the vehicle. However, integrating a bass-frequency loudspeaker module into a vehicle door is problematic. Installing the loudspeaker module in the door can compromise the soundproofing of the door, causing reduced comfort for the passenger(s) and / or driver of the vehicle (especially at high vehicle speeds where theairflow around the vehicle can be uncomfortably loud for people inside the cabin of the vehicle). Further,water leakage through the door into the loudspeaker module might arise because the loudspeakermodule is installed in the wet zone of the door. Additionally, the operation of the loudspeaker module mayinduce vibrations in the door that result in audible artefacts and / or discomfort for a person inside the cabin that is resting their arm on a part (e.g., an internal part of the frame) of the door.The present invention has been devised in light of the above considerations.There are several examples known to the inventors in which the generation of bass is done withloudspeakers positioned in other locations and with alternative solutions to provide sufficient acoustic back volume, see for example: ^EP3282714A1, which describes a loudspeaker which back side radiates through an acousticvolume and a duct towards the exterior of the vehicle. ^EP0904985A1, which describes the mounting of a loudspeaker onto a long hollow area in thestructural side beams of the floor section of the underbody.

[0002] 008695603^ JPS5757687U, which describes the use of the volume in a B-Pillar as an enclosure, where a partof the pillar is provided with acoustic holes to radiate sound from the rear of the speaker. ^US2007154055A1, which describes an acoustic assembly to be an element of a vehicle pillar.^ EP1407934B1, which describes the coupling of a first cavity inside a vehicle door with a secondcavity outside that door. ^EP2043382A1, which shows a loudspeaker mounted to a vehicle column, but it sticks out.^ CN216960109U, which describes a vehicle mounted bass box structure comprising a subwoofer,a body B-pillar sheet metal part and a seat belt retractor. The following examples describe recent examples of loudspeakers developed by the present inventors: ^WO2023194163A1, which describes a compact bass loudspeaker with a moving magnet.^ WO2024 / 003028A1, which describes another compact bass loudspeaker.^ PCT / EP2023 / 073013, which describes another compact bass loudspeaker.^ GB2219587.9, which describes another compact bass loudspeaker.^ GB2302099.3, which describes another compact bass loudspeaker.^ GB2314913.1, which describes a vehicle incorporating a compact bass loudspeaker.^ GB2314915.6, which describes another compact bass loudspeaker.Summary of the InventionIn a first aspect, there is provided a method of installing a loudspeaker module in a vehicle frame. Theloudspeaker module is for producing sound at bass frequencies. The loudspeaker module comprises a loudspeaker and a module housing. The loudspeaker comprises a diaphragm, a drive unit configured to move the diaphragm to produce sound, and a movable assembly that includes the diaphragm and a movable part of the drive unit. A mass of the movable part of the drive unit is at least 60% of a mass of the movable assembly. The diaphragm of the loudspeaker and the module housing together enclose an acoustic volume. The method comprises installing the loudspeaker module in a pillar of the frame such that the acoustic volume is contained within the pillar, and such that sound produced by the loudspeaker module propagates out from an aperture in the pillar when the loudspeaker module is in use. By enclosing the acoustic volume of the loudspeaker module with components of the module itself (e.g., the diaphragm and the module housing), it is possible to design and accurately calibrate the loudspeaker module with a known, predictable acoustic volume. Importantly, the loudspeaker module is installed with the acoustic volume being contained within the pillar, and so the loudspeaker module does not rely on an interior volume of the pillar itself to define the acoustic volume. This means that the same loudspeaker module can be installed across a wide variety of vehicles, irrespective of any variations in the dimensions and / or geometry of the pillars of those vehicles, into which loudspeaker modules are installable.

[0003] 008695603 By providing a relatively heavy drive unit (i.e., a drive unit where a movable part of said drive unit makes up at least 60% of the mass of the movable assembly), the resonant frequency of the acoustic volume of the loudspeaker module may be reduced relative to the expected resonant frequency of another loudspeaker module of the same size having a relatively lighter drive unit. Moreover, the forces generatedby the drive unit are large enough to able to produce louder bass sound for a smaller size (compared withmore conventional loudspeaker modules). This allows the loudspeaker module to produce adequatelyloud bass sound for use in a typical vehicle (e.g., a car), despite the size restrictions present in a typicalvehicle pillar. A vehicle frame may be understood as a supporting structure for use in a vehicle.For avoidance of any doubt, the vehicle frame need not be part of a manufactured vehicle when theloudspeaker module is installed in the pillar of the vehicle frame. For example, the vehicle frame may be a “body-in-white” at the time the loudspeaker module is installed in the vehicle frame. However, it is alsopossible for the vehicle frame to be part of a manufactured vehicle when the loudspeaker module isinstalled in the vehicle frame.The vehicle frame may enclose a cabin, which can be understood as a space suitable for accommodatingone or more occupants. If / when the vehicle frame forms part of a manufactured vehicle, the cabin may beenclosed by further components of the vehicle (e.g., windows, sound proofing material, etc.).Vehicle pillars may be understood to be parts of the vehicle frame that connect a floor of the vehicleframe to a roof of the vehicle frame. Vehicle pillars are sometimes identified as ‘A’, ‘B’, ‘C’, ‘D’, etc. withthe A-pillars of a vehicle being the forwardmost pillars of the vehicle, and successive letter-indicators being indicative of pillars that are sequentially further towards the rear of the vehicle. For example, in atypical car incorporating a vehicle frame: the A-pillars may be the pillars that frame sides of the frontwindscreen of the car; the B-pillars may be pillars that are positioned between front and rear doors of thecar (e.g., the B-pillars may approximately bisect the car into front and rear halves); the C-pillars may bethe pillars that are positioned immediately rearward of the rear doors of the car; the D-pillars may be thepillars that frame sides of a rear windscreen of the car. Such pillars are well known in the contexts of cars.Installing the loudspeaker module in a pillar of vehicle frame may be beneficial for several reasons.Firstly, the pillars of vehicle frames typically do not include wet zones (unlike, for example, a typicalvehicle door), meaning that waterproofing the area into which the loudspeaker module is installed may be less of a concern. Moreover, installing a loudspeaker module in the pillar of a vehicle frame may assistwith soundproofing of a cabin enclosed by that vehicle frame. Also, installing the loudspeaker module intoa pillar of the vehicle may reduce the risk, likelihood and / or severity of audible artefacts in the sound produced by the loudspeaker module, when in use, relative to the case of installing a similar or corresponding loudspeaker module in an alternative location such as in a door of the vehicle. Also, as discussed in more detail below, judicious selection of a particular pillar of the vehicle frame into which the loudspeaker is installed may lead to improved cabin gain of sound produced by the loudspeaker module within a desired frequency range.

