Because of the area differences. Acoustic impedance is per area dependent and as the area gets smaller the impedance goes up. So the higher impedance of the small opening is transferred to the larger diaphragm through the compression ratio resulting in an impedance increase seen by the mechanical system.
The same is true going the other way. As a driver gets larger its per area acoustic impedance falls and it better matches the air.
This is also the reason that high-bypass turbo fans are more efficient as the larger area of slower moving air is better at propulsion that a smaller area with higher velocities. Same volume velocity, but one is more efficient.
The same is true going the other way. As a driver gets larger its per area acoustic impedance falls and it better matches the air.
This is also the reason that high-bypass turbo fans are more efficient as the larger area of slower moving air is better at propulsion that a smaller area with higher velocities. Same volume velocity, but one is more efficient.
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