This d&b audiotechnik Ci-SUB 18 subwoofer offers great sound. However, the grille foam is missing.

Using this subwoofer is easy. Just connect it to your audio system and adjust the settings according to your needs. When using, make sure it's placed on a stable surface to avoid vibrations. As for maintenance, keep it clean by using a soft, dry cloth to wipe it regularly. Since the grille foam is missing, be extra careful to prevent dust from getting inside. Also, don't expose it to extreme temperatures or humidity as it can damage the internal components.