2 18" LLT Sonotubes: Preliminary Planning - Page 3

How are these for mounting?

http://www.parts-express.com/pe/show...number=260-778

I plan to use a good quality plywood. Either Baltic Birch, or the German equivalent thereof. Google translate translates "Baltic birch" into "Birkenmultiplex". Running it backwards, it translates into "Birch Plywood". So looks promising.

For techniques, I heard pre drill a hole for the T-nut, then use an adhesive. Screw a screw into the nut nice and tight while the glue sets. This should assure the nut is straight when it comes time to install the driver. Sound about right?

For connections, I think I may use a Speakon connector. I was going to connect to the bottom with a 90 degree angle, but I realized I have the grill there. I suppose I could run the grill behind one of the legs to give me room to do the connector. Or I could put a plate on the side of the tube near the base. Is that an acceptable practice, or am I asking for trouble if I start cutting holes into the tube?

Also, feet. Should I use rubber feet, spikes, or just leave the base plate naked and call it good?


Didn't the Russians have an LLT array that could be used as a first strike weapon?



I'm pretty sure that's an array of 28 LLT subs with 80" drivers powered by a nuclear reactor. Guess that's why they called it a "nuclear sub"!

Now that I think of it, I do remember Captain Ramius (Sean Connery) saying in his speech to his sailors "We will pass through the American patrols, past their sonar nets, and lay off their largest city, and listen to their rock and roll..."

You see? This movie wasn't about a cold war nightmare submarine! It was simply Kryptonitewhite's fantasy put to film!

So anyway...

Okay, I believe I have the complete manifest of things I will need. Here goes...


Maelstrom X 18" driver
Crown XTi 2 1002
750mm "Sonotube"
1yd Speaker Grill Cloth
1m 200mm "Sonotube"
Neutrik NL4MPR Speakon 4 Pole Round Chassis Mount
Neutrik NL4FC Speakon Connector 4 Pole Cable Mount
Ditto
Cast Frame 1/4"-20 Speaker Mounting Kit
Speaker Cabinet Carpet jet Black 54" Wide 2.5yd
2 sheets plywood

Multiply everything above by 2...
Plus common items:

More items common between the two:
Speaker Gasketing Tape 1/8" x 1/2" x 50ft
Jasper Circle Jig Model 2000
Dayton Audio SKRL-10-100 10 AWG OFC Speaker Wire 100 ft.
Mineral Wool
36oz wood glue
Wood Putty (to form the horns)
Stain
Polyurethane

Total: $2,980.89

Plus probably another hundred or so for the inevitable incidental costs.


I went back to the XTi amp since the XTi2 is now out, and looks to have some nice features. Plus, it's only perhaps $60 more than the MiniDSP, and has a much more robust PEQ. And it's one less box.

Regarding that, I decided to do two 1002s instead of one 4002 because I figure if I have two separates, the fans will be less likely to come on than if I had one unit doing all the work. Speaking of fans, the XTi2s have three user selectable fan options. Low, Early, and Full. Hopefully the low setting will be inaudible. It will be interesting to see user impressions of these amps once they are released on March 15th. They are available for pre-order at Parts Express.

Decided to do 10AWG cable since my runs will be 50' each, and I'll be pushing almost a KW of power at times. From the connector reviews, some say 12AWG is the biggest they can handle, some say they can handle 10AWG. Guess I'll find out...

I decided to go with the Speakons for safety. Two shiny gold terminals are probably tempting for a kid who can't be watched every second. And I don't need him shorting the terminals, or getting lit up himself.

Well, now I can hit the computer render again and put everything on it. I want to try to make it as close to a 1:1 model as possible. That way hopefully somebody can raise a BS flag before I build something with a major flaw...

Okay, I have come up with an "Alpha" design. I think this one should be pretty close to how the real thing will be built.



So, two questions.

