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Consider slot-loading ports, across the 18" height, but what is the internal? Say 16.5?

I'm not to a place where I can do the calcs but it wouldn't be hard to fab a slot port based off the walls. Or one very big single port, need to look into it. But ~16.5" internal height x (unknown yet) width, you'd just need to cut that piece pretty square and then secure it in place, and you'd probably contend with one 90 degree angle, again not a big deal.

After I finish my project out there, I'll hop on and see what it takes to do that. But find me the internal height dimension (assuming 16.5) to be sure.
 

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Discussion Starter #42
Consider slot-loading ports, across the 18" height, but what is the internal? Say 16.5?

I'm not to a place where I can do the calcs but it wouldn't be hard to fab a slot port based off the walls. Or one very big single port, need to look into it. But ~16.5" internal height x (unknown yet) width, you'd just need to cut that piece pretty square and then secure it in place, and you'd probably contend with one 90 degree angle, again not a big deal.

After I finish my project out there, I'll hop on and see what it takes to do that. But find me the internal height dimension (assuming 16.5) to be sure.
Update..

I wasn't thinking clearly late last night when I was trying to figure out port arrangement..

I took a look today, it seems simple enough, I can add the 4" round ports front or rear, then just bend them 90 degrees..

A few issues I am having now..

A) I don't exactly know what I have in terms of internal volume now that I've added all the bracing
B) I'm still a bit unclear on calculating port lengths with the 90, additionally, a bit unclear on displacement with said ports on 90..

I am going to upload a video to Youtube, it's about 3.5 minutes long, it will clearly explain and illustrate what I've ended up with..

I am posting some pics, I'll try to explain once they're up
 

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Discussion Starter #43 (Edited)
so, that second photo shows the center brace, which is two pieces of 3/4 laminated.. It measured 19.1/8" front to back, 16.50" top to bottom, finally, a tick under 1.50" thick. I cut out the center, leaving 2.50" on all 4 sides..

The pic also shows triangular bracing.. Those started life as 4x6" boards, I ripped 6 squares which measured 5.50 sq x 3.50" thick.. I cut those squares into 12 triangles which are +/- 1/8" off.. I now have 12 triangular braces which measure 5.25" on two sides, x 7.45 (ish) on one side, by 3.50" thick..

My guess was to just subtract 5.50" x 5.50" x 3.50 x 6 from the internal volume.. The confusion lies with the center brace and it's relationship with the triangular braces I've surrounded it with..

Bear in mind, the rear of the box is a single piece of 3/4" ply, vs the face which will be a pair of 3/4" laminated, will yield a tick under 1.50", same as thickness of center brace..

With that in mind, I kept bracing on the sub side to minimum, limiting it to the 4 outer corners..

I am completely lost in terms of internal volume now.. (I don't do maths..)

Also, displacement of each sub is .149 CF as per JBL specs.. mounting depth is 10.25", I'll have the additional 3/4" which should subtract from both depth and displacement no?

(EDIT)

I forgot to mentiion, there are two braces which run top to bottom on rear of box.. Those measure 16.50" top to bottom, 2.50" deep and it's 3/4" plywood.. Tons of glue, predrilled and screwed like an inmate..
 

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Discussion Starter #44 (Edited)
It started life as this.. In hindsight, would have been so much easier to just block all but one of the 5" x 2 vents on each side, used the box as is..

But the woodworking experience I picked up was well worth it.. Again, working on the street, self taught, had to totally rig the table saw for both a rip fence, as well as a jig to cut the triangles, which I then had to carefully eyeball..

(Edit) what a disgrace LMAO
 

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Discussion Starter #45
I had to add a piece of the 4x6" to the angle fence or whatever it's called, this put my fingertips to within mere inches of the blade of the table saw on either side..

The results? A stack of near perfect triangles..

Improvisation has always been strong with me.. The photo shows a scrap piece screwed to the jig from the back..

The other pic shows a makeshift rip fence for circular saw, using a level as straight edge, of course I have a square which made all of this possible..

End result, the box is almost dead square atm.. although I must admit, I butchered the inside cut of the center brace.. I was using a jigsaw with dull blade, rushing (hot as blazes outside) plus I was distracted by almost every neighbor in my neighborhood.. In hindsight, I wish I had trimmed it cleaner before I glued it in..

Also, everything was predrilled, tons of wood glue and I used 2 1/4" fine thread drywall screws, screwed the crap out of everything in sight LOL..



