LLT Explained

[davepete]

WillyD wrote:

I am sorry, but are you saying xmax is an informal standard but Vd is set in stone as peak to peak displacement?

Thats a bit odd, don't you think?

Yes, it is. I suppose Vd might not be set in stone, but I do believe it's typically calc'd using peak-to-peak excursion. In any case, I suppose we could check with LinearTeam to see which way they intended the Xmax to be entered. A definitive answer on this would be nice.

Xmax is almost always given as the one-way linear excursion. I can't think of many examples where it isn't. Its not our fault that in WinISD, the formula used to calculate Vd is simply xmax x Sd, when usually it is 2 * xmax * Sd. I don't know why you think you need to put in the peak-to-peak xmax simply because of this.

"Having the right Vd value for your model" is completely irrelevant. That value it gives you for Vd is not used in the actual simulation. You only need to pay attention to what the simulation gives you (i.e SPL)

Absolutely. I was only using Vd as a means to understand how to enter the Xmax.

And you're correct about the resonance, 156Hz shouldn't be much of an issue. Do you actually have any intentions of building an 5400 LLT? That would be interesting..to say the least.

Yes it would. I don't know that I'll do it using the LMS driver just yet, but I'll probably put an LLT together using either a 12" or 15" TC-2000 to evaluate it vs my sealed subs. I'm leaning toward using Sonotube in this effort, even though I've never built a sonosub before. The larger enclosures required for LLTs would make MDF enclosures extremely heavy and difficult to work with. So, for those of you who have built sonotube enclosures and don't mind offering up some of your wisdom on what works and what doesn't, I'd be interested in hearing it. Stuff like how to make an endcap. A Jasper Jig will cut a disk about 18" in diameter, but not 24" or 30". How is it normally done? I suppose I could rig something to use as a pivot for a router...

[WillyD]

Well, I built an LLT using the 15" TC-2000 and have been very pleased with it so far.

Yeah, a 12-13ft^3 MDF enclosure would be pretty **** heavy, which is one of the main reasons I chose to go the sonotube route.

Most folks make their own jig to cut the big diameters, but there is a jasper jig available that is capapble of much larger diameters. http://www.rockler.com/product.cfm?page=5960

[Exocer]

SteveCallas wrote:

The RLp15 LLT design doesn't suffer from this because I accounted for it in the design. 260 effective liters with a ~15hz tune minimizes the discrepancy in the tie in of port output to driver rolloff enough that it isn't a significant issue.

Right, it isn't a significant issue...thats exactly right. If the issue can be resolved with proper volume and tuning frequency, then its totally possible to take the same precautions with another driver that may also suffer from the effects of high Bl and low Qts in this alignment obviously. But keep in mind, we were talking about the driver itself and how it effects the entire allignment...not one of your designs.

SteveCallas wrote:

That's because an it's an in room measurement room gain and/or reflections easily mask any small FR changes.

That pretty much goes without saying...and I never said in-room measurements should or normally do look like simulations. This was said only in reference to a comment you made about port output and driver rolloff... at this point its a non-issue even with drivers with high bl and low Qts because we account for them in the design phases, except for those extreme situations...like a Tc-5200 for example.

SteveCallas wrote:

To match the simulations, you'd want to do a ground plane measurement.....since that's not very easy, close mic measurements of the drivers and port with no crossovers in play is the next best option. Ryan happend to do something close to that, except he left the 100hz crossover in play.



You take out the crossover and the upper frequency bass will be even higher in magnitude. In the case of Ryan's specific design, max output should be somewhere in the neighborhood of 110hz. You combine the close mic driver response with the port output and you have a response that looks VERY similar to the simulation. All said and done, the simulations are very accurate. A ported sub response is no more difficult or no less accurate to predict than a sealed sub with an EQ boost (the EQ boost is replaced by port output).

The above also goes without saying, and is certainly good information for people to know

SteveCallas wrote:

Aside from the issues a resurgence in port output will create if left unattended to, the bigger problem is that such drivers that are prone to that want smaller enclosures to get away with lower tunes. This goes against being able to create an affective LLT, and this is why the RLp15 is ALMOST not a good choice. Much smaller than 260 effective liters and you'd fall into port troubles as well as reduce low end efficiency to the point that in room response probably wouldn't be as flat as it is.

Whether or not the Rl-p 15 is or isn't a good choice for an LLT alignment was never questioned..............not by me or anyone else in this thread IIRC. There are many other great things about the driver that make it suitable for this use but having a relatively high bl and low qts isn't its strong point for reasons already discussed here.

Will, **** thats huge

[SteveCallas]

This was said only in reference to a comment you made about port output and driver rolloff... at this point its a non-issue even with drivers with high bl and low Qts because we account for them in the design phases, except for those extreme situations...like a Tc-5200 for example.

