I've been experimenting with ducting for purpose of reducing sound and later directing heat.  I have a s9i and a t9 with insulated 6" flexible duct.  Straight run right now and have been playing with length to monitor the sound.

I am experimenting with length but have not introduced change in direction. 3-10 feet have no noticeable negative effect on miners temps or fan speed.  Temp and fan speed have both reduced since introducing ducts.  The tube has nearly silenced the high fan noise.  Still hear the intake fan, but its a hum vs. squeal.

I haven't bought a y yet and i have one booster ready to put in use.  I'm looking about 15ft distance from miners to exit point.

I am wondering if I bring the two ducts together with a y and a booster would that handle continued length of 6" flexible ducting to direct heat outside.  If this is possible I just buy the y and assemble.

Option 2 bring ducts together but booster both ducts before y and added length.

My fall back option is booster both ducts before adding length to both.