IXL 18.4 build - Home Theater Forum and Systems - HomeTheaterShack.com

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post #1 of 17 Old 10-09-12, 10:13 PM Thread Starter
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IXL 18.4 build

So I'm going to finally build the rest of my IXL 18.4's into my theater. I originally bought 8 around five years ago with the intent to go IB, but for this particular application in our new home it looks like I'll be better served going ported. My better half has given me a nice chunk in each of the front corners of the room to play with, but I'm otherwise fairly limited in regards to placement and space consumption. So I'm trying to make the best of it.

It's looking like the best option going forward is for (6) ported enclosures, one IXL 18.4 for each, triple stacked in the front corners of the room outside the mains, spaced 4-6" out from the walls, floor, and ceiling.

I've got enough room for 9.5cf each ported to 18hz. Plan is to run a Linkwitz/Riley SSF at 11-13hz, with maybe 650-1000w per driver on tap. Does this sound about right?





What do you think, can I get away with using two of the 4" precision ports per enclosure in this project? Any thoughts on dimpled vs smooth... would it be worth the extra $$$? If the 4" ports will chuff I'll have to do a slot port instead, as I can't conceive an aesthetically balanced design with a single 6" port on each enclosure.

Would I be able to rear port them with the enclosures sitting 4-6" away from the wall, or am I better off front porting them into unrestricted space?

Thanks for your input!
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post #2 of 17 Old 10-09-12, 10:22 PM
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Re: IXL 18.4 build

It looks like you have linear excursion to spare, so if you are at the sub's thermal limit there with 1000W then you are good to go. That looks like a crazy amount of SPL, and 130dB at 20Hz is pretty nuts.

There is no way that two 4" round ports is enough for a sub that big making that much SPL that low. Can you attach your project file so I can look at it and help size your ports?


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post #3 of 17 Old 10-09-12, 11:35 PM Thread Starter
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Re: IXL 18.4 build

Hey thanks for responding. I think 800w is about all these can take in a ported enclosure, after that I think I've heard the tinsel leads start to fry with constant pounding at 1000w.

The models above are for a single 57cf enclosure with all six drivers blasting to the full 130db. In reality, I'd be looking at a single driver per enclosure with around 800w, more accurately represented by the model in green below:



Here's a copy of the file as well:

SingleDriver800w9.5cf18hz.wpr

So if the 4" ports are out it looks like I'd have to do a slot port then... at 22.75" wide what do you think a good minimum height would be? At 2" height I'm looking at having to wrap the port up the backside for a total of 36.5" or so in what is now becoming closer to a 9cf enclosure.

My current plan allows for external dimensions of 24.25"W X 32.25H X 26.5"D, constructed entirely of .75" MDF with a 1.5" baffle. With no port, bracing or driver that enclosure measures 9.8cf. So realistically I'm looking at closer to 9cf. Is an 18hz tune still a reasonable goal in a 9cf enclosure?

Last edited by zacjones; 10-10-12 at 12:21 AM.
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post #4 of 17 Old 10-10-12, 12:01 AM Thread Starter
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Re: IXL 18.4 build

Here's a file with the more realistic 9cf cabinet.

Last edited by zacjones; 10-10-12 at 02:03 AM.
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post #5 of 17 Old 10-10-12, 01:18 AM
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Re: IXL 18.4 build

Looks like about a 2"x22.75"x36" slot would get velocity to an acceptable range. To be on the safe side, you could do something do a little large yet like 2.25" or 2.5". If you use your router and roundover your slot ports so that they have a flare, that will also help a lot in reducing possible port noise.

Placing the subs apart will lose some additive gain compared to having them locallized but it should help even out your response in-room. Do you have any measurment equipment and EQ to apply? If not it seems like quite the system to not have all of the bases covered.


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post #6 of 17 Old 10-10-12, 07:13 AM
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Re: IXL 18.4 build

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fusseli wrote: View Post

Placing the subs apart will lose some additive gain compared to having them locallized but it should help even out your response in-room. Do you have any measurment equipment and EQ to apply? If not it seems like quite the system to not have all of the bases covered.
This is absolutely spot on. With all those cabinets, rather than stacking them, I'd look into using Earl Geddes' sub placement techniques if you've got some wiggle room on placement. Also, having something like a MiniDSP will greatly improve your experience. You can get a decent calibrated mic and usb preamp for less than 100 dollars, while the MiniDSP will probably set you back about $130. You would be able to measure with REW, use some of Geddes' techniques moving subs around to deal with some room modes, and in the end use the MiniDSP to put a final smooth over on it. REW can export EQ settings directly from measurements that will load into the MiniDSP and set EQ settings.

With that many subs, you have a fairly uncommon, yet awesome opportunity to make an absolutely remarkable subwoofer system.

Check out some of Earl's papers here:
https://docs.google.com/file/d/0BxgU...Ums/edit?pli=1

Second Part:
https://docs.google.com/file/d/0BxgU...tHX09aTzA/edit
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post #7 of 17 Old 10-10-12, 01:30 PM Thread Starter
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Re: IXL 18.4 build

Oh I've got plenty of wiggle room on placement. I can either put the subs 3" away from the walls in the corners or I can do 4 or maye even five inches away from the walls in the corners! I can literally wiggle the subs and that's it.

