The SITES anniversary show used quite a few kiosks with directional
speakers.  It was interesting to have kiosks about 10 feet away from each
other with no sound overlap.  You may want to call the people at SITES or
hit their Web page.   The Official Museum Directory lists many audio
vendors as well; there's a company listed there called SECRETSOUND, with
directional speaker systems, in Winchester, MA, #617-729-5895 (we've
never used this company, but it may be helpful to pick their brain).  For
technical stuff like this, we turn to local vendors who have helped us in
the past with film production and sound tracks.  Normally they'll know of
a company who sells specific things like speakers with amplifiers and
such and they help us with wiring the stuff correctly.   Good luck.

O
Olivia S. Anastasiadis, Curator
Richard Nixon Library & Birthplace
Yorba Linda, CA  92886
(714) 993-5075 ext. 224; fax (714) 528-0544