8-10Hz LLT with a pair of RL-p18's

**Chris in Dallas** · **04-03-07, 08:49 PM**

Well, this seems like a pretty good place to make my first post. I was directed to this forum from another after inquiring about the construction of a sub-subwoofer. I read about the LLT designs, and decided that a pair of the Soundsplinter RL-p18's in a really big box would do the trick nicely.

I'm currently designing in 3d Autocad the addition to our home in Dallas, and, of course, it will have a dedicated theater room. The LLT will serve a second purpose as a raised structural platform for the second row seating. I reckon on a couple dozen cubic feet within. I have in my possession an eager Crown Macrotech 1200 that would like to take it to those big 18's.

The sub-sub will actually take over the lowest end from my pair of Polk PSW 1200's which I will cut off at 28 Hz. I'd like to tune the LLT for 8-10 Hz. From the specs on the Soundsplinters, I think I should be some pretty high SPL's that I'll hear mostly with my bones!

Thanks to the Shacksters for providing this forum. I plan to be around here a lot and will post updates on the design/construction of my dream theater.

**Rodny Alvarez** · **04-03-07, 09:49 PM**

Hey Chris!!! welcome to the SHACK

How many watts on the amp??
Steve is going to love this, single digits tune

, my LLT is tune to 11Hz two 15" RL-ps 35cft its BIG!! and I have to build the other side

, two EP 2500 bridge

.
You need to check Sonnie's LLT.......
http://www.hometheatershack.com/foru...b-project.html

Spoiler

**Chris in Dallas** · **04-03-07, 10:14 PM**

Thanks for the welcome, Rodny! The Crown is conservatively rated at 495 WPC at 4 ohms, and 700 wpc at 2 ohms. I guess I'll run the Soundsplinters in parallel (I assume they are 4 ohm nominal drivers) to get the 2 ohm load (I just want OUTPUT from 28 Hz on down). Here's the specs: http://www.gbaudio.co.uk/data/ma1200.htm

I am pulling the plate amps out of my PSW 1200's, selling them, and using a Hafler P-7000 to drive them in stereo. I'll have one behind each LS50. The Hafler is rated at 350 wpc at 8 ohms, which is how I'll run it, to maintain lower distortion levels in the 28 to 80 Hz range it will be responsible for.

Looking at the truck in your avatar, I'd bet that you'd appreciate my second ride: a lght metallic blue 84 Chevy Silverado 4x4. I'll have to post a pic of that sometime...

**Sonnie** · **04-03-07, 10:26 PM**

Quote:

Rodny Alvarez wrote:

Sonnie is going to move this tread somewhere else

Spoiler

Yeah... I would definitely say Chris deserves his very own thread for this discussion.

Hi Chris and welcome to the Shack!

8-10Hz LLT... that will be awesome indeed...

You've found the right spot and we'll certainly be looking forward to seeing some pics and following your progress.

**brucek** · **04-03-07, 10:31 PM**

Quote:

The sub-sub will actually take over the lowest end from my pair of Polk PSW 1200's which I will cut off at 28 Hz

What manner of low pass crossover will you use with the LLT (at 28Hz) and high pass crossover with the Polks (at 28hz) at their bottom end to get a smooth transition between the two?

brucek

**Sonnie** · **04-03-07, 10:38 PM**

I'm gonna suggest (I'd bet, but I won't gamble even for a cola) that after hearing the LLT, there will quite possibly be no PSW1200's in the picture anymore.

The CX2310 could do the job.

**Rodny Alvarez** · **04-03-07, 10:41 PM**

Quote:

Sonnie wrote:

Now how did you know... :scratch

Spoiler

I'm not an expert but you probable need another amp, so you can run one amp on each sub, using the 4ohm dual voice coil parallel for 2ohm load 700watts

on each sub

My truck is a 96, a lot of

and time

Spoiler

**SteveCallas** · **04-03-07, 11:05 PM**

Quote:

Sonnie wrote:

I'm gonna suggest (I'd bet, but I won't gamble even for a cola) that after hearing the LLT, there will quite possibly be no PSW1200's in the picture anymore.

