1. Decoupling:
If your subwoofer is creating powerful resonances in the floor, you can use resonance dampers such as anti-vibration pads or an anti-vibration mat. If you choose to use a mat, it is best to place a ceramic plate on top of it and beneath the subwoofer.
2. Coupling:
If you would like the vibration to be directed into your floor, you can use spikes. Their conical shape and small contact area direct the vibrations through the housing into the floor. Their shape also helps to avoid vibration being directed back into the subwoofer. Coupling can be very effective for floors with carpet.
For additional information, read our blog article: Speaker decoupling & coupling for better sound