[0004] 008695603 Since the acoustic volume of the loudspeaker module is enclosed by components of the module itself, the loudspeaker module installed based on the methods described herein may be installed in a “plug-and- play” type manner because the loudspeaker module’s configuration does not need to be specifically calibrated to the pillar in which the loudspeaker is installed. In some examples, the diaphragm and / or movable assembly may be suspended from the module housingof the loudspeaker module by one or more suspension elements. The one or more suspension elements(from which the diaphragm is suspended from the module housing) may contribute to the enclosing of the acoustic volume. In some examples, the loudspeaker may further comprise a loudspeaker frame from which the diaphragmand / or movable assembly are suspended by the one or more suspension elements, wherein theloudspeaker frame is attached to the module housing. In such examples, the diaphragm can be viewed as being suspended from the module housing via the loudspeaker frame. In such examples, the loudspeaker frame may also be arranged to contribute to the enclosing of the acoustic volume. In other words, in some examples, the acoustic volume may be enclosed by the module housing, by thediaphragm, and by the loudspeaker frame (and by the one or more suspension elements).The one or more suspension elements may include a first suspension element, e.g., a roll suspension(that may also be referred to as the “surround”), which attaches to the loudspeaker frame at a first landing surface on the loudspeaker frame. The first suspension element may be attached directly or indirectly tothe diaphragm. In some examples, the first suspension element may attach (directly) to an outer edge ofthe diaphragm. In other examples, the first suspension element may be attached to another element of the moveable assembly.The one or more suspension elements may include a second suspension element, e.g., a damper, whichattaches to the loudspeaker frame at a second landing surface on the loudspeaker frame. The second suspension element may be attached directly or indirectly to the diaphragm. In some examples, the second suspension element may be attached (directly) to the diaphragm at a location inwardly located with respect to the outer edge of the diaphragm. In other examples, the second suspension element maybe attached to another element of the moveable assembly (e.g., the moveable part of the drive unit,particularly where the moveable part is the magnet unit). The centre of gravity of the moveable part of the drive unit may have a position along the movement axis that is between the first landing surface and the second landing surface. By locating the centre of gravity of the moveable part of the drive unit between the first landing surface and the second landing surface, rocking of the moveable assembly may be inhibited. More particularly, the rocking modes of the loudspeaker module may be pushed outside of the working frequency range of the loudspeaker module. The drive unit may include the moveable part attached to the diaphragm and a stationary part attached to the module housing. For avoidance of any doubt, the stationary part may be attached to the modulehousing directly, or indirectly (e.g., the stationary part may be attached to a loudspeaker frame, in which

[0005] 008695603 case the stationary part may be viewed as being attached to the module housing indirectly, via the loudspeaker frame). The loudspeaker module may be operable to energise the drive unit to cause movement of the moveable part of the drive unit (and thus the movable assembly) relative to the stationary part of the drive unit along a movement axis of the loudspeaker module so as to move the diaphragm to produce sound. The terms “stationary” and “moveable” are relative terms and in principle dependent on the particular frame of reference. In this context, the terms “stationary” and “moveable” are intended to refer to aconventional frame of reference according to which the diaphragm is considered to be moveable, and inuse to be moving, whereas other parts of the loudspeaker module are considered to be stationary. As such those parts of the loudspeaker module which in use move with the diaphragm, such as the moveable part of the drive unit, are referred to as moveable, while other parts of the loudspeaker module, which in use do not move with the diaphragm (and which may be stationary with respect to an external apparatus to which the loudspeaker module is attached), are referred to as stationary, e.g. the stationarypart of the drive unit. Those parts of the loudspeaker module which are moveable, i.e., the diaphragm andparts that in use move together with the diaphragm, may collectively be referred to as the moveable assembly. The drive unit may include a magnet unit and a voice coil. The magnet unit may be included in one of the stationary part and the moveable part, and the voice coil may be included in the other of the stationarypart and the moveable part. When the drive unit is energised (e.g., by supplying a time-varying electriccurrent to the voice coil), the moveable part of the drive unit and the stationary part of the drive unit maymagnetically interact to cause the movement of the moveable part relative to the stationary part.In some examples (referred to herein as “moveable voice coil” examples), the moveable part of the driveunit may be the voice coil and the stationary part of the drive unit may be the magnet unit. In suchexamples, when the drive unit is energised, magnetic flux generated by the flow of electric current in the (moveable) voice coil may interact with magnetic flux generated by the (stationary) magnet unit of thedrive unit to cause the movement of the moveable part, which is the voice coil, relative to the stationarypart, which is the magnet unit.In other examples (referred to herein as “moveable magnet unit” examples), the moveable part of thedrive unit may be the magnet unit and the stationary part of the drive unit may be the voice coil. In such examples, when the drive unit is energised, magnetic flux generated by the flow of electric current in the (stationary) voice coil may interact with magnetic flux generated by the (moveable) magnet unit of thedrive unit to cause the movement of the moveable part, which is the magnet unit, relative to the stationarypart, which is the voice coil.The magnet unit may include a permanent magnet and one or more flux guiding elements for guidingmagnet flux produced by the permanent magnet in a magnetic circuit and across an air gap, wherein thevoice coil is configured to be located in the air gap when the moveable part of the drive unit is at rest.Herein, a reference to the moveable part of the drive unit being at rest, or the diaphragm being at rest,may be taken to correspond to a state in which the drive unit is not energised (e.g. an electric current is

[0006] 008695603not being supplied to a voice coil of the drive unit) with the moveable part of the drive unit and thediaphragm having been given time to reach a state of rest.The magnet unit may include at least two flux guiding elements. The at least two flux guiding elements may be configured to guide magnet flux produced by the permanent magnet across the air gap. The air gap may be formed between the at least two flux guiding elements. The at least two flux guiding elements may include a washer and a yoke. The permanent magnet may belocated between the washer and the yoke. The washer and the yoke may be arranged to define the airgap between the washer and the yoke. The yoke may include a base and an upright portion extending from the base. In some examples, the yoke may be a U-yoke wherein the upright portion is an annular sidewall. In some examples, the yoke may be a T-yoke wherein the upright portion is a central post. The magnet unit may form a magnetic circuit. The magnetic circuit may provide a substantially closed circuit (or loop) for the magnetic flux. The magnetic circuit may have a comparatively high magnetic reluctance. For example, the magnetic reluctance of the magnetic circuit may be at least 2.5 x 10^6 [1 / H] or even 3 x 10^6 [1 / H], where “H” represents the physical unit “Henry”. The majority of the magnetic reluctance of the magnetic circuit may be attributed to the air gap. For example, the air gap may have a magnetic reluctance of at least 2 x 10^6 [1 / H]. By utilising a magnetic circuit with high magnetic reluctance, and particularly a high-reluctance air gap, it is possible to utilise comparatively small flux guiding elements. Thus, it is possible to reduce the weight of the magnet unit. This weight reduction of the magnet unit may more than compensate for the weight of a large voice coil, meaning that the comparatively high magnetic reluctance of the magnetic circuit enables designing of particularly lightweight loudspeakers. Further detail relating to high-reluctance magnetic circuits in the context of loudspeakers is described in WO2024 / 003028A1. The voice coil may have a first perimeter and a second perimeter. The first perimeter may be an outerperimeter or an inner perimeter of the voice coil, and the second perimeter may correspondingly be theinner perimeter or the outer perimeter. The distance between the first perimeter and the second perimeter may be referred to as a winding thickness of the voice coil. Accordingly, the magnetic flux density permeating the voice coil may drop over the winding thickness of the voice coil as specified above.If the voice coil is generally circular, the inner perimeter of the voice coil may have a corresponding innerdiameter of the voice coil, and the outer perimeter of the voice coil may have a corresponding outer diameter of the voice coil.When the voice coil is located in the air gap, i.e., the moveable part of the drive unit is at rest, a magneticflux density at the first perimeter of the voice coil may be 50% or less of a magnetic flux density at the second perimeter of the voice coil. By having a magnetic flux density at an outer perimeter of the voice coil is 50% (percent) or less of a magnetic flux density at an inner perimeter of the voice coil, the loudspeaker is able to have a magnet unit

