RL-p18 with a Linkwitz Transform... good, bad, or ugly?

Has anyone tried this yet?
I originally planned for an LLT, but I am starting to consider an LT design.
LT for a Q0=.684 seems to model really well for a 250l net cabinet in WinISD(unless I am doing something wrong). I also added a 3db parametric at 18 and this thing models flat to 20.4 with -3 at about 15.5 and -6 around 13 with 600w.
Am I doing something wrong when modeling this?

I like the idea of having 2 250l boxes in my room more than 2 650l boxes.

Maybe I haven't found it yet, but there don't seem to be any complete build threads with the RL-p18s in sealed cabinets.

[Owen Bartley]

Mark, that model sounds great. I still haven't seen anyone actually build one of these, so I guess we're still all theoretical. I think this sounds like a great sub, I just don't have the experience to make a reasonably accurate judgment based on the numbers.

[Brian Bunge]

I've done an LT with the original Adire Audio Tumult but not any other drivers recently.

The 250L model looks good without any boost as I'd imagine it'd be very flat down low in room. I think you could skip the LT all together and just use a parametric EQ. I don't really see what reason you'd have for the LT in this design. If you wanted to go with a smaller enclosure and use the LT to transform to a lower Qtc and Fb then the LT would make sense.

Otherwise, I'd just build the 250L sealed enclosure and use the EQ for any low end boost you want to dial in.

[Owen Bartley]

Thanks Brian, that's not only a cost savings, but also probably also sanity-saving with the design and construction of the circuit itself. You'd have to build a seriously beefy box, but what a sub you'd have! I'm pretty sure I remember reading about your Tumult, I think it was one of the subs that got me very interested in LTs in the first place.

[Brian Bunge]

Well, you're going to want a beefy box either way if you want to contain that monster! BTW, what dimensions have you worked up for a 250L box. It sounds pretty huge.

Brian Bunge wrote:

Well, you're going to want a beefy box either way if you want to contain that monster! BTW, what dimensions have you worked up for a 250L box. It sounds pretty huge.

I have two of these monsters waiting for a big wood box.
36"h x 26.5"d x 22"w is about 280L gross. Net is about 250-260 after bracing and driver.
This is a subject that I am torn over. I want to do a LLT but I also want a smaller box. 250L is a lot smaller than 650L especially since I will be building 2 (I have about 6400ft^3 to fill). This looks to be a good compromise, if it works.
I could always do sealed for now and LLT later. If I knew for sure it wouldn't unbalance things too much I would build one of each.
I need to figure out how to add a 3db boost at 18Hz. I currently have a DSP1124 and EP2500.
I thought I read somewhere a little while back, about using one of the Behringer crossovers or EQs to set up a LT. I forgot to bookmark it and haven't been able to find it again.

[Owen Bartley]

Mark, as far as I recall the BFD can't be used as a true LT because it doesn't have the ability to use shelf filters. If Brian is right (and I'd bet that he is), this alignment may not need a real LT, so you could do some selective boosting and cutting with the BFD to add a little weight to the bottom end. You could, for example, insert a wide boost at 15Hz, and a narrower cut at 8 or 10Hz for a little driver protection. I guess you'd have to play around with the settings a bit, but it sounds very promising.

[Warmon]

NewbieMark wrote:

IThis is a subject that I am torn over. I want to do a LLT but I also want a smaller box.

So I guess this means you're rethinking that decision to replace the A/V rack you talked about on "that other forum"? That's a nice piece and I wouldn't replace it unless I had to.. Plus, it will be a lot more work and you won''t have too much flexibility on placement. Perhaps you should make a list of all the pros and cons to each alignment...may help to figure out what's more important to ya.

I hope you decide to go sealed. I wanna see somebody break new ground and do something nobody else is doing with these drivers...

Warmon wrote:

So I guess this means you're rethinking that decision to replace the A/V rack you talked about on "that other forum"? That's a nice piece and I wouldn't replace it unless I had to..

Correct.

Warmon wrote:

I hope you decide to go sealed. I wanna see somebody break new ground and do something nobody else is doing with these drivers...

