NSD4015N is a 1.5 inch exit, 4" voice coil neodymium compression driver has been designed for extremely high quality sound systems application. The titanium nitride coated dome - so called TPM True Piston Motion technology - dramatically improves stiffness with obvious benefits in transient and intermodulation distortion response. With its very high value of elasticity modulus (six times higher than standard titanium), the ultra-thin nitride coated film applied both sides of the dome doubles the treated dome stiffness. The piston frequency range motion extends then by 25% when compared to regular titanium diaphragm, showing a predictable, ideal frequency response decay and avoiding top-end spurious resonances. This results in a more natural sound character up to the top end part of the spectrum. The nitride-free ellipsoidal suspension shape has been designed to maintain constant titanium stiffness, assuring a 3rd harmonic distortion lower than 0.05% over the whole working frequency range. The NSD4015N extremely powerful neodymium magnet assembly has been designed to obtain 22 KGauss in the gap for major benefits in transient response. The motor structure, throughout the precisely coherent phase plug with 4 circumferential slots and copper ring on the pole piece, reduces inductance effect and distortion. Four top plate air ducts have been designed to act as a loading chamber for the diaphragm, implementing mid band distortion and response figures. The custom designed O-ring creates a tight seal between the plate and the cover assuring air chamber loading. Excellent heat dissipation and thermal exchange are guaranteed by the direct contact between the magnetic structure and the aluminum cover which gives a lower power compression value. A special epoxy coating is applied to the ring magnet and the top and back plates of the magnetic structure making the driver more resistant to the corrosive effects of salts and oxidization.