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Discussion Starter · #1 ·
I have a JBL W12GTi http://www.jbl.com/estore/jbl/us/products/W12GTi-MkII/W12GTI MKII_JBL_US

and a http://www.crownaudio.com/xls-drivecore.html

I bought the W12GTi for a future CA build, but it's a lovely sub and want to use it instead of having it just sit around.

I have 2 issues I know of:

1) The W12GTi is dual 6 ohm. The amp does not say it is stable at 3 ohm, or 12 ohm for that matter. Any opinions/advice? My plan was to level match the channels and run it stereo, from the subwoofer output on the E300 (using a Y-cable).

2) I would like to put the W12Gti in the wall, IB. The only place I have available is behind the couch. The room is about 14 x 12, wall for IB is about 5 feet behind the couch. The wall opens into empty space under the stairs and should be more than plenty for true IB. Any opinions/advice?

I am new to HT, so I'm really just looking for some direction and advice. I have Denon E300, Polk TSX330 towers and TSX150 center.
 

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I modeled the JBL, Adire Shiva, and Stereo Integrity 15", & 18". It models pretty close to an Adire Shiva (12", seen these used IB before) in IB (I just picked a huge box size) with WinISD:


1) Personally I'd wire it to be 3ohm mono and just make sure the amp is well ventilated and don't crank it for long periods of time especially on hot days. You don't want to give a DVC sub a stereo signal. 12ohm will work fine but you won't be using that amp to it's full potential but you won't have to worry about burning it up.

2) The only way to know is to try it. Usually I wouldn't recommend using a car sub in a house but this seems to model ok in WinISD though that high FS (31hz) isn't really ideal for HT applications. Look at the graphs, the JBL has a sharper roll off. Car subs are designed to take advantage of cabin/room gain in the smaller space to reinforce the low end.

For what that JBL costs new you could sell it and get something a little more suited for HT, you could probably get enough for two of the SI subs if you have the room. Plus the wiring options would be better.
 

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Discussion Starter · #3 · (Edited)
Thanks!

I like the look of that SI 18. Might just use one of those instead. It comes out to $211 shipped.

Right now I have the SUB-1200, and it's just not as loud at low frequencies as I would like.

I am afraid to wire the JBL to the amp at 3 ohm. I worry that it will heat up too fast to even use it or damage it. That's why I intended to use the mono out from the E300 to the XLS1000 and it would be 6 ohm to each channel. I know it's not ideal but if the channels are set with a DMM then they should be very close.
 

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I have 2 issues I know of:

1) The W12GTi is dual 6 ohm. The amp does not say it is stable at 3 ohm, or 12 ohm for that matter. Any opinions/advice? My plan was to level match the channels and run it stereo, from the subwoofer output on the E300 (using a Y-cable).
According to the manufacturer's info at the link you posted, the amp is stable at 2 ohms, so I’m not sure what the issue is?

2) I would like to put the W12Gti in the wall, IB. The only place I have available is behind the couch. The room is about 14 x 12, wall for IB is about 5 feet behind the couch. The wall opens into empty space under the stairs and should be more than plenty for true IB. Any opinions/advice?
Probably won’t work. With an IB there is no enclosure to keep the drivers from over-extending their X-max, so to compensate typically multiple drivers are used. I wouldn’t consider it with only one. You might want to check to see if the Theile-Small parameters are even suitable for IB, but there are many IB-suitable drivers available that are way cheaper than this one.

Regards,
Wayne
 

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Discussion Starter · #5 · (Edited)
According to the manufacturer's info at the link you posted, the amp is stable at 2 ohms, so I’m not sure what the issue is?
The sub is dual 6 ohm. So the issue is that to use the amp in bridged mode it would need to handle either 3 ohm or 12 ohm. Since the amp is only rated to 4 ohm bridged, I planned to use it in "stereo" mode at 6 ohm per channel, and I'm aware this would work, but how well was my concern.

Probably won’t work. With an IB there is no enclosure to keep the drivers from over-extending their X-max, so to compensate typically multiple drivers are used. I wouldn’t consider it with only one. You might want to check to see if the Theile-Small parameters are even suitable for IB, but there are many IB-suitable drivers available that are way cheaper than this one.
I tend to think you are right, it will not be an ideal sub for what I want. The sub does well in automotive IB applications so that is why I am considering it. My backup plan was to build a ported enclosure. All the ported enclosures I modeled had a hump near roll off, even more so when I lowered the tuning frequency...is this normal. I have not built any ported HT enclosures.

