Hey all! Been away for a while, I went through a "Gonna get a Subaru STi" phase since I came into a little bit of $$, but opted to keep the Runner instead (say what you want about them, but I LOVE those STi's). So now I have a pair of JL Audio 12W7's but don't know the dimensions for a good box.

I don't want to buy some at a shop if I don't have too. I pm'd BumpinYota since I bow down to his db level, but I guess he's been away too. Anyone have good dimensions, or perhaps could build a pair of boxes for me? Thanks!

 

Go to the JL website, they have spec sheets for their speakers and "tutorials".

 

are you wanting sealed or ported? Ill make some nice boxes for them if ya give me the subs

 

those subs are badass, I dropped JL Audio at my shop right before they came out. I like JL alot and I didn't drop them for the product, we just couldn't get along with the rep, he was a total dickhead... I have been pushing Diamond Audio hard in my area and they seem to be doing really well, kinda taken Kicker over!

 

Thanks for the reply's guys. COYOTA thanks I just found the pdf file with all the specs. I have a couple more questions... What type of material should I use? I've never built boxes before and the only material I've heard about is particle board, but it seems kinda weak for how heavy these are (45lbs).

Also, how would I "tune" the box? It says to tune the ported box to 32 Hz. How do I do that and how do I know IF/WHEN I've done it? Oh yea, I'm not really interested in db level, just the sound quality (since I know these are gonna be LOUD anyway). Would a sealed box be better or ported?

DBIKEMAN - I'll give you the subs if you give me your Runner

 

I've always wanted a pair of those, just never wanted to pay for an amp to push those things! What type of amp do you have?

 

I am not a box pro, I will have to ask the boxbuilder at the shop I work at tomorrow, but I do know that vented is definatley the way to go. We always use 3/4 inch thick MDF(medium density fiberboard), particle board sucks ass don't use it!

 

I would personally go with a ported box. I'd say about 2 cu. ft. per chamber. make sure the port is a slot port.

Scarface is right use at least 3/4 mdf. For a W7 I would use 1" thick because that are very heavy. Ive been checking out new subs and cant decide between the W7, the Diamond Audio TDX, the mtx 9500 or Eclipse 15" Pro titanium.

 

Jethro has a good question there. You have JLW7's. They deserve to be done right. Amplifier(s), box, wiring, vehicle power etc. Whole 9.9999 yards.


Go with the sealed box. less hassle, better power handling. One of those places where keeping it simple goes a long ways for a guy that doesnt want to spend more time tweaking the stereo than listening to it. If you dont calculate the dimensions right (box internal volume and port dimensions) it could easily sound like crap. For a guy of your skills and experience, GO SEALED !!!!!!

MDF is a much more dense material than particle board. The grains are almost dust like and its a light mocha color. Not the same stuff as under your house carpet. Sometimes the Lumberyard does not have it, you may have to shop around.

 

very hard decision to make on the subs...I have personally owned a Ti 15 and it owned all in the hatch of my CRX with 1 Kicker zr600 amp on each voice coil(around 800 watts a coil)..I must say that sub was abused very hard and still asked for more! The TDX is very hard to beat also, I haven't had the pleasure of hearing one yet, but my boss just recieved his demo system and guess what was in it? 1 tdx 15 with the new d51500.1(not in yet) going on it! We are gonna use the bassboxpro program and do a street box and probably achieve high 40's maybe low 50's with it. TDX are built very very strong, I don't know much about the mtx but if the eclipse or da is installed by authorized dealer you get 3 year warranty!

 

From what I remember W7's are better off in sealed boxes. You'll want to make it out of 1" MDF. DO NOT USE PARTICAL BOARD. When these first came out the JL folks said they required professional installation, but I think that was just a ploy due to the way the surround is installed. These subs are no joke, so I hope you have some good work working skills.