I have a calibrated CM-140 and UCA-202, and I've run some REW sweeps with just the two subs I built before. I used to have a DCX2496, but it bricked on me out of the blue after a few years. Then I got a miniDSP, but that failed as well. I think that one was my fault. I swapped RCA's while the amps were still turned on, and it never worked again after that. I think I'm just going to get a Reckhorn B2 for a HPF and let the XT32 on the receiver do the EQ, a Denon AVR-4311ci, unless I can be convinced that it truly is worth all the trouble to add an additional EQ before letting the XT32 do its thing.

Unfortunately, my wife won't just let me leave sub droppings all over the room. She's given me the front two corners to play with. End of story. To make matters worse, the theater is wide open to the rest of the house, so I don't get the low end room gain I'd love to get. I've even thought about hiding a couple subs in the guest room and office closets (rooms adjacent to the theater), and opening up those doors and firing them up when she's not home! Those would be perpetually "for sale" and in storage...

I've only done a couple sweeps with REW and my current setup. I can't figure out where I'm screwing up. I use the appropriate calibration file that came with the mic, I calibrate the soundcard loop with no problems, but then I run the rca's to my receiver and through my speakers, and I get clipping at the beginning of the sweep every time. Just a quick clip and then the sweep starts. I haven't done any troubleshooting with that yet. But I'm working on an 8yr old laptop on its last legs with a windows 7 upgrade, and I just can't figure why it's clipping. But if I remember right, if I ignored the clipping, it looks like I have a severe, steady rolloff (similar in appearance to a sealed sub in winisd, but sharper) of about 20db from 50-20hz with the speakers in their current position.

My harebrained solution: add more woofers and a few thousand more watts and hope XT32 tames the peak, roll off the mains to the subs around 50-60hz.

The good news is that for music the mains sound really good pretty much anywhere in the room, and have a huge sweet spot in the middle of the room, so if you like the bass response of a certain song in a certain place, odds are it'll sound pretty good over there too, as long as you don't mind standing. I usually end up standing a couple feet in front of the couch with a pretty big grin on my face. But there are a few songs that really highlight the fact that the upper end of the bass range is way overpowering and the lower range is just there and sounding pretty good, not great, with the two subs right now, hammering away near their limit.

I guess my next move will be to set the desktop up for REW and drag it upstairs for some sweeps to see if I can eliminate the clipping and get a result I'm not questioning. I'm thinking I'll do that after I'm done typing here. I've got the next five days off from work. I'm tempted to try and take a reading from just in front of the driver as well next time. I shouldn't expect to see the massive rolloff there too should I? I was hoping to get a pretty good start on building the subs in this next week, but it won't hurt to run a few more sweeps anyway, even though I really can't do much about the location of the subs. I did take the previous sweeps under consideration when deciding what to do with these subs. I figured a sealed sub wouldn't work well with it's steady decline combined with the steady decline of the room. OK off I go to run some sweeps upstairs then.

Last edited by zacjones; 10-10-12 at 01:42 PM.
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post #8 of 17 Old 10-10-12, 02:20 PM
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Re: IXL 18.4 build

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zacjones wrote: View Post
I'm tempted to try and take a reading from just in front of the driver as well next time. I shouldn't expect to see the massive rolloff there too should I? I was hoping to get a pretty good start on building the subs in this next week, but it won't hurt to run a few more sweeps anyway, even though I really can't do much about the location of the subs. I did take the previous sweeps under consideration when deciding what to do with these subs. I figured a sealed sub wouldn't work well with it's steady decline combined with the steady decline of the room. OK off I go to run some sweeps upstairs then.
I would probably take a few different measurements around the room from where people might end up sitting, perhaps 5-10 sweeps at different locations. Average them out and see if you have any spots that are trouble spots.

Sometimes, moving subs out of the corner or up (on blocks) a few inches is all that it might take to kill a pesky room mode.

Looking forward to seeing how this ends up!
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post #9 of 17 Old 10-10-12, 08:07 PM Thread Starter
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Re: IXL 18.4 build

So I got the desktop upstairs and setup. No more clipping problems with REW. The theater is basically a 3 seater. The following graph is of one sweep taken from each seat on the couch at ear level. Pretty even across the seating, really. This is just the subs with 125hz crossover from the Denon, and the amp for the mains turned off.



Then here is at just a few inches from the driver on each of the subs -- the pink is the larger, lower tuned enclosure and the red one is the smaller, higher tuned enclosure. I seem to remember the larger one was just over 12cf and tuned at 17hz, and the smaller one around 9.5cf and tuned at 20.5hz, but that was just from the theory. The execution looks like both of them may actually have ended up tuned a little higher, which could easily explain my history of bottoming out and reconing drivers in each of these enclosures.



Looking at the in-room response I started thinking about maybe two 13cf 15hz in each corner vs three 8.5cf 19hz in each corner. Graph looks like this. Not too difficult of a decision. Hands down more drivers and amplifiers get the win here...


Last edited by zacjones; 10-10-12 at 09:28 PM.
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post #10 of 17 Old 10-11-12, 12:06 AM
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Re: IXL 18.4 build

Yikes... that null in your 20-30Hz range looks like a problem, it shouldn't be there.


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