Vehicle and horn apparatus for vehicle

Abstract

There is provided a horn apparatus for a vehicle, the horn apparatus including: a loudspeaker that includes a diaphragm and a drive unit to move the diaphragm; a horn signal generator configured to supply a horn signal to the drive unit such that the diaphragm produces a horn sound based on the horn signal, wherein the horn signal contains at least one fundamental frequency; wherein the loudspeaker has a second radial breakup frequency associated with a second radial breakup of the diaphragm; and wherein the second radial breakup frequency is in the 2.5kHz, 3.15kHz or 4kHz one-third octave band.

Description

[0001] 008850430

[0002] 1

[0003] VEHICLE AND HORN APPARATUS FOR VEHICLE

[0004] This application claims priority to GB2415168.0, filed 15 October 2024.

[0005] Field of the Invention

[0006] The present invention relates to a vehicle including a horn apparatus and a horn apparatus for a vehicle.

[0007] Background

[0008] Most automotive vehicles are equipped with a horn apparatus for producing an audible warning sound to alert other road users. A typical audible warning sound produced by a horn apparatus is easily recognized by people as a vehicle horn and, worldwide, people have grown accustomed to how vehicle horns sound.

[0009] A particular type of horn apparatus used in a vehicle includes a loudspeaker, typically an electrodynamic loudspeaker, which may be referred to as an “loudspeaker-based” horn apparatus or as an “electronic horn” (cf. Regulation No 28 of the Economic Commission for Europe). The loudspeaker is configured to produce an audible warning sound based on an audio signal, which is typically stored in memory and provided to the loudspeaker via an amplifier. This audio signal may be a recording of an audible warning sound produced by a conventional horn apparatus and may contain multiple frequencies for playback by the loudspeaker simultaneously.

[0010] WO2024115672A1 describes a loudspeaker with integral surround and capable of reproducing a dualtone horn signal faithfully. It also describes the combination of the loudspeaker with a passive radiator for improved low-frequency extension. The loudspeaker speaker described in WO2024115672A1 can also be used in an Acoustic Vehicle Alerting System (or“AVAS” system), c.f. Regulation No 138 of the Economic Commission for Europe of the United Nations (UNECE) - Uniform provisions concerning the approval of Quiet Road Transport Vehicles with regard to their reduced audibility [2017 / 71] (“ECE 138”) or Federal Motor Vehicle Safety Standard No. 141 , Minimum Sound Requirements for Hybrid and Electric Vehicles (“FMVSS 141”). An AVAS system may be used where a slow driving electric vehicle produces too little noise to be noticed by pedestrians and therefore poses a safety issue, particularly in front of schools, at pedestrian crossings or traffic lights. Legislation has been adapted to address this matter by making mandatory the generation of an artificial sound by an AVAS system to alert pedestrians to the presence of electric drive vehicles. These include hybrid (HEVs), plug-in hybrid (PHEVs), and full battery electric vehicles (BEVs) travelling at low speeds, especially in the lowest speed range below which the noise generated by rolling tires can no longer be easily heard.

[0011] The present invention has been devised in light of the above considerations. 008850430

[0012] 2

[0013] Summary of the Invention

[0014] The inventors observed that known loudspeakers for use as an electronic horn and an AVAS system in a vehicle may produce sound dominated by high frequency output and may fall short with regards to lower frequencies, such as midband output including frequencies from the 800Hz one-third octave band to the 1 ,6kHz one-third octave band. The above-mentioned WO2024115672A1 describes such a loudspeaker dominant high frequency output. WO2022128595A1 and WO2022253924A1 describe further examples of such loudspeakers with dominant high frequency output.

[0015] According to the first aspect set out below, lower frequency output may be improved by suitably designing a front cavity through which to propagate the sound produced by a loudspeaker, e.g. suitably integrating the loudspeaker into a vehicle such that the front cavity is provided by the vehicle. According to the second aspect set out below, lower frequency output may be improved by a diaphragm having a second radial breakup at a high frequency exceeding the midband frequencies, redirecting power from frequencies around the second radial breakup to frequencies below the second radial breakup. Furthermore, that the first aspect and the second aspect may be combined further boost lower frequency output.

[0016] According to a first aspect, there is provided a vehicle including a horn apparatus, wherein the horn apparatus includes: a loudspeaker that includes a diaphragm and a drive unit to move the diaphragm, wherein the diaphragm has a front face and a rear face; a horn signal generator configured to supply a horn signal to the drive unit such that the diaphragm produces a horn sound based on the horn signal, wherein the horn signal contains at least one fundamental frequency; wherein the vehicle includes: a rear enclosure configured to receive sound produced by the rear face of the diaphragm; a front cavity configured to receive sound produced by the front face of the diaphragm and to allow the sound produced by the front face of the diaphragm to exit the front cavity via one or more openings in the front cavity; wherein the front cavity is configured to boost the sound pressure level (“SPL”) in a one-third octave band, referred to as the front cavity boosted band, which corresponds to a fundamental frequency contained in the horn signal or a harmonic of a fundamental frequency contained in the horn signal, wherein the front cavity boosted band is one of the 400Hz, 500Hz, 800Hz, 1 kHz, 1.25kHz or 1.6kHz one- third octave bands; and wherein the maximum level of the horn signal in the front cavity boosted band is either the maximum level of the horn signal in any one-third octave band or is no more than 3dB less than the maximum level of the horn signal in any one-third octave band.

[0017] In use, the front cavity may act as an acoustic resonator for the sound generated by the loudspeaker and in use boost SPL at the front cavity boosted band which contains a fundamental frequency or a harmonic of the horn signal. By aligning the front cavity boosted band with a fundamental frequency (or harmonic thereof) of the horn signal, and by having the maximum level of the horn signal (or no more 3dB less than the maximum level of the horn signal) in this front cavity boosted band, the present inventors have found that the horn apparatus can be able to generate a horn sound which has improved timbre when compared to a horn sound generated without the front cavity (or a horn sound generated with a front 008850430

[0018] 3 cavity that does not provide a boost in a band containing the fundamental frequency or harmonic thereof) for which the present inventors have found that the horn sound can be dominated by high frequencies.

[0019] Here, the one-third octave bands are specified in terms of the nominal centre frequency, as is normal in the art. For example, the 400Hz one-third octave band has a nominal centre frequency of 400Hz. In practice, a sound level meter (such as Bruel & Kjaer 2245 Sound Meter) may be used to measure SPL across one-third octave bands.

[0020] The front cavity boosted band may correspond to a harmonic of a fundamental frequency contained in the horn signal.

[0021] In some examples, the front cavity boosted band may correspond to an even harmonic of a fundamental frequency contained in the horn signal. By aligning the front cavity boosted band with an even harmonic, the warmth of the horn sound may be increased.

[0022] In some examples, the front cavity boosted band may correspond to the second harmonic of a fundamental frequency contained in the horn signal. Since traditional horns may have a strong second harmonic, aligning the front cavity boosted band with a second harmonic may increase warmth of the horn sound and provide for a more recognisable horn sound. In practice, the horn signal may contain a fundamental frequency in the range of 400Hz to 550Hz, so the front cavity boosted band may correspond to the 800Hz one-third octave band or the 1 kHz one-third octave band.

[0023] The front cavity boosted band may be one of the 800Hz, 1 kHz, 1 ,25kHz or 1 ,6kHz one-third octave band.

[0024] The front cavity may be configured to boost the SPL by the most in the front cavity boosted band or in a one-third octave band adjacent to the front cavity boosted band.

[0025] The particular boost to the SPL as provided by the front cavity may be determined by comparing the SPL produced by the loudspeaker and the front cavity against the SPL produced by the loudspeaker without the front cavity.

[0026] The front cavity boosted band may be the one-third octave band with the highest relative positive gain when comparing the SPL produced by the loudspeaker and the front cavity against the SPL produced by the loudspeaker without the front cavity.

[0027] The front cavity may be provided by a tube. One end of the tube may be attached to the loudspeaker. The other end of the tube may include the one or more openings via which sound produced by the diaphragm exits the front cavity.

[0028] Optionally the one or more openings are provided by a protective grille. In some examples, the protective grille may be a perforated region in the underbody of the vehicle.

[0029] In some examples, the front cavity may be formed from a sound hard material for the relevant frequencies, e.g. of the horn signal, and may be mechanically compliant material (e.g. rubber or similar material). 008850430

[0030] 4

[0031] The tubular (e.g. cylindrical) portion of the cavity can be part of the loudspeaker, the openings can be part of the vehicle such that the resonance chamber is created only when the loudspeaker is mounted to the vehicle.

[0032] The loudspeaker may be exposed to an exterior of the vehicle, so that in use sound produced by the loudspeaker may primarily radiate from the vehicle. In some examples, the loudspeaker may be mounted on the exterior of the vehicle.

