Need help with the box on a JL Audio 12w7-3

[Nugu]

I'll be honest, I'm a bit in over my head. I had only halfheartedly bid on it on Ebay but ended up winning for only 325$ shipped.

I've seen Annuki's (sorry spelled wrong) sealed box and I've also looked all over the forum regarding the 12w7 and found that the Kappa box has been said to be pretty good for it, maybe with a few changes. This kind of box is doable by me with a lot of time.

My abilities at woodworking are rather limited and I don't have a router so I need straight cuts and the Kappa box looks perfect for me. Can someone model it and tell me what/if the box needs alterations to work with a 12w7?

Specs for the speaker are in link below:
http://mobile.jlaudio.com/products_subs.php?series_id=9


If I can pull the box off then I plan to buy a DCX and EP2500, however if I can't I'll have to resell.

 

[lsiberian]

I'll be honest, I'm a bit in over my head. I had only halfheartedly bid on it on Ebay but ended up winning for only 325$ shipped.

I've seen Annuki's (sorry spelled wrong) sealed box and I've also looked all over the forum regarding the 12w7 and found that the Kappa box has been said to be pretty good for it, maybe with a few changes. This kind of box is doable by me with a lot of time.

My abilities at woodworking are rather limited and I don't have a router so I need straight cuts and the Kappa box looks perfect for me. Can someone model it and tell me what/if the box needs alterations to work with a 12w7?

Specs for the speaker are in link below:
http://mobile.jlaudio.com/products_subs.php?series_id=9


If I can pull the box off then I plan to buy a DCX and EP2500, however if I can't I'll have to resell.

Building a sub without a router is a bad idea IMO. 4.2 cuft with a 22 hz tuned in a lined box will give you excellent results.

1.5cuft sealed with heavy fill is the suggested ported build.

 

[Nugu]

Right now I'm looking at something like:

5.9 cubic ft, tuned to 21 hz
23"H, 22.5"W, 22.5"D
3"x12" slot, 31.07 long


Basically it's a 2 inch shorter Kappa box with a shorter slot. Cab size takes into account driver displacement but not bracing displacement, but anything 5.1-5.9 cubic ft models very close according to WinISD. I will try to iron out displacement later.

this leaves -3 db @ 19 hz and a fairly flat response as far as I understand. -6db is ~17 hz


My main worry is bracing, I noticed on Annuaki's sealed sub he used (drywall?) screws a lot, but on the Kappa you just glue as far as I can tell?



Does Vent Length or Internal Volume determine the frequency the box is tuned to? Also how do I find port speed to avoid chugging sounds?



5.0 cubic @ 22 hz gives -3 db @ 20 hz and a flatter line but we can't tell the difference between +/-3 db right?


WinISD "optimized" box keeps trying to tell me to do shallow depth but tall/wide, is there any real merit to this? There would only be ~4 inches clearance at the depth it wants (~13 inches) and I'd have to do the porting sideways.

 

[annunaki]

Right now I'm looking at something like:

5.9 cubic ft, tuned to 21 hz
23"H, 22.5"W, 22.5"D
3"x12" slot, 32.35 long


Basically it's a 2 inch shorter Kappa box with a shorter slot. Cab size takes into account driver displacement but not bracing displacement, but anything 5.1-5.9 cubic ft models very close according to WinISD.

this leaves -3 db @ 19 hz and a fairly flat response as far as I understand. -6db is ~17 hz


My main worry is bracing, I noticed on Annuaki's sealed sub he used (drywall?) screws a lot, but on the Kappa you just glue as far as I can tell.

I use screws with glue as I do not have enough large clamps to do the job without.

As for the 12W7 in a vented enclosure, I have looked into it myself but size is what holds me back.

Here is what I would do if I went vented, though there are two options:

Option 1:
This requires the use of a 12db/oct highpass (infrasonic) filter at 20hz.
5.80ft^3 net tuned to 21hz using a 3.5"H x 15.0"W x 49.15" L slot vent
The vent velocity peaks at 16m/s using 1000 watts rms input power.
Excursion is well below xmax throughout the range.
Estimated output: 19.8hz-85.8hz +/-3db (112.2db-115.2db)
F3 of 19.8hz
+/-1db range of 22.5hz-65.5hz!

Option 2:
This will gain a little bit more extension but may or may not be worth the efforts.
This also requires the use of a 12db/oct highpass (infrasonic) filter at 15hz.
5.80ft^3 net tuned to 19hz using a 3.75" H x 15.0" W x 65.90" L slot vent
Peak vent velocity is at 16.7m/s with 1000 watts of rms input power.
Excursion stays within linear limits so long as the infrasonic filter is used.
Estimated output: 17.7hz - 88hz +/-3db (111.8db - 114.8db)
F3 of 17.7hz
+/-1db range of 21.6hz - 68.3hz!!

Option 3: (smallest option and the same performance as option 2 with no vent to construct!!)

