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.
I have a similar situation with ML SL3s surrounding a fireplace that has a TV in it - another large glass area that bounces sound. I have a wool numdah (wall hanging) that I hang over the fireplace when I'm not using the TV. My advice is to try something cheap and quick and see if it makes a difference for you and then take it from there.

I just finished reconfiguring my room because of the hearth problem. For 8 years I've had one speaker up on the hearth and one on the floor. I got new speakers and decided to re-wire everything so that I could get the right speaker placement and I am so glad that I did. The issue I had was no flexibility in terms of placement. The bigger problem now is the WAF, which is quite low at the moment. Oh well.
These are front port bipolar speakers? The fireplace has folding glass doors. What would you suggest that I hang???
Should I use the spikes??
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.
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.