Time Doman Measurement Of Moving Coil Loudspeaker Driver Parameters

A novel method for the measurement of the Thiele-Small small-signal parameters of a moving-coil electromagnetic transducer driver is disclosed. The technique is based on a time domain analysis of the transient response of a loudspeaker voice coil circuit to a current step of excitation. By sampling the damped sinusoidal transient generated by such an excitation, the loud-speaker parameters can be calculated from a linear predictive analysis of the recorded data.Georgia Tech Research Institut

Improving particular components of the audio signal chain: optimising listening in the control room

In the field of audio engineering there is a constant need for optimising the listening situation. Listening to, judging and finally optimising the recorded material are essential tasks of audio engineers. The author of this contextual statement has been working in the field of audio engineering since 1993. In addition, various research projects have been undertaken in this field. A selection of three research areas and their published outputs are presented in this contextual statement: Research Area 1: Improving acoustic modules to increase efficiency in the acoustical treatment of control rooms Research Area 2: Measuring time alignment errors, testing their impact on the listening experience and providing solutions for time alignment of loudspeakers Research Area 3: Using equalisation for correcting and shaping a loudspeaker's frequency response These research areas relate to a consistent listening 'defect' that leads to a blurred and broader sound image. Measures to overcome these defects are presented and proven to be effective by built prototypes and/or products. The results of the research are published in articles and books and can be experienced in the form of hardware systems such as acoustic modules or modified loudspeakers

LOW FREQUENCY GROUP DELAY EQUALIZATION OF VENTED BOXES USING DIGITAL CORRECTION FILTERS

ABSTRACT In this paper methods to determine the group delay of vented boxes and techniques for the design of filters for group delay equalization are presented. First the transfer function and the related group delay are explained. Then it is shown how the group delay can be computed or approximated for a certain alignment of the box. Furthermore it is shown how to derive the required parameters of the transfer function from a simple electrical measurement of the box, which allows the determination of the group delay without knowledge of the box design parameters. Two strategies for the design and implementation of digital correction filters are shown where one approach allows for a real-time adjustability of the delay. Finally, the performance with a real speaker is evaluated

Equivalent circuit analysis of a seventh order bandpass loudspeaker system

A seventh order bandpass loudspeaker system was designed using an equivalent circuit analysis. The electrical, mechanical and acoustic systems were each modeled as separate subcircuits derived by using a Voltage-Force-Pressure or impedance analogy; the interactions between the subcircuits were modeled using coupled controlled-sources. The equivalent circuit was analyzed using SPICE (Simulation Program with Integrated Circuit Emphasis). A technique for modeling port and cavity resonances inside the enclosure using distributed element approximations for the resonant components was developed and verified by measurement. A complete microcomputer based experimental loudspeaker testing system was designed incorporating a sweep frequency oscillator, a gain-controlled audio power amplifier, a true rms microphone interface, and a 12-bit, multiplexed, 100 ksamples/second AID data acquisition system connected to an IBM compatible personal computer. The frequency response of the system, as measured by a microphone in dB SPL (decibels, Sound Pressure Level), agreed with the predicted response to within 2 dB in the passband. Above the bandpass cutoff frequency, peaks in the response are shown to be caused by port and enclosure cavity resonances; dips in the response are shown by finite element modal analysis to be caused by enclosure wall resonances. The technique of modeling the electro-mechanical-acoustic system using an equivalent circuit analysis with distributed element resonant components has been shown to be a valid design tool for high-order loudspeaker systems

Experimental measurement of the nonlinearities of electrodynamic microphones

International audienceThis paper presents an experimental way of characterizing the nonlinearities of electrodynamic microphones used as acoustical sources. This functioning occurs for reciprocal calibration techniques. For this purpose, its electrical impedance is measured with a Wayne Kerr wedge which has an excellent precision. Moreover, it can be noted that the Thiele and Small model is used to characterize its electrical impedance. Furthermore, an experimental method based on Simplex algorithm allows us to construct polynomial laws which describe the dependence of the Thiele and Small parameters with the input voltage. The nonlinear variations obtained allow us to determine the nonlinear differential equation of the electrodynamic microphone. Then, this equation is solved numerically in order to confirm the accuracy of the polynomial laws obtained by the Simplex algorithm. The distortions are measured with a laser Doppler velocimeter and compared with the ones obtained by the numerical solving of the nonlinear differential equation. The experimental displacement spectrum is consistent with the theoretical one