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View Full Version : I'm horrible at this ported box stuff



Chrisku13
11-14-2005, 01:54 AM
http://img498.imageshack.us/img498/2885/subbox8sm.png
Ok, I'm having troubles with the whole ported box concept. Maybe I just haven't seen enough good pictures, but some things still confuse me. I'm trying to build a ported box tuned to 32 hz pretty soon, and was trying to find the dimensions of my port using an applet on bcae1.com. I have posted a very crude picture depicting what I found in the program's output. What I don't get is why my side lengths change for the square port when I enter a different diameter into the program (I put 3", and it gives me these sides, but when I put 2", it will give me smaller sides and a shorter length). I don't even know how the diameter applies to the square port, because isn't that for the round port? Aren't all sides going to be 2.659"? At this point, I've searched all over the forum and still can't find some of these answers. Is my drawing of the different ports accurate? I know round ports, but is the square port basically the same, but with a square instead of a circle? Could I use the walls of the enclosure for those two sides? And also, I don't believe the program tells me how to make a slot port. If I keep the length of the port the same, but make it taller to look like the slot port I drew, I know I would mess with the volume, but would that change the tuning? Is it the length or the volume that does this? Sorry for all of the questions, I hope someone can make sense of all this and help out.

brandontw
11-14-2005, 02:23 AM
if my common sense serves me correctly, then it seems like scince your round port should be a 3 inch diameter and 6.875 deep, that you slot port should be the same port area with the same depth, so you do Pi x Rsquared and you get 7.065 square inches so then you qould figure out what size the port would have to be to get you that area. then just make it 6.875 deep, but that may turn out to be a very skinny port, so you can make the port area bigger, but the you have to make the port deeper as well.
there is alot of very good box builders on here, I am not one of them, ive only done a few, and i struggle through em'

I know you should be able to find alot of help by searching

Chrisku13
11-14-2005, 03:27 AM
Actually, I did search a lot. But I still had a few questions. Anyways, I found another formula that sort of helped me out, but I still want to know if I'm going to be doing this right. Will I basically be putting a rectangular port 6.875" in length with 2.659" sides into a sealed enclosure? I'm guessing I can't use the sides for two sides of the port, because the calculation didn't account for that, but can I place it in the corner like that? Basically cut a square out of the baffle for my port size and slide it in the box and seal it up? I chose this square vent, because I will be making it out of the material used for my box (3/4" MDF). Would this create significant port noise?

skmfkr
11-14-2005, 03:27 AM
if those are the internal dimensions the box vol is 2.879 and with a 3" round port @ 32hz it needs to be 4.xx somthin inches i forgot....use this site

http://www.carstereo.com/help/Articles.cfm?id=31

but you need to factor in subwoofer displacement and port displace into the box volume, and i would just a 4" round port instead of 3"

Chrisku13
11-14-2005, 03:45 AM
But I'm doing a square port. I'm pretty sure I have all of the displacements figured out, because the program gave me the net volume as 2.039 cubic feet, and gross as 2.067 cubic feet. I'm choosing not to go with the round port, because I can just use materials I already have for the square port, and I was under the impression that a round one would possibly create more port noise. Although, if I'm using the same port area, would it matter which one I use? I think I almost have it figured out, but I just don't want to set it all up and get some nasty port noise. By the way, did my last post about the square port sound right?

brandontw
11-14-2005, 04:16 AM
i would do the volume calcs yourself, im skeptical of those calculators... if your worried about port noise make a bigger port and adjust the length accordingly, and sand all of the edges nicely. But dont be afraid of slot ports, they are really easy, probly easier that your square port idea.

skmfkr
11-14-2005, 04:21 AM
that box is way bigger than 2cubes, what sub are you using, most smaller subs are like only .1cf displacement, my rlp is .18 which is almost 7inches deep, and port displacement will be about another .2cf

brandontw
11-14-2005, 04:21 AM
i figure if you have ~2.8 Cube box, and you want it tuned to 32 hz and you want a slot vent on the side the height of the box, and you made it 1 inch wide(a little small) it should be about 12 inches long

skmfkr
11-14-2005, 04:39 AM
a port 11x1 would beed to be 7inches and a port 11x2 would need to be 15.5

Chrisku13
11-14-2005, 12:28 PM
The thing is, if I'm even off by a little bit, it would change the tuning. I'm not doubting your assesment, but is your calculation for my port just a guess or did you use some sort of calculation? If I can do a slot port, I will, but I need to know: What's the difference between a slot port and square port? Would a slot port basically be a wall going through the enclosure that has an opening on the side? If anyone has suggestions for accurate calculators or maybe pictures, I would understand better. I'm considering just doing a round port, because that's the only one I'm understanding at the moment. I don't want to spend the money for a flared aeroport, but if I must, I must. How suitable would a 3 or 4" PVC pipe be for a round port with minimal port noise? Anyways, thanks for all of the help.

brandontw
11-14-2005, 09:25 PM
i just used sort of a proportion...i figured IF your round port is **** then your sqaure or slot port would be****, you know i didnt just come up with it off of the top of my head.

I really wish you would tell us what sub you are using fo this project, it may help to speed the process. I dont even know what size it is..10" 12"? i would guess 12" by looking at your drawing. I have used 4 inch ABS pipe as a port before and it worked awsome, and there wasnt any port noise. You could also make dual round ports with say..3" ABS or PVC , and that would further reduce port noise, but also you would need to adjust the volume of the box for the extra port displacement.

if you give me a while, ill draw you up a drawing or two of possible designs just cause im a nice guy.

skmfkr
11-14-2005, 09:41 PM
http://www.carstereo.com/help/Articles.cfm?id=31

port size calculator right there...

