But i just shaved 7 dB(A) off a whistling HVAC return by adding a lined 90-degree elbow and a short plenum baffle, and the room’s clarity jumped without touching the DSP. Anyone else seeing big gains from simple duct path tweaks, or have a go-to liner for tight 6" runs?
That ‘7 dB(A)’ tracks — on tight 6" runs I use 1/2" Armaflex; watch pressure drop. What velocity?
Nice win on the lined 90 and that “short plenum baffle.” I’ve had the last bit of hiss vanish by swapping to a curved-blade return grille and keeping face velocity under about 300 fpm — , stamped grilles can whistle. For tight 6" runs I like 1" Linacoustic RC with a perf sleeve plus 12–18" straight after the elbow; @harper_finch75 is right on drop — what’s your branch cfm and static?