Abstract: Remotely operated rotary actuated shear wave generating apparatus and methods that generate horizontally polarized vertically propagating shear waves for use in down-hole shear wave velocity measurements. Seismic signals are generated by an offset mass rotating in a plane perpendicular to the surface of the ground, which impacts an impact member coupled to the ground. The energy of impact is transmitted to the ground parallel to the surface of the ground. The apparatus uses a spring-loaded rotating mass that has a rotary motion. Because acceleration of the mass is not horizontal, reaction forces caused by acceleration of the mass create less horizontal shear stress in the ground prior to the desired time (impact). Reaction forces of the accelerated rotating mass does not generate undesirable waves that obscure the desirable waves caused by impact with the impact member. The source generates transient shear waves repeatedly at constant intervals.

Abstract: A seismic vibrator includes a transducer, a reactive mass, a base plate to couple motion of the reactive mass to subsurface formations and a linkage system configured to couple motion of the transducer to the reactive mass and the base plate. The linkage system cooperates with the reactive mass and the transducer to define a first resonant frequency and a second resonant frequency within a range of 1 to 300 Hz.

Abstract: A seismic source signal generator includes a mass, a primary accumulator and a secondary accumulator, the secondary accumulator having an internal volume smaller than an internal volume of the primary accumulator. A method for generating a signal using a seismic vibrator includes operating the seismic vibrator using hydraulic fluid, damping hydraulic pressure deviations in the hydraulic fluid using a first accumulator in hydraulic communication with the hydraulic fluid, and damping pressure deviations in the hydraulic fluid using a second accumulator in hydraulic communication with the hydraulic fluid, the second accumulator having an internal volume smaller than an internal volume of the first accumulator.

Abstract: Elastodynamic waves are generated by a tool having a hammer rotatably connected with a housing by a first hinge and an actuator arm rotatably connected with the hammer by a second hinge. An axial force applied to the actuator arm by a drive shaft and spring is translated and amplified to a radial impact force by rotation of the hammer around the first hinge. The tool may also include a stabilizer arm connected to the actuator arm by a third hinge, and connected to the housing by a fourth hinge. The housing may be an acoustic wireline tool cylinder having an opening that permits the hammer mass to extend outside the housing when rotated in a first direction. The housing may also include a second opening that permits the hammer mass to extend outside the housing when rotated in a second direction, and a third opening that permits the hammer mass to extend outside the housing when rotated between the first and second openings.

Abstract: The present invention discloses an acoustic borehole source and method of using the source for generating elastic waves through an earth formation that may be used for logging or permanent installations. The acoustic source is comprised of a first motorized reaction mass and at least two pads, each pad connected to the sonde and the motorized reaction mass using pushing rods. In an alternate embodiment, the source has a first and second motorized reaction mass and at least two pads. The motorized reaction masses may be activated to allow the pads to move at an angle ? relative to the axis of the sonde. In a third embodiment, the acoustic borehole source includes additional pairs of motorized reaction masses so that pads may be independently activated.

Abstract: An apparatus for generating a seismic signal in a wellbore includes an elongated housing configured to be disposed in the wellbore; a piston slidably disposed in an internal bore in the elongated housing; a strike plate fixed on the elongated housing proximate one end of the internal bore; and an energizing mechanism configured to move the piston to hit the strike plate. A downhole system for seismic survey of a formation penetrated by a wellbore includes at least one seismic receiver; a seismic source; and at least one inflatable packer configured to separate the seismic source and the at least one seismic receiver in different compartments in the wellbore when inflated.

Abstract: Methods and apparatus for generating a signal with a signal generator comprising a tool body disposed in a tubular member. A first and second electromagnets are disposed within the tool body such that the second electromagnet is opposite the first electromagnet. A power supply selectively provides electrical current to the first and second electromagnets so as to displace the tubular member and generate a signal in the surrounding formation.

Abstract: A downhole receiver for gathering seismic and sonic data from inside a borehole includes a substantially tubular housing adapted for axial connection to a tool string, and one or more sensors. A damping element is provided to flexibly couple each sensor to the tubular housing. An actuator extends the one or more sensors substantially radially with respect to the tubular housing to clamp the sensors against the wall of the borehole. In selected embodiments, the sensors may be one or multiple component geophones, accelerometers, hydrophones, vibrometers, or the like.

