Bass drum hole accessory, red color. It's said to be eye-catching and cool. For use as a bass drum subwoofer. Tube hole diameter is 10.6 cm, requires a hole of about 11 cm. Instructions on how to make the hole can be found on YouTube, etc. Compass cutters are commercially available (for those who need one, it's an extra 500 yen, please comment). To cut, remove the head, remove the round packing film, and attach it to the surface of the head. Insert the main tube body and insert the rubber from the back. It's easier if you use water. Place it in the microphone hole and connect it to the amplifier (photo). Have someone listen and adjust the sound. No profit! Ready to ship immediately after packaging.