Phil L wrote:

Most replies here are saying that it's OK to use this fixing or that
fixing, but I've a feeling they're missing the (major) point in that they
are fixing to a plasterboard stud wall, and yours are not stud walls.

Your walls are built with two sheets of PB stood upright with basically a
giant eggbox keeping them apart, and no timber or metal struts are used
for rigidity.

That's exactly what we had in our previous house, Paramount partition board.
The speakers must have been there for about 20 years with no problems.

A stud wall has (usually timber, but more recently, box aluminium) struts
running up and down and also across - this gives the wall much more
strength, and using PB fixings here is usually OK because each fixing will
generally be no more than 6 inches away from one or more of these

.... with a studs only 12 inches apart ?

--
Mike Clarke