Appendix 3
Bidirectional Microphones for Stereo and Surround Sound
For working in stereo, two bidirectional microphones, oriented at 90 degrees with respect to each other,
create the classic crossed bidirectional pair. This also is commonly called a Blumlein pair, in recogni-
tion of Alan Blumlein who first proposed this technique in his seminal patent of 1934. This technique
provides what many engineers consider the most natural sounding stereophonic image of any micro-
phone configuration because it provides an extremely even spread with precise and accurate localiza-
tion within the stereo stage.
As with a single bidirectional microphone, a Blumlein pair can be worked from opposite sides with
equal effect. This allows multiple actors or musicians to group in the front and back quadrants of the
microphone pair for a full stereophonic performance. Notice, as shown in Figure-9, that the stereo
channels in the back quadrant are reversed with respect to the front, and this must be kept in mind
when arranging the stereo stage perspective. It also is important to realize that the two side quadrants
are out of phase with each other, so any direct sound should be avoided here, lest it become vague and
difficult to localize; under extreme conditions, it can cancel entirely when summed to mono.