 

Yeah I remember when we went to the JL Audio training and they showed us the w7 and how to mount it and all..It hadn't been released yet but they wanted us to be ready, but like I said not long after that we dropped them..Great subs though I have always liked their subs and their amps.

 

Right now I just have a 4 channel Sony (don't worry, I wouldn't even THINK of using that thing for the subs), but I'm going to get either two JL 1000.1 or a couple PPI amps. There's a little shop by my house that had a better price for new 12W7's than the used ones on Ebay, so I'm probably going there.

I'm also going with an Optima yellow top and probably a bigger alternator.

Yea I was thinking it would be easier right now to just go with the sealed since I hace no idea what to do with the whole tuning thing. I mean the JL pdf has good specs, but I don't want to mess up and have to do it all over again...

 

If you have the money just have the shop build a box. To me if the box is built right, i would almost always go ported.

 

Building good boxes isn't too hard at all, as long as you have the right tools and materials and take your time. I would be happy to help you with the project. Let's take it in steps...
Get a good idea of the outside dimensions of the box. From that, we can come up with the box designs. You can decide if you want it sealed or ported a little later. I always figure out two constant dimensions, and leave the depth as a variable to make the box the size I need it to be. I have a 1998, and I bet our trunks are different so you will need to measure it yourself. Go out and measure the width and height of your hatch on the floor. Visualize a big rectangle box filling up that area right behind the seats and running from wheel well to wheel well. If you have a hatch cover, make sure the box isn't too high to keep it from being used. In my 98, My width is 38.5, and my Height is in the 16” range. I am still waiting for my hatch cover to get a good height number. It arrives tomorrow.

Let’s go with my measurements and we can change them after you get your numbers.

You need to subtract the .75” x 2 pieces for the thickness of your ¾” MDF or higher quality knot free plywood (lighter). You can get either at Home Depot, or Lowe’s.

38.5” – 1.5” = 37” Wide internal
x
16” – 1.5” = 14.5” Tall Internal
------------------------------
536.5 inches square - This is 2 of the 3 internal dimensions of your box.

Here is where you make the decision between sealed and ported. Ported usually take up a lot more area than sealed, and are a little trickier to built. I would just go with sealed, and if you don’t like it, you can build it ported later. The practice wouldn’t kill you anyhow. So JL’s site says 1.375 per driver. You need to add air space for everything else that takes up space inside your box (bracing, woofer basket, etc). I will account for woofer, but bracing will be added in later when we decide how much we want to do.

1.375 ft3
.14 ft3 for woofer
-------------------------
1.515 ft3 total air space needed per driver x 2 drivers = 3.03 ft3

Take 3.03 and multiply by 1728 (which is 1ft3 converted to inches or 12x12x12). This equals 5235.84 cubic inches

Now divide 5235.84 / 536.5 = 9.759 inches internal. Add 1.5” to that to find external, or 11.25” Deep. With this size we ended up with, the subs are going to be vertical and facing either forwards or backwards. 11.25” isn’t enough depth to mount flat facing up.

So for two sealed 12w7s, each in 1.375 ft3, my external dimensions would be 28.5Wx16Tx11.25D. This is basically one big box with no bracing, no divider between the subs. Without bracing, it will flex. Bracing is very important, especially when you have 90 lbs of woofer alone!

Below is how to adjust for bracing. You can add as much bracing as you want. Just use this technique to adjust for it.

I want to add a vertical divider between the subs, but I want to cut a huge square in the middle because I don’t want these subs in their own chamber. Since this is your first box, make it easy on yourself. A single box holding two woofers will equalize, and the woofers will share the volume of the box evenly. I just want to use the divider as a brace. Also, if this is your only brace, it’s takes up such a small amount of airspace that you probably don’t need to account for it, but I always do. It’s part of the fun of building boxes.