[0007] 008695603 which is smaller or lighter, thereby facilitating a lighter overall loudspeaker (even if the coil is made heavier to compensate). Further detail regarding the advantages of such an arrangement are described for example in WO2024 / 003028A1. In an arrangement in which the at least two flux guiding elements include a U-yoke, the magnetic flux density at the outer perimeter of the voice coil may be 50% or less of the magnetic flux density at the inner perimeter of the voice coil. In an arrangement in which the at least two flux guiding elements include a T-yoke, the magnetic flux density at the inside perimeter of the voice coil may be 50% or less of the magnetic flux density at the outside perimeter of the voice coil. An extent of the voice coil as measured in direction parallel to the movement axis (which may be referredto as the ‘height’ of the voice coil) may be in a range of 85% and 100% of the separation between the firstand second landing surfaces as measured in direction parallel to the movement axis. This configurationmay enable large linear displacement of the voice coil while effectively inhibit rocking motion.The loudspeaker module may have a resonant frequency in a range of 30-100Hz (Hertz), optionally 40-80Hz. The resonant frequency of the loudspeaker module may be referred to as the “in-box” resonantfrequency of the loudspeaker module (since it is the resonant frequency that occurs when the acousticvolume is enclosed by the diaphragm and the module housing). The loudspeaker module may be a subwoofer configured to produce sound with frequencies in a bass frequency range. The bass frequency range may include 60-80Hz, more preferably include 40-100Hz. By way of example, the bass frequency range may be 20Hz-100Hz.A ratio of the mass of the moveable assembly to the effective radiating area Sd of the diaphragm may beat least 5 kilograms per square-metre, optionally at least 7 kilograms per square-metre. The ratio of themass of the moveable assembly to the effective radiating area Sd of the diaphragm may be at most 20 kilograms per square-metre, optionally at most 15 kilograms per square-metre, optionally at most 12 kilograms per square-metre. For example, the ratio of the mass of the moveable assembly to the effective radiating area Sd of the diaphragm may be in a range of 5 to 20 kilograms per square-metre, optionally in a range of 5 to 15 kilograms per square-metre, optionally in a range of 7 to 12 kilograms per square- metre.Such a ratio, particularly when combined with the mass of the moveable part of the drive unit being atleast 60%, more preferably 70%, of the mass of the moveable assembly, may represent a compact yet heavy moveable assembly. Such a moveable assembly may in use generate large forces, but the presentinventor has observed that such forces can be absorbed by the heavy (100kg+) body of a vehicle, leadingto good sound performance (despite the significant forces), or such forces can be cancelled out by havingtwo loudspeakers in the module mounted back-to-back (see below).The effective radiating area Sd is a concept known in the art. For a round diaphragm, the effectiveradiating area Sd is quantified using the half-roll-to-half-roll diameter and hence the suspension contributes to the effective radiating area Sd. Particularly for a loudspeaker with a comparatively small

[0008] 008695603 diaphragm, the contribution of the suspension to the effective radiating area Sd may not be negligible. For a diaphragm having a circular perimeter which is suspended from the module housing (e.g. via aloudspeaker frame) by a roll suspension having an outer diameter do (“d_o”) and an inner diameter di(“d_i”), the effective radiating surface area of that diaphragm may be estimated as (“Sd equals pi times the square of d over the square of 2”) where d is the half-diameter of the roll suspension, (do + di) / 2, (“d_o d_i over 2”). In other examples, the effective radiating surface area of the diaphragm Sd may be measured using known techniques, see e.g. “Dynamical Measurement of the Effective Radiating area SD”, Klippel GmbH (https: / / www.klippel.de / fileadmin / klippel / Files / Know_How / Application_Notes / AN_32_Effective_Radiation_ Area.pdf).The acoustic volume may be in the range 0.25 litres to 8 litres, preferably in the range of 0.5 litres to 3litres, and more preferably in the range of 0.5 litres to 1.5 litres. Such volumes are relatively small forsubwoofers, but the present inventors have found that they are adequate with a loudspeaker (or pair ofloudspeakers) having a design as set out herein. The loudspeaker module may be operable to cause displacement of a volume VD of air by the diaphragm. The volume VD displaced by the diaphragm may be defined as the volume of air displaced by the diaphragm as it moves from its rest position in the air gap to a position of maximum displacement. As such, twice the volume VD is displaced by the diaphragm when the diaphragm is moved from nominalmaximum displacement inwards to nominal maximum displacement outwards or vice versa, i.e., a peak-to-peak stroke. The volume VD of air displaced by the diaphragm may be at least 0.05 times the acoustic volume (5 percent of the acoustic volume). This may result in a loudspeaker module having a comparatively large diaphragm and enclosing a comparatively small acoustic volume. A ratio of the acoustic volume over the effective radiating surface Sd may be in a range of 0.01 to 0.5 metres. This ratio of the acoustic volume over Sd may provide an alternative parametrisation of a comparatively large diaphragm and a comparatively small acoustic volume. A ratio of the acoustic volume VB over the effective radiating surface Sd may be in a range of 0.01 to 0.5 metres. This ratio of the acoustic volume VB over Sd may provide an alternative parametrisation of a comparatively large diaphragm and a comparatively small acoustic volume. In some embodiments, the loudspeaker may be a first loudspeaker, the diaphragm may be a first diaphragm, the drive unit may be a first drive unit, and the movable assembly may be a first movableassembly. The loudspeaker module may further comprise a second loudspeaker, the second loudspeakercomprising a second diaphragm, a second drive unit configured to move the second diaphragm to produce sound, and a second movable assembly that includes the second diaphragm and a movable part of the second drive unit. A mass of the movable part of the second drive unit may be at least 60% of a mass of the second movable assembly. The acoustic volume may be further enclosed by the diaphragm of the second loudspeaker.

[0009] 008695603 In other words, the acoustic volume may be enclosed by the loudspeaker module housing, and by the first and second diaphragms. In some examples, the first and second loudspeakers may be substantially identical. This may facilitate configuring the first and second loudspeakers identically such that the sound produced by the first loudspeaker reinforces the sound produced by the second loudspeaker and vice versa.In some examples, the second diaphragm and / or second movable assembly may be suspended from themodule housing of the loudspeaker module by one or more suspension elements. The one or moresuspension elements (from which the second diaphragm is suspended from the module housing) may contribute to the enclosing of the acoustic volume. In some examples, the second loudspeaker may further comprise a second loudspeaker frame fromwhich the second diaphragm and / or second movable assembly are suspended by one or moresuspension elements, wherein the second loudspeaker frame is attached to the module housing. In such examples, the second diaphragm can be viewed as being suspended from the module housing via the second loudspeaker frame. In such examples, the second loudspeaker frame may also be arranged to contribute to the enclosing of the acoustic volume. In other words, the acoustic volume may be enclosed by the module housing, by the first and second loudspeaker frames, and by the first and seconddiaphragms (and also by the one or more suspension elements by which the first and second diaphragmsare suspended from the first and second loudspeaker frames). In some examples, the / each diaphragm may comprise a front face, which faces away from the drive unit configured to move the diaphragm. For example, in examples where the loudspeaker module includes the first and second loudspeakers, the first diaphragm may comprise a front face which faces away from the first drive unit, and the second diaphragm may comprise a front face which faces away from the second drive unit. Similarly, the / each diaphragm may comprise a back face, which faces towards the drive unit configured to move the diaphragm. For example, in examples where the loudspeaker module includes the first and second loudspeakers, the first diaphragm may comprise a back face which faces towards the first drive unit, and the second diaphragm may comprise a back face which faces towards the second drive unit. The acoustic volume may be configured to receive sound produced by the back face of the / eachdiaphragm (e.g., the back face of the first loudspeaker and the back face of the second loudspeaker, inexamples where the loudspeaker module includes the first and second loudspeakers) when the loudspeaker module is in use. The loudspeaker module may be installed in the pillar of the vehicle frame such that sound produced bythe front face of the / each loudspeaker (e.g., the front face of the first loudspeaker and the front face of thesecond loudspeaker, in examples where the loudspeaker module includes the first and second loudspeakers) propagates out from the aperture in the pillar when the loudspeaker module is in use.

