Microphone Techniques: Blumlein Stereo Miking

Our exploration of numerous stereo miking techniques now takes us to the Blumlein method. Named after British stereo pioneer Alan Blumlein, the Blumlein technique takes advantage of the polar patterns inherent in figure 8 (bidirectional) mics such as M-Audio’s popular Solaris. Figure 8 patterns pick up equally well on two sides while exhibiting strong rejection at 90 degrees off axis to those sides. In the Blumlein technique, two figure 8 patterns are oriented 90 degrees from each other with the positive sides facing the left and right sides of the sound source. Due to the inherent side rejection, the area of greatest sensitivity of one mic is the area of least sensitivity of the companion mic. While the patterns overlap in the center, the signal from each is 3dB down and, when combined, pick up a uniform center signal.

The Blumlein arrangement relies on a matched pair of coincident figure-8 patterns

The Blumlein arrangement yields very good stereo separation. Due to the fact that figure 8s are equally sensitive on the back lobes, this configuration also picks up significant room reflections. There are drawbacks to this technique, however. The fact that the back of the left mic is also picking up reflections from the right rear of the room makes for poor mono compatibility. Further, reverberant sounds coming from the sides of the acoustic space can enter the positive lobe of one mic and the negative lobe of the other, thus causing the impression of poor localization and/or hollow effects that can be disturbing. In that light, Blumlein is best used in situations where the sound source, acoustic space and mic placement are optimal. Since this is a rarity, other stereo techniques offering superior control are often more favored.

Next month we’ll check out the ORTF stereo technique.

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