Sound Quality Evaluation of Automotive horn

Mahanta, T K and B, Venkatesham (2018) Sound Quality Evaluation of Automotive horn. PhD thesis, Indian institute of technology Hyderabad.

Full text not available from this repository. (Request a copy)

Abstract

Product Sound Quality (SQ) is one of the desire requirement in product design and customer preferences. Several product manufacturers would like to know their product’s SQ acceptance amongst the customers. One of the several industries which use acoustic products is automobile industry, where automotive horns have a major function. The horn, while being irreplaceable for safe driving has a flip side of being a major source of noise pollution as well. Keeping this in mind, it was attempted to understand and improve the SQ of horn without compromising on its basic functionality and also how it could substantially decrease its contribution to noise pollution. The research aims at proposing a new methodology to evaluate and analyze SQ of automotive horn and its vibro-acoustic analysis. To begin with, few automotive horn samples were recorded using Head Measuring System (HMS-IV). This allowed capturing of sound samples in a process similar to as it would normally occur in a human ear. Then for SQ analysis, two test methodologies namely Subjective and Objective were developed. Subjective test included jury based listening test while Objective method provided quantitative SQ metrics from empirical equations. Extensively used horn models in passenger cars like Disc and Shell horns were considered for this study. A total of twenty-two horn sound samples are judged by thirty participants. In subjective test, three type of tests, namely Relevant Test (RT), Semantic Differential Test (SDT), and Pair Comparison Test (PCT) were developed and performed to evaluate horn SQ. A Graphical User Interface (GUI) was also developed to conduct subjective test. Sound Pressure Level (SPL), a conventional acoustic parameter, cannot describe the sound impact or perceived SQ effectiveness. Hence, it was necessary to study the psychoacoustic objective parameters responsible for SQ. Objective parameters like loudness, sharpness, roughness, fluctuation strength, tonality and index of relative sensory pleasantness were calculated for all samples. As results obtained from both test methods were completely independent there was need to correlate them using Principal Component Analysis (PCA). PCA was performed on objective parameters to obtain appropriate orthogonal (principal) components. Based vii on PCA, a metric profile was computed for each sound. Transformation matrix was calculated based on jury ratings and metrics profile. Jury rating was predicted using transformation matrix and objective parameters. Using this method, subject responses were predicted without performing the actual subject test. Group classification of sound samples was done on basis of objective test using Mahalanobis distance (MD) method and subjective test using Tukey’s method. Finally obtained results were compared. An attempt was made in this study to develop validated vibro-acoustic prediction model for SPL radiated from the disc horn. Modal and Harmonic analysis of the horn were performed using Finite Element Method (FEM) and Acoustic analysis using Boundary Element method (BEM). As known, automotive disc horn works on principle of Electromagnetism. It includes a movable iron core and diaphragm with varying electromagnetic force, which was calculated and used for Harmonic Analysis. From Numerical Modal Analysis, natural frequency and mode shapes results were obtained and compared to experimental modal analysis for validation. Modal Assurance Criteria (MAC) value was calculated for mode shapes obtained from both results. An attempt to study modal parameters of a horn diaphragm with housing, analytically, by simplifying it as circular membrane backed by cylinder cavity was made. It was noticed that natural frequencies of the membrane were influenced by presence of acoustic cavity. This interaction is named as structuralacoustic coupling approach. Here too, uncoupled natural frequencies and coupled natural frequencies obtained are compared to numerical results. A numerical model was developed to obtain vibration responses under electromagnetic force excitations. The actual vibrations were measured experimentally. Then, sound radiation prediction from the horn’s diaphragm was established using BEM. SPL was measured using microphone at 2m distance from the horn’s frontal direction. Sound pressure levels obtained experimentally and by prediction were then compared.

[error in script]

IITH Creators: