Alright! A topic I have come across before.
I remember reading about bends in air ducts and the decrease of airflow efficiency in one of my grow books when I was doing indoor gardening.
I know this probably isn't the exact same as a sub pushing air through a port, but it can't be that much different compared to a fan pushing air through a duct right?
Anyways, here is the info from the book. Take it as you will:
A 30 Degree bend can decrease airflow by up to 30%
A 45 degree bend can decrease airflow by up to 40%
A 90 degree bend can decrease airflow by up to 60%
The longer the bend the better. This means that a 90 degree bend over the course of 2 feet will be more efficient than a 90 degree bend over the course of 1 foot.
Test it out for yourself. Take a fan and attach a duct to it. Turn on the fan and feel how much air comes out of the duct when it is straight. Then bend the duct and feel how much air is coming out. You will feel a significant decrease of air when the duct is bent.
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