[0010] 008695603 The first and second drive units may be configured to drive the first and second diaphragms respectivelyin phase with one another, i.e., so sound produced by the front faces of the first and second diaphragmsis in phase. In some examples, each of the first and second diaphragms may comprise a respective front face, facing away from the corresponding drive unit. The front faces of the first and second diaphragms may face in opposite directions. The first and second drive units may be configured to drive the first and second diaphragms synchronously.Driving the first and second diaphragms synchronously facilitates sound produced by the front face of thefirst diaphragm being in phase with sound produced by the front face of the second diaphragm.In other words, in examples where the loudspeaker module includes the first and second loudspeakers, the first and second loudspeakers may be mounted with the front faces of the first and seconddiaphragms facing in opposite directions. The first and second drive units may be configured to drive thefirst and second diaphragms respectively in phase with one another i.e., so that sound produced by thefront face of the first diaphragm is in phase with sound produced by the front face of the seconddiaphragm. This sound may be low-frequency sound having a wavelength that is relatively largecompared to the difference in the acoustic path length from the front faces of the first and second diaphragms to a listener within the vehicle. In examples where the loudspeaker module includes the first and second loudspeakers, the first andsecond loudspeakers may be mounted back-to-back, i.e., with the back face of the first diaphragm facingtowards the back face of the second diaphragm. In other examples, the front faces of the first and second diaphragms may face in opposite directions but with the positions of the first and second loudspeakers offset from each other within the module housing so that the back face of the first diaphragm not facing towards back face of the second diaphragm. When the first and second loudspeakers are mounted back to back and the first and second drive units are configured to drive the first and second diaphragms respectively in phase with one another, i.e. so sound produced by the front faces of the first and second diaphragms is in phase, the forces generated by the first and second loudspeakers may cancel out, thereby reducing or even substantially eliminating the risk of inducing vibrations through the cabin of the vehicle. In examples where the loudspeaker module includes a single loudspeaker, installing the loudspeaker inthe pillar of the vehicle frame may comprise orienting the loudspeaker module such that the front face ofthe loudspeaker faces into the interior of a cabin enclosed by the vehicle frame. In other examples, theloudspeaker may be oriented in any suitable alternative orientation provided that sound can propagate into the interior of the cabin of the vehicle. In some embodiments (where the loudspeaker module includes the first and second loudspeakers),installing the loudspeaker in the pillar of the vehicle frame may comprise orienting the loudspeakermodule such that the front face of the first diaphragm faces towards a front end of the vehicle frame, andthe front face of the second diaphragm faces towards a rear end of the vehicle frame after theloudspeaker module has been installed. 008695603 This orientation may be referred to as a front-to-back orientation of a pair of loudspeakers.In other examples where the loudspeaker module includes the first and second loudspeakers, installingthe loudspeaker in the pillar of the vehicle frame may comprise orienting the loudspeaker module suchthat the front face of the first diaphragm faces towards a top of the vehicle frame, and the front face of thesecond diaphragm faces towards a bottom of the vehicle frame after the loudspeaker has been installed.This orientation may be referred to as a top-to-bottom orientation.In other examples where the loudspeaker module includes the first and second loudspeakers, installingthe loudspeaker in the pillar of the vehicle frame may comprise orienting the loudspeaker module suchthat the front face of the first diaphragm faces towards an interior of a cabin enclosed by the vehicle framein a direction transverse to both an axis that extends from a front end of the vehicle frame to a rear end ofthe vehicle frame and an axis that extends from a bottom of the vehicle frame to a top of the vehicleframe, and the front face of the second diaphragm faces towards an exterior of the cabin in a directionopposite to the direction in which the front face of the first diaphragm faces. This orientation may be referred to as a side-to-side orientation. The front-to-back orientation of the first and second loudspeakers may be particularly beneficial in certain examples (for example in cases where the loudspeaker module is installed in a B-pillar of the vehicle frame, as, in said orientation at such a location, there may be little / substantially no phase difference between the sound produced by the front faces of the first and second diaphragms at a point within the cabin at which a passenger / drive of the vehicle may sit. In other words, a passenger and / or driver withinthe vehicle may experience little / substantially no deterioration in the sound quality arising from phasedifferences between the sound produced at the front faces of the first and second diaphragms.When installed at other locations (i.e., locations different from the B-pillar), other orientations may be more suitable to minimise the impact of phase difference for people sat inside the cabin. The pillar in which the loudspeaker module is installed may be selected from amongst a plurality of pillarsof the vehicle frame, each pillar being positioned at a respective pillar location in the vehicle frame. Theselected pillar may be a pillar amongst the plurality of pillars that positions the installed loudspeaker module in a pillar location that is the most susceptible of the plurality of pillar locations to cabin gain for the bass frequency sound that the loudspeaker module is configured to produce, e.g. when the vehicle frame forms part of a manufactured vehicle. In other words, the pillar into which the loudspeaker module is installed may be chosen to position theloudspeaker module in a location within the vehicle frame that optimises the cabin gain for soundproduced within the operating frequency range of the loudspeaker module.In some examples, the vehicle frame is for use in a car.In some examples, the loudspeaker module is installed in the B-pillar of the vehicle frame.In some examples, the loudspeaker module may define a woofer or subwoofer loudspeaker module.Preferably, the woofer or subwoofer is installed in the B-pillar of the vehicle frame (e.g., car).008695603 Installing a woofer, subwoofer or another loudspeaker module that operates in the bass frequency rangein a B-pillar of the vehicle frame as the B-pillar is a particularly suitable location for inducing cabin gain ofbass frequency sound. In some embodiments, installing the loudspeaker module in the B-pillar may include positioning the loudspeaker module above or below a seatbelt reel installed in the B-pillar. In many vehicles, seatbelt reels for seatbelts configured to secure a passenger or driver of the vehicle are installed at the bottom of the B-pillar. It is therefore advantageous to fit the loudspeaker module into the B-pillar without compromising the positioning and functioning of the vehicle’s seatbelts to ensure that thevehicle is safer for people inside a cabin enclosed by the vehicle frame.In some examples, the loudspeaker module housing may be shaped and / or arranged to fit around one ormore structures (e.g., protrusions or other installations) in the pillar of the vehicle frame. In this way, theloudspeaker module may be installed in a way that fits the loudspeaker module around pre-existing and / or required structures in the pillar. In some embodiments, installing the loudspeaker module may comprise inserting the loudspeaker module through the aperture in the pillar and securing the loudspeaker module within the pillar. Securing the loudspeaker module within the pillar may comprise using any suitable securing means including, for example, screws, clamps, hooks, adhesive and / or any other suitable mechanism for securing the loudspeaker module to the pillar.Vehicle frame pillars typically include, as part of their manufacture, one or more apertures / holes.Exploiting a pre-existing aperture in the pillar may simplify the installation methods described herein. Further, installing the loudspeaker module by inserting the module through the aperture allows the installation process to take place after the vehicle cabin has been manufactured, thereby providing a vehicle manufacturer with enhanced flexibility for when, in the vehicle manufacturing process, they install the loudspeaker into the pillar. In some embodiments, the loudspeaker module may be contained entirely within the pillar after being installed. In this way, the loudspeaker module may beneficially not encroach into an interior volume of a cabin enclosed by the vehicle frame, thereby providing more space for the passenger(s) and driver of the vehicle to occupy the cabin. This may facilitate an increased occupancy limit for the cabin and / or improvethe level of comfort of people inside the cabin when the vehicle is in use.Containing the loudspeaker module entirely within the pillar can be rendered easier by a mass of the movable part of the drive unit being at least 60% of a mass of the movable assembly. This is because it is possible to reduce the size of the acoustic volume, and thus the overall size of the loudspeaker module, as the mass of the movable part of the drive unit (relative to the mass of the overall movable assembly) increases, for a given resonant frequency. 