Selecting a fan for optimized noise. The blue sound and PQ curves shown here represent the 109P model fan performance, intersecting with the black example system impedance curve. Now adding sound and PQ curves for a second fan model, the 9GA in green, the customer can see that both fans satisfy the same operating point, even though the 9GA fan has less max airflow and pressure listed in the catalog. However, the 9GA model emits 10 dBA less sound pressure. Therefore, sound level can be reduced with the proper selection of a fan.