W12gti Mkii

[Slare]

I know this is a little bit out of the target here, but I recently picked one of these subs up on a pretty good local deal. I have high hopes for it to use as a very solid 12" compact home sub.

I have a ~550 watt plate amp (which may not be stable enough for this woofer) and also an older NHT studio subwoofer amplifier which should be fine for ~300 watts x2 rms into the 6 ohm coils. So power wise, I think I'm covered.

What I'm baffled by is that JBL recommends a 1.0 cuft sealed box for this thing (which is what it came with). Can this really be right?

Hooking the plate amp up I expected more out of the woofer, but I'm suspicious of the tiny box. Any experience with these out there?

[Hoerninger]

Others have experience, you will see.
____________
Peter

[toddalin]

I have a ~550 watt plate amp (which may not be stable enough for this woofer) and also an older NHT studio subwoofer amplifier which should be fine for ~300 watts x2 rms into the 6 ohm coils. So power wise, I think I'm covered.

Are you planning on using two of these in parallel or series? Each speaker runs at either 12 ohms (two 6-ohm coils in series) or 3 ohms (two 6 ohm coils in parallel). You do not run one channel into each coil as with a standard dual voice coil sub.

At 3 ohms, your amp may not be stable and probably can't be bridged to this load, unless it is intended for automotive duties. At 12 ohms, you won't have enough power to get any real volume out of it. (Maybe it could be OK bridged into 12 ohms if your amp can bridge.)

I run the W15GTi in a ported 4 cu ft cabinet and use a Crown PSA-2XH that puts out ~800 watts RMS bridged into the 12 ohm load.

[Slare]

The plate amp was intended to run at the parallel 3ohm loading but after some time it seems like the clipping auto shutdown gets more and more sensitive. I was worried about the low ohm loading causing this but that doesn't make much sense to me because the impedance of the driver should go up with heat. I guess the driver load is going up, the amp puts out less power, and thus clips/shuts down faster?

I've also read that the mkii may as well be a parallel 4 ohm load.

Maybe a ported enclosure and a high pass filter would fix it.

The NHT rack amp is stereo 4 ohm stable so I can run it in dual 6 ohm mode no issues. I really wanted to use the plate amp to keep total space limited, but I guess hiding the amp would be an option, too. About the coil configuration - I can't use the NHT amp to send two identical mono signals one channel to each coil? I don't ask to be difficult, but why not?

I'm typically just fine with sealed subs but what I really want out of this sub is maximum 20-40Hz SPL from the smallest manageable enclosure. JBL's ported box seems mangeable - anyone have plans or pictures?

It will likely end up paired with L5's if I can keep the box size manageable.

[toddalin]

About the coil configuration - I can't use the NHT amp to send two identical mono signals one channel to each coil? I don't ask to be difficult, but why not?

anyone have plans or pictures?

Though it may work, it is not the way JBL says to do it. I guess both channels would need to be pretty much exactly the same for it to work properly in this configuration, but ???

Enclosure is internally separated. W15GTi gets ~4 cu ft and a 4" dia x 13" port and 2235 gets ~6 cu ft and a 4" dia x 8" port.

[baldrick]

I bought 4 of those for my sub project, put them in closed boxes of 1,5 cu ft and feed them by a Crown MA3600. After a few days I put them up for sale It did not play as good as I was hopeing so I sold them all.

I think W15GTI in a vented box is much better suited for home use than W12GTI in sealed.

[toddalin]

I bought 4 of those for my sub project, put them in closed boxes of 1,5 cu ft and feed them by a Crown MA3600. After a few days I put them up for sale It did not play as good as I was hopeing so I sold them all.

I think W15GTI in a vented box is much better suited for home use than W12GTI in sealed.

These are W10GTi's in ~1.25 cu ft cabinets. A small port would have helped as it makes a big difference.

[4313B]

I bought 4 of those for my sub project, put them in closed boxes of 1,5 cu ft and feed them by a Crown MA3600. After a few days I put them up for sale It did not play as good as I was hopeing so I sold them all.

I think W15GTI in a vented box is much better suited for home use than W12GTI in sealed.

