The
physics states that the doubling effect of the pressure zone
will happen equally right across the frequency spectrum if the
“Boundary” is infinitely long and infinitely wide
but unfortunately, infinite surfaces are difficult come across
even in the most expensive studios and microphones exhibit different
frequency responses dependant on the size of the surface they
are placed. Most applications for boundary microphones are in
the conference or audio visual field for sound re-enforcement
where they make great lectern mics and table top mics for discussion
groups but studio engineers being what they are have tried using
them over the years on all kinds of instruments, sometimes to
great effect. Boundary mics can be taped to the lid of a grand
piano or placed on the floor in front of a drum kit and the
only application where they can't realistically be tried is
on vocals. One of the first studios I worked in had a pair of
cheap Tandy PZM mics Gaffer taped to the walls of the drum room
and with a bit of eq they made a pretty good job as drum overheads.
Today most companies make a boundary mic and prices range from
a few pounds to a few hundred depending on application and quality
but at the top end Crown produce a very high quality stereo
boundary mic, the SASS system based on a form of dummy head
and priced around $1000.
