Need enclosure design advice for Titanic 1200 subs (1 Viewer)

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Hello all:


I have a pair of original Titanic 1200 subwoofers that I have been running sealed (2.2cu ft) for a couple of years. They were great when paired up with a pair of small two ways. Now I have incorporated a pair of Martin Logan Sequel IIs into my home theater and the Titanics are kind of redundant. So I was looking at the original datasheet for the Titanic 1200 and saw that there was a plan for a 3.7 cu ft vented isobaric design that is tuned to 17hz. Going to a vented isobaric design seems to be the only reasonable way to get these drivers to reach lower and not end up with two crazy oversized subs in my living room. The thought is to build the isobaric sub into a custom entertainment console that will replace the stand for my Samsung DLP as I also want to clean up the wall with the home theater equipment - less boxes and cables running everywhere.


I did some modeling myself using the free program from AJ Design and I am coming up with a similar volume for an SBB4 alignment, but closer to 4.75 cu ft for the QB3 or SC4 alignment. With the latter alignments I am getting a 4" port length of about 22-24". Inside dimensions of the current idea are 33" x 20.5" x 15". The port will have to make one 90 degree bend.


I was hoping somebody with more experience and a different modeling program like WinISD (I can't figure that one out to save my life) could give me a sanity check here. I don't really know what to expect when choosing SBB4, QB3 or SB4 alignment in this AJ design program. Why is the SBB4 alignment choice coming up with the smaller box volume, I thought it was supposed to be the other way around? Is 17hz too low to try to tune this to?

Here's some pertinent info:


Receiver: Onkyo with LFE output (60,80, 100, 120 hz settings available)

Subwoofer Amp: Behringer EP2500 with FBD

Drivers: 2 original Titanic 1200 (4ohm, Fs=16.26, Qts=0.407, Qes=0.428, Vas=280.16L, Xmax=14.22mm


Thanks for any input!

 

[Robert_J]

It's been so long since I've seen those initials, I had to go look them up again. Taken from another site:

Super Boom Box 4th order , and quasi-butterworth 3rd order. Both are so-called "maximally-flat" alignments (flat passband), with the QB3 having the advantage of a smaller box size and shallower rolloff.

I also found a good explanation at http://www.diyaudio.com/forums/multi-way/38623-what-underdamped-overdamped.html It's been years since I read about them so I'll let you sift through the discussion at that link. I have my own ideas when designing a sub and I really don't pay much attention to those alignments.


I like Unibox for my modeling. It isn't as picky as WindISD is about the order you enter the parameters and according to people in the industry it is one of the most accurate, free programs.


No, 17hz isn't too low especially since I don't see a subsonic filter listed in your equipment. That's the main reason I went with sealed subs in my home theater. Also, even with the new speakers, I don't see the Titanics as redundant. With a good sub or two or 10 in place, they take the heavy lifting away from the receiver's amp and allow the speaker to run with much less distortion.

 

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Robert, thank you for the response. I should have clarified that I'm not driving the Sequel IIs with the receiver. I have a pair of 100w plate amps modified to run full range that are driving them right now. A bit unconventional, but running those and setting the receiver up to drive them full range ("sub=no") surprised me enough to leave the subs out of the equation for now. Also, I am running a phantom center, so the "75wpc" receiver is free to just handle the duties of the surrounds. The Sequel IIs throw such a great soundstage I do not miss the center channel at all.


I am not hung up on the SBB4, SC3 thing either; I juthought I'd explore something ported in an effort to reach down to the lower frequencies. The Titanic 1200s are great for music but for home theater they seem to lose control anytime they are presented with an intense scene - like Darla thumping the tank in Finding Nemo. Nearly everywhere I have read about the Titanic 1200 (or the NHT 1259 it was copied from) people seem to say stay away from anything but a sealed box. I've been there, done that and for home theater use it just doesn't seem like a good choice. The vented isobaric design is kind of a last shot at making these perform differently and I'm worried that it too will result in disappointment. I had thought about following the PE design for a vented isobaric but was a bit nervous about using a single 3" dia x 12.25" long port in such a design.


I played around with Unibox last night, but it doesn't seem nearly as intuitive as the AJ program. Any help / advice working with it would be appreciated.

 

[Robert_J]

Based on the specs - http://www.partsexpress.com/Tech/295-400.html this is a great little driver.


I don't have MS office on this PC so I can't run sims in Unibox. I'll have to do that after work. I'll describe how I go about doing this so hopefully it will help. To me, it's very, very easy.


Finally, I'm not crazy about isobaric subs. They were great back in the 80's when motor power was not that high. This sub is more of a transitional design with a stronger motor but nothing like what is available now.

 

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Yes, you have hit one of other nails on the head. While this is a great driver it may not be so great in a vented box, and the box size gets quite large to do so. There is no way I am going to run two of these, vented, in individual enclosures of 6-7 cu ft each. So it is a question of either trying the isobaric approach, revisiting the size of my sealed enclosures and some new eq settings, or simply moving away from these and going with something like the 15" RSS390HF driver in a 5 cu ft ported box like you helped John Bilbrey with.


Regarding a 5 cu ft enclosure for either approach, Is it realistic to perch my Samsung DLP on top of this thing if I build it low and wide? Will it vibrate the Samsung to death? I'm really trying to reduce the equipment footprint in my living room. I had been thinking about doing IB up in the attic but the cost of 2 or 4 drivers is a bit overwhelming to say the least.


Thanks!

 

[Robert_J]

How did you set up your BFD? I set mine up with an SPL meter and spreadsheet. I also run an EP-2500 and a pair of sealed subs. The only difference is that my subs are 2 ohms each so I'm getting about 800w per driver at 20hz. With their massive excursion, I am able to boost the low end and get a flat response down to 17hz and usable bass below 15hz.


If you are going to use a sub for a projector stand, you will have to build that enclosure like a tank. Another option is dual, opposed drivers. That way any vibrations are canceled out.


The cheapest drivers on the market right now for IB subs are the surplus AV123 MFW subs. Danny Ritchie has a bunch that he is blowing out for $79 each plus shipping.

 

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$79 for IB subs, now you have my attention! I found that thread at AudioCircle but it is months old; do you know if he still has any? I left him a voicemail today (late). This price would definitely motivate me to give IB a try.


I set up the BFD the old fashioned way, yes, and was able to get the response pretty flat from 22hz to 100hz. At 20hz I was down 2db and at 18hz I was down 10db. At 16hz I see nothing happening - is that to be expected? Again, I am running these in 2.2 cu ft sealed enclosures; perhaps too small. The product page on the PE website suggested 2.2 cu ft, but the printed sheet in the box suggested 3.3cu ft. Gotta love a consistent message...


Another odd thing is that at 56 and 63hz one of the woofers makes an odd buzzing noise - a leak perhaps?

 

[Robert_J]

I think as of last week he had about 80 or so. Your Behringer will be way, way overkill. In fact, it would easily power 8 or 16 of them.


I'm guessing the "old fashioned way" is the PEQ spreadsheet. That's the same way I did. I did have to use a couple of filters at 17hz to get the low end up enough. My subs are are designed more for the car audio world but play great with a little EQ.


Without hearing the "buzz" I can't really tell. But leaks can sound funny. Make sure you use gasket tape or closed cell foam weather stripping between the driver and enclosure.

 

[John_Bilbrey]

I wouldn't want to set anything of great value on top of the sub Robert helped me build. It's possible it needs more internal bracing.