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B&C sub 15 for midbass - tuning for jbl 2226

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Guillaume Mays View Drop Down
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    Posted: 04 November 2018 at 11:43pm
Hi all, I'm looking to build ported boxes for JBL 2226H drivers. 
I've narrowed down my search to B&C Sub 15. I want the flexibility of single 15" for modularity and transport ease. This is for a 4-way reflex system processed with BSS Blu-100 and built around 12x 2226H, 8x 2242H in JBL SP128s (eventually to be rebuilt). The top end currently is from 4x JBL 2380 horns & 2447J drivers (800hz-8kHz) + Beyma CP-21F (8kHz-20kHz). I'm currently building DIY synergy horns from BMS 4550 + Pyle PMDR5 using Bill Walso's SynergyCalc so the 2226's will eventually only play up to about 500hz. 

I'm looking at the possibility of tuning the B&C sub 15 by either internal volume reduction or port length tuning, since the subs are usually ran from 25Hz to 80Hz with good results when crossing to JBL SP215-9 (2226H+2447J). From experience, I am enclined to think the 2226 should play flat from 80hz-800hz which I'm unsure if the current design for the B&C sub 15 would allow. What do you think? Would it seem optimal to shift the design's tuning from 40Hz up to about 60Hz? Would this help in any way or should I give the current port design a shot and simply aim to adjust volume with lining? I've tried playing around in WinSD but im unable to share simulations at the moment. In the meantime, and if it can avoid me any unnecessary tinkering around modifications that could hurt the design more than help it, any guidance would be greatly appreciated.

Current:
4x JBL SP128s double 2242H 18": 30-90hz
4x JBL SP215-9 (2226 LF only): 90hz-800hz
4x JBL 2447J mid/hi horn: 800hz-8khz 
4x Beyma CP-21F: 8khz-up

Upgraded:
4x double 2242H 18": 30-90hz
12x single 2226 15": 90hz-500hz
4x 500hz Synergy horns: 500hz-20khz 

Thanks!


Edited by Guillaume Mays - 05 November 2018 at 10:55pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote ceharden Quote  Post ReplyReply Direct Link To This Post Posted: 04 November 2018 at 11:55pm
If you only need to run down to 80Hz then you could easily use a smaller enclosure.  Once you start adjusting the design, you're not building Sub15's any more so you do need to do the simulations.  Personally for your application I'd probably go for compact twin 15 but if you want to stick to singles that's fine, you might just end up with quite small boxes that aren't very stable when stacked.

The other consideration is that you do get some benefit when you start running into the midrange of non-square boxes.  You might want to consider a trapezoid box.

Or... just build the SUB15's as-is and have the benefit of being able to run your system without the 18" low end if you want to.

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Post Options Post Options   Thanks (0) Thanks(0)   Quote Guillaume Mays Quote  Post ReplyReply Direct Link To This Post Posted: 05 November 2018 at 12:11am
My goal was originally to build a more compact 2x15" but this also needs to be designed from scratch as most 2x15" designs are subs. I could also shave off the HF section of pretty much all 2x15" full range JBL boxes that are factory loaded with 2226's. 

I actually decided to go for single 15" when I stumbled upon the B&C SUB 15. It's size and width/depth led me to think it would be stable enough and more portable. But you raise a valid point that the box just doesn't have to be this big. 

Bottom line is there isn't much in terms of available designs for those drivers in this application. even though it's one of the most popular drivers, and designed for that specific frequency range in PA application. Yet it's not as modern or capable as some of the newer high power 15" drivers. Problem is when it comes to builds, everyone nowadays is using the 2226 as standalone sub/mid bass in home audio environments (in which it does still shine today). I'm considering selling the JBLs off at some point so there's also that to consider when building boxes that could work for both temporary and long term needs.

That said I like the idea of a trapezoidal box, splaying could would help with lobing. Yet type of design seems to be more common in the realm of PA manufacturers. Any design ideas welcome.






Edited by Guillaume Mays - 05 November 2018 at 1:39am
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Post Options Post Options   Thanks (0) Thanks(0)   Quote DMorison Quote  Post ReplyReply Direct Link To This Post Posted: 05 November 2018 at 12:03pm
If you're absolutely sure you'll always use them with subs capable of getting up to around 95Hz, you don't even need to port them - 45litres sealed per driver will get you a nice well behaved rolloff at that frequency. It would be a 12dB per octave rolloff, to which you'd add a 12dB Butterworth high-pass in your crossover (at the same frequency), and you'd then have created the equivalent of a 24dB LR aligned crossover, again, at that 95Hz mark.

Not having to worry about porting simplifies design and construction, and the small box size is amenable to angling the sides to create that trapezoidal shape.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Meat Quote  Post ReplyReply Direct Link To This Post Posted: 05 November 2018 at 8:17pm
JBL 2226 in a proper ported box sounds really good. It'll likely work well in the Sub15. It's not the smallest box out there but it should work with that driver and be a nice cab for smaller parties too.

Plans for popular designs that are built to the plans are much easier to sell on than custom things if you change your mind for a different kick section later.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Guillaume Mays Quote  Post ReplyReply Direct Link To This Post Posted: 05 November 2018 at 10:41pm
Thanks for your feedback everyone. 

I'd like to keep things simple and build the SUB 15 as per the plans, I just wanted to make sure that I wouldn't benefit from tuning the box a little higher to actually use the port, otherwise as suggested I'd be better off building a sealed enclosure.

That said I like the idea of being able to use these as low-end for smaller parties where I don't need the 18's. I just wanted to make sure that the boxes's 40hz tuning wouldn't hurt performance of the box between 60hz-120hz. Above that, I understand the port or box tuning should have no impact on the drivers performance, hence the use of the 2226 to get a little more upper extension.

