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Discussion Starter #1
Hi Guys, Just bought a JBL W15GTi MKII 60th Anniversary subwoofer (technically the same T/S as the MKI). Pretty nice piece of car audio gear, and I have read of people very successfully using them in the house. I got offered a really good deal on it and figured I might as well give it a shot.


I want to go sealed, but the box size recommended by JBL is 1.5ft^3 including the driver displacement. I'm thinking that is going to be way too small for the house and was looking for some recommendations. I plan on powering it at 3 ohms with a Buttkicker BKA1000-4A.


I've already modeled the driver out in BB Pro and WinISD. WinISD for some reason is giving me a recommendation of a much larger box (4.4ft^3) for a .704 QTC, while BB Pro is telling me pretty much the same as JBL.


Sub will be used for music and movies, mostly music though.


I figure I'll be making a couple enclosures before I am happy. Any thoughts on how many cubic feet I should start with?


Thanks ahead of time.
 

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Wow thats exactly what I'm thinking of doing. In fact I just sent an e-mail to JBL asking them for enclosure information. I'll post if I get anything back from them. Please keep us posted with how this turns out.
 

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Discussion Starter #3
Just got off of the phone with JBL car audio tech support and JBL Pro tech support, neither could really give any recommendations.


The JBL Pro tech rep did say that the W15GTi is in fact very similar to the 2256G and that they use it exclusively in a ported application. He said that they had never used it in a sealed application for Pro audio that he was aware of so he really couldn't help.


Here are the T/S specs if anyone feels like taking a look and recommending a sealed enclosure size...


Revc(ohms) - 2.95

Levc (mH)- 1.0

Sd (ft2)- 0.839

Sd (m2)- 0.078

BL(Tm) 15.39

Vas(ft3) 4.67

Vas(liters) 132.20

Cms 153.02

Mms(grams) 260.67

Mmd(grams) 248.15

Fs(Hz) 25.20

Qms 7.20

Qes 0.51

Qts 0.48

Hag(in) 1.00

Hag(mm) 25.40

Hvc(in) 2.60

Hvc(mm) 66.04

Xmax(in) 0.80

Xmax(mm) 20.32
 

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~3 ft^3 will give you the .707 box that you want.


The W15GTi is a middle-of-the-road sub ... its .45-.50 qts lend it well to both ported or sealed applications, however it is not "optimized" for either according to most simulations.


Are you planning on using any form of EQ shaping?
 

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Discussion Starter #5
Just so I know for future reference, how did you reach that enclosure size for a QTC of .707?


Also, what would you recommend for EQ shaping and will it really be necessary if I highpass the W15GTi at 80Hz?


Thanks for the help!
 

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UniBox simulation software.


You can "guess" at it by looking at the Vas (130L) and the Qts (0.48). Off the bat, you can look at it and see that the 1ft^3 box that you looked at is gonna raise the Q by a lot (as 1ft^3 = ~28L and 28L is a heck of a lot smaller than the Vas of 130L). Some of the guys here like the Infinite baffle as it leaves the Qts relatively the same (but you need a box ~4-5x Vas ... ~20ft^3).


The one thing you can do is build a bigger box (as big as possible) since you get your most low end sealed efficiency that way. From there, you can either EQ of subtract volume (place wood blocks in the box) to get the sound you like.


A good EQ for a design like that would really depend on what your room does for you. Order a radio shack SPL meter for $25 and measure everything once you are done. From there, we can work on a "house" curve for you
 

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Discussion Starter #7
Thanks for the help Jim. I downloaded Unibox and I'm thinking I'll start with a 4.0 ft^3 box.


If you weren't all the way out in Cali I'd buy you a beer.
 

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You meant lowpass..???... right

WGTi rocks, never got around to building a box, was just breaking in the suspension before measuring params





Quote:
Originally Posted by Luke G /forum/post/0


Just so I know for future reference, how did you reach that enclosure size for a QTC of .707?


