Horn apparatus for a vehicle

Abstract

A horn apparatus for a vehicle is provided. The horn apparatus is configured to produce an audible warning sound having a fundamental frequency. The horn apparatus comprises a signal unit configured to provide a signal; and a loudspeaker configured to produce an audible warning sound based on the signal provided by the signal unit. A signal, as provided by the signal unit, is also provided. The signal is defined by a waveform that alternates between a positive peak and a negative peak of the waveform multiple times within a period corresponding to the fundamental frequency of the warning sound. A time between each alternation of the waveform varies across the period. A method of providing a signal for use by the horn apparatuses to produce an audible warning sound is also provided. The method comprises providing a waveform that defines the signal and providing the signal defined by the waveform. Computer-readable media and computer program products are provided that comprise logic and / or instructions that, when executed by a computer / processor, cause the computer / processor to carry out the methods described herein.

Description

[0001] HORN APPARATUS FOR A VEHICLE

[0002] This application claims priority to GB2403410.0, filed 8 March 2024.

[0003] Field of the Invention

[0004] The present invention relates to a horn apparatus for a vehicle, signals therefor, and methods for generating said signals.

[0005] Background

[0006] Motor vehicles are equipped with one or more horns configured to produce audible warning sounds. These sounds may be used, for example, to alert other road users and / or pedestrians of the presence of the vehicle and may, therefore act as a warning for other road users and / or pedestrians. It is therefore important that vehicle horns are readily identifiable by road users and pedestrians.

[0007] Traditional vehicle horns tend to come in one of two main varieties: tone-disc horns, as are typically used in commoditized (or lower-class) vehicles, and bell-type horns that are predominantly used in premium cars.

[0008] Tone-disc horns comprise a solenoid with a movable slug inside the solenoid. The slug is suspended above a core of the tone disc horn and is connected to a clamped suspension disc of the tone disc horn. The tone disc horn further comprises a tone disc that is connected centrally to the slug and the suspension disc that is free to vibrate and generate sound. Upon activation of the solenoid, the slug hits the core, thereby generating an impact sound and exciting the tone disc. When the slug is attracted away from its rest position (by energising the solenoid upon operation of an activation mechanism of the tonedisc horn) an electrical contact to the solenoid is interrupted and a movable assembly of the tone-disc horn moves due to the inertial forces hitting the core. Meanwhile, the clamped suspension disc provides a restoring force such that, when the solenoid of the tone-disc horn is no longer energised, the suspension disc returns the movable assembly back to its rest position, thereby reconnecting the solenoid to the electrical contact such that the cycle can start again. This making and breaking of the electrical contact can be achieved mechanically or electronically and may be timed (e.g., by means of a solid-state component). Typical tone-disc horns operate with a cycle frequency of approximately 400 Hz or 500 Hz, which is the fundamental frequency of the tone-disc horn.

[0009] In contrast, bell-type horns evolved from air horns. Bell-type horns also comprise a solenoid with a core, a slug, and a clamped disc. However, when the solenoid of a bell-type horn is energised, the slug is attracted towards the core but does not make contact with the core. The slug mass and suspension disc stiffness are selected such that a movable assembly of a bell-type horn resonates at either approximately 400 Hz or 500 Hz. Despite the slug being only attracted to the core, the movement of the slug of a belltype horn is still approximately sinusoidal due to resonant behaviour, with a high quality factor, at the fundamental frequency of the bell-type horn.

[0010] The bell-type horn further comprises a bell mounted in close proximity to the suspension disc. A cavity between the suspension disc and the entrance to the bell is sized to be small enough that the mechanical resonance of the movable assembly ejects almost all air from within the cavity into the mouth. In this way, a puff of high velocity air is pushed down the bell. The length of the bell is chosen such that it resonates at the mechanical resonance of the movable assembly (i.e., approximately either 400 Hz or 500 Hz). As an example, the bell may be a half-lambda type bell having a length that is approximately one half of the wavelength of sound having a frequency at the resonant frequency.

[0011] Pushing the high velocity puff of air through the bell generates high pressure at the bell mouth, which is shaped such that a full series of harmonics of the resonant frequency can build up and resonate. In this way, the sound of a bell-type horn can closely approximate that of a traditional airhorn.

[0012] As is clear from the discussion above, both tone-disc horns and bell-type horns are mechanical systems, whose mechanical resonances have been configured and selected to generate a sound that is recognisable as a vehicle horn’s audible warning sound. Such systems have reliable performance - for example, a bell-type horn configured with electronic timing and current interruption (e.g., through use of a MOSFET), and including a circumferentially clamped and round suspension disc, together with a narrow bell may be able to generated loud pulses with loud harmonics up to and beyond 10 kHz in frequency. However, as will be apparent from the discussion above, the mechanical structures that need to be provided to emulate a traditional horn sound are complex and require precise tuning and maintenance to ensure the sound quality and tone is maintained over the horn apparatus’ lifetime. Meanwhile, electronic bell-type horns lack versatility in that they can only be used as a horn.

[0013] The present invention has been devised in light of the above considerations.

[0014] Summary of the Invention

[0015] In an aspect there is provided a horn apparatus for a vehicle. The horn apparatus is configured to produce an audible warning sound having a fundamental frequency. The horn apparatus comprises: a signal unit configured to provide a signal; and a loudspeaker configured to produce an audible warning sound based on the signal provided by the signal unit. The signal is defined by a waveform that alternates between a positive peak and a negative peak of the waveform multiple times within a period corresponding to the fundamental frequency of the warning sound. A time between each alternation (e.g. zero-crossing) of the waveform varies across the period.

[0016] In a further aspect, there is provided a signal for use by the horn apparatuses described herein to produce an audible warning sound having a fundamental frequency. The signal is defined by a waveform that alternates between a positive peak and a negative peak of the waveform multiple times within a period corresponding to the fundamental frequency of the warning sound. A time between each alternation (e.g. zero-crossing) of the waveform varies across the period.

[0017] The period may, for example, be determined as being a time period equal to the inverse of the fundamental frequency (e.g., Length of period in seconds = 1 / [fundamental frequency in Hz]).

[0018] For example, the signal may be defined by a voltage waveform. In some examples, the waveform may be a square-wave waveform. In other words, the wave profile of the waveform may, for example, be a square wave. In such examples, the peaks of the waveform may be flat or substantially flat.

[0019] Alternatively, the wave profile may be any other suitable wave profile shape. For example, the wave profile may be sinusoidal, a modified sinusoid (e.g., a rectified sinusoid such as a full-wave rectified sinusoid or a half-wave rectified sinusoid), a triangle wave profile, a sawtooth wave profile, a pulse-width modulated (PWM) profile, or any other suitable wave profile.

[0020] A square wave profile may be particularly beneficial because, as is discussed below, the square wave benefits from a very low crest factor (or peak-to-average power ratio, PAPR) - indeed a perfect square wave has the lowest possible crest factor - meaning that the coupling of signal amplitude into sound amplitude is particularly efficient.

[0021] The loudspeaker may be configured to produce sound by, for example, moving / vibrating a movable assembly of the loudspeaker in accordance with the signal to generate the audible warning sound.

[0022] By generating the audible warning sound based on a signal defined by a waveform as described herein, it is made possible to synthesise an audible warning sound that closely mimics the sound produced by conventional vehicle horns. In this way, the audible warning sound produced by the horn apparatuses described herein may be (more easily) recognisable by road users and / or pedestrians as being a warning sound produced by a horn apparatus of a vehicle.

[0023] By varying the time between each alternation of the waveform, the signal upon which the audible warning sound is based may be defined by a waveform comprising a plurality of frequency components. In this way, a waveform may be provided that comprises audible elements having frequencies that are harmonics (i.e., integer multiples) of the fundamental frequency of the audible warning sound. In this way, a broadband harmonic frequency spectrum can be built into the audible warning sound such that the audible warning sound produced by the horn apparatuses described herein more reliably and accurately mimics the sound produced by a conventional bell-type vehicle horn.

[0024] In some examples, the alternations (e.g. zero-crossings) of the waveform are configured (e.g. spaced apart in time) so that the frequency spectrum of the square wave signal mimics the frequency spectrum of an analogue horn sound having the predetermined fundamental frequency. Such mimicking can be achieved by the techniques taught herein.

[0025] In some examples, the horn apparatus may further comprise one or more amplifiers configured to amplify the provided signal and deliver the amplified signal to the loudspeaker, wherein the loudspeaker may be configured to generate the audible warning sound in accordance with the amplified signal.

[0026] As will be discussed in more detail below, in some examples, the horn apparatus may be configured (e.g., via the one or more amplifiers) to vary an amplification of the signal over time based on a desired / required amplitude profile of the audible warning sound. In some examples, each positive peak of the waveform may have a common positive amplitude (i.e. the same positive amplitude as other positive peaks of the waveform).

[0027] In some examples, each negative peak of the waveform may have a common negative amplitude (i.e. the same negative amplitude as other negative peaks of the waveform).

[0028] In some examples, the common positive amplitude may be equal to the common negative amplitude (i.e. the amplitude of the positive peaks may be the same as the amplitude of the negative peaks).

[0029] By providing the waveform with common positive and / or negative amplitudes, the number of degrees of freedom in the waveform profile shape for adjusting the tonality / quality of the audible warning sound may be produced. For example, it may be possible to adjust the tonality / quality of the audible warning sound by adjusting just one parameter of the waveform - this parameter being the variations in times between each successive alternation (e.g. zero-crossing) of the waveform. In this way, it may be possible to provide a more efficient method for adjusting the audible warning sound produced by the horn apparatuses described herein. For example, it may be possible to implement a simple one-parameter optimisation algorithm that is computationally efficient (e.g. to store) and does not require significant processing or storage capacity to implement. In this way, the horn apparatus may be able to produce an audible warning sound (or even a tuneable audible warning sound) using relatively low amounts of processing power.

[0030] In some examples, an average amplitude of the waveform across the period may be zero, or substantially zero.

[0031] In other words, a direct-current (DC) component of the signal may be zero; that is the signal may be a pure alternating current (AC) signal.

[0032] In this way, all the amplitude of the signal may be useable by an amplifier of the horn apparatus to induce the loudspeaker to generate sound.

[0033] In examples where the average amplitude of the waveform is non-zero, or substantially non-zero, (i.e., where the signal could be viewed as containing a DC component, where implemented as a voltage waveform), the DC component of the signal may induce the application of mechanical forces on the loudspeaker (e.g., on a movable assembly of the loudspeaker) without the production of sound. In other words, the loudspeaker may only be able to produce sound using an AC component of the signal, while any DC component of the signal may simply cause the application of a monodirectional displacing force to a movable assembly of the loudspeaker.

