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 can be adjusted within some limits. Basically 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 which then will vibrate. The mass of the moving part has direct influence on the low lying main resonance peak and the frequency response in the region. But the mass also has direct influence on the maximum VFL for low frequencies. An extra mass element is used to adjust these properties.
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
As stated just above the magnets will affect the resonance behavior and the stability of the system but more directly the will have 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 and thus raising the force level.