Noise Source Visualization for Small DC Motors Using Current Reference without a Reference Microphone

Noise and vibration sources from small direct current (DC) motors should be clearly visualized for optimal design of low noise motors. For accurate visualization, relatively good reference measurements at optimal locations are required. For some very small motors, the optimal position for a stationary reference microphone may not be accessible during measurement. However, strategies for small motor noise visualization without using a reference microphone have been developed in this study. Only scanning microphones and current measurements of a small motor were used to visualize sound sources. Scanning microphone signals combined with current measurements were used as moving reference signals. Motor noise visualization results based on different moving reference locations have been estimated and reported. Consistent motor noise visualization results from motor current and different, moving reference locations for the major electro-magnetic force excitation frequencies have been shown. Furthermore, for frequencies with relatively low current amplitude, clear motor noise visualization results have been produced for a moving reference located at the center of the motor. Also, the relationship between motor noise and current has been shown, and motor noise has been reduced by connecting an optimal capacitor to the motor power input

Noise Source Visualization Using a Digital Voice Recorder and Low-Cost Sensors

Accurate sound visualization of noise sources is required for optimal noise control. Typically, noise measurement systems require microphones, an analog-digital converter, cables, a data acquisition system, etc., which may not be affordable for potential users. Also, many such systems are not highly portable and may not be convenient for travel. Handheld personal electronic devices such as smartphones and digital voice recorders with relatively lower costs and higher performance have become widely available recently. Even though such devices are highly portable, directly implementing them for noise measurement may lead to erroneous results since such equipment was originally designed for voice recording. In this study, external microphones were connected to a digital voice recorder to conduct measurements and the input received was processed for noise visualization. In this way, a low cost, compact sound visualization system was designed and introduced to visualize two actual noise sources for verification with different characteristics: an enclosed loud speaker and a small air compressor. Reasonable accuracy of noise visualization for these two sources was shown over a relatively wide frequency range. This very affordable and compact sound visualization system can be used for many actual noise visualization applications in addition to educational purposes

Characterizing Sources of Small DC Motor Noise and Vibration

Small direct current (DC) motors are widely used due to their low cost and compact structure. Small DC motors of various designs are available on the market in different sizes. The smaller the motor, the more closely it may be used by individuals. Contrary to the size and simplicity of these motors in terms of structural design, sources of motor noise and vibration can be quite diverse and complicated. In this study, the source of motor noise and vibration was visualized over a very wide range of frequencies. The particle velocity of the motor was reconstructed from nearfield sound pressure measurements of motor noise. In addition to noncontact measurements conducted on a motor running at constant speed, the particle velocity of a stationary motor due to the impulse of an impact hammer was measured with an accelerometer. Furthermore, motor noise was measured under motor run-up conditions with different rotational speeds. As a result, by combination of these three methods, the sources of motor noise were accurately identified over a wide range of frequencies

Holographic projection of sound fields based on spatially-limited data sets

In the past, it has been demonstrated that nearfield acoustical holography (NAH) is a useful tool for visualizing noise sources. At present, planar and cylindrical holography are the most widely used among the various nearfield acoustical holography techniques. However, to avoid spatial Fourier transform-related truncation effects in conventional implementations of the latter procedures, the measurement aperture (i.e., the hologram surface) must typically extend well beyond the source to a region where the sound pressure level drops to a level significantly lower than the peak level within the measurement aperture. In contrast, statistically optimized nearfield acoustical holography (SONAH), does not suffer from the effects of spatial truncation and can be used to visualize limited areas of a source without compromising the accuracy of the projection. Here the implementation of SONAH in cylindrical coordinate is described, and its performance is compared with patch holography, an extrapolation procedure. It was found that SONAH is faster and more accurate than patch holography, but significantly slower than conventional, DFT-based holography. In addition to the identification of acoustical properties on the source plane, farfield radiation properties of sources were also investigated. Farfield prediction beyond the measurement region requires extrapolation in addition to forward projection of measurement pressure. Further, in contrast to conventional NAH procedures, which cannot be implemented in non-regular geometries, SONAH was here implemented in conical geometry to facilitate the measurement of aeroacoustic sources. Acoustical holography usually requires a large number of measurements that cover the entire source area. Here, a technique for estimating the sound field radiated by composite sources where sub-sources have fixed component directivity is introduced. This procedure allows sound fields to be reconstructed by using only a very small number of measurements when certain conditions are satisfied. Finally, various acoustical holography procedures have also been verified experimentally in measurements using loudspeakers and simulated multipole noise sources. In both cases, reliable results were obtained if appropriate procedures were followed. Thus it was concluded that acoustical holography can be a flexible and robust tool for noise source identification and for farfield projection based on nearfield measurements

Noise Source Visualization for Small DC Motors Using Current Reference without a Reference Microphone

Noise and vibration sources from small direct current (DC) motors should be clearly visualized for optimal design of low noise motors. For accurate visualization, relatively good reference measurements at optimal locations are required. For some very small motors, the optimal position for a stationary reference microphone may not be accessible during measurement. However, strategies for small motor noise visualization without using a reference microphone have been developed in this study. Only scanning microphones and current measurements of a small motor were used to visualize sound sources. Scanning microphone signals combined with current measurements were used as moving reference signals. Motor noise visualization results based on different moving reference locations have been estimated and reported. Consistent motor noise visualization results from motor current and different, moving reference locations for the major electro-magnetic force excitation frequencies have been shown. Furthermore, for frequencies with relatively low current amplitude, clear motor noise visualization results have been produced for a moving reference located at the center of the motor. Also, the relationship between motor noise and current has been shown, and motor noise has been reduced by connecting an optimal capacitor to the motor power input

Visualization of Broadband Sound Sources

In this paper the method of imaging of wideband audio sources based on the 2D microphone array measurements of the sound field at the same time in all the microphones is proposed. Designed microphone array consists of 160 microphones allowing to digitize signals with a frequency of 7200 Hz. Measured signals are processed using the special algorithm that makes it possible to obtain a flat image of wideband sound sources. It is shown experimentally that the visualization is not dependent on the waveform, but determined by the bandwidth. Developed system allows to visualize sources with a resolution of up to 10 cm