2021 Onkyo 4" Full Range Speaker Unit OM-OF101 Backload Horn Enclosure Russian birch sub-baffles increase rigidity and bring out the characteristics of OM-OF101. Furthermore, it increases the rigidity of the entire enclosure, reducing the box noise and cloudless sound. It features a large amount of information, delicate treble that translates to nuances and crisp midbass. Quality materials are NC machined for precise dimensions. Since it is hard growing in severe Scandinavian environments and is packed with grain, the Russian Birch plywood t15 is used for baffle boards and front boards that reproduce clear and high sound quality when used for enclosures. The top board is made of shina plywood t12 and other components made of MDF board t12. Stronger construction and better seal The dowel structure has a high sealing rate and is easy to assemble.