NOVELTY - System (20) for processing biomass, comprises: a reactor chamber having rigid walls and adapted for operation under a net positive static pressure; a fluid inlet port in reactor chamber to receive a fluid or mixture containing biomass; a fluid outlet port in reactor chamber to discharge fluid or mixture once it has been processed in the chamber; and many acoustic drivers (201a, 201b) coupled to rigid walls of chamber to cause an acoustic field (substantially in a portion of chamber in which biomass is located) within chamber in at least an area of chamber under a net positive static pressure.    USE - The system is useful: for processing biomass (claimed) (preferably cellulosic biomass), where the biomass is useful in making fuels or fuel precursors; for the conversion of carbohydrates e.g. hemicelluloses and celluloses, into glucose by depolymerization of the bigger bio-macro-molecules.    ADVANTAGE - The system utilizing acoustical energy comprising ultrasound, provides increased cavitation activity, which cause enhanced processing effects on the cellulosic material.    DETAILED DESCRIPTION - An INDEPENDENT CLAIM is also included for substantially converting a biomass from a first form to a second form, comprising receiving the biomass in the first form in combination with a fluid matrix into an inlet port of an acoustic resonator reactor, pressurizing the biomass and the fluid matrix to a given static pressure above atmospheric pressure within the reactor, applying an acoustic field to the pressurized biomass and fluid matrix so as to cause acoustic cavitation in at least a portion of the reactor containing at least some of the biomass, applying mechanical or chemical catalyzing factors to the biomass in the fluid matrix so as to cause conversion of the biomass from the first form to the second form, discharging the biomass in the second form and the fluid matrix from an outlet port of the reactor and recovering the biomass in its second form.    DESCRIPTION OF DRAWING(S) - The figure illustrates a fluid and acoustic circuit for delivering fluid media into an acoustic resonator under pressure.    System (20)    Electrical circuit (200)    Acoustic drivers (201a, 201b)    Resonator chamber (220)    Processor (250)