[0034] In some examples, a peak-to-average power ratio, PAPR, of the waveform across the period may be 2 dB or less.

[0035] Alternatively, in some examples, the PAPR of the waveform may be 3 dB or less, 2.5 dB or less, 1 .5 dB or less, 1 dB or less, or 0.5 dB or less.

[0036] Alternatively, in some examples, the PAPR of the waveform may be 0 dB or more, 0.5 dB or more, 1 dB or more, 1 .5 dB or more, 2 dB or more, or 2.5 dB or more. Alternatively, in some examples, the PAPR of the waveform may be between 0 and 3 dB, 0 and 2.5 dB, 0 and 2 dB, 0 and 1 .5 dB, 0 and 1 dB, 0 and 0.5 dB, 0.5 and 3 dB, 0.5 and 2.5 dB, 0.5 and 2 dB, 0.5 and 1 .5 dB, 0.5 and 1 dB, 1 and 3 dB, 1 and 2.5 dB, 1 and 2 dB, 1 and 1 .5 dB, 1 .5 and 3 dB, 1 .5 and 2.5 dB, 1 .5 and 2 dB, 2 and 3 dB, 2 and 2.5 dB, or 2.5 and 3 dB.

[0037] In particular examples, the PAPR of the waveform may be 0 dB.

[0038] The PAPR of the waveform may be equated to the crest factor of the waveform, by the following relationship:

[0039] CF [dB] = 20 log where the logarithm is taken with base 10, and where N is total number of samples defining the waveform, and xnis the value of the n-th sample of the waveform.

[0040] As such, the terms crest factor and PAPR may be used interchangeably herein.

[0041] The crest factor of a (digitally stored) signal is indicative of the power available to produce sound from a given signal when transferring said signal from an amplifier of the horn apparatus to the loudspeaker of the horn apparatus. In other words, a lower crest factor is indicative that a relatively lower amount of power is available to produce sound from the corresponding signal. The availability of power to produce sound is maximised when the crest factor, or PAPR, is equal to 0 dB - i.e., the waveform of the signal is shaped such that the power available to produce sound is maximised for a given peak signal voltage.

[0042] It may therefore be advantageous to minimise the crest factor / PAPR of the signal to optimise the availability of the power from the signal that is useable to produce the audible warning sound through the horn apparatus.

[0043] In some examples, the overall crest factor associated with the transfer of the signal through the horn apparatus may be larger than the intrinsic crest factor described above. For example, various components of the horn apparatuses described herein may be ‘lossy’ components in that the power transfer is not 100% efficient. Minimising the intrinsic crest factor may therefore be important to reduce the risk that a series of incremental crest factors add up to (severely) negative impact the efficiency of power transfer through the horn apparatuses described herein.

[0044] In some examples, each alternation between a positive peak and a negative peak of the waveform may be instantaneous, or substantially instantaneous. For example, the waveform may be a square-wave waveform. In this way, an (intrinsic) crest factor of 0 dB may be achieved.

[0045] In some examples, the signal unit may be configured to retrieve the signal from a storage medium.

[0046] In some examples, the storage medium may be a component of the horn apparatuses described herein. This conveniently allows the horn apparatus to produce the audible warning sound based on the signal, without the signal needing to be synthesized on the fly, or retrieved from an external component. Alternatively, in some examples, the storage medium may be an external component that is communicatively connected (or communicatively connectable) to the signal unit of the horn apparatuses described herein.

[0047] For example, the storage medium may be a storage unit on a remote computer that may be communicatively connected to the signal unit through a wired or wireless connection. In some examples, the storage medium may be a cloud-based memory or similarly accessible storage medium accessible via an internet or intranet connection.

[0048] In some examples, the signal unit may comprise a memory unit configured to store one or more signals retrieved from the storage medium. In this way, a permanent connection between the horn apparatuses described herein and an external storage medium need not be maintained. Instead, an intermittent connection to the external storage medium may be provided such that the signal unit can update its catalogue / database of stored signals that are stored on the memory unit of the signal unit.

[0049] In some examples, the signal may be stored in the storage medium as a 16-digit binary number and / or as a 4-digit HEX number that is an encoding of the signal.

[0050] Such a format may be beneficial because it is a particularly efficient use of memory capacity. For example, in cases where the signal unit comprises a memory unit, minimising the necessary memory capacity of the memory unit may be advantageous as it may reduce the manufacturing and processing costs associated with the horn apparatuses described herein.

[0051] In examples where the waveform is a square-wave waveform, the period of the signal may, for example, be divided into 16 segments. An alternation between a positive and negative peak may (or may not) occur after each segment of the square-wave waveform. In such an example, a negative peak portion of the square wave may be encoded in binary as ‘O’, while a positive peak portion of the square wave may be encoded in binary as ‘1 ’. In this way, the square wave may be encoded digitally as a string of 16 ‘0’ or ‘1 ’ bits that indicate when the square-wave waveform alternates between a positive and negative peak of the waveform. Such a 16-digit binary number may subsequently be condensed in a straightforward manner into a 4-digit HEX number wherein, for example: ‘0’ in HEX corresponds to a binary bit string ‘0000’, ‘1 ’ in HEX corresponds to a binary bit string ‘0001 ’, ‘2’ in HEX corresponds to a binary bit string ‘001 O’, ‘3’ in

[0052] HEX corresponds to a binary bit string ‘0011 ’, ‘4’ in HEX corresponds to a binary bit string ‘0100’, ‘5’, in

[0053] HEX corresponds to a binary bit string ‘0101 ’, ‘6’ in HEX corresponds to a binary bit string ‘0110’, 7’ in

[0054] HEX corresponds to a binary bit string ‘0111 ’, ‘8’ in HEX corresponds to a binary bit string ‘1000’, ‘9’ in

[0055] HEX corresponds to a binary bit string ‘1001 ’, ‘A’ in HEX corresponds to a binary bit string ’1010’, ‘B’ in

[0056] HEX corresponds to a binary bit string ‘1011 ’, ‘C’ in HEX corresponds to a binary bit string ‘1100’, ‘D’ in

[0057] HEX corresponds to a binary bit string ‘1101 ’, ‘E ’ in HEX corresponds to a binary bit string ‘1110’, and ‘F’ in HEX corresponds to a binary bit string ‘1111 ’.

[0058] In some examples, the signal may be stored in the storage medium in any other suitable format, with consideration given to a balance between the need to provide a satisfactorily high resolution / sampling rate of the signal against the need to minimise the storage requirements associated with storing an encoded form of the signal.

[0059] In some examples, the signal unit may be configured to generate (e.g., synthesize) the signal (e.g. without retrieving the signal from a storage medium or external component) .

[0060] For example, the signal unit may comprise a signal generation unit configured to generate the signals described herein. In this way, the need for storage capacity to store an encoded form of the signal may be reduced or even entirely eliminated.

[0061] In some embodiments, the horn apparatus may further comprise an activation mechanism operable by a user of the vehicle. The loudspeaker may be configured to produce the audible warning sound in response to the activation mechanism being operated by the user of the vehicle.

[0062] Such activation mechanisms are well-known. For example, the activation mechanism may be any one or more of: a pressure-activated mechanism mounted in the steering wheel / steering column of the vehicle, a switch or lever mounted on an indicator-stick adjacent to the steering wheel / steering column of the vehicle, a button or dial mounted on an interior of the vehicle (e.g., on the dashboard of the vehicle), and / or a mechanism operatively coupled to a gearstick of the vehicle that may be activated by pushing the gearstick into a predetermined position (e.g., by pushing the gearstick into a ‘reverse’ position to put the vehicle into ‘reverse gear’).

[0063] In some examples, the audible warning sound may include: a rising portion in which the amplitude of the audible warning sound may increase towards a maximum amplitude; and / or a falling portion in which the amplitude of the audible warning sound may decrease to a minimum amplitude.

[0064] In this context, the “amplitude” of the audible warning sound at a given time may be taken to correspond to the sound pressure level (SPL) of the audible warning sound at that time, as measured in a fixed position with respect to the loudspeaker.

[0065] In some examples, the audible warning sound may further comprise a steady-state portion in which the audible warning sound may have an amplitude equal to the maximum amplitude. The steady-state portion may occur after the amplitude of the audible warning sound has increased to the maximum amplitude.

[0066] The amplitude of the audible warning sound during the steady-state portion of the audible warning sound may be constant, or substantially constant.

[0067] In some examples, the rising portion may increase towards the maximum amplitude gradually, which may in some examples be over a time long enough for human hearing to perceive the increase in amplitude.

[0068] An audible warning sound as described above may be achieved by the horn apparatus comprising one or more amplifiers appropriately configured. For example, the horn apparatus may comprise one or more amplifiers configured to amplify the provided signal and deliver the amplified signal to the loudspeaker, wherein the amplified signal delivered to the loudspeaker includes: a rising portion in which the amplitude of the amplified signal increases towards a maximum amplitude; optionally, after the amplitude of the amplified signal has increased to the maximum amplitude, a steady-state portion in which the amplitude of the amplified signal is maintained at the maximum amplitude; and a falling portion in which the amplitude of the amplified signal decreases to a minimum amplitude.

[0069] In this context, the “amplitude” of the amplified signal in a given time window may be taken to correspond to a maximum amplitude of the amplified signal in that time window.

[0070] In some examples, the minimum amplitude (of the audible warning sound and / or amplified signal) may be a zero amplitude. In other words, the falling portion may define an ending portion of the audible warning sound and / or amplified signal.

[0071] In some examples, the falling portion (of the audible warning sound and / or amplified signal) may decrease to the minimum amplitude gradually - that is over a time long enough for human hearing to perceive the decrease in amplitude.

[0072] In some examples, an onset of the rising portion (of the audible warning sound and / or amplified signal) may be triggered by a user operating an activation mechanism of the horn apparatuses described herein that is configured to induce the horn apparatus to generate the audible warning sound.

[0073] In some examples, an onset of the falling portion (of the audible warning sound and / or amplified signal) may be triggered by a user ceasing to operate that same activation mechanism.

[0074] In this way, the proportion of the audible warning sound and / or amplified signal defined by each of the rising, steady-state and falling portions of the audible warning sound may be adjustable by the user dependent on the way they operate the activation mechanism.

[0075] In some embodiments, the horn apparatus may further comprise: a frequency modifying component configured to modify the frequency spectrum of the amplified signal during the rising portion and / or falling portion of the audible warning sound and / or amplified signal.

