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Measurement of Loudspeakers with a Laser Doppler Vibrometer and the Exponential Sine Sweep Excitation Technique
摘要： This paper presents an experimental study of vibrations of the cone of loudspeakers. Measurements of the axial acceleration have been performed in hundreds of points on the surface of the cone employing a Laser Doppler Vibrometer and using the exponential sine sweep excitation signal. The recorded signal has been transformed into an impulse response by convolution with the matched inverse sweep signal. From the knowledge of the acceleration in each point of the radiating surface, the free field sound pressure in axis at 1 m distance has been computed. The research focuses on obtaining results comparable to FEM simulations based only on the linear mechanical behavior of the loudspeaker cone and avoiding any acoustic interference. Moreover, comparing the laser measurements of many samples, the authors seek to evaluate the influence of known variations in the loudspeaker components or production process on the final performances of the device. Post-processing of experimental results is carried out employing a Matlab script, which also computes operational deflection shapes of the loudspeaker cone.
关键词： loudspeaker vibrations,exponential sine sweep,accumulated acceleration level,sound pressure level,Laser Doppler Vibrometer
更新于2025-09-19 17:13:59
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Measurement of the local sound pressure on a Bias-flow liner using high-speed holography and tomographic reconstruction
摘要： Bias-?ow liners (BFL) are used as part of the cooling mechanism in airplane turbines and they also enable the reduction of noise emission. The attenuating principle is based on the interaction between sound waves and air ?ow. This turbulent aeroacoustic interaction occurs on a microscopic level and under harsh conditions. Therefore, in order to investigate local aeroacoustic phenomena, the distribution of the local sound ?eld impedance, de?ned as sound pressure over acoustic particle velocity, is measured non-invasively. This work focuses on the non-invasive measurement of the local sound pressure. A fast camera-based holographic measurement system for the two dimensional tomographic measurement of the local sound pressure with high spatial resolution is presented. It features a spatial resolution of 52 μm with a simultaneous acquisition of up to 1600 measuring points. This enables the observation of sub-mm aeroacoustic effects, which are expected in the near ?eld over the BFL’s surface, while reducing the measurement duration by three orders of magnitude compared to single point measurement systems. An experimental validation of the camera-based tomographic system is carried out by reference measurements. The system was applied at an acoustical model and an aeroacoustic model. The measured local sound pressure variations are discussed for both models. This work seeks to enable the non-invasive investigation of sound pressure, in order to further understand aeroacoustic effects, their sound attenuating properties and increase the attenuation capability of a BFL without degrading the overall performance of turbines.
关键词： optoacoustics,bias-?ow liner,Flow measurement,tomography,sound pressure,aeroacoustic attenuation
更新于2025-09-16 10:30:52
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Feasibility of using acoustic method in monitoring the penetration status during the Pulse Mode Laser Welding process
摘要： In this paper, the feasibility of using acoustic method to monitor the depth of penetration was investigated by determine the characteristic of the acquired sound throughout the pulse mode laser welding process. To achieve the aim, the sound signal was acquired during the pulsed laser welding process on the 2 mm structural carbon steel plate. During the experiment, the laser peak power and pulse width was set to be varied while welding speed was constantly at 2 mm/s. Result from the experiment revealed that the sound pressure level of the acquired sound was linearly related to the pulse energy as well as the depth of penetration for welding process using 2ms pulse width. However, as the pulse width increase, the sound pressure level show insignificant change with respect to the change in the depth of penetration when the pulse energy reaches certain values. The reported result shows that this was happen due to the occurrence of spatter which suppressed the information associated with the generation of plasma plume as the product of high pulse energy. In this work, it was demonstrated that in some condition, the acoustic method was found to be potentially suitable to be used as a medium to monitor the depth of weld on online basis. To increase the robustness of this method to be used in wider range of parameter, it was believed that some other post processing method is needed in order to extract the specific information associated with the depth of penetration from the acquired sound.
关键词： depth of penetration,acoustic method,sound pressure level,plasma plume,pulse mode laser welding
更新于2025-09-11 14:15:04