Speaker brackets to plasterboard?

Hi All,
I'm trying to fit speaker brackets to a room. I've hidden the wires and tried the following fixtures for each speaker:
http://www.diy.com/bq/product/product.jhtml?PRODID 706&CATID304
The speakers are around 6 kilos each. The plaster is horse-hair I believe, and is about a centimetre thick, followed by a void of around 1.5 cm, then brick.
I filled the void with expanding foam during installation, hoping that it would relieve some of the strain on the plaster by spreading the load. I also cut a small frame of hardboard to put the fixings onto, again to spread the load and make it easier for them to expand. This worked very well on one, but after a weight test, the other failed, damaging the plaster. I've removed it, and having a filling-job ahead :-(
There doesn't actually seem to be a void at this one, the plaster seems to go back to the brick. This is visible now that half the wall is apart! Is this normal? There is definitely a void at the bottom of the wall.
Can anyone suggest any options? Having routed the wires, I don't want to give up. My thoughts are:
-speaker/picture frames, like these http://www.wharfedale.co.uk/lpanel1.htm , but sonically, they wouldn't be the best, especially given the corner layout I'm now stuck with. I wanted these for rear-surrounds in the front room, but I could swap over and use them in the bedroom.
-buy a stud detector to find a more solid part of the wall to attach onto
-mount on the adjacent wall (it's a corner). Could have the same problems. This wall also has a similar void mentioned above at the bottom (where I worked on another backbox), but the void may not exist at the top, like the one I'm working with.
-somehow mount directly into the brick (possible?), with some sort of stage to bring it out to flush with the wall. I now have a hole in the wall that would facilitate this already, as a result of the first attempt!
-give up, assuming plaster just can't take the weight
Can anyone help? Googling seems to get me nowhere useful...
I've had the same speakers up on the wall in another home successfully, which was more modern and had prefab plasterboard, so it shouldn't be beyond the realms of impossibility!
F.
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square of plaster equal in size to the speaker bracket's wall-plate. Find a piece of wood or MDF which is the right thickness to go from the brickwork to the surface of the plaster, and cut it to fit where the plaster has been cut out. Drill clearance holes through the wood to allow the fixing screws to pass through. Drill the wall and fit heavy duty rawlplugs (the plastic ones requiring a 7mm hole should do). Use 3" No. 10 screws to screw the brackets to the brickwork, with the screws passing through the clearance holes in the wood or mdf. That'll never fall off!
[To make it easier to assemble, stick the wood/mdf to the brickwork with Gripfill before screwing the bracket on - making sure that the clearance holes for the screws line up with the rawlplugs! You could also beautify the cut edges of plaster with Pollyfilla at this stage - blending it with the wood/mdf, so that nothing untoward shows once the brackets are on].
Roger
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wrote in message

yup, just confirming.
Regards, NT
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Agreed.
Mike P.
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Thanks! Sounds like that ought to hold anything. As I will be drilling into brick, I guess I'll be needing a hammer-action drill. Are the sub-20 ones I've seen any good, or just cheap garbage? I already have two other drills, so don't want to go nuts on price! Will go on a borrow-hunt first though!
What about the other bracket, the one I think is OK? I'm thinking about attaching a 6kg weight for a few days to make sure it's sound. Is this something that might just fail at a random future date, even if it passes this test? If so, I might do the same to it.

Sure! This also means that should you take the brackets off, the wall won't start to fall apart!! ;-)
Thanks for the help, was getting quite worried about getting this sorted out; getting the carpet delivered in two weeks!!
F.
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You can get all that you need (dirt cheap drills) at: www.screwfix.com
Mike P.
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If it *is* brick - and not breeze or Thermalite - you'll need at least a hammer drill. If you expect to be drilling lots of holes in brick (as most d-i-y-ers do) get an SDS drill. You'll find all sorts of uses for it!

good tug - equivalent to several times the weight it needs to support. If it stays put without any movement, it will be ok.
Roger
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Thanks to all who helped out. Bracket is now fitted and finished and very very strong!!
Cheers!
F./
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