[0076] In conventional vehicle horns (e.g., bell-type horns), as the amplitude of the vibrations passing through the horn increases, more energy is propagated through the horn apparatus, thereby activating progressively higher-order harmonics. Similarly, as the amplitude of the vibrations passing through the horn decreases, less energy is propagated through the horn apparatus, and consequently higher-order harmonics are successively lost from the sound output of the horn apparatus.

[0077] Therefore, in order to more effectively mimic the sound output (or acoustic output) of a conventional horn apparatus, it may be beneficial to modify the frequency spectrum and, in particular, the higher-frequency components of the frequency spectrum of the amplified signal so as to progressively introduce higher- order harmonics into the audible warning sound during the rising portion and / or successively remove higher-order harmonics from the audible warning sound during the falling portion.

[0078] In some embodiments, the frequency modifying component may be a lowpass filter.

[0079] In some examples, the lowpass filter may be configurable and / or controllable to adjust the passband of the lowpass filter over the course of the rising portion and / or falling portion to controllably modify the frequency spectrum of the amplified signal during said portions. In some examples, the frequency modifying components may be any configurable or controllable component that is useable to selectively block / permit signals of different frequencies.

[0080] In some embodiments, the fundamental frequency may be between 320 Hz and 480 Hz.

[0081] In some examples, the fundamental frequency may be 480 Hz or less, 440 Hz or less, 400 Hz or less, or 360 Hz or less.

[0082] In some examples, the fundamental frequency may be 320 Hz or more, 360 Hz or more, 400 Hz or more, or 440 Hz or more.

[0083] In some examples, the fundamental frequency may be between 320 Hz and 440 Hz, 320 Hz and 400 Hz, 320 Hz and 360 Hz, 360 Hz and 480 Hz, 360 Hz and 440 Hz, 360 Hz and 400 Hz, 400 Hz and 480 Hz, 400 Hz and 440 Hz, or 440 Hz and 480 Hz.

[0084] In particular examples, the fundamental frequency may be 400 Hz.

[0085] In particular examples, the fundamental frequency may be between 380 Hz and 440 Hz.

[0086] In some embodiments, the fundamental frequency may be between 400 Hz and 600 Hz.

[0087] In some examples, the fundamental frequency may be 600 Hz or less, 550 Hz or less, 500 Hz or less, or 450 Hz or less.

[0088] In some examples, the fundamental frequency may be 400 Hz or more, 450 Hz or more, 500 Hz or more, or 550 Hz or more.

[0089] In some examples, the fundamental frequency may be between 400 Hz and 550 Hz, 400 Hz and 500 Hz, 400 Hz and 450 Hz, 450 Hz and 600 Hz, 450 Hz and 550 Hz, 450 Hz and 500 Hz, 500 Hz and 600 Hz, 500 Hz and 550 Hz, or 550 Hz and 600 Hz.

[0090] In particular examples, the fundamental frequency may be 500 Hz.

[0091] In particular examples, the fundamental frequency may be between 475 Hz and 550 Hz.

[0092] In some examples, the horn apparatus may be configured to produce an additional audible warning sound at the same time as the audible warning sound (e.g. with both audible warning sounds being triggered by a user operating an activation mechanism as described herein). The audible warning sound and the additional audible warning sound may have a respective (different) fundamental frequency. In this way, the horn apparatus can mimic a conventional dual-tone audible warning sound.

[0093] The signal unit may be configured to provide an additional signal which corresponds to the additional audible warning sound. The additional signal may be defined by a waveform. Said waveform may alternate between a corresponding positive peak and a corresponding negative peak multiple times within a period corresponding to the fundamental frequency of the additional audible warning sound. A time between each alternation of said waveform may vary across the respective period. The horn apparatus may further comprise: an additional loudspeaker. The additional loudspeaker may be configured to produce the additional audible warning sound based on the additional signals provided by the signal unit. Any feature(s) described above in relation to the signal (based on which the loudspeaker is configured to produce an audible warning sound) may be applied to the additional signal.

[0094] In theory, it would be possible to generate the audible warning sound and the additional audible warning sound from the same loudspeaker by combining the signal and audible warning signal, and supplying the combined signal to that loudspeaker. However, doing this will likely raise the crest factor of the combined signal, compared to that of each of the two individual signals, which could mean less efficient utilisation of the power of the loudspeaker, compared with if just one of the two signals were supplied to that loudspeaker. Whereas supplying the signal and additional signal to two different loudspeakers allows for more efficient utilisation of the power of each loudspeaker.

[0095] In some examples, there could be yet additional signals and additional loudspeakers (i.e. the number of signals and loudspeakers need not be limited to two).

[0096] Where the horn apparatus is configured to produce an additional audible warning sound, the audible warning sound may be referred to as the first audible warning sound, and the additional warning sound may be referred to as the second audible warning sound.

[0097] In some examples, the fundamental frequency of the first audible warning sound may be between 320 Hz and 480 Hz.

[0098] In some examples, the fundamental frequency of the first audible warning sound may be 480 Hz or less, 440 Hz or less, 400 Hz or less, or 360 Hz or less.

[0099] In some examples, the fundamental frequency of the first audible warning sound may be 320 Hz or more, 360 Hz or more, 400 Hz or more, or 440 Hz or more.

[0100] In some examples, the fundamental frequency of the first audible warning sound may be between 320 Hz and 440 Hz, 320 Hz and 400 Hz, 320 Hz and 360 Hz, 360 Hz and 480 Hz, 360 Hz and 440 Hz, 360 Hz and 400 Hz, 400 Hz and 480 Hz, 400 Hz and 440 Hz, or 440 Hz and 480 Hz.

[0101] In particular examples, the fundamental frequency of the first audible warning sound may be 400 Hz.

[0102] In particular examples, the fundamental frequency of the first audible warning sound may be between 380 Hz and 440 Hz.

[0103] In some examples, the fundamental frequency of the second audible warning sound may be between 400 Hz and 600 Hz.

[0104] In some examples, the fundamental frequency of the second audible warning sound may be 600 Hz or less, 550 Hz or less, 500 Hz or less, or 450 Hz or less.

[0105] In some examples, the fundamental frequency of the second audible warning sound may be 400 Hz or more, 450 Hz or more, 500 Hz or more, or 550 Hz or more.

[0106] In some examples, the fundamental frequency of the second audible warning sound may be between 400 Hz and 550 Hz, 400 Hz and 500 Hz, 400 Hz and 450 Hz, 450 Hz and 600 Hz, 450 Hz and 550 Hz, 450 Hz and 500 Hz, 500 Hz and 600 Hz, 500 Hz and 550 Hz, or 550 Hz and 600 Hz. In particular examples, the fundamental frequency of the second audible warning sound may be 500 Hz.

[0107] In particular examples, the fundamental frequency of the second audible warning sound may be between 475 Hz and 550 Hz.

[0108] The wave profile of the waveforms defining the first and second signals may, for example, be a square wave or any other suitable wave profile shape. For example, the wave profile may be sinusoidal, a modified sinusoid (e.g., a rectified sinusoid such as a full-wave rectified sinusoid or a half-wave rectified sinusoid), a triangle wave profile, a sawtooth wave profile, a pulse-width modulated (PWM) profile, or any other suitable wave profile.

[0109] In particular examples, the waveforms defining the first and second signals may both be square waves.

[0110] In some examples, the first and second signals and the waveforms defining said signals may include any one or more of the properties described herein in relation to examples and embodiments wherein the horn apparatuses described herein produce just a single audible warning sound.

[0111] In some examples, the activation mechanism may be a first activation mechanism. The horn apparatus may further comprise a second activation mechanism operable by a user of the vehicle. The second loudspeaker may be configured to produce the second audible warning sound in response to either the first or second activation mechanisms being operated by the user of the vehicle.

[0112] In some examples, the loudspeaker may be configured to produce the second audible warning sound with different amplitudes (or amplitude envelopes) based on whether the production of the second audible warning sound is in response to operation of the first or second activation mechanism.

[0113] For example, in response to the operation of the first activation mechanism, the horn apparatus (by first and second loudspeakers) may be configured to produce the first and second audible warning sounds simultaneously, thereby mimicking a dual-tone vehicle horn.

[0114] Meanwhile, in some examples, in response to the operation of the second activation mechanism (e.g., putting the vehicle in reverse-gear), the second loudspeaker may be configured to produce the second audible warning sound with a different amplitude and / or amplitude envelope (e.g., an intermittent beeping at lower amplitude to indicate to other road users and pedestrians that the vehicle is reversing).

[0115] In some embodiments, the horn apparatus may be operable as an Acoustic Vehicle Alerting System (AVAS).

[0116] In another aspect, there is provided a method of providing a signal for use by the horn apparatuses described herein to produce an audible warning sound. The method comprises: providing a signal defined by a waveform. The waveform alternates between a positive peak and a negative peak of the waveform multiple times within the period corresponding to the fundamental frequency of the audible warning sound. A time between each alternation of the waveform varies across the period.

[0117] The signal of this aspect may be as set out in relation to any horn apparatus or method as described herein, and / or may be used as the signal in any horn apparatus or method as described herein. In some embodiments, providing the signal comprises: providing one or more different candidate waveforms. Each candidate waveform may be a respective waveform that alternates between a respective positive peak and a respective negative peak of said waveform multiple times within a period corresponding to the fundamental frequency of the audible warning sound. A time between each alternation of said waveform may vary across the period. The method may further comprise: comparing each candidate waveform with a set of predetermined criteria; and selecting a candidate waveform that satisfies the predetermined criteria from amongst the plurality of different candidate waveforms as the waveform to define the signal.

[0118] In this way, it can be ensured that the audible warning sound(s) produced by the horn apparatuses described herein may satisfactorily mimic the tonality / quality of a desired sound (e.g., a conventional vehicle horn sound).

[0119] The predetermined criteria may, for example, include a criterion related to the relative amplitudes of one or more of the harmonics of the frequency spectrum of the signal. For example, in some cases, the predetermined criteria may include a criterion that the amplitude of the second harmonic in a frequency spectrum of the signal must be greater than the amplitude of the fundamental frequency in the frequency spectrum of the signal.

[0120] The predetermined criteria may, for example, include a requirement that a certain number of amplitude thresholds in one or more frequency bands are met. For example, the predetermined criteria may include a requirement that at least a predetermined number of a set of frequency bands of the signal have an amplitude that exceeds an amplitude criterion threshold. In some examples, the predetermined criteria may relate to an amplitude of e.g., three frequency bands of the signal (for example three frequency bands in the one-third octave frequency spectrum of the signal). In such examples, the predetermined criteria may be that the amplitude in at least one, at least two, or at least three of the frequency bands exceeds a respective amplitude criterion threshold. In some examples, the amplitude criterion threshold may be the same for each of the plurality of frequency bands.

