18 inch woofers produce great low bass and subsonic bass with a huge amp and a huge box. BUT, you will be losing what 8, 10 and 12 inch woofers produce, which is great mid bass or the frequencies around 100-250 because they can move faster. The 8, 10 and 12's also produce decent bass when boxed right. 18's will make an excellent and expensive anchor, magnetic fishing device or ballast.