Thanks Wayne
 

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Okay, I think I get it now. There’s some confusion in your posts because you never stated if you intended to connect both amp channels directly to the two voice coils, or use a single amp channel with the voice coils series. When you mention running the amp in stereo mode my natural assumption is that you’re going to use both channels.

Looks to me like simply connecting an amp channel directly to each VC is going to be your best option, since bridging is off the table in this case. According to the specs, the amp doubles its power as impedance is halved. Using a DVC 2-ohm speaker with the XLS1000 as a reference, connecting each VC to an independent amp channel gets you 550 to each VC. However wiring the two VCs in series for 4-ohms and connecting to a single amp channel gets you only 350 watts total, which is divided between the two VCs. So you get only 175 watts per VC that way.

Stereo 6-ohm is not an issue; available power should be somewhere mid-point between the 8- and 4-ohm ratings. Since the amp is stable at 2 ohms, I’d just run the JBL in stereo and give each 3-ohm VC its own channel. Available power will be between 350-500 watts per channel, i.e. about 425 watts (in the case of the XLS1000).

Ultimately DVC speakers don’t make any sense to me. For the same power, two 4-ohm speakers (for example) will move twice as much air as a single DVC 4-ohm speaker. :huh:

Regards,
Wayne
 

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Ultimately DVC speakers don’t make any sense to me. For the same power, two 4-ohm speakers (for example) will move twice as much air as a single DVC 4-ohm speaker. :huh:
DVC speakers just open up different wiring options to achieve whatever ohm load is optimal for the particular amp you're using. People don't usually have an amp per coil with DVC speakers. Usually a DVC 4 ohm speaker would be wired for 2 ohm or 8 ohm or a DVC 2 ohm would be wired to 1 ohm or 4 ohm. Add in multiple subs and you can change it up to your needs. This sort of thing is much more common in car audio with 1 ohm stable amps and such. This sub was probably meant to run in multiples of 3. 3 DVC 6 ohm parallel would be 2 ohm for the class D amps or 3 DVC 6 ohm ran series (12 ohm) for each sub then parallel would be 4ohm for the class A/B amps.

Like I said personally I think he'd be fine wiring it at 3ohm mono as long as he has adequate ventilation and not abusing it for long periods of time. IB is pretty efficient (though less so since he'd only be using one sub, with IB in house you usually see at least 4 subs) so I think with proper care 3ohm could be ok, though not necessarily recommended. I'd gather the protection circuits would at kick in first, you could wire it 3ohm mono for a bit and see if it triggers and if it does use a channel for each coil then.

FWIW I ran an old school Rockford Fosgate 200.2 at 2ohm mono (only rated for 4ohm mono) off a PC PSU for nearly a year before buying a pro amp and the RF amp would only get a little warm.
 

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Discussion Starter · #8 · (Edited)
I am going to try it ported. What volume/tuning should I go with? I have a 4" aero port that I would like to use.

EDIT: I got some Birch plywood and plan to do 4 cu. ft. as WinISD suggests tuned to 23Hz. With about 600W it should be an improvement over the SUB1200. What I don't know is which direction to face the sub and the port.
 

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I'd place the driver and port on the same side of the box. Check out this website:
http://www.trueaudio.com/st_ventq.htm

After you build it then experiment with if you want front, rear, up, or down firing. That's more personal preference or if you have a way to measure then see which way measures best.
 

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Discussion Starter · #11 ·
A friend was selling a BNIB SI HT-18 DVC 2-ohm, so I bought that. Will be putting it in 4.3-4.5 cubes, wiring it in series, with a 4 ohm final impedance the amp should put out 1,100W.

Saving the JBL for later and no more having to worry about matching channel outputs over and over till I get the gain right.

Thanks for all the advice guys. It really did help me straighten things out in my thinking. :)
 

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Ah you're thedude over at EMSQ! I saw that F/S thread, I was so tempted to grab both of those but I'm not ready for them just yet. Enjoy your new sub, I bet that thing is going to POUND hardcore. :hsd: :T
 

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Discussion Starter · #13 ·
Haha, yeah, that's me, I recognize your name now.

It's crazy that those HT18's came up for sale right now, and for that price, I'm thrilled. Was getting real bored with the SUB1200, I think this new build will cure that. :)
 
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