LLT Explained

**SteveCallas** · **08-03-07, 09:13 PM**

UPDATE!

I have tweaked and rewritten my entire LLT explanation with the main area of focus reflecting the change in my guidelines regarding amp limiting. This comes as a result of the hard work by member Ilkka and the real world usage of LLTs by enthusiasts and their informative discussions on this forum.

**Zene** · **08-09-07, 06:09 AM**

Steve ... I just got feedback not to use my PA woofer (P.Audio C18-650L) for an LLT, mainly that I need a more linear driver and heavier cone. My 18" has 15% excursion (0.75mm of the 5mm xMax) at 25hz for 100dB vs. a BMS 18" that is 12.5% (1mm of 8mm xMax) at 25hz for same 100dB. Mms of PA is 178g and BMS is 195g.
Seems close enough for me. The approx 260-300 L's tuned to 16hz looks OK.
Is there something else I should consider?
I have not addressed the spider and surround stiffness especially for lower operating levels. It has dual stiff spiders.
Can you help?
BTW, now I get to read your entire first post again for the 10th time. tee hee
Thanks, Zene

**SteveCallas** · **08-09-07, 07:37 PM**

Neither a driver with 5mm nor 8mm xmax is suitable for a LLT, not unless it was something like a 30" driver

**Zene** · **08-09-07, 08:13 PM**

I get no where near Xmax at 110dB+ with this speaker according to WinISD and UniBox as LLT. Excursion is only 1/2 of Xmax.
Why do I need large Xmax?
Low Q speakers work well for higher frequencies, they should do well for subs as well.
I am concerned with it's stiffness not being able to play at low levels. PA speakers were never intended for lullabies.
Zene

**SteveCallas** · **08-09-07, 11:46 PM**

You are of course free to do what you want, I'm just letting you know I definitely wouldn't do it myself, as I know it wouldn't give me the performance I am after, and it wouldn't end up being a LLT. As the frequency lowers, the amount of air that needs to be moved to maintain a certain output level increases exponentially. 5-8mm just isn't enough to do the low end any justice, even with an 18" driver. On top of that, it sounds like your driver is designed for small enclosures, and a <300 liter enclosure tuned to 16hz means a 6" diameter port, which is far from ideal with an 18" driver.

You won't have the proper FR for a LLT, you won't have proper porting, and you won't have enough displacement.

**Zene** · **08-09-07, 11:51 PM**

Thanks Steve appreciate.
Zene

**Brian Hinther** · **11-23-07, 09:37 PM**

I really love this thread. I'm ashamed to admit that I'd never even thought about room gain before you brought it up. But now that you have, and have said most rooms contribute 4-8 db of gain per octave, I am wondering why the graph that you describe as being "too low" isn't closer to right than the one you label "good." Granted the curve could be more shallow, but at 20 Hz it's down 6 db (between 4 & 8), compared with only -2 db on the "good" one.

Your Subwoofer-DIY reference seems to suggest that the ideal curve would be down one db at 30 Hz, and then fall off a cliff down to -9 db at 20 Hz. (Watch out for that first step--it's a killer!)

I'll be the first to admit that designing a sub to be down 9 db at 20 Hz on purpose seems sick and wrong, so what gives? Am I misinterpreting the data? Is the data flawed? Or is this one of those cases where you just do what sounds right and forget about the data?

**SteveCallas** · **11-25-07, 11:04 PM**

For the sub to be -6db at 20hz and still get a flat in room response, room gain would have to start at 40hz and be 6db/octave. Room gain typically doesn't start at 40hz unless you live in a very small room.

**hotshoetom** · **02-04-08, 10:12 AM**

Hi Steve, as a new member here I have to give you a hearty thumbs up for your sonosub...That strikes me as one of the most imposing and "in your face" things I have ever seen in home audio...WOW! Totally impressed. What sort of budget would be required to duplicate your efforts? I have a moderately sized room in my basement I would like to fill with jaw-rattling bass...and have been considering the IB approach but after reading your low tune approach, I feel like the sonosub or a variation thereof may be better overall. Also, where can one get help designing such a thing???? Many thanks for answering my questions.....in advance.

