Unfortunately this isn't true in all cases. A former SPL competitor, on another forum, sealed off and direct fired his 15" RE XXX in a 2000 Civic and lost 3 dB on the Termlab from doing so. He also said it seemed like he lost his ultra low bass that you could feel. He showed before and after videos of his setup on the TL and he was telling the truth.//content.invisioncic.com/y282845/emoticons/frown.gif.a3531fa0534503350665a1e957861287.gifi have my subs sealed off and the vibration of the sub enclosure creates the trunk to still rattle a bit, but it is the best thing i have ever done to my system. Plus, i have done tests and you will likely lose no SPL by doing this.