A limitation currently facing active structural acoustic control (ASAC) researchers is that an ideal minimization quantity for use in the control algorithms has not been developed. A novel parameter termed the "weighted sum of spatial gradients" (WSSG) was recently developed for use in ASAC and shown to effectively attenuate acoustic radiation from a vibrating flat simply supported plate in computer simulations. This paper extends this research from computer simulations and provides experimental test results. The results presented show that WSSG is a viable control quantity and provides better results than the volume velocity approach. The paper also investigates several of the challenges presented by the use of WSSG. These include determining a method to measure WSSG experimentally, an analysis of the influence of noise on WSSG control results and complications presented when degenerate modes exist. Results are shown and discussed for several experimental configurations.

The weighted sum of spatial gradients (WSSG) control minimization parameter is developed for use in active structural acoustic control (ASAC) on a clamped flat rectangular plate. The WSSG minimization parameter is measured using four accelerometers grouped closely together on the test structure. In previous work, WSSG was developed on a simply supported flat rectangular plate and showed promise as a control metric. The displacement on the clamped plate has been modeled using an approximate analytical solution assuming shape functions corresponding to clamped-clamped beams. From the analytical formulation, weights, which were found to be the reciprocal of the wave number squared, have been derived to produce a uniform WSSG field across the plate. In active control simulations, this quantity has been shown to provide better global control of acoustic radiation than volume velocity. Analysis is presented which shows that comparable control, regardless of the sensor location, can be achieved using WSSG. Experimental results are presented which demonstrate that WSSG works effectively in practice, with results similar to the simulations. The results show that minimization of WSSG can be used as an effective control objective on clamped rectangular plates to achieve attenuation of acoustic radiation.

Active structural acoustic control (ASAC) is an active noise control technique, which provides global control by targeting and minimizing the structural vibrations which contribute to radiated sound power. The majority of research in ASAC has focused on validating various proposed concepts on flat rectangular plates, an important but not comprehensive class of structures. To extend the body of knowledge, ASAC has been investigated on finite ribbed plates under a variety of boundary conditions. Simulated results have shown that two different approaches, minimizing the volume velocity and minimizing the weighted sum of spatial gradients (WSSG) provide comparable average attenuation of radiated sound power on ribbed plates. With regards to sensing, minimizing WSSG has several advantages over minimizing volume velocity. In particular, WSSG has been formulated to be easier to measure than volume velocity, without requiring a priori information about the structure or its modes. WSSG has also been shown to be relatively uniform spatially and relatively insensitive to boundary conditions, while also providing improved control over volume velocity at structural modes higher than the first mode. These results suggest that more practical, complex vibrating structures can be effectively controlled for the reduction of radiated sound power using the WSSG approach.

During the advent of active structural acoustic control, attempts were made to target and control structural vibration mode shapes to reduce radiated sound power. In the late 1980s and early nineties work on acoustic radiation mode shapes developed an alternative way to target structural acoustic radiation. By attempting to control the radiation mode shapes, contributing structural modes could be more easily targeted. Radiation mode shapes have been examined previously for rectangular plates. The method has been extended to demonstrate radiation mode shapes of circular plates and cylindrical shells. Certain spatial derivatives of plate vibration have been found to be highly correlated with the most efficiently radiating radiation mode shapes at low frequencies. A weighted sum of these spatial derivatives is proposed as a new, generalized control metric.