rodemic NT1 Manual De Instrucciones página 18

Recording piano (stereo)
To record a piano using a matched pair of NT1s using X/Y stereo
technique, the matched microphones should be angled 90 - 110
degrees to each other, over the hammers, with one mic aimed
towards the lower strings and the other to the higher strings
(see Diagram 6). The gold dots should face the piano.
Thus a stereo image can be achieved, with lower frequencies
recorded on the left, and higher frequencies on the right.
90°-110°
Diagram 6 Recording piano in stereo.