LOL...I just don't want to be that somebody.
I really want to give this a shot, so I may try one and see what happens. I might build one of each(sealed and LLT), to compare side by side. If I don't finish the boxes, I will only be losing a couple sheets of MDF, glue and time on the sealed box. I think it will work good sealed, but the cost involved in the extra power requirements(another ep2500) and DCX is the major downside for sealed.
Ultimately, I think I will end up with two LLTs.

BTW...As I understand it, and I may be wrong(nothing new there). The DCX2496 can simulate a LT. I know this models fairly well without the LT, but I want that extra umph in the infrasonics that an LLT offers. I think the LT simulation will get me there at the expense of power.

[Warmon]

NewbieMark wrote:

I think it will work good sealed, but the cost involved in the extra power requirements(another ep2500) and DCX is the major downside for sealed..

That's the down side alright...more

But, no matter how you slice and dice it, every alignment is a compromise of some sort. i waffled a bit too, but ultimately decided to go sealed - three 12's in three boxes.

Hope you have a forklift - gonna need one...

[Owen Bartley]

NewbieMark wrote:

The DCX2496 can simulate a LT.

I think you're right on this Mark, since I think it has the capability to add shelf filters. Actually I think a few Shack members are using the DCX in this way, so if you run a quick search you might find some potential sources for direct questions if you need them.

[Ricci]

I hope someone tries these sealed at some point. Both enclosures together would be smaller than one big vented box and should still have solid output down deep.

[Owen Bartley]

I'm dying to do this, but I'm fairly broke right now, and have an HT improvement budget of approximately $0. If things change in the near future (like if I pick up a big client or two) I'll be doing it. Unfortunately, all I can do right now is doodle enclosures, play with the design software, and egg others on!

Yeah, yeah...Now look what you made me go and do.


I drew this up using double wall, window bracing, and tripple wall baffle around the sub. All this excess bracing really ate up the volume. It looks like it is about 224L with double wall. If I don't use the double wall on the top, bottom, and sides(still double on front), and just use the bracing, I am back up around 260L.
How about some opinions on this thing?
Anyone have a DCX laying around/for sale?

[Brian Bunge]

I'm at work right now so I can't run the numbers, but what kind of Qtc does 224L give you? If it's still in the .6-.65 range I'd say stick with the double/triple walls and bracing.

[Owen Bartley]

Way to go Mark!! I assume you're using two layers of 3/4" MDF for your walls. How about using one layer of MDF and making the inside layer out of 1/2" plywood? It would get you a little more volume, and I've always thought that varying the material helped to dampen the box, but I may be wrong. Even just by expanding one dimension by an inch could squeeze a little more volume out too, it looks like some more depth wouldn't hurt.

Brian Bunge wrote:

I'm at work right now so I can't run the numbers, but what kind of Qtc does 224L give you? If it's still in the .6-.65 range I'd say stick with the double/triple walls and bracing.

Brian
I am work right now too, so I will have to post it later tonight.

Owen Bartley wrote:

Way to go Mark!! I assume you're using two layers of 3/4" MDF for your walls. How about using one layer of MDF and making the inside layer out of 1/2" plywood? It would get you a little more volume, and I've always thought that varying the material helped to dampen the box, but I may be wrong. Even just by expanding one dimension by an inch could squeeze a little more volume out too, it looks like some more depth wouldn't hurt.

Yes, I am using double layer 3/4 MDF. I had actually though about using 3/4" oak veneer ply on the outside, but I would rather test this setup first before sinking that kind of money into it. I could use ply on the inside, but I don't know much about how it would affect dampening either. Maybe someone with more wisdom will chime in on this.

Mark

[ISLAND1000]

I'm currently using a Crown XTi 4000 to drive an LMS 5400 in a 6.8 cu. ft. (approx 190L) sealed box. I modeled the two in WinISD adding the Linkwitz Transform filter type selection to extend the response to 12Hz @ -3db.
The Crown's DSP PEQ can simulate the response curve of the Linkwitz Transform circuit very well plus modify for in room nodes and nuls. The result has been stunning.
Ilkka is currently experimenting with the same setup (sealed box with LT) but different amp plus EQ in a 100L box. His first impressions are very good.
The RL-p18 models very similar response properties to the LMS 5400 with the major differences being power handling, excursion, and apparent amplifier load. The driver box combination is flat to 20Hz and will easily reach 12Hz @ -3db. The Linkwitz Transform selection needs an f0 = 36Hz and an fp = 12.00Hz. The "group delay" is a mere 9ms @ 20Hz! This is a huge difference between a sealed box and either the ported or IB design.

