A pneumatically insulating and acoustically permeable symposer device for a noise transmission duct of an internal combustion engine; the symposer device comprises: an outer casing with a tubular shape, which has an inlet opening designed to be connected to an initial part of the transmission duct, and an outlet opening, which is opposite the inlet opening and is designed to be connected to a final part of the transmission duct; and an actuator plate, which is housed in the outer casing, is arranged towards the inlet opening, and is mounted so as to slide longitudinally; the symposer device is characterized in that it comprises: an emitter plate, which is housed in the outer casing, is arranged towards the outlet opening, is mounted so as to slide longitudinally, and is rigidly constrained to the actuator plate; an insulating element, which is housed in the outer casing and supported by it, insulates pneumatically without allowing any fluid passage through itself, and is arranged between the actuator plate and the emitter plate; and a communication duct with an adjusted cross section, which establishes a limited pneumatic communication between an inlet chamber arranged upstream of the actuator plate between the inlet opening and the actuator plate and an intermediate chamber arranged downstream of the actuator plate between the actuator plate and the insulating element, so that the inlet chamber and the intermediate chamber have the same static pressure but do not have the same dynamic pressure. an outer casing with a tubular shape, which has an inlet opening designed to be connected to an initial part of the transmission duct, and an outlet opening, which is opposite the inlet opening and is designed to be connected to a final part of the transmission duct; and an actuator plate, which is housed in the outer casing, is arranged towards the inlet opening, and is mounted so as to slide longitudinally; the symposer device is characterized in that it comprises: an emitter plate, which is housed in the outer casing, is arranged towards the outlet opening, is mounted so as to slide longitudinally, and is rigidly constrained to the actuator plate; an insulating element, which is housed in the outer casing and supported by it, insulates pneumatically without allowing any fluid passage through itself, and is arranged between the actuator plate and the emitter plate; and a communication duct with an adjusted cross section, which establishes a limited pneumatic communication between an inlet chamber arranged upstream of the actuator plate between the inlet opening and the actuator plate and an intermediate chamber arranged downstream of the actuator plate between the actuator plate and the insulating element, so that the inlet chamber and the intermediate chamber have the same static pressure but do not have the same dynamic pressure. an emitter plate, which is housed in the outer casing, is arranged towards the outlet opening, is mounted so as to slide longitudinally, and is rigidly constrained to the actuator plate; an insulating element, which is housed in the outer casing and supported by it, insulates pneumatically without allowing any fluid passage through itself, and is arranged between the actuator plate and the emitter plate; and a communication duct with an adjusted cross section, which establishes a limited pneumatic communication between an inlet chamber arranged upstream of the actuator plate between the inlet opening and the actuator plate and an intermediate chamber arranged downstream of the actuator plate between the actuator plate and the insulating element, so that the inlet chamber and the intermediate chamber have the same static pressure but do not have the same dynamic pressure.