Flaming Oak Cinema - (S)LLT sub design/build

[Cathan]

Hi everyone.

Based on Steve Callas's suggestion I've wandered over here to solicit some design assistance for the sub portion of my dedicated home theater construction.

Quick bit of background - for the past year or so I'm been reading various forums (here, AVS, the Cult... etc.) getting ready for when I was going to get the wife approval to build a dedicated theater in our basement. Most of my early efforts were spent learning construction, sound isolation, sound acoustic/treatment techniques. After reading for over a year the most important thing I learned was how little I truly knew. It just takes a massive amount of knowledge and experience not to screw up some detail that at the end may make or break all of your efforts. But I opted to start building anyway, figuring that since the project was going to take a year or two to complete that I'd have plenty of time to continue studying/learning/reading to fill in the major gaps. As a safety net I hired an audio/theater consultant (Bryan Pape) for input on design aspects just to make sure that I wasn't going to screw things up to badly.

So what does all of this have to do with you? Well I've just realized that I'm at a stage where I need to lock in some space construction as it pertains to building the integrated sub enclosure. My vision was that since I had a fair amount of basement space, I could allocate some of it to build a giant sub enclosure. I've looked at IB subs, but I don't think the wife would be too pleased if I defeated all of the sound proofing efforts by dumping the back waves into the rest of the house. So my thoughts were to build a sealed room that could serve as an enclosure for either a ported or sealed sub design.

After having exchanged emails with Steve and having re-read his LLT FAQ and Rodney's IB to LLT conversion thread, I've been sold on the merits of building a (S)LLT. But given that I'm sooo far behind the ball on my sub construction knowledge, I really need to get some experts to help with the actual design.

To get the ball rolling, here is a diagram of the basement project.

You can see the basic layout of the room, the location of the transparent SMX screen wall, and the rough allocated space for the LLT enclosure. I really would like to keep the costs for the sub equipment (amp and drivers) to around $2500, but could be talked up or down. Wall construction I'm just figuring to be part of the basement construction costs (just don't tell my wife).

So first question - how much space would you allocate to the enclosure. Moving that wall back and forth a few feet isn't a big deal right now as I'm still framing other parts of the basement.

Second question - equipment? Number and type of drives (FiCar Q's?), pro amp to drive them? I figure to get a BFD to help equalize the beast.

Third -design? While I may not get to building the actual thing for a few more months, getting the design locked down would be most helpful.

Anyway, I realize I'm asking a lot, but hopefully with everyone's help, I'll end up with a final product that will thrill the family for years to come.

best,

Michael

[brucek]

I don't know much about sub design, but I have a few questions that others may have also, that you could answer.

I have a bit of trouble figuring out the diagram and maybe you could answer some questions I wrote on the attached pic. Maybe if you could blow that area up and show a bit more detail of the specifics, now that everyone has a large picture feeling for it.


theater.jpg

brucek

[Cathan]

What?!? You can't ready size 2.5 fonts?!?


The full width of the theater room will be around 13'.

I don't have my notes with me at work, but the black area is the screen - width 104" and height around 44".

The space behind the screen is 2' 1/2". What you circled is the wall that would have the ports and drivers.

The sub area text reads - "223 cu feet assuming a 7' ceiling height - 6318 liters". It is based on a space that is 2' 6" wide x 12' 9" long and 7' tall.

The green "wall" is a support ceiling I-beam and the red circle is the loly column that supports one end of the I-beam. I need to build around it as part of the screen wall construction, but it should have no impact on designing the sub.

[Sonnie]

You can do some serious woofing with all that area. You might want to check out Rodny's IB Makeover thread for some ideas. I look forward to following your progress.

Cathan wrote:

... the black area is the screen - width 104" and height around 44".

Is that a 2.35:1 AR?

[Cathan]

Thanks, Sonnie!! And yep, I looked at Rodny's thread. It's what convinced me not to go the IB route. And yes, the screen will be a 2.35:1 CIH set-up.

[Rodny Alvarez]

Looking good!!!
Do you want Fi audio subs or something else??

My 4 RLp's and the two EP 2500 cost me about $1700, the only problem the I see is with the ports length, you might need to let the port come out the wall.
Slide1.JPG

Can't wait to see the results!
Good luck!!!

