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Acoustic Energy Harvesting Inside Loudspeaker Enclosures

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This study employs physical modeling prototypes for investigating acoustic energy harvesting inside closed-box loudspeaker enclosures via a biomimetic mechanism and a piezoelectric transducer. Test results indicate that the proposed device can generate up to 0.34 mW (0.64 µW/cm2) for Lp = 129 dB and 6.58 mW (256 µW/cm2) for Lp = 159 dB inside a large and a small enclosure respectively (for driving power of 1 W) having also an effect similar to that of absorption material.

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JAES Volume 66 Issue 7/8 pp. 516-524; July 2018 Permalink
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An Objective Audio Quality Measure Based on Power and Envelope Power Cues

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The generalized power spectrum model (GPSM), which has been shown to account for a large number of psychoacoustic and speech intelligibility (SI) experiments, was extended to assess audio quality. Like the GPSM, the suggested audio quality model, GPSMq, combines features from the power spectrum model (PSM) and envelope power-spectrum model (EPSM). GPSMq utilizes signal-to-noise ratios (SNRs) in the power and envelope power domains to model the addition or removal of energy by the signal processing under test. Four audio quality databases that introduce linear and nonlinear distortions to music and speech signals were assessed to cover a large variety of distortions cases. GPSMq provided better overall prediction performance than other state-of-the-art auditory-model-based objective quality measures. The results demonstrate that the power and envelope power SNR metric is appropriate for predicting audio quality for a variety of signal distortions in addition to psychoacoustics and SI. This supports the notion that the auditory system extracts a universal set of auditory features to be analyzed in a task-dependent decision stage.

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JAES Volume 66 Issue 7/8 pp. 578-593; July 2018 Permalink
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Creating Real-Time Aeroacoustic Sound Effects Using Physically Informed Models

Aeroacoustics is a branch of engineering within fluid dynamics that encompasses sounds generated by disturbances in air, either by an airflow being disturbed by an object or an object moving through air. An example of a fundamental aeroacoustic sound source is the Aeolian tone, generated by vortex shedding as air flows around an object. A compact source model of this sound is informed from fluid dynamics principles, operating in real-time and presenting highly relevant parameters to the user. A swinging sword, Aeolian harp, and propeller are behavior models presented to illustrate how a taxonomy of real-time aeroacoustic sound synthesis can be achieved through physically informed modeling. Evaluation indicates that the resulting sounds are perceptually as believable as sounds produced by other synthesis methods, while objective evaluations reveal similarities and differences among these models, pre-recorded samples, and those generated by computationally complex offline methods.

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JAES Volume 66 Issue 7/8 pp. 594-607; July 2018 Permalink
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Evaluating Live Loudness Meters from Engineers’ Actions and Resulting Output Levels

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Loudness discrepancies in television and radio frequently produce listener annoyance. Variations in loudness can be traced to the use of quasi-PPM based audio level meters in conjunction with different amounts of compression dynamics. A satisfactory live loudness meter should assist the engineer to: (a) achieve the recommended target level for a program, (b) compensate for content-dependent delimited offsets in loudness, and (c) compensate for fast changes in loudness. This paper investigates how the ballistic properties of live loudness meters affect the engineers’ actions with fader position and the resulting output levels. In order to explore the quality of loudness meters, the researchers simulated a live broadcast show with mixing engineers who had different degrees of experience. The resulting output levels were analyzed and interpreted using a linear mixing model. The results showed that the meters with the slower integration times produced less dispersion of output levels for parts of the program. Varying integration times of the meters did not cause a significant difference in the reaction time.

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JAES Volume 66 Issue 7/8 pp. 556-577; July 2018 Permalink
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Fractional Derivative Loudspeaker Models for Nonlinear Suspensions and Voice Coils

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Moving-coil loudspeakers exhibit a number of linear effects, such as viscoelastic suspension creep and lossy inductance of the voice coil, which complicate their frequency response. Nonlinear models of the loudspeaker must include these effects in order to make accurate predictions for nonlinear compensation algorithms. While viscoelasticity and lossy inductance have been modeled using a variety of methods in the frequency domain, the discrete time-domain description using fractional order derivatives is both accurate and easily incorporated into existing nonlinear models. The influence of the fractional order derivative is demonstrated using a fractional order oscillator, resulting in a response that closely resembles viscoelastic suspension creep in a loudspeaker or an increase in displacement toward low frequencies. A full bandwidth loudspeaker model with a fractional order viscoelastic suspension and a fractional order lossy voice coil was used to fit measurement data from two loudspeakers. Further simulations with a nonlinear position-dependent suspension and a nonlinear position-dependent inductance were conducted, and this revealed unexpected frequency components due to the infinite memory of fractional derivatives.

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JAES Volume 66 Issue 7/8 pp. 525-536; July 2018 Permalink
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Room Acoustics: Modeling, Enhancement, Measurement

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[Feature] There’s some fascinating work going on in room modeling and equalization, both for natural acoustic performance and reproduced sound. Applications range from concert halls, to small auditoria, from cinemas, to cars—in fact any space in which humans listen to sound. The availability of sophisticated modeling and simulation tools makes scale models things that are largely of the past, and it enables ideas to be tested without having to put them into full scale manufacture. Poor acoustics in a space can increasingly successfully be compensated by electronic means.

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JAES Volume 66 Issue 7/8 pp. 637-641; July 2018 Permalink
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The Frequency and Loudspeaker-Azimuth Dependencies of Vertical Interchannel Decorrelation on the Vertical Spread of an Auditory Image

In horizontal stereophony, it is known that interchannel correlation relates to the horizontal spread of a phantom auditory image. However, little is known about the perceptual effect of interchannel correlation on vertical image spread (VIS) between two vertically-arranged loudspeakers. The present study investigates this through two subjective experiments: 1) a multiple comparison of relative VIS for stimuli with varying degrees of correlation; and 2) the absolute measurement of upper and lower VIS boundaries for extreme stimuli conditions. Octave-band (center frequencies: 63 Hz to 16 kHz) and broadband pink noise signals have been decorrelated using two techniques: all-pass filtering and complementary comb-filtering. These stimuli were presented from vertically-spaced loudspeaker pairs at three azimuth angles (0°, ±30°, and ±110°), with each angle assessed discretely. Both the relative and absolute test results show no significant effect of vertical correlation on VIS for the 63 Hz, 125 Hz, and 250 Hz bands. For the 500 Hz band and above, there is a general tendency for VIS to increase as correlation decreases, which is observed for both decorrelation methods.

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JAES Volume 66 Issue 7/8 pp. 537-555; July 2018 Permalink
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