Hybrid feedforward-feedback ANR topology.
Open loop transfer function from an internally generated signal, through the cancellation speaker, to the error microphone. (a) Circumaural earcup on flat plate; (b) ANR earplug in flat plate, human ear, and two insertion depths in HEAD Acoustics manikin.
Active attenuation performance of the ANR systems for circumaural earcup and (a) pure-tone noise, (b) F-16 cockpit noise, and (c) Huey helicopter noise.
Comparison of the frequency response function of identified models with transfer function estimate from identification data.
Comparison of identified cancellation path model frequency responses for two different deep insertions and one shallow insertion of the ANR earplug in the LFATC.
ANR performance measured using the B&K microphones (solid) and the ANR microphones (dashed) for sum-of-tones in the LFATC evaluation.
ANR performance with no communications signal present (solid) and with a communications signal present (dashed) for sum-of-tones in the LFATC evaluation.
Total attenuation of sum-of-tones for hybrid ANR as measured by transmission loss between the B&K microphones in the LFATC.
Sound level measured at unoccluded manikin ear and unmodified CEP occluded manikin ear for (a) sum of tones noise , (b) UH-60 cockpit noise.
Sound level at unoccluded manikin ear and after hybrid ANR for ANR-modified CEP and (a) sum-of-tones , and (b) UH-60 cockpit noise. Performance is measured at both the manikin microphone and ANR microphones. Passive levels are provided for sum-of-tones.
Total attenuation at error microphone with no communication signal present, and with a communication signal present. Total attenuation also reported at manikin ear microphone. (a) Sum-of-tones , (b) UH-60 cockpit noise.
Ratio of maximum stable gain of the hybrid system and of the feedforward system alone when the feedback gain is set to provide a gain margin.
Overall C-weighted passive, active, and total noise reduction performance for feedback, feedforward, and hybrid ANR in earcup testing within a low frequency acoustic test cell.
Overall C-weighted total attenuation of sum-of-tones and UH-60 cockpit noise in the band, both at source levels.
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