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Low TCR voice coil wire
Thermal Coefficient of Resistivity (TCR) Maintains constant impedance
For electric coil windings, particularly in moving coils such as the voice coil of a heavy duty bass loudspeaker or other electro-acoustic transducer, the present invention has found metallic materials, as alternatives to copper or aluminum in the voice coil wire, that can provide increased available maximum SPL (sound pressure level) exceeding an empirical limit, just under 120 dB/1 m, that has been found to apply to various loudspeakers of known art regardless of efficiency and structural differences. Through study of known art regarding this limitation and theoretical analysis of the factors in voice coil structure and design that limit the maximum attainable SPL, a novel basis for selecting voice coil wire material has been developed. By selecting wire material for low TCR (temperature coefficient of resistance) along with suitable resistivity and density, rather than for low resistivity alone which has conventionally dictated copper or aluminum, the present invention has led to the identification of new wire materials that can increase the available SPL. Such materials include alloys of aluminum containing between two and five component basic metals selected from the following group: magnesium, silicon, manganese, zinc and copper. The alloy Al Mg(3.5%) in extruded form yields maximum SPL 1.5 dB above that of pure aluminum and 3.32 dB above that of pure copper.

Patented 1994 JBL Incorporated.