008695603 In some embodiments, the method may further comprise covering the aperture with an acoustically transmissive material. In other words, in some examples, the aperture may be covered by an acoustically transmissive material.The covering of the aperture may be carried out as part of the installation process or may be carried outbefore or after the installation methods described herein, as appropriate. Covering the aperture may provide a physical barrier that shields the loudspeaker module from damage, but in a manner that does not negatively impact the quality of the sound transmitted throughout the cabin of the vehicle. The aperture may take various forms, so long as it is able to transmit the majority of sound radiated from the loudspeaker module. In some examples, the aperture may be a hole in the pillar, a perforated interiorpanel, a metal grille, or a plastic grille covered with an acoustically transparent plastic. In other examples,the aperture may be a duct, slit, waveguide or fully closed material with sufficient flexibility to transmit the majority of sound radiated from the loudspeaker module. In some embodiments, after installing the loudspeaker module, a portion of the acoustic volume may occlude at least 70% of a cross-sectional area of the pillar.For example, the pillar may extend in an upwards direction along an upstanding axis which extends froma bottom of the vehicle frame to a top of the vehicle frame. The cross-sectional area of the pillar maytherefore be a cross-section that is perpendicular to the upstanding axis.At least a portion of the acoustic volume may therefore occlude (i.e., fill, obstruct, or occupy) at least 70%of this cross-section (e.g., at one or more locations along the upstanding axis).By filling in an area that is a majority of the cross-section, the risk of the loudspeaker module (by virtue ofits operation) setting up standing acoustic waves within the pillar is reduced. Avoiding the setting up ofstanding acoustic waves is beneficial because these standing waves can resonate and induce significant resonant vibrations in the cabin of the vehicle. In some examples, the portion of the acoustic volume may occlude at least 80%, at least 90%, at least95% or at least 99% of the cross-sectional area of the pillar (e.g., at one or more locations along theupstanding axis). In some embodiments, the method may further comprise inserting an acoustically absorbent material into the pillar to occupy a portion of the cross-sectional area of the pillar that is not occluded by the acoustic volume. At least a portion of the acoustic volume and acoustically absorbent material may together occupy (i.e.,fill, obstruct or occlude) at least 90% of (preferably at least 95% of, preferably substantially the entirety of)the cross-sectional area of the pillar (e.g., at one or more locations along the upstanding axis).The acoustically absorbent material may, for example, be a foam. The foam may be a closed cell, open cell or reticulated foam. In particular examples, the foam may be melaminefoam (basotect), a 008695603 polyurethane foam, a polyester based foam, an EPDM foam, or a foam formed from any other suitable material. The foam may have a density in the range of 25 kg m-3to 250 kg m-3. By filling out the portion of the cross-sectional area of the pillar that is not occluded by the acoustic volume with the acoustically absorbent material, any standing waves that may be set up can be further dampened by the material, thereby preventing the inducement of resonant vibrations in the cabin of the vehicle. In some embodiments, the / each loudspeaker in the loudspeaker module may be positioned below anenclosure section of the module housing after installing the loudspeaker module in the pillar, wherein theenclosure section of the module housing encloses at least 60% of the acoustic volume. The cabin gain achieved by the sound generated by the loudspeaker module may be enhanced if the loudspeaker(s) of the loudspeaker module is / are positioned at a lowest possible position in the pillar. Therefore, it may be advantageous to position the loudspeaker substantially below the enclosure section of the module housing and, in particular, below the majority of the acoustic volume to promote improved cabin gain. The / each loudspeaker included in a loudspeaker module as described above may include one or more features as described in WO2023194163A1, WO2024 / 003028A1, PCT / EP2023 / 073013, GB2219587.9,,GB2302099.3, GB2314913.1, GB2314915.6 (the entirety of these documents being incorporated byreference herein), all of which describe examples of compact bass loudspeakers developed by thepresent inventors.In another aspect, there is provided a frame for a vehicle comprising a loudspeaker module installed in apillar of the frame, using the methods described herein.In some examples, the vehicle frame may form part of a manufactured vehicle. In other examples, thevehicle frame may be for use in forming a manufactured vehicle (e.g., a “body-in-white”).The invention includes the combination of the aspects and preferred features described except where such a combination is clearly impermissible or expressly avoided. Summary of the Figures Embodiments and experiments illustrating the principles of the invention will now be discussed with reference to the accompanying figures in which:Figure 1 shows an exemplary vehicle frame, in the form of a ‘body-in-white’, into which a loudspeakermodule may be installed in accordance with the methods described herein.Figure 2 shows an exemplary loudspeaker module installed in a B-pillar of a vehicle frame.Figure 3 shows an exemplary loudspeaker module comprising two back-to-back loudspeakers oriented ina side-to-side orientation within a B-pillar of a vehicle frame. 008695603Figure 4 shows an exemplary loudspeaker module comprising two back-to-back loudspeakers oriented ina front-to-back orientation within a B-pillar of a vehicle frame.Figure 5 shows an exemplary loudspeaker module comprising two back-to-back loudspeakers oriented ina top-to-bottom orientation within a B-pillar of a vehicle frame.Figure 6 shows a method of installing a loudspeaker module in a vehicle frame.Figure 7 is a sound-pressure level graph for an exemplary loudspeaker module as used in the methodsdescribed herein.Figure 8 is graph showing a relation between the mass, Mms, of a movable assembly of the loudspeakermodule; a volume, VB, enclosed by the loudspeaker module; and the resonant frequency, fc, of the loudspeaker module. Detailed Description of the Invention Aspects and embodiments of the present invention will now be discussed with reference to the accompanying figures. Further aspects and embodiments will be apparent to those skilled in the art. All documents mentioned in this text are incorporated herein by reference. Figure 1 shows an exemplary vehicle frame 100 into which a loudspeaker module may be installed in accordance with the methods described herein.The vehicle frame 100 into which the loudspeaker module is installable may be a vehicle frame 100 of amanufactured vehicle, or it may be a ‘body-in-white’ cabin frame 100. In this example, the vehicle frame 100 is for use in a car. The vehicle frame 100 may be considered to be divided into two portions, a unibody 102 comprising a plurality of pillars 104, 106, 108, 110; and an underbody 112 comprising a main floor 114, a cowl beam 116, and a firewall 118. The unibody 102 comprises a pair of A-pillars 104 extending upwards from the underbody 112 towardsthe roof of the vehicle frame 100. The pair of A-pillars 104 may be suitable for framing a front windscreenof a car manufactured from the vehicle frame 100. The unibody 102 further comprises a pair of B-pillars 106 extending upwards from the underbody 112 towards the roof of the vehicle frame 100. The pair of B-pillars 106 may be disposed between front and rear door positions of the vehicle frame, effectively bisecting the vehicle frame 100 into front and rear portions of the vehicle frame 100. The unibody 102 further comprises a pair of C-pillars 108 extending upwards from the underbody 112towards the roof of the vehicle frame 100. The pair of C-pillars 108 may be disposed rearwards of reardoor positions of the vehicle. 008695603 The unibody further comprises a pair of D-pillars 110 extending upwards from the underbody 112 towards the roof of the vehicle frame 100. The pair of D-pillars 110 may be suitable for framing a rear windscreen of a vehicle. The underbody 112 comprises a main floor 114 that may define a floor of the vehicle frame 100. The underbody 112 further comprises a cowl beam 116 that may be suitable for framing a bottom edge of the front windscreen of a car manufactured from the vehicle frame 100. The underbody 112 further comprises a firewall 118 that may be suitable from insulating a cabin enclosedby the vehicle frame 100 from a portion of the vehicle frame 100 in which the engine is installed (e.g.,under the bonnet of the vehicle).Figure 2 shows an exemplary loudspeaker module 200 installed in a B-pillar 106 of the vehicle frame 100.The loudspeaker module 200 comprises a loudspeaker 210 and a module housing 220. The loudspeaker210 comprises a diaphragm 212 suspended from the module housing 220 (via a loudspeaker frame 218)by one or more suspension elements 214a, 214b. The loudspeaker comprises a movable assembly thatincludes the diaphragm 212 and a movable part of the drive unit 216.The loudspeaker 210 further comprises a drive unit 216 configured to move the moveable assembly, andthus the diaphragm 212, along a movement axis 211 so as to generate sound. The loudspeaker frame is218 defined by a one or more frame elements 218a, 218b. The diaphragm 212 is aligned with an aperture120 in the B-pillar 106 such that, in use, sound produced and emanating from a front face of thediaphragm 212 (i.e., a face of the diaphragm 212 facing away from the drive unit 216) propagates outfrom the aperture 120 into the cabin of the vehicle to which the B-pillar 106 belongs. The drive unit 216 