Abstract: An automatic underwater acoustic impedance measuring apparatus is instrumented with transducers whose outputs are led to a computer for the automatic measurement of acoustic impedance. One hydrophone is positioned so that it senses the incident and reflected signals to compute reflection factor. A second hydrophone is positioned at the face of the sample material so that it senses the incident and reflected waves from which it is possible to compute the phase angle. Acoustic impedance is obtained from the phase angle and reflection factor, computed and printed out in real time and automatically swept through a frequency range of interest.

Abstract: The lightweight underwater acoustic baffle with enhanced performance chareristics particularly at low frequencies is provided by a stiffened resistive screen means affixed in front of a compliant material for allowing the baffle to reflect on the compliant side and on the screen side, a rigid irregular shaped material means with a primary open surface area affixed to the screen as a means for attaining maximum stiffness with a minimum weight, a compliant means affixed behind the screen means, a water fluid sealing and container means within the baffle means for suffusing the stiffening core area and its attached screen for generating miniscule acoustic resistance in the screen and producing a greater impedance mismatch thus enhancing the insertion loss and baffle performance, and, an attachment affixed to the container means for attachment to a vessel.

Abstract: An automatic underwater acoustic impedance measuring apparatus is instrumented with transducers whose outputs are led to a computer for the automatic measurement of acoustic impedance. One hydrophone is positioned so that is senses the incident and reflected signals to compute reflection factor. A second hydrophone is positioned at the face of the sample material so that is senses the incident and reflected waves from which it is possible to compute the phase angle. Acoustic impedance is obtained from the phase angle and reflection factor, computed and printed out in real time and automatically swept through a frequency range of interest.

Abstract: A method for preparing a resistive screen for underwater sound absorption consisting of a metallic honeycomb structure, adding a thermosetting plastic material to the cells within said structure, heating said structure under pressure and forming small apertures within said thermosetting plastic material.