Abstract: The present invention provides an accelerated weight drop for use as a seismic energy source, a method for operating an accelerated weight drop for use as a seismic energy source, and a seismic survey system including the accelerated weight drop. The accelerated weight drop, among other elements, includes a strike plate positionable on a surface, and a striker positionable over the strike plate. The accelerated weight drop further includes a compressed gas spring configured to drive the striker toward the strike plate thus creating seismic waves within the surface, wherein the striker is slidably coupled to the compressed gas spring and the striker and the compressed gas spring rotatably coupled to the strike plate about an axis.

Abstract: An acoustic source for delivering acoustic energy to a ground formation, particularly a rock formation, the source including (a) a solenoid to generate an electromagnetic field, (b) a bullet positioned within the influence of the electromagnetic field, (c) a casing surrounding and enclosing the solenoid and bullet so that both the solenoid and the bullet are protected from the surrounding environment, in use the solenoid being electrically energized to cause the bullet to be propelled by electromagnetic force so that the bullet impacts an anvil portion of the casing in contact with the ground formation is provided.

Abstract: A marine seismic source method capable of retaining low frequencies is disclosed. One embodiment of the method comprises a seismic source that generates an up-going wave and first down-going wave with opposite polarity. The up-going wave reflects off the ocean surface as a second down-going wave having the same polarity as the first down-going wave and the first and second down-going waves combine substantially in-phase to form a third down-going wave. A source apparatus to accomplish the method is also disclosed. One source apparatus embodiment comprises a device wherein at least part of the device is below the surface of the water and the device is adapted to cause oscillations below the surface of the water, and means for oscillating the device in the water to create an up-going wave and a first down-going wave and the up-going wave has reverse polarity relative to the first down-going wave.

Abstract: A method and system for controlling a producing cycle in a well, during the production cycle, for optimizing production from the well including disrupting fluid in a wellbore with a pulse generator to create a pressure pulse transmitted through the fluid in the wellbore, detecting the pressure pulse created and the pressure pulse reflected from objects located within the wellbore, wherein the objects may include a liquid/gas interface and a producing apparatus such as a plunger, converting the detection of the pressure pulse and the reflected pressure pulses to a signal, computing the signals to determine the well status and controlling production of the fluid from the wellbore based on the well status.

Abstract: Elastodynamic waves are generated by a tool having a hammer rotatably connected with a housing by a first hinge and an actuator arm rotatably connected with the hammer by a second hinge. An axial force applied to the actuator arm by a drive shaft and spring is translated and amplified to a radial impact force by rotation of the hammer around the first hinge. The tool may also include a stabilizer arm connected to the actuator arm by a third hinge, and connected to the housing by a fourth hinge. The housing may be an acoustic wireline tool cylinder having an opening that permits the hammer mass to extend outside the housing when rotated in a first direction. The housing may also include a second opening that permits the hammer mass to extend outside the housing when rotated in a second direction, and a third opening that permits the hammer mass to extend outside the housing when rotated between the first and second openings.

Abstract: The invention relates to an apparatus and method for imparting a precise amount of impulse energy to be delivered to the ground. The apparatus includes an anvil for operative deployment against the earth a hammer operatively connected to the anvil for striking the anvil; and a control system operatively connected to the hammer for controlling the impulse energy of the hammer striking the anvil. The control system includes a linear feedback system for measuring the linear position of the hammer with respect to the anvil during a force stroke and a processor for receiving linear position data from the linear feedback system for controlling the relative speed of the hammer with respect to the anvil during a force stroke through an actuation system.

Abstract: The present invention provides an accelerated weight drop for use as a seismic energy source, a method for operating an accelerated weight drop for use as a seismic energy source, and a seismic survey system including the accelerated weight drop. The accelerated weight drop, among other elements, may include a striker positionable over a surface, and a compressed gas spring configured to drive the striker toward the surface thus creating seismic waves within the surface. In this embodiment the striker is slidably coupled to the compressed gas spring.

Abstract: A downhole tool for gathering formation data from inside a borehole includes a substantially tubular housing adapted for axial connection to a drill string and multiple sensors coupled to the tubular housing. The sensors include a first pair of sensors aligned along a first axis and adapted to measure a spatial derivative along the first axis, a second pair of sensors aligned along a second axis and adapted to measure a spatial derivative along the second axis, and a third pair of sensors aligned along a third axis and adapted to measure a spatial derivative along the third axis. In selected embodiments, the spatial derivatives are used to differentiate seismic or sonic compression and shear waves measured in a downhole environment.

