Monkey see, monkey do... two RL-P18s for me too! - Home Theater Forum and Systems - HomeTheaterShack.com

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post #1 of 151 Old 10-02-07, 04:23 PM Thread Starter
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LLT "Lite" with dual RL-P18s (was: Monkey see, monkey do...)

Well, normally I would hate to be so unoriginal... but in this case I must make an exception! After countless hours reading and researching, both here and on AVS, I've reached the inevitable conclusion: the RL-P18 is the way. Hard to argue with 6 liters displacement.

First off, I want to thank [email protected] for fast and courteous service, including prompt and hassle-free shipping. The pair of RL-P18 D2s arrived in my office yesterday and I have to say THE PICTURES DO NOT DO THEM JUSTICE. Those of you who own them know what I mean. They are jaw-droppingly massive and gorgeous drivers.

I also have to give credit to SteveC for his in-depth explanation of the LLT alignment and its many virtues. I was "this close" to building a sonotube, but ultimately decided a box (or two) would fit better in my HT room. To that end, I've definitely been inspired by ScottS, Blaser, and Tjambro and their monster RL-P18 subs.

I'm also impressed by the passion and generosity of guys like Collo that share freely the results of a lot of research and publish handy software programs to assist in building subs. The same goes for the makers of WinISD, Unibox and REW -- although I am not personally acquainted with them. Finally, let me recognize the Home Theater Shack for providing a valuable alternative and more "focused" venue for sharing these passions.

This is my first DIY speaker/sub project. It is similar to what others have done here but perhaps a little more "modest", if you can even use a word like that in this context. Here's the overview:

Two RL-P18 D2 drivers, each in its own 17 ft^3 net cabinet tuned to 14.5 Hz.
Two 6" inch ports in each cabinet, with a 1.5" radius flare at both ends.
Both subs powered by QSC RMX 1850 HD, rated 600W into 4 ohms x 2 channels.
BFD 1124P to be ordered soon.

So, I will be asking questions and posting a lot of pictures in the days and weeks to come. I appreciate all the help I've gotten so for and hope I can return the favor somehow, some way, in due time.

Bradley

P.S. I sold my Def Tech PF15TL+ subs the other night, so I am now 100% subwooferless and therefore highly MOTIVATED to get the RL-P18 show on the road.

Last edited by Bradley; 10-09-07 at 03:45 PM.
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post #2 of 151 Old 10-02-07, 04:42 PM
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Re: Monkey see, monkey do... two RL-P18s for me too!

The RL-P18 is a good choice. There are a lot of people who are happy with them. 17 ft^3 net is a big box. What are the dimensions going to be?



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post #3 of 151 Old 10-02-07, 04:50 PM Thread Starter
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Box design.

I'm going to install Google Sketchup tonight and start learning how to draw boxes (love the 3D drawings NeoDAN on AVS has posted). Box material selected is 3/4" MDF. Tentative dimensions:

27.5" high
46.0" wide
30.0" deep

Driver to be centered on front panel. Twin 6" ports exiting on side panel. MDF cross bracing throughout: all the way down the middle "long wise" and at 3 places "cross wise" (spaced about 11.5" apart).

The height limit is based on what will fit under my projection screen and fit through a standard 30" doorway (with trim on it). The width is mostly limited by the size of the sheet of MDF, so it could potentially go up to a max of 49". The depth is my preference as to how far forward I am willing to have them "protrude" from where the projection screen is. Pictures of the area in question coming soon.

Edit: I'm at about 19 ft^3 using the internal dimensions, minus about 1.3 ft^3 for the ports, 0.2 ft^3 for the driver, and the rest for bracing. That sound about right? Calculating the actual volume of all the bracing is going take some time once the brace design is worked out in detail.

Last edited by Bradley; 10-02-07 at 05:03 PM.
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post #4 of 151 Old 10-02-07, 05:45 PM
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Re: Monkey see, monkey do... two RL-P18s for me too!

Ahhh, two RLp18's will be a HUGE step up from a single Def Tech 15. I know, I had the same one. (well, not the + version. Same thing but yours has a slightly bigger amp.)