Tom

**SteveCallas** · **02-05-08, 12:46 AM**

The two drivers that seem to most closely resemble the Avalanche 18 I am using in terms of modeled performance would be the SS RL-p18 for $420 and the FiCar Q18 for $309. A decent pro amp is going to cost you about $350. 28" diameter tube was ~$85 and 8" tube ~$12. 3/4" MDF is ~$20 a sheet. Everything else is odds and ends - wood glue, screws, wire, paint, batting, quick disconnects, legs, etc. When I added it all up, in my case, I was able to make two of these for ~$1500.

Best place to get help and advice on building a LLT is here at Home Theater Shack in this DIY Subwoofers - Sealed and Ported Forum

**hotshoetom** · **02-05-08, 11:18 AM**

many thanks for the info Steve....I don't have 1500 to throw at a project like this right now, but might try an alternate approach...an infinite baffle in the basement might do the job without lowereing the SAF too much....saving a bunch of money on the cabinet seems like a worthwhile endeavor when funding limited...

Any "gotchas" to the IB approach??? Other than the obvious thing of having less control over the cone(s) and a higher risk of over excursion of the cone(s)?

hotshoetom

**SteveCallas** · **02-06-08, 01:19 AM**

I'd just give you a heads up that most IB installations can actually be made into LLTs pretty easily. Instead of leaving the rear cavity wide open, you can box it off, making it a large enclosure, and then just add a port. You'll be buying MDF anyway, so another sheet or two shouldn't be a big deal, and 8" sonotube isn't all that expensive. Rodny's experiment in which he converted his two IBs into two LLTs is well documented on this site, and he preferred the benefits the LLTs offer.

**digitalbeast** · **05-03-08, 05:31 PM**

Hello Steve,
I am a new member here and I have been reading many threads on the LLT design, and it has inspired me to try my own DIY LLT sonosub. I am especially impressed with your design philosophy and I want to take this time to commend you on your work, and your generosity to help others achieve there goals.
Steve you seem to be the guru on this design, what driver would you recommend.
I have a preference for a 15" driver, I was thinking of a CSS SDX15, real cheap here in Canada, or a RL-P15. Are there any other 15" drivers that would be better for this design? Enclosure size is of no concern. I am also thinking of a Butt Kicker BKA1000-4 amp. My Home theater is 22' x 20'. Probably no need to mention that I would love to fill all this SPACE with thunderous BASS.
I would greatly appreciate any advice you could offer.
DB

**SteveCallas** · **05-03-08, 08:42 PM**

The SDX15 and RL-p15 would both work great - there is also the Tempest X.

**atledreier** · **05-04-08, 12:31 AM**

I can vouch for the RL-p15. It's awesome! I'd get as many as I could get my hands on with the current TC sounds situation, though.

**sparky77** · **05-04-08, 01:39 AM**

So what would you suggest for a person that happens to have an extra dozen emenance lab12's in they're garage, that is besides a couple pairs of labhorns?

**digitalbeast** · **05-04-08, 08:02 PM**

Thank You for you recommendations Steve and atledreier.
I decided to go for the CSS SDX15, just purchased it today,
only $273.00 CAD tax and delivery included. I can't wait to start building this beast.
What enclosure volume do you guys think would be optimum for this driver?
Same as TC 2000? 320ltrs. I guess I should try out some plots on winisd, but I just wanted to get some advise from experienced builders first.

Thanks

DB

**SteveCallas** · **05-09-08, 11:32 PM**

Specific build questions are better suited to their own threads - this one is more of a general LLT information thread.

**Blaser** · **05-10-08, 01:58 AM**

Quote:

SteveCallas wrote:

UPDATE!

I have tweaked and rewritten my entire LLT explanation with the main area of focus reflecting the change in my guidelines regarding amp limiting. This comes as a result of the hard work by member Ilkka and the real world usage of LLTs by enthusiasts and their informative discussions on this forum.

That's great Steve!

**kjgarrison** · **05-29-08, 11:09 PM**

Hi Steve,

I'm working on a diagram of something maybe a bit unusual in the LLT vs IB category (Was going to be IB, now after looking at all the LLT threads, not so sure.) Would this be a place to ask for some advice? And can Google sketchup files be used here?

**atledreier** · **05-30-08, 12:33 AM**

Start your own thread. You'll get more specific answers thenl, and you'll keep this thread cleaner.

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