The Sub 15 is a little bit deeper than my 2x18 sub so I might be looking at reducing depth from 736mm to 572mm. This would bring internal volume down from 183L to 145L. Then I need to figure out how this modification affects the port area and length. I believe this would get me pretty close to 60hz with the port as-is?

I'm still struggling with installing WinSD or BassBox Pro on my Mac via Parallel, but I'll try bootcamp and hopefully will be able share simulations of these modifications shortly to confirm with you guys that this does make sense.

Thanks to everyone for your feedback!



Edited by Guillaume Mays - 05 November 2018 at 10:52pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote bob4 Quote  Post ReplyReply Direct Link To This Post Posted: 06 November 2018 at 10:17am
You can also use "wine" to run winisd on a mac. Works for me. Don't ask me how i installed it......
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Post Options Post Options   Thanks (0) Thanks(0)   Quote DMorison Quote  Post ReplyReply Direct Link To This Post Posted: 06 November 2018 at 12:16pm
Hi Guillaume,
First, I think you’ve mixed up the dimensions of the Sub 18 with the Sub 15 – the 18 is the one that’s 736mm deep and 183l nominal, the 15 is already smaller.

For your driver, there would be a small benefit to tuning a little higher, which relates to Xmax when used as a stand-alone bass unit.
The lower you tune a box, the more excursion you get for a given power input at frequencies in the half-octave or so above tuning frequency.
So with a 40Hz tuning, you’d run out of clean, undistorted headroom a little earlier (in the 60-80Hz range, right where a lot of kick drum is at) than if you tune a little higher.

Herewith SPL and excursion for the 2226 in 114l tuned to 40Hz in orange and 100l tuned to 47Hz in green, each driven to Xmax. You can see that the higher tuned box gets a couple of dB extra above approx. 50Hz. That’s not a huge increase, but nice to know you’ve got it anyway.


The higher tuning would require a shorter vent of approx. 170mm total length if the other vent dimensions were kept the same. This would take up less space in the box, combined with the lower Vb to start with meaning you could reduce the internal depth of the box to 533mm.
This allows for the vent, the driver, a couple of litres for handles and a couple of litres for any extra bracing you put in.

HTH,
David.



Edited by DMorison - 06 November 2018 at 12:20pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote nickyburnell Quote  Post ReplyReply Direct Link To This Post Posted: 06 November 2018 at 12:20pm
The Fane sub 15 plan turned 90 degrees so it's taller than wide with two  not four ports 100mm diameter 125mm long with  baffle 35mm back is perfect for 2226. I have 8Smile It's also damn close to jbl recommended  Box

https://www.jblpro.com/pub/manuals/enclgde.pdf

Edited now not on phone



Edited by nickyburnell - 06 November 2018 at 3:48pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Guillaume Mays Quote  Post ReplyReply Direct Link To This Post Posted: 06 November 2018 at 9:48pm
Hey Dave, thanks for those sims.

I did have the plans for the SUB 15 so I don't know how I made that dimensions mistake. Clap

My subs are 572mm deep. SUB15's depth is 626mm. I guess that's close enough and not worth redesigning external box dimensions to shave off only 40mm total. I could just make a plate with a bracket that extends to the floor to sit the Sub15's on. This would ensure the stack is stable. 570mm depth for a 7' stack sounds like trouble waiting to happen.

The 47Hz tuning does look very promising. Just to confirm, you would not recommend going any higher for cabinet tuning? From the sim it seems optimal at 47Hz but wondering if it would get me that extra +1dB at 60Hz.





Edited by Guillaume Mays - 06 November 2018 at 10:02pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote DMorison Quote  Post ReplyReply Direct Link To This Post Posted: 07 November 2018 at 12:17pm
Well, you could nudge the tuning up a little more, but it’s getting into a diminishing returns situation: 1dB extra is even less of a gain than the 2dB already achieved. (Remember that this excursion limitation only applies when using it as your only bass bin – when used with a crossover, you’ll still be able to use full program power with any of these tunings.)

There’s also another consideration going back to Xmax: the higher you tune it, the smaller the vent, so the larger the residual net internal box volume. Larger box volume equals more excursion for a given power input, meaning you may have to reduce the input power a bit to compensate.

Also, the higher you tune it the less versatile it becomes if you ever want to use it without subs as a general purpose small-gig bass bin.

If you do want to use a higher tuning, I’d make sure you keep the net internal volume to around 100l rather than letting it go any higher. If you were to just shorten the vent to a 50Hz tuning keeping the external box dimensions as per the original, you’d end up with around 118l net – a little too big IMO.


There’s a couple of ways you can get rid of that extra volume – shorten the box as already mentioned, though if that doesn’t suit for stacking practicalities then you could stick an internal panel in to block off part of the space. Doing that at an angle can help add bracing to some panels, and have some of the same benefits as converting to a trapezoidal cab in terms of reducing internal reflections.

One other thing I’d say about overall box dimensions is remember to include a little extra length on the front to create clearance for the grille – B&C for some reason omit this but to be a practical cab you definitely want that.

To be honest, if your subs are already shallower than the Sub15, I’d recalculate the sizes to match.

This plan should give you 100l net tuned to 50Hz, and if laid on its side is exactly the same width and depth as your subs for neat stacking. You should however build a test cab and check the tuning before committing to building multiples – that’s because when we calculate the vent length, there’s often a bit of trial and error in the tuning. This is because when the vent is built as a shelf, three out of the 4 sides continue on longer than the actual shelf – so it behaves as if it’s longer than the actual shelf. There is a calculation to adjust for this, which I’ve followed, but I haven’t yet built a cab myself to test how closely it matches reality.

(Click for fullsize if it doesn't display right in the forum)

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