[0033] The front cavity may be defined by a chassis of the vehicle. For example, the loudspeaker may be mounted to the chassis, e.g. facing down, and may be configured to radiate sound through the front cavity defined by the chassis. In this position, sound produced by the loudspeaker may be primarily radiated outwards from the vehicle. Such positioning may be preferred in some examples since it may decrease the sound that can be heard inside of the vehicle. Also, such positioning may mean that in use the front cavity may protect the loudspeaker in case an underbody panel moves, e.g. when mounting a curb.

[0034] DE102023001631 A1 shows a loudspeaker radiating through a cavity in the underbody of a vehicle, but said cavity is not configured to boost frequencies produced by the loudspeaker, and in particular not lower frequencies, such as midrange frequencies, to improve timbre.

[0035] The vehicle may further include a grille to boost the SPL in a one-third octave band, referred to as the grille boosted band. The grille may in use contribute to high SPL output when using the horn apparatus to generate a horn sound.

[0036] The grille may be configured to receive sound produced by the front face of the diaphragm and to allow the sound produced by the front face of the diaphragm to propagate through the grille into the front cavity.

[0037] The grille may partially close one end of the front cavity and, where provided, the protective grille may partially close the other end of the front cavity.

[0038] The grille may be arranged across the front face of the diaphragm. The grille may be contoured to at least partly follow contours in the front face of the diaphragm when the diaphragm is in its rest position.

[0039] The grille may be attached to or integrated with the loudspeaker. In some examples, the grille may be attached to the rear enclosure which receives the sound produced by the rear face of the diaphragm. In some examples, the grille may be attached to a loudspeaker frame of the loudspeaker.

[0040] The grille boosted band may correspond to a harmonic of a fundamental frequency contained in the horn signal.

[0041] In some examples, the grille boosted band may correspond to an even harmonic of a fundamental frequency contained in the horn signal. By aligning the grille boosted band with an even harmonic, the warmth of the horn sound may be increased.

[0042] In some examples, the grille boosted band may correspond to the second harmonic of a fundamental frequency contained in the horn signal. This may increase warmth of the horn sound and provide for a more recognisable horn sound. 008850430

[0043] 5

[0044] The grille boosted band may be one of the 2kHz, 2.5kHz or 3.15 kHz one-third octave bands.

[0045] In some examples, the grille defines a plurality of passages extending through the grille for sound to propagate through the grille. The plurality of passage may be distributed across substantially the entire front face of the diaphragm.

[0046] Sound produced by the horn apparatus at some frequencies may exhibit high directivity, e.g. around 2.5kHz. Output of sound with high directivity may be improved by providing the plurality of passages (as opposed to, for example, a single large passage).

[0047] WO2022189546A1 , the content of which is incorporated herein by reference, contains further technical information about how to configure a grille so as to boost SPL at certain frequency bands of sound generated by loudspeakers used on the outside of vehicles. Any one of the features described in WO2022189546A1 may therefore be incorporated into the vehicle according to the first aspect of the invention.

[0048] Thus, in some examples, V1 / V2 < 0.7, optionally V1 / V2 < 0.5, optionally V1 / V2 < 0.3, where V1 and V2 are defined as in WO2022189546A1 .

[0049] Thus, in some examples, A1 / A2 > 5, optionally A1 / A2 > 10, optionally A1 / A2 > 20, wherein A1 and A2 are defined as in WO2022189546A1 .

[0050] Thus, in some examples A1 / A3 > 3, optionally A1 / A3 > 6, optionally A1 / A3 > 10, wherein A1 and A3 are defined as in WO2022189546A1 .

[0051] The diaphragm may have an inside perimeter and an outside perimeter. A distance from a centre of the diaphragm to the outside perimeter, as measured in a radial direction perpendicular to the movement axis (see below), may be referred to as the radial extent of the diaphragm. For a circular diaphragm, the radial extent corresponds to half of the outside diameter.

[0052] The loudspeaker may have a second radial breakup frequency associated with a second radial breakup of the diaphragm.

[0053] The second radial breakup frequency may be in the 2.5kHz, 3.15kHz or 4kHz one-third octave band.

[0054] In examples where the grille is provided, the grille boosted band may be between the front cavity boosted band and the second radial breakup frequency.

[0055] The second radial breakup may help provide for an SPL boost at frequencies below the second radial breakup frequency. In use, the second radial breakup frequency in one of the specified one-third octave band may therefore help to improve high SPL output during horn operation. Moreover, this boost may be in combination with the boost resulting from the grille to further boost SPL.

[0056] So-called breakup of a diaphragm is a phenomenon known in the art and describes a resonance of the diaphragm itself, i.e. a breakup mode of the diaphragm, which occurs at a breakup frequency. Radial breakup is a particular kind of breakup where the breakup mode is radially across the diaphragm (see e.g. discussion of Figure 10, below). 008850430

[0057] 6

[0058] The second radial breakup typically results in a second radial breakup mode which has a single annular node around the diaphragm which is located between the inside perimeter of the diaphragm and the outside perimeter of the diaphragm. Without wishing to be bound by theory, the location of the annular node is thought to be determined by boundary conditions at the inside perimeter and the outside perimeter of the diaphragm. In some examples, the inside perimeter may be clamped or driven and the outside perimeter may be free and mass-loaded. This may in practice locate the annular node closer to the outside perimeter (than the inside perimeter) of the diaphragm. In some examples, the annular node may be located at 50% to 100% of the radial extent of the diaphragm (measured from the centre of the diaphragm and in the radial direction); or may be at 60% to 100% of the radial extent of the diaphragm.

[0059] The second radial breakup mode can therefore be identified by looking for the single annular node, e.g. using a laser scan of the diaphragm movement as discussed below.

[0060] Within the second radial breakup mode, portions of the diaphragm inside and outside of the annular node move out of phase. More particularly, an inner portion of the diaphragm, which is inside relative to the annular node (i.e. at the inside perimeter), and an outer portion of the diaphragm, which is outside relative to the annular node (i.e. at the outside perimeter), move out of phase. The inventors observed that the second radial breakup mode results in a boost to SPL at frequencies close to and below the second radial breakup frequency. This may be considered surprising since the inside portion and the outer portion of the diaphragm move out of phase, but the inventors’ observation is that this results in an SPL boost (rather than no SPL boost, as might be expected by mutual cancellation). Without wishing to be bound by theory, it is believed that the SPL boost may be caused by there being an imbalance between the respective (out-of-phase) contributions provided to the SPL by the outer and inner portions of the diaphragm (resulting from factors such as surface area of the outer and inner portions, displacement of the outer and inner portions, etc).

[0061] The boost to SPL at frequencies close to the second radial breakup frequency has been found to typically be more prominent at frequencies below the second radial breakup frequency, and less prominent at frequencies higher than the second radial breakup frequency. Thus, by designing the loudspeaker to have a second radial breakup at a comparatively high frequency (in the 2.5kHz, 3.15kHz or 4kHz one- third octave band), SPL at frequencies close to and below the second radial breakup frequency may in use be helpfully boosted.

[0062] The skilled person is familiar with the phenomenon of breakup of the diaphragm, and how a loudspeaker can be designed to have the second radial breakup frequency in the specified once-third octave bands. In some examples, the desired second radial breakup frequency may be achieved by a loudspeaker with a comparatively stiff diaphragm and a comparatively soft suspension element. Suitably the diaphragm may be formed separately from the suspension element and / or may be formed from a different material.

[0063] The diaphragm may have a Young’s modulus in the range of 2 to 16GPa, optionally 6 to 16 GPa.

[0064] In some examples, the diaphragm may be formed at least in part from a plastic material, e.g. a polymer such as a thermosetting polymer. The diaphragm may be made using any suitable manufacturing 008850430

[0065] 7 process, e.g. compression moulding, vacuum-forming or injection moulding. In some examples, the diaphragm may be a thermoformed film formed from the plastic material, optionally polyethylene naphthalate.

[0066] In some examples, the diaphragm may be formed from glass fibre and epoxy resin, e.g. epoxy coated glass fibre.