[0121] In some examples, the three frequency bands may be frequency bands in the one-third octave frequency spectrum of the signal and may be the 2 kHz band, the 2.5 kHz band, and the 3.15 kHz band. The amplitude criterion threshold may be that the amplitude of at least one of the bands, at least two of the bands, or all the bands must exceed -20 dB. In particular examples, the predetermined criteria may include a requirement that the amplitude of at least two out of the 2 kHz band, the 2.5 kHz band, and the 3.15 kHz band have an amplitude exceeding -20 dB.

[0122] In some examples, the predetermined criteria may include a requirement that the average amplitude of the waveform across the period is zero.

[0123] For example, the criteria may, for example, include a criterion related to the relative amplitudes of one or more of the harmonics of the frequency spectrum of the signal. For example, in some cases, the predetermined criteria may include a criterion that the amplitude of the second harmonic in a frequency spectrum of the signal must be greater than the amplitude of the fundamental frequency in the frequency spectrum of the signal.

[0124] The predetermined criteria may, for example, include a requirement that a certain number of amplitude thresholds in one or more frequency bands are met. For example, the predetermined criteria may include a requirement that at least a predetermined number of a set of frequency bands of the signal have an amplitude that exceeds an amplitude criterion threshold. In some examples, the predetermined criteria may relate to an amplitude of e.g., three frequency bands of the signal (for example three frequency bands in the one-third octave frequency spectrum of the signal). In such examples, the predetermined criteria may be that the amplitude in at least one, at least two, or at least three of the frequency bands exceeds a respective amplitude criterion threshold. In some examples, the amplitude criterion threshold may be the same for each of the plurality of frequency bands.

[0125] In some examples, the three frequency bands may be frequency band in the one-third octave frequency spectrum of the signal and may be the 2 kHz band, the 2.5 kHz band, and the 3.15 kHz band. The amplitude criterion threshold may be that the amplitude of at least one of the bands, at least two of the bands, or all the bands must exceed -20 dB. In particular examples, the predetermined criteria may include a requirement that the amplitude of each of the 2 kHz band, the 2.5 kHz band, and the 3.15 kHz band have an amplitude exceeding -20 dB.

[0126] In some examples, the predetermined criteria may include a requirement that the average amplitude of the waveform across the period is zero.

[0127] In some embodiments, comparing each candidate waveform with the set of predetermined criteria may include: comparing a respective frequency spectrum of each candidate waveform with a reference frequency spectrum; and selecting a candidate waveform, from amongst the plurality of different candidate waveforms, whose respective frequency spectrum satisfies a similarity criterion with respect to the reference frequency spectrum.

[0128] For example, the selected candidate waveform may be that waveform that most closely matches the reference frequency spectrum.

[0129] Matching the reference frequency spectrum may be evaluated by, for example, comparing the amplitudes of selected harmonic pairs of the frequency spectrum (e.g., comparing the relative amplitudes of the fundamental and second harmonics, fundamental and first harmonics, first and second harmonics, or any other pair of harmonics in the frequency spectrum).

[0130] In some examples, providing the or each candidate waveform may comprise: retrieving the or each waveform from a memory.

[0131] In some examples, an appropriately trained algorithm may be used to determine whether a given waveform satisfies any one or more of the criteria set out above.

[0132] In some examples, providing the or each candidate waveform may comprise generating the or each waveform (e.g. without retrieving each candidate from a memory). In some examples, the method may further comprise: storing the signal in a storage medium accessible by the horn apparatus.

[0133] In some examples, the storage medium may be a component of the horn apparatuses described herein.

[0134] Alternatively, in some examples, the storage medium may be an external component that is communicatively connected (or communicatively connectable) to the signal unit of the horn apparatuses described herein.

[0135] For example, the storage medium may be a storage unit on a remote computer that may be communicatively connected to the signal unit through a wired or wireless connection. In some examples, the storage medium may be a cloud-based memory or similarly accessible storage medium accessible via an internet or intranet connection.

[0136] In some examples, the signal unit may comprise a memory unit configured to store one or more signals retrieved from the storage medium. In this way, a permanent connection between the horn apparatuses described herein and an external storage medium need not be maintained. Instead, an intermittent connection to the external storage medium may be provided such that the signal unit can update its catalogue / database of stored signals that are stored on the memory unit of the signal unit.

[0137] In some embodiments, the signal may be stored in the storage medium as a 16-digit binary number and / or as a 4-digit HEX number that is an encoding of the signal.

[0138] Such a format may be beneficial because it is a particularly efficient use of memory capacity. For example, in cases where the signal unit comprises a memory unit, minimising the necessary memory capacity of the memory unit may be advantageous as it may reduce the manufacturing and processing costs associated with the horn apparatuses described herein.

[0139] In examples where the waveform is a square-wave waveform, the period of the signal may, for example, be divided into 16 segments. An alternation between a positive and negative peak may (or may not) occur after each segment of the square-wave waveform. In such an example, a negative peak portion of the square wave may be encoded in binary as ‘O’, while a positive peak portion of the square wave may be encoded in binary as ‘1 ’. In this way, the square wave may be encoded digitally as a string of 16 ‘0’ or ‘1 ’ bits that indicate when the square-wave waveform alternates between a positive and negative peak of the waveform. Such a 16-digit binary number may subsequently be condensed in a straightforward manner into a 4-digit HEX number wherein, for example: ‘0’ in HEX corresponds to a binary bit string ‘0000’, ‘1 ’ in HEX corresponds to a binary bit string ‘0001 ’, ‘2’ in HEX corresponds to a binary bit string ‘001 O’, ‘3’ in HEX corresponds to a binary bit string ‘0011 ’, ‘4’ in HEX corresponds to a binary bit string ‘0100’, ‘5’, in HEX corresponds to a binary bit string ‘0101 ’, ‘6’ in HEX corresponds to a binary bit string ‘0110’, 7’ in HEX corresponds to a binary bit string ‘0111 ’, ‘8’ in HEX corresponds to a binary bit string ‘1000’, ‘9’ in HEX corresponds to a binary bit string ‘1001 ’, ‘A’ in HEX corresponds to a binary bit string ’1010’, ‘B’ in HEX corresponds to a binary bit string ‘1011 ’, ‘C’ in HEX corresponds to a binary bit string ‘1100’, ‘D’ in HEX corresponds to a binary bit string ‘1101 ’, ‘E ’ in HEX corresponds to a binary bit string ‘1110’, and ‘F’ in HEX corresponds to a binary bit string ‘1111 ’. In some examples, the signal may be stored in the storage medium in any other suitable format, with consideration given to a balance between the need to provide a satisfactorily high resolution / sampling rate of the signal against the need to minimise the storage requirements associated with storing an encoded form of the signal.

[0140] The order of the operations of the methods described herein is exemplary, but the steps may be carried out in any suitable order, or simultaneously where appropriate. Additionally, steps may be added or substituted in, or individual steps may be deleted from any of the methods without departing from the scope of the subject matter described herein. Aspects of any of the examples described above may be combined with aspects of any of the other examples described to form further examples without losing the effect sought.

[0141] Moreover, the acts described herein may be embodied using computer-executable instructions that can be implemented by one or more processors and / or stored on a computer-readable medium or media. The computer-executable instructions can include routines, sub-routines; programs; threads of execution, and / or the like. Still further, results of acts of the methods can be stored in a computer-readable medium, displayed on a display device, and / or the like.

[0142] In a further aspect, there is provided a computer-readable medium comprising instructions that, when executed by a computer, cause the computer to carry out a method as described herein.

[0143] In another aspect, there is provided a computer program product comprising logic that, when executed by a processor, causes the processor to carry out a method as described herein.

[0144] Various functions described herein can be implemented in hardware, software, or any combination thereof. If implemented in software, the functions can be stored on or transmitted over as one or more instructions or code on a computer-readable medium. Computer-readable media may include, for example, computer-readable storage media. Computer-readable storage media may include volatile or non-volatile, removable or non-removable, media implemented in any method or technology for storage of information such as computer readable instructions, data structures, program modules or other data. A computer-readable storage media can be any available storage media that may be accessed by a computer. By way of example, and not limitation, such computer-readable storage media may comprise RAM, ROM, EEPROM, flash memory or other memory devices, CD-ROM or other optical disc storage, magnetic disc storage or other magnetic storage devices, or any other medium that can be used to carry or store desired program code in the form of instructions or data structures and that can be accessed by a computer.

[0145] The term 'computer' is used herein to refer to any device with processing capability such that it can execute instructions. Those skilled in the art will realise that such processing capabilities are incorporated into many different devices and therefore the term 'computer' includes PCs, servers, mobile telephones, personal digital assistants, and many other devices.

[0146] Those skilled in the art will realise that storage devices utilised to store program instructions can be distributed across a network. For example, a remote computer may store an example of the process described as software. A local or terminal computer may access the remote computer and download a part or all the software to run the program. Alternatively, the local computer may download pieces of the software as needed or execute some software instructions at the local terminal and some at the remote computer (or computer network). Those skilled in the art will also realise that by utilising conventional techniques known to those skilled in the art that all, or a portion of the software instructions may be carried out by a dedicated circuit, such as a DSP, programmable logic array, or the like.

[0147] It will be understood that the benefits and advantages described above may relate to one embodiment or may relate to several embodiments. The embodiments are not limited to those that solve any or all the stated problems or those that have any or all the stated benefits and advantages. Variants should be considered to be included into the scope of the invention.

[0148] The invention includes the combination of the aspects and preferred features described except where such a combination is clearly impermissible or expressly avoided.

[0149] Summary of the Figures

[0150] Embodiments and experiments illustrating the principles of the invention will now be discussed with reference to the accompanying figures in which:

[0151] Figure 1 shows a schematic block diagram of a system including a horn apparatus as described herein.

[0152] Figure 2a shows an exemplary vehicle having the horn apparatus of Figure 1 in an exemplary configuration.

[0153] Figure 2b shows an exemplary vehicle having the horn apparatus of Figure 1 in an alternative exemplary configuration.

[0154] Figure 3a shows an exemplary time signal of a used to produce an audible warning sound, having a fundamental frequency of 410 Hz, by a conventional bell-type vehicle horn.

[0155] Figure 3b shows a frequency spectrum corresponding to the sound signal of Figure3a.

