I have forced air extraction with a duct running through one classroom then a second. The classroom which is ducted closer to the fan receives much greater air flow through its vents.
To combat this we have to use airflow regulators- basically metal shutters- to restrict the airflow in vents 1 and 2 in order that 3 and 4 receive flow. As these are classrooms a fairly powerful motor is used to renew the air around 15 times per hour so this is rather noisy with a horrible whistling noise.
In this photo you can see vents 3 and 4 with 1 and 2 behind that wall.
I have spoken with a ventilation contractor who says having larger vents would alleviate the problem but I imagine I would still need to close large vents in 1 and 2 as much as with the smaller vents and the noise would persist. In all honesty I have had a poor experience in general with ventilation contractors so I don't want to waste more money.
I would appreciate advice and imagine this is a fairly typical scenario. I hope so at least. :)