[0067] Further technical information on the configuration of the diaphragm is provided in WO2022253924A1 and in WO20241 15676A1 , including also discussion of further material choices. For example, the diaphragm may be formed by a single-layer woven fabric of orthogonal woven fibres and a thermoset resin. Suitable materials for the diaphragm include glass fiber, carbon fiber or poly-paraphenylene terephthalamide (Kevlar) and a matrix or coating of thermoset resin such as epoxy or phenolic resin. Of that woven fabric, the weaving pattern is preferably a canvas or twill, and may suitably use the same thread count for the warp and the weft. That thread count may be, for example, 20-100 threads per inch (tpi), and preferably is 30-60 tpi. In other examples, the single piece of material may comprise a polymer. For example the diaphragm may be formed by vacuum-forming or by injection molding. Suitable diaphragm materials comprising a polymer may include but are not limited to: Polypropylene, optionally with one or more filler materials such as glass fibers, talcum, MICA etc, which may be uniaxially or biaxially oriented;

[0068] Polycarbonate, optionally with one or more filler materials; Acrylonitril-butadieen-styreen, optionally in blends with other materials such as PC-ABS; Polyethyleentereftalaat, which may be uniaxially or biaxially oriented (e.g. Mylar®); Polyvinylchloride; Polyethylene naphthalate; Polyethylene terephthalate;

[0069] Polyethylene terephthalate; Biaxially oriented Polyethylene terephthalate; Polyetherimide; and Polyether ether ketone.

[0070] The diaphragm may have an average isotropic loss factor eta of less than 0.1 . It is known to the skilled person that the average isotropic loss factor eta quantifies damping, i.e. the loss of energy to the material, when bending the material. The average isotropic loss factor eta of less than 0.1 may be less, and even significantly less, than what is seen in at least some conventional diaphragms. As a result, the present diaphragm may have comparatively little damping, which may provide for a stronger second radial breakup and therefore an increased boost to SPL at frequencies close to the second radial breakup frequency.

[0071] The diaphragm may have a density in the range of 1 to 2 grams per cubic-centimetre (g / cm3). Conventional loudspeakers may use materials with lower density, such as paper, or higher density, such as metals (e.g. aluminium).

[0072] In combination, the specified parameters (Young’s modulus, isotropic loss factor and density) may provide a particularly surprising diaphragm as the specified parameter ranges are believed to be outside of the ranges typically considered by the skilled person. When compared to a typical paper diaphragm, the diaphragm with the specified parameters is comparatively stiff and has less damping. When compared to a typical metal diaphragm, the specified diaphragm is comparatively soft and light. In either case, the diaphragm with the specified parameter ranges may provide for a comparatively strong second 008850430

[0073] 8 radial breakup and a comparatively high breakup frequency. A particularly convenient choice of material for manufacturing of such a diaphragm may be the plastics specified above.

[0074] The loudspeaker may include a loudspeaker frame, which may house the drive unit; one or more suspension elements may be attached to the loudspeaker frame. The diaphragm may be suspended from the loudspeaker frame by the one or more suspension elements. Preferably, the loudspeaker includes at least two suspension elements.

[0075] The one or more suspension elements may be formed separately from the diaphragm, and may be attached to the diaphragm (directly or indirectly).

[0076] The one or more suspension elements may include a first suspension element, e.g. a surround suspension element (which may also be referred to as the roll suspension). The first suspension element may be attached directly or indirectly to the diaphragm. In some examples, the first suspension element may attach (directly) to the outside perimeter of the diaphragm.

[0077] The first suspension element may have a Young’s modulus in the range of 6 to 16 MPa.

[0078] The surround suspension element may be formed from a thermoplastic elastomer, a thermoplastic vulcanisate, an ethylene propylene diene monomer rubber, or a nitrile butadiene rubber.

[0079] The one or more suspension elements may include a second suspension element, e.g. a damper. 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 the inside perimeter of the diaphragm. In other examples, the second suspension element may be attached to another element, e.g. the moveable part of the drive unit. The second suspension element, irrespective of whether attached at the inside perimeter of the diaphragm or the other element, may not significantly affect breakup behaviour of the diaphragm since the diaphragm is driven at the inside perimeter.

[0080] The loudspeaker may have an in-box resonant frequency. The in-box resonant frequency is a resonant frequency associated with loudspeaker being used with the rear enclosure and is well understood in the art. Further information about the in-box resonant frequency may be found, for example, in L.L. Beranek, Acoustics, McGraw-Hill, 1954.

[0081] The in-box resonant frequency may lower than the front cavity boosted band.

[0082] The in-box resonant frequency may be 250Hz or less.

[0083] By providing a low resonant frequency, the low frequency reproduction may be improved and low frequency content increased when outputting audio content. This may make for a more pleasant AVAS signal.

[0084] The horn signal may be an electrical signal. The electrical signal may be configured to generate a horn sound, when supplied to the drive unit of the loudspeaker. Such signals are known in the art, and discussed e.g. in WO2024 / 115676A1 . 008850430

[0085] 9

[0086] The horn signal may include a fundamental frequency in the range of 400Hz to 600Hz. The fundamental frequency may be in the range of 405Hz to 420Hz, or in the range of 500Hz to 530Hz.

[0087] In some examples, the horn signal may include multiple fundamental frequencies, for example two fundamental frequencies. For example, the horn signal may include a first fundamental frequency in the range 405Hz to 420Hz, and a second fundamental frequency in the range of 500Hz to 530Hz;

[0088] The first fundamental frequency and the second fundamental frequency may be spaced by a minor interval.

[0089] In some examples, the horn signal may include only the fundamental frequency / frequencies and harmonics thereof.

[0090] Herein a “fundamental” frequency in an audio signal may be understood as the lowest frequency contained in the audio signal that is the common denominator of the harmonic frequencies. Herein, a “harmonic” of a fundamental frequency may be understood as an integral (whole number) multiple of the fundamental frequency. The fundamental frequency may be referred to as f_1 , with each harmonic referred to as f_2 (second harmonic), f_3 (third harmonic) and so on.

[0091] The audio signal may be configured to mimic a single tone vehicle horn sound (which typically includes a fundamental frequency and harmonics thereof). For example, the weights for each of the plurality of harmonics corresponding to the fundamental frequency may be selected so that the precursor audio signal (and consequently the (compressed) audio signal) mimics a single tone vehicle horn sound. Additionally / alternatively, the compressing step(s) may be configured so that the (compressed) audio signal) mimics a single tone vehicle horn sound. Further detail regarding the precursor audio signal and its use in synthesising an audio signal for use by a horn apparatus is provided in WO2024115672A1 .

[0092] The fundamental frequencies in the range of 400Hz to 600Hz may be useful frequencies in the human hearing range for use in a vehicle horn and correspond to the frequencies which are typically present in a recognisable vehicle horn sound.

[0093] The horn apparatus may be operable to generate a horn sound in front of the vehicle; wherein at a distance of 7 metres from the vehicle the horn signal may be louder than 93dB.

[0094] The loudspeaker may include the rear enclosure.

[0095] In any aspect of the invention, the drive unit may be configured to move the diaphragm along a movement axis of the loudspeaker. More particularly, the diaphragm may be caused to move in a forward direction and in a rearward direction parallel to the movement axis. Such movement is also referred to as “axial movement” of the diaphragm.

[0096] The drive unit may include a moveable part attached to the diaphragm and a stationary part attached to the loudspeaker frame. The loudspeaker may be operable to cause the moveable part and the stationary part to magnetically cooperate to cause movement of the moveable part along the movement axis. A moveable assembly, which may include the moveable part of the drive unit and the diaphragm, may thus 008850430

[0097] 10 be caused to move along the movement axis of the loudspeaker to produce sound. The moveable assembly may also be referred to as a “moving” assembly.

[0098] 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 a conventional frame of reference according to which the diaphragm is considered to be moveable, and in use to be moving, whereas other parts of the loudspeaker are considered to be stationary. As such those parts of the loudspeaker 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, which in use do not move with the diaphragm (and which may be stationary with respect to an external apparatus to which the loudspeaker is attached), are referred to as stationary, e.g. the stationary part of the drive unit. Those parts of the loudspeaker which are moveable, i.e. the diaphragm and parts that in use move with the diaphragm, may collectively be referred to as the moveable assembly.

[0099] According to a second aspect, there is provided a horn apparatus for a vehicle, the horn apparatus including: a loudspeaker that includes a diaphragm and a drive unit to move the diaphragm; a horn signal generator configured to supply a horn signal to the drive unit such that the diaphragm produces a horn sound based on the horn signal, wherein the horn signal contains at least one fundamental frequency; wherein the loudspeaker has a second radial breakup frequency associated with a second radial breakup of the diaphragm; and wherein the second radial breakup frequency is in the 2.5kHz, 3.15kHz or 4kHz one-third octave band.

[0100] So-called breakup of a diaphragm is a phenomenon known in the art and describes a resonance of the diaphragm itself, i.e. a breakup mode of the diaphragm, which occurs at a breakup frequency. Radial breakup is a particular kind of breakup where the breakup mode is radially across the diaphragm (see e.g. discussion of Figure 10, below). As set out above with respect to the first aspect, the second radial breakup may help to provide an SPL boost at frequencies close to and below the second radial breakup frequency. The horn apparatus according to the second aspect therefore is able to have improved SPL at frequencies close to and below the second radial breakup frequency.

