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Title: Looking for plans for dual 18 cab for JBL 2241H drivers
Post by: Mike Holtzinger on October 24, 2014, 07:56:10 pm
 I've got 4 2241H drivers and want to build some boxes for them. I know the SR4719 box is the standard and pretty easy to build, but
1) I can't find any complete plans.
2)I'm open to other designs.

 I'll be using these for my band and I've built cabinets before. I'm not concerned about the cost/time as I enjoy the process and this is not for profit.
Thanks!
Title: Re: Looking for plans for dual 18 cab for JBL 2241H drivers
Post by: Lee Buckalew on October 24, 2014, 11:32:11 pm
I've got 4 2241H drivers and want to build some boxes for them. I know the SR4719 box is the standard and pretty easy to build, but
1) I can't find any complete plans.
2)I'm open to other designs.

 I'll be using these for my band and I've built cabinets before. I'm not concerned about the cost/time as I enjoy the process and this is not for profit.
Thanks!

Here are the spec sheet and JBL's recomendations for cabinet sizes.  The spec sheet shows a tuning with a sealed enclosure and one tuned to 30Hz while the published cabinet dimensions recomend a tuning to 30Hz.  Given the recommended internal volume of 10 cu. ft. Per driver building single driver cabinets may be best for ease of movement and configuration.  There are not complete plans here but if you can calculate your internal volume losses for bracing and you do a little study on constructing sub cabs they are not that difficult if you have good woodworking skills.

https://www.jblpro.com/pub/manuals/enclgde.pdf
http://www.jblpro.com/pub/components/2241.pdf


Lee
Title: Re: Looking for plans for dual 18 cab for JBL 2241H drivers
Post by: Mike Holtzinger on October 25, 2014, 08:26:47 am
Thanks Lee.
 I've decided to go with the big  dual driver box. Can you point me in the direction of some port calculating info for this? I think the single slot type would be the easiest to build.
Title: Re: Looking for plans for dual 18 cab for JBL 2241H drivers
Post by: Lee Buckalew on October 25, 2014, 10:45:51 am
Thanks Lee.
 I've decided to go with the big  dual driver box. Can you point me in the direction of some port calculating info for this? I think the single slot type would be the easiest to build.

My recomendation would be to build to JBL's suggested internal volume from the document that I linked.  To do a dual version you build to twice the volume (not twice all the dimensions) and have an internal wall that se oersted the drivers.  That is what many manufacturers do for dual driver configurations.
Read through the notes at the end of the JBL enclosure page.  They give suggestions for damping material and how it effects cabinet volume.  They also give suggestions for bracing.  They mention port/duct sizing and going with other sizes but maintaining the same port volume. 
Once you start changing the box volume and the loading type you really need to be able to plug in the Thiele Small parametres (included on the JBL driver spec sheet) to calculate cabinet volume and loading needs/effects.

Lee
Title: Re: Looking for plans for dual 18 cab for JBL 2241H drivers
Post by: Nick Enright on October 25, 2014, 11:01:32 am
I've got 4 2241H drivers and want to build some boxes for them. I know the SR4719 box is the standard and pretty easy to build, but
1) I can't find any complete plans.
2)I'm open to other designs.

 I'll be using these for my band and I've built cabinets before. I'm not concerned about the cost/time as I enjoy the process and this is not for profit.
Thanks!

not exactly the same driver, but very similar, and this was my solution.

(Not saying it will be yours, but it might give you an idea.)
Title: Re: Looking for plans for dual 18 cab for JBL 2241H drivers
Post by: Paul G. OBrien on October 25, 2014, 04:27:39 pm
I've got 4 2241H drivers and want to build some boxes for them. I know the SR4719 box is the standard and pretty easy to build, but
1) I can't find any complete plans.
2)I'm open to other designs.

Download a copy of WinISD Pro and simulate various box sizes and tunings to see what combo will work best for you. The thing you have to know for reflex subs is the bigger the box and lower the tuning the less power the driver will take before exceeding excursion limits, so you have to decide on what to compromise.. power handling or low end extension.

