My first LLT sub build :)

**audio newbie** · **01-10-08, 12:04 AM**

I'm just finishing my first LLT build and had to share my excitment! After a LOT of reading here (and pressure from my speaker engineer friend

) I finally built a LLT sub... ok actually two LLT subs

The two subs were built with a total of 8 10" woofers in a 25ft^3 box, tuned to 16hz (8 4"x32" ports).
It mounts in the garage directly behind our entertainment center. Two 11"x41.5" holes were cut in the living room (had to do that while the wife was on vacation

) behind the enterainment center. The nice thing is that you cant see anything unless you look behind the enterainmnet center.

Based on the computer modeling, the plan was to use some slight EQ'ing to get the response flat down to 18hz. After the first test of the system, I'm so blown away that I'm having second thoughts about wanting any more low bass output! Things at the opposite end of the house are rattling

Once I figure out how to get consistant results from REW, I'll post the in room results. I just used REW for the first time a couple of days ago... still in the learning curve part.

If you are interested in some pictures, they are here-
http://home.comcast.net/~jhidley/Subwoofers/index2.html

If you happen to notice the uneven mounting strips, the local hardware store ran out of metal. Also, the tan boxes under the subs are my old 10" sealed sub boxed that I was using until this project.

I also wanted to thank everyone here who has posted there sub building projects. I probably wouldnt have made the commitment to cutting holes in the living room if it wasnt for all of the happy sub stories!

**bonehead848** · **01-10-08, 02:07 AM**

Wow, that box mounting was really creative. Its great to see how happy you are with the sound!

**SteveCallas** · **01-10-08, 02:10 AM**

Congrats on the build

I don't want to be a party pooper

but that's really more of a normal ported sub than a LLT, as the tuning isn't <=15hz, the ports don't have clearance at lest equal to their diameter in all directions, a high pass filter is said to be needed in the design, and there won't be a ~4db/octave rolloff from the lowest room node to tuning.

Should still be a great sub though by all means.

**Owen Bartley** · **01-10-08, 03:25 PM**

Wow, it may not be an official LLT, but it's still a honkin big sub. I know you're getting some good rumbling, which is key, but how's the overall response? I assume because you have so many smaller drivers they must handle the regular (as in not extremely low) bass pretty well too, but I don't really have any basis for that.

**Warmon** · **01-10-08, 10:08 PM**

Quote:

audio newbie wrote:

The two subs were built with a total of 8 10" woofers in a 25ft^3 box, tuned to 16hz (8 4"x32" ports).

Hi there and thanks for posting. Did you use the NPT-11-075-2 NHT Sub2 Subwoofers? Is it true?...8 of these are veerrrrry scary?

**audio newbie** · **01-11-08, 12:41 AM**

Steve - I wasnt really shure how to classify the sub. LLT seemed like the best guess.

Owen - The overall response seems excellent so far. I havent had a chance to EQ it yet but already I'm thinking this will probably be the best sounding sub I'll ever build.

Warmon - Yes I did use the NHT NPT-11-075-2. $160 for all of them... I'm still in shock. Actually I am scared. Running a 18hz test tone (weakest SPL of system) I got worried that the window next to the entertainmnet center was going to break. It had to be flexing at least 1/4 inch so I gave up before finding out the limits.

Here is a graph of the response at the wall opening. I set the low limit to 10hz if anyone cares to see how the roll off is.

And one of the in room response with the standard limits set. Check out the room modes - yikes!

**Eric Mathews** · **01-11-08, 02:42 AM**

thats pretty nuts man, i would have put that in my living room!! but then again i dont have a wife i have to please lol. nice furniture too looks nice and comfy.

**Warmon** · **01-11-08, 09:00 AM**

Nice! I am in the process of buying four of these NHT NPT-11-075-2's for my next project - sub nightstands for the bedroom.

**thxgoon** · **01-11-08, 10:50 AM**

That thing is enormous! Interesting build thanks for sharing!

What are you using to power them? Any thoughts of using a BFD?

