Ported Box, Dual 12’s, com or div chamber?
Printed From: the12volt.com
Forum Name: Car Audio
Forum Discription: Car Stereos, Amplifiers, Crossovers, Processors, Speakers, Subwoofers, etc.
URL: https://www.the12volt.com/installbay/forum_posts.asp?tid=83982
Printed Date: May 02, 2024 at 4:09 AM
Topic: Ported Box, Dual 12’s, com or div chamber?
Posted By: greenbroncoguy
Subject: Ported Box, Dual 12’s, com or div chamber?
Date Posted: October 10, 2006 at 11:39 PM
Well, I completed my new box a couple days ago, put it in my trunk and was really impressed with how it turned out/sounded(major thanks to WinSD and the guide on here). I have made other boxes before, but they were always sealed so they were a little bit more forgiving. So, long story short, I played around with WinSD for a week or so, and thought about what I could do with the trunk space I have(1997 Nissan Maxima 4dr, fairly large trunk, small hole behind armrest from trunk to back seat area) and what I expected out of my final system(mostly SQ but I would like it to get loud when I want it too, but sound well while doing so. So in the end, this is what I came up with... 
3/4" MDF(naturally), sealed up extremely well, rubber undercoating on the inside, yes, I know I used too many screws but for the power level I am running at I do not see the box comming apart. Total inside area, after taking out port/divider/driver displacement is 3.66cu.ft. IIRC, leaving 1.83cu.ft. per sub. Ports are tuned @36hz IIRC and after listening to it in the car hooked up, well, I was really impressed... here's what's going in the trunk... 
the subs are (2) Earthquake DBX12's, and are being driven by(I know, please don't flame: it was free and I am in the process of upgrading) an Audiobahn A8000T supposedly 800w rms X 1 @ 2ohm, which would(if that amp produced that kind of power, which I doubt it does) put me right where I should be being that the 12's need 400w rms each and they both have single 4ohm coils, which gives me 2ohm when wired in paralell(which they are). so finally, my question is, I posted my finished results over at my Maxima forum in the Audio section, and a few guys were asking me why I put a divider in there, that I should put some holes in it and make my box a common chamber design that I could possibly gain a few db or maybe some better sq.... one guy in particular was saying someting about phasing issues if I had one side of my divided box different from the other(which I know there isn;t since I built it), but even if this were true, wouldn't there have to be a fairly substantial difference between the 2 sides to make a noticable difference in sq inside the car??? would I even realize any sq/spl difference by makeing my box a common chamber??? I need some advice from the experts. I do not want to go messing with my box if I don't have to. also, would removing some of the divider make a substancial differece in my box volume that would throw my tuning off, or would I have to do anything to retune or mess with my port area??? sorry for the long post, I just need some advice before I go tearing my stuff apart... by the way, here's a pic of it in the car, and yes I will be doing somethign aboutthe way it looks. this thing REALLY sounds good the way it is(considering what's pushing the subs), it popped my speaker grilles off my back dash and makes them jump up about 8" and hit the top of the back window... 
Replies:
Posted By: aznboi3644
Date Posted: October 10, 2006 at 11:47 PM
PRE-DRILL PLEASE!!!!!
I see some badly split wood there...that is a weak point
But if you made it a common chamber box the tuning would change for the worse.
Oh yeah and nice box...besides the badley split wood...did you just use screws or glue also???
Posted By: greenbroncoguy
Date Posted: October 10, 2006 at 11:49 PM
aznboi3644 wrote:
PRE-DRILL PLEASE!!!!!
I see some badly split wood there...that is a weak point
But if you made it a common chamber box the tuning would change for the worse
I knew someone on here would catch that, I test fitted the top on there and put a screw in each side and it split, but I did pre-drill the rest of the holes, i swear... so, one vote for no change???
Posted By: aznboi3644
Date Posted: October 10, 2006 at 11:55 PM
Um...making cutouts would RAISE THE TUNING!!!!!
So if you wanna change it to a common chamber the vents must be a lot longer which would lower the total usuable space also.
Well this is what I found out from WinISD...correct me if I am wrong
If you want them in a single chamber and sound good you would HAVE to build another enclosure
Posted By: greenbroncoguy
Date Posted: October 11, 2006 at 12:04 AM
^^^right, I wold have to make another box, that is wat I was thinking. so, do you think it would gain anyting by having the same setup but with a common chamber???-that is my question! I never said otherwise. you typed that like was saying making cutouts would lower the tuning, which I did not. I was only askig if it wold mess with it at all. the guy on the other forum said that it would not, he said that changing box volume would not change the tuning freq of the box, which I believe it will if you do not change port length to compensate, which in turn will give you less box volume and so on and so forth... all else being equal ,if you lower box volume, you are either going to loose spl or loose go up in freq, depending on what you do to your port, but you will not be able to get back to where you were...