I had to use the full length of the MDF boards, myself. Gotta be careful at the lumber yard. Make sure before you leave to check if they are a full 49".

First off, you are fine shape regarding the alignment. I knew I would have awesome room gain and I love being able to go real low so I opted for an 11hz tune. 14.5hz should get you awesome output. At some point you may want more, get a second amp. I may need to get another as well as I am using a single EP2500 to run both. Havent clipped it once yet but then I may never...heheh.

Don't know a whole lot about shaping a box and all that. I just know how much I need, so you may have to get someone to throw up a box for you if you're unsure.

One thing I would change....go with an 8" port if possible. I think you will be much less likely to run into chuffing if you push them to the extreme. Dont know about your bass habits. EDIT: Ooooh, yeah. I just ran the sims on a single d2 with 600w and the 6" port. Definitely gonna have some heavy airflow in those ports. You dont want that! Not sure if you are gonna be able to see the ports of if its a big deal or not. I got both my 8" ports from a lumber yard. They were 8" sonotubes, actually. Total cost of both cut down to size....about $15. I'd do that if I were you. Unless you just had to have flared ports.

Last edited by Scott S; 10-02-07 at 05:57 PM.
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post #5 of 151 Old 10-02-07, 06:26 PM Thread Starter
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Re: Monkey see, monkey do... two RL-P18s for me too!

Hey, Scott!

Quote:
Scott S wrote: View Post
Ahhh, two RLp18's will be a HUGE step up from a single Def Tech 15. I know, I had the same one. (well, not the + version. Same thing but yours has a slightly bigger amp.)
I had two of those PF15TL+ subs. Bought a second one for parts/troubleshooting after pushing the first one a little too hard and fearing something wrong with it.

Quote:
Scott S wrote: View Post
One thing I would change....go with an 8" port if possible. I think you will be much less likely to run into chuffing if you push them to the extreme. Dont know about your bass habits. EDIT: Ooooh, yeah. I just ran the sims on a single d2 with 600w and the 6" port. Definitely gonna have some heavy airflow in those ports. You dont want that! Not sure if you are gonna be able to see the ports of if its a big deal or not. I got both my 8" ports from a lumber yard. They were 8" sonotubes, actually. Total cost of both cut down to size....about $15. I'd do that if I were you. Unless you just had to have flared ports.
There will be two 6" ports in each cabinet. This afford 12.5% more cross sectional area than a single 8" port, and gave me a little more room inside the cabinet as far as staying one port diameter away from the wall(s). With a 1.5" radius flare, I should be in good shape. Collo's testing showed improvement going up to a 40mm flare on a 6" port, so I figured 1.5" (38 mm) was where I wanted to be.

While I have your attention... I have a few questions about your build. What speaker terminals did you use? Happy with them? Did you wind up using the 10-32 size machine screws (instead of 1/4-20) with the hurricane nuts? Any particular reason you used fiberglass insulation inside the cabinet instead of polyfill or some other material? I'm not sure which is best, but I would like to avoid fiberglass if I can help it.

Thanks!

Bradley
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post #6 of 151 Old 10-02-07, 06:46 PM Thread Starter
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Re: Monkey see, monkey do... two RL-P18s for me too!

The pic below illustrates approximate placement of the subs relative to the 110" diagonal (8' W x 4.5' H) projection screen.



Please note this is an old pic. None of that furniture is still there. I presently have 9 HT recliners, row of 4 up front, and row of 5 in back. Drop ceiling will most likely be removed and sheetrocked as it buzzes a lot. The HT room is a serious "work in progress"... i.e., a lot of work and very little progress!
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post #7 of 151 Old 10-02-07, 06:59 PM
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Re: Monkey see, monkey do... two RL-P18s for me too!

Oops! I missed the (two) 6" ports per box part. Still in "work-mode" here at the office.

Air speed is much better with the two. For sure. They will be just as long as my 8" ports are...hehe, but it should all work in the end. As long as you have at least 6" from the inner opening of the port to the back end of the box...