**Owen Bartley** · **01-11-08, 08:48 PM**

Nate that looks like a pretty good in room response graph. If you wanted to get picky about it, it should be pretty easy to tame those peaks and the dip in the middle, and maybe even introduce a little boost at 18Hz or so to flatten you out down low. You wouldn't even need to worry about building in a house curve!

**audio newbie** · **01-12-08, 01:45 AM**

Thanks to all for the feedback.

I plan to get a BFD this week based on all of the overwhelming success everyone here seem to have with it. It should get the response reasonably flat down to around 18hz. Pretty wimpy compared to thxgoons system, but I think I'll be ok with that

I will definatly post before and after graphs for everyone if I get a BFD.

I'm only using a 250W amp (NHT A1) to power the subs. WINISD is calculating 119db which should be plenty for me. WAAAYYY to much for the wife. My rear projector tv gets blurry on the lower frequencies as it is. I dont think it would be enjoyable to watch if the SPL's get much higher. Might be fun for an audio demo though

Warmon - keep us posted with your nightstand project. The quality of your "three sons" was incredible!

**Owen Bartley** · **01-14-08, 09:39 AM**

Nate, don't worry about not hitting way down low on the graph. I was actually pretty shocked to see my sub's graphed response, and that it was rolling off as high as it was. From the sound and feel alone I figured I was dipping a lot lower. I guess all that matters is that it sounds good, not how it looks on paper! (at least that's what I keep telling myself!

)

**audio newbie** · **02-13-08, 12:25 AM**

Here is an "after BFD" graph at the listening position. I'm still trying different house curves, this is my baseline.

**thxgoon** · **02-13-08, 01:02 AM**

Wow, most would kill for that kind of response. Good job!

**SteveCallas** · **02-13-08, 02:00 AM**

Very nice and flat

To pick nits, I'd see if you could soften that very sharp rolloff a little bit by using a wide but small amount of attenuation ~20hz. That very sharp rolloff will be causing some ringing, but whether it's audible or not is debatable.

**audio newbie** · **02-17-08, 01:01 PM**

REW got the response close to flat. Manually tweeking the BFD from there really helped.
Steve - when you say ringing, I think of a speaker or box harmonic. I dont know enough to understand what would cause that from a steep roll-off. Can you explain what causes that? Also, I'm pretty sure the x-over I'm using has a built in 15hz HP filter and the sub tuning ended up at 15hz. Does ringing occur when the box rolls off that quickly, or does it happen when the FR of the system rolls off that fast (I got a double wammy from the box and the x-over both at 15)?

Thanks

**SteveCallas** · **02-18-08, 12:01 AM**

It doesn't really matter how it is caused, but when there is a sharp rolloff like that, there will be built up energy created anytime frequencies near that region are asked to be reproduced, usually resulting in ringing or harmonics. You can read a bit more about this in my LLT Explained post. You can also see a more extreme example with Ilkka's measurements of the Axiom EP 600 here. Notice how the distortion, group delay, and spectral decay take a big hit due to the extremely sharp rolloff. Obviously your scenario isn't nearly that bad, and it may not be audible down that low, so I wouldn't lose sleep over it or anything, but you may want to experiment with a gentle rolloff starting a bit higher up in frequency on a rainy day.

**Owen Bartley** · **02-19-08, 01:02 PM**

Steve, is that effect present anywhere in the frequency of a speaker with a sharp rolloff? I'd never really thought about the side effects of having a very steep rolloff curve, just figured that it may sound odd. Would this occur naturally due to the speaker just running out of gas at low frequencies sometimes, or is that usually more gradual?

**SteveCallas** · **02-19-08, 07:04 PM**

This should take place in any frequency range. If a speaker runs out of steam on the low end because of enclosure size (air spring) or a high pass built in the crossover, the rolloff shouldn't be all that sharp, and there shouldn't be as much transient degredation. If it runs out of steam due to overexcursion or some sort of suspension compliance issue, then yeah, it would happen, and it would be pretty bad.

Advertisement