You spike a sub to couple it to resonant subflooring for improved bass signal propagation. This can also be used on over-resonant hard flooring to DEcouple the subwoofer. So, the answer depends on what you have underneath the subwoofer enclosure--carpeting (spikes may help), hardwood floor (spikes not needed unless floor is TOO resonant), concrete (spikes won't work anyway), etc. As for the height, how thick is your carpet (most subs are not downfacing for obvious reasons, but if yours is, you need at least an inch between the sub surface and the floor material to avoid whooshing noises etc.). This is in addition to the coupling issue. In getting the best response, experimentation is key, as long as it is permitted by the OTHER residents (particularly female, I suspect) of your listening area.