Once again... these are automotive transducers and are expecting an automotive environment.

While you can get them to work in a home they are expecting "room rise" to begin at ~ 50 Hz instead of much lower as in a home environment...

In other words, that graph in the image above is going to have a hole in the response below ~ 50Hz, not quite as "bad" as the dashed line but very probably "bad" enough. Just stick the subwoofer box in a closet and it should be ok (That's about the size of free air it's looking to fire into).

If I remember correctly these drivers, when used like a typical home transducer, end up in weird vented alignments with huge volumes and tons of group delay. Alot of people wouldn't care, or notice, especially if they've never heard anything better.

[toddalin]

Once again... these are automotive transducers and are expecting an automotive environment.

While you can get them to work in a home they are expecting "room rise" to begin at ~ 50 Hz instead of much lower as in a home environment...

In other words, that graph in the image above is going to have a hole in the response below ~ 50Hz, not quite as "bad" as the dashed line but very probably "bad" enough. Just stick the subwoofer box in a closet and it should be ok (That's about the size of free air it's looking to fire into).

If I remember correctly these drivers, when used like a typical home transducer, end up in weird vented alignments with huge volumes and tons of group delay. Alot of people wouldn't care, or notice, especially if they've never heard anything better.

Why not plug the T/S parameters of the W15GTi in a 4 cu ft box with a 4" dia x 13" port into the WinISD for all to see? I bet you would be suprised how smooth the curve is and how low this speaker can go with authority.

[grumpy]

... if someone wants to do this, make sure to compare group delay with
another non-automotive LF driver. May not be an issue for all, but you
don't get sumthin for nuthin.

[Robh3606]

... if someone wants to do this, make sure to compare group delay with
another non-automotive LF driver. May not be an issue for all, but you
don't get sumthin for nuthin.

Just drop in a 2235 to compare. Night and day especially in the same volume.

Rob

[toddalin]

Just drop in a 2235 to compare. Night and day especially in the same volume.

Rob

Was night and day that the W15GTi went lower, smoother than the 2235 when both in the same sized cabinets (4 cu ft) with the same port configuration. I posted that data here a few years ago.

Could not monitor group delay though.

[Slare]

In the tiny 1.0cft box I have the sub in (with acoustistuff) the sub actually "subs" quite well. It is every bit as loud as any commercial home sub I have heard in the ~$300 range and to my ears isn't a one note box at 40-50Hz like the free air response would suggest. I will admit that room is a nightmare though so I'm probably used to less than ideal response at my listening position. I can only qualify by saying it is not a fixed one note box like a Onkyo HTIB sub, there's lots of healthly output at 25-30Hz.

The bigger problem I have is my ~550 plate amp won't drive the 3 ohm load without clipping into protection shut down; it seems 4 ohms is really the hard limit for it. So I think the sub is going to find a new owner. I could use the NHT amp but by doing so I lose my stealth tiny install and the project becomes much less attractive to me at the moment. Bleh.

[Robh3606]

same sized cabinets (4 cu ft) with the same port configuration.

Hello Toddalin

Did you ever redo the ports?? They shouldn't be the same for those drivers. You should have tuned the W15 lower than the 2235 to get the most LF extension out of it. The group delay goes up but it always will when you lower the tuning frequency. If you look at them in the same box and tuned to optimize a 2235 the difference in group delay isn't as much but you are not getting the most out of the W15 if you do that. You also have a peak in the W15 response that tuning lower helps smooth out.

Rob

[toddalin]

Hello Toddalin

Did you ever redo the ports?? They shouldn't be the same for those drivers. You should have tuned the W15 lower than the 2235 to get the most LF extension out of it. The group delay goes up but it always will when you lower the tuning frequency. If you look at them in the same box and tuned to optimize a 2235 the difference in group delay isn't as much but you are not getting the most out of the W15 if you do that. You also have a peak in the W15 response that tuning lower helps smooth out.

Rob

Yes, I redid the cabinet since those data were obtained. The W15GTi now gets 4 cu ft and a 4" dia x 13" long port. The 2235 gets 6 cu ft and a 4" dia x 8" long port.