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is the name for a stereo recording technique invented by Alan Blumlein
Alan Dower Blumlein was a British electronics engineer, notable for his many inventions in telecommunications, sound recording, stereo, television and radar...
for the creation of recordings that, upon replaying through headphones or loudspeakers, recreate the spatial characteristics of the recorded signal.
The pair consists of an array of two matched microphone
A microphone is an acoustic-to-electric transducer or sensor that converts sound into an electrical signal. In 1877, Emile Berliner invented the first microphone used as a telephone voice transmitter...
s of bi-directional (figure 8) pickup pattern, positioned 90° from each other. Ideally, the transducers should occupy the same physical space; as this is impossible the microphone capsules are placed as close to each other as physically possible, generally with one centered directly above the other. The array is oriented so that the line bisecting the angle between the two microphones points towards the sound source to be recorded (see diagram). The pickup patterns of the pair, combined with their positioning, delivers a high degree of stereo separation in the source signal as well as the room ambiance.
The Blumlein pair produces an exceptionally realistic stereo image, but the quality of recordings is highly dependent on the acoustics of the room and the size of the sound source.
Both ribbon and condenser microphones can be used for Blumlein pair recording. A few types of stereo ribbon microphones (B & O, Royer, AEA) have even been purpose-built for just this type of recording. Several types of stereo condenser microphone (Neumann, AKG, Schoeps) have also offered a Blumlein arrangement as one of their possible configurations.
In his experiments at EMI with what he called "binaural
Binaural recording is a method of recording sound that uses two microphones, arranged with the intent to create a 3-D stereo sound sensation for the listener of actually being in the room with the performers or instruments. This effect is often created using a technique known as "Dummy head...
" sound, Blumlein did not actually use this technique since he had no figure-8 microphones available, but the theoretical possibility of such a recording method was one of the claims he made in his U.K. patent application in 1931 (granted as patent #394325). This recording technique was named in his honor many years after his death.
|Bidirectional (Figure 8)
Microphone Sensitivity Pattern
(Red dot is microphone, viewed from above)
|Blumlein Pair Array
(2 crossed Figure-8s)
|Blumlein Pair Array
(Small arrows indicate front of individual
microphones, large arrow indicates front of array.)