Building a box is simple enough to do without plans but there are loads of plans available on the web.. just do a search and look for one with the same tuning as your favorite sim.
Title: Re: Looking for plans for dual 18 cab for JBL 2241H drivers
Post by: duane massey on October 26, 2014, 11:18:24 pm
+1 on WinISD. I don't normally build vented boxes but the ones I've built using this program have been well-liked by the clients who requested them.
Title: Re: Looking for plans for dual 18 cab for JBL 2241H drivers
Post by: Mike Holtzinger on November 01, 2014, 08:44:51 am
I've downloaded WinISD and plugged in the driver. Everything looks OK except the port parameters. When I asked for a rectangular port of 4"x 24" or 4"x 18" etc...it says Vent length "too Short and Vent Mach: .08 (in Green ?). What is Vent Mach? Help is not available.
Title: Re: Looking for plans for dual 18 cab for JBL 2241H drivers
Post by: Paul G. OBrien on November 01, 2014, 11:20:41 am
What is Vent Mach?
That is port air velocity. Did the software accept all the TS parameters without complaint? If not go back into the database editor for it and erase some of them and let the software fill in those fields.
Title: Re: Looking for plans for dual 18 cab for JBL 2241H drivers
Post by: Richard Turner on November 05, 2014, 07:39:54 am
I've downloaded WinISD and plugged in the driver. Everything looks OK except the port parameters. When I asked for a rectangular port of 4"x 24" or 4"x 18" etc...it says Vent length "too Short and Vent Mach: .08 (in Green ?). What is Vent Mach? Help is not available.

vent length too short means the vent is shorter than the thickness of the front baffle (plywood)

I forget if it has settings to use multiple triangular corner ports. those make excellent bracing structures
Title: Re: Looking for plans for dual 18 cab for JBL 2241H drivers
Post by: Mike Holtzinger on November 05, 2014, 11:35:39 am
WinISD says Vent diameter 4.02x4.02in. Vent length .24in. :o Vent mach .13. I like the idea of triangular ports, but Win ISD apparently doesn't have a triangular port option AFAIK.
Title: Re: Looking for plans for dual 18 cab for JBL 2241H drivers
Post by: David Morison on November 06, 2014, 08:27:48 am
WinISD says Vent diameter 4.02x4.02in. Vent length .24in. :o Vent mach .13. I like the idea of triangular ports, but Win ISD apparently doesn't have a triangular port option AFAIK.

Can you confirm what Vb & Fb you're modelling, and the number of drivers and ports please?
I'll try replicating that when I'm back at home and see what might be up.

One simple option may be to increase the number of ports until you get the port length up to at least the thickness of the baffle - this will have the secondary benefit of reducing port airspeed (Mach) further.

As a first approximation, you can change the shape of a vent as long as you keep its area and length the same, so if you find a size where 4 vents of XX area work, building them as triangles may work.
There are a couple of catches though, for example when a port is built in along the wall of a cabinet it will behave as if it's longer than it really is to some extent. This is due to 2 (or more, depending on shape) of the port walls being longer than the nominal length of the port. Some trial and error may be required to finalise that, by starting with a longer vent and cutting it down until it's right.

HTH,
David.
Title: Re: Looking for plans for dual 18 cab for JBL 2241H drivers
Post by: Mike Holtzinger on November 06, 2014, 11:48:12 am
 Thanks David,
 According to Win ISD, Vb is 21.4 cu Ft and Fb is 35.31.
Title: Re: Looking for plans for dual 18 cab for JBL 2241H drivers
Post by: David Morison on November 06, 2014, 03:10:47 pm
Thanks David,
 According to Win ISD, Vb is 21.4 cu Ft and Fb is 35.31.

Okay, that's laaaaarge.

As a rough rule of thumb, typical 218s would be from about 10ft3 at the compact end of the scale up to 14-16ft3 for a more generously sized unit.

So first question, are you sure you want to handle a box that big?

Now, a consequence of a large box is that it allows the driver to move pretty freely, which means high excursion at even modest power levels, so a box this big will start to exhibit distortion at lower power levels than a smaller box. In this case, you reach the nominal Xmax at an input of about 40V for the pair, which equates to 400W into 4Ω or 500W into the minimum (in-band) impedance of 3.17Ω.  (The 640W mentioned in the pic refers to that voltage being applied at the minimum impedance overall, which is at about 200Hz so wouldn't be as relevant for subwoofer use.)
(http://i.imgur.com/iY06WXo.png)

Reducing Vb &/or increasing Fb will help with that, however at the expense of LF extension.

So, assuming you stay with the big box: Vent sizes.

