Journal Article•
Preliminary investigation of active control of dipole noise sources
TL;DR: In this article, the effectiveness of a control system on a directional dipole noise source was discussed and it was found that a primary source with a noncylindrical radiation directivity affected the performance of the control system.
Abstract: The effectiveness of a control system on a directional dipole noise source was discussed. It was found that a primary source with a non-cylindrical radiation directivity affected the performance of the control system. The analysis showed that the control system worked more effectively when it was used to create quiet zones in the area with the strongest primary-radiation directivity.
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Journal Article•
TL;DR: In this article, the measured narrow-band and 1/3 octave band spectra were calculated and analyzed in order to determine the blade-passing frequencies (BPF) and noise directivities for three different engine settings.
Abstract: The measured narrow-band and 1/3 octave band spectra were calculated and analyzed in order to determine the blade-passing frequencies (BPF) and noise directivities for three different engine settings. Thus decibel subtraction of the idling engine spectra from the 50% engine power spectra was performed to estimate the power spectra of a single engine. The results were compared to determine if and how an ANC system must be changed to obtain the best noise attenuation for the different run-up conditions.
Cites background from "Preliminary investigation of active..."
...It has been determined experimentally [2] that an ANC system is most effective when it is placed facing the lobe of strongest directivity from the primary source....
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Journal Article•
TL;DR: In this paper, the performance of an active control system can be improved by using multiple control channels, which not only increased the attenuation of the control area, but also increased the size of the quiet zone.
Abstract: Experimental results have clearly shown that the performance of an active control system can be improved by using multiple control channels. A multi-channel system not only increased the attenuation of the control area, but also increased the size of quiet zone. Moreover, it showed that more complex noise sources can be controlled by using a multi-channel system.
Cites background from "Preliminary investigation of active..."
...RESULTS For active control of a dipole noise source, it has been found experimentally that an active control system is most effective when it is placed in the direction o f the strongest primary noise directivity [2]....
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TL;DR: In this paper, a closed-form analytic solution for an arbitrarily oriented dipole placed above an impedance plane was derived for the total sound field in a form similar to the classical formula for a monopole.
Abstract: A closed-form analytic solution has been derived for an arbitrarily oriented dipole placed above an impedance plane. Asymptotic approximations for the total sound field can be written in a form similar to the classical formula for a monopole. Analytic approximations derived for horizontal and vertical dipoles give predictions that agree well with those obtained from a program of the fast field type. The asymptotic results have been confirmed also by laboratory measurements. Compared with numerical methods, the analytic approximations offer the combined advantages of easier physical interpretation and a much reduced computational time. It is found that the variation of the sound-pressure level from a vertical dipole above an impedance plane differs significantly from that due to a monopole above this plane, particularly as a result of differences in the ground wave component. However, the excess attenuation due to a horizontal dipole is found to be rather similar to that for a monopole except for source and receiver heights that are comparable with range.
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