[SteveCallas]

Right, 2'6" depth will restrict you from having optimal port clearance or even fitting the ports in at all. Not a big problem though, as you don't need 6300 liters - I'm looking at 4000 as an absolute max for four 18" drivers. Once the room starts coming together, I would use a "test" subwoofer of whose anechoic FR ther are measurements of to measure the FR at your seat while placing it at different spots alongthe front wall. The smoothest looking FR and best sounding response will be where you would want to locate the drivers. Once that is determined, I would cut this proposed chamber in half lengthwise and increase the depth. 5' depth or so would be great, see attached.

As for drivers, your choices for 18"s right now would be the SS RL-p18, the FiCar Q18, and the Mach5 IXL18. Similar performance would be had from four RL-p18s, four Q18s, or six IXL18s. Since the Q18 price includes shipping, I think that would end up being your best bet by a fair margin. Either way you go, 4000 liters with four 8" diameter ports that are ~28" long and 2000+ watts would do it. You should have plenty of money left after four Q18s to buy a couple of beefy pro amps. What we are essentially talking about here is 125db+ from about 8hz on up in room, and that is a fairly conservative estimate - yeah, no kidding

The only thing I'd be concerned with is the integrity of that front wall if all four drivers were mounted directly onto it. I'm thinking some sort of a manifold would provide much more rigidity. A vertically orientated manifold with the drivers in an array fashion should work out pretty nicely, with two ports to each side.

Looking forward to this one!

[brucek]

Well, as I said before, I can't read a thing on that diagram, but the room looks to be about 13' x 19' with a 7' ceiling. Not very big.

Would he really need that many drivers and ports?


What about two SS RL-P18 D2's in a ~1500 liter enclosure tuned to 12Hz, driven from a single EP2500 amp with each channel driving a single driver at 4 ohms of 750 watts a channel.

The single 10" port would only need to be ~20.3" long, allowing 10" extra space to the back wall.

SPL looks OK. Excursion looks OK. Velocity at 1500 watts is a little high, but it is a 10" port. Much like Rodneys setup.

Or am I way off? Would this not fill that room?


SPL RL-P18 d2 x two.jpg
Excursion.jpg
Velocity.jpg


brucek

[SteveCallas]

Yes, two ported RL-p18s would definitely do the trick - even one high excursion 18" driver in a LLT would......but uhhh, if he's willing to go for more, I'm not gonna be the one to talk him down Thing is, even if going the dual RL-p18 route, I'd be weary to only use a single 10" for two high excursion 18" drivers. I'd use no less than two 8" ports.

Just so you understand though Cahan, like what bruce is alluding to, the quad Q18 LLT would be simply ridiculous in terms of capability. At that point, you really would have to seriously sit down and question your actual speakers and amplification to make sure they could keep up with the sub, even though the unavoidable answer would be no, not unless you have line arrays or large horns.

But "nailing" the bass on the first try in a home theater is always a good thing Better to have lots of excess on hand than not enough.

[Cathan]

Man you guys are great!! I need a bit of time to digest all of this info. Right now I need to hustle and finish up a few things before the plumbing inspector shows up. So more later.

One quick thing though...

brucek wrote:

Well, as I said before, I can't read a thing on that diagram, but the room looks to be about 13' x 19' with a 7' ceiling. Not very big.

brucek

Actually the room is technically 21' long for audio purposes. The screen wall will be entirely transparent (a false wall) so that the speakers can be behind the screen. For all practical purposes, this isn't much different, but when you are trying to scrape out every last inch of space it matters.

Rodny Alvarez wrote:

Looking good!!!
Do you want Fi audio subs or something else??

My 4 RLp's and the two EP 2500 cost me about $1700, the only problem the I see is with the ports length, you might need to let the port come out the wall.

Fi or Soundsplinter would be fine. Really for me it's more about selecting the right tool for the job as suppose to picking a tool and then figuring what you can do with it.

[Cathan]

One more thing. The main speakers are being placed behind the screen wall. The sub needs to be constructed so that it doesn't screw with the main speaker placements. So carving out that red area behind the screen may not work if that is suppose to be floor to ceiling area.

I don't know if it's feasible, but what about something like this where the ports and drivers could be mounted below the screen? (Pardon the crude sketch-up)

[brucek]

I'd be weary to only use a single 10" for two high excursion 18" drivers. I'd use no less than two 8" ports.

Yeah, that does looks better with two 8" ports @ 29.5" in a 1500 litre working volume (tuned to 12Hz).

