The Balanced Electromagnetis Separation Transducer (BEST) - a new bone conduction transducer

Ortofon is the holder of the BEST license for conventional bone conductors

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The BEST transducer

Conventional bone conduction transducers, which are relatively large, suffer from poor performance at low frequencies. A new type of electro-dynamic transducer, the Balanced Electromagnetic Separation Transducer (BEST), was developed to improve the performance of the conventional transducers. The development was undertaken by Professor Bo Håkansson from Chalmers University of Technology.

By using a balanced suspension principle, the quadratic distortion forces, as well as the static forces between the vibrating parts, are principally counterbalanced. Both the distortion and the size of the transducer can therefore be considerably reduced. Moreover, the static and dynamic magnetic  fluxes are separated, except in the air gap regions, giving a more efficient transducer.

A new bone conduction BEST transducer

The BEST motor design allows for flexibility in a customized solution, with a number of parameters that can be customized.

The coil: Change of wire and or number of windings will affect the electrical impedance. For the low frequencies, the DC-resistance will dominate but at higher frequencies, the inductance of the coil will dominate. This means that the balance between low and high frequencies is adjustable within some limits. The vibrator needs current to vibrate, so lower impedance means higher vibration force level (VFL). A battery-driven device will therefore be limited in performance by the available current.

The moving mass:
The BEST vibrator is a recoil device, meaning that the moving part of the generator will cause a recoil force on the housing making it vibrate. The mass of the moving part has direct influence on the low-lying main resonance peak and the frequency response in the region. The mass also has direct influence on the maximum VFL for low frequencies. Additional mass element adjust these properties. For a given vibrational level of force, the internal movement of the vibrator unit reduces when adding extra mass. Therefore, extra mass will also reduce distortion and the possibility for mechanical overload.

The spring: The spring force holding the moving mass into place and giving the main resonance peak is made out of two counteracting components namely the two blade springs plus the stationary magnetic field. The balance between these components is very critical in order to achieve the correct compliance and having a stable system

The magnets: Not only will the magnets affect the resonance behavior and the stability of the system, but they will also have a direct influence on the sensitivity of the vibrator. This means that a stronger magnetic field will give more VFL for a given current level.

The housing: Design of the housing can provide an extra resonance peak in the high frequency region thus raising the force level.

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