[0101] The second radial breakup typically results in a second radial breakup mode which has a single annular node around the diaphragm which is located between the inside perimeter of the diaphragm and the outside perimeter of the diaphragm. Without wishing to be bound by theory, the location of the annular node is thought to be determined by boundary conditions at the inside perimeter and the outside perimeter of the diaphragm. In some examples, the inside perimeter may be clamped or driven, and the outside perimeter may be free and mass-loaded. This may in practice locate the annular node closer to the outside perimeter (than the inside perimeter) of the diaphragm.

[0102] The diaphragm may have an inside perimeter and an outside perimeter. A distance from a centre of the diaphragm to the outside perimeter, as measured in a radial direction perpendicular to the movement axis (see below), may be referred to as the radial extent of the diaphragm. For a circular diaphragm, the radial extent corresponds to half of the outside diameter. In some examples, the annular node may be located 008850430

[0103] 11 at 50% to 100% of the radial extent of the diaphragm (measured from the centre of the diaphragm and in the radial direction); or may be at 60% to 100% of the radial extent of the diaphragm.

[0104] A skilled person familiar with the phenomenon of breakup of the diaphragm would be able to design a loudspeaker to have the second radial breakup frequency in the specified once-third octave bands. In some examples, the desired second radial breakup frequency may be achieved by a loudspeaker with a comparatively stiff diaphragm and a comparatively soft suspension element. Suitably the diaphragm may be formed separately from the suspension element and / or may be formed from a different material.

[0105] The diaphragm may have a Young’s modulus in the range of 2 to 16 GPa, optionally 6 to 16GPa.

[0106] In some examples, the diaphragm may be formed at least in part from a plastic material, e.g. a polymer such as a thermosetting polymer. The diaphragm may be made using any suitable manufacturing process, e.g. compression moulding, vacuum-forming or injection moulding. In some examples, the diaphragm may be a thermoformed film formed from the plastic material, optionally polyethylene naphthalate.

[0107] In some examples, the diaphragm may be formed from glass fibre and epoxy resin, e.g. epoxy coated glass fibre.

[0108] Further technical information on the configuration of the diaphragm is provided in WO2022253924A1 and in WO2024115676A1 , including also discussion of further material choices. For example, the diaphragm may be formed by a single-layer woven fabric of orthogonal woven fibres and a thermoset resin. Suitable materials for the diaphragm include glass fiber, carbon fiber or poly-paraphenylene terephthalamide (Kevlar) and a matrix or coating of thermoset resin such as epoxy or phenolic resin. Of that woven fabric, the weaving pattern is preferably a canvas or twill, and may suitably use the same thread count for the warp and the weft. That thread count may be, for example, 20-100 threads per inch (tpi), and preferably is 30-60 tpi. In other examples, the single piece of material may comprise a polymer. For example the diaphragm may be formed by vacuum-forming or by injection molding. Suitable diaphragm materials comprising a polymer may include but are not limited to: Polypropylene, optionally with one or more filler materials such as glass fibers, talcum, MICA etc, which may be uniaxially or biaxially oriented;

[0109] Polycarbonate, optionally with one or more filler materials; Acrylonitril-butadieen-styreen, optionally in blends with other materials such as PC-ABS; Polyethyleentereftalaat, which may be uniaxially or biaxially oriented (e.g. Mylar®); Polyvinylchloride; Polyethylene naphthalate; Polyethylene terephthalate;

[0110] Polyethylene terephthalate; Biaxially oriented Polyethylene terephthalate; Polyetherimide; and Polyether ether ketone.

[0111] The diaphragm may have an average isotropic loss factor eta of less than 0.1 .

[0112] The diaphragm may have a density in the range of 1 to 2 grams per cubic-centimetre (g / cm3).

[0113] The loudspeaker may include a loudspeaker frame, which may house the drive unit; one or more suspension elements may be attached to the loudspeaker frame. The diaphragm may be suspended from the loudspeaker frame by the one or more suspension elements. Preferably, the loudspeaker includes at least two suspension elements. 008850430

[0114] 12

[0115] The one or more suspension elements may be formed separately from diaphragm, and may be attached to the diaphragm (directly or indirectly).

[0116] The one or more suspension elements may include a first suspension element, e.g. a surround suspension element (which may also be referred to as the roll suspension). The first suspension element may be attached directly or indirectly to the diaphragm. In some examples, the first suspension element may attach (directly) to the outside perimeter of the diaphragm.

[0117] The first suspension element may have a Young’s modulus in the range of 6 to 16 MPa.

[0118] The surround suspension element may be formed from a thermoplastic elastomer, a thermoplastic vulcanisate, an ethylene propylene diene monomer rubber, or a nitrile butadiene rubber.

[0119] The one or more suspension elements may include a second suspension element, e.g. a damper. 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 the inside perimeter of the diaphragm. In other examples, the second suspension element may be attached to another element, e.g. the moveable part of the drive unit.

[0120] The second suspension element may have a Young’s modulus in the range of 200MPa to 1 GPa.

[0121] The horn apparatus may further include a rear enclosure configured to receive sound produced by the rear face of the diaphragm. The loudspeaker may have an in-box resonant frequency. As noted above, the in-box resonant frequency is a resonant frequency associated with loudspeaker being used with the rear enclosure and is well understood in the art.

[0122] The in-box resonant frequency may lower than the front cavity boosted band.

[0123] The in-box resonant frequency may be 250Hz or less.

[0124] By providing a low resonant frequency, the low frequency reproduction may be improved and low frequency content increased when outputting audio content. This may make for a more pleasant AVAS signal.

[0125] The diaphragm may have a front face and a rear face. The front face of the diaphragm may in operation be used to produce audible sound.

[0126] The horn apparatus, or a vehicle in which the horn apparatus is included, may include a rear enclosure configured to receive sound produced by the rear face of the diaphragm.

[0127] The loudspeaker may further include a grille to boost the SPL in a one-third octave band, referred to as the grille boosted band. The grille may in use contribute to high SPL output when using the horn apparatus to generate a horn sound.

[0128] The grille may be configured to receive sound produced by the front face of the diaphragm and to allow the sound produced by the front face of the diaphragm to propagate through the grille.

[0129] The grille may be arranged across the front face of the diaphragm. The grille may be contoured to at least partly follow contours in the front face of the diaphragm when the diaphragm is in its rest position. 008850430

[0130] 13

[0131] The grille may be attached to or integrated with the loudspeaker. In some examples, the grille may be attached to the rear enclosure which receives the sound produced by the rear face of the diaphragm. In some examples, the grille may be attached to a loudspeaker frame of the loudspeaker.

[0132] The grille boosted band may correspond to a harmonic of a fundamental frequency contained in the horn signal.

[0133] In some examples, the grille boosted band may correspond to an even harmonic of a fundamental frequency contained in the horn signal. By aligning the grille boosted band with an even harmonic, the warmth of the horn sound may be increased.

[0134] In some examples, the grille boosted band may correspond to the second harmonic of a fundamental frequency contained in the horn signal. This may increase warmth of the horn sound and provide for a more recognisable horn sound.

[0135] The grille boosted band may be one of the 2kHz, 2.5kHz or 3.15 kHz one-third octave bands.

[0136] In some examples, the grille defines a plurality of passages extending through the grille for sound to propagate through the grille. The plurality of passage may be distributed across substantially the entire front face of the diaphragm.

[0137] The horn signal may include a fundamental frequency in the range of 400Hz to 600Hz. The fundamental frequency may be in the range of 405Hz to 420Hz, or in the range of 500Hz to 530Hz.

[0138] In some examples, the horn signal may include multiple fundamental frequencies, for example two fundamental frequencies. For example, the horn signal may include a first fundamental frequency in the range 405Hz to 420Hz, and a second fundamental frequency in the range of 500Hz to 530Hz;

[0139] The first fundamental frequency and the second fundamental frequency may be spaced by a minor interval.

[0140] In some examples, the horn signal may include only the fundamental frequency / frequencies and harmonics thereof.

[0141] According to a third aspect, there is provided a vehicle including the horn apparatus according to the second aspect. In some examples, the diaphragm of the loudspeaker may have a front face and a rear face; the vehicle further may further comprise: a front cavity to receive sound produced by the front face of the diaphragm and to allow the sound produced by the front face of the diaphragm to exit the front cavity via one or more openings in the front cavity; wherein the front cavity is configured to boost the SPL in a one-third octave band, referred to as the front cavity boosted band, which corresponds to a fundamental frequency or a harmonic of a fundamental frequency contained in the horn signal, wherein the front cavity boosted band is one of the 400Hz, 500Hz, 800Hz, 1 kHz, 1.25kHz or 1.6kHz one-third octave band; and wherein the level of the horn signal is either maximum in the front cavity boosted band, or is no more than 3dB from the maximum level of the horn signal in any one-third octave band.

