new mach 5 IMJ-18.4 or TC1k 15?????

Either one will work fine. The IMJ will want a larger enclosure, but it will also move more air than the TC-1K.

Either one should work great with 500W.

I think 500+ liters?

I am not sure about the Le of the IMJ, but assuming it isn't too high, both subs should be ok up to a 100Hz xover, but I don't think I'd go beyond that.

Ported the new IXL will need about 13.5 cubic feet tuned to around 17 hz. 500 watts in that configuration would work very well.

What do you consider a high crossover point?

The TC1k has a really good motor. IMO, it surpasses most of TC's longer-throw subwoofers in bass quality, though not bass quantity. While inductance is close on both drivers (3mH on the Mach5, which was a pleasant surprise for me as when I first read about it I thought it would be a TC3k-style train wreck with over 9mH of inductance) 2.64mH on the TC1k) the TC1k's motor has a nice big copper Faraday ring to linearize inductance by excursion and improve bass quality in the crucial top octave of the sub's passband at high SPL. OTOH, the Mach5 driver will have to move less to produce a given output, so the TC's motor advantage isn't perhaps as great.

And, as others have mentioned, the Mach 5 will ultimately move more air if given enough power. But then again, perhaps not as much as one might think. In a 180L sealed box fed 500W, the TC1k model shows about 106dB out output at 20Hz, limited by excursion. In the same box, the Mach 5 will give you about 1.5dB more at 20Hz on paper, limited both by power and excursion. Qtc for both drivers in 180L is on the high side (0.6's) but probably acceptable. Depending on each driver's relative behavior up to and beyond rated xmax, the difference may be even less than that.

FWIW, I'm sort of in the same boat as you. I'm going to replace my current subwoofer for a variety of reasons. (None of them have anything to do with performance; I'm actually going to lose some of that in the bargain.) I have a driver sitting in my closet that's close to a TC1k, the 15" TC2+ Oaudio used to sell. (Hey, if anyone around here also has one of those sitting in your closet that you're not planning to use, send me a PM. Push-pull ones might be fun...) But the new Mach5 18 has piqued my interest, too. The reasons are psychological more than anything else. I just like bigger woofers that need to move less to reach a given SPL.

They made a mistake at htguide.com. The new sub is the IXL-18.4
with 22mm xmax. Not to be confused with the MJ-18
with 12mm xmax.

The 15" TC2+ is capable of moving approx 3.1L of air while the IXL-18.4 can move approx 5.3L of air.

Just put my money down on the IXL-18.4. I think I'm planning on a 550l (~19.4cuft) enclosure tuned to 14Hz. With 350 Watts it puts out 112db at 12Hz without running a risk of overexcursion. I'm excited =D

I think you mean cubic feet

But the size depends on the tunning point really. I don't have a windows machine at the moment, but play around with WinISD and you'll see what happens.

You should be able to get away with one large port, probably 8" will do. As long as the port velocity is below 27m/s (I think...). That can be taken care of with a nice flared port.

You have to use PVC or Sonotube-like material.

You can easily build your own flare. Search and you will find. As for how important it is, it depends on how much port velocity you have. In this case, it's probably pretty important, but then again I haven't run the simulations on my own to see. Anyone?

Right (I tend to calculate Vd as xmax*Sd rather than 2*xmax*Sd, but you're probably right.) At 20Hz, per Unibox that equates to about 1.5dB.

Took the plunge and ordered two. Now I'm going to model this to death.

Does a very nice job moving alot of air!

What does the excursion look like with 550 L tuned to 14Hz with 500Watts?

I assume there's an 3-4mm Xmech. Don't know. Maybe Mark can answer this.

Mark from Mach5 made this very interesting comment regarding adjustments to the new 18 driver.

"The production unit is slightly different from the big pictures posted. It uses a larger motor with a slightly thicker top plate.

The future will bring different soft parts of varying configurations, so folks who purchased the IXL-18 can make changes to it without having to purchase a completely new driver. It will be a real money saver in the long run.

Best regards,
Mark"

What do you think of 700l tuned to 13hz with 250 watts? I was just on my roommates computer modeling some of it and that doesn't look to bad. Your thoughts?

I actually like the dB-500's in that scenario. Assuming you have average room gain, they'd most likely mesh better with your room than the 15" TC-1K.

Yes, of course.

Mark from Mach5 has answered a few of my questions regarding impendence and Xmech.

4ohm SVC
26mm Xmech

Any news lately about the coming driver?

It's shipping across seas as we speak... errr, type.

I got an email Tuesday which proclaimed the new driver has been put on a slow boat from ???. Will take a long time to arrive in the North America's.

Speaking of which, does anyone know where it's coming from?

Uh oh, I hope quality control is top notch. Perhaps Mark can chime in.

Mark said they're on the way. When? Didn't say.