Instead of a whole plaque behind the speaker, why not just create two roughly triangular wooden shims the width of the t-bracket arms. The angles of the shim would fill in the gap between where the t-bracket sticks out and the telepost cover.
Predrill it and paint it black. Then use a screw long enough to secure the t-bracket arms all the way to the telepost cover. The arms would be nice and solid and the small shims would just look like part of the t-bracket mounting hardware.

Last edited by 80'sMan; 12/31/10 12:54 AM.
Epic 50 - 500 System ( M50 / QS4 / VP100 / EP500 )