Chrisku13
11-15-2005, 12:38 AM
I guess I should have put some more information in. Well, I am going with a 12" Alpine Type-R (who would have guessed?), and the displacement is going to be .071 cubic feet. Anyways, I have a funny little story to share. I guess I'm not the most unknowledgeable about ported boxes after all. Today, I went into a local car audio shop (which I thought to be reputable), but walked away amazed at their poor customer service and stupidity. They go by the name of Audio Express. Anyways, I walk in and have to wait for some guy to stop screwing around with his friend before I can get some help, and when I do, it's not help at all. I was looking for someone to just talk about ported boxes and stuff with, but he didn't know about it, so he told me to try the other guy who was working. About thirty seconds into the conversation, I knew that the second guy wouldn't be much help either, because he was just trying to sell me a box that was $500 (slot ported) for a 10" JL sub. I told him my sub wasn't meant for that box, and he told me to cut the hole bigger. When I asked what the tuning frequency for that box was, I was told "You can't tune boxes, you tune subs." I gave him a :confused: look and asked him to elaborate. He proceeded to treat me like I was stupid and didn't know what I was talking about and showed me the manual for my sub and asked me to point to where it says how the box is tuned. I told him I've already looked at it, and Alpine didn't state that, but I could find it using the various calculators online. He kept telling me you can't tune a ported box, and that all of the ports were going to be the same. I walked out of there on pretty bad terms, because he told me "You don't know what you're talking about, you're only 16." I've hated the way they've treated me everytime I walk in there, but this just put the icing on the cake. Anyways, just thought i'd vent (pun intended) that to all of you.

brandontw
11-15-2005, 12:50 AM
http://img397.imageshack.us/img397/5466/drawing17cu.jpg this is an idea
1.5 inch wide port, 26 inches long

Chrisku13
11-15-2005, 04:09 AM
You know, that diagram was really helpful. I really appreciate you making that. The calculator on carstereo.com was also very helpful, but could somebody clear up what the "enclosure volume" would be within the "calculate your vent length" section? Is that without all displacements (so just interior measurements), or with them? I just have a couple last things to clear up. #1- The height of that vent in the picture takes up the whole interior height of the box, correct? (so it's 14.5"?) #2- The length is going to be started from right behind the baffle? The 3/4" of extra length you drew to make it 12.75" is not going to be in the length? #3- How important is the "golden ratio" in making a ported box? The general answer I got is that it won't make a difference whether I stick to it or not, but I was just wondering.

Chrisku13
11-15-2005, 05:26 PM
Ok, I now have all of the measurements of the box. It will be 15" x 31" x 14". I will post pics when the construction is finished. Hopefully it goes well. Thanks to everyone who helped me out

brandontw
11-17-2005, 04:36 PM
good luck..sorry i didnt answer your other questions - ive been busy.

brandontw
11-17-2005, 04:38 PM
You know, that diagram was really helpful. I really appreciate you making that. The calculator on carstereo.com was also very helpful, but could somebody clear up what the "enclosure volume" would be within the "calculate your vent length" section? Is that without all displacements (so just interior measurements), or with them? I just have a couple last things to clear up. #1- The height of that vent in the picture takes up the whole interior height of the box, correct? (so it's 14.5"?) #2- The length is going to be started from right behind the baffle? The 3/4" of extra length you drew to make it 12.75" is not going to be in the length? #3- How important is the "golden ratio" in making a ported box? The general answer I got is that it won't make a difference whether I stick to it or not, but I was just wondering.

Yes. it was a full height port.



The lenth of the port should be measure from beginning to end down the center of the port, even if it has a 90 degree turn in it, so yess, the 3/4 baffle should ba counted in the legth, sorry if i forgot it in my sketch

James Bang
11-17-2005, 08:39 PM
if those are the internal dimensions the box vol is 2.879 and with a 3" round port @ 32hz it needs to be 4.xx somthin inches i forgot....use this site

http://www.carstereo.com/help/Articles.cfm?id=31

but you need to factor in subwoofer displacement and port displace into the box volume, and i would just a 4" round port instead of 3"

for the "Enter Enclosure Volume" box, do you put the volume b4 or after port displacement?

Chrisku13
11-18-2005, 02:01 PM
I believe that would be after the port's displacement. That calculator was my main resource for making the box. Also, you can't really factor in extra volume for bracing and such, so what I would do is figure out how much space any extra things you want to put in the box will take up, and add that to the driver/subwoofer displacement.

brandontw
11-22-2005, 03:48 AM
I believe that would be after the port's displacement. That calculator was my main resource for making the box. Also, you can't really factor in extra volume for bracing and such, so what I would do is figure out how much space any extra things you want to put in the box will take up, and add that to the driver/subwoofer displacement.
You’re getting the hang of it.

(total internal volume) - (port displacement) - (sub displacement) - (any other stuff (bracing))= (total volume for tuning calculations)

I’m glad I could help you, and that you learned something from all of this; you are one of the few people asking for help that isn’t totally helpless...you tried to do some stuff on your own and asked lucid, intelligible questions. I respect and thank you for that.:D


Peace.

-Brandon

P.S. I'll let this thread R.I.P. now.;)

Chrisku13
11-22-2005, 11:12 AM
Actually, I must bring it back from the dead for a second. :) I am almost done with the box, but had a question. My port is to the left of where the sub will go, on the same side. Then, it runs behind it's magnet and it's opening is to the right of the sub. Should I put the sub so that it's magnet is closest to the port opening in the box, or as far away as possible? What difference in sound would I notice? Mucho Gracias to everyone.

tRiGgEr
11-22-2005, 11:18 AM
Should I put the sub so that it's magnet is closest to the port opening in the box, or as far away as possible? What difference in sound would I notice?

There will be no difference.

brandontw
11-23-2005, 01:33 AM
yup - it doesnt matter