Design of electric vehicle warning sound systems to minimise drive-by noise

Electric and hybrid-electric vehicles are required to emit artificial warning sounds at low speeds, as their quiet operation poses a potential hazard for vulnerable road users. At the same time, concerns have been expressed over the increase in environmental noise levels this measure might bring. This thesis aims to design a warning sound system that can both fulfil its role as a safety measure while minimising its noise contribution. In addition, the proposed system must be viable for a wide scale implementation by keeping the manufacturing and maintenance costs low, and ensuring that it is physically robust for long-term operation within a vehicle. For this purpose, a directional sound system based on structural vibration has been designed, utilising an array of inertial actuators forcing the structure upon which they are attached to vibrate and radiate a sound field of controllable directivity. An analytical model was formulated to describe the physical system, combining existing models of structural vibration and sound radiation. A simulations-based parametric study performed using this model provided insight into the design parameters, indicating that a larger number of actuators distributed evenly along the entire radiating surface ensures the greatest possible bandwidth and steerability for the system. The construction and measurement of a simple physical prototype system allowed for the experimental validation of the analytical model. The proposed system was evaluated in its intended implementation by installing the array in a test vehicle and measuring the directivity of the radiated sound field for different arrangements of the actuators on the vehicle. Experimental results indicated that an actuator array installed in the bumper of the vehicle can achieve directivity of at least 10 dB in terms of acoustic contrast level, for a bandwidth from 300 Hz to 5 kHz, while minimising interior and drive-by noise. An additional approach to reducing the impact of warning sounds was also investigated, in the form of an environmentally adaptive warning sound system. The proposed system employs an algorithm that estimates the auditory thresholds due to a changing sonic environment, and uses this information to adapt the warning sound. This aims to render the vehicle detectable in all environments without unnecessarily increasing its level, therefore limiting noise pollution. The adaptation algorithm was tested in a simulation-based application study for a variety of environmental noise scenarios, showing that it is capable of selectively adjusting the output of the warning sound at specific frequency bands to match the audibility threshold

An environmentally adaptive warning sound system for electric vehicles

Electric vehicles are quiet at low speeds compared to their internal combustion engine counterparts, leading to regulations on the mandatory use of artificial warning sounds for their detection, as a safety measure for other road users. Arguments against the concept have been voiced focusing on the resulting environmental noise pollution, while at the same time some of the practical implementations have been shown to be somewhat ineffective when tested in an urban environment. To satisfy the need to both minimise noise pollution and ensure that the warning sound is sufficiently audible within any noise environment, an environmentally adaptive warning sound system is conceptualised and investigated. The system employs an adaptation algorithm that estimates the auditory masking thresholds due to a potentially changing sonic environment, and uses this information to adapt the warning sound not only in level, but also in spectral content. The system aims to render the vehicle detectable in both quiet and noisy environments without unnecessarily increasing its overall sound output level, therefore limiting noise pollution. The effectiveness of the adaptation algorithm is tested and evaluated for different auditory filter models and equalisation strategies in a variety of environmental noise scenarios

A system for controlling the directivity of sound radiated from a structure

Directional sound fields can be generated by arrays of multiple sound sources such as loudspeaker drivers. These systems, though potentially capable of high levels of directivity control over a broad bandwidth, may prove prohibitively expensive, fragile, or impracticable in certain applications. To overcome these limitations, this paper presents an investigation into the design and limitations of a directional structural-actuator-based array. This provides an affordable and robust alternative to conventional loudspeakers, particularly when the actuators can be used to radiate via a pre-existing structure and where the required audio quality is lower, or the bandwidth somewhat limited. In the first instance, an analytical model is formulated, and used to perform a simulation-based parametric study, which provides insights into the design trade-offs. Based on this study, a physical prototype is constructed using six actuators and a flat panel, which enables the model to be experimentally validated and an evaluation of the directional radiation capabilities of the proposed system to be carried out. Experiments show that the simple analytical model is an effective tool in designing such arrays, predicting the trends in the behaviour of the prototype, and that the structural actuator-based system is capable of controlling directivity within its intended operational bandwidth

Directivity control using a structural actuator array

Directional sound fields can be generated by arrays of multiple sound sources, with the most common and straightforward method being an array of loudspeaker drivers. Although such a system, when appropriately designed, is capable of high levels of directivity control over a broad bandwidth and with good audio quality, it can be prohibitively expensive and too fragile in certain applications. This work presents and investigates the idea of using an array of actuators mounted to a structure to generate a directional sound field. Structural actuators have previously been used as an affordable and robust alternative to conventional loudspeakers, particularly in applications where the actuators can be used to drive a structure that would already be in place to radiate the desired sound field and where the required audio quality is lower. By distributing a number of actuators on a structure, and controlling the relative amplitudes and phases with which they are driven, it is possible to manipulate the structural vibration such that it generates a controlled directional sound field, similar to that resulting from an array of individual sound sources. In this work, an analytical model is first formulated of a rectangular panel excited by an array of structural actuators, which are approximated as point forces acting perpendicularly to the surface of the panel. This model is used to perform a simulation based parametric study, which provides insights into the design trade-offs for a structural actuator array based system. In particular, this considers how the number of actuators, their geometry and the dimensions of the structure influence the directivity control and achievable bandwidth. Based on this parametric study, a structural actuator array is assembled using a rectangular aluminium panel and six actuators. The system is tested and evaluated through measurements in an anechoic chamber

Structural actuator array experiments

Data in support of PhD thesis &quot;Design of Electric Vehicle Warning Sound Systems to Minimise Drive-by Noise&quot;. Awarded University of Southampton, 2020 Acoustic measurements for the structural actuator array, from experiments using the prototype configuration, and the array installed on the bumper of a vehicle.</span

The design of a low-cost directional warning sound system for electric vehicles

Electric vehicle warning sounds are now required by law in many countries due to safety concerns, but this additional noise source may increase unwanted noise pollution. Therefore, the design of an electric vehicle warning sound system that can produce a directional sound field has been investigated. This paper introduces two design suggestions for a system with comparable performance to the conventional loudspeaker array, but at a significantly lower manufacturing and maintenance cost, suitable for wider commercial adoption. The first method utilises a single loudspeaker attached to a length of perforated piping which acts as a directional acoustic radiator, which is analogous to the shotgun microphone. The second approach replaces the standard loudspeaker array with inertial actuators mounted to a vehicle body panel and these are driven to radiate a controlled directional sound field. A simulation based comparison between the suggested configurations and a conventional loudspeaker array of equivalent physical dimensions is presented

A semi-circular microphone array configuration for indoor pass-by noise sound synthesis

status: Published onlin

Investigation of a directional warning sound system for electric vehicles based on structural vibration

Warning sound systems for electric vehicles with advanced beamforming capabilities have been investigated in the past. Despite showing promising performance, such technologies have yet to be adopted by the industry, as implementation costs are generally too high, and the components too fragile for implementation. A lower cost solution with higher durability could be achieved by using an array of inertial actuators instead of loudspeakers. These actuators can be attached directly to the body of the vehicle and thus require minimal design modifications. A directional sound field can then be radiated by controlling the vibration of the panel, via adjustments to the relative magnitude and phase of the signals driving the array. This paper presents an experimental investigation of an inertial actuator-based warning sound system. A vehicle placed in a semi-anechoic environment is used to investigate different array configurations in terms of the resulting sound field directivity and the leakage of sound into the cabin. Results indicate that the most efficient configuration investigated has the actuators attached to the front bumper of the vehicle. Using this arrangement, real-time measurements for different beamformer settings are performed to obtain a thorough picture of the performance of the system across frequency and steering angle