What should have taken a few hours ended up taking a full day to do.. (all the rigging, plus the learning curve and "winging it" with improvisation)

So, how'd I do so far?
 

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Discussion Starter #46
Could you guys please help with 4- 4" ports, mounted front or rear? One other thing I wanted to point out.. It seems that I get some bonus low end, a definite extension in low end when I face subs toward rear deck..

Now, this was true when I briefly ran the pair of 15" JBL 2226HPLs in the 8CF 4648 sub cab which was 8cf tuned to 40hz.. When I faced that toward the rear deck, I heard a definite increase in low end extension..

I also ran these W12s in a large slot ported box (which was crumbling due to water damage) subs facing me with large slot port in center.. Output was ludicrous..

Point is, should I port from front or rear? Or is that an unknown variable, subject to variation as per vehicle type?
 

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Discussion Starter #47
Or 2 slot ports on bottom front, I have approximately 6" x 8" available on both sides, and they can go as far and 16 inches deep
 

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OK there's a lot going on here in all these posts, let's try to get some answers but let's do it in an organized way.

First, I would usually recommend the ports go on the same face as the sub. It doesn't always have to be that way, but I'd say it is optimal. Face everything toward the rear, if the enclosure will be near the rear of the vehicle.

Second, bracing can be calculated very simply, just get your math out and add things together. A triangle is 1/2 a square of the same size, so it is (L*W*H/2) or if you cut a piece to make two, then just count two at a time as a square. Braces with holes in them are simple as well, just take the size of the brace (L*W*H) and then subtract the same from the hole in it.

Third, to calculate a 90 degree or 180 degree bend in a port, you're looking for the port's average length, the inside number. So you can measure the outside of the bend, and then the inside bend, and divide by 2, or just measure as if you're 1/2 way in the port by width.

Fourth, the addition of a 3/4" board to lift the subwoofer up 3/4", won't change displacement in any way you'll need to worry about, so use the factory displacement number.


Did I miss anything? Oh, are you committed to doing the round ports, or do you want to explore a slot port with that 16.5" side?
 

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Discussion Starter #49
OK there's a lot going on here in all these posts, let's try to get some answers but let's do it in an organized way.

First, I would usually recommend the ports go on the same face as the sub. It doesn't always have to be that way, but I'd say it is optimal. Face everything toward the rear, if the enclosure will be near the rear of the vehicle.

Second, bracing can be calculated very simply, just get your math out and add things together. A triangle is 1/2 a square of the same size, so it is (L*W*H/2) or if you cut a piece to make two, then just count two at a time as a square. Braces with holes in them are simple as well, just take the size of the brace (L*W*H) and then subtract the same from the hole in it.

Third, to calculate a 90 degree or 180 degree bend in a port, you're looking for the port's average length, the inside number. So you can measure the outside of the bend, and then the inside bend, and divide by 2, or just measure as if you're 1/2 way in the port by width.

Fourth, the addition of a 3/4" board to lift the subwoofer up 3/4", won't change displacement in any way you'll need to worry about, so use the factory displacement number.


Did I miss anything? Oh, are you committed to doing the round ports, or do you want to explore a slot port with that 16.5" side?
Ports on sub side, got it..

As for the triangles, I had already assumed I'd be subtracting the dimensions of 6 squares vs 12 triangles, which is why I posted both. The part I'm a little hazy on is where the center brace meets with the triangles.. not sure how the relationship between the two affects calculation of displacement..

At this point, I am open to suggestion.. My woodworking skills have slightly improved *pfft* so I am open to slot porting.. (I wouldn't dream of posting those pics anywhere but here)

When you say slot port with the 16.5" side, which side are you referring to?

Were you able to figure out from the pics and all the haphazard babble what I've got going on at the moment? LOL..

At this point, I'm ready to follow step by step instructions.. Just tell me what to put where, I'm all ears :D

If you need a better description or pics of what I have, please let me know..
 

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To help with spacial descriptions, I'm going to label your box sides, so when I say a certain side, you'll know. Now, assuming the box with the subwoofer baffle (yet to be made) is on its side as shown in most of the pictures so the woofers would be vertically placed directly in front of me, let's call the subwoofer baffle (to be) "FACE". Still as viewed from this position, lets call the left side "SIDE 1". We'll call the back wall "BACK", and right side "SIDE 2". The top will be "TOP" and bottom "BOTTOM", just for accuracy's sake.

