I've been watching the debate on this thread with keen interest. As many of you know, I started out planning on saving up for dual JTR Captivators to go with my DTS-10 and have been trying to become comfortable with DIY as a viable alternative. If I had a dedicated theater room, I'd build a wall of inexpensive DIY subs with iNukes to match or outperform the Captivators. However my theater is part of a nicely decorated multipurpose family room in a very large 10,000cf open floor plan. There are only two spots to add new subs and I must live within those limitations. It's not about lack passion or commitment, it's just practicality.
I've spent enough money over the years on the rest of my system that I don't want to skimp now on the rear subs. That's why the Cap's appealed to me - relatively small (compared to giant DIY boxes), legendary SPL and extension (at all the AVS shootouts), AVS reviews for tight bass (to match my electrostats), good resale value (when they do come up used, they're "Gone in 60 Seconds"), simple decision process (save, buy, move on to improving other parts of my system). The only downside is they're very expensive (read: takes longer to save for) and a matched pair seldom if ever comes up used for local purchase in Los Angeles (read: impossible).
At first I looked at the 24"x24"x24" Marty Cube with a UXL-18 but wasn't convinced a pair would give me the same performance as a pair of Cap's. Then I looked at Eric's new Stonehenge sub, but at 30"x30" it would block the HVAC main return vent, and at 16" deep it gave up performance I could get in a thicker sub for which I have the clearance. The 24"x24"x40" MiniMarty was too tall to fit under the rear speakers, so I modeled bigger variations of the Marty Cube to get more performance and PM'ed LDT02 for help. He responded with a 8.5cf design at 32"x32"x21" which was spectacular but unusable as anything over 27-29" wide still blocks my HVAC return:
I also started a campaign to get my wife comfortable with ever larger DIY enclosures by stacking some small boxes around the existing rear subs. First I got up to 24"x24"x30" and she didn't object. Then I added 2 more inches for height to 32" and she didn't balk. Eventually, I modeled a 24"x24"x32" enclosure in WinISD and talked to chalugadp about building a version coated in veneer. I showed her a picture of his lemans build in teak and she thought it looked OK:
As we got acclimated to having the stack of boxes behind the sofa, I began to think she might accept something even larger with capabilities closer to the MiniMarty and equal the Captivator. I got two 27.5"x23.5"x32" boxes from the UPS store, placed some leftover 3/4" finished teak plywood on both sides for appearance and let her percolate without saying a word:
It's been two weeks with the 29"x24"x32" boxes behind the sofa. At first she frowned when she saw them, then eventually didn't react, and finally indicated she might be able to live with them assuming they were nicely veneered. I've also gotten more comfortable with their size and really don't think they look that bad behind the sofa when the lights are dimmed:
First, I wanted to get an idea of the performance gain, so I modeled the new 29"x24"x32" size against the Marty Cube (yellow) and Mini Marty (white) at three tuning frequencies between 17.5 to 19 Hz:
Second, I wanted to see if it was worth the additional size and expense to go with the larger approx. 8.0 cu ft
(29"x24"x32" side port) over the smaller 7.09 cu ft
(25.5"x24"x32" front port). The smaller sub is simpler to build and I already have a reasonable estimate from chalugadp to make it. The larger sub would require more effort, materials and shipping costs plus a reprice from chalugadp (if he's willing to do it). The larger 8 cubic foot enclosure should allow slightly greater SPL and deeper extension approaching the Mini Marty. I modeled both box sizes at 19 Hz
for maximum SPL and 17.5 Hz
for maximum extension, again compared to Marty Cube (yellow) and Mini Marty (white) for reference:
Obviously the 19 Hz tune comes the closest to the MiniMarty response curve. However my rear subs are so close to the L.P. that I may be able to benefit from some near field affect with 17.5 Hz tuning at the lower frequencies and not loose near field SPL because of wall/floor/sofa back boundary reinforcement.
Unlike a dedicated theater where one would try to optimize bass for EVERY seat in the room, what I really care about is optimizing bass at the primary listening position. My wife and I love cinema. We use our system to watch one (or more) movies almost every day, 365 days of the year. We often have friends over on weekends for a movie on Saturday nights but most of the time it's just us with the dogs. With 10,000 cu ft of space we're not going to get a lot of room gain. So the question becomes what direction for ports and drivers will optimize the LFE at the main listening position without creating a peak across the middle sofa where we usually sit.
The DTS-10 "mouth" can be configured to open corner loaded on the left or mid-wall on the right. The rear subs can be ported forward into the room or mirror-imaged into the small space behind the sofa for wall/floor reinforcement to maximize near field boundary response.
With the 24"x24"x32" front port Marty variation I don't have any choice except to turn them sideways facing each other along the back wall or face both into the room. I have read the discussion at Databass.com about how hard it is to measure off-axis response at 1 meter from a ported sub where the port and driver face different directions. It indicates that I might experience a null at the LP between the subs if both drivers and ports are facing into the room with the L.P. so close (about 1.3m) directly beside and between them.
With the 29"x24"x32" enclosure the ports could be configured to fire mirror imaged toward the L.P. while the drivers fire into the room. I was hopping that someone with more experience might know if I'm completely off base. Which of these scenarios do you think is best for my application?
Response and Gain
Lastly, as the OP stated at the beginning of this thread, my goal is to build a PAIR
of DIY subs that will match (or exceed) the SPL, extension, low distortion or linearity of a PAIR
of JTL Captivators. If I can save some money doing it then DIY is the way to go. If the Cap is about the same performance in a much smaller 20"x22.5"x30" box, then ID is the way to go. I think at this point, I'm pretty far along the road toward DIY subs, just still working out the details before taking the plunge.
Come in LDT02...