[Warmon]

ISLAND1000 wrote:

The "group delay" is a mere 9ms @ 20Hz! This is a huge difference between a sealed box and either the ported or IB design.

That's the thing right there!...ported [in MC Hammmer voice] can't touch this! Mark, that HD box is beautiful man and I wouldn't change a thing - stuffing will make up any lost volume and add dampening...no worries.

[Warmon]

NewbieMark wrote:

How about some opinions on this thing?

Dropped by to see the latest. Just wanted to mention something about the braces and driver mounting. You see where the horizontal and vertical bracing intersects with the driver cutout? Assuming you want to mount the driver aligned properly so that the logo on the dust cap or cone is level, you won't be able to use the normal mounting kit nuts there unless you mount them first before you install the bracing. I know, cause I made this mistake. You need to mount them on the back first slightly recessed. Once you have the brace installed, drill a hole smaller than the bolt threads through the front side so the bolt can seat all the way in.

[Brian Bunge]

I much prefer threaded inserts over T-nuts. They work much better and are less likely to tear out.

[Warmon]

Brian Bunge wrote:

I much prefer threaded inserts over T-nuts. They work much better and are less likely to tear out.

Brian, is this the type that you're using?

http://www1.mscdirect.com/CGI/NNSRIT...97428&PMT4NO=0

[thxgoon]

Things are looking good! I hope you do have the chance to make one of these because I would love to hear your listening impressions!

Brian Bunge wrote:

I'm at work right now so I can't run the numbers, but what kind of Qtc does 224L give you? If it's still in the .6-.65 range I'd say stick with the double/triple walls and bracing.

Brian,
Sorry I didn't get back to you on this last night.
I am showing .686

ISLAND1000 wrote:

I'm currently using a Crown XTi 4000 to drive an LMS 5400 in a 6.8 cu. ft. (approx 190L) sealed box. I modeled the two in WinISD adding the Linkwitz Transform filter type selection to extend the response to 12Hz @ -3db.
The Crown's DSP PEQ can simulate the response curve of the Linkwitz Transform circuit very well plus modify for in room nodes and nuls. The result has been stunning.

That's a nice setup you got there.
Wish I could afford a crown right about now. I will trade you my EP2500 for it.
I still need a DCX.

ISLAND1000 wrote:

The RL-p18 models very similar response properties to the LMS 5400 with the major differences being power handling, excursion, and apparent amplifier load. The driver box combination is flat to 20Hz and will easily reach 12Hz @ -3db. The Linkwitz Transform selection needs an f0 = 36Hz and an fp = 12.00Hz. The "group delay" is a mere 9ms @ 20Hz! This is a huge difference between a sealed box and either the ported or IB design.

When I modeled it again last night, it looked like it would take over 4000W to reach 12Hz on the apparent amplifier load. That's just a little out of the conservative 500-1000W range specified for these subs. I would have to fill the box with liquid nitrogen to keep from melting the coils if that is the case(wonder what that would do to the q).

thxgoon wrote:

Things are looking good! I hope you do have the chance to make one of these because I would love to hear your listening impressions!

I am still seriously considering one of each, LLT and Sealed. Hopefully with a DCX and 1124, I could clean up any crazy room response and smooth the transition between the two.

[Brian Bunge]

Warmon,

No, more like these, the ones with the lip on them.

http://www1.mscdirect.com/CGI/NNSRIT...17945&PMT4NO=0

They screw into the wood and usually require an allen wrench to install. I use these to install spikes on the bottom of subs and towers as well. Of course, any driver under 20-30lbs. I just use the coarse thread panhead screws that PE sells. But for my Tumult I used the inserts.

Mark,

Hummm.... I think .68 isn't too bad. Is that with or without stuffing? I generally prefer something closer to .6 or so. Let me model it again myself this evening and see what I come up with. I think possibly going double-walled but thinner layers internally might get us a little lower.

I'm still debating on whether to go with dual RS 15" HO's or go with a single, higher excursion driver. Whatever I do, I'll probably have to keep cabinet size down so I'll probably re-use my LT circuit and change out the parts values for the specific design. Thankfully I built it so I could swap parts without having to break out the soldering iron.