[0156] Figure 3c shows an exemplary audible warning sound produced by the signal shown in Figure 3a.

[0157] Figure 3d shows a build-up of harmonic orders over the production of the audible warning sound depicted in Figure 3c.

[0158] Figure 4 shows the evolution of the one-third octave band spectrum of the audible warning sound depicted in Figure 3c.

[0159] Figure 5a shows an exemplary waveform useable by the horn apparatus described herein to produce an audible warning sound that mimics the tonality / quality of the audible warning sound depicted in Figure 3c.

[0160] Figure 5b shows a frequency spectrum corresponding to the signal of Figure 5a.

[0161] Figure 6 shows an exemplary envelope of an amplified signal used to produce an audible warning sound by a horn apparatus as described herein.

[0162] Figure 7 shows a schematic of an exemplary operation of the horn apparatus of Figure 1. Figure 8a shows an exemplary audible warning sound producible by the horn apparatus described herein using the signal of Figure 5a and the envelope of Figure 6.

[0163] Figure 8b shows a build-up of harmonic orders over the production of the audible warning sound depicted in Figure 8a.

[0164] Figure 9 shows the evolution of the one-third octave band spectrum of the audible warning sound depicted in Figure 8a.

[0165] Figure 10a shows an alternative exemplary waveform useable by the horn apparatus described herein to produce an audible warning sound that mimics the tonality / quality of an audible warning sound produced by a conventional vehicle horn.

[0166] Figure 10b shows a frequency spectrum corresponding to the signal of Figure 10a.

[0167] Figure 10c shows a one-third octave band spectrum of an audible warning sound having the frequency spectrum of Figure 10b.

[0168] Figure 11a shows an alternative exemplary waveform useable by the horn apparatus described herein to produce an audible warning sound that mimics the tonality / quality of an audible warning sound produced by a conventional vehicle horn.

[0169] Figure 11b shows a frequency spectrum corresponding to an audible warning sound produced in accordance with the signal of Figure 11 a.

[0170] Figure 11c shows a one-third octave band spectrum of an audible warning sound having the frequency spectrum of Figure 11 b.

[0171] Figure 12a shows an exemplary waveform that is not suitable for use by the horn apparatus described herein to produce an audible warning sound that mimics the tonality / quality of an audible warning sound produced by a conventional vehicle horn.

[0172] Figure 12b shows a frequency spectrum corresponding to an audible warning sound produced in accordance with the signal of Figure 12a.

[0173] Figure 12c shows a one-third octave band spectrum of an audible warning sound having the frequency spectrum of Figure 12b.

[0174] Figure 13a shows a further exemplary waveform that is not suitable for use by the horn apparatus described herein to produce an audible warning sound that mimics the tonality / quality of an audible warning sound produced by a conventional vehicle horn.

[0175] Figure 13b shows a frequency spectrum corresponding to an audible warning sound produced in accordance with the signal of Figure 13a.

[0176] Figure 13c shows a one-third octave band spectrum of an audible warning sound having the frequency spectrum of Figure 13b. Figure 14 shows a method of providing a signal for use by a horn apparatus of a vehicle to produce an audible warning sound.

[0177] Detailed Description of the Invention

[0178] 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.

[0179] Figure 1 shows a schematic block diagram of a system including a horn apparatus 100. The horn apparatus 100 comprises a signal unit 110, a storage 120 (that may be in-built with the signal unit 110) a first loudspeaker 130 a first activation mechanism 140, and a first frequency-modifying component (e.g., a first lowpass filter 150).

[0180] The horn apparatus 100 may comprise one or more additional loudspeakers, activation mechanisms and / or frequency-modifying components. For example, the horn apparatus 100 may further comprise a second loudspeaker 135, a second activation mechanism 145, and a second lowpass filter 155.

[0181] The horn apparatus 100 is suitable for installation in a vehicle and is configured to produce an audible warning sound. For example, the horn apparatus 100 may be suitable for use as part of an Acoustic Vehicle Alerting System (AVAS).

[0182] The signal unit 100 is communicatively linked to the first loudspeaker 130. In examples where the horn apparatus 100 comprises a second loudspeaker 135, the signal unit 100 (or another signal unit) is communicatively linked to the second loudspeaker 135.

[0183] The signal unit 100 is configured to provide a signal to the first loudspeaker 130. In examples where the horn apparatus 100 comprises a second loudspeaker 135, the signal unit 100 is configured to provide a signal to the second loudspeaker 135.

[0184] The signal unit 100 may further comprise a processing unit 112 configured to execute instructions / logic embodied in a computer-readable medium or computer program product to carry out the methods described herein.

[0185] The signal unit 100 may be configured to retrieve the signal (or one or more candidate signals) from the storage 120 of the horn apparatus 100, a cloud-based storage 210 from a cloud server 200, and / or a storage unit 310 embodied in a computer 300 that is remote from the horn apparatus. The signal unit 100 may be communicatively linked to each of the storage 120 of the horn apparatus 100, the cloud-based storage 210 of the cloud server 200, and the storage unit 310 of the remote computer 310.

[0186] The signal unit 100 may further comprise a signal generation unit 114 configured to generate the signal to be transmitted to the first and / or second loudspeaker 130, 135 (or one or more candidate signals).

[0187] The signal unit 100 may further comprise a memory 116 configured to store signals retrieved from the storage 120 of the horn apparatus 100, retrieved from the cloud-based storage 210 of the cloud server 200, retrieved from the storage 310 of the remote computer 300, and / or generated by the signal generation unit 114.

[0188] The first loudspeaker 130 comprises a first loudspeaker processing unit 132 configured to receive a first signal provided by the signal unit 100 and to cause the first loudspeaker 130 to generate a first audible warning sound in accordance with the first signal.

[0189] Similarly, the second loudspeaker 135 comprises a second loudspeaker processing unit 136 configured to receive a second signal provided by the signal unit 100 and to cause the second loudspeaker 135 to generate a second audible warning sound in accordance with the second signal.

[0190] The first activation mechanism 140 is communicatively linked to the first loudspeaker 130 and is operable by a user of the vehicle to cause the first loudspeaker 130 to produce the first audible warning sound. In some examples, the first activation mechanism 140 may additionally or alternatively be communicatively connected to the signal unit 110. In other words, the first loudspeaker processing unit 132 is configured to cause the first loudspeaker 130 to generate the first audible warning sound in accordance with the first signal, in response to an operation of the first activation mechanism 140 by the user.

[0191] Similarly, the second activation mechanism 145 is communicatively linked to the second loudspeaker 135 and is operable by a user of the vehicle to cause the second loudspeaker 135 to produce the second audible warning sound. Correspondingly, in some examples, the second activation mechanism 145 may additionally or alternatively be communicatively connected to the signal unit 110. In other words, the second loudspeaker processing unit 136 is configured to cause the second loudspeaker 135 to generate the second audible warning sound in accordance with the second signal, in response to an operation of the second activation mechanism 145 by the user.

[0192] In preferred examples, the first and second activations mechanisms 140, 145 may be provided by a single (common) activation mechanism, e.g., such that both the first and second audible warning sounds are generated at the same time, in response to operation of the single (common) activation mechanism.

[0193] The first lowpass filter 150 is configured to modify the frequency spectrum of the first audible warning sound during a rising portion and a falling portion of the first audible warning sound (as discussed in more detail below) in accordance with the methods described herein. The first lowpass filter 150 may be provided as part of the first loudspeaker 130 and is connected to a first filter control unit 152 configured to adjustably control a passband of the first lowpass filter 150.

[0194] Similarly, the second lowpass filter 155 is configured to modify the frequency spectrum of the second audible warning sound during a rising portion and a falling portion of the second audible warning sound (as discussed in more detail below) in accordance with the methods described herein. The second lowpass filter 155 may be provided as part of the second loudspeaker 135 and is connected to a second filter control unit 156 configured to adjustably control a passband of the second lowpass filter 155.

[0195] The application of the first and / or second lowpass filter 150, 155 to a signal received from the signal unit 110, occurs before said signal is received by an amplifier of the corresponding loudspeaker 130, 135 to ensure that the respective lowpass filter 150, 155 filters the signal before it is amplified to cause the loudspeaker to produce sound. In other words, a received signal is preferably filtered and subsequently amplified, such that the sound produced by the corresponding loudspeaker 130, 135 is produced in accordance with a filtered-then-amplified-signal.

[0196] The horn apparatus 100 of Figure 1 may be suitable for use as part of an AVAS. In AVAS, audible warning sounds may be produced having distinct frequencies. Correspondingly, the first and second loudspeakers 130, 135 of the horn apparatus 100 described herein are also configured to produce sounds having distinct frequencies. For example, the first loudspeaker 130 may produce a first audible warning sound having a first fundamental frequency in the range 380 Hz to 440 Hz (e.g., 400 Hz or 420 Hz), and the second loudspeaker 135 may produce a second audible warning sound having a second fundamental frequency in the range 475 Hz to 550 Hz (e.g., 500 Hz). As will be discussed in more detail below, maintain a low crest factor in the signals used to produce the first and second audible warning sounds improves the efficiency of power transfer from signal power input to acoustic power output and so superposing two signals such that a single loudspeaker 130, 135 produces both audible warning sounds may lead to a reduction in the power transfer efficiency.

[0197] Therefore, it may be beneficial for the horn apparatus 100, as discussed above, to include a first loudspeaker arrangement (including the first loudspeaker 130, the first activation mechanism 140, and the first lowpass filter 150) configured to produce the first audible warning sound, and a second loudspeaker arrangement (including the second loudspeaker 135, the second activation mechanism 145, and the second lowpass filter 155) configured to produce the second audible warning sound.

[0198] As discussed above, in some examples, the first and second activation mechanisms 140, 145 may be a common activation mechanism. In this way, the horn apparatus 100 may be useable as a dual tone horn of a vehicle.

[0199] Figure 2a shows an exemplary vehicle 400 having the horn apparatus 100 of Figure 1 installed in an exemplary configuration in which the horn apparatus 100 is useable as a dual-tone horn with the horn apparatus 100 including a first loudspeaker arrangement (A), and a second loudspeaker arrangement (B) both installed towards a front of the vehicle 400. The configuration of the horn apparatus 100 may be such that a person 7 m in front of the vehicle hears sound at a level of 87 dBA when the horn apparatus is activated by a user of the vehicle 400.

