Directional does not mean equally quiet everywhere except the front. A supercardioid microphone can still pick up sound from directly behind it, while its strongest rejection occurs toward rear-side directions. Check the actual model's polar plot before placing a fan or computer behind the microphone and assuming that it is hidden from the recording.
Identify the pattern you really have
Read the microphone model and selected pattern if it is switchable. Cardioid, supercardioid, hypercardioid, and other patterns describe different directional responses. A long tube or professional-looking body is not sufficient evidence of one particular response, and sensitivity can also vary with frequency.
Sennheiser's supercardioid guidance describes greater focus at the front, remaining rear sensitivity, and stronger rejection toward rear-side angles. Treat its diagram as an explanation of the pattern rather than a calibration of your entire room. Reflections can carry a fan's sound toward the microphone from more than one direction.
Plan positions without changing the performance distance
Draw a simple overhead sketch showing the mouth, microphone axis, fan, walls, and camera. Identify the speaking distance that already produces an acceptable voice. Keep that distance comparable while exploring a different microphone-and-speaker orientation relative to the noise, so the comparison is not dominated by moving the person much closer.
If practical, move or switch off an unnecessary noise source rather than forcing the microphone into a poor angle for speech. Never block equipment ventilation as a recording trick. If the camera framing constrains microphone placement, discuss a different authorized recording setup or separate narration instead of promising directional rejection will remove everything.
A proposed rear-versus-rear-side comparison
This is an unexecuted room test. Record the same short sentence and a pause in two permitted arrangements. Keep microphone pattern, talker distance, gain, and recording format unchanged. In one arrangement the unwanted source lies behind the mic; in the other it lies closer to a lower-sensitivity direction shown for the actual model.
Log the source direction, voice clarity, noise during the pause, and noise underneath words. Compare at matched listening settings. A quiet pause is not enough if the new angle makes consonants dull or the talker repeatedly leaves the useful pickup area during natural gestures.
Approve the real room result
Listen with any planned music removed first, then with the intended mix. Record the chosen orientation and limitations, including reflected or intermittent noise that remains. Do not label the recording noise-free merely because the fan is absent from the frame or a polar diagram contains a null.
This equipment-placement method can prepare narration for an Imagild film. It does not imply built-in microphone direction controls or automatic source removal. Acceptance requires the actual approved voice to remain intelligible in the selected setup, not a generic claim that a directional microphone ignores its surroundings.