comprises the movable part and a stationary part. In this example, the movable part isa voice coil 217a of the drive unit 216, while the stationary part is a magnet unit 217b of the drive unit216. In other examples (not shown), the movable part may be the magnetic unit, while the stationary partmay be the voice coil (such a loudspeaker arrangement is disclosed, for example, in WO2023194163A1).In this example, the suspension elements 214a, 214b include a roll suspension 214a and a damper214b.In this example, the roll suspension 214a attaches to the loudspeaker frame 218 at a first landingsurface on the loudspeaker frame, the damper 214b attaches to the loudspeaker frame 218 at a second landing surface on the loudspeaker frame 218, and the centre of gravity of the voice coil 217a (i.e. themoveable part of the drive unit) has a position along the movement axis 211 that is between the firstlanding surface and the second landing surface. This helps with stability against rocking motion of the moveable assembly.The mass of the movable part of the drive unit 216 makes up at least 60% of the mass of the movableassembly. Preferably, the mass of the movable part of the drive unit 216 may make up 70%, 80%, or 90% of the mass of the movable assembly. Together, the diaphragm 212, the loudspeaker frame 218 and the module housing 220 define an acoustic volume 230 (or ‘back volume’) of the loudspeaker module 200. The acoustic volume is a fully enclosedvolume – in other words, the diaphragm 212, loudspeaker frame 218 and module housing define the008695603 boundary of the back volume of the loudspeaker module 200, with no part of the acoustic volume’s boundary being defined by the body of the B-pillar 106. The loudspeaker module 200 is held securely in place by one or more securing means 240a, 240b. The securing means may be any suitable mechanism. For example, the one or more securing means may include screws, clamps, hooks, adhesive and / or any other suitable mechanism for securing the loudspeaker module 200 to the B-pillar 106.The loudspeaker module 200 is installed to be positioned above a seatbelt reel 250 from which a seatbeltuseable by a person sitting in one of the front seats of the vehicle extends. The seatbelt reel 250 is installed at a base of the B-pillar 106 and secure therein by a seatbelt fixation mechanism 252. The seatbelt fixation mechanism 252 may be any suitable fixation mechanism. For example, the seatbelt fixation mechanism 252 may include a screw, a clamp, a hook, adhesive and / or any other suitable mechanism for securing the loudspeaker module 200 to the pillar 106. Figure 3 shows an exemplary loudspeaker module 200 comprising two back-to-back loudspeakers 210a, 210b installed in a B-pillar 106 of a vehicle frame 100 in a side-to-side orientation.The loudspeaker module 200 comprises two back-to-back loudspeakers 210a, 210b and a modulehousing 220. The first loudspeaker 210a comprises a first diaphragm 212a suspended by one or more suspension elements 214a, 214b. The first loudspeaker 210a further comprises a first drive unit 216a configured to drive the first diaphragm 212a to generate sound. The first loudspeaker 210a further comprises a firstframe defined by one or more frame elements 218a, 218b. The first diaphragm 212a is suspended fromthe module housing 220 via the first frame by the suspension elements 214a, 214b. The first diaphragm 212a comprises a front face facing away from the first drive unit 216a.The first loudspeaker comprises a first movable assembly that includes the first diaphragm 212a and amovable part of the first drive unit 216a. The first drive unit 216a comprises a movable part and a stationary part. In this example, the movablepart is a first voice coil 217a of the first drive unit 216a, while the stationary part is a first magnetic unit217b of the first drive unit 216. In other examples (not shown), the movable part may be the first magnetic unit, while the stationary part may be the first voice coil. The mass of the movable part of the first drive unit 216a makes up at least 60% of the mass of the movable assembly. Preferably, the mass of the movable part of the first drive unit 216a may make up 70%, 80%, or 90% of the mass of the movable assembly. The second loudspeaker 210b comprises a second diaphragm 212b suspended by one or more suspension elements 214c, 214d. The second loudspeaker 210b further comprises a second drive unit 216b configured to drive the second diaphragm 212b to generate sound. The second loudspeaker 210b comprises a second frame defined by one or more frame elements 218c, 218d. The second diaphragm 212b is suspended from the module housing 220 via the second frame by the one or more suspension 008695603 elements 214c, 214d. The second diaphragm 212b comprises a front face facing away from the second drive unit 216b. The second loudspeaker comprises a first movable assembly that includes the second diaphragm 212b and a movable part of the second drive unit 216b. The second drive unit 216b comprises a movable part and a stationary part. In this example, the movablepart is a second voice coil 217c of the second drive unit 216b, while the stationary part is a secondmagnetic unit 217d of the second drive unit 216b. In other examples (not shown), the movable part maybe the second magnetic unit, while the stationary part may be the second voice coil. The mass of the movable part of the second drive unit 216b makes up at least 60% of the mass of the movable assembly. Preferably, the mass of the movable part of the second drive unit 216b may make up 70%, 80% or 90% of the mass of the movable assembly. The first and second loudspeakers 210a, 210b are arranged in a back-to-back configuration. By this, it is meant that the front faces of the first and second diaphragms 212a, 212b face in opposite directions. In this example, the suspension elements 214a, 214b include a roll suspension 214a and a damper 214b.In this example, the roll suspension 214a attaches to the first loudspeaker frame 218a, 218b at a first landing surface on the loudspeaker frame, the damper 214b attaches to the first loudspeaker frame 218a, 218b at a second landing surface on the first loudspeaker frame 218a, 218b, and the centre of gravity of the first voice coil 217a (i.e. the moveable part of the first drive unit 216a) has a position along the movement axis 211 that is between the first landing surface and the second landing surface. This helps with stability against rocking motion of the moveable assembly. Similarly, the suspension elements 214c, 214d include a roll suspension 214c and a damper 214d.In this example, the roll suspension 214c attaches to the second loudspeaker frame 218c, 218d at a first landing surface on the loudspeaker frame, the damper 214b attaches to the second loudspeaker frame 218c, 218d at a second landing surface on the second loudspeaker frame 218c, 218d, and the centre of gravity of the second voice coil 217c (i.e. the moveable part of the second drive unit 216b) has a position along the movement axis 211 that is between the first landing surface and the second landing surface. This helps with stability against rocking motion of the moveable assembly. Together, the first and second diaphragm 212a, the loudspeaker frame elements 218a-d and the module housing 220 define an acoustic volume 230 (or ‘back volume’) of the loudspeaker module 200. Theacoustic volume is a fully enclosed volume – in other words, the first and second diaphragms 212a, 212b,loudspeaker frame elements 218a-d and module housing 220 define the boundary of the back volume of the loudspeaker module 200, with no part of the acoustic volume’s boundary being defined by the body of the B-pillar 106. The loudspeaker module 200 is held securely in place by one or more securing means 240a, 240b. The securing means may be any suitable mechanism. For example, the one or more securing means may include screws, clamps, hooks, adhesive and / or any other suitable mechanism for securing the loudspeaker module 200 to the B-pillar 106. 008695603 The loudspeaker module 200 is installed to be positioned above a seatbelt reel 250 from which a seatbelt useable by a person sitting in one of the front seats of the vehicle extends. The seatbelt reel 250 is installed at a base of the B-pillar 106 and secure therein by a seatbelt fixation mechanism 252. The seatbelt fixation mechanism 252 may be any suitable fixation mechanism. For example, the seatbelt fixation mechanism 252 may include a screw, a clamp, a hook, adhesive and / or any other suitable mechanism for securing the loudspeaker module 200 to the pillar 106. In the example of Figure 3, the first and second loudspeakers 120a, 120b are arranged in a side-to-side orientation, meaning that the first diaphragm 212a is facing towards an interior of a cabin enclosed by thevehicle frame 100 of the vehicle in a direction transverse to both the vertical direction in which the B-pillar106 extends, and the front-to-back horizontal direction from a front end of the vehicle frame 100 to a backend of the vehicle frame 100. In other words, the first diaphragm 212a is facing inwards in a sidewaysdirection. Meanwhile, the second diaphragm 212b is facing in the opposite direction towards an exterior ofthe vehicle frame 100 of the vehicle in that direction (i.e., outwards in a sideways direction).The first and second loudspeakers 120a, 120b are aligned with an aperture 120 in the B-pillar 106 suchthat, in use, sound produced and emanating from the front faces of the first and second diaphragms212a, 212b propagates out from the aperture 120 into a cabin enclosed by the vehicle frame 100 to whichthe B-pillar 106 belongs. Figure 4 shows an exemplary loudspeaker module 200 comprising two back-to-back loudspeakers 210 installed in a B-pillar 106 of a vehicle frame 100 in a front-to-back orientation. The loudspeaker module 200 of Figure 4 is substantially the same as that described above in relation to Figure 3, save that the loudspeaker module 200 is oriented and arranged in a front-to-back orientation, meaning that the first diaphragm 212a is facing towards a front of the vehicle frame 100, and the second diaphragm 212b is facing towards a rear of the vehicle frame 100. Figure 5 shows an exemplary loudspeaker module 200 comprising two back-to-back loudspeakers 210a, 210b installed in a B-pillar of a vehicle frame in a top-to-bottom orientation. The loudspeaker module 200 of Figure 5 is substantially the same as that described above in relation to Figures 3 and 4, save that the loudspeaker module 200 is oriented and arranged in a top-to-bottom orientation, meaning that the first diaphragm 212a is facing towards a bottom (or main floor 114) of thevehicle frame 100, and the second diaphragm 212b is facing towards a top (or roof) of the vehicle frame100. Additionally, as can be seen from Figure 5, the module housing 230 is shaped and arranged to fit around one or more structural features 130a, 130b of the B-pillar. This modification of the shape and arrangement of the module housing 230 is equally applicable to the other embodiments described herein (e.g., the single loudspeaker example of Figure 2, the side-to-side orientation of Figure 3, or the front-to- back orientation of Figure 4). In the examples depicted in Figures 3 to 5, the first and second loudspeakers 120a, 120b may be substantially identical. 