[0200] Figure 2b shows an exemplary vehicle 450 having the horn apparatus 100 of Figure 1 installed in an alternative exemplary configuration in which the horn apparatus 100 is useable as an AVAS that produces different audible warning sounds from separate locations of the vehicle 450. In particular, the first loudspeaker arrangement (A) configured to produce a low-town audible warning sound (e.g., having a fundamental frequency of 420 Hz) is installed towards a front of the vehicle 420, while the second loudspeaker arrangement (b) configured to produce a higher-tone audible warning sound (e.g., having a fundamental frequency of 500 Hz) is installed towards a rear of the vehicle 450. In this way, the first loudspeaker arrangement (A) may be useable as part of a vehicle horn operable by pressing a first activation mechanism 140 mounted in the steering wheel of the vehicle, while the second loudspeaker arrangement (B) may be useable as an audible indicator that the vehicle 450 is reversing (in addition to being useable as part of the same vehicle horn as the first loudspeaker arrangement (A)), operable by the user of the vehicle 450 putting the car into reverse-gear. In some such contexts (but not all), while the first loudspeaker arrangement (A) may be configured to produce a first audible warning sound that is hearable at a distance of 7 m with an amplitude of 87 dBA, the second audible warning sound produced by the second loudspeaker arrangement (B) may be quieter, thereby reducing the power consumption requirements of the horn apparatus 100. This may, for example, be a result of the second loudspeaker arrangement (B) being less efficient than the first loudspeaker arrangement (A) - e.g., due to using a smaller magnet unit in the second arrangement (B) relative to the first arrangement (A).

[0201] In some examples of both the vehicles 400, 450 depicted in Figures 2a and 2b and discussed above, activation of the first loudspeaker arrangement (A) to produce the first audible warning sound may simultaneously cause activation of the second loudspeaker arrangement (B) to simultaneously produce the second audible warning sound such that a dual-tone audible warning sound is produced. Even in examples such as that shown in Figure 2b where the second loudspeaker arrangement (B) is installed towards a rear of the vehicle 450, the second audible warning sound (despite being quieter than the first audible warning sound) may still contribute to the duality of the tone of the overall audible warning sound.

[0202] Figure 3a shows one period of the steady state of an exemplary signal representative of an audible warning sound, having a fundamental frequency of 410 Hz. The signal is a recording of a conventional bell-type vehicle horn. The signal(s) provided by the signal unit 110 of the horn apparatus 100 are defined by a waveform that is constructed / generated / selected to cause the first / second loudspeaker 130, 135 to produce an audible warning sound that mimics the tonality / quality of the time signal depicted in Figure 3a.

[0203] Figure 3b shows a frequency spectrum corresponding to the sound signal of Figure 3a. Mimicking the tonality / quality of the time signal may involve providing a signal that produces an audible warning sound having a similar (or same) frequency spectrum as that shown in Figure 3b.

[0204] Figure 3c shows the onset of an exemplary warning sound produced by a conventional bell-type vehicle horn of which Figure 3a shows a steady state period. As can be seen from the graph of Figure 3c, the output is steadily increasing with progressively higher amplitudes during an onset of the audible warning sound up to a maximum steady-state amplitude.

[0205] Figure 3d shows a build-up of harmonic orders over the production of the audible warning sound depicted in Figure 3c. Figure 3d demonstrates the significant impact of onset transients in the tonality / quality of the produced audible warning sound. In particular, in the context of bell-type vehicle horns, the high quality factor of their mechanical and acoustic resonances in the bell means that time is needed to build up the amplitude of higher harmonics (i.e., harmonics of the fundamental frequency of the audible warning sound). During onset of the audible warning sound, it takes several cycles of a period corresponding to the fundamental frequency (e.g., for a fundamental frequency of 410 Hz, the period is 2.44 ms) for the signal to reach its steady-state frequency spectrum. During the initial transient onset period (e.g., approximately the first 20 ms of the audible warning sound), the waveform of the acoustic output morphs from a quiet, almost sinusoidal state to the asymmetric pulse train depicted in Figures 3a and 3c having sharp spikes in amplitude with portions of relative silence therebetween. As can be seen from Figure 3d, higher-order harmonics build up more slowly than lower-order harmonics and the rate of increase in amplitude of each harmonic is neither the same nor necessarily constant (or even monotonic - for example, as can be seen from Figure 3d, the tenth harmonic exhibits some initial oscillatory behaviour in its amplitude).

[0206] The development of the frequency spectrum of the audible warning sound of Figure 3c can also be demonstrated by considering the development of the one-third octave band spectrum over time, as shown in Figure 4.

[0207] Figure 4 shows that at the onset of the audible warning sound, only the fundamental harmonic is activated, and that the transient frequency spectrum (after 5 cycles at e.g., 12 ms) qualitatively differs significantly from the steady-state frequency spectrum (e.g., that is achieved after 10 cycles at e.g., 24 ms and 30 cycles at e.g., 72 ms).

[0208] It is an objective of the methods and systems described herein to provide a digital signal that is useable by the first / second loudspeaker 130, 135 to produce an audible warning sound that mimics the tonality / quality of audible warning sounds produced by bell-type vehicle horns (such as that discussed above in relation to Figures 3 and 4).

[0209] To improve the quality of the sound produced by the first / second loudspeaker 130, 135, a high power transfer between an amplifier (or the signal unit 110) of the horn apparatus 100 and the first / second loudspeaker 130, 135. In the context of digital signal transfer, high power transfer is achievable by ensuring that the signal has a high PAPR (i.e. , a low crest-factor).

[0210] For this reason, digital recordings of traditional air trumpet car horns (such as shown in Figure 3a) are unsuitable for use in the horn apparatuses 100 described herein. The crest factors of such digital recordings are typically high (e.g., on the order of 16 dB). As an example, for a peak voltage of 12 V and a nominal loudspeaker impedance of 4 Q, the peak power output of the horn apparatus 100 would be 36 W. In such a system, playing back a signal with a crest factor of 16 dB would result in as little as 0.9 W of power transfer between an amplifier and the loudspeaker of such a system.

[0211] It may therefore be desirable to provide a signal that is defined by a waveform whose profile shape is selected to reduce (or even minimise) the crest factor of the signal. As an example, a crest factor of OdB may provide an ideal (i.e., a most efficient possible) power transfer, and consequently a highest quality output from the horn apparatus.

[0212] An ideal square-wave waveform profile has a crest factor of 0 dB. As such, it may be beneficial for the signal provided by the signal unit 110 to be defined by a square-wave waveform profile.

[0213] Figure 5a depicts an exemplary waveform 502 useable to define the signal 500 provided by the signal unit 110 to the first / second loudspeaker 130, 135 to produce an audible warning sound that mimics the tonality / quality of audible warning sounds produced by conventional bell-type vehicle horns (such as that discussed above in relation to Figures 3 and 4). The signal 500 is defined by a square-wave waveform 502 having a series of positive peaks 504 and a series of negative peaks 506. The amplitude of the each of the positive peaks 504 is a common positive amplitude. The amplitude of each of the negative peaks 506 is a common negative amplitude. The magnitude of the common positive amplitude is the same as the magnitude of the common negative amplitude. The period of the waveform 502 corresponds to a fundamental frequency of 420 Hz and is sampled with a sampling frequency of 44.1 kHz - i.e., the waveform is defined by 106 samples.

[0214] To increase the acoustic output of an audible warning sound produced by a loudspeaker 130, 135 in accordance with the signal 500, it is beneficial for the signal to have an average amplitude (over the full period of the waveform 502) of zero, or approximately zero - as discussed above.

[0215] In the case of the signal 500 shown in Figure 5a, the average amplitude of the waveform 502 is zero, and the crest factor is also zero (because the waveform 502 has a perfect square-wave wave profile.

[0216] Figure 5b shows a frequency spectrum corresponding to the signal 500 of Figure 5a. As can be seen from Figure 5b, In the frequency spectrum of the square wave signal 500 shown in Figure 5a mimics the frequency spectrum of the analogue horn sound depicted in Figure 3b. That is, the frequency spectrum of an audible warning sound produced in accordance with the signal 500 of Figure 5a is markedly similar to the frequency spectrum shown in Figure 3b, meaning that the tonality / quality of the audible warning sound produced in accordance with the signal 500 (as perceived by a person that hears the sound) is very similar to the sound perceived by a person that hears an audible warning sound produced by a conventional vehicle horn apparatus..

[0217] Additionally, the efficiency of converting electrical input to acoustic output using the signals such as the signal 500 depicted in Figure 5a is particularly high. Taking the example discussed above of a peak voltage of 12 V and a nominal loudspeaker impedance of 4 Q, the zero-value of the crest factor of the signal 400 means that the theoretical power transfer from electrical input to acoustic output is the full 36 W. Even taking into account losses associated with converting the signal 500 from the digital domain to the analogue domain, power transfers of over 80% of peak-voltage to transferred-power (e.g., 30 W of power in the acoustic output) are still achievable - significantly greater than the 2.5% transfer (0.9 W) that is achievable when simply using digital recordings of conventional vehicle horn apparatuses.

[0218] To further improve the recognisability of an audible warning sound produced in accordance with the signal 500 of Figure 5a, it is beneficial to also mimic the transient behaviour of an audible warning sound (e.g., in the rising portion and falling portion of the audible warning sound) of a conventional vehicle horn apparatus. To do this, an amplitude envelope needs to be applied to the signal 500 such that the amplified of successive repetitions of the waveform 502 is amplified to a different level corresponding to the envelope.

[0219] Figure 6 shows an exemplary envelope 600 that is applicable to the signal 500 of Figure 5a to produce an audible warning sound (in accordance with the combination of the envelope 60 and the signal 500) that mimics the tonality / quality of the audible warning sound produced by a conventional vehicle horn apparatus (e.g., the audible warning sound discussed above in relation to Figures 3a to 3d). The envelope 600 comprises a rising portion 602, a steady-state portion 604, and a falling portion that correspond to a rising portion, a steady-state portion, and a falling portion of a produced audible warning sound.

[0220] The rising portion 602 of the envelope 600 lasts for approximately 0.19s (i.e., the steady-state portion 504 is reached after approximately 0.19 s).

[0221] In addition to the amplitude envelope 600, a frequency-modifying component (e.g., the first / second lowpass filter 150, 155) can be used (e.g., adjustably controlled through the operation of a corresponding filter control unit 152, 156) to modify the frequency spectrum of an audible warning sound produced in accordance with the signal 500 to more accurately mimic the transient portion of the frequency spectrum shown in Figure 3b.

