To develop this new Illusion Audio speaker line we combined our decades of experience manufacturing high-end audiophile speakers with our passion for maximum performance mobile audio. The development process covered several years and literally months of listening to each individual model to fine tune musical quality and durability. We applied the highest available technologies in construction materials, Finite Element Analysis engineering and manufacturing to develop speakers that are compact and lightweight for easy installation without making any performance compromises. Our artistic design team has paid careful attention to aesthetics, as we feel they are beautiful speakers too!Aluminum coated injection polypropylene cone with rubber surround powder coated steel basket. Illusion Audio E6CX 6.5 Electra Series Coaxial Speaker Kit - Pair. Free Air Resonance: 86.07 Hz. Titanium-coated injection polypropylene cone with rubber surround.