HK Audio Linear SUB 1800A - Aktiv Subwoofer18" bass reflex subwoofer with superior bottom end SPL up to 132 dB Frequency range down to 38 Hz Perfect fit for Linear 3 Series, Linear 5 Series Ideal as an extension to the Elements Big Base system HK Audio Linear SUB 1800A Active Subwoofer 18" bass reflex subwoofer with superior bottom end. A powerful subwoofer with an SPL of up to 132 dB and a bass range as low as 38 Hz. Perfect for the Linear 3 Series, Linear 5 Series and as an extension to the