Abstract: Compensation for interaction between separate channels of a noise cancellation system in a vibrating or noisy structure is obtained by the addition of pre- and post-processing circuits for channel controllers to electronically separate the channels so that each channel operates on uncoupled modes of vibration. The processing circuits include sum and difference elements.

Abstract: In a hot gas duct wherein it is desirable to retain heat within the duct by insulated sidewalls and wherein the duct is substantially longer than it is wide, it is necessary to support the duct against excessive deformation in the lateral direction. Exterior support structures are unacceptable because locating cross members or struts becomes problematic. Interior support structures must be carefully designed so as not to inhibit thermal expansion and contraction within the duct. It is proposed that a lateral bracing system or truss be disposed entirely inside the hot gas path and provision be made to ensure adequate facility for uniform expansion of the truss within the hot gas duct.