Posted By: aznboi3644
Date Posted: October 11, 2006 at 3:27 PM
Sorry...I thought you kept asking about cutting holes in the center divider...my apologies.
Well there prolly won't be much of a difference at all in making it a common chamber box...What I would do if you want some higher numbers is to make it a single chamber with a very big port...at port tuning frequency is port makes almost all of the sound...bigger port=higher spl
My box for my JL 15W4 is gross volume of about 7.2 cubes but actual usuable space for the woofer is 4.3 cubes...the rest is my vent...big vent it is...15 inces tall by 7.5 inches wide. Well its big enough I can fit my head in it...tuned around 40 Hz and is LOUD
Posted By: greenbroncoguy
Date Posted: October 11, 2006 at 8:00 PM
so if I was to make another box, make it same interior volume, common chamber, and put one big port in the middle that = the port area of the 2 smaller ports combined??? sounds doable... wouldn't having just one big port also slow down my port air-velocity??? that is al little too high now as it is, but it can;t be heard from inside the car so I don;t really care...
Posted By: greenbroncoguy
Date Posted: October 11, 2006 at 8:46 PM
nouseforaname wrote:
so let me get this straight, you want to build a new box, one open chamber, then run one big port in the middle..........soooo....wouldn't that just be almost the same as what you have now with the exeption of the space against the back wall for the port? if you want one single chamber, build one that has the port on one side of the box. this way, there will be nothing between the subs for a true open chamber. just my thoughts. one big port doesn't slow down the air, a too a small port or a port that is too long does that. you either want a nice big port if going slot vented or 2 or 3 ports if going with round ports. if you're familiar with winisd, this shouldn't be hard to figure out.
I AM NOT going to build another box.... it just sounded to me like that is what he was saying. I have got this sounding the way I want it and I am not changing until I upgrade to all new equiptment. I I was just trying to see where he was comming from and figure out what he was advising me to do, but yes, I was thinking that wether you have 2 small ports or on big one you still have the same port area and it would make no difference... I will be making a box for my bronco(LOTS of room!) for my 2 15's in a week or so and it will be vented, so I was thinking of maybe making it a common chamber if that is the way to go, since I will be making it from scratch and designing it to be common chamber from the begining... one word to those thinking of going vented... DO IT!!! I have always built sealed boxes, partly due to my lack of experience, but with a little thought, and of course I cannot praise WinSD enough, I made it happen and I don't think I will ever go sealed again...
Posted By: greenbroncoguy
Date Posted: October 11, 2006 at 9:07 PM
naw d00d, wasn't getting excited, just meant I really do not want to fool with what's in my car now, it's all good... so I still have not gotten any other opinions as to wether it would be better to have the 2 subs divided or common chamber???
Posted By: stevdart
Date Posted: October 11, 2006 at 10:10 PM
Divided is the way to go, as long as it works with your port design.
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Build the box so that it performs well in the worst case scenario and, in return, it will reward you at all times.
Posted By: aznboi3644
Date Posted: October 11, 2006 at 11:28 PM
Hell my vent is 15 by 7.5 and I can hardly even feel the air moving but its damn loud...zero port noise
Posted By: greenbroncoguy
Date Posted: October 12, 2006 at 8:42 PM
aznboi3644 wrote:
Hell my vent is 15 by 7.5 and I can hardly even feel the air moving but its damn loud...zero port noise
so, should there not be much air moving out of my ports??? I think there is quite a bit...
Posted By: aznboi3644
Date Posted: October 14, 2006 at 4:28 AM
It all depends...How my box is designed and the size of the vent...there is a hell of a lot of air moving through it.
It's just because of the size of the port you can't really feel or hear the air/sound comming from the port unless you literally stick you head in the vent lol...its a cool feeling
Posted By: greenbroncoguy
Date Posted: October 14, 2006 at 7:40 PM
aznboi3644 wrote:
It all depends...How my box is designed and the size of the vent...there is a hell of a lot of air moving through it.
It's just because of the size of the port you can't really feel or hear the air/sound comming from the port unless you literally stick you head in the vent lol...its a cool feeling
that's what I thought, cause I have a heela bunch of air comming out of mine...
Posted By: greenbroncoguy
Date Posted: October 15, 2006 at 12:37 AM
why would it not work, like maybe if you were using only one port for the whole box?
Posted By: stevdart
Date Posted: October 15, 2006 at 9:50 PM
Right, it's primarily space considerations. With a divided box you need two ports, and each port has a structure that takes up airspace. A divided box will use more gross space but will more than likely be the sturdiest build because of the dividing baffle. But every car and situation is different, and there are times where there is no room for the extra cubic inches of the second port. It's all about looking at how much space you have to work with and going from there.
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Build the box so that it performs well in the worst case scenario and, in return, it will reward you at all times.
Posted By: greenbroncoguy
Date Posted: October 15, 2006 at 11:08 PM
cool, that's what I figured. thanks for the input guys -Matt
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