Volume 119, Issue 2, February 2006
Index of content:
- TRANSDUCTION 
A comparison of the underwater acoustic performance of single crystal versus piezoelectric ceramic-based “cymbal” projectors119(2006); http://dx.doi.org/10.1121/1.2150153View Description Hide Description
For nearly , piezoelectricceramics (primarily from the PZT family) have been the materials of choice as the active elements in underwater electroacoustic sound projectors. There is currently great interest in the materials science community for the consideration of newly discovered single crystal relaxor ferroelectric compositions as a potential replacement in applications that utilize piezoelectricceramics. One of the salient features of single crystal ferroelectrics is piezoelectric coefficients that are three to seven times greater than those found in PZT. Most of the single crystal data reported in the open literature, however, are for near static drive conditions. This paper reports on the acoustic performance of prototype underwater sound projectors built from single crystalmaterials and driven at high drive levels over the frequency range of to . It is shown that the single crystal-based projectors exhibit at least a higher source level as compared to identical PZT-based units. In addition, the volt-amp product required to produce of acoustic output is approximately one-third as much. It has also been demonstrated that when driving either the PZT-based or single crystal projectors for under high drive, no significant degradation in acoustic performance occurs.
119(2006); http://dx.doi.org/10.1121/1.2151694View Description Hide Description
In conventional loudspeaker system design, the force factor is chosen in relation to enclosure volume, cone diameter, and moving mass to yield a flat response over a specified frequency range. For small-cabinet loudspeakers such a design is quite inefficient. This is shown by calculating the efficiency and voltage sensitivity. The frequency response is manipulated electronically in a strong nonlinear fashion, which has consequences for the sound quality, but it then turns out that systems using much lower force factors can provide greater usable efficiency, at least over a limited frequency range. For these low-force-factor loudspeakers, a practically relevant and analytically tractable optimality criterion, involving the loudspeaker parameters, will be defined. This can be especially valuable in designing very compact loudspeaker systems. An experimental example of such a design is described. This new, optimal design has a much higher power efficiency as well as a higher voltage sensitivity than current bass drivers, while the cabinet can be much smaller.