Since systems with denser layouts have more airflow resistance, this results in the fan operating with more noise. To illustrate this, the engineer shows a fan PQ curve, with a system impedance curve superimposed. The sound pressure level curve in yellow shows sound levels varying across the PQ curve. At free air, the sound level is the lowest, and it is the highest at max pressure. Therefore, a steeper impedance curve results in a higher operating noise level for the fan.