Hi-rigid woofer and reduced inherent resonance HR diaphragm is employed. By using the radial papermaking technique and whizzy hybrid materials, HR diaphragm realizes low distortion, high durability, large internal-loss and fast propagation speed like a metal diaphragm. This unique-shaped diaphragm offers smooth frequency response and superior low frequency reproduction that the conventional cone diaphragm has never achieved. Newly developed zincky die-cast frame based on the strength analysis by the fineelement method. Stronger magnetic circuit using 3,100g alnico magnet is equipped for higher input durability and larger amplitude driving. Oval mounting hole can be adjusted between 370 - 375mm. W400A-HR has the compatibility with not only OSTEX old 15” drivers but some famous woofers’ replacements. UDR tangential surround & spider are equipped to realize the less anti-resonance and superior amplitude characteristic.