[0142] The grille boosted band, where a grille is provided, may be between the front cavity boosted band and the second radial breakup frequency. 008850430

[0143] 14

[0144] The front cavity boosted band may correspond to a harmonic of a fundamental frequency contained in the horn signal.

[0145] In some examples, the front cavity boosted band may correspond to an even harmonic of a fundamental frequency contained in the horn signal. By aligning the front cavity boosted band with an even harmonic, the warmth of the horn sound may be increased.

[0146] In some examples, the front cavity boosted band may correspond to the second harmonic of a fundamental frequency contained in the horn signal. Since traditional horns may have a strong second harmonic, aligning the front cavity boosted band with a second harmonic may increase warmth of the horn sound and provide for a more recognisable horn sound. In practice, the horn signal may contain a fundamental frequency in the range of 400Hz to 550Hz, so the front cavity boosted band may correspond to the 800Hz one-third octave band or the 1 kHz one-third octave band.

[0147] The front cavity boosted band may be one of the 800Hz, 1 kHz, 1 ,25kHz or 1 ,6kHz one-third octave band.

[0148] The front cavity may be configured to boost the SPL by the most in the front cavity boosted band or in a one-third octave band adjacent to the front cavity boosted band.

[0149] The front cavity boosted band may be the one-third octave band with the highest relative positive gain when comparing the SPL produced by the loudspeaker and the front cavity against the SPL produced by the loudspeaker without the front cavity.

[0150] The front cavity may be provided by a tube. One end of the tube may be attached to the loudspeaker. The other end of the tube may include the one or more openings via which sound produced by the diaphragm exits the front cavity.

[0151] Optionally the one or more openings are provided by a protective grille. In some examples, the protective grille may be a perforated region in the underbody of the vehicle. The protective grille may partially close one end of the front cavity. Where the grille is also provided, the grille may partially close the other end of the front cavity.

[0152] In some examples, the front cavity may be formed from a sound hard material for the relevant frequencies, e.g. of the horn signal, and may be mechanically compliant material (e.g. rubber or similar material).

[0153] The tubular (e.g. cylindrical) portion of the cavity can be part of the loudspeaker, the openings can be part of the vehicle such that the resonance chamber is created only when the loudspeaker is mounted to the vehicle.

[0154] The loudspeaker may be exposed to an exterior of the vehicle, so that in use sound produced by the loudspeaker may primarily radiate from the vehicle. In some examples, the loudspeaker may be mounted on the exterior of the vehicle.

[0155] The front cavity may be defined by a chassis of the vehicle. For example, the loudspeaker may be mounted to the chassis, e.g. facing down, and may be configured to radiate sound through the front cavity defined by the chassis. In this position, sound produced by the loudspeaker may be primarily radiated 008850430

[0156] 15 outwards from the vehicle. Such positioning may be preferred in some examples since it may decrease the sound that can be heard inside of the vehicle. Also, such positioning may mean that in use the front cavity may protect the loudspeaker in case an underbody panel moves, e.g. when mounting a curb.

[0157] The horn apparatus may be operable to generate a horn sound in front of the vehicle; wherein at a distance of 7 metres from the vehicle the horn signal may be louder than 93dBA.

[0158] The invention includes the combination of the aspects and preferred features described except where such a combination is clearly impermissible or expressly avoided.

[0159] Summary of the Figures

[0160] Embodiments and experiments illustrating the principles of the invention will now be discussed with reference to the accompanying figures in which:

[0161] Figure 1 is a cross-sectional view of a loudspeaker assembly including a loudspeaker, a front cavity assembly, a grille and a rear enclosure.

[0162] Figure 2 shows an impedance magnitude curve for the loudspeaker assembly of Figure 1 .

[0163] Figure 3 is another cross-sectional view of the loudspeaker assembly but without the rear enclosure.

[0164] Figure 4 is a schematic illustration of a horn apparatus including the loudspeaker assembly.

[0165] Figure 5 illustrates a horn signal in use fed to the horn apparatus.

[0166] Figure 6 is a graph illustrating the effect of the front cavity assembly.

[0167] Figure 7 is a cross-sectional view of part of the loudspeaker.

[0168] Figure 8 shows the transfer function of the loudspeaker, with and without grille.

[0169] Figure 9 shows a vehicle including the horn apparatus.

[0170] Figure 10 is a simplified drawing showing the first and the second breakup modes for a clamped beam with constant thickness.

[0171] Figure 11 is a simplified drawing illustrating the second breakup mode without and with additional mass attached at a free end of the beam.

[0172] Detailed Description of the Invention

[0173] 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.

[0174] In particular, aspects relating to bandwidth and maximum output of electronic horns are discussed below, e.g. increased SPL in the midband frequencies ranging from the one-third octave bands of 800Hz to 1 ,6kHz. An electronic horn incorporating some or all of the discussed aspects can be used for low frequency AVAS output at significantly improved level when compared to conventional electronic horns. 008850430

[0175] 16

[0176] Figures 1 and 2 illustrate a loudspeaker assembly 100 for use in a horn apparatus 900, as described below. Figure 1 is a cross-sectional view of the loudspeaker assembly 100, while Figure 2 shows an impedance magnitude curve of the loudspeaker assembly 100 and therefore illustrates performance of the loudspeaker assembly 100.

[0177] The loudspeaker assembly 100 includes a loudspeaker 200, a rear enclosure 300, a front cavity assembly 400, and a grille 500. The loudspeaker 200 is received into the rear enclosure 300 such that a front face 201 of the loudspeaker 200 remains exposed but otherwise an acoustically sealed box is formed. The grille 500 extends across the front face 201 of the loudspeaker 200 such that a grille cavity 501 is formed between the front face 201 and the grille 500, and the front cavity assembly 400 extends from the grille 500. In use, sound produced by the loudspeaker 200 propagates through the grille 500, through the front cavity assembly 400 and exits from the front cavity assembly 400 into an ambient environment.

[0178] The loudspeaker assembly 100 is capable of producing low frequency output, which may be useful for AVAS applications, as well as high SPL output, e.g. during horn operation, both on vehicle level and component level. The horn apparatus 900 described in detail below has been configured to align the spectral content of the audio signal fed to loudspeaker 200 with at least one resonance in the transfer function. The at least one resonance in the transfer function may include the resonance generated by the loudspeaker 200 in combination with the front cavity 410, the resonance generated by the diaphragm 220 in combination with the grille 500, and / or the resonance generated by diaphragm breakup. That is to say, the loudspeaker assembly 100 is designed so that the resonances occur at frequencies useful for operation of the loudspeaker assembly 100 in a horn apparatus 900, e.g. mounted to a vehicle 1000, such that in use sound may be produced at increased SPL and with increase low frequency output.

[0179] The impedance magnitude curve of Figure 2 relates the electrical input impedance of the loudspeaker 200 against frequency from 20Hz to 10kHz. There are four distinct peaks A, B, C, D visible in the impedance magnitude curve (or ‘local maxima’ A, B, C, D) which indicate the resonances of the loudspeaker assembly 100.

[0180] A first peak A is present at a comparatively low frequency of around 180Hz. The first peak A is the highest peak and is associated with a mechanical resonance of the loudspeaker 200, the so-called in-box resonant frequency of the loudspeaker 200 (associated with the loudspeaker 200 being used with its enclosure 300).

[0181] A second peak B is present at around 1 ,04kHz. The second peak B, which is located in the same one- third octave band, is in the vicinity of the second harmonic of the fundamental of the HIGH tone at 520Hz of a dual tone horn signal, and is associated with an acoustic resonance relating to the front cavity assembly 400. The front cavity assembly 400 is configured to boost the SPL in a one-third octave band, which is referred to as the front cavity boosted band. The front cavity assembly 400 and the front cavity boosted band are discussed in detail below. 008850430

[0182] 17

[0183] A third peak C is present at around 2.5kHz. The third peak C is associated with an acoustic resonance relating to the interaction of the grille 500 and the grille cavity 501 between the loudspeaker 200 and the grille 500. The grille 500 is configured to boost the SPL in a one-third octave band, referred to as the grille boosted band. WO2022189546A1 contains further technical information about the design of a grille for boosting SPL.

[0184] A fourth peak D is present at around 3.88kHz. The fourth peak D is associated with another mechanical resonance, the so-called second radial breakup of the loudspeaker 200. The second radial breakup provides an SPL boost at frequencies close to and below the second radial breakup frequency, which in this example is 3.88kHz. The second radial breakup has been discussed above, and is further discussed below.

[0185] It is noted that in the example shown in Figure 2 all four resonances are present, but that in some examples some of the resonances may be absent. For example, the grille may be omitted in some examples and / or the front cavity may be omitted in some examples and / or the radial breakup may be omitted in some examples and / or the in-box resonant frequency may be omitted in some examples.