[0222] For example, at the onset of the envelope 600 - when applied to the signal 500 of Figure 5a having a period that corresponds to a fundamental frequency of 420 Hz - a lowpass filter 150, 155 having a cut-off frequency of 400 Hz is deployed to reduce the high-frequency content of the signal 400. In other words, the lowpass filter 150, 155 is used to suppress the production of higher-order harmonics in the audible warning sound that is produced in accordance with the signal 500 of Figure 5a. As time progress through the rising portion 602 of the envelope 600, the lowpass filter 150, 155 is adjustably controlled (e.g., via the corresponding filter control unit 152, 156) to gradually ramp up the cut-off frequency of the lowpass filter 150, 155 up to a higher frequency (e.g., 14 kHz), thereby reducing the suppression of higher-order harmonics and allowing the amplitude of each of these higher-amplitude harmonics to build up to a respective steady-state amplitude in the steady-state portion 604 of the audible warning sound / envelope 600. Finally, during the falling portion 606, the cut-off frequency of the lowpass filter 150, 155 is gradually ramped back down to a lower cut-off frequency (e.g., the original 400 Hz cut-off frequency) to suppress higher-order harmonics during the falling portion 606 of the audible warning sound / envelope 600.

[0223] Figure 7 shows a schematic of an exemplary operation of the horn apparatus 100 of Figure 1 in a dualtone configuration, wherein the first and second audible warning sounds are produced using signals 500 such as that shown in Figure 5a and envelopes 600 such as that shown in Figure 6.

[0224] As can be seen from Figure 7, both the first and second audible warning sounds include a respective first and signal altered by corresponding envelopes (which may be a common envelope), each envelope having a rising portion, a steady-state portion, and a falling portion.

[0225] In the example of Figure 7, the falling portion of the audible warning sounds is triggered by a user of the vehicle 400, 450 ceasing to operate the activation mechanism(s) 140, 145 of the horn apparatus 100. Accordingly, a brief activation of the horn apparatus 100 may produce an audible warning sound in which the steady-state portion is never reached. This may, therefore, lead to an audible warning sound that sounds muffled or damped, in the same way as is done with conventional vehicle horns. In other words, the application of the envelope having rising, steady-state, and falling portions facilitates the faithful mimicry of even the transient acoustic behaviour of conventional vehicle horns. Figure 8a shows the onset of a digital time signal produced by the horn apparatuses 100 described herein in accordance with the combined signal 500 and envelope 600 as described above.

[0226] It can be seen from Figure 8a that, as a result of the harmonic suppression by the lowpass filter 150, 155 the shape of the waveform of the audible warning sound is rounded at the immediate onset of the audible warning sound and that, as the rising portion 602 progresses to the steady-state portion 604 of the envelope 600, the steady-state square-wave waveform 502 is eventually reached, wherein the steadystate square-wave waveform 502 is not modified by the transient adjustments applied to the lowpass filter 150, 155 during the rising portion 602 of the envelope 600.

[0227] Figure 8b shows the corresponding build-up of harmonics during the onset of the signal shown in Figure 8b. As can be seen from Figure 8b, even with relatively simple adjustable control of a lowpass filter 150, 155, it is possible to mimic the broad trends of harmonic onset heard in audible warning sounds produced by conventional horn apparatuses (as can be seen e.g., by comparing Figure 8b with Figure 3b).

[0228] Similarly, Figure 9 shows the evolution of the one-third octave band spectrum during the onset of the signal, as shown in Figure 8a, at the same time points as shown in Figure 4. As with the comparison of Figure 8b with Figure 3b, a comparison of Figure 9 with Figure 4 clearly shows that the broad trends of harmonic onset heard in audible warning sounds produced by conventional horn apparatuses can be mimicked using the horn apparatuses 100 and methods described herein. Moreover, replication of more complex harmonic onset (e.g., the oscillatory onset of the tenth harmonic seen in Figure 3) can be achieved with more nuanced frequency control using a more finely controllable frequency modifying component, or combination of frequency modifying components to further enhance the quality of the mimicry.

[0229] There are many possible methods of synthesising (or generating) the signal 500 shown in Figure 5a, or another signal that is also suitable for use by the horn apparatuses 100 described herein to produce an audible warning sound that mimics the tonality / quality of an audible warning sound produced by a conventional vehicle horn apparatus. Importantly, there are many possible (or candidate) waveforms 502 that may be suitable for defining a signal 500 that is useable to produce an audible warning sound that mimics the tonality / quality of an audible warning sound produced by a conventional vehicle horn apparatus, provided each of the candidate waveforms share the common features of alternating between respective positive peaks and respective negative peaks multiple times within a period corresponding to the fundamental frequency of the audible warning sound, wherein a time between each alternation of the waveform varies across the period.

[0230] However, it is important to note that there are a wide variety of waveforms 502 that may satisfy this profile definition and that some candidate waveforms may be more suitable for mimicking particular conventional vehicle horn apparatuses than other candidate waveforms. Consideration may therefore need to be given to methods of generating / synthesizing candidate waveforms and one or more criteria that may need to be satisfied by the candidate waveform in some examples and circumstances. For example, the signal 500 may be defined by a waveform 502 that is digitally defined using e.g., 80 samples at a suitable sampling frequency. Generating the wave may be done in multi-sample segments of e.g., 5 samples such that the waveform 502 is defined by 16 segments.

[0231] To ensure that the time between each peak-to-peak alternation varies across the period corresponding to the fundamental frequency of the audible warning sound, the signal 500 may be generated by randomly assigning each of the 16 segments of the signal the (common) positive amplitude or the (common) negative amplitude. In this way, the time between each alternation between a positive peak and a negative peak of the waveform 502 may be randomly (or pseudo-randomly) varied across the period corresponding to the fundamental frequency of the audible warning sound.

[0232] Generating the waveform profile in this way may be particularly susceptible to efficient encoding and storage. For example, the waveform profile may be digitally encoded as a 16-digit binary number wherein each segment that is assigned the (common) positive amplitude is encoded with a T and each segment that is assigned the (common) negative amplitude is encoded with a ‘O’. In this way, a 16-digit binary string may fully define the waveform profile by highlighting where the waveform alternates from a positive peak to a negative peak (i.e., when the portion of the binary string reads ‘...10 ...’) or vice versa (i.e., when the portion of the binary string read ‘...01 ...’).

[0233] The 16-digit binary string may further be encoded into hexadecimal format to further improve the storage and encoding efficiency as a 16-digit binary string can be converted straightforwardly into a 4-digit HEX number, as described above.

[0234] However, due to the potentially random nature with which the candidate waveforms may be synthesized (or generated), one or more criteria may be applied to ensure the suitability of each candidate waveform for use by the horn apparatuses 100 described herein to produce an audible warning sound that mimics the tonality / quality of a particular conventional vehicle horn apparatus (or, indeed, any other reference sound).

[0235] In other words, it may be advantageous to consider one or more (predetermined) suitability criteria and rejecting / discounting those candidate waveforms that do not satisfy one or more of those (predetermined) suitability criteria.

[0236] The criteria may, for example, include a criterion related to the relative amplitudes of one or more of the harmonics of the frequency spectrum of the signal. For example, in some cases, the predetermined criteria may include a criterion that the amplitude of the second harmonic in a frequency spectrum of the signal must be greater than the amplitude of the fundamental frequency in the frequency spectrum of the signal.

[0237] The predetermined criteria may, for example, include a requirement that a certain number of amplitude thresholds in one or more frequency bands are met. For example, the predetermined criteria may include a requirement that at least a predetermined number of a set of frequency bands of the signal have an amplitude that exceeds an amplitude criterion threshold. In some examples, the predetermined criteria may relate to an amplitude of e.g., three frequency bands of the signal (for example three frequency bands in the one-third octave frequency spectrum of the signal). In such examples, the predetermined criteria may be that the amplitude in at least one, at least two, or at least three of the frequency bands exceeds a respective amplitude criterion threshold. In some examples, the amplitude criterion threshold may be the same for each of the plurality of frequency bands.

[0238] In some examples, the three frequency bands may be frequency band in the one-third octave frequency spectrum of the signal and nay be the 2 kHz band, the 2.5 kHz band, and the 3.15 kHz band. The amplitude criterion threshold may be that the amplitude of at least one of the bands, at least two of the bands, or all the bands must exceed -20 dB. In particular examples, the predetermined criteria may include a requirement that the amplitude of each of the 2 kHz band, the 2.5 kHz band, and the 3.15 kHz band have an amplitude exceeding -20 dB.

[0239] In some examples, the predetermined criteria may include a requirement that the average amplitude of the waveform across the period is zero.

[0240] Figure 10a shows an exemplary waveform (different from that shown in Figure 5a) that satisfies the criteria of: (i) the average amplitude of the waveform across the period corresponding to the fundamental frequency is zero; (ii) having an amplitude of the second harmonic being greater than an amplitude of the fundamental frequency component; and (iii) the amplitude of each of the 2 kHz band, 2.5 kHz band and 3.15 kHz band in the one-third octave band frequency spectrum exceeds -20 dB. The meeting of criterion (i) can be deduced from the signal amplitude depicted in Figure 8a; the meeting of criterion (ii) can be deduced from Figure 10b, which shows a frequency spectrum corresponding to the signal of Figure 10a, and the meeting of criterion (iii) can be deduced from Figure 10c, which shows a one-third octave band spectrum of an audible warning sound having the frequency spectrum of Figure 10b.

[0241] Figure 11 a shows an alternative exemplary waveform (different from that shown in Figures 5a and 10a) that satisfies criteria (i) to (iii) above. The meeting of criterion (i) can be deduced from the signal amplitude depicted in Figure 11 a; the meeting of criterion (ii) can be deduced from Figure 11 b, which shows a frequency spectrum corresponding to the signal of Figure 11 a, and the meeting of criterion (iii) can be deduced from Figure 11 c, which shows a one-third octave bad spectrum of an audible warning sound having the frequency spectrum of Figure 11 b.

[0242] Meanwhile, Figure 12a shows an exemplary waveform that does not satisfy criterion (ii) above. While criteria (i) and (iii) may be met (as can be deduced from the signal amplitude depicted in Figure 12a for criterion (i) and from Figure 12c, which depicts the one-third octave band spectrum of an audible warning sound having the frequency spectrum shown in Figure 12b for criterion (iii)), it is clear from Figure 12b, which depicts a frequency spectrum corresponding to the signal of Figure 12a that the amplitude of the fundamental frequency component of the signal is greater than the amplitude of the second-harmonic frequency component.