Abstract: A method for generating acoustic waves, the method having the steps of: extending a tine from a support structure so that a proximal end of the tine is attached to the support structure and a distal end of the tine is uninhibited; positioning an oscillator so as to be supported by the support structure and to mechanically communicate with the tine; and oscillating the tine with the oscillator.

Abstract: An apparatus for generating acoustic waves, the apparatus having: a support structure; two tines extending from the support structure so that proximal ends of the two tines are attached to the support structure so that distal ends of the two tines are positioned with standoffs relative to a dimension of the support structure and the distal ends of the two tines are uninhibited, wherein the two tines each comprise a moment arm; and an oscillator in mechanical communication with the two tines.

Abstract: A gerotor and bearing apparatus for a whirling mass orbital vibrator which generates vibration in a borehole. The apparatus includes a gerotor with an inner gear rotated by a shaft having one less lobe than an outer gear. A whirling mass is attached to the shaft. At least one bearing is attached to the shaft so that the bearing engages at least one sleeve. A mechanism is provided to rotate the inner gear, the mass and the bearing in a selected rotational direction in order to cause the mass, the inner gear, and the bearing to backwards whirl in an opposite rotational direction. The backwards whirling mass creates seismic vibrations.

Abstract: A method of conducting seismic evaluation of a subterranean formation wherein a rigid, elongate member having a first end and a second end is positioned such that the first end of the elongate member is at a point on the earth's surface, imparting an impulsive force to the elongate member to urge the member into the earth, the positioning of the rigid member and the impulsive force being sufficient to generate and propagate primary seismic waves into the subterranean formation and positioning one or more seismic wave detectors on the surface of the earth to detect and receive reflected seismic waves from the subterranean formation.

Abstract: An electromechanical device for generating elastic waves in a material medium such as the subsoil in a frequency range where the wavelengths of the waves generated are great in view of the dimensions of the device, and method of implementation. The device comprises one or more vibrators which are buried in the medium, associated with a control system. Each vibrator comprises at least one inertia mass (1), several plates (2, 3) providing mechanical coupling with the medium, electromechanical transducers (4, 5) connecting inertia masses (1) to plates (2, 3). A control system (7) applies to the various transducers (4, 5) respective control signals so that the resulting elastic wavefield generated in the medium by the device is preferentially oriented in one or more directions.

Abstract: In one embodiment of the present invention, a drive assembly for a seismic land vibrator is provided. The drive assembly comprises at least a first spring element. The first spring element operates in at least two vibration modes in a seismic frequency band of interest. The drive assembly also comprises a baseplate, a driver, and a reaction mass. The driver interacts with the reaction mass and the first spring element to transfer energy to the baseplate.

Abstract: The present invention provides a system for, and method of determining an azimuth of a seismic energy source. In one embodiment, the system includes a directional assembly having a mount configured to be coupled to a seismic energy source, a rotatable mass assembly coupled to the mount, a compass rose coupled to one of the mount or the rotatable mass assembly and a direction reference coupled to the other of the mount or the rotatable mass assembly. The compass rose is registered with the direction reference to provide a direction orientation of the rotatable mass assembly with respect to the mount.

Abstract: In one embodiment of the present invention, a drive assembly for a seismic land vibrator is provided. The drive assembly comprises at least a first spring element. The first spring element operates in at least two vibration modes in a seismic frequency band of interest. The drive assembly also comprises a baseplate, a driver, and a reaction mass. The driver interacts with the reaction mass and the first spring element to transfer energy to the baseplate.

Abstract: A non-contact vibrometer is employed to measure seismic energy imparted to the earth by a land vibrator. The non-contact vibrometer can be a laser vibrometer operable to measure the motion of a baseplate of the land vibrator. A computing device can be used to record both the imparted seismic energy detected by the non-contact vibrometer and reflected seismic energy sensed with geophones.

Abstract: A dynamic force transducer for generating vertically oriented compressional forces and motions at the surface of a solid medium. A frame is rigidly coupled in direct contact with the solid medium surface. At least one pair of identical driver units are mounted to the frame to impart vertically oriented forces to the medium. Compliant springs support the drivers and introduce mechanical resonances. The driver units are excited to produce the vertically oriented pushing and pulling forces along a common collinear vertical direction. The driver units also impart either continuous or pulsed oscillatory forces to produce prescribed seismic compressional waves in the medium.