This requires 2 18" passive radiators the PR18-2100 from AE speakers would be perfect.
4.75ft^3 net volume would would be ideal here. This tunes to 19.79hz.
You will need a highpass (infrasonic) filter 4th order 24db/oct. Butterworth at 15hz.
F3 of 18hz at 112db anechoic
Either option would be heavily braced as the driver can generate huge internal pressures

 

[Nugu]

I think I'll go with option 1, option 2 looks painful with such a long vent. Size isn't too big an issue for me as long as it goes through a door. (Hurrah for being single... I spose)

The plan is build box, then buy the DCX and EP frequently recommended in other threads. So filtering isn't an issue (setting it up will be, but till then...).

Assuming I build the box like a size-altered Kappa, how much more bracing is going to be needed? I can do straight cut slat braces, but nothing like the curved artwork stuff in your sealed build. And I'm thinking I should probably go 1.5" thick on the mounting surface... the driver size scares me.

 

[annunaki]

I think I'll go with option 1, option 2 looks painful with such a long vent. Size isn't too big an issue for me as long as it goes through a door. (Hurrah for being single... I spose)

The plan is build box, then buy the DCX and EP frequently recommended in other threads. So filtering isn't an issue (setting it up will be, but till then...).

Assuming I build the box like a size-altered Kappa, how much more bracing is going to be needed? I can do straight cut slat braces, but nothing like the curved artwork stuff in your sealed build. And I'm thinking I should probably go 1.5" thick on the mounting surface... the driver size scares me.

Please see my post I just edited and added a 3rd option which may work perfectly for you!

 

[Nugu]

The third option sounds ideal, it will take me longer due to cost though. Not to mention harder for me to brace I think?


For the moment though I want to focus on bracing so I could layout a box and piece sizes on paper. How do I know how much is adequate bracing? Bracing will be my achilles heel as I don't have a router, all my braces will have to be straight cuts. I will ask around about possibly borrowing one from friends but I see that as unlikely.

This is the main reason I keep coming back to something like the kappa in design.



edit: I'd also like to "Thank" you but nothing happens when I press the thank button now. It disappears and nothing happens. I've tried disabling NoScript and it still doesn't work.

 

[annunaki]

The third option sounds ideal, it will take me longer due to cost though. Not to mention harder for me to brace I think?


For the moment though I want to focus on bracing so I could layout a box and piece sizes on paper. How do I know how much is adequate bracing? Bracing will be my achilles heel as I don't have a router, all my braces will have to be straight cuts. I will ask around about possibly borrowing one from friends but I see that as unlikely.

This is the main reason I keep coming back to something like the kappa in design.

You are worrying too much. I cut all my bracing with a jig saw ($20-$30 at your local store). I simply take my time when I make cuts.

A router is a fantastic tool for round holes, finishing, etc. but not needed.

Adequate bracing ties all 6 panels together ideally while strengthening all the panels. With a sub such as the W7 you will want to brace around every 7 inches or so. Essentially leaving no area unbraced or in contact with another panel of 7"x7". This is not always easy to do which is why most don't do it or try to discount the necessity of bracing (at least to a proper level).

Take a look at the build thread of the 13W1v2 I did (Build Thread 1 in my signature). That technique worked extremely well and was suitable enough for a W7 if needed.

 

[Nugu]

I could do that I think. Just not sure how I'd go about reliably calculating how much space the bracing was taking up.

If I use 3/4 cabinet grade ply for the box, can I use 3/4 mdf for bracing with no ill effect? I ask because I can get 2ftx4ft mdf sheets for only 10$ and I have one sitting unused.

 

[annunaki]

I could do that I think. Just not sure how I'd go about reliably calculating how much space the bracing was taking up.

If I use 3/4 cabinet grade ply for the box, can I use 3/4 mdf for bracing with no ill effect? I ask because I can get 2ftx4ft mdf sheets for only 10$ and I have one sitting unused.

You could use 3/4" MDF for the entire enclosure if you wanted. I would factor in about .25ft^3 to.35ft^3 or so for bracing plus another .14f^3 for the woofer. You will also have to find out the displacement on the passive radiators.

Mixing MDF and 13 ply is no worry. Make sure you get void free ply if you are going that route.

 

[lsiberian]

As far as bracing goes You don't need a lot of cross braces in a sub design because you aren't really bracing against cabinet resonances. You are bracing against the woofer power. For that I use corner braces because they are easier to cut to fit the box.

 

[Nugu]

Thinking about going back to the 4.2 cubic ft tuned to 22.67 hz box. that should get me around -3@20hz. Working around the 5.8 size the best I could accommodate would of been a monolith at 15"W x 45.5"H x 24"D.

While the radiator version would be sweet, I can probably go without that last bit of extension for now. Plan to model it out before I chuck the idea though. I need to get some graph paper.


I'm starting to feel less like I'm going to totally fail at this though. I feel confident I can do this, especially since you showed me such a easy way to do the bracing annunaki.

Can you tell me the ideal slot port size and length for a 4.2 cubic @ 22.67 hz annunaki? I still haven't figured out how that's calculated.