There are different rules of thumb regarding just how high an airspeed can be tolerated, the highest I've seen quoted for PA use is Mach 0.1 (ie approx 34ms-1), with lower estimates for really keeping clear of a risk of hearing the air movement in the vent down to half that.
If you accept that higher level, then 4 ports each being 4" x 4" will get you just under 34ms-1 even without an HPF. Each one would need an effective length (after allowing for any "extra" length from building in against the cab walls) of 3.14".
(http://i.imgur.com/MAw3ni9.png)

If you want to hit the lower target you'd need twice the area, so 8 4" square vents, each needing to be 9.58" long now:
(http://i.imgur.com/Fqb9ogG.png)

Alternatively, 4 square vents each 5.5" per side would give similar area and require less length (a large vent is predicted to be more efficient than smaller ones, so you won't eat into the cabinet volume as much this way):
(http://i.imgur.com/igKVD8F.png)

Hope this helps,
David.
Title: Re: Looking for plans for dual 18 cab for JBL 2241H drivers
Post by: Mike Holtzinger on November 06, 2014, 03:54:52 pm
Thanks again David. First off, it is Large, but it's the roughly same size as the JBL 4719. So I know what I'm in for as far as moving them. How about a single large port in the middle like the SR4719x has? Seems it would be easy to build and it would add some rigidity (if that's a word) to the box.
Title: Re: Looking for plans for dual 18 cab for JBL 2241H drivers
Post by: David Morison on November 06, 2014, 04:40:53 pm
Thanks again David. First off, it is Large, but it's the roughly same size as the JBL 4719. So I know what I'm in for as far as moving them. How about a single large port in the middle like the SR4719x has? Seems it would be easy to build and it would add some rigidity (if that's a word) to the box.

Re SR4719X, it's about 21.4ft3 external, so will be more like 15-16ft3 internal after accounting for the cabinet walls, baffle being set back to give grille clearance, the drivers themselves, the ports, handles and any bracing. You're looking at about 50% bigger on the inside, which would be about 14% extra on each linear dimension.

Re single mid mounted vent, yes that can be an effective option. WinISD predicts that if you go for a single rectangular port with the same area as the 4x5.5" square ports (eg 22"x5.5") then the required length drops to 3.1".

Cheers,
David.
Title: Re: Looking for plans for dual 18 cab for JBL 2241H drivers
Post by: Mike Holtzinger on November 06, 2014, 04:59:05 pm
So if I recess my baffle(s) I can get the volume down to 16.9 cu ft. Will this affect the mid vent dims?
Title: Re: Looking for plans for dual 18 cab for JBL 2241H drivers
Post by: David Morison on November 06, 2014, 05:25:19 pm
So if I recess my baffle(s) I can get the volume down to 16.9 cu ft. Will this affect the mid vent dims?

Yup, you'd need to recalculate those for any change in Vb or Fb.
If you get that net internal volume and want to keep the same Fb, then my previous example vent of 22" x 5.5" would need to be 6.35" long. That would take up 0.5ft3 in the box, don't know if you've already factored that in in your 16.9ft3.

Cheers,
D.
Title: Re: Looking for plans for dual 18 cab for JBL 2241H drivers
Post by: Mike Holtzinger on November 07, 2014, 12:14:06 pm
Thank you David for making me use my brain. I believe Win ISD is working for me now. Maybe you could do me a favor and confirm my results.
 With 2 2241 drivers in a 17.255 ft3 box, for a tuning freq. of 30 hz, a single vent 5x18" should be 6.89" deep and will give me a vent mach of .11.
 
Title: Re: Looking for plans for dual 18 cab for JBL 2241H drivers
Post by: Richard Turner on November 07, 2014, 06:25:23 pm
https://www.jblpro.com/pub/manuals/enclgde.pdf

vent quantity and length are given on these plans, if you cannot calculate the panel cut list you are in over your head, dont forget to add the lip ahead of the baffle to protect the driver/attach grille to.

These plans work well, I made single and dual 15" cabinets off these plans many years ago and they were quite serviceable.
Title: Re: Looking for plans for dual 18 cab for JBL 2241H drivers
Post by: David Morison on November 08, 2014, 09:02:49 am
Thank you David for making me use my brain. I believe Win ISD is working for me now. Maybe you could do me a favor and confirm my results.
 With 2 2241 drivers in a 17.255 ft3 box, for a tuning freq. of 30 hz, a single vent 5x18" should be 6.89" deep and will give me a vent mach of .11.

My version of WinISD (version 0.7.0.9) gives a fractionally longer vent for that config, (7.72"). I'm not sure where that difference is coming from - I don't recall port calculations changing between any of the older versions of the program I've used in the past. Have you perhaps selected "2 flanged ends" rather than the default "1"?

If anything, I'd go with the shorter of the 2 anyway, as I think 30Hz is a little low for these drivers. In common with large box sizes, low tunings allow the speaker to run out of excursion more easily, so a slightly higher tuning will help mitigate that.