How many other high Bl and low Qts drivers have been used in LLT designs? The problem is as I mentioned, to resolve the issue of a resurgence in port output one must use a smaller enclosure with a lower tune, and this gets away from a successful LLT design. Try making a LLT with a RLp12 D2 - just ain't gonna happen. The RLp15 just makes it. The reason I keep saying that is to make the point that high Bl and low Qts work against a LLT design.

[Exocer]

Couldn't answer that as I'm nowhere near qualified to answer that. I haven't kept track of every LLT design built Plus, Its totally irrelevant to my entire post, even the section you're quoting.

The problem is as I mentioned, to resolve the issue of a resurgence in port output one must use a smaller enclosure with a lower tune, and this gets away from a successful LLT design.

Correct, but...now where did I say this wasn't the problem? An Rl-p 12d2 LLT just would not happen for the same reasons (although not to the same degree) an LMS-5200 LLT would not work. Your observation (and pretty much common knowledge for people that can read/understand programs like Unibox or WinISD etc) regarding Low Qts/High Bl drivers and the methods of overcoming those two factors hasn't been challenged in this entire thread and SHOULD be noted. We're agreeing with each other, Gosh!

So I hope that at this point everyone understands why low Qts/high Bl aren't something to look for to use in an Xl-sized Ebs alignment...its been repeated enough times in this thread

Now, Someone build me a large and low tuned Sono for my 1030ft^3 bedroom!

[davepete]

WillyD wrote:

Well, I built an LLT using the 15" TC-2000 and have been very pleased with it so far.

Yeah, a 12-13ft^3 MDF enclosure would be pretty **** heavy, which is one of the main reasons I chose to go the sonotube route.

Most folks make their own jig to cut the big diameters, but there is a jasper jig available that is capapble of much larger diameters. http://www.rockler.com/product.cfm?page=5960

I wasn't aware Jasper made a larger jig. Thanks for the pointer, Willy.

BTW, what are the particulars on your TC-2000 LLT? I was looking at using the TC2K 15" SVC, going about 13 cu ft with a 13hz tune and three 4" ports.

[WillyD]

NP.

I used the SVC model as well, and the enclosure is roughly 335liters net, tuned to around 14Hz. I used a single 6" double-flared port from PSP, and I am happy with it.

http://s27.photobucket.com/albums/c199/wadeere/Sonosub/

Here is the thread that chronicles the entire build.

http://www.avsforum.com/avs-vb/showthread.php?t=725955

[davepete]

Looks like nice work. What kind of carpet is that you used? How did you attach it to the tube?

[SteveCallas]

Plus, Its totally irrelevant to my entire post, even the section you're quoting

Your observation (and pretty much common knowledge for people that can read/understand programs like Unibox or WinISD etc) regarding Low Qts/High Bl drivers and the methods of overcoming those two factors hasn't been challenged in this entire thread and SHOULD be noted. We're agreeing with each other, Gosh!

I guess the part I am misunderstanding or getting hung up on is this:

at this point its a non-issue even with drivers with high bl and low Qts because we account for them in the design phases

It's only really been accounted for with a design for one driver, and it just gets by. In fact, the main reason it had to even get by was because there was no other quality 15" driver available at a reasonable price from a reputable dealer from about Sept. '05 to something like early summer '06. Ideally, such things shouldn't have to be worried about or dealt with (ideally ). If some wanted a good LMS driver to use for a LLT, the 4000 would be it aside from its poor sensitivity, so it would be nice if the 4100 was similar with just a more efficient or sensitive motor.

[Exocer]

Ahh, yeah I understand that completely. That was the time when I first started getting into DIY subs...unfortunately.

Anyway, I hope the 4100neo proves to be a good LLT contender. It'll be good to have yet another option out there...especially after that dry spell you mention. Its slowly beginning to look better for DIY again. From what I've heard it'll model very similarly to the LMS-5400 which will be a good thing.

Can't wait for that rl-p18 either. Its going to be ridiculous.

[WillyD]

davepete wrote:

Looks like nice work. What kind of carpet is that you used? How did you attach it to the tube?

Marine carpet from Lowes.

Contact cement.

[soho54]

I wasn't aware Jasper made a larger jig.

Yes, and Rockler is where I bought mine. Just be aware that it only has 1/4inch stops, which can be a problem. Be prepared to put a custom stop/hole in it.

[SteveCallas]

Just a heads up, an Avalanche 18 driver has become available. PM me for details if you are interested - it is essentially the ideal driver for a LLT.

