JBL 15" box recommendation - AVS Forum
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post #1 of 16 Old 04-21-2014, 12:15 AM - Thread Starter
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Hey Guys

I'm looking to build a sub for my home theatre and needing a little advice on cabinet plans. I've read a lot of threads and narrowed down some options on amp's and driver's and as I'm in New Zealand freight cost does rule out most options from the likes of parts express, so looking closer to home I can get JBL GT5-15 or GTO1514D both at a really good price and for the amp the Minidsp ice125 plate amp seems to fit the bill.
I've got a pretty big open plan area it will be going in and it's predominately going to be used for movies. I've built sealed sub's for cars so was leaning towards a sealed box but a ported box probably makes the most sense though not sure what the JBL's would suit best when used for home use, I'm not adverse to a largeish sized box but lilwrecker towers etc aren't really an option so any suggestions on the hardware I've listed an any recommendations on the design and ideally any plans out there online that suit would be great.

Thanks
Dean
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post #2 of 16 Old 04-21-2014, 02:01 AM
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I have 4 of the GTO1514 either here or on order and am going to use them sealed. A 2 second sim shows they need about 105L each for a Q=0.707 sealed. You could go smaller and use EQ to get the desired response.
Ported needs a larger box: 200L and a 20Hz tune looks good for a first try.

How big can you go with the box size, how big is your room and what results are you looking for? You need to define where you're going to actually get there. Box volume is easily determined by deciding on the size you can go, LxWxH in cm, then divide by 1000 to get volume in litres. More accurate is to take the cabinet thickness off before multiplying; if using 18mm, then remove 3.6cm from each dimension first. None of it is particularly difficult but usually takes a couple of iterations to home in on a final design.

Mine will be in two dual opposed enclosures, one driver near the floor in each, the other at half wall height in about 180L net.
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post #3 of 16 Old 04-21-2014, 02:30 AM - Thread Starter
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Ideally I'd like to stick with something in the 50-60cm square cube size which will give me that 100-200lt size which is fine, the open plan area is 8x4.2x2.8 and the kitchen hangs of the end which adds something like another 25% ball park. As far as results I was originally looking to get an SVS PB12-NSD but decided I'd be better off building my own 15" for less money. I'm not trying to reach the lowest levels possible just want to get a good solid performing sub, thats part of the reason I thought about a sealed unit to start as I wasn't really sure what I should be aiming for regarding port tuning and room gains etc so thought it would be an easy option to go with.
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post #4 of 16 Old 04-21-2014, 02:51 AM
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Quote:
Originally Posted by dmckiwi View Post

Ideally I'd like to stick with something in the 50-60cm square cube size which will give me that 100-200lt size which is fine, the open plan area is 8x4.2x2.8 and the kitchen hangs of the end which adds something like another 25% ball park. As far as results I was originally looking to get an SVS PB12-NSD but decided I'd be better off building my own 15" for less money. I'm not trying to reach the lowest levels possible just want to get a good solid performing sub, thats part of the reason I thought about a sealed unit to start as I wasn't really sure what I should be aiming for regarding port tuning and room gains etc so thought it would be an easy option to go with.
Sealed with no EQ as mentioned in the previous post gets you an F3 of 38Hz.

My suggestion then would be your 60cm cube, with a pair of drivers dual opposed, sealed, with a MiniDSP and a Behringer EP4000.

They seem like decent drivers but they don't have a lot of Xmax and they're cheap, so I'd go with 2 to double the volume displacement and give you some more SPL potential, and lower distortion.
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post #5 of 16 Old 04-21-2014, 03:28 AM - Thread Starter
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Looking at the spec'd again I see they listed the GTO incorrectly as it's a dual 4ohm drive so that's probably out unless I do two which is pushing the budget, an EP4000 and 2x GTO's is over a $1000 here plus I'd still need to build the box and get a MiniDSP, its pretty much double what I could do a single 15" with ice125 with built in DSP so probably rules it out for the moment.
Normally I'd go with the first option but I've just moved into my new house and I'm spending a fortune on boring things like curtains and landscaping supplies so the sub budget is a little tight at the moment. I might look at selling the W1070 projector I got and spend the money on a sub, I can't really afford a sub and a screen with everything else going on at the moment so might have to prioritise and I can live without the projector for a while as I picked up a new ST60 plasma on run out.
I'll see what the GT5 looks like in a sealed box or maybe see if I can get a Type S Alpine 15" for a decent price as they seem to get solid reviews. Thanks for the input.
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post #6 of 16 Old 04-21-2014, 08:24 PM
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That sucks. I bought 4 NIB for $A500.