That would mean he would have to extend the two ports through the driver wall a bit to allow for space behind the ports.

I think it would be easier to not use the middle wall shown and simply build the 1500 litre (52.97cu.ft) (working volume) structure and then the ports would mount fine using the MDF for the flares. He could build it structurally with 2" x 4" 's and then cover it with MDF, with a double front thickness.

Really, really rough (on a napkin) calculation would be about 60" high, 40" wide and 45" deep outside dimension (would realize near the 1500 litres inside with bracing etc, etc). You would have to of course work that out correctly. This is just messing around to give you ideas (and others to refute them).

That would give enough room I would think to mount the two drivers on top of each other and the same for the two ports. It would leave about a 15" in front of the ports to the screen wall - you'd have to work that out to be sure.

Something like this pic below. I'm assuming about 5 feet behind the screen to the wall.

See any real problems with that Steve? Rodney?


theater.jpg


brucek

[bpape]

Having the sub box off to that side is not an option - sorry. Those corners are needed for bass absorbtion - not to mention having the ability to have the speakers basically at the edges of the screen. I also don't want any boundaries any closer to the main speakers than necessary to avoid additional SBIR issues.

If the box can be made smaller than the 'room' we originally designed for IB use, that's great. We just need to figure out how to do the porting. IMO, we could do the box down low and behind the wall still - just not as large. That would allow approx 4'5" from wall to cloth wall. Part of the port would stick out in front of the box or the box could be built to be deep enough provided it doesn not intrude with proper main speaker placement.

Bryan

[WillyD]

Maybe I am crazy...but why not use four or more of those $125 15" Brahma-like drivers in such a situation? They need a lot of volume, but he certainly has that.

http://www.soundsolutionsaudio.com/f...howtopic=10024

[SteveCallas]

Cathan wrote:

The main speakers are being placed behind the screen wall. The sub needs to be constructed so that it doesn't screw with the main speaker placements. So carving out that red area behind the screen may not work if that is suppose to be floor to ceiling area.

Not a problem, I didn't realize that was a false wall. You are fine with leaving that behind the screen area open and starting from the original wall you planned, just shorten the original length and increase the depth. See attached.

Now on that picture you posted, it leads me to believe you will be using bookshelves for your mains? If that's the case, they will be way, WAY behind in terms of performance compared to the sub. You will be extremely limited on how much of the sub you can put to use before the mains get harsh and distortion-laden. A great sub needs speakers with great midbass, otherwise the mismatch becomes very noticable. Just something to keep in mind.

What is the false wall going to be made of?

[Cathan]

Right now the plan is to use Ascend CMT's. If in the end they are lacking and I once again have a budget it's an easy upgrade. What's more important is to get the bones of the theater correct from the start.

The false wall will hold the screen, and is made of SMX screen material and black GOM.

[bpape]

Is there a reason why the box has to be over on the one side like that? How tall is this box going to be? I'm very concerned with SBIR issues - especially being different from left to right side which will voice the mid/upper bass in the mains quite differently.

If at all possible, it would be nice to keep the box to less than 30" high and make it symmetric to the room left to right. IOW, wider, deeper, shorter, and centered.

Bryan

[Sonnie]

Or maybe do two boxes... one on each side... kinda like Rodny did on his IB makeover?

[brucek]

Is there a reason why the box has to be over on the one side like that? How tall is this box going to be?

That's up to Cathan. I had it about 5' high, but I don't see why you can't have it any height that you want as long as it houses the two 18" drivers and two 8" ports.

it would be nice to keep the box to less than 30" high and make it symmetric to the room left to right. IOW, wider, deeper, shorter, and centered.

Yep, it could be centered. It may not be the best spot to take advantage of room gain, but it would certainly fit in the center.

(In lieu of any direction), if you accepted 1500 litres of working volume tuned to 12Hz, using two SS RL-P18 D2 drivers and two 8" ports @ 29.5" in length, then (a rough) size of ~30" (Height) x ~50" (Deep) x ~72" (Wide) would be the required for 52.97 cu.ft. (1500 litres) volume. You'd have to account for framing thickness and thickness of panels and bracing and ports and driver volumes, so that you obtain a final interier working volume of 1500 litres (if that's what Cathan wants).

Really rough idea of that below..... You have to get a general idea of what's wanted first and then details would come from that.

theater.jpg

brucek

[Cathan]

That's helpful. Thanks, Bruce.