Answer two quick questions and we'll point you to the right port option for your sound, your kit, and your budget.
A bass drum port hole is a cut in the front (resonant) head that lets you mic the kick from inside the drum and tightens the low-end response. From there you can leave it as a clean cut, reinforce it, add a finished ring, or step up to a KickPort for more punch. The full guide to bass drum port holes walks through each option in detail.