So, in the case of a slot port, let's start on SIDE 1 from FACE to BACK, one single board to the back wall, basically reinforcing that whole side. We need to do this because the SIDE 1 has a big ass hole in it already, so we need to make a new flat board for the port to work. So, first part of the port is this piece, which should be 16.5" by whatever depth we need, and we can assume it will probably need to be a 90 degree port. The second board would then be this second part of the port, a board that needs to be placed on the BACK, up against our new port board over next to SIDE 1. The length of this is still unknown, but we'll figure that out. Together, these two boards make up the OUTSIDE half of the port, make sense? The INSIDE half of the port will be determined once we know how much width the slot port needs. You'll be able to use the smooth TOP and BOTTOM walls to make the thing work right.

Over the course of this conversation, we covered a lot of numbers. Let's get clarity over some specific numbers one more time, you probably already have them written down"

A: What is the height from the inside of BOTTOM to TOP (aka how tall our port should be)? Is that 16.5"?

B: How deep is the box from FACE to BACK, with the bracing in place? Have you glued the braces on the BACK wall by SIDE 1, down to the point where they could not possibly be removed safely?

So once we know all of that for certain, then we can calculate the slot port's planned width, and then length properly. With that, then you can fabricate the INSIDE two port boards, and your port is basically done! Slot ports can actually be easier in some ways, because you're able to use the box itself to make most of it, plus it is basically free bracing.

To skip ahead to the future just a bit, Once the port is fabricated, then the top FACE board can be built for the subs, and the port itself. Because we're talking about a slot port, it will be as easy as cutting a rectangle hole in a board, which is easy with a jigsaw and a straight edge. If you have a way of sanding or filing, after the slot board is installed directly over the port, you can slowly sand or file a smoother "roundover" around the port to keep the airflow smooth as possible.


OK all this make sense?





OK so the easiest way to make a slot port is to have the side of the box be part of the port. Now because you have a hole in that side, imagine just laying a sheet up against the wall there, basically level with your box's opening. So that would 16.5 x whatever the depth is we need. I haven't yet modeled how big the slot port would need to be, but if it needs to go 90 deg, then you just lay another board on the back wall (opposite the sub baffle)

Ports on sub side, got it..

As for the triangles, I had already assumed I'd be subtracting the dimensions of 6 squares vs 12 triangles, which is why I posted both. The part I'm a little hazy on is where the center brace meets with the triangles.. not sure how the relationship between the two affects calculation of displacement..

At this point, I am open to suggestion.. My woodworking skills have slightly improved *pfft* so I am open to slot porting.. (I wouldn't dream of posting those pics anywhere but here)

When you say slot port with the 16.5" side, which side are you referring to?

Were you able to figure out from the pics and all the haphazard babble what I've got going on at the moment? LOL..

At this point, I'm ready to follow step by step instructions.. Just tell me what to put where, I'm all ears :D

If you need a better description or pics of what I have, please let me know..
 

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Discussion Starter #51
To help with spacial descriptions, I'm going to label your box sides, so when I say a certain side, you'll know. Now, assuming the box with the subwoofer baffle (yet to be made) is on its side as shown in most of the pictures so the woofers would be vertically placed directly in front of me, let's call the subwoofer baffle (to be) "FACE". Still as viewed from this position, lets call the left side "SIDE 1". We'll call the back wall "BACK", and right side "SIDE 2". The top will be "TOP" and bottom "BOTTOM", just for accuracy's sake.

So, in the case of a slot port, let's start on SIDE 1 from FACE to BACK, one single board to the back wall, basically reinforcing that whole side. We need to do this because the SIDE 1 has a big ass hole in it already, so we need to make a new flat board for the port to work. So, first part of the port is this piece, which should be 16.5" by whatever depth we need, and we can assume it will probably need to be a 90 degree port. The second board would then be this second part of the port, a board that needs to be placed on the BACK, up against our new port board over next to SIDE 1. The length of this is still unknown, but we'll figure that out. Together, these two boards make up the OUTSIDE half of the port, make sense? The INSIDE half of the port will be determined once we know how much width the slot port needs. You'll be able to use the smooth TOP and BOTTOM walls to make the thing work right.

Over the course of this conversation, we covered a lot of numbers. Let's get clarity over some specific numbers one more time, you probably already have them written down"

A: What is the height from the inside of BOTTOM to TOP (aka how tall our port should be)? Is that 16.5"?

B: How deep is the box from FACE to BACK, with the bracing in place? Have you glued the braces on the BACK wall by SIDE 1, down to the point where they could not possibly be removed safely?