Exactly. As much as you may enjoy your current subs, two of those SS RL-p18s will just completely dominate them in accuracy (linearity, distortion, headroom) over the entire subwoofer range, not just below 30hz. Using them just below 30hz would be an enormous waste of potential in my opinion, and I doubt I would be able to sleep well at nights, let alone you

As for the subs, I don't see much benefit tuning lower than 10hz, and even that is extremely low (I'd personally shoot for a wee bit higher tuning myself). The best bet would be something like Rodny's project, enclosing an adjacent space, because these drivers like a LOT of volume for a LLT. Let me know if that is an option or if these have to be discrete boxes o tubes within the room.

**Chris in Dallas** · **04-06-07, 06:18 PM**

Quote:

brucek wrote:

What manner of low pass crossover will you use with the LLT (at 28Hz) and high pass crossover with the Polks (at 28hz) at their bottom end to get a smooth transition between the two?

brucek

Hey Brucek, thanks for asking! I plan to use a Velodyne SMS-1. I could use my pre-amp, which by then will be a Carver Sunfire Cinema Grand III or IV, to send 80 Hz and below to the SMS-1, and as the SMS-1 outputs a single signal, I would need to find an external xover to put in that line to split the signal. Hmmm. My Rane AC-22's won't do it (70 Hz bottom), got any suggestions?

As far as smoothness, the SMS-1 could easily take care of that.

**Chris in Dallas** · **04-06-07, 06:30 PM**

Quote:

Sonnie wrote:

I'm gonna suggest (I'd bet, but I won't gamble even for a cola) that after hearing the LLT, there will quite possibly be no PSW1200's in the picture anymore.

The CX2310 could do the job.

...and there's my answer. Thanks! I was really worried I'd have to get a SECOND SMS-1 to do the crossing over, but it looks like I could just use that Behringer after the Velodyne unit. Man, that Behringer goes low...

BTW, in case anyone googles the SMS-1, the software update lets you defeat the subsonic filter for a response down to 5 Hz. Bass eq still is restricted to 15 Hz, but after that, I figure you just take whatever you can get!

ETA: Thanks for giving me my own thread! The reason I took so long to respond is that I was no longer updated via email after the thread was moved. Sorry if that appeared rude.

**Chris in Dallas** · **04-06-07, 06:35 PM**

Quote:

Sonnie wrote:

I'm gonna suggest (I'd bet, but I won't gamble even for a cola) that after hearing the LLT, there will quite possibly be no PSW1200's in the picture anymore.

The CX2310 could do the job.

Oh yes, I thought about just letting the one big super-sub do the job, but I really like having dual subs with my mains in the audible range, and I like having them right up front where they are needed. I've found that down to about 40 Hz, a single sub placed anywhere else is distracting; it draws the ear toward that area, especially if it is placed beside just one of the front speakers. But maybe I'm just imagining things.

**Chris in Dallas** · **04-06-07, 06:54 PM**

Quote:

SteveCallas wrote:

Exactly. As much as you may enjoy your current subs, two of those SS RL-p18s will just completely dominate them in accuracy (linearity, distortion, headroom) over the entire subwoofer range, not just below 30hz. Using them just below 30hz would be an enormous waste of potential in my opinion, and I doubt I would be able to sleep well at nights, let alone you

As for the subs, I don't see much benefit tuning lower than 10hz, and even that is extremely low (I'd personally shoot for a wee bit higher tuning myself). The best bet would be something like Rodny's project, enclosing an adjacent space, because these drivers like a LOT of volume for a LLT. Let me know if that is an option or if these have to be discrete boxes o tubes within the room.