Ill have to look at the specific part numbers for my binding posts for you as my brain is at critcal meltdown about now...(long day at the office). I dont know if I even mentioned which ones I ordered in my build thread or not. I ended up using some 10-32 screws from a Parts Express subwoofer installation package. That one is linked somewhere on my build thread. You could take a look if you like. They seem to work fine. I soldered the speaker wire to the posts and they were installed with much ease. Very clean look. Wish the binding posts on my amp were as good.

As for the insulation I used...when I was in the build process and got to the part of insulating them, I wasnt getting any responses on my thread about what to use so I just searched around for people using anything other than egg-crate variety and saw a few projects with the same stuff....ooof! I forgot the number...gosh Im tired. I wanna say R33 or something but I could be wrong. Ill have a looksey. I liked it best cause it was easyish to cut and was really cheap. Got the job done...

So far, other than trying to get a flat FR in my seat I am loving these! Great SQ and awesome extension. The Def Techs barely got into the 20's when I had one...then I had a vented Tempest for about 5 years. That blew away the Def Tech, bar none! Now these....

You're gonna have a lot of fun. *nods*
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post #8 of 151 Old 10-02-07, 09:48 PM
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Re: Monkey see, monkey do... two RL-P18s for me too!

Congrats on the wise decision!!

Two 6" diameter ports in that size enclosure with a 14.5hz tuning means the ports will be ~38" long - I'd personally stay away from anything 36" or longer unless you are sure you will be crossing over at 60hz and not 80hz, as the port resonance could very well become audible. I think you'd gain flexibility and "safety" by using a single 8" that is 31-32" long, as you could cross over higher without worry, and none of us 18" LLT owners have experienced any chuffing with a single 8". I just don't really see much being gained with the two 6"s at the expense of a potentially audible resonance - just something to think about.


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post #9 of 151 Old 10-02-07, 11:20 PM Thread Starter
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Re: Monkey see, monkey do... two RL-P18s for me too!

Quote:
SteveCallas wrote: View Post
Two 6" diameter ports in that size enclosure with a 14.5hz tuning means the ports will be ~38" long - I'd personally stay away from anything 36" or longer unless you are sure you will be crossing over at 60hz and not 80hz, as the port resonance could very well become audible. I think you'd gain flexibility and "safety" by using a single 8" that is 31-32" long, as you could cross over higher without worry, and none of us 18" LLT owners have experienced any chuffing with a single 8". I just don't really see much being gained with the two 6"s at the expense of a potentially audible resonance - just something to think about.
Are you using WinISD or Unibox or something else to calculate port length and resonance? I'm still a little fuzzy about how WinISD changes the port length and resonance frequency based whether you pick zero, one, or two flared ends for the port. My understanding was that you could assume half of the flare length functions as effective port length, as a rough approximation. Obviously, in reality, the flare radius would have to factor into the calculation. So when you pick two flared ends instead of one or zero, the port length value goes down. Does this value refer only to straight section of the port (not including the flares)? Why do I feel like I need to RTFM?!

At what frequency does port resonance become an issue? With this alignment I'm flirting with around 180 Hz. Is there some rule of thumb, like 3 times the crossover freq? I could either use the 8" port or increase the box size to get it closer to 200 Hz if that would make a meaningful difference.

Thanks for your input. Certainly nothing is etched in stone (or MDF) yet.

Bradley

Last edited by Bradley; 10-02-07 at 11:34 PM.
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post #10 of 151 Old 10-03-07, 12:17 AM
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Re: Monkey see, monkey do... two RL-P18s for me too!

I mentioned a first port resonance > 190hz in the LLT explained thread based primarily on various enthusiasts using longer and longer ports until it started to become noticable. When you start using a port longer than 36" and a crossover at 80hz, the resonance can actually show up in the FR with the mains in play.

One note - and I apologize if I am sounding pushy about this port thing, I just don't want to see you end up with something that could potentially be considered a fatal flaw - if you do go with a larger enclosure, say 20 cubes, I think you'd be better served still going with an 8" port and dropping the tune to ~13.3hz as opposed to keeping the 14.5hz an dusing dual 6" ports.


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