virtual int add_speaker (const PBD::AngularVector&);
virtual void remove_speaker (int id);
virtual void move_speaker (int id, const PBD::AngularVector& new_position);
virtual void clear_speakers ();
virtual int add_speaker (const PBD::AngularVector&);
virtual void remove_speaker (int id);
virtual void move_speaker (int id, const PBD::AngularVector& new_position);
virtual void clear_speakers ();