The arbitrator shall, so far as practicable, in assessing compensation act on his own knowledge and experience, but, subject as aforesaid, at any inquiry or arbitration held under this schedule the person holding the inquiry or arbitration shall hear, by themselves or their agents, any authorities or parties authorised by or under this Act to appear, and shall hear witnesses, but shall not, except in such cases as the Board otherwise direct, hear F1counsel or expert witnesses.