1) Can the sub be built so that the top endcap can be removed? Not sure why I would want to remove it, but it just bothers me that once the endcap is all glued in, it's in forever. what if I were to put a thin strip of gasket material along the top rim of the tube and just set the top cap on it? Would it's weight hold it in place, or would the driver bounce it up and down? Might the middle support ring vibrate inside if it is not glued in?

2) In order to prevent buying a whole extra sheet of plywood to just cut a ring or two, what's the word on routering out two semicircles, and gluing them together atop a whole circle? For example, On the bottom endcap, have the lower cap a complete circle, and make the inside cap which the speaker mounts to out of two semicircles (which join to form a complete circle). And the same thing for the top. Should it work, or bad idea?

Thanks!

yeah, I'm not sure if I want to screw through the side of the tube. I'm thinking that might not look all that great. Well, I guess I could try setting it on, and just glue it once I'm satisfied. The driver can be removed, so I can remove anything that falls in that way. But hopefully the top grill will prevent that.

Actually, you'll probably be done before me. I won't be able to start until next year... at least I have a working design I'm familiar with now! But hopefully this year I'll be able to finish a sonosub with my Klipsch driver. That will be my practice round for the big boys!

Almost 2 years later and I'm finally (almost) ready to start! I'll start ordering parts around February 15th once my tax return comes in. In the meantime, I need to finalize the driver. I've narrowed the list down to two:

XCON 18D2
Fi Q18



At this point, the XCON is the winner, and the one I'd order if I had the cash today. I like the way it's modeled response is smoother than the FiQ18, and the fact that it doesn't require as much power to drive.

Any other suggestions on drivers to use? One limitation I have is that any driver I get has to weigh less than 70lbs shipped because it's coming to an APO address, and there is a 70lb weight limit. Also, the de-facto LMS5400 Ultra is out. It's just too expensive.

A summary of the details:

650 Liters
7.8" (200mm) x 33.2" port
12Hz tune
29.29" (750mm) sonotube

Planned power:
EP4000 in stereo mode
BFD1000 for PEQ



Notes: The one internal brace is to protect from external impacts. These subs will need to endure being moved several times.

I looked at that driver, but when I modeled it in WinISD, I found that it comes right up against it's XMax above tuning.





The lower Xmax of the Stereo Integrity driver makes me a little leery of trying it out. My goal is to be able to play at reference levels at 20Hz. While I don't normally listen at reference, I have demoed at reference, and even with my modest sound treatments, reference level is tolerable. (Normally I listen at -5 to -10db) I know that the fact I'm running two subs should give me 3-6db to play with, and room gain will get me more, but I'd still prefer not to give up that extra 7.5mm of movement that the XCON offers over the StereoIntegrity model.

Ah, OK, I see on their page they list a 36mm xmech, so that gives me some leeway for those theoretical above reference spikes that may occur from time to time.

So the next question is, when will these drivers be available? Their site lists the Dual 2s as sold out. I hope this isn't going to be like every other promising 18" HT driver that has come and gone over the years...

If I got a pair of the Dual 4s, I suppose I could wire the voice coils in parallel and end up with a 2 ohm load to the EP4000. Which would be more desireable? Wiring a D4 driver in parallel for a 2 ohm load, or wiring a D2 driver in series for a 4 ohm load? I suppose since I am building two, I could wire two parallel D4s in series with each other for a total 4 ohm load, but then I wouldn't be able to play with their phasing if necessary.

Ok, that's good to know. Probably the hardest part is going to be acquiring the sonotubes. It's hard enough in the states. Here in Germany I don't speak the language well at all, and I need to try to communicate that I as a private individual and not a building contractor want to buy 4 meters of 750mm tubes. Doesn't help that it's 80 Euros per meter!

OK! 2 HT18D4s have been ordered!

Now, some questions for those here who know what they're doing...

I plan to run each driver with the voice coils in parallel, which should give me 2 ohms, which the EP4000 in stereo mode should be able to handle. How would I alter the TS specs, or should a D4 model similarly to a D2?

