Sound Pressure Frequency Response Research Articles

Study on the Characteristics of Trackside Acoustic Flow Field of High-Speed Train under the Influence of Crosswind.

During the on-track acoustic detection process, a potential flow model and an acoustic finite element mathematical model based on synthetic wind are utilized, taking into account the combined effects of vehicle speed, wind direction angle, and crosswind speed. Simulation and modeling are achieved using Automatic Matching of Acoustic Radiation Boundary Conditions (AML) technology, enabling obtaining a distribution map and sound pressure frequency response curve of the trackside acoustic field under crosswind conditions by setting up field point grids. It is found that sound pressure values at the same location gradually increase as the vehicle speed increases in the frequency range of 10 Hz to 70 Hz, at different vehicle speeds. The sound pressure values and distribution area of the trackside acoustic field are the largest when the crosswind speed is 10 m/s (wind force at level five), allowing for easier location of the sound source when a fault occurs. The study also reveals that under different wind direction angles, the same location's sound pressure value on the trackside gradually decreases as the wind direction angle increases, to lower than that of the non-crosswind condition, severely hindering the reception and diagnosis of acoustic signals.

Control of structure-borne noise for a vehicle body by using power flow analysis and acoustic path participation method

This paper is aimed to analyze and control the structure-borne noise of a vehicle body by using the power flow and acoustic path participation method. The modal test is conducted to calibrate the simulation model, and the sound pressure frequency response analysis is carried out to obtain the critical frequencies. The power flow through the interface of the powertrain and vehicle body is analyzed. Then the main paths are identified. Before carrying out an acoustic path participation analysis, the coupled energy of the vibration transfer path was evaluated. For a decoupled vibration system, the sound pressure synthesis method of the multi-path vibration transmission is proposed. The relative errors between the synthetized sound pressure and the finite element calculated sound pressure are small. The interaction mechanisms between the power flow of a path, the acoustic participation of a path and the control characteristics are investigated. The results indicate that, the positive power flow is reduced by pertinently optimizing the stiffness parameters of the engine mounts. The acoustic participation of the corresponding path decreases and the structure-borne noise gets controlled.

Force to sound pressure frequency response measurements using a modified tapping machine on timber floor structures

In recent years, research has shown that the lower frequency portion of impact sound, down to 20 Hz, is of significant importance to residents’ perception in buildings that have lightweight timber floors. At low frequencies, the finite element method is a useful tool for predictive analysis. Impact sound frequency response functions, which are easily calculated using finite element software, are useful as they offer a common ground for studies of correlations between measurements and analyzes. On the measurement side, the tapping machine is well defined and has become the standard excitation device for building acoustics. When using a tapping machine, the excitation force spectrum generated – necessary to achieving experimental frequency force to sound response functions – is unknown. Different equipment may be used for excitation and force measurements and if a structure behaves linearly, the use of any excitation devices should result in the same frequency response functions. Here, an ISO tapping machine hammer is fitted with an accelerometer, enabling estimates of input force spectra. In combination with measurements of the sound in the receiver room, frequency response functions are then achieved using an ISO tapping machine. Various excitation devices have been used on a floor partition in a timber building and on a cross-laminated timber (CLT) lab. floor in order to compare the resulting frequency response functions. Structural nonlinearities are evident, implying that for accurate frequency response measurements in acoustically low frequencies, excitation magnitudes and characteristics that are similar to these which stem from human excitations, should preferably be used.

A study of tyre cavity resonance and noise reduction using inner trim

A study of tyre inner trim as a method for reducing tyre cavity resonance noise is presented. The tyre is modelled as a rectangular toroid where only the outside shell is flexible. A modal series solution of the sound pressure frequency response inside the tyre cavity is derived from the wave equation using modal superposition. In the solution with the rigid and flexible wall boundary condition, the effect of placing a trim layer onto the inner surface of the tyre tread plate wall is reflected by adding a damping loss term in the sound pressure frequency response function. The numerical simulation result was then compared with the result obtained from a roving impact test performed on a tyre. The results show that selective trim material may be effective for reducing the structure-borne noise magnitude resulting from the tyre cavity resonance.

Correlations between sound field characteristics and subjective ratings on reproduced music sound quality

The partial-space power, a sound field property for a loudspeaker, was newly defined in order to obtain general characteristics including on-axis sound pressure and total-space power. For typical loudspeakers, it was confirmed that the partial-space-power frequency response reflects the principal features, dips, peaks, and gradients of space-averaged sound-pressure frequency response in ordinary rooms. An all-inclusive listening test was performed with six subjective rating scales for ten loudspeakers. Then, the correlation between the sound field characteristics and the subjective rating data were examined. The sound dispersion as well as the frequency response seems to correlate with most normally employed subjective rating scales used in listening tests.

Analysis of vibration by the substructure synthesis method. 6th report. Application to acoustic analysis.

Substructure synthesis methods, which are applicable to the vibration analysis of large complex machine structures, are applied to acoustic analysis. At first, the frequency response spectra of sound pressure emitted from a flat rectangular steel plate in a cubical steel box are analyzed by the finite element method or by the boundary element method. Comparing the calculated results with experimental ones, their accuracy is discussed. Next, the reduced impedance method and the component mode synthesis method, which are the substructure synthesis methods previously proposed by the authors for the vibration analysis of machine structures, are applied to acoustic analysis. The sound pressure frequency response spectra calculated by these methods are quite close to experimental ones.

Out-of-head localized sound reproduction system for headphone

In stereo sound reproduction circuitry for use with a stereo signal source and stereo headphones, the improvement of dip filter means disposed between the stereo signal source and the stereo headphones, the dip filter means having a dip in the transmission characteristic thereof, the dip being in substantially the same frequency position as a dip which occurs in the sound pressure frequency response characteristic at the ear canal entrance when a sound source is disposed in front of a listener.

An analysis of design conditions for a phase-inverter speaker system with a drone cone

In this paper useful design conditions for a phase-inverter speaker system with a drone cone, which realize a flat response, are given for the first time by applying the network synthesis theory to the sound-pressure transfer function of this speaker system. The design conditions are obtained in relation to the sound-pressure zero below the reproducing region for the cases of the general Butterworth and the general Chebyshev rational function characteristics, and also obtained in relation to the amount of ripple of the sound-pressure frequency response in the reproducing frequency region for the case of the general Chebyshev rational function characteristic. The effects of equivalent resistance of the box due to the absorbing material on the design conditions are also considered. The calculated sound-pressure frequency response based on the design conditions obtained agrees fairly well with the measured response. Comparison of the sound-pressure frequency response of this speaker system with those of the closed box and the bass-reflex system is also given.