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A spherical wave generating diffuser positioned in front of the sound emission side of a sound source. The diffuser comprises an inner horn and an outer horn positioned concentrically around the inner horn. The diffuser generates pseudo-spherical waves centered on the inner horn because the emission speed of the sound waves emitted from between the outer horn and the inner horn are slower than the emission speed of sound waves emitted from within the inner horn.

Information about the target strength (TS) of a vesicle is important to estimate the acoustic scattering of Sargassum plants. Experimental TS (TSe) of a vesicle was obtained at 70 and 200 kHz using quantitative echo sounders in a freshwater tank (10×10×15 m). The TSe of ten vesicles examined here were −56.88–51.68 dB at 70 kHz and −60.30–‐50.90 dB at 200 kHz. The TSe′s of small vesicles were 2.56−−3.70 dB higher at 70 kHz than at 200 kHz, suggesting that these small vesicles were affected by the airbladder resonance. Theoretical TS (TSt) was estimated by airbladder−scattering models to confirm this effect. The gas radii of 418 vesicles (containing the experimented ten vesicles) were measured using a soft x−ray system and applied to the theoretical models. Their radii were 0.52−−6.00 mm; calculated TSt matched with TSe. According to the theoretical model, the vesicles were not affected by the resonance when argument ka is ka>1 (where k is the wave number and a is the radius). However, the vesicles were affected by the resonance when ka

A multi-speaker apparatus generates and transmits sound waves in all directions toward and away from a surface upon which the apparatus is installed or mounted. The multi-speaker apparatus includes a middle/high frequency sound range speaker and a low frequency sound range speaker. The middle/high frequency sound range speaker and the low frequency sound range speaker are arranged relative to each other such that center axes thereof are aligned with an axis that is substantially perpendicular the surface upon which the apparatus is installed or mounted. A horn and a cabinet are arranged such that sound waves generated from the middle/high frequency sound range speaker and the low frequency sound range speaker are emitted in all directions both toward and away from the surface upon which the apparatus is supported or mounted.

A speaker is adapted to transmit sound waves in an omni-directional manner relative to an installation surface upon which the speaker is mounted. The speaker includes an oscillator (12) having a hemispherical oscillating body (14) comprising a piezoelectric body polarized in a thickness direction thereof, a pair of electrodes (16a,16b) provided on an inner surface and an outer surface of the oscillating body, input terminals (20) connected to the electrodes via lead wires, an end portion of the oscillator being connected to spacers (29) in a groove (27) to cover a projecting portion (24) of a horn (22), a cavity (30) communicating with a passage (28) in the horn and being defined between the oscillator and the horn and support members (32) fixed to a flange portion (26) of the horn whereby a sound transmission path (36) communicating with the passage in the horn is defined between the horn (22) and the installation surface upon which the speaker is mounted such that the sound transmission path extends in all directions relative to the installation surface.

The disclosure is directed to a piezoelectric vibrator or resonator which includes a vibrating plate employing expansion mode vibration, and a groove or grooves formed at a center and/or in the vicinity of the center of the vibrating plate in a direction intersecting sides of the vibrating plate contributing to the vibration so as to make vibration propagating speed slower than that in the absence of the groove or grooves, and also to a method of adjusting vibrating frequency of such a piezoelectric vibrator.

A tuning fork and a manufacturing method thereof which is obtained by punching and folding a material of invariable elasticity. The material is formed in the shape of a plate and processed through a rolling operation, wherein the plate is punched into an approximately V-shape such that the folding line appears at a right angle with respect to the rolling direction of the plate. A piezoelectric element serving as an electrical mechanical conversion device is provided on a vibrating portion.

A piezoelectric vibrator operating in a spreading vibration mode has a vibrating plate of permanently elastic metal. At least one main surface of the vibrating plate is mirror-finished.