So once we know all of that for certain, then we can calculate the slot port's planned width, and then length properly. With that, then you can fabricate the INSIDE two port boards, and your port is basically done! Slot ports can actually be easier in some ways, because you're able to use the box itself to make most of it, plus it is basically free bracing.

To skip ahead to the future just a bit, Once the port is fabricated, then the top FACE board can be built for the subs, and the port itself. Because we're talking about a slot port, it will be as easy as cutting a rectangle hole in a board, which is easy with a jigsaw and a straight edge. If you have a way of sanding or filing, after the slot board is installed directly over the port, you can slowly sand or file a smoother "roundover" around the port to keep the airflow smooth as possible.


OK all this make sense?





OK so the easiest way to make a slot port is to have the side of the box be part of the port. Now because you have a hole in that side, imagine just laying a sheet up against the wall there, basically level with your box's opening. So that would 16.5 x whatever the depth is we need. I haven't yet modeled how big the slot port would need to be, but if it needs to go 90 deg, then you just lay another board on the back wall (opposite the sub baffle)
Ok, I get what you're saying.. A few things I forgot to mention..

As for the "big ass holes" on the side/s (LOL) I forgot to mention, there were handles on BOTH sides which I still have, planned on putting them back on in the interest of covering the two "big ass holes" on either side, for ease of removing the box (when I need to move bass guitar equipment around) holes will be airtight, handles fit snug, made of metal..

There's also a "big ass hole" on the rear of the box, that which had a pair of speakon input terminals (Pro Audio use) which I also planned on re-using since I already have a pair of heavy duty Speakons.. They are essentially a pair of sleeved/insulated 10 gauge wires, both capped with a twist on plug on one end, bare wire on the amp end.. I'd essentially push a clip, twist, pull, cab safely disconnected from amp, no fear of accidental grounding etc..

As for all of the bracing, it's all been thoroughly glued and screwed, it's in for life.. I don't think I can remove any of it without actually destroying the box at this point..

The center brace however, let's focus for a minute on that.. I can easily cut the middle portion of the center brace out, leaving both the sides and the back intact.. Would this afford us ample space/clearance to port dead center of box? If so, could we then also use the remaining side and rear bracing as reinforcement for the port?

As for measurements, if you're referring from lengthwise from left to right as side 1 and side 2, then the INTERNAL/bare box measurements before bracing were as follows,

- 46.5" (side 1 to 2) or left to right as it were..
- 16.5" top to bottom
- 19 1/8" front or face (sub) to rear of box (deep)

I had a tick under 8.5 cf before any bracing was added..

the triangles were 6 squares, each measuring

-5.5" x 3.5" ( 6 squares)

Then the two thin slats on the rear of box, running top to bottom are

- 16.5" top to bottom x 2.5" deep x 3/4" thick or wide (3/4" ply cut to 16.5" long, then 2.5" wide, glued to rear of box with cut side facing rear for strength, 2 of those as pictured, 1 per side)

Thoughts?
 

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Discussion Starter #52
Oh wait, I get it.. You're talking about a single slot port vertically mounted against side 1, heading straight back, then 90 toward center along back? this could be accomplished using 2 pieces of wood, using the actual box as makeup of outer portions of port.. I wish I had known before I glued those triangles in place..

I could possibly remove all 4 triangles from side 1, it would most certainly cause damage to the top layer of ply (1/8 veneer) but then again, that type of damage exists all over the box.. Technically, I should be able to remove the triangles if it would greatly simplify things in the end.. I could also trim the center brace as well..

As for the big ass hole (LOL) on side 1, I could just put the handle back in, and pour epoxy to fill any gaps and level it smooth to avoid any turbulence?

However, all things considered, I'd be complicating things in order to simplify things..

Had I known the port would be on one side, with a 90 bend prior to all that hard work with bracing, I would have gone for it..

If center port is not an option, then I'll remove bracing and port from side 1..
 

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Discussion Starter #53 (Edited)
Hold on a minute, what about porting outside the box?

I can simply add a few strips of 2x4, or 4x6, or I have precut 2.5" x 48" strips of 3/4" ply, could trim and add those to form 3 outer edges of the vent, create the framework for an external vent.. top or bottom of box (although I prefer top) then simply cover with a sheet of 3/4 MDF or ply?

If it's possible to do this, I can cut the box open to form the opening for the vent.. I don't mind an odd shaped box either, so if the vent has to be smaller/narrower than the actual width of the box, I'd be willing to do that (top or bottom) If it has to be bottom, I can always add "legs" on the bottom of sides 1 and 2 for stability.