[hardman]

Steve,

Recently, a friend asked me to help assist him in putting together a “budget” home theater setup. Together we decided to start with a subwoofer as our first project. Our budget for the sub is about $400. I have this plate amp on order http://www.apexjr.com/Apexsenior.htm . Side note… this plate is on special until the end of the month for $125.

I stumbled upon this thread today (not really had a ton of time to read all the info at AVS) and like what I have read so far. While the RL-P15 and TC2000 15” drivers are a great value and work in an LLT subwoofer, I think the needed power and cost of these drivers blows our budget. Which leads me to my question… is there a 12” option out there suitable for an LLT?

Using the T/S recommendations outlined in this thread, would the new CSS SD12 fit the bill http://www.creativesound.ca/details.php?model=SD12 ? How about the new TC DB-500 12”, or even the TC1000 12”?

One thing in our favor is the WAF isn’t opposed to a large enclosure aside from the finished product needs to match the existing color/finish of the entertainment wall unit. Which sparks another question… is there any benefit in using a sona tube over an MDF/BB plywood cabinet? I am afraid the cabinet guy is going to have a hard time making a cardboard tube look like painted knotty alder.

Thanks,
Chris

[hardman]

Well I have had a little more time to play around with Unibox and also read more on the web about LLT designs. From what I have been able to gather, the 15” drivers previously mentioned are still the best options. However, I am determined to make a 12” driver work. Of the drivers in the 12” range the CSS SD12 seems to be the best. Here is what I have come up with so far...

Will someone please comment on this proposed design?

[SteveCallas]

Well you'd want to avoid the resurgence in output, you want a smooth, shallow rolloff prior to the 4th order rolloff below tuning. Without modeling this driver, I just don't think a 12" will really be suitable without giving up too much in the more usable bass ranges. Larger drivers "get away with it" because the headroom is already typically more than enough in higher bass frequencies, so some efficiency is shifted down low. I'd go a little smaller, raise the tuning to ~19-20hz, use the 18hz highpass in the plate amp, and end up with a nice subwoofer

[hardman]

Steve,

Thanks for your reply… Your right! I have had a very difficult time getting a 12” driver to work. In the end I really want to avoid doing another boring sealed sub. I was also hoping an LLT sub could cure me of my "ported is bad" stigma. It’s beginning to look like maybe this isn’t the project to go LLT on.

Well either way my interest is perked and hopefully sometime in the future I will be able to experience the LLT subwoofer.

Before I completely abandon the idea, do you mind taking a look at the CSS SD12? I did as you suggested and changed the volume and tuning frequency (120 liters, 19 Hz, 5” port 31” long) I know this configuration doesn’t provide the desired roll off, but it is next to impossiable to get the desired roll off without generating very low port resonance. Please take a look at the attached graph and let me know if the CSS SD12 is really worth porting.

Here are the driver specs from Creative Sound’s website. Re: 3.6, Le:1.45, Fs: 23.3, Qms: 2.87, Qes: 0.447, Qts: 0.387, Vas: 83.3, Cms: 0.25, SD: 490, Xmax 19.5, Xmech: 32, BL: 14.6, Mms: 186.4, SPL: 85.6.

Thanks again for your imput.

[SteveCallas]

To give you an idea of what something close to a LLT would be like with this driver, I'd go 140 effective liters with a 4" diameter port that is 25" long being fed with ~400 watts. Unfortunately, this still wouldn't meet the criteria, and such a design has port chuffing issues and might not achieve "enough" headroom.

What I would aim for is something like 150 effective liters with a 5" diameter port (if possible) that is 24" long being fed with ~600 watts and using a 17hz 2nd order highpass. Is it guilty of the majority of traditional ported subwoofer issues? Yeah, but hey, considering it's a 12" driver, overall performance looks pretty good.

[hardman]

Your suggestions/info confirmed the same issues I was running into too. The 140 liter option will suffer port noise at about 100 watts and even the 150 liter, 5” X 24” port suggestion runs into port chuffing around 200 watts (provided my sims are accurate). Again, thanks so much for your help. Even though I will most likely end up building a sealed sub, unless I can convince my friend to spend more money on a larger driver, this has been a good learning experience.

I am beginning to questions my own current stereo subs and think maybe an LLT TC2000 is in order. I have a pro amp that is about 1100 watts bridged into 4 ohms...

[WillyD]

I am beginning to questions my own current stereo subs and think maybe an LLT TC2000 is in order. I have a pro amp that is about 1100 watts bridged into 4 ohms...

Yes, do that.

[kano32]

SteveCallas wrote:

Just a heads up, an Avalanche 18 driver has become available. PM me for details if you are interested - it is essentially the ideal driver for a LLT.

I sent you a PM. I was goint to use a Mach5Audio MJ-18 (due to budget reasons) but I may be interested in the Avalanche.