The USRD type G40 calibrator is a shipboard system for conveniently calibrating hydrophones and their associated measuring systems by the comparison method in the fr.equency range 25-1000 Hz.This system provides isolation from mechanical deck vibrations and ship roll or pitch, and it can generate sound pressure levels from 130 to 190 dB re 1 j•Pa from 0.22-to 22.3-V driving signals.Subject Classifications: 30.85.

This paper presents the design and development of a truly omnidirectional, low-frequency, high-power, underwater sound projector standard. The transducer is operational within the frequency range from 1 Hz to 10 kHz, with a transmitting response which is stable with hydrostatic pressures up to 1524 kPa (152-m depth) and temperatures from 5 to 35°C, and can be used as a hydrophone or a projector. The sensitive element is a 22.9-cm (9.0 in.) o.d. piezoelectric lead zirconate–lead titanate (MIL-STD 1376, Type 1) hollow sphere encapsulated in polyurethane. This transducer, designated the USRD type F80, produces an undistorted omnidirectional source level that is linear with driving voltages up to 1000 V rms, and can also be electrically tuned for a higher response at predetermined, discrete frequencies. This paper includes an electroacoustic equivalent circuit model of the transducer, compares the predicted to the measured transmitting response, and discusses the mechanical and electrical design.

A hydrophone calibrator has been developed by the Naval Research Laboratory to calibrate hydrophones as large as 12 cm in diameter by the comparison method in the frequency range 25–1000 Hz at sound pressure levels from 130 to 190 dB re 1 µPa. Thus, it is possible to calibrate a hydrophone immediately before deployment and immediately after recovery. The calibration can include the complete electronic measuring system as well as the hydrophone. Vertical stabilization of the calibrator for ship roll and pitch of 10° and isolation from ship's noise are provided.

Development of a hydraulically powered acoustic projector with a minimum source level of 160 dB re:1 μPa at 1 m over the 1 to 10 Hz range will be presented. This projector will be used at the Underwater Sound Reference Detachment for low-frequency underwater acoustic testing. Design parameters and their relation to the unique capabilities of hydraulic power for this low-frequency application will be discussed. Construction details, and acoustic as well as mechanical performance will also be presented. [Work supported by Naval Sea Systems Command, Code 63R.]

Unrealistic requirements are often placed on sonar transducers employed in ocean acoustical tests. This is because projectors and hydrophones are often the last components considered when system requirements are established. Acoustical systems for performing these tests are typically designed for one application, but are frequently used for additional tests. This can cause conflicting system requirements and place constraints on the transducer design which result in failure to meet test objectives and redesign of the whole system. This paper provides an approach for first establishing realistic transducer design requirements which, in reality, drive those for the complete system. Experience with important transducer acoustical parameters such as operating frequencies, sensitivity and transmitting response, directivity, dynamic range, self-noise, and flow noise is discussed. Also discussed are experiences with at-sea effects of system deployment while stationary or maintaining a constant velocity, operating depth, cable dynamics, hydrodynamically configured tow bodies, and costs.