Is it good to polyfill any and every box, like ported ones for example with plenty of cuft?
Also why do some custom boxes have 2 ports?
Anonymous
Posted on
some times there are 2 ports because either a, its a diveded box and there are two subs so each sub gets a port, or if someone just wants the look of two ports or however many they want. it doesnt really help any. but u only need to polyfill a box when u dont have enough cubic feet in it, its a way of tricking the sub into thinking there is more room when there isnt, otherwise u dont need it.
Polyfill also helps disperse standing waves within the enclosure that may cause cancellation. And by 'tricking' the driver, it is actually slowing the movement of the air inside the enclosure, a factor that transmission lines often rely on, to emulate a larger enclosure.
Multiple ports are needed when the velocity of air coming from the port is high enough to cause noise. For example: a 15"x4" port with have a vent mach of approx 0.06 while 4 ports at 15"x1" will have a vent mach of 0.02. Noise generally won't be apparent until around 0.16, so in that situation it wouldn't matter.
Width restrictions in a trunk may also require the use of multiple smaller ports.
I do recall an ABC enclosure a while back with 12 ports total to achieve appropriate air velocity.