Daniel G. Cole
Adaptive Technologies, Inc., 620 N. Main St., Ste. 306, Blacksburg, VA 24060
William R. Saunders
Virginia Polytechnic Inst. and State Univ., Blacksburg, VA 24061-0238
The fixed-gain feedback methods often provide the only means of limiting transient noise and excessive sound pressures due to unmeasurable, incoherent disturbances. The use of direct acoustic rate feedback (DARFB) to control an enclosure's reverberant energy has the benefit over other feedback methods of larger stability margins and improved stability robustness. It also provides a means for achieving acceptable sound pressure levels in locations and environments which are not suited to surface treatments of sound absorbing materials. The effect of DARFB on the growth and decay of sound in enclosures is investigated and the change in the reverberation time of a sound field is discussed for active absorption using single and multiple controllers. Various models for the dynamics of sound growth are used and are shown to provide equivalent or similar results. Effective Sabine absorption coefficients are shown for active absorption and are compared with sound absorbing materials. The effectiveness of transducer placement is also discussed with respect to active absorption and the closed-loop reverberation time. Numerical examples of acoustic absorption are given for a rectangular enclosure.