Also, what would you recommend for EQ shaping and will it really be necessary if I highpass the W15GTi at 80Hz?


Thanks for the help!
 

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Discussion Starter #9

Quote:
Originally Posted by NEO Dan /forum/post/0


You meant lowpass..???... right

WGTi rocks, never got around to building a box, was just breaking in the suspension before measuring params



Good catch, meant to say lowpass.


So how did the parameters look and what were your plans for an enclosure?
 

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I've found the W15GTi to be higher performing in high-Q enclosures than any other driver I've ever played with. I can't tell you why, but my suspicion is that it has something to do with the braking force offered by the dual-gap/dual-coil motor JBL's licensing from Hyperdynamics.


With EQ, even in 2.5 cubic feet (which yielded a Qtc of about 0.75 on the one I measured, or much higher than I would ever think to use; the driver was well within reasonable tolerances of factory spec.) sounded incredibly good. To be honest, in the test box I couldn't reliably tell a difference between 7, 5, 3.5, and 2.5 cubic foot internal volumes (set by adding bricks to the 5.5 cubic foot test box) in single-blind conditions, whereas with most woofers I can hear a difference even with EQ. (Going smaller than 2.5 cubes, the sound quality did degrade, albeit not as markedly as the reference driver used, an Oaudio TC2+. That is to say, I could not reliably guess the box volume post-EQ with the W15GTi, but with its own EQ curves I never missed one when guessing effective box size with the TC2+.) Based on those listening tests, and my friend's desire for the smallest possible sub, the final box was 2.5 cubic feet. Yes, he lost some paper low-end efficiency and max output by going that route, but realistically it will never be an issue.


If you really want to get every last drop of bass out of a W15GTi, though, you're looking at eight cubes. That will give you a Qtc reasonably close to 0.577. (0.5 you won't see except in an I-B.)
 

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Discussion Starter #11
Excellent info! Thanks for posting that up.



Just out of curiousity, how much power is your friend putting through it and how much do you think it can handle on a daily basis in a small sealed (
 

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The amp he's using is the Dayton Class G rack amp rated at 1000W/4ohms from Parts Express. I don't know that I'd use much more power than that, nor do I think more power is especially useful.
 

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Was gonna build another one of theese...


Now I have an 87 year old permanent house guest, so big bass is not a priority




--- JBL W15GTi

--- Parameters marked with ** are not tested using the WT2

--------------------------------------------------------

--- mechanical ---

Fs 25.664E+00 Hz Free air resonance

Qms 6.020E+00 Q mechanical

Vas 130.944E-03 m^3 Suspension compliance

Cms 142.930E-06 m/N 1/(suspension stiffness)

Mms 269.080E-03 kg Moving mass

Rms 7.207E+00 kg/s Mechanical resistance

Xmax ** 0.000E+00 m Maximum acoustic linear motion

Xmech** 0.000E+00 m Mechanical displacement

Dia 320.675E-03 m Piston diameter

Sd 80.764E-03 m^2 Piston area

Vd ** 0.000E+00 m^3 Displacement volume

--- electrical ---

Qes 600.699E-03 Q electrical

Re 2.847E+00 ohms Voice coil DC resistance

Le 915.409E-06 Henries Inductance @1 kHz

Z 8.314E+00 ohms Impedance @1 kHz

BL 14.341E+00 Tm Motor force - Newtons/Amp

Pe ** 0.000E+00 W Max Electrical Power

--- electro-mechanical ---

Qts 546.198E-03 Q total

no 355.186E-03 % 1/2-space ref efficiency @ 1m/1W

1-W SPL 87.505E+00 dB sensitivity at 1m on-axis

2.83V SPL 91.991E+00 dB sensitivity at 1m on-axis

--- motor constants ---

Krm 1.855E-03 ohms constant resistive motor impedance

Erm 850.607E-03 exponent resistive motor impedance

Kxm 16.845E-03 Henries constant reactive motor impedance

Exm 669.410E-03 exponent reactive motor impedance

--- End BassBox Export ---
 
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