008695603 Further, the first and second drive units 216a, 216b may be configured to respectively drive the first and second diaphragms 212a, 212b synchronously, as described above. In any of the examples and embodiments described herein, the aperture 120 of the B-pillar 106 may be covered by an acoustically transmissive material (not shown). In any of the examples and embodiments described herein, the acoustic volume 230 of the loudspeaker module 200 may occlude at least 70% (or, optionally, at least 80%, at least 90%, at least 95%, or at least 99%) of the cross-sectional area of the pillar into which the loudspeaker module 106 is installed. A portion of the pillar not occluded by the acoustic volume 230 of the loudspeaker module 200 may be filled with an acoustically absorbent material (not shown), such as a foam. Figure 6 shows a method of installing a loudspeaker module 200 in a vehicle frame 100. The method comprises, in an operation 602, inserting the loudspeaker module 200 through an aperture (e.g., aperture 120) of a pillar of the cabin frame 100 (e.g., the B-pillar 106). The method further comprises, in an operation 604, securing the loudspeaker module 200 to the pillar (e.g., the B-pillar), for example by the one or more securing means 240a-c. The method further comprises, in an operation 606, inserting an acoustically absorbent material into the pillar to fill a portion of the cross-section of the pillar not occluded by the loudspeaker module 200. The method further comprises, in an operation 608, covering the aperture with an acoustically transmissive material. In examples and embodiments where the loudspeaker module 200 is installed in the B-pillar 106 of the cabin frame 100, the seatbelt reel 250 may be installed before, after, or simultaneously with the installation of the loudspeaker module 200.Figure 7 shows the in-vehicle frequency response of a loudspeaker module 200 wherein the movable partof the drive unit 216 is the voice coil and the first and second diaphragms 212a, 212b have an effectiveradiating diameter of 8 cm, installed in the B-pillar, in the orientation depicted in Figure 4, on the right-sideof a vehicle frame of a manufactured vehicle (in the example of Figure 7, the vehicle was a BMW ® iXMY2023 car), measured at 70 W (35 W of power were supplied each to the first and second loudspeakers210a, 210b of the loudspeaker module 200 to a microphone on the front left seat that was positioned atear level 10 cm in front of the headrest. The frequency response shown in Figure 7 demonstrates thatthere is usable output for frequencies below 200 Hz, particularly in the range 40 to 200 Hz. The totalharmonic distortion for the sound produced by the loudspeaker module 200 whose frequency response is depicted in Figure 7 was below 10% for all frequencies below 200 Hz. Figure 8 is a graph illustrating parameter ranges applicable to loudspeaker modules according to the present disclosure, such as the loudspeaker module 200. The horizontal axis represents a normalised moving mass Mms / Sd, which corresponds to the mass Mmsof the moveable assembly over the effective radiating surface Sd and ranges from 0 to 20 [kg / m2]. Thevertical axis represents a normalised volume VB of the enclosure, which corresponds to the volume VB 008695603over the effective radiating surface Sd and ranges from 0 to 1 [m3 / m2]. Accordingly, Figure 8 is Sdnormalised; and Kms / Kb is equal to 0.5. A set of frequency curve (solid lines) corresponds to different in-box resonant frequencies of 20Hz, 30Hz, 40Hz, 50Hz, 60Hz, 70Hz and 80Hz, respectively. As such, Figure 8 relates the mass Mms of the moveable assembly, the volume VB of the loudspeaker module, and the resonant frequency fc. The grey area indicates preferred parameter ranges, with darker areas being more preferred. Thus, Mms / Sd is preferably in a range of 5 to 15 [kg / m2], and more preferably in a range from 7 to 12 [kg / m2].VB / Sd is preferably greater than 0 and up to 0.5 [m], and more preferably in a range from 0.03 to 0.3 [m].The in-box resonant frequency is preferably in a range from 30Hz to 80Hz, and more preferably in arange of 40Hz to 80Hz. The top left corner of Figure 8 may be considered to represent conventional loudspeaker design where either the moving mass is small, or the volume VB is large, or both are small. The lower right corner is a preferred area, and relates to comparatively high masses Mms, such as 180g, in a volume VB such as 6 litres. These parameters may not be preferred for music reproduction but may be preferred for cinema applications. As an example, when choosing a volume VB of 1.5 litres, then in order to achieve a target in-box resonant frequency fc of 60Hz, according to Figure 8 the normalised moving mass Mms / Sd is estimated at approximately 8.5 Mms / Sd. For an effective radiating surface Sd of 110cm2, this would correspond to a moving mass of approximately 93.5g. Such estimation may give a first indication of approximate parameter values during the design process. It is noted that effects of the mechanical suspension contribution may in practice not be negligible and have been taken into account in Figure 8 (Kms / KB=0.5). *** The features disclosed in the foregoing description, or in the following claims, or in the accompanying drawings, expressed in their specific forms or in terms of a means for performing the disclosed function, or a method or process for obtaining the disclosed results, as appropriate, may, separately, or in any combination of such features, be utilised for realising the invention in diverse forms thereof. While the invention has been described in conjunction with the exemplary embodiments described above, many equivalent modifications and variations will be apparent to those skilled in the art when given this disclosure. Accordingly, the exemplary embodiments of the invention set forth above are considered to be illustrative and not limiting. Various changes to the described embodiments may be made without departing from the spirit and scope of the invention.For the avoidance of any doubt, any theoretical explanations provided herein are provided for thepurposes of improving the understanding of a reader. The inventors do not wish to be bound by any of these theoretical explanations. Any section headings used herein are for organizational purposes only and are not to be construed as limiting the subject matter described. 008695603 Throughout this specification, including the claims which follow, unless the context requires otherwise, theword “comprise” and “include”, and variations such as “comprises”, “comprising”, and “including” will beunderstood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integers or steps. The use of the term “comprise” and “include” to refer to the inclusion of integers, steps and / or operations nonetheless also encompasses aspects, examples and embodiments that may be analogously described with the term “consist” in respect of those integers, steps and / or operations. It must be noted that, as used in the specification and the appended claims, the singular forms “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise. The terms “a” (or “an”), as well as the terms “one or more” and “at least one” can be used interchangeably herein. The term “and / or” as used herein is to be taken as specific disclosure of each of specified listed features or components with or without one or more of the others. Thus, the term “and / or” as used in a phrase such as “A, B and / or C” encompasses each of: A and B and C; A and B; A and C; B and C; A or B or C; A or C; A or C; B or C; only A; only B; and only C. Ranges may be expressed herein as from “about” one particular value, and / or to “about” another particular value. When such a range is expressed, another embodiment includes from the one particularvalue and / or to the other particular value. Similarly, when values are expressed as approximations, by theuse of the antecedent “about,” it will be understood that the particular value forms another embodiment.The term “about” in relation to a numerical value is optional and means for example + / - 10%.References A number of publications are cited above in order to more fully describe and disclose the invention and the state of the art to which the invention pertains. Full citations for these references are provided below. The entirety of each of these references is incorporated herein. ^EP3282714A1^ EP0904985A1^ JPS5757687U^ US2007154055A1^ EP1407934B1^ EP2043382A1^ CN216960109U^ WO2023194163A1^ WO2024 / 003028A1008695603^ GB2219587.9^ GB2302099.3^ GB2314913.1^ GB2314915.6008695603