So the inside dimensions that we need are 14.5 x 9.75. So I already know I need a board that is 14.5 x 9.75 to fit in there perfectly. The board is .75” thick, so it takes up 106 inches of space. Now I want to cut a hole out of that board to let air pass from one side of the box to the other, and I want it to be a 8”x 5” rectangle in the middle of the board. That thing will give me back 30 inches, so my total air space for the board is 76 inches. That’s only .043 ft3 (76/1728=.043).

You could also just jam a couple of 2x4s in there too, but I always just build half walls or more dividers like the one we just did. They are stronger than 2x4s because they brace multiple sides of the box at one time. Once you have all your braces accounted for, add up all of their required air space and add it to your target internal airspace, and readjust your box dimensions.

1.375 ft3
.14 ft3 for woofer
.043 for my single brace
-------------------------
1.558 ft3 total air space needed per driver x 2 drivers + 1 divider = 3.07 ft3
or 5310.14 cubic inches

Now divide 5310.14 / 536.5 = 9.89 inches internal. Add 1.5” to that to find external, or 11.39” Deep. You can see how it adds up pretty quickly the more braces you add. Brace enough, and you can probably gain enough depth to mount those subs on the top instead.

New external dimensions are 38.5 x 16 x 11.39

Anyhow, I hope that helps. I would be happy to just design if for you, and then go over how I got to that so we are all on the same page. Sealed boxes aren’t as critical as ported, and you can mess up a little on the air space and not really hear any difference, but it is nice to know that it was exact anyhow.

Ported is the same way, but you need to account for the port, and actually build the port. www.jlaudio.com has a great tutorial on bracing and box building, which might make my gibberish make more sense. The ported enclosure will be at least 4” deeper than the sealed, maybe bigger. Let me know if you want to see that figured out so you know exactly.

Later,
Wes

 

This topic needs to be moved to the audio section of the forum.

 

Use 3/4 HDF, yes HIGH density fiberboard. I'm 90% sure that's what was used for my 2 W6's. Heavy, but it was incredibly stiff allowing for better response.

 

I have never seen HDF. I was happy to find MDF. I believe the theory of MDF is that it is denser, which in turn lowers it's resonant frequency so the box doesn't actually vibrate causing coloration and or bass cancelation. It doesn't hold screws real well though, and doesn't compress like plywood does. It's cheap though.
I suggest good quality plywood, but it's expensive. It doesn't have to be baltic berch, or oak plywood, as long as it is void free and you brace it well. Bracing will lower that resonant frequency as well, and make it structurly stronger as well. It will also weight around 20% less. Using MDF is absolutely fine though.
Companies have been using good grade plywood to make massive 18" PA subs and they work great. The do it because it can get wet, it holds up to moving it around without falling apart, and it is much lighter than MDF. Plywood is good if you brace it.
Its your choice!
Wes

 

Great info below....
And... thats the simple version!!

If you want to maximize the area of your interior (IE minimize how much usuable room your big ol box a speakers now sucks-up in your truck) and if you want it to look good like its part of the truck, your box will be custom fitted to the contour of the interior, and this gets a little more fun to calculate all the additional angles and odd spaces rather than a rectangle. You may have to mount your amps to it too (box), and if you want things flush without dead space, theres more angles and odd spaces to calculate.



You probably ought to get your whole system figured out, planned on paper, wires and everything mapped out, before you build your box.

''''WES WROTE....
A single box holding two woofers will equalize, and the woofers will share the volume of the box evenly.'''' (goes on to tell you not to use seperate chambers for each speaker)

That is "true" as long as both speakers are performing equally, if you have each sub running a differnt channel that is not correct, and if one sub blows, or the amps arent equal, or the amp quits..... you can damage the other speaker(s) with it being in a less suspended air space as well as it may not be visually obvious (at a casual glance) that one woofer isnt firing.

Do a seperate chamber for each speaker.

A box should look good AND sound good or else youll never be happy. That will cost you time and money down the road. Do it right the first time.

 

The competition circle and manufacturer standard (when using wood) is MDF.