PDA

View Full Version : Port area for RD Alpha 18



Savag3
05-10-2009, 03:17 PM
Anyone have any designs for an RD Alpha 18" right now my port is 3Wx19Tx15 deep @34.5 im thinking this is too much area , 40sqin. was suggested , input ?

Looney_Tune
05-10-2009, 03:20 PM
id like to have a 18" Alpha...my 15" was tha shyt.

Savag3
05-10-2009, 03:25 PM
id like to have a 18" Alpha...my 15" was tha shyt.

yea alphas get nasty loud i had two 18's on two 3250.'s and i was crushin pretty good

DNick454
05-10-2009, 03:49 PM
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.

mlstrass
05-10-2009, 04:22 PM
what is net size of the enclosure? I'd assume 12-16^2 per cube would do just fine...

hatemonger
05-10-2009, 04:53 PM
what is net size of the enclosure? I'd assume 12-16^2 per cube would do just fine...

agreed. port area depends more on box size than the sub. i'd go on the high side. around 16 sq. inches per cubic foot.

Savag3
05-10-2009, 04:55 PM
enclosure is 6.5 and the 40 sqin was suggested by Steve Miller , 90 sqin ? that is waaay too much

hatemonger
05-10-2009, 04:59 PM
enclosure is 6.5 and the 40 sqin was suggested by Steve Miller , 90 sqin ? that is waaay too much

90 square inches isn't too much. i've done single 12 boxes that had 36.

DNick454
05-10-2009, 05:07 PM
enclosure is 6.5 and the 40 sqin was suggested by Steve Miller , 90 sqin ? that is waaay too much

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.

Savag3
05-10-2009, 05:08 PM
ok so the design i have now has 57sq in tuned @ 34.5 maybe im better off than i thought

DNick454
05-10-2009, 05:11 PM
ok so the design i have now has 57sq in tuned @ 34.5 maybe im better off than i thought

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 *** box and spend money on materials to find out your box is choking the sub and all you're hearing it port turbulence.

Savag3
05-10-2009, 05:12 PM
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.

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

d-REW
05-10-2009, 05:18 PM
sounds like you already made up your mind why ask for help?

DNick454
05-10-2009, 05:19 PM
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

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.

Savag3
05-10-2009, 05:27 PM
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.

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

DNick454
05-10-2009, 05:30 PM
Well, I just watched a build for 6 18's. And it had just a hair short of 500 sq in of port area, so thats around 85 sq in of port area per sub. I would definitely talk to that guy and confirm all numbers and whatnot.

Savag3
05-10-2009, 05:31 PM
sounds like you already made up your mind why ask for help?

why does it sound like that ? because ive tried what he suggested before and it worked well ? you assume too much, i am just trying to figure out why more than a few people are suggesting 12-16 per cube , maybe il try and see, although it would be a waste of 1"mdf if its wrong

Savag3
05-10-2009, 05:32 PM
Well, I just watched a build for 6 18's. And it had just a hair short of 500 sq in of port area, so thats around 85 sq in of port area per sub. I would definitely talk to that guy and confirm all numbers and whatnot.

ya il check it out , i want everything i can get out of this enclosure , so maybe il explore some other designs . . .

Savag3
05-10-2009, 06:13 PM
Can anyone run a plot for me im just getting used to my program bass box pro 6 , and im wondering what anyone else thinks TS parameters here 18" D2 http://www.rdaudio.net/alpha/alpha.htm

Box specs = External Dimensions 41Wx21Tx18.5D (1"mdf) woofer back port back [jeep Cherokee] , left side slot port 3Wx19T is what I had tuned @ 34.5hz . . thanx in advance