Loudspeakers' general construction includes a diaphragm, typically a thin film attached to a frame under tension, an electrical circuit, and magnetic sources creating a flux field adjacent to the diaphragm. Electrical current is applied to the circuit, which interacts with the magnets and causes a vibration of the diaphragm, which produces the sound from an electro-dynamic loudspeaker.
Several difficulties in loudspeaker design, manufacturing and materials have presented challenges to be overcome. The diaphragm material and construction needs to achieve an optimum or desired resonance frequency, with minimal or reduced changes in frame attachment or tension occurring during extended operation, while minimizing or reducing any sound distortion, damping or frequency loss to deliver an extended bandwidth of sound. For many speakers, the conductor (i.e. coil) in electro-dynamic loudspeakers is attached directly to the thin diaphragm, necessitating that the conductor be constructed of a material having a low mass and be securely attached to the diaphragm by high temperature and power (large current). The diaphragm is then driven when current passes through the conductor within a magnetic field creating a motive force.
Prior conductor construction has been done by winding 32 AWG magnetic wire (solid copper with thin epoxy coating, either heat or solvent activation) into a “race-track” oval. The limitation of this coil size is approximately six inches due to pre-stress in the wire and an increasingly lower yield and poor performance. Wire breakage is a problem and the number of “race-track turns” is reported to be about 56 turns before the wire pre-stress makes it impossible to achieve the flatness required for use in proximity to the magnets and within the magnetic flux field required.
Transducers of substantially rigid planar diaphragms present a challenge to current electro-magnetic drive systems and specifically to linear moving coils by presenting a low impedance to the amplifier which reduces high fidelity performance by not driving the transducers properly.
Loudspeaker enclosures, rear-planar-surfaces, or multiple transducer positioning have been configured and used to compensate for acoustic problems of backwaves, cancellation “dead spots”, and frequency damping all causing undesirable resonances or other loss of sound quality. The space limitations and configuration of a wide variety of listening environments have presented a big challenge to past designers of loudspeakers and audio systems to try to create a system and known directivity pattern. These specifications are then delivered to the user to compensate by locating or mounting speakers in such a way to avoid the limitations inherent in the design. Size and space constraints of a particular environment have made it difficult in the past to achieve the desired performance from traditional audio systems.
Loudspeakers include a frame that supports magnets used to move the coils, the diaphragm and the terminal, consequently, has faced its own design difficulties. It has to bond to the diaphragm, be rigid enough to maintain uniform tension. Ferrous frames in the past had the advantage of being capable of carrying magnetic energy or flux. Another alternative was using a plastic frame with spring-loaded inserts to achieve very precise control of the separation distance between the top of the embedded magnets and the film conductor. The plastic frames overcame the difficulties of increased weight and could compensate for magnet lots with high thickness variation which allowed cost-savings in the magnet specifications. Plastic frames also helped to address the design capability by minimizing the mean separation distance between driver and magnets.
Historically, loudspeaker technology has relied on a single magnet, dual pole drive system, which resulted in a flux field that was non-linear and limited the dynamic response of the speaker. This non-symmetrical operation is also seen with single ring magnets (adapted for driving traditional cone-shaped speaker diaphragms) and dual pole electro-magnetic drive units, due to the differences in mass, size and configuration of the pole pieces again giving a non-linear pistonic action of the moving coil.
A need exists for an improved loudspeaker having a high performance linear moving coil magnetic drive system.