S218 +SUB low-frequency speaker expansion remained the peculiar characteristics of voice, which applies to all low-frequency amplification expansion. 
SUB speakers use 18MM imported multi-layer birch plywood material, the interior according to different SUB speakers can withstand low frequency monomer stronger impact. with a layer of anti-hit lacquer enclosure, the front panel use metal mesh as protection,  cover the replacement acoustic foam material, both sides of the box are artificially mechanical type design, handling more convenient. 
When two or more SUB pile up in the box, four rubber gasket at the bottom of the cabinet can be embedded into a box prevent box sliding, two parallel NL4 embedded into the rear panel. 
The driver of the SUB uses dual voice differential drive technology and peak to peak. Show a real perfect voice, large annularity heat dissipation design enhanced the dissipation efficiency greatly., ensure the low temperature of the drive unit and greatly enhance the power of compression performance and reduce the distortion. SUB low-frequency speakers can provide clean, dark, the explosive low frequency sound effect.