In order to further understand the importance of selecting the proper fan based on its operating point, the characteristic curves for the different fan types should be considered. These three graphs show the characteristic air flow, efficiency, and noise curves for axial fans, backward curved impellers, and forward curved centrifugal blowers. The green shaded area of the air performance curve represents the area of peak efficiency (blue curve). This shaded area also correlates to the area where the noise (red curve) is the lowest.