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Port area for RD Alpha 18

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40 sq in is WAAAAAAAY too small for an 18. You need atleast 90 for that sub based on cone area and Xmax. Even if you're going for an aero port, you'd still want around 60.

 
enclosure is 6.5 and the 40 sqin was suggested by Steve Miller , 90 sqin ? that is waaay too much
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The 16 sq in of port area per cubic foot is a good rule. Do the math, 6.5 cubic feet times 16. That's 104, so... no, 90 is not too much. I've got 50 sq in of port on my two 10's in 3 cubic feet. More port area can't hurt, too little can. A bigger port area just means it takes up a bit more space because the port is then longer to achieve the same tuning. I'd rather have a huge mass of slow moving air waves than a high speed whisle of port noise coming from my box. But whatever, build the box as "Steve Miller" told you.

 
ok so the design i have now has 57sq in tuned @ 34.5 maybe im better off than i thought
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I'd still say that's cutting it short unless you use aero ports with that much area. Even if you use a more conservative 12 sq in per cubic foot, you still get a minimum of 78 sq in of port area. I'd hate for you to build a giant ass box and spend money on materials to find out your box is choking the sub and all you're hearing it port turbulence.

 
The 16 sq in of port area per cubic foot is a good rule. Do the math, 6.5 cubic feet times 16. That's 104, so... no, 90 is not too much. I've got 50 sq in of port on my two 10's in 3 cubic feet. More port area can't hurt, too little can. A bigger port area just means it takes up a bit more space because the port is then longer to achieve the same tuning. I'd rather have a huge mass of slow moving air waves than a high speed whisle of port noise coming from my box. But whatever, build the box as "Steve Miller" told you.
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Ive heard that same thing said before 16sqin. per cuft . . , and I mean he does own RD im pretty sure he knows what his woofers "like". . dont you lose musicality when your ports are so big ? wouldnt the woofer unload alot faster ? just wondering , i am just looking for input, and this is the second time ive heard 12-16 per cube . . and just for the record none of the box's steve designed for me have ever had whistle or noteable port noise

 
Ive heard that same thing said before 16sqin. per cuft . . , and I mean he does own RD im pretty sure he knows what his woofers "like". . dont you lose musicality when your ports are so big ? wouldnt the woofer unload alot faster ? just wondering , i am just looking for input, and this is the second time ive heard 12-16 per cube . . and just for the record none of the box's steve designed for me have ever had whistle or noteable port noise
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Did he recommend 40 sq inches of aero port or slot port? Because 40 sq in of slot port seems way too small for an 18". Even if he is the owner of the company, that just doesn't seem logical to me to be honest. Also, I don't see why you'd lose musical ability by making the port larger in area because you also make it longer to keep the same tuning so the resonant properties of the port are still the same. I've never used RD products so I'll just stay out of this for now I guess, but unless RD subs are some crazy never before used concept in woofer design, I would say the port would be a tad small.

 
Did he recommend 40 sq inches of aero port or slot port? Because 40 sq in of slot port seems way too small for an 18". Even if he is the owner of the company, that just doesn't seem logical to me to be honest. Also, I don't see why you'd lose musical ability by making the port larger in area because you also make it longer to keep the same tuning so the resonant properties of the port are still the same. I've never used RD products so I'll just stay out of this for now I guess, but unless RD subs are some crazy never before used concept in woofer design, I would say the port would be a tad small.
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40 sq in of slot , i had two alpha 18's with 84sq in of port @33hz in my full size bronco that went 151.5 with some voltage drop. I unno thanx for the input guess il try and figure out whats going on. Wouldnt the pressure inside the box change ? i realize that the tuning is the same but i would think it would cause unloading . . i unno thanx

 
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