limits the magnitude of active (i.e., real) current. Torque bursts two to three times higher than the maximum design torque are realizable. The brushless wound-rotor synchronous doubly-fed (BWRSDF) machine is the only electric machine with a truly dual ported transformer circuit topology (i.e., both ports independently excited with no short-circuited port). The dual ported transformer circuit topology is known to be unstable and requires a multiphase slip-ring-brush assembly to propagate limited power to the rotor winding set. If a precision means were available to instantaneously control torque angle and slip for synchronous operation during operation while simultaneously providing brushless power to the rotor winding set, the active current of the BWRSDF machine would be independent of the reactive impedance of the transformer circuit and bursts of torque significantly higher than the maximum operating torque and far beyond the practical capability of any other type of electric machine would be realizable. Torque bursts greater than eight times operating torque have been calculated. Continuous torque density The continuous torque density of conventional electric machines is determined by the size of the air-gap area and the back-iron depth, which are determined by the power rating of the armature winding set, the speed of the machine, and the achievable air-gap flux density before core saturation. Despite the high coercivity of neodymium or samarium-cobalt permanent magnets, continuous torque density is virtually the same amongst electric machines with optimally designed armature winding sets. Continuous torque density relates to method of cooling and permissible operation period before destruction by overheating of windings or permanent magnet damage. Other sources state that various e-machine topologies have differing torque density. One source shows the following: where—specific torque density is normalized to 1.0 for the surface permanent magnet (SPM)—brushless ac, 180° current conduction. Torque density is approximately four times greater for liquid cooled motors, compared to those which are air cooled. A source comparing direct current, induction motors (IM), PMSM and SRM showed: Another source notes that PMSM up to 1 MW have considerably higher torque density than induction machines. Continuous power density The continuous power density is determined by the product of the continuous torque density and the constant torque speed range. Electric motors can achieve densities of up to 20KW/KG, meaning 20 Kilowatts of output power per kilogram. Acoustic noise and vibrations Acoustic noise and vibrations are usually classified in three sources: mechanical sources (e.g. due to bearings) aerodynamic