[0186] Figure 3 is another cross-sectional view of the loudspeaker assembly 100 of Figure 1 , but in Figure 3 the rear enclosure 300 is not shown for ease of illustration.

[0187] The loudspeaker 200 includes a loudspeaker frame 210, a diaphragm 220, and a drive unit 230. The drive unit 230 includes a moveable part 240, which is attached to the diaphragm 220, and a stationary part 250, which is attached to the frame 210. The loudspeaker 200 is operable to energise the drive unit 230 to cause displacement of the moveable part 240 relative to the stationary part 250. In particular, the moveable part 240 and the stationary part 250 magnetically interact with each other to effect the displacement of the moveable part 240.

[0188] The diaphragm 220 and the moveable part 240 of the drive unit 230 are joined together to define a moveable assembly, such that in use they move together ‘as a unit’ when the moveable part 240 is caused to move. When causing the moveable assembly to move along the movement axis 202, the diaphragm 220 acts as a piston and produces sound.

[0189] The moveable assembly is suspended from the frame 210 by a surround suspension element 262 and a spider suspension element 264. The surround suspension element 262 is attached to the frame 210 at a first landing surface on the frame 210 and the spider suspension element 264 is attached to the frame 210 at a second landing surface on the frame 210.

[0190] The surround suspension element 262, which may also be referred to as a “roll suspension” or “roll edge”, is arranged around the diaphragm 220 and is attached to an outside perimeter 223 of the diaphragm 220.

[0191] The diaphragm 220 has a first sound radiating surface 221 and a second sound radiating surface 222. The first sound radiating surface 221 faces in a forward direction 203 and in use is utilised for producing audible sound. The second sound radiating surface 222 faces in a rearward direction 204 and in use sound produced by the second sound radiating surface 222 is captured by the rear enclosure 300 (not 008850430

[0192] 18 shown in Figure 3; see Figure 1 instead). The forward direction 203 and the rearward direction 204 are opposite directions parallel to the movement axis 202.

[0193] The diaphragm 220 and the surround suspension element 262 are made from any suitable materials. Generally, the diaphragm 220 and the surround suspension element 262 may be made from different materials.

[0194] In some examples, the diaphragm 220 is made from a stiff engineering plastic. For example, the diaphragm 220 may be thermoformed film of biaxially oriented polyethylene naphthalate.

[0195] The diaphragm 220 may have a Young’s modulus in the range of 6 to 16GPa, for example in multiple directions; e.g. in the machine direction and the cross direction (which is also referred to as the “transverse direction”). The machine direction and the cross direction refer to directions relevant to some manufacturing processes, such as extrusion, and in some examples are useful for describing material properties of the diaphragms so manufactured.

[0196] The diaphragm 220 may have comparatively low internal damping. The average isotropic loss factor eta is estimated to be approximately 0.035 for the diaphragm 220, for example when made as a film from stiff engineering plastic using extrusion. Generally, the average isotropic loss factor eta may be less than 0.1 .

[0197] The surround suspension element 262 may be made from a soft material, for example rubber or rubberlike materials such as TPE, TPV, EPDM or NBR. As the loudspeaker 200 may be mounted below the wading line of a vehicle, it may in use reach a high operating temperature, such as 100degC, and then be submerged in cold water, e.g. around 0 to 4degC. This may decrease the pressure inside the loudspeaker 200, as enclosed by the rear enclosure 300, relative to the ambient pressure and may force to diaphragm 220 to inwards. The surround suspension element 262 made from soft material, in particular rubber or rubber-like material, may allow for a large excursion capability as the surround suspension element 262 can stretch so that the loudspeaker 200 can be exposed to the described quenching process repeatedly without being damaged. By contrast, having a diaphragm with integral surround, as in WO2022253924A1 , from a composite comprised from fibres and stiff thermoset resin may be substantially less suitable under such conditions, as the composite may crack under the load generated by the pressure difference.

[0198] The surround suspension element 262 may have a stiffness which may be considerably lower than the stiffness of the diaphragm 220, e.g. 1 / 1000th of the stiffness of the diaphragm 220. At higher frequencies, where modal behaviour of the second radial mode becomes significant, the surround may may act like an annular mass. This is described below, with reference to Figure 7, which shows a breakup mode with a fixed (or driven) circumference at the diaphragm neck, where the diaphragm 220 is joined to the integral dust cap 270, and a free edge where the diaphragm is attached to the surround suspension element 262. This is further illustrated in Figure 11 , which illustrates the effect of an additional mass at the free end, i.e. “mass loading”.

[0199] The surround suspension element 262 may have a Young’s modulus in the range of 6 to 16MPa. 008850430

[0200] 19

[0201] The surround suspension element 262 is suitably attached to the outside perimeter 223 of the diaphragm 220, for example using adhesive or by an overmoulding process.

[0202] The surround suspension element 262 may have a uniform thickness in the range of 0.2 to 0.4mm.

[0203] The loudspeaker 200 includes a dust cap 270 provided in front of the drive unit 230 to prevent dust or other foreign particles from getting into the drive unit 230. In this example, the dust cap 270 is integral with the diaphragm 220.

[0204] As shown in Figure 3, the moveable part 240 of the drive unit 230 is a voice coil while the stationary part 250 includes a magnet unit which generates a magnetic flux with which the voice coil interacts when energised.

[0205] The loudspeaker 200 has an in-box resonant frequency of less than 250Hz when used with a 1 .5 litre enclosure. The “in-box” resonant frequency is known to describe the resonant frequency when the second sound radiating face 222 is configured to radiate into an acoustically closed box, as provided by the rear enclosure 300 shown in Figure 1 . The in-box resonance is the fundamental, mechanical resonance of the moveable assembly plus the airload onto the diaphragm resonating on the suspension elements (e.g. the surround and damper) and the spring force generated by the diaphragm acting onto the air enclosed inside the enclosure.

[0206] The comparatively compliant surround suspension element 262 may contribute to achieving the low inbox resonant frequency. Such a configuration of the surround, and accordingly of the resonant frequency, may be difficult to achieve for some known loudspeakers for electronic horns which have integrally formed surrounds, such as those described in WO2024115672A1 or WO2022253924A1 . With low in-box resonant frequency, more pleasant AVAS signals with increased low frequency content below 250Hz may be produced by the loudspeaker assembly 100 whilst at the same time providing a simpler and lower cost solution when compared to known loudspeakers with diaphragm with integral surround and passive radiator (e.g. as described in WO2024115672A1). Moreover, the AVAS signals may be produced from a compact enclosure.

[0207] The loudspeaker 200 has a suspension linearity of xCms(75%) >3mm in combination with a drive unit linearity xBL(82%) >2mm and as such allow for a usable excursion capability of +-5mm, which may be considered surprisingly high for a loudspeaker that can also be used as an electronic car horn.

[0208] The front cavity assembly 400 defines a front cavity 410. The front cavity 410 is a partially enclosed space through which sound produced by the first sound radiating surface 221 in use propagates and which provides for the front cavity boosted band. The front cavity assembly 400 may also serve to protect the loudspeaker 200, for example when the underbody panel moves when driving over a curb.

[0209] The front cavity assembly 400 includes a cavity member 420 bounding the front cavity 410. The cavity member 420 may cross-sectionally generally match the shape of the diaphragm 220, for example the cavity member 420 may be tubular where the diaphragm 220 is circular. The cavity member 420 has a first cavity member end 422 which is attached to the loudspeaker 200 directly or indirectly. In some 008850430

[0210] 20 examples, the cavity member 420 is attached to the grille 500 and therefore indirectly attached to the loudspeaker 200.

[0211] The cavity member 420 has a second cavity member end 424, opposite to the first cavity member end 422, which includes a protective grille 426 (or ‘second grille’) with a plurality of openings 428 openings via which sound produced by the diaphragm 220 exits the front cavity 410. In some examples, the protective grille 426 is a perforated region in the underbody of the vehicle, and may in some examples be designed to protect the loudspeaker 200. In some examples, the protective grille 426 is provided separately from the cavity member 420, for example where the protective grille 426 is the perforated region in the underbody, in which case the front cavity 410 (or ‘resonance chamber’) is created only when the loudspeaker 200 is mounted to the vehicle.

[0212] This cavity member 420 can be formed from a sound hard material for the relevant frequencies and which may be mechanically compliant material (e.g. a rubber-like material).

[0213] The grille 500, which in some examples is formed by a plurality of grille elements, has a rear face 502 and a front face 504. The rear face 502 faces the loudspeaker 200, while the front face 504 faces away from the loudspeaker 200. With respect to the movement axis 202, the front face 504 faces in the forward direction 203 while the rear face 502 faces in the rearward direction 204.

[0214] The grille 500 defines passages 506 extending through the grille 500, i.e. from the rear face 502 to the front face 504. In use, sound produced by the first sound radiating surface 221 propagates through the passage 506.