[0243] Similarly, Figure 13a shows an exemplary waveform that does not satisfy criteria (i) or (iii) above. While criterion (ii) may be met (as can be deduced from Figure 13b, which shows a frequency spectrum corresponding to the signal of Figure 13a), it is readily deducible from Figure 13a that the waveform has a non-zero average amplitude over a period corresponding to a fundamental frequency of the audible warning sound producible in accordance with the signal defined by the waveform. As such, criterion (i) is not satisfied. Further, it can be seen from Figure 13c, which shows a one-third octave band spectrum of an audible warning sound having the frequency spectrum of Figure 13b, that the amplitude of the 2 kHz one-third octave band is less than -20 dB, and therefore criterion (iii) is also not satisfied.

[0244] As such, when synthesising one or more candidate waveforms, waveforms such as those described above in relation to Figures 12 and 13 may be rejected for failing to satisfy all of criteria (i) to (iii), while waveforms such as those described above in relation to Figures 5, 10 and 11 may be retained for possible selection because they do satisfy all of criteria (i) to (iii). Those candidate waveforms that satisfy all of criteria (i) to (iii) may be available for selection by a processor (e.g., a processing unit 112 of the signal unit 110 of the horn apparatus 100) for use in defining the signal that is useable by the loudspeaker 130, 135 of the horn apparatus 100 to produce an audible warning sound (that preferably mimics the tonality / quality of an audible warning sound produced by a conventional vehicle horn apparatus).

[0245] Figure 14 shows a method of providing a signal for use by a horn apparatus 100 of a vehicle 400, 450 to produce an audible warning sound (that mimics an audible warning sound producible by a conventional vehicle horn).

[0246] The method comprises, in an operation 702, providing one or more different candidate waveforms. The one or more candidate waveforms may be provided by generating one or more of the candidate waveforms (e.g., by using the methods described above) and / or by retrieving one or more of the candidate waveforms e.g., from a storage unit such as the storage 120 of the horn apparatus 100, the cloud-based storage 210 of the cloud server 200 or the remote storage 310 of the remote computing device 300.

[0247] The method further comprises, in an operation 704, comparing each candidate waveform with a set of criteria, e.g., a set of predetermined suitability criteria indicative of whether a given candidate waveform is suitable for use in defining a signal that is useable by the horn apparatus 100 to produce an audible warning sound (in accordance with said signal) that mimics the tonality / quality of an audible warning sound producible by a particular conventional vehicle horn.

[0248] The criteria may, for example, include any one or more of the criteria described above.

[0249] The comparing against a set of criteria may, for example, include a comparison of a frequency spectrum associated with each candidate waveform with a reference frequency spectrum. The reference frequency spectrum may be characteristic of a particular audible warning sound producible by a particular conventional vehicle horn.

[0250] The method further comprises, in an operation 706, selecting a candidate waveform that satisfies the set of criteria to be the waveform that defines a signal.

[0251] Operations 704 and 706 may be implemented, in some examples, as a two-stage filtering process. For example, in a first stage, the criteria described above (e.g., criteria (i) to (iii) described above in relation to Figures 10 to 13) may be considered and those candidate waveforms that do not satisfy the set of criteria may be filtered out, discarded, or otherwise removed from consideration. In a second stage of the filtering process, all those candidate waveforms that satisfy all of the criteria described above may be subject to frequency analysis in which a respective frequency spectrum is generated from each candidate waveform (e.g., by carrying out an appropriate Fourier transform algorithm such as an FFT) and compared with a reference frequency spectrum indicative of a frequency spectrum of an audible warning sound that the user of the methods described herein wants to mimic with the horn apparatus 100.

[0252] Subsequently, the waveform amongst the one or more candidate waveforms in the second stage of the two-stage filtering process whose frequency spectrum most closely matches the reference frequency spectrum.

[0253] Comparing two frequency spectra may, for example, involve comparing the Fourier transforms of the two corresponding signal by any suitable method (e.g., a suitably trained comparison algorithm).

[0254] The method further comprises using the selected waveform to define the signal.

[0255] The method may further comprise, in an operation 708, storing the signal in a storage medium 120, 210, 310 that is accessible by the horn apparatus 100.

[0256] The method further comprises, in an operation 710, providing the signal to a loudspeaker 120, 125 of the horn apparatus 100 so that the loudspeaker 120, 125 can produce an audible warning sound in accordance with the signal. Providing the signal to the loudspeaker may be carried out in response to a user of the horn apparatus 100 operating an activation mechanism 140, 145 that triggers the production of the audible warning sound by the corresponding loudspeaker 120, 125.

[0257] ***

[0258] 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.

[0259] 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.

[0260] 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.

[0261] Any section headings used herein are for organizational purposes only and are not to be construed as limiting the subject matter described.

[0262] 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.

[0263] 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.

[0264] 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.

[0265] 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%.

Claims

Claims:1 . A horn apparatus for a vehicle, the horn apparatus being configured to produce an audible warning sound having a fundamental frequency, wherein the horn apparatus comprises: a signal unit configured to provide a signal defined by a waveform that alternates between a positive peak and a negative peak of the waveform multiple times within a period corresponding to the fundamental frequency of the warning sound; and a loudspeaker configured to produce an audible warning sound based on the signal provided by the signal unit, wherein a time between each alternation of the waveform varies across the period.

2. The horn apparatus according to claim 1 , wherein the waveform is a square-wave waveform.

3. The horn apparatus according to claim 1 or 2, wherein each positive peak of the waveform has a common positive amplitude, and / or wherein each negative peak of the waveform has a common negative amplitude.

4. The horn apparatus according to any preceding claim, wherein an average amplitude of the waveform across the period is zero.

5. The horn apparatus according to any preceding claim, wherein a peak-to-average power ratio of the waveform across the period is 2 dB or less.

6. The horn apparatus according to any preceding claim, wherein the signal unit is configured to retrieve the signal from a storage medium, wherein the signal is optionally stored in the storage medium as a 16-digit binary number and / or as a 4-digit HEX number that is an encoding of the signal.

7. The horn apparatus according to any of claims 1 to 5, wherein the signal unit is configured to generate the signal.

8. The horn apparatus according to any preceding claim, further comprising: an activation mechanism operable by a user of the vehicle, wherein the loudspeaker is configured to produce the audible warning sound in response to the activation mechanism being operated by the user of the vehicle.

9. The horn apparatus according to any preceding claim, wherein the audible warning sound includes: a rising portion in which the amplitude of the audible warning sound increases to a maximum amplitude; and / or a falling portion in which the amplitude of the audible warning sound decreases to a minimum amplitude.

10. The horn apparatus according to claim 9, further comprising: a frequency modifying component configured to modify the frequency spectrum of the signal during the rising portion and / or falling portion of the audible warning sound.

11. The horn apparatus according to claim 10, wherein the frequency modifying component is a lowpass filter.

12. The horn apparatus according to any preceding claim, wherein the fundamental frequency is between 320 Hz and 480 Hz, or between 400 Hz and 600 Hz.

13. The horn apparatus according to any preceding claim, wherein the audible warning sound is a first audible warning sound, the fundamental frequency is a first fundamental frequency, and wherein the horn apparatus is further configured to produce second audible warning sound, having a second fundamental frequency, at the same time as the first audible warning sound wherein the signal is a first signal, the waveform is a first waveform, the period is a first period, and wherein the signal unit is further configured to provide a second signal, corresponding to the second audible warning sound, the second signal being defined by a second waveform that alternates between a corresponding positive peak and a corresponding negative peak of the second waveform multiple times within a second period corresponding to the second fundamental frequency of the second audible warning sound, wherein a time between each alternation of the second waveform varies across the respective period, and wherein the loudspeaker is a first loudspeaker, and wherein the horn apparatus further comprises: a second loudspeaker being configured to produce the second audible warning sound based on the second signal provided by the signal unit.

14. The horn apparatus according to claim 13, wherein the first and second audible warning sounds are respectively different audible warning sound.

15. The horn apparatus according to claim 13 or 14, wherein the activation mechanism is a first activation mechanism, and wherein the horn apparatus further comprises: a second activation mechanism operable by a user of the vehicle, wherein the second loudspeaker is configured produce the second audible warning sound in response to the either the first or second activation mechanism being operated by the user of the vehicle..

16. The horn apparatus according to any preceding claim, wherein the horn apparatus is operable as an Acoustic Vehicle Alerting System.

17. A method of providing a signal for use by the horn apparatus of any preceding claim to produce an audible warning sound, the method comprising: providing a signal defined by a waveform that alternates between a positive peak and a negative peak of the waveform multiple times within the period corresponding to the fundamentalfrequency of the audible warning sound, wherein a time between each alternation of the waveform varies across the period, wherein the square-wave waveform defines the signal.

18. The method according to claim 17, wherein providing the signal comprises: providing one or more different candidate waveforms, wherein each candidate waveform is a respective waveform that alternates between a respective positive peak and a respective negative peak of said waveform multiple times within a period corresponding to the fundamental frequency of the audible warning sound, wherein a time between each alternation of said waveform varies across the period; comparing each candidate waveform with a set of predetermined criteria; and selecting a candidate waveform that satisfies the predetermined criteria from amongst the plurality of different candidate waveforms as the waveform to define the signal.

19. The method according to claim 18, wherein comparing each candidate waveform with the set of predetermined criteria includes: comparing a respective frequency spectrum of each candidate waveform with a reference frequency spectrum associated a sound produced by a bell-type vehicle horn; and selecting a candidate waveform, from amongst the plurality of different candidate waveforms, whose respective frequency spectrum most closely matches the reference frequency spectrum.

20. The method according to any of claims 17 to 19, wherein providing the or each waveform comprises: retrieving the or each waveform from a memory, wherein the or each waveform is optionally encoded in the memory as a 16-digit binary number and / or as a 4-digit HEX number.

21. The method according to any of claims 17 to 19, wherein providing the or each waveform comprises: generating the or each waveform.

22. The method according to any of claims 17 to 21 , the method further comprising: storing the signal in a storage medium accessible by the horn apparatus, wherein the signal is optionally stored in the storage medium as a 16-digit binary number and / or as a 4-digit HEX number that encodes the signal.

23. A computer-readable medium comprising instructions that, when executed by a computer, cause the computer to carry out the method of any of claims 17 to 22.

24. A computer program product comprising logic that, when executed by a processor, causes the processor to carry out the method of any of claims 17 to 22.

25. A signal for use by the horn apparatus according to any of claims 1 to 16 to produce an audible warning sound having a fundamental frequency, wherein the signal is defined by a waveform that alternates between a positive peak and a negative peak of the waveform multiple times within a period corresponding to the fundamental frequency of the warning sound, wherein a time between each alternation of the waveform varies across the period.

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