Claims

Claims:

1. A method of installing a loudspeaker module in a vehicle frame, wherein the loudspeaker module isfor producing sound at bass frequencies and comprises a loudspeaker and a module housing; wherein the loudspeaker comprises a diaphragm, a drive unit configured to move the diaphragm to produce sound, and a movable assembly that includes the diaphragm and a movable part of the drive unit, wherein a mass of the movable part of the drive unit is at least 60% of a mass of the movable assembly; wherein the diaphragm of the loudspeaker and the module housing together enclose an acoustic volume; andwherein the method comprises installing the loudspeaker module in a pillar of the cabin frame such that the acoustic volume is contained within the pillar, and such that sound produced by the loudspeaker module propagates out from an aperture in the pillar when the loudspeaker module is in use.

2. The method according to claim 1, wherein the loudspeaker is a first loudspeaker, the diaphragm isa first diaphragm, the drive unit is a first drive unit, and the movable assembly is a first movable assembly; and the loudspeaker module further comprises a second loudspeaker, the second loudspeaker comprising a second diaphragm, a second drive unit configured to move the second diaphragm toproduce sound, and a second movable assembly that includes the second diaphragm and a movable part of the second drive unit, wherein a mass of the movable part of the second drive unit is at least 60% of a mass of the second movable assembly, andwherein the acoustic volume is further enclosed by the second diaphragm.

3. The method according to claim 2, wherein each of the first and second diaphragms comprises arespective front face, facing away from the corresponding drive unit, and wherein the front faces ofthe first and second diaphragms face in opposite directions; and wherein the first and second drive units are configured to drive the first and second diaphragms synchronously.

4. The method according to claim 3, wherein installing the loudspeaker module in the pillar of thevehicle frame comprises orienting the loudspeaker module such that the front face of the firstdiaphragm is facing towards a front end of the vehicle frame, and the front face of the seconddiaphragm is facing towards a rear end of the vehicle frame after the loudspeaker module has beeninstalled.

5. The method according to any preceding claim, wherein the pillar in which the loudspeaker moduleis installed is selected from amongst a plurality of pillars of the vehicle frame, each pillar beingpositioned at a respective pillar location in the vehicle frame, and the selected pillar being a pillaramongst the plurality of pillars that positions the installed loudspeaker module in a pillar location 008695603that is the most susceptible of the plurality of pillar locations to cabin gain for the bass frequencysound that the loudspeaker module is configured to produce.

6. The method according to any preceding claim, wherein the vehicle frame is for use in a car, andthe loudspeaker module is installed in a B-pillar of the vehicle frame.

7. The method according to claim 6, wherein installing the loudspeaker module in the B-pillar includespositioning the loudspeaker module above or below a seatbelt reel installed in the B-pillar.

8. The method according to any preceding claim, wherein installing the loudspeaker modulecomprises inserting the loudspeaker module through the aperture in the pillar and securing the loudspeaker module within the pillar.

9. The method according to any preceding claim, wherein the loudspeaker module is containedentirely within the pillar after being installed.

10. The method according to any preceding claim, wherein the method further comprises covering theaperture with an acoustically transmissive material.

11. The method according to any preceding claim, wherein, after installing the loudspeaker module, aportion of the acoustic volume occludes at least 70% of a cross-sectional area of the pillar.

12. The method according to claim 11, the method further comprising inserting an acousticallyabsorbent material into the pillar to occupy a portion of the cross-sectional area of the pillar that is not occupied by the acoustic volume.

13. The method according to any preceding claim, wherein the or each loudspeaker is positionedbelow a section of the module housing after installing the loudspeaker module in the pillar.

14. The method according to any preceding claim, wherein:the or each drive unit comprises a movable part and a stationary part, wherein the moveable part of the drive unit is the voice coil and the stationary part of the drive unit is themagnet unit; and the voice coil may has a first perimeter and a second perimeter and, when the moveablepart of the drive unit is at rest, a magnetic flux density at a first perimeter of the voice coil is 50% orless of a magnetic flux density at the second perimeter of the voice coil. .

15. A vehicle frame comprising a loudspeaker module installed in a pillar of the vehicle frame, usingthe method of any preceding claim. 008695603

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