You could easily run a single driver off an EP4000. Put the coils in series and run it on one channel, or one coil per channel with the amp set in parallel mode. They're only rated at 350W so it would provide more than enough either way and the amp has the capacity to run 4 drivers if desired.

If funds are tight, you could build the box for 2 drivers and install only only one for the time being and add the other later. It would only require a slight EQ change later. Just a serving suggestion.
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post #7 of 16 Old 04-21-2014, 10:01 PM - Thread Starter
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I can get the GT5's for $120 and the GTO for $170 so they aren't to expensive, the amp's aren't the cheapest though as its $800 for an EP4000 and even an iNuke 1000 is going to cost me around $450. Would be easier if the freight wasn't so much from the US but will just have to work on what I can get.
I'll work on my options and decide what to do soon, a friend has just built a CNC Router so is going do all the panel's for me so that should make it massively easier so all I need to do now is work out what design to run with.
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post #8 of 16 Old 04-21-2014, 10:37 PM
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Not worth importing from the US as the mains voltage is different and not all amps are easily convertible.
What's shipping like from the Big West Island to the Little East Islands?
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post #9 of 16 Old 04-22-2014, 12:22 AM - Thread Starter
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Yeh I've only looked at options that are switching, not sure on pricing from Aus but I got my projector from there and it wasn't overly expensive. Weight might be the killer still but anyone worth looking at other than just checking ebay?
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post #10 of 16 Old 05-10-2014, 10:27 PM - Thread Starter
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Not sure what I'm doing wrong but using a couple of the calculators online I keep getting very strange numbers for both of the JBL's, I've run the numbers on an Alpine SWS-15D2 and getting a mid 90lt sealed box but the JBL's both come out 10x that? I'm presuming the GT5 will work pretty happily in a 90-100lt box and leaning towards doing a 50x50x50 sealed cube. I can get the Alpine from eBay for a reasonable price but the not as cheap as the JBL but both fit the budget. Leaning towards the sealed box and a plate amp for this one and see how things go, I'm sure I'll probably want to build more later so getting an iNuke 1000 now would probably need upgrading later on so a plate amp is the cheaper options for now.
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post #11 of 16 Old 05-10-2014, 10:33 PM
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It helps to post your results so we can work out what you're doing wrong.
My previous posts outline my simulation results.
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post #12 of 16 Old 05-10-2014, 10:44 PM - Thread Starter
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Using the calculator on this site,

http://www.diyaudioandvideo.com/Calculator/Box/

These are the results I'm getting, I did have a play with WinISD but was getting a ton of errors so couldn't get a decent result from it, not sure if its my version of 64bit Win7 I'm running on my Mac or not but ended up just using a couple of online calculators to get recommended size.

JBL 15" GT5

Vas = 106.5 lts
fs = 27.3 Hz
Qts = 0.67
Qtc = 0.707
Dimensions
Vb = 33.14 ft3 = 938.35 lts
= L x W x H
f3 = 28.81 Hz
fb = 28.81 Hz
Alpine SWS-15D2


Vas = 107 lts
fs = 27 Hz
Qts = 0.48
Qtc = 0.707
Dimensions
Vb = 3.23 ft3 = 91.49 lts
= L x W x H
f3 = 39.77 Hz
fb = 39.77 Hz

As you can see its spitting out a massive litre-age for the box for the JBL.
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post #13 of 16 Old 05-10-2014, 11:01 PM
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That's a really crap calculator. Try Unibox, Hornresp or WinISD.

I plugged it into Unibox and for a QT=0.707, I got 1147L. The reason is that the driver has a high Vas and a weak motor, so to ensure that the air spring in the enclosure doesn't push it's free air Qt of 0.671 up even higher, it needs a large enclosure or to be used infinite baffle. Not a good driver for home use in a moderate size box. The GTO1514 is a much more suitable driver, as are the Alpines.
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post #14 of 16 Old 05-10-2014, 11:06 PM - Thread Starter
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Yeh I did have a go with WinISD and as I said it wasn't playing nice, I had a quick look at Unibox but need more time to play with it. I can only get the dual 4ohm GTO so unless I go dual opposed to get a 4ohm load then it is looking like the Alpine is the best option for a single 15" sealed box out of what I can get. Thanks for checking the numbers.
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post #15 of 16 Old 05-11-2014, 12:28 AM
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Quote:
Originally Posted by dmckiwi View Post

I can only get the dual 4ohm GTO
An the problem with that is?
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post #16 of 16 Old 05-11-2014, 12:53 AM - Thread Starter
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The plate amp's I've looked at do 500w at 4ohms, so ideally I need a single 4ohm model or dual 2ohm if I'm going to do a single sealed box.
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