Also, fine tuning the tuning. Playing around in Sonosub, the largest volume I can do while not making this thing too tall is 750l (26.5 cubic feet) and the longest port length I can do is about 47", for a subterrenian 9.6Hz tune. However, this alignment puts me past Xmax above tuning with 600W of input power. I would think with this alignment it would be too easy for an above reference spike (according to some discussions, a 126db spike is theoretically possible) to destroy the driver. I could set my AVR to not go above -10, but that's no fun!




Such a low tune is tempting, however, because it gives me +3db at 10Hz, and +5db at 9Hz and lower. If I did go with such an alignment, I'd have to take careful measurements of exactly how far I'm excurding, and limit my system accordingly. It doesn't take me past Xmech, and depending on how much I actually benefit from two sonotubes and room gain, I may actually be able to hit reference without even exceeding xmax. The stink of it is it's really hard to re-tune if things don't pan out, unless I can think of a way to secure the top endcap in such a way that It will seal, and yet be removeable in case I need to cut some volume and port length... hmmm...

According to the charts, I'm hitting 111-112db at 20Hz depending on the tune. As I understand, you get an extra 3-6db for having two sonotubes, and some room gain at 20Hz as a bonus. So let's say I aim for 111db at 30Hz in expectation of a 4db bump for having two subs. In this case, I can play to reference while staying within XMax. If I got a 118db peak, I'd still be barely within XMech, and my amp would probably clip.




Thoughts?

For those of you who have been following this, a major design change has occurred due to the fact that I've determined that even for native German language speakers, it's difficult to acquire the required tubes. And those who do pay so much that building an enclosure out of 3/4" MDF costs about the same, if not less! So...



This picture shows the two completed subwoofers side by side. I like this design in that they now also serve as a riser for a 3rd row of seating. The internal volume should end up just a little over 650l. Internally, I plan to use 2" wide strips of 3/4" MDF as bracing. They will be placed every 8 inches, and their edges will all be rounded. Also, they will be glued to each other at the intersections. The top of each woofer will be carpeted like the riser for my 2nd row of seating. I'm not sure how I'll finish the sides as of yet.

Also, if you look at the large version of the picture above, you will notice a diagnal cut in the MDF between the subs, The concept is that the board in the middle has one half glued to one sub, and the other one is glued to the other. The slanted cut is so that one will rest atop the other, and the diagonal cut will "lock" them together. this should prevent the enclosures from "walking", provided I don't run them out of phase with each other.







For my port, I decided to go with a 6.25" port, as I can source a PVC tube that size at local hardware stores. Also, the smaller diameter puts my first port resonance at more than double the maximum expected frequency of 120Hz.. Both ends of the ports will be flared with 1 1/2" flares. According to "Flare It", I will experience chuffing at 10Hz with a 0db FS signal. However, I expect that that point, all the other noise during such a scene will make the chuffing inaudible. Chuffing begins at just above -2db FS.

For the excursion, I do plan to use some sort of filtering. I will have to experiment, however, to determine how much and what sort of filtering I will use. My AV Receiver's LFE output is flat into single digits, with the -3db point at 3Hz. I will have to measure the output of the iNuke with an O-scope to see where it's rolloff begins. Ideally it will be high enough that I won't need a highpass due to my low tuning. But if not, I'll experiment with the iNuke's filters to see where I get best results. I do understand that the filters can't be set lower than 20Hz. However, I have read that by combining a highpass with a shelf filter, one can achieve a highpass with a lower cutoff.

For amplification, I will be using the iNuke 3000. I plan to run the speakers, Stereo Integrity HT18 D4s with the coils in series, so 8 ohms per channel. That should give me 400wpc, which is enough to get me to reference volume (300W required according to WinISD) If that doesn't work out, I'll try them in parallel, and see if the iNuke can deliver the required current. If all else fails, I'll bridge the iNuke and buy a second.

So, does anybody notice any glaring oversights, or does it look like I'm good to begin construction?