[0215] Further technical information relating to the design of a grille for boosting SPL can be found in WO2022189546A1 .

[0216] Figure 4 shows a schematic of an example horn apparatus 900 for a vehicle including a horn activation mechanism 902, a processing unit 904, an amplifier 910, and the loudspeaker assembly 100.

[0217] In this example, the horn activation mechanism 902 is located on a steering wheel of the vehicle (for example as a button). The horn activation mechanism 902 is operable by a user of the vehicle to activate the horn apparatus 900 to cause the loudspeaker assembly 100 produce an audible warning sound based on an audio signal provided by the processing unit 904, using the loudspeaker assembly 100.

[0218] In this example, the processing unit 904 is an ECU (engine control unit) of the vehicle. In some examples, the processing unit 904 could be a dedicated computing unit for the horn apparatus 900.

[0219] The processing unit 904 is connected to a memory 908 for storing an audio signal for playback by the loudspeaker assembly 100 for producing the audible warning sound. The loudspeaker 200 is also configured to produce low frequency sound between at least 150 to 300Hz as part of an AVAS system.

[0220] The resonances discussed with reference to Figure 2 provide for an improved horn sound generated by the horn apparatus 900, in particular the SPL of the horn sound, and improved AVAS sound generated by the loudspeaker assembly 100, in particular in terms of low frequency output. 008850430

[0221] 21

[0222] Figure 5 shows an exemplary horn signal which may in use be fed to the loudspeaker 200. More particularly, Figure 5 illustrates 1 / 3rd octave band levels over frequency and is therefore indicative of the electrical input power vs frequency to the loudspeaker 200 which the horn signal causes in operation. As can be seen when comparing Figures 2 and 5, the one-third octave band level containing the front cavity boosted band is the loudest one-third octave band (as shown in Figure 5) or, more generally, no softer than 3dB compared to the loudest one-third octave band.

[0223] Figure 6 illustrates the effect of the front cavity assembly 400 on the sound generated by the loudspeaker 200. In particular, Figure 6 shows the relative amplitude of the loudspeaker assembly 100 compared to a corresponding loudspeaker assembly wherein the front cavity 410 is absent as a result of removing the front cavity assembly 400.

[0224] Figure 6 shows that the loudspeaker transfer function has a boost in the 800Hz band, which in this example is the front cavity boosted band, such that frequencies in the horn signal will be boosted if they are in the 800Hz band. This may make the horn apparatus 900 sound more convincingly like a traditional car horn. The front cavity boosted band is identified with the one-third octave band with the highest relative positive gain when comparing the SPL produced by the loudspeaker 200 against the SPL produced by the loudspeaker 200 but without the front cavity 410.

[0225] In some examples, the front cavity boosted band is aligned with the energy contained in a one-third octave band of the horn signal. This one-third octave band of the horn signal preferably corresponds to the second order harmonic of a fundamental frequency contained in the horn signal, but in other examples it may be, for example, the fourth harmonic (the 1 ,6kHz band). The horn signal contains most energy in the front cavity boosted band. As can be seen from Figure 6, the integration of the front cavity 410 results in a boost of +8dB in the 800Hz band, leading to a strong second harmonic of the 420Hz fundamental frequency contained in the horn signal. The horn sound thus produced may be perceived as “warm” by some listeners.

[0226] As seen in Figure 6, the sound radiated through the front cavity 410 without significant attenuation is higher for sound produced around 2.5kHz, since the directivity of sound around 2.5kHz is comparatively high. That is, the 2kHz band, 2.5kHz band and 3.15kHz band are not decreased in level dramatically by the front cavity 410, but the effect of boosting at 800Hz is that the overall sound (including the boosted 800 Hz band and the not particularly affected 2kHz band, 2.5kHz band and 3.15kHz ) may be perceived as a more pleasant overall sound on car-level, further improving the timbre.

[0227] For context, it is noted that to meet the requirements of ECE-28 PART I, the horn signal contains frequencies in relevant bands for the loudspeaker to radiate them. The type approval, i.e. “homologation”, according to ECE 28 requires the electronic horn to reach an A-weighted SPL of no less than 105dBA in the sum of the 2kHz, 2.5kHz and 3.15kHz one-third octave bands. Such high SPL for horn components were required in the past as horns were typically mounted in the motor compartment of a vehicle and sound could only indirectly radiate out from under the bonnet. The new types of electronic horns, such as described in present disclosure, are typically mounted radiating through the underbody of the vehicle. The sound of an electronic horn is then particularly harsh and unpleasant, particularly if the 2kHz, 2.5kHz and 008850430

[0228] 22

[0229] 3.15kHz bands are strongly represented. A solution to this problem envisaged by the present inventors is the addition of the front cavity 410 between the loudspeaker 200 (including its grille 500, where provided) and the underbody of the vehicle. As set out above, the front cavity 410 is tuned to amplify certain lower frequencies of the horn sound to improve the timbre.

[0230] It is noted that the acoustic horn component homologation measurement requirements do not need to be met with the front cavity 410 in place, as it may be part of the vehicle or an additional independent component and as such only be effective once the loudspeaker 200 is installed.

[0231] Figures 7 and 8 illustrate the second radial breakup and the effect on the sound produced by the loudspeaker assembly 100. Figure 7 is a schematic illustration of the second radial breakup mode, showing a cross-sectional view of part of the loudspeaker 200. Figure 8 shows the transfer function of the loudspeaker 200 from 100Hz to 10kHz.

[0232] In Figure 7, the diaphragm 220 is shown with the surround suspension element 262 attached to the outside perimeter 223, and the dust cap 270 is integrally formed with the diaphragm 220. In this example, the diaphragm 220 is of engineering plastic and has an outer diameter of 114mm and a uniform thickness falling in the range of 0.19mm - 0.25mm.

[0233] The geometry of the diaphragm 220, the surround suspension element 262, and the materials are chosen such that the so-called second radial breakup mode is in one of the 2.5kHz, 3.15kHz or 4kHz one-third octave band. In some examples, the diaphragm 220 is designed to be relatively shallow, with little geometrical stiffness, but made from a comparatively stiff material as described above.

[0234] So-called breakup of a diaphragm is a phenomenon known in the art and describes a resonance of the diaphragm itself, i.e. a breakup mode of the diaphragm, which occurs at a breakup frequency. Radial breakup is a particular kind of breakup where the breakup mode is radially across the diaphragm. It is noted that this breakup mode results in motion of the diaphragm 220 which is in addition to the axial movement of the diaphragm 220.

[0235] The mode shape of the second radial breakup is shown in Figure 7 as a dashed line. The second radial breakup results in a second radial breakup mode which has an annular node 225 around the diaphragm 220 at which minimal motion occurs, and which may be in the diameter range of 60 to 120mm. In this example, the annular node 225 is around two-thirds along the radius This corresponds to a mode with a fixed (or driven) circumference at the diaphragm neck, where the diaphragm is joined to the integral dust cap 270, and a free edge where the diaphragm is attached to the surround suspension element 262. An inner portion 226 of the diaphragm 220, which is inside relative to the annular node 225, and an outer portion 227 of the diaphragm 220, which is outside relative to the annular node 225, move out of phase.

[0236] The presence of the second radial breakup mode can be detected by means of a laser scan of the diaphragm movement, e.g. using Klippel’s Scanning Vibrometer System (SCN) Module. Further information relating to measurement of diaphragm vibrations may be found here: https: / / www.klippel.de / fileadmin / klippel / Files / Know_How / Application_Notes / AN_31_Cone_Vibration_and_ Radiation_Diagnostics.pdf 008850430

[0237] 23

[0238] It is noted the first radial breakup may also create a peak in the midband but that this may have little influence on the frequency response of the loudspeaker assembly 100.

[0239] Figure 8 illustrates the frequency response of the loudspeaker assembly 100. The solid line shows the frequency response without the grille 500 and without the front cavity 410, while the dashed line shows the frequency response with the grille 500 and without the front cavity 410. Figure 8 therefore also illustrates the effect of the grille 500.

[0240] As shown in Figure 8, there is no visible dip at the first radial breakup frequency, which in this example is at around 1 kHz. At the second radial breakup frequency, which in this example is at around 3.9kHz, a substantial peak is shown in the transfer function. A rising frequency response is visible from around 1 kHz to 3.9kHz (i.e. close to and below the second radial breakup frequency), due to increased diaphragm motion at frequencies below the second radial breakup frequency. This is in use beneficial for producing louder sound at frequencies close to and below the second radial breakup frequency, especially when the loudspeaker 200 is used with the grille 500. The frequency response of the loudspeaker 200 including the grille 500 is shown in Figure 8 as a dashed line. As can be seen, there is a substantial boost in SPL from 2 to 4kHz, owing to the grille 500 having a resonance in this region (at around 2.5kHz, see Fig. 2). At 3kHz, the SPL is increased from 10OdB to 107dB.

