speakers on fireplace hearth???


Anyone have any experience with placing speakers on bricks in front of unused fireplace? The hearth is raised about 8 inches. Should I place anything under the speakers?...use the spikes? The back of the speakers will be about 10 inches from brick. Should I hang something between the speakers and the brick? Advice or websites that address this issue would be appreciated.
papertrail
My parents have their moderate sized bookshelf speakers on a travertine fireplace hearth bench about a foot and a half off the floor. They are using BDR cones under each speaker. No problems, sounds great.
Are the speakers bi-polar, di-polar, or have a significant backwave (ported)? If so you may have issues with that large resonating chamber called a chiminey ;<{) Consider hanging something over the fireplace if that is an issue.
These are front port bipolar speakers? The fireplace has folding glass doors. What would you suggest that I hang???
Should I use the spikes??