An ultra-thin Schroeder diffuser comprises a backing-plate, wherein the backing-plate is provided with 7×p rows and 7×q columns of unit cells, p and q are integers greater than or equal to 1, a side length of the unit cell is 0.48λ, a depth of the square unit cell is 0.04λ, the unit cell is provided with a square neck, a side length of the square neck is less than the side length of the unit cell, a depth of the neck is 0.01λ, λ is a wavelength of the diffuser corresponding to the design at a center frequency center f.sub.0, the neck widths w of different unit cells are different, and a distribution of the widths satisfies a certain sequence.

Disclosed is a method for determining a difference in depth or a lateral distance in relation to the vertical between two points of an underwater environment, in particular by measuring a propagation time of a sound wave. The determination is based on a single-layer model of the environment in which the wave is supposed to propagate in a straight line along an effective propagation direction, at a mean velocity that is independent of the propagation direction. Also disclosed is a method for determining the profile of the mean velocity based on the measurements of differences in depths per se, a determination of the local velocity profile over the variation interval of the sounded depths, and a related sonar system.

A transducer assembly comprises a housing and a plurality of frequency steered transducer array elements. Each of the transducer array elements includes a plurality of piezoelectric elements. The frequency steered transducer array elements are configured to receive a transmit electronic signal including a plurality of frequency components and to transmit an array of sonar beams into a body of water. Each sonar beam is transmitted in an angular direction that varies according to one of the frequency components of the transmit electronic signal. The frequency steered transducer array elements are positioned within the housing in a fan-shaped configuration where an end section of at least two of the frequency steered transducer array elements are within an intersection range of each other.

Acoustic measurement systems include an enclosure having a high efficiency yet very thin acoustic absorber coating portions thereof, in order to diminish background reflections. The thin acoustic absorber includes a reflective sublayer having a periodic array of indentations on its surface. The periodic array of indentations can be one-dimensional or two dimensional. The thin acoustic absorber further includes a thin absorbing layer overlaid on the reflective sublayer, and typically formed of a viscoelastic foam. The thin acoustic absorber possesses unprecedented absorption efficiency across a broad frequency range and at normal or oblique angles of incidence.

A sound system with upfiring speakers and a redirecting baffle is shown and described. Upfiring speakers simulate overhead speakers by using a ceiling to reflect sound toward the listener from above the listener's head. However, in rooms with high ceilings, such reflection is not practical. The redirecting baffle is spaced apart from the upfiring speakers along a height axis and is oriented downward so that a surface normal to the baffle is neither parallel to nor perpendicular to the floor. By adjusting the angle of orientation, the location at which the reflected sound quality is best can be adjusted toward or away from the upfiring speakers. The system is particularly useful for in-store displays as many stores have ceiling heights that make sound reflection from an upfiring speaker impractical.

A sound system with upfiring speakers and a redirecting baffle is shown and described. Upfiring speakers simulate overhead speakers by using a ceiling to reflect sound toward the listener from above the listener's head. However, in rooms with high ceilings, such reflection is not practical. The redirecting baffle is spaced apart from the upfiring speakers along a height axis and is oriented downward so that a surface normal to the baffle is neither parallel to nor perpendicular to the floor. By adjusting the angle of orientation, the location at which the reflected sound quality is best can be adjusted toward or away from the upfiring speakers. The system is particularly useful for in-store displays as many stores have ceiling heights that make sound reflection from an upfiring speaker impractical.

An acoustic structure includes a plate and at least one acoustic scatterer having a resonant frequency and coupled to a side of the plate. The at least one acoustic scatterer has an opening, a first channel and a second channel. The first channel has a first channel open end and a first channel terminal end with the first channel open end being in fluid communication with the opening. The second channel has a second channel open end and a second channel terminal end with the second channel open end being in fluid communication with the opening. The first channel terminal end and the second channel terminal end are separate from one another.

An acoustic structure includes a plate and at least one acoustic scatterer having a resonant frequency and coupled to a side of the plate. The at least one acoustic scatterer has an opening, a first channel and a second channel. The first channel has a first channel open end and a first channel terminal end with the first channel open end being in fluid communication with the opening. The second channel has a second channel open end and a second channel terminal end with the second channel open end being in fluid communication with the opening. The first channel terminal end and the second channel terminal end are separate from one another.

A semi-passive acoustic transponder providing identity information related to the transponder when it is reflecting a received pulsed acoustic signal underwater. The transponder includes a memory unit holding ID-sequence data controlling operation of the switching device, and an electronic circuit includes frequency adjusting means for adjusting the frequency and duration of the switch such that the duration of the ID-sequence data is shorter than the duration of pulses of the received acoustic signal. Additionally, a method and system may provide position and identity information related to one or more of said semi-passive acoustic transponders.

An acoustic reflector for a microphone to measure flyover noise generated by an aircraft. The microphone is configured to measure flyover noise generated by an aircraft flying on a preset path. The acoustic reflector includes at least a central portion having the shape of an ellipse having a major axis and a plurality of peripheral portions distributed around the central portion. The acoustic reflector allows edge effects to be attenuated at the low frequencies of the noise to be measured.