[0241] For use of the loudspeaker 200 as an electronic horn in combination with an amplifier and a suitable horn signal, the relevant frequency ranges for component level homologation such es ECE 28-00 PART I are the 2kHz, 2.5kHz and 3.15kHz bands. The second radial breakup may therefore be configured such that it is at the upper end of the band that is boosted, e.g. close to 3.55kHz or, as in this case, 3.8kHz.

[0242] Figure 9 shows a car 1000 comprising the horn apparatus 900 wherein the loudspeaker 200 of the horn apparatus 900 is mounted to the underbody of the car 1000.

[0243] In this example, the loudspeaker 200 is mounted facing downwards and is configured to radiate sounds through a circular cut-out provided in the underbody of the car 1000. In this position, sound provided by the loudspeaker 200 is primarily radiated outwardly from the car 1000. This arrangement is advantageous as it decreases the amount of sound produced by the loudspeaker 200 that is heard inside of the car.

[0244] The described horn apparatus 900 allows for low frequency output comparable with traditional AVAS boxes of the same size. It also allows for meeting and exceeding the requirements of ECE 28-00 PART I and PART II and this by a large margin. While ECE 28-00 only requires the SPL on car level to be >87dBA at a distance of 7m, the horn apparatus 900 described herein allows for an SPL >93dBA. This higher horn level may be preferred and may not result in increased cost when over comparable traditional AVAS boxes. Moreover, the described horn apparatus 900 may be used with a traditional 12V automotive amplifier without the need for boost circuitry to achieve improved performance.

[0245] Figure 10 is a simplified drawing showing the first and second, breakup modes for a beam 2000 where the left end of the beam is clamped, right end is free. This simplified system is used purposes of illustration of to approximate the radial behaviour of the loudspeaker assembly of Figure 1 . 008850430

[0246] 24

[0247] As shown in Figure 10, for the first breakup mode, there are zero nodes (i=0) between the clamped end (on the left-hand side) and free end (on the right-hand side). The first breakup mode is shown in dashed lines.

[0248] For the second breakup mode, there is one node (i=1) at four-fifth of the length of the beam 2000. The second breakup mode is shown in dotted lines.

[0249] Figure 11 is a further simplified drawing showing the effect of mass-loading on the second breakup mode of the beam 2000. In Figure 11 , the beam 2000 is shown as a thick line and the second breakup mode is illustrated by thin lines. More particularly, the beam 2000 is shown without additional mass (upper drawing) and with additional mass 2100 (lower drawing). As can be seen in Figure 11 , an effect of the additional mass 2100 is that the node 2225 of the second radial breakup is shifted towards the free end.

[0250] 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.

[0251] 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.

[0252] For the avoidance of any doubt, any theoretical explanations provided herein are provided for the purposes of improving the understanding of a reader. The inventors do not wish to be bound by any of these theoretical explanations.

[0253] Any section headings used herein are for organizational purposes only and are not to be construed as limiting the subject matter described.

[0254] Throughout this specification, including the claims which follow, unless the context requires otherwise, the word “comprise” and “include”, and variations such as “comprises”, “comprising”, and “including” will be understood 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.

[0255] 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. 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 particular value and / or to the other particular value. Similarly, when values are expressed as approximations, by the use 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%. 008850430

[0256] 25

[0257] References

[0258] 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.

[0259] The entirety of each of these references is incorporated herein.

[0260] WO2022128595A1

[0261] WO2022189546A1

[0262] WO2022253924A1

[0263] WO2024115672A1 WO2024115676A1

Claims

00885043026Claims:1 . A horn apparatus for a vehicle, the horn apparatus including: a loudspeaker that includes a diaphragm and a drive unit to move the diaphragm; a horn signal generator configured to supply a horn signal to the drive unit such that the diaphragm produces a horn sound based on the horn signal, wherein the horn signal contains at least one fundamental frequency; wherein the loudspeaker has a second radial breakup frequency associated with a second radial breakup of the diaphragm; and wherein the second radial breakup frequency is in the 2.5kHz, 3.15kHz or 4kHz one-third octave band.

2. The horn apparatus of claim 1 , wherein the diaphragm is formed at least in part from a plastic material; optionally the diaphragm is a thermoformed film formed from polyethylene naphthalate, or the diaphragm is formed from glass fibre and epoxy resin.

3. The horn apparatus of claim 1 or 2, wherein the loudspeaker includes a loudspeaker frame and a surround suspension element; wherein the diaphragm is suspended from the loudspeaker frame by the surround suspension element.

4. The horn apparatus of claim 3, wherein the surround suspension element is made from an elastomer; wherein optionally the elastomer is one of: thermoplastic elastomer, a thermoplastic vulcanisate, an ethylene propylene diene monomer rubber, or a nitrile butadiene rubber.

5. The horn apparatus of claim 3 or 4, wherein the surround suspension element has a Young’s modulus in the range from 6 to 16 MPa; wherein the diaphragm has a Young’s modulus in the range from 2 to 16 GPa.

6. The horn apparatus of any preceding claim, wherein the diaphragm has an average isotropic loss factor eta of less than 0.1 .

7. The horn apparatus of any one of claims 1 to 6, wherein the horn apparatus includes a rear enclosure configured to receive sound produced by the rear face of the diaphragm; wherein the loudspeaker has an in-box resonant frequency which is 250Hz or less.008850430278. The horn apparatus of any preceding claim, further comprising a grille to receive sound produced by the front face of the diaphragm and to allow the sound produced by the front face of the diaphragm to propagate through the grille into the front cavity; wherein the grille is configured to boost the SPL in a one-third octave band, referred to as the grille boosted band, wherein the grille boosted band is one of the 2kHz, 2.5kHz or 3.15 kHz one-third octave bands.

9. The horn apparatus of claim 8, wherein the grille boosted band corresponds to a harmonic of a fundamental frequency contained in the horn signal; and / or wherein the grille boosted band is one of the 2kHz, 2.5kHz or 3.15 kHz one-third octave bands.

10. The horn apparatus of any preceding claim, wherein the horn signal includes a fundamental frequency in the range of 400Hz to 600Hz; optionally the fundamental frequency is in the range of 405Hz to 420Hz or the range of 500Hz to 530Hz.

11. The horn apparatus of claim 10, wherein the horn signal includes a first fundamental frequency in the range 405Hz to 420Hz and a second frequency resonance in the range of 500Hz to 530Hz; wherein the first fundamental frequency and the second fundamental frequency are spaced by a minor interval.

12. The horn apparatus of claim 10 or 11 , wherein the horn signal includes only the fundamental frequency / frequencies and harmonics thereof.

13. A vehicle comprising the horn apparatus of any preceding claim, wherein the diaphragm of the loudspeaker has a front face and a rear face; the vehicle further comprising: a front cavity to receive sound produced by the front face of the diaphragm and to allow the sound produced by the front face of the diaphragm to exit the front cavity via one or more openings in the front cavity; wherein the front cavity is configured to boost the SPL in a one-third octave band, referred to as the front cavity boosted band, which corresponds to a fundamental frequency or a harmonic of a fundamental frequency contained in the horn signal, wherein the front cavity boosted band is one of the 400Hz, 500Hz, 800Hz, 1 kHz, 1.25kHz or 1.6kHz one-third octave band; and wherein the level of the horn signal is either maximum in the front cavity boosted band, or is no more than 3dB from the maximum level of the horn signal in the front cavity boosted band.0088504302814. The vehicle of claim 13 as dependent on claim 8 or 9, wherein the grille boosted band is between the front cavity boosted band and the second radial breakup frequency.

15. The vehicle of claim 13 or 14, wherein the front cavity boosted band corresponds to a harmonic of a fundamental frequency contained in the horn signal; and wherein the front cavity boosted band is one of the 800Hz, 1 kHz, 1 ,25kHz or 1 ,6kHz one-third octave band.

16. The vehicle of any one of claims 13 to 15, wherein the front cavity is configured to boost the SPL by the most in the front cavity boosted band or in a one-third octave band adjacent to the front cavity boosted bands.

17. The vehicle of any one of claims 13 to 16, wherein the horn apparatus is operable to generate a horn sound in front of the vehicle; wherein at a distance of 7 metres from the vehicle the horn signal is louder than 93dBA.

18. The vehicle of any one of claims 13 to 17, wherein the front cavity is provided by a tube; wherein one end of the tube is attached to the loudspeaker and the other end of the tube includes the one or more openings; optionally the one or more openings are provided by a protective grille.

19. The vehicle of any one of claims 13 to 18, wherein the front cavity is defined by a chassis of the vehicle.

20. The vehicle of any one of claims 13 to 19, wherein the loudspeaker includes the rear enclosure.

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