If it's possible to vent outside the box, I can then have a vent with which I can retain internal bracing, as well as volume, vent would face forward.



Another benefit to the external port would be aesthetics.. when I tore the box down, outside of box got a little beat up.. tore up the 1/8" veneer or outermost layer of ply all along the outside.. I'll need a bunch of wood filler and a day with a sander to prep it for spray on finish..

Thoughts?
 

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Woah, lots of stuff going on again.

You can vent outside the box, but you really don't need to. The box doesn't need to be any bigger, and there's no reason to go outside of the box. Around 7 to 7.5 cubic feet, and you're still golden. One big slot port should do. The outside can always be re-worked, or you can add thin wood as a new cover for it. It would be nice to see cover boards made to match the contours of the rest of the car, and then carpeted. Use the box as a skeleton for a more "installed" setup.

What I need to know at this point before we build a model (and I plan on 3D-ing this for you) is, those handles, how deep do they intrude into the box? Do they sit flush with the 3/4" wall, or do they go further inboard?

You can build a port in the center, but you'd have to run the port short, and not go all the way to the back wall because that would divide the box. This can still be done, and done right if you want to use the "port" as a brace in the center. No problem. We can either build two slot ports and have them come from center toward BACK (but not all the way back, say about 10" back first) and then split to SIDE 1 and SIDE 2, which would serve as internal bracing as well. A little more complicated, a little more wood, but doable.

What I'm thinking at the moment, is to leave the center brace in place, and use it as a guide to build slot ports from the center to each side, twin ports. This will give you maximum bracing, minimal re-working of the box, and really the only "cost" is more wood than a single port. But it should sound and look really good.
 

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Discussion Starter #55
Woah, lots of stuff going on again.

You can vent outside the box, but you really don't need to. The box doesn't need to be any bigger, and there's no reason to go outside of the box. Around 7 to 7.5 cubic feet, and you're still golden. One big slot port should do. The outside can always be re-worked, or you can add thin wood as a new cover for it. It would be nice to see cover boards made to match the contours of the rest of the car, and then carpeted. Use the box as a skeleton for a more "installed" setup.

What I need to know at this point before we build a model (and I plan on 3D-ing this for you) is, those handles, how deep do they intrude into the box? Do they sit flush with the 3/4" wall, or do they go further inboard?

You can build a port in the center, but you'd have to run the port short, and not go all the way to the back wall because that would divide the box. This can still be done, and done right if you want to use the "port" as a brace in the center. No problem. We can either build two slot ports and have them come from center toward BACK (but not all the way back, say about 10" back first) and then split to SIDE 1 and SIDE 2, which would serve as internal bracing as well. A little more complicated, a little more wood, but doable.

What I'm thinking at the moment, is to leave the center brace in place, and use it as a guide to build slot ports from the center to each side, twin ports. This will give you maximum bracing, minimal re-working of the box, and really the only "cost" is more wood than a single port. But it should sound and look really good.
DONE.. It's settled then.. let's do it that way..

As for the handles I will double check, but I am almost certain they do not extend into the box.. assuming we'll need that area smooth and flush on both sides, I'll make sure to it, no problem..

I love the idea of dual ports from the center down to a pair of 90s left and right, that's 10 gauge birdshot on a flock of pigeons.. (killing more than two birds with one stone)

Ready when you are.. (can't wait!)
 

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If you want to get a head start, DL WinISD pro 0.7 if you haven't already, throw the specs in and then start modeling ideal ports given a slot size of 16.5" by (X), and we can fool with anything with 1000W of power or so, getting air velocity in the 30m/s range or less should be ideal.

Fiddling with box size a bit here and there, and fiddling with the tune hz a bit should find the sweet spot. Taking a wild guess without the software around me (here at work), I'd guess 16.5 x 2.5" should be a good starting point. We'll need to also watch for port resonance, you don't want a port to resonate in the range we'll be playing.

Once we know approximately how big (wide) that port needs to be, of course its length will end up being calculated relative to how big the box is. Now of course, the box will end up having less displacement with the port inside of it, so this becomes the "moving target", I was talking about. But it won't be hard because you can fudge a few inches here and there, and still end up good to go. Like a moving target but we're hitting a big target anyway.



DONE.. It's settled then.. let's do it that way..

As for the handles I will double check, but I am almost certain they do not extend into the box.. assuming we'll need that area smooth and flush on both sides, I'll make sure to it, no problem..

I love the idea of dual ports from the center down to a pair of 90s left and right, that's 10 gauge birdshot on a flock of pigeons.. (killing more than two birds with one stone)

Ready when you are.. (can't wait!)
 