Vent airspeed is dependent on power applied, I'm getting a max of 37.8ms-1 (that's your Mach 0.11) at full program power, but you'd be so far over Xmax at that power level that I don't think any air noise would matter - distortion would already be through the roof anyway.

At the 40V input I mentioned earlier, excursion is only a little over Xmax (8mm vs 7.6) and vent airspeed is 19.5ms-1 or Mach 0.56, which should be perfectly fine.

Cheers,
D.
Title: Re: Looking for plans for dual 18 cab for JBL 2241H drivers
Post by: Mike Holtzinger on November 08, 2014, 01:36:17 pm
My only option for ports are square or round so I changed the tuning to 35hz and my 5.5"x18" vent length is now 3.77. No flare is available. BTW, my WinIsd free version is 0.44.
Title: Re: Looking for plans for dual 18 cab for JBL 2241H drivers
Post by: David Morison on November 09, 2014, 09:51:36 am
My only option for ports are square or round so I changed the tuning to 35hz and my 5.5"x18" vent length is now 3.77. No flare is available. BTW, my WinIsd free version is 0.44.

OK, maybe the older versions of WinISD do calculate vent length differently then.
I've checked using formulae published here (http://www.ajdesigner.com/phpsubwoofervented/port_length_equation.php#ajscroll) and here (http://www.diysubwoofers.org/misc/portcal.htm) and those both agree with WinISD 0.7.0.9.

For your latest iteration this gives a target length of 4.35", so not too big a difference.

I'd definitely agree with keeping the tuning frequency up at 35+Hz, that helps avoid the worst losses of headroom from running out of excursion.

D.
Title: Re: Looking for plans for dual 18 cab for JBL 2241H drivers
Post by: Mike Holtzinger on November 10, 2014, 01:22:38 pm
As I'm laying this out, I have the grill supports that protrude 1.75" from the baffle. 2 of them are essentially extensions of the port but on the 18" sides only. How should I account for this?
Title: Re: Looking for plans for dual 18 cab for JBL 2241H drivers
Post by: Spenser Hamilton on November 10, 2014, 01:29:54 pm
As I'm laying this out, I have the grill supports that protrude 1.75" from the baffle. 2 of them are essentially extensions of the port but on the 18" sides only. How should I account for this?

If I am picturing it correctly, the extensions will effect port tuning, it will likely take a physical build to determine how much,
Title: Re: Looking for plans for dual 18 cab for JBL 2241H drivers
Post by: David Morison on November 10, 2014, 02:51:27 pm
As I'm laying this out, I have the grill supports that protrude 1.75" from the baffle. 2 of them are essentially extensions of the port but on the 18" sides only. How should I account for this?

I'd agree with Spenser, it'll probably take building and measuring to be sure.
My hunch is that it'll fall somewhere in between the tuning you would achieve without those extensions and that which would come from having all 4 sides of the vent extended.
I'd be very tempted to just extend the short sides as well to make everything match as long as that's physically possible. That also means the vent takes up a bit less room in the cabinet, essentially by pulling the whole thing forward by that amount.

David.
Title: Re: Looking for plans for dual 18 cab for JBL 2241H drivers
Post by: Mike Holtzinger on November 11, 2014, 10:23:42 am
So I'm going to extend the port outside of the cab to the baffle and I've figured approximately .65sf for the internal bracing which will bring my port length to 4.5". I think I'm ready to start cutting!
 Thanks for all the help!
Title: Re: Looking for plans for dual 18 cab for JBL 2241H drivers
Post by: David Morison on November 11, 2014, 03:17:02 pm
So I'm going to extend the port outside of the cab to the baffle and I've figured approximately .65sf for the internal bracing which will bring my port length to 4.5". I think I'm ready to start cutting!
 Thanks for all the help!

Nice one, good luck!
D.
Title: Re: Looking for plans for dual 18 cab for JBL 2241H drivers
Post by: Mike Holtzinger on November 29, 2014, 01:23:37 pm
 What material and how much should I use for dampening on the inside? I know the stuff JBL uses is like a flexible 1" thick yellow fiberglass that isn't available at Home Depot.
Title: Re: Looking for plans for dual 18 cab for JBL 2241H drivers
Post by: Jim McKeveny on December 10, 2014, 08:40:24 am
Most manufacturers have moved away from fiberglass based products to polyester. It is easier on the the assemblers - and us - over the long run. Convoluted foam is also a choice.

"Typical" padding in a VLF box reduces internal reflections up the frequency range that may present themselves at the vent or even through the cone. Kind of a "hamburger helper".

"Overstuffing" can change response.


All of that said...Owens Corning 703 semi-rigid is a top quality product for this app.