I won't have a sealable adjacent room in my application, so an IB is out. From the product page http://www.soundsplinter.com/rlp18_s...formation.html it looks like they are recommending an 18 cft vented box for a tuning freq of 14 Hz. I am going to be using the second row seating plinth for the enclosure, and it will span the room from side to side, so I can get that kind of volume, and more if ideal. I suppose if I want to tune it to 10 Hz then I need a bigger enclosure. Now that SS has posted all the specs, I guess I can use one of those enclosure calculators.

I suppose I could also just put all my rack gear in the plinth, and build a stage in the front that could contain the mondo sub, and then I wouldn't mind letting it run clear up to 80 Hz like you say. I could even use a pair of the 18's down low on each side of the stage...

Then I could sell the PSW-1200's and use that for financing the SS stuff. Hmm...

**Chris in Dallas** · **04-06-07, 06:59 PM**

Quote:

Rodny Alvarez wrote:

Spoiler

I'm not an expert but you probable need another amp, so you can run one amp on each sub, using the 4ohm dual voice coil parallel for 2ohm load 700watts

on each sub

My truck is a 96, a lot of

and time

Spoiler

I think the Crown should be adequate. The 18's suggesting power supply is 500-1000 watts, and if I use two of them in the 4 Hz model, in parallel (2 ohm load) the Crown pushes 700 wpc. My theater will only be about 14' x 19.5', so I figure that should do the job. Correct me if there is something out of whack about my figurin', please.

**Chris in Dallas** · **04-06-07, 07:10 PM**

Quote:

SteveCallas wrote:

Exactly. As much as you may enjoy your current subs, two of those SS RL-p18s will just completely dominate them in accuracy (linearity, distortion, headroom) over the entire subwoofer range, not just below 30hz. Using them just below 30hz would be an enormous waste of potential in my opinion, and I doubt I would be able to sleep well at nights, let alone you

As for the subs, I don't see much benefit tuning lower than 10hz, and even that is extremely low (I'd personally shoot for a wee bit higher tuning myself). The best bet would be something like Rodny's project, enclosing an adjacent space, because these drivers like a LOT of volume for a LLT. Let me know if that is an option or if these have to be discrete boxes o tubes within the room.

Reading your great LLT essay, I see that a 14 Hz tune would be just great. I guess I'll want to use the 18 cft option. I think the cabinet could be built so that the 18(s) would be mounted facing up, and the port(s) could fire into the room out of the front. That would keep my stage to a height of less than 1' or so.

**Sonnie** · **04-06-07, 07:12 PM**

Quote:

Chris in Dallas wrote:

...and there's my answer. Thanks! I was really worried I'd have to get a SECOND SMS-1 to do the crossing over, but it looks like I could just use that Behringer after the Velodyne unit. Man, that Behringer goes low...

BTW, in case anyone googles the SMS-1, the software update lets you defeat the subsonic filter for a response down to 5 Hz. Bass eq still is restricted to 15 Hz, but after that, I figure you just take whatever you can get!

ETA: Thanks for giving me my own thread! The reason I took so long to respond is that I was no longer updated via email after the thread was moved. Sorry if that appeared rude.

There just happens to be a CX2310 for sale in Classifieds...

Sorry about the thread thingy... I thought it would notify you. I guess I need to start posting my response first so that it will notify you and then moving the thread/post, etc. Then it would redirect you.

Quote:

Oh yes, I thought about just letting the one big super-sub do the job, but I really like having dual subs with my mains in the audible range

Actually I do the same thing sorta... except I run my other pair of subs, which are up front behind my mains, full sub range. IOW, all my subs are crossed over at 80Hz. Of course my other two are SVS PB12-Plus/2's and they are really serious hoss daddy's. They compliment my Dual RL-p15 Behemoth very well.

**Rodny Alvarez** · **04-06-07, 07:51 PM**

Quote:

Chris in Dallas wrote:

Correct me if there is something out of whack about my figurin', please.

Quote:

and if I use two of them in the 4 Hz model

4 Hz model...................

...............

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