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Discussion Starter #57
If you want to get a head start, DL WinISD pro 0.7 if you haven't already, throw the specs in and then start modeling ideal ports given a slot size of 16.5" by (X), and we can fool with anything with 1000W of power or so, getting air velocity in the 30m/s range or less should be ideal.

Fiddling with box size a bit here and there, and fiddling with the tune hz a bit should find the sweet spot. Taking a wild guess without the software around me (here at work), I'd guess 16.5 x 2.5" should be a good starting point. We'll need to also watch for port resonance, you don't want a port to resonate in the range we'll be playing.

Once we know approximately how big (wide) that port needs to be, of course its length will end up being calculated relative to how big the box is. Now of course, the box will end up having less displacement with the port inside of it, so this becomes the "moving target", I was talking about. But it won't be hard because you can fudge a few inches here and there, and still end up good to go. Like a moving target but we're hitting a big target anyway.
2- ports 16.5 x 2.5" (ish) got it..
 

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Discussion Starter #58
I tried using the program.. I'm a bit unfamiliar with some of the features (not sure what data to input in certain areas)

Also, driver integrity is corrupt or inconsistent in their database, without correct data, aren't we farting in the wind?

Just sent JBL an email requesting all of the missing info for the Winisd database.. Hopefully they'll provide the info needed to fill in the blanks..
 

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I tried using the program.. I'm a bit unfamiliar with some of the features (not sure what data to input in certain areas)

Also, driver integrity is corrupt or inconsistent in their database, without correct data, aren't we farting in the wind?

Just sent JBL an email requesting all of the missing info for the Winisd database.. Hopefully they'll provide the info needed to fill in the blanks..

You don't need every spec, most can be extrapolated (automatically) by the program.

This spec
JBL W12GTI SPECIFICATIONS Pdf Download.

and what is in WinISD are close, it is suspected the one in WinISD was actually measured and not as written in the book. I built one with the included measurements and built one with JBL's specs, and pretty much got the same result +/- a few %. Anyway, I'll just use the specs gathered from JBL here, and give you some info.

So, at first I modeled with two ports, but really it is overkill. There is nothing wrong with overkill, of course. Here's the table with two ports, all of these are well below any chuffing noises, FYI.

For 24 Hz tune, 16.5 x 1.5 x (X) port

  1. Box size 8 cu ft, 24.72"
  2. Box size 7.75 cu ft, 25.65"
  3. Box size 7.5 cu ft, 26.64"
  4. Box size 7.25 cu ft, 27.70"
  5. Box size 7 cu ft, 28.84"
for 25 Hz tune, 16.5 x 1.5 x (X) port

  1. Box size 8.0 cu ft, 22.46"
  2. Box size 7.75 cu ft, 23.32"
  3. Box size 7.5 cu ft, 24.23"
  4. Box size 7.25 cu ft, 25.21"
  5. Box size 7 cut ft, 26.26"

You can go single port if you want to, and as example of that, a 16.5 x 3 x 23.02" vent would fit an 8 cu ft box at 24 Hz. So if you want to go that route (single slot) we can re-calculate.




Oh and I'd like to point out there is a rule I'm breaking, with the 16.5" x 1.5 x (X) slot ports, which is the port ratio rule, most people suggest a max of 8:1 and this 16.5 x 1.5 idea here is 11:1 Basically, a port with two much ratio of height to width has the propensity to chuff. However, I still feel that even with this narrow port, you should still not be able hear it unless you are completely full-tilt at ~25Hz. The single larger port doesn't break this rule, if it matters to you. Personally, I don't think it will.




Oh and the reason I made you the table of all the sizes, those ports of course take up room themselves. Some may be in the .7 to .75 cubic foot range per port (assuming the wood that makes the the outside of the port also becomes displaced space), so my hope is you can use my calcs to then find the sweet spot.
 

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question for fourthmeal, i also plan to run a pair of jbl w12mk II subs, but with a 4.5 cuft vented enclosure. My question is which port design is better for sq, slotted or ported? i was under the impression a slotted port design was better than the round ports. which is better for these subs? forgive me because i never ran a vented sub setup, always sealed. and the only reason i'm going vented because i have been reading as many older threads on this sub as i can and everybody who i know has a ear has stated that with this sub, going vented , you still keep the SQ of the sealed but adds the spl and efficiency of a vented box. BTW my music taste is fusion jazz and limited rap (roots/dr.dre).
 
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