Abstract: A logging tool having a tool body, which can be positioned in a fluid-filled borehole, including a receiver section and a dipole transmitter; wherein the dipole transmitter includes a transducer with a shell having a reaction mass and a motor located therein, the motor operatively connecting the shell and the reaction mass such that only an outer surface of the shell is in contact with the fluid in the borehole. This new type of dipole source for well logging involves shaking all or part (axially) of a dipole tool body to produce a pure, broadband acoustic dipole signal while at the same time coupling as little energy as possible into the tool body. Important variations on this idea include a linear phased array of shaker sources, and active cancellation of tool borne noise.

Abstract: A method of seismic investigation using the swept impact seismic technique involves measuring the response of a site to be investigated to a series of controlled impact sequences applied at different points of the site, each sequence using impacts generating pulses of energy at 100-2500 Hz., the impacts of the sequence having a repetition frequency swept between frequencies in the range of 10 to 500 Hz., the end frequencies having a ratio of at least 1.5 to 1, and the number of impacts in the sequence being at least 100 (and preferably at least 500). The invention also extends to apparatus for implementing such a method, comprising an electrically-actuated hammer having an impact frequency variable through a range of at least 1.5:1 within the range 10 to 500 Hz., and generating impacts characterized by substantial energy within a frequency range of 100-5000 Hz.

Abstract: Compact vibrator for emitting elastic waves in a material medium such as the subsoil. The vibrator comprises a baseplate (3) intended to be coupled in operation with a surface of this medium, an inertia mass (5) and at least a pair of electromechanical transducers (1, 2) comprising each one or more pillars (A, B) made for example of a piezoelectric or magnetostrictive material. Pillars (A) of first transducer (1) are interposed between baseplate (3) and a relay plate (4). Pillars (B) of the second transducer are interposed between relay plate (4) and inertia mass (5), on the same side of relay plate (4) as pillars (A) preferably, so that inertia mass (5) is positioned in the vicinity of baseplate (3), which contributes to the compactness and to the stability of the vibrator that can therefore be used on slightly sloping surfaces.

Abstract: A method and device for generating a high amplitude sound wave is provided. The device includes a housing having an open end. A piston is slidably disposed in the open end of the housing and forms a chamber for holding a pressurized liquid. The pressurized liquid acts on the piston to move the piston relative to the housing. A latch is operable to fix the piston relative to the housing and to release the piston. Upon release of the latch, the piston moves relative to the housing to generate the sound wave. In the method of the present invention, a piston is fixed relative to a housing to form a chamber between the housing and the piston. The chamber is filled with a pressurized fluid and the piston is released to allow the pressurized fluid move the piston relative to the housing and generate the sound wave.

Abstract: A dynamic force transducer for generating horizontally oriented shear forces and motion at a surface of a solid medium. A rigid frame is placed in direct contact with the surface of the solid medium. At least one pair of identical dynamic-force driver units is mounted on the frame to impart horizontally oriented forces to the frame. Symmetrical pairs of compliant springs support the force drivers, but the compliances of each pair of springs may be adjusted or interchanged with other similar springs to introduce different predetermined mechanical resonances. The driver units are excited to produce the horizontally oriented forces with one or more driver units imparting a pushing force and one or more driver units simultaneously imparting a pulling force.

Abstract: Method for generating seismic intersection waves in an underground formation, wherein poles that are previously driven into the formation for other purposes or poles that are driven down for this purpose, said poles being used as a transfer medium for the intersection waves into the formation. The poles are put into transversal vibration by means of an oscillating mass, the oscillations being suitable for forming mainly horizontal polarized waves. In order to achieve a best possible impression of the formation, transversal waves may be generated in a first direction in a first period of time, and a second direction, different from the first direction, in a second period of time. Alternatively, the oscillating mass can be arranged to swing parallel to the pole in order to be able to generate pressure waves. The poles can be equipped with a "skirt", and/or with radially extending flanges in order to secure the best possible attachment in loose formations.

Abstract: A seismic vibrator system for imparting compressional and shear wave vibrations into the earth has an earth contacting base with a vertical post. A tubular hub is slidably received on the post in a piston/cylinder relationship. Spaced apart horizontal top and bottom plates are secured to the hub. A mass is slidably supported between the plates. Pistons interconnect the hub and the mass. Hydraulic energy is used to reciprocate the mass vertically on the post and horizontally between the plates.

