Port question?

[nocturnalrites101]

ok quick specs on the box 13 cu ft NET 192 sq of port approx tuned to 35hz. box is for pair of b2 xm18s

heres the question. the port is 8.25 WIDE. the port is approx 5.25 from the back wall.. being the port splits off left in right which would be 4 1/8th each direction. will the tuning beign effected by the back wall. How far does it have to be from the back wall for it NOT ride the back wall. as it would drastically lower the tuning

[Triticum Agricolam]

Yes, that way you have it, it will affect the tuning. It would probably lower it a couple Hz. It would need to be end 8.25" from the back wall and even then it might effect tuning slightly.

My suggestion would be to just increase the width of your port a little bit until you get enough port area to tune to 35 Hz with the port splitting at the back wall. Hopefully you understand what I mean, I don't think I'm describing it well.

[nocturnalrites101]

its a 15sq of port to 1 cu ft ratio as it stands now. i assumed being the port is splitting off left and right half the air would go in each direction. if it directly is effected by the back wall its more than a couple hrz its more like drops it down to 29hz

id imagine widening it would make the effect far worse.. the idea is I DO NOT want it to ride the back wall.

[ShadeTreeMechanic]

widen it so when it rides the back wall its ok. when a port is along a wall, 1/2 port width along the wall belongs to the port.

[nocturnalrites101]

i think both of you are missing what im getting at. im trying to stop it from riding the back wall. if i wanted it to make it ride the back wall i would have just made the port longer.

how far does it need to be from the back wall for the correct factor not not take a effect. Thats all im asking

i do not want it to ride the back wall.. please let me know how to AVOID that not steer into it

[ShadeTreeMechanic]

Ok let us back up.

Choice #1: Make the port shorter so it is more than a port width away. This raises tuning.

Choice #2: make port wider. This raises tuning. Except for the back wall that it rides that makes it longer.

You need to juggle the numbers to make it come out right. This is the fun part.

[nocturnalrites101]

ok ill ask this in another way. pretend you were installing aero 4 inch aero ports how far would you want them from the back wall

would it half to be 4 inchs away from the wall then?

[Triticum Agricolam]

ok ill ask this in another way. pretend you were installing aero 4 inch aero ports how far would you want them from the back wall

would it half to be 4 inchs away from the wall then?

It would be 4", like I said in my first post, the port would need to end 8.25" from the back wall, even then it might effect tuning slightly.

I understand what you are saying just fine, like ShadeTree said, you have two choices, you can shorted the port which will raise tuning (which is probably not what you want to do), or you can increase port area and keep tuning the same, which is what I was suggesting. I guess there is a third option, which is to have the port extend out the front of the box, which would keep port area and tuning the same, but you may not like having an external port.

[ShadeTreeMechanic]

Or just keep asking the same question until you get the answer you want. You are hung up on the wrong thing instead of being hung up on making it work.

[nocturnalrites101]

i thinkt he effective solution is make the box longer and shorter to pull the port away from the back wall. which is what i was thinking from the start i just needed a number figure of how far it needed to be away from the wall was all.