The Decca Tree is used mainly for recording orchestras and large ensembles. It was developed in the 1950s by engineers at Decca Records. The Decca Tree uses a special T-shaped mic stand suspended above the conductor’s head. On the T-shaped stand are 3 cardioid microphones facing left, right and centre which are then panned to match their configuration.
There are no fixed measurements for the distance between the microphones but the standard seems to be around 5-7 feet. The mics are usually placed closer together for smaller orchestras and further apart for larger ones.