Abstract: A seismic source for crosshole testing comprises a hammer rod supported by axial bearings in the ends of a cylindrical housing. Fasteners attach a down-blow hammer to the hammer rod inside the housing. A helical spring inside the housing biases the hammer rod in a downward direction. A hammer cable, attached to the upper end of the hammer rod, raises the hammer rod against gravity and spring pressure until an up-blow hammer attached to the hammer rod below the cylindrical housing strikes the bottom end cap which serves as an anvil. Relaxation of the hammer cable tension results in the down-blow hammer striking the anvil. The device provides compression waves and highly repeatable and selectable-phase shear waves. The device is simple, light and operable by a single person.

Abstract: An apparatus for generating signals and energy for transmission to a large mass. The apparatus incorporates a pulsed generator such as a compensated pulsed alternator for storing and for discharging large amounts of energy in a controlled manner for transmission through a vibrator or similar electromechanical device. In the field of seismic exploration, the apparatus discharges seismic source energy into a land mass or water to generate seismic waves which are reflected from the interface between subsurface geologic formations. The pulsed generator permits the seismic source energy to be discharged in a controlled manner to shape the energy signal, and permits large quantities of energy to be discharged to increase the penetration depth and strength of the reflected signals.

Abstract: A rotary vibrating system is used in surveys of the acoustic properties of the shallow earth. The vibrator itself is of eccentric-mass (or "swinging-weight") form. Coupled to a flywheel, it decelerates freely from a selected high frequency to a selected low frequency. The observed deceleration rate is manipulated to give a measure of the acoustic properties of the near-surface. The eccentricity of the vibrator is then annulled, and the flywheel and vibrator accelerated back to the selected high frequency for another measurement at another location. A display in map form is provided to facilitate visual interpretation of the results.

Abstract: Seismic exploration for hydrocarbons may use an eccentric-mass (or "swinging-weight") vibrator as the seismic source. According to the invention, a vibrator undergoes alternate periods of acceleration and deceleration, during one of which the vibration may be annulled. For example, the rotating mass may be formed in a plurality of parts; then the several parts are disposed in a manner that rapidly and automatically balances their vibratory forces during the period when the vibration is to be annulled, and that adds their vibratory forces during the other period. The invention further provides for modulation of the frequency-time relation during deceleration, for synchronization of several vibrators, and for modulation of the effective output force by controllable variation of the mass, eccentric radius or relative phase of the several parts of the rotating mass; in such modulation, only resultant forces are applied to the vibrator bearings.

Abstract: A three-axis seismic vibrator is provided which imparts compressional and shear wave seismic vibrations, either sequentially or simultaneously, into the Earth's surface. The seismic vibrator includes an earth-contacting baseplate which transmits vibrational energy into the Earth's surface; a support structure; a vibrator assembly pivotally supported at one end by the support structure; and servo-hydraulic control circuits which activate reciprocal vibration along the vibratory axis of the vibrator assembly and sustained oscillatory vibration of the vibrator assembly. The vibrations thus generated are transferred to the baseplate and injected into the Earth's surface. These vibrations and their reflections can then be recorded and analyzed to determine the mineral content of the Earth's surface in the immediate area.

Abstract: An apparatus and method for generating a seismic signal in the earth consisting of positioning a force-modulating means on the surface of the earth and then positioning a vehicle such that at least some of the weight of the vehicle is supported by the force-modulating means. At least one of the vehicle drive wheels is then rotated to cause the force applied to the earth by the force-modulating means to change thereby generating a seismic signal in the earth.

Abstract: In a bore holes, a plurality of resilient members and plates are piled up alternately to form a laminate, and a deadweight is dropped onto the laminate. The resilient members are deformed due to the impact force of the dropped deadweight to cause bore hole water among the plates to be forced out in the outward direction, and elastic waves to occur in the bore hole wall.

Abstract: An apparatus and a method for generating seismic waves utilizes a heavy flywheel positioned for rotation in a vertical plane to generate and store energy which is then transferred to the ground. The device includes two balanced hammers mounted on the flywheel as impact members. In operation, the flywheel is spun to a predetermined speed and then, on command, the hammers are extended outward from the flywheel so that one hammer strikes either a vertical or a horizontal strike member, thus providing a rapid transfer of a large amount of kinetic energy to the ground resulting in the generation of a set of seismic waves.

