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Discussion Starter #1
In reference to the new FTW-21's, how big in diameter would a sonotube have to be to in a LLT build to get the tune <= 15 and keep the height under 6 foot? Would 30" be sufficient or closer to a 36" be better?

Thanks!
 

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This is a driver that is IMO better suited to being sealed. An LLT could be done, but I have a feeling it would be a lot larger than your projections. How would one even get a 30" or 36" sonotube through the door?

I will model it for you and give you a more precise answer when I get an opportunity later today.
 

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Okay, here's the deal. In a vented box, this driver wants.. either...

A) A huge huge box (IE 800L)
B) A large and long vent (IE 44" x 8") in a smaller box (650L - by no means small)

Now the 8" diameter vent is actually inadequate if you were trying to push this thing to its max SPLs. I'm not saying it's a realistic scenario as the vent tuning would be near 10hz, but basically you'd be SPL limited by the vent. In the 800L box the driver gets a bit out of control and needs an electronic filter to limit its movement, and I think that's rather convoluted (personally).

Honestly, I don't see any need to vent this driver. It can produce 103db in an ~290L sealed box - at 10hz in 2 pi space!!! In a room that essentially means reference levels with any level of gain, and i can't imagine any movie content requiring much more SPL at those extremely deep frequencies. At 20hz you're still looking at around 114db, which is essentially just short of reference level. Your front L-C-R mains are very likely to give out long before this sub does!!! A roughly 24 inch diameter x 42 inch long would do it, and unless I'm mistaken, that means you could make two of these sonosubs from one sonotube! :devil: :dumbcrazy: :hsd: :T :bigsmile:
 

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Discussion Starter #4
Still new to all of this so bear with me here ...

Had read Steve's article on LLT builds and was impressed.

Have heard nothing but good reviews for Mark's Mach5 series so decided to give his drivers a try. Apparently the FTW-21's are the only drivers in production(?). (Havent been able to get in touch with him directly have been playing phone tag there) Prefer the idea of a large driver now and adding another later rather than two smaller divers now.

Size of the sonotube is pretty open. Have a double door leading into the house and into the theater room. Although there is a set of steps to navigate through. My local store has 24"x 12' sontubes at $77 with larger sizes only moderately higher.

A sealed tube design sounds great, easy to build - and still have the other half of the tube for a second driver down the road. Just bought a behringer ep4000 and did the fan mod - that would be plenty of power even if i ugrade to a pair right?
 

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Discussion Starter #5
Was having a hard time letting the LLT idea die. I went and downloaded the sonotube calculators and ran the drivers through with the specs from the IST website. Even 30" diameter by 72" tube is too small. Went and took a second look at my basement access and realized thats as big as i'm reasonably going to get squeezed in. Just had to see the numbers myself, but you were spot on GranteedEV.

Sounds like your thoughts on a sealed enclosure would be the best bet. Would the tube require any bracing in the middle? Just line the interior with fiberglass batting, cap the top end with double ¾ mdf, make an identical bottom cap with a speaker cutout, make short feet attached to a solid bottom stand to keep it from hopping around, and decorate for maximum WAF. Sounds almost too simple?

Cant wait to get started, should take about a month or so for the speakers to be built and shipped.

Thanks for the help!
 

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Careful on the "Buy one; plan for another later" bit. You never know when the driver will go out of production. It happened to me with the exodus maelstrom series =(

Just bought a behringer ep4000 and did the fan mod - that would be plenty of power even if i ugrade to a pair right?
To my knowledge the behringer is around 600W @ 4 ohm into stereo and around 1800W bridged into 4 ohm mono. So while the answer is probably yes, I'd still prefer one amp per driver; each with its own 20A line feeding it. It's all about having headroom ;D

Was having a hard time letting the LLT idea die.
I've been there!

Would the tube require any bracing in the middle?
Depends on the passband. If it will be crossed over at 100hz there will be still meaningful output as high as 200hz (~80db) that you might not want resonating. If crossing at 60hz then you're probably good to go; but you lose many of tue advantages of the higher crossover point. I say yes - get some cross brace dowels in there if you can; every 12 to 20 inches or so. It won't hurt and it will open up much flexibility.

Just line the interior with fiberglass batting, cap the top end with double ¾ mdf, make an identical bottom cap with a speaker cutout, make short feet attached to a solid bottom stand to keep it from hopping around, and decorate for maximum WAF. Sounds almost too simple?
I would especially use around 12 inches of insulation on that top endcap in order to minimize internal standing waves from the tall enclosure.

As for "Too Simple"; It's around 9 cu ft and uses a $500+ 21" driver. You're setting yourself up for success with that! Depending on how your room responds to the sub, you may still want to implement a minor linkwitz transform eq filter but for now just get the sub built.
 

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A nice FTW-21 with an LT circuit, my ears just perked up. :) I would very much like to see this built. I had been wondering if the LT was beneficial or detrimental with things like XT32 processing setting sub levels. With or without Audyssey in the mix, I would still love to see this project. Tyredman, whatever you choose, you're going to love it.
 

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Discussion Starter #8
Bought a second EP4000 amp - should arrive this week. Will run an additional 20a line for it as well. Hopefully that will have any headroom issues resolved. :heehee:

Waiting on the drivers is giving me too much time to ponder on all of the possibilities for the enclosures. If they were here now I'd drop them in a tube and be done with it. Now I'm thinking a slightly curved box might be interesting to match my EMP E55Ti mains. :dontknow:
 
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