Box tuning help

[Miles 128]

Well, here's the deal. I'm going to be building a box for 2 Fi Bl 18's. I figured up the box will be 11.27 cubes before displacement, which is about 10.81 cubes after sub displacement. I figured that I will have 158 sq. inches of port area total. The question I have is, since I want to tune the box to 34hz, how long do I make the port? The port will be 44.5" wide, and 3.55" tall (inside measurements).

[KU40 173]

I get about 23.5 inches.

[SPY 2]

Well, here's the deal. I'm going to be building a box for 2 Fi Bl 18's. I figured up the box will be 11.27 cubes before displacement, which is about 10.81 cubes after sub displacement. I figured that I will have 158 sq. inches of port area total. The question I have is, since I want to tune the box to 34hz, how long do I make the port? The port will be 44.5" wide, and 3.55" tall (inside measurements).

I get 25.19"

The problem is you will still have to subtract the port displacement from your volume (2.3ft^3) which will also affect your tuning. So...

10.81ft^3 - 2.3ft^3 for port displacement = 8.51ft^3 net (after sub and port displacement)

So with 8.51ft^3 and a 25.19" long port your tuning goes up to 38.24hz

This means your port will have to be longer to get the tuning back down to 34hz, it also means you will loose more vol due to the longer port.

[KU40 173]

jeez I can't believe I forgot to take out the port displacement. Guess it's been a while since I designed a ported box. idiot.

anyways, I get 41 inches long. that will drop your internal net volume down to 7.2 cubes, though, which I'm sure is less than you want.

however, you're also violating the 9:1 port width:length ratio with your 44.5 x 3.5 port opening. This might give you some grief with the port not acting the way you want. I'd say you could drop the width down to something like 30" x 4". that would also make your port less deep because of the smaller port area. You'd need to make it 21" long in that case, and your internal volume would rise to 9.3 cubes.

[Miles 128]

Ok, thanks guys. I've redone my port figures and made it 30" wide and 4.5" tall. And to make this easier on me and everyone else who's trying to help me, how do y'all figure how long to make the port in comparison with the box volume and the sq. inches of port? I've used the RE box calculator before, but I don't see where they get their numbers.

[Kranz38 0]

so your going to be just at 5 cubes per subwoofer??

[bigdog829 0]

Ok, thanks guys. I've redone my port figures and made it 30" wide and 4.5" tall. And to make this easier on me and everyone else who's trying to help me, how do y'all figure how long to make the port in comparison with the box volume and the sq. inches of port? I've used the RE box calculator before, but I don't see where they get their numbers.

Use winisd & I sent you a P.M. to a real good tutorial for designing a ported enclosure.

Don't know if we can post links to other sites on here so that's why I sent the P.M. rather then just posting the link.

Edited May 26, 2008 by bigdog829

[Miles 128]

Yeah, I will only be using about 5 cubes per sub. But you have to realize, this is going in the extended cab part of a Ford Ranger, so there's not much room to work with. And to bigdod, I didn't get your PM for some reason.

[KU40 173]

i use winISD pro alpha. but in this circumstance it's kinda backwards since you already have the box size and are trying to fit the port in it, so getting the port length and box volume are a bit tricky. You kinda just have to plug in a box volume, find the displacement of the port, then subtract that from the gross volume and see if the net volume you put in matches. If it doesn't, adjust the box volume in the program, get a new port length, and try again. etc. etc.

[bigdog829 0]

Yeah, I will only be using about 5 cubes per sub. But you have to realize, this is going in the extended cab part of a Ford Ranger, so there's not much room to work with. And to bigdod, I didn't get your PM for some reason.

Sorry about that I sent it to the wrong person, My apologies Kranz didn't mean to send that P.M. to you.

Here it comes miles !!!

[Miles 128]

Well, I'm using WinISD right now, and it kind of makes sense. The only thing I don't get is, when I put in my box dimension, port tuning, and everything else, the graph shows my box will peak at 200hz. Am I doing something wrong? And, I put in my box volume to be 11.27 cubes, and the box tuned to 34hz, with the port being 30 x 4.5 x 19.39, and I got a final box volume of 9.3. Does this sound right to you?

[Kranz38 0]

Yeah, I will only be using about 5 cubes per sub. But you have to realize, this is going in the extended cab part of a Ford Ranger, so there's not much room to work with. And to bigdod, I didn't get your PM for some reason.

Sorry about that I sent it to the wrong person, My apologies Kranz didn't mean to send that P.M. to you.

Here it comes miles !!!

haha, i was actually just going to ask for it, its okay!!

[KU40 173]

can you do a screen capture and show me that peak at 200 hz? did you put in the parameters for the sub or just use one of the subs already in there?

Also, make sure the box volume you put in is after sub and port displacement. i.e.- don't put in 11.27 cubes into the box in winisd, you have to put in the 9.3. it doesn't subtract out the displacement for you.

Edited May 26, 2008 by KU40

[Miles 128]

Sorry, I don't know how to upload a screen shot that I've got saved. I put in the T/S parameters off Fi's website, and even after putting in 9.3 cubes, it still peaks at about 210hz.

[KU40 173]

you may have input some of the parameters wrong. look at the units and make sure they're right. to change them you just have to click on them and they'll change, like from feet to inches to cm, etc.

and to screen capture, push print screen, then open up paint or something and push control + v to paste it in. then you can save it.

[Miles 128]

I checked all my parameters, but they were all right. And I did save the screen shot onto a word document, put photobucket wouldn't let me upload it to my account.

[Kranz38 0]

I checked all my parameters, but they were all right. And I did save the screen shot onto a word document, put photobucket wouldn't let me upload it to my account.

print screen it into word save it upload via PB

[Miles 128]

I checked all my parameters, but they were all right. And I did save the screen shot onto a word document, put photobucket wouldn't let me upload it to my account.

print screen it into word save it upload via PB

That's exactly what I did, put photobucket won't let me upload it because its not a picture or video.

[KU40 173]

like I said, try putting it into paint.

[Miles 128]

Finally got it. Here ya go. And I also have a picture I drew up on CAD of the box and the port dimensions.

[Miles 128]

Bump. I still need to know if it looks like I've got the right amoung of port area for a 34 hz tune.

[Miles 128]

Bump. I'm still waiting on someone to tell me if the port length looks right for a 34 hz tune.

[Miles 128]

I still need to know if the port length looks right for a 34 hz tuning. The CAD picture shows everything you need to know about the box, but I want to make sure I've got the right length. I really need to know soon since we're starting the box next week.