Abstract: In a bore holes, a plurality of resilient members and plates are piled up alternately to form a laminate, and a deadweight is dropped onto the laminate. The resilient members are deformed due to the impact force of the dropped deadweight to cause bore hole water among the plates to be forced out in the outward direction, and elastic waves to occur in the bore hole wall.

Abstract: A multivibrator waveform monitoring system uses a plurality of seismic energy sources for giving vibrations to strata and a prospector, connected to a geophone, for measuring reflected vibrations. Each of the plurality of seismic energy sources includes a vibrator, a communication unit and a control unit for controlling the starting of the vibrator based on phase difference cancellation information and an operation starting instruction from the prospector. The prospector includes a communication unit and a synchronization control unit for controlling the synchronization of each of the seismic energy sources.

Abstract: A removable bore liner is provided that substantially increases the dependability, flexibility and field-serviceability of seismic vibrators and other hydraulically actuated devices. A method for installing the removable bore liner in a seismic vibrator is also provided.

Abstract: The seismic source (5) according to the invention is associated with a drill string (1) linking a drill bit to a surface installation close to the bit. It comprises a closed chamber (6) fastened inside a drill cellar (4) of the drill string. The section thereof is smaller than the inner section of the drill string, so as to allow free circulation of the drilling fluid. A reactive mass (8) may move within this chamber (6) and along the axis of drill string (1). Hydraulic or electro-mechanical means allow a strong alternating force of controlled frequency and duration to be applied to this mass. The energy necessary to the operating thereof is taken from the fluid current. This source requires no substantial modification in the usual drilling equipments. Drilling a well and performing seismic measurings may be achieved at the same time by means of the source by arranging sensors at the surface and/or in one or several adjacent wells.

Abstract: A sweep frequency vibrator is set forth. It has an elongate cylindrical housing closed at the top and bottom ends. On the interior, there is a reactionary mass fixed to identical upper and lower piston ends. They are received in seal isolated chambers, one being formed in a moveable plug. The plug is moved to thereby vary the spacing of the chambers. As the frequency is changed, plug is moved to assure sufficient clearance from the excursion of the reactionary mass. Hydraulic oil under pressure is delivered to control valves, one for each piston end. The two control valves and piston ends have very short flow lines. Moreover the excursion permitted for the plug assures operation without bottoming out.

Abstract: A multivibrator waveform monitoring system uses a plurality of seismic energy sources for giving vibrations to strata and a prospector, connected to a geophone, for measuring reflected vibrations. Each of the plurality of seismic energy sources includes a vibrator, a communication unit and a control unit for controlling the starting of the vibrator based on phase difference cancellation information and an operation starting instruction from the prospector. The prospector includes a communication unit and a synchronization control unit for controlling the synchronization of each of the seismic energy sources.

Abstract: Methods are provided for making use of an apparatus for generating vibrational energy in a borehole, the apparatus utilizes a mass and a rotary source for suspending the mass in a borehole or in casing in a borehole or in an instrument housing that may be positioned in an opened or cased borehole arranged to cause frictional contact with the surface of the rotating mass, the mass being rotatable about is rotational axis in one direction to cause it to backward whirl in the opposite direction, the centrifugal force of the whirling mass serving to generate vibrational energy that is used to obtain geophysical information as to the structure of the earth surrounding and adjacent to the borehole and for enhancing cementing and production enhancing techniques in oil or gas wells.

Abstract: A broad band seismic vibrator includes a hydraulically-operated actuator with a piston shaft depending from the actuator. A spherical member or ball is secured to an end of the shaft and received in a socket provided in an anvil. The spherical member or ball is securely clamped to the end and in its clamped condition affords the sole support for the actuator. Hydraulic means is provided for unclamping the spherical member to enable the positioning of the actuator in selected degrees of inclination from vertical and azimuth.

Abstract: Low frequency underwater acoustic radiator apparatus includes an air-trapping chamber with a lower portion open to the water, characterized by a mean density higher than that of water. A closed, rigid float element having a mean density equal to or lower than that of water is disposed with a selected loose fit within the chamber. When the chamber and float combination are submerged in water with a substantially vertical orientation of the chamber, the float element floats within the chamber, with the trapped air functioning as a spring coupling. A vibromotive element is coupled to the float element or the chamber element to induce oscillation of the coupled element. The coupling of the chamber and the float by the air spring converts the dipole oscillation of the oscillating element into a monopole pulsation suitable for a low frequency underwater sound radiator.