PianoDisc PDS150 User Manual page 11

Placement of a PDS Powered Speaker
The PDS150 and 250 speakers are designed for mounting to a beam
under a grand piano that is equipped with a PianoDisc® player system.
If this is what you have, the speaker was installed at the factory or by a
certified PianoDisc® field technician using the supplied bracket and
screws.