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Loudspeaker drive systems employing negative velocity feedback, by directly controlling the voice-coil motion, can improve the over-all linearity and largely suppress the fundamental resonance. These features permit good results using reasonably efficient loudspeakers in small sealed-box enclosures. In stable systems the degree of control provided is directly related to the loop gain. Instability and overloading problems can arise in partially capacity-coupled amplifiers unless special phase-compensation circuits are employed. For comparable distortion reduction at higher frequencies one must employ the same number of valves in the main amplifier as in conventional high-quality amplifiers. An additional valve stage is needed outside the main feedback loop to provide correction for the loss of 20 db per decade in radiating efficiency below the point of ultimate resistance of the equivalent piston radiator. The main amplifier is developed from Mullard circuits. Additions include a bridge in the voice-coil circuit and low-frequency phase-compensation elements. Reliable design procedures for these are given in detail. Specifications necessary for satisfactory performance are discussed.