LAM SENG FATT:
Since a subwoofer vibrates a lot, you need to place something that absorbs vibrations between it and the floor. If the vibrations are not absorbed, they will simply be transmitted to the floor which in turn will vibrate especially if the floor is made of wooden strips.
You can use pieces of foam (not too soft), rubber mat, thick felt mat or a piece of carpet.
Other audiophiles have told me that they had experienced good results with something that is called an 'Earthquake Pad' which is commonly available in Japan (since it is prone to earthquakes) and is sold in Daiso stores worldwide.
It is blue in colour and is made of elastomer resin. It is gel like and looks like the gel heel pads meant for slipping into shoes. Earthquake pads are meant to be stuck on the bottom and sides of electrical items like fridges, computers and microwave ovens so that they will not topple easily during an earthquake. And if they do topple, the pads are meant to absorb the impact of the fall and reduce damage to the items.
