### ASA 129th Meeting - Washington, DC - 1995 May 30 .. Jun 06

## 1pNS6. Optimal design of enclosures for active noise control and
isolation.

**Vasundara V. Varadan
**

**
Jaehwan Kim
**

**
Vijay K. Varadan
**

**
**
*Res. Ctr. for the Eng. of Electron. and Acoust. Mater., Dept. of Eng. Sci.
& Mech., Penn State Univ., University Park, PA 16802
*

*
*
An optimal design technique is used to find the optimal conditions for
several parameters of an enclosure to reduce the noise radiated from an
internal source. Design variables in the optimization procedure are the size
and thickness of the enclosure, size and thickness of actuators, the location
of actuators, and the applied voltage on the actuators. The objective function
in optimal design is the total radiated sound power at far field. The practical
limits of the design variables are taken as constraints. The acoustic field
acts as a distributed load on the walls of the enclosure. A 3-D finite element
model is used to model the walls and the PZT actuators. With an applied voltage
on the actuators and with acoustic pressure loading, the velocity distribution
on the outside of the walls can be found by solving the finite element
equations. These are used in the Helmholtz integral representation to compute
the radiated sound field to the exterior of the enclosure. The design is
performed at a single frequency which may represent the dominant frequency in
the noise spectrum. By comparing the initial design and the optimal design
results, a noise reduction of 12--18 dB has been achieved.