The Effect of Attenuation from Fish on Passive Detection of Sound Sources in Ocean Waveguide Environments

Attenuation from fish can reduce the intensity of acoustic signals and significantly decrease detection range for long-range passive sensing of manmade vehicles, geophysical phenomena, and vocalizing marine life. The effect of attenuation from herring shoals on the Passive Ocean Acoustic Waveguide Remote Sensing (POAWRS) of surface vessels is investigated here, where concurrent wide-area active Ocean Acoustic Waveguide Remote Sensing (OAWRS) is used to confirm that herring shoals occluding the propagation path are responsible for measured reductions in ship radiated sound and corresponding detection losses. Reductions in the intensity of ship-radiated sound are predicted using a formulation for acoustic attenuation through inhomogeneities in an ocean waveguide that has been previously shown to be consistent with experimental measurements of attenuation from fish in active OAWRS transmissions. The predictions of the waveguide attenuation formulation are in agreement with measured reductions from attenuation, where the position, size, and population density of the fish groups are characterized using OAWRS imagery as well as in situ echosounder measurements of the specific shoals occluding the propagation path. Experimental measurements of attenuation presented here confirm previous theoretical predictions that common heuristic formulations employing free space scattering assumptions can be in significant error. Waveguide scattering and propagation theory is found to be necessary for accurate predictions.

Comparison of the Vibration Damping of the Wood Species Used for the Body of an Electric Guitar on the Vibration Response of Open-Strings

Research show that the vibrations of the strings and the radiated sound of the solid body electric guitar depend on the vibrational behavior of its structure in addition to the extended electronic chain. In this regard, most studies focused on the vibro-mechanical properties of the neck of the electric guitar and neglected the coupling of the vibrating strings with the neck and the solid body of the instrument. Therefore, the aim of the study was to understand how the material properties of the solid body could affect the stiffness and vibration damping of the whole instrument when comparing ash (Fraxinus excelsior L.) and walnut (Juglans regia L.) wood. In the electric guitar with identical components, higher modal frequencies were confirmed in the structure of the instrument when the solid body was made of the stiffer ash wood. The use of ash wood for the solid body of the instrument due to coupling effect resulted in a beneficial reduction in the vibration damping of the neck of the guitar. The positive effect of the low damping of the solid body of the electric guitar made of ash wood was also confirmed in the vibration of the open strings. In the specific case of free-free vibration mode, the decay time was longer for higher harmonics of the E2, A2 and D3 strings.

A compact active structural acoustic control method for minimizing radiated sound power

Active structural acoustic control is an active control method that controls a vibrating structure in a manner that reduces the sound power radiated from the structure. Such methods focus on attenuating some metric that results in attenuated sound power, while not necessarily minimizing the structural vibration. The work reported here outlines the weighted sum of spatial gradients (WSSG) control metric as a method to attenuate structural radiation. The WSSG method utilizes a compact error sensor that is able to measure the acceleration and the acceleration gradients at the sensor location. These vibration signals are combined into the WSSG metric in a manner that is closely related to the radiated sound power, such that minimizing the WSSG also results in a minimization of the sound power. The connection between WSSG and acoustic radiation modes will be highlighted. Computational and experimental results for both flat plates and cylindrical shells will be presented, indicating that the WSSG method can achieve near optimal attenuation of the radiated sound power with a minimum number of sensors.

Traveling-wave control of the bending wave in a beam for high quality sound radiation

The bending wave generated by the actuator exciting a panel can be controlled to be in the traveling wave form void the structural resonances, which deteriorates the radiated sound if the panel is used as a speaker. Although such traveling-wave control method (TCM) yields a wider effective frequency range than the modal control method, the requirement of using many actuators is the practical problem yet. If a beam is employed instead of a plate as a panel speaker, the number of actuators can be reduced despite a smaller radiating surface than a plate. This study adopts three actuators for the beam control using TCM. An actuator excites the beam in the middle position, and the two actuators near the two edges are used to suppress the reflected waves from the boundaries. The control result shows that the driving-point mobility of the primary actuator is converted into that of an infinite beam, which means that the boundaries are changed into anechoic ones and the structural resonances are eliminated. Accordingly, the beam radiates a smooth sound spectrum without sharp peaks and troughs related to the resonant responses. Effects of material and dimension in determining the effective frequency range are also explored.

Effect of sound source movement at low Mach number on radiated noise level

Change in A-weighted sound pressure level or Noise level of radiated sound due to sound sources moving at low Mach number at the same speed along a straight track is discussed in this paper. When a sound source move, frequency and amplitude modulation is observed in the radiated sound field. Without their modulation, the noise level at a receiving point is determined only by distance and A-weighted sound power level of each sources. Solution of modulated frequency and amplitude of radiated sound can be obtained by using the Duhamel's efficient calculation. The modulated frequency and amplitude increase for approaching sources and decrease for receding sources. The difference of maximum noise level,and the equivalent sound level during the sources passing-by, with or without considering the modulation, increases monotonically with respect to source velocity, and independent of distance from the track. This difference increases as dominant frequency band of the sources decreases due to A-weighting below 1 kHz.

Shaping acoustic radiation induced by vibrotactile rendering on a touch surface

Many electronic devices with touch-sensitive surfaces aim to provide vibrotactile feedback, along with visual or auditory feedback, to facilitate the interaction between the user and the interface. In parallel to these efforts, recent studies developed various vibration rendering techniques, enabling more complex vibration patterns to be generated on the touch surface. However, few have addressed sound radiation induced by vibrotactile rendering on a touch surface, which could significantly impact the haptic interaction's overall perception. This study presents a method to shape the acoustic radiation due to rendering high-fidelity vibrotactile feedback on a touch surface. The proposed method utilizes measured frequency response functions and a vibroacoustic representation of the touch surface to define the relationship between actuator driving signals, vibration responses on the touch surface, and radiated sound power. Proper actuator driving signals are derived from the optimization problem formulated using the relationship. The proposed method was demonstrated through vibration rendering experiments on a touch surface comprising an acrylic plate and voice coil actuators. The results showed that the proposed method could shape the acoustic radiation while rendering target vibration patterns at desired positions on the touch surface. This study's proposed method could allow haptic engineers to design vibrotactile feedback and sound radiation simultaneously for a more compelling haptic experience.