 

[annunaki]

Thinking about going back to the 4.2 cubic ft tuned to 22.67 hz box. that should get me around -3@20hz. Working around the 5.8 size the best I could accommodate would of been a monolith at 15"W x 45.5"H x 24"D.

While the radiator version would be sweet, I can probably go without that last bit of extension for now. Plan to model it out before I chuck the idea though. I need to get some graph paper.


I'm starting to feel less like I'm going to totally fail at this though. I feel confident I can do this, especially since you showed me such a easy way to do the bracing annunaki.

Can you tell me the ideal slot port size and length for a 4.2 cubic @ 22.67 hz annunaki? I still haven't figured out how that's calculated.

Ensuring that you use a 2nd order infrasonic filter at 20hz, a 3.25" H x 14" W X 54.5" L would keep vent velocities in check. This tunes to 22hz in 4.2ft^3.

Here is the problem I see for you. Enclosure size seems to be a potential issue for you. A slot vent of adequate size in a 4.2ft^3 enclosure adds an additional 1.766ft^3 to your overall gross volume!. You then need to add in about .3ft^3 for bracing and another .14ft^3 for the driver displacement. This puts you at a gross internal volume of of about 6.46ft^3!!

With a passive radiator option (estimating here) the gross internal volume would need to be about 5.41ft^3. This also gets you the same type of extension & linearity as the larger vented option as well.

 

[Nugu]

I think you're right about the size. I just dislike not being able to butt the sub into a corner with the PRs, that and complicating bracing more.

I downloaded and got started with sketchup today. The external box is layed out, but I had to guess the PR mount hole size till they get back to me on displacement and mount size. I'll add the bracing to the model another day.

Box size could be subject to change but till then

4.746 ft^3 assuming 0.44 displacement (0.14 driver, guessed 0.30 bracing/PR?)

 

[Nugu]

John got back to me with the PR specs, 16.625 mount hole and ~1 liter displacement (per).


I still have to add the horizontal bracing but beforehand I wanted to see if this was too much or good. bracing is 1" wide 0.75" thick.

Once I have the rest of the bracing layed out I'll do the math and add up displacement from bracing and dampening material and adjust the box size accordingly.

 

[lsiberian]

John got back to me with the PR specs, 16.625 mount hole and ~1 liter displacement (per).


I still have to add the horizontal bracing but beforehand I wanted to see if this was too much or good. bracing is 1" wide 0.75" thick.

Once I have the rest of the bracing layed out I'll do the math and add up displacement from bracing and dampening material and adjust the box size accordingly.

bracing and dampening normally counter each other enough to make the variation insignificant. Boxnotes calcs the average driver and bracing for you in the modeling. It also gives a cut sheet(though I have my own method0.

 

[annunaki]

John got back to me with the PR specs, 16.625 mount hole and ~1 liter displacement (per).


I still have to add the horizontal bracing but beforehand I wanted to see if this was too much or good. bracing is 1" wide 0.75" thick.

Once I have the rest of the bracing layed out I'll do the math and add up displacement from bracing and dampening material and adjust the box size accordingly.

Looks good so far! I would caution on the mounting depth behind the passive radiators however. How deep are they?

You may want to use a large hole in the bracing behind the passives to promote good air flow.

You may also want to tie the 3 braces together as well, but is not necessary. I think you would be quite happy if you built this as is.

 

[Nugu]

Mounting depth was something I forgot to ask John and I didn't want to submit another question again so soon after already forgetting to ask the displacement and sending in 2 separate inquiries one after the other. Though judging from the pictures they should be shallow mounts. If I need more space I'll just move the outside braces inward and make them the same pattern as the center brace (or maybe eliminate the center one).

I plan to add horizontal braces, my wrists were just hurting too much from making the design in sketchup using a laptop touch pad so I've been taking a break.


I was actually looking at how I could do the side braces different but nothing else fits very well with how I want to tie the PR walls and braces together, though now I think moving the braces in and cutting out the middle one maybe better. I think I may mock up a 2 and a 3 brace version.

 

[annunaki]

Mounting depth was something I forgot to ask John and I didn't want to submit another question again so soon after already forgetting to ask the displacement and sending in 2 separate inquiries one after the other. Though judging from the pictures they should be shallow mounts. If I need more space I'll just move the outside braces inward and make them the same pattern as the center brace (or maybe eliminate the center one).

I plan to add horizontal braces, my wrists were just hurting too much from making the design in sketchup using a laptop touch pad so I've been taking a break.


I was actually looking at how I could do the side braces different but nothing else fits very well with how I want to tie the PR walls and braces together, though now I think moving the braces in and cutting out the middle one maybe better. I think I may mock up a 2 and a 3 brace version.

You may want to consider doing some "rib" style braces to tie the bracing together in areas it does not make sense to do a window.


Check out this build I did where I utilized a lot of ribs. This enclosure I went kind of "soft" on bracing in the interests of time. http://forums.audioholics.com/forums/showthread.php?t=64412

 

[Nugu]

I think I'm a bit happier with this layout. Not quite finished though.

Red is where I intend to add small windows to tie into the bracing. I think once those are added that should be good yes?