The Blumlein pair is one of the most accurate and famous stereo microphone arrangements named after its inventor Alan Blumlein who was working in the film industry in the 1930s and wanted a good accurate stereo image for Film sound. Because of the nature of microphone design back then he was working with Ribbon mics which have a figure 8 pick up pattern and Blumlein discovered that if you set up two figure 8 mics as coincident (close) as possible at right angles to each other you get a very realistic stereo picture. The front lobes of each mic produce a stereo picture very similar to our XY coincident pair but with figure 8s you pick up equally from the rear of each mic, capturing the natural room ambience behind the mics. So basically, the Blumlein array creates a four-lobed polar pattern that gets summed to two channels and when the two mics are panned left and right, the left channel is made up of front-left and rear-right signals, and the right channel consists of front-right and rear-left signals.

I think that the stereo picture from a properly positioned Blumlein pair is hard to beat and I often use a pair of Sennheiser MKH30 microphones set in Blumlein to record quite large choirs and Brass bands. These mics are superb in all ways but are very expensive: so if you are interested in this stereo technique you could buy a pair of inexpensive multi pattern condenser mics and have a go with them set to figure 8, or alternatively invest in a pair of the very affordable Ribbon mics coming out of the far east. There are issues with dual diaphragm mics as opposed to the single diaphragm Sennheisers and Ribbon mics, but just have a go. The main problem that you will hear straight away is that because figure 8s pick up equally from the rear you need to put them fairly close to the sound source to avoid excessive room sound and this can overemphasize sound from the centre. Its horses for courses and if you have a nice sounding room then use it and record with a Blumlein pair. If the room is a bit problematic then try an XY coincident pair or the other secret weapon of stereo recording Mid-Side stereo.