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Discussion Starter #1
Hi Folks,

I've been lurking here for a couple of months now and I guess it's time to start my first post. I have a dedicated theater room which is 14'x21'x8.5' that I built back in November 2003 and currently I have a pair of Definitive Technology BP-2002s behind my perforated 10.5' wide 2.35:1 screen. The BP's have a 12" sub built into them powered by a 125 or 150 watt plate amp. During most movies, the bass seems adequate but during some movies, presumably movies with notable LFE, I can hear the subs distort. I was watching Alien 3 the other day and at the very beginning of the movie, a spaceship pans across the screen and it was the first time I actually tried to lower the volume of the movie. Naturally, my wife or friends don't even notice the problem, but I have been noticing it more and more. I don't have REW setup yet and haven't used my newly aquired SPL meter from Sonnie to check FR and SPLs but I do intend to do that before switching over to the new subs. I'm sure the BP's don't go down as far as I thought they did when I first got them.:hissyfit:

I was considering a dual RL-p15 project but I have been waiting for the RL-p18's and I snagged two at Mike's introductory offer. I figured if one was good, two had to be better. :bigsmile: I received the drivers Thursday and I must say, they are absolutely huge! You can measure 18" with a ruler and try to estimate their size but until you have them sitting in front of you, you just can't imagine how big these things are! Getting the drivers and picking up the 6 pieces of MDF today made me realize that maybe one RL-p18 would have been enough but I am going to press on.:coocoo:

I would have went with an IB, but I don't like the idea of attaching the drivers directly to the structure of the house. I have 1400lbs of sand in my stage area and thought a LLT would be better in my situation. I think the bass traveling through my attic and into the rest of the house would freak my wife out even more than the two large boxes.:scared: At least she will only see the boxes during construction...

I don't have any pix yet but I will try to get some uploaded here as I make a little more progress. I am making two MDF boxes that will each have an internal area of 64.5"x37.5"x16". Each box will have one driver and one port. When I built the theater, I had never heard of LLT subs so I didn't leave gobs of space behind the screen so that is why I only have 16" or so of internal depth for these boxes. If I calculated correctly after bracing and the 8" port I should come in around 550L. I really wanted to go with 650L per box but that would have forced me to move my speakers up too high. Maybe I won't loose as much volume as I calculated...

If anyone can tell me how much volume the RL-p18 is going to take away from my internal volume, I would appreciate it. I will not be countersinking the drivers as I don't care what these boxes look like as they will be totally hidden behind the screen. Also, I am going to use 5/8" closed cell foam to line the inside of the box. Do I subtract the foam volume when calculating effective area? Lastly, should I line the port as well?

-Tom A.
 

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Hi Tom and welcome to the Shack! Glad you got the meter okay and congrats on the pair of 18's. No doubt you are jumping in with a big bang here... :T I'll be looking forward to your build and the results. We have plenty of guys to help you figure things out... they should be along soon.
 

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If anyone can tell me how much volume the RL-p18 is going to take away from my internal volume, I would appreciate it.
Around 4.5 liters.

Also, I am going to use 5/8" closed cell foam to line the inside of the box. Do I subtract the foam volume when calculating effective area?
If it's really closed cell foam (I recommend open cell foam instead), then you should subtract the foam volume when calculating effective volume.

Lastly, should I line the port as well?
Doesn't make a huge difference but doesn't hurt either. If you have some foam left - why not.
 

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I you want to go for more volume, you may want to consider boxing in that space in the attic where you would have put the IB. Rodny just partially completed a similar project and the results look very promising so far. Two of these drivers will give you plenty of output, so you could get away with a nice low tune.
 

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Discussion Starter #6
Here's some pix of my progress thus far. I know my woodworking skills are nowhere near that of most on this forum but the boxes will be behind my screen so it shouldn't really matter.

I'm standing on a step ladder looking down at the box laying on its side. Remember that is an 18" driver and it looks much bigger in person!:rubeyes: I haven't siliconed anything yet, just glued and screwed the braces and box sides so far. The port will be cut smaller once the total volume is determined.

My port hole didn't come out quite as good as I would have liked. I personally don't own a router but I borrowed a buddy's Ryobi but I couldn't come up with a good reliable way to cut circles. I tried a piece of clear acrylic I had laying around as a circle jig. I started ok but the router bit melted or cut into the acrylic and I went off course. I tried with a piece of 1/4" plywood I had laying around, making sure only the shaft would touch the wood but it still didn't work for me. The hole ended up getting elongated and burnt! My hats off to you wood workers! I ended up using my cheapo Black and Decker jig saw which naturally didn't cut perfect circles but it should be ok since it will be out of sight. Do you think turbulence will create a problem with my not so smooth roundover job? Also, I could only find a 5/8" roundover bit at the local big box stores so that's what I used. Oh well, hopefully it will still sound good.

The last photo shows my 10.5' wide screen where the two boxes will go behind.

-Tom A.
 

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You can sand that port flare on out some, but I doubt you'll notice any noise because of it not being perfect. You do however need to make sure the port end is sealed well and even with the port opening in the wood. I think that might make a difference.

If you have to cut that end again and redo the port, you can make a circle jig that will not burn the acrylic. The router bit should actually never touch the acrylic. You could even use a wooden yard stick, but cut a larger hole where the bit will not touch the sides of the hole... then mount the stick to the router... as follows:



Notice how the bottom plate of the router is removed and the screws used to mount the home made circle jig.

Then don't cut the entire hole out with the router. Just cut two half moons with about 1/4" left on each side. Use your jig saw to finish cutting that tiny bit that is holding the cutout to the panel. What we did was make one complete round about half way through the wood, then we made the two half moons and finished the cutout with the jig saw. This way there's no chance of the router sliding when you cut that last little bit.
 

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Discussion Starter #8
Doh!

Sonnie, thanks for the router tips. I can see why that would work much better!

Don't worry about the port, I do plan on sealing it up good. It is just sitting there for the photo. I plan on using your router tricks for the next box and the cutout for the Rl-p18! :T
 

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Wow. Tom, that is going to be an insane bass maker. I can't wait to see how your project goes, please keep us up to date with lots of pics!

Thanks Owen, I think you are right, it should make plenty of bass. One probably would have been enough but as my friends always tell me, I never do anything small. :bigsmile: That of course doesn't mean I should have started out small.:dumbcrazy:

I forgot to take pictures this weekend of my progress...I'm basically just working on it on Saturday. Since the pictures above, I have added more bracing, cut the port to its actual size and cut the hole for the RL-p18. I was shooting for 550L per box and with all my bracing added and discounting some extra volume for the closed cell foam I purchased I came up with an effective area of 549L. Of course this doesn't mean I calculated it correctly but I hope I did! I also started on the second one this weekend, it's amazing how that one is coming together quicker. What's even more amazing is that I have gone through 7 tubes of liquid nails already and I need to go to Lowes and get more 2x2's, liquid nails and drywall screws.

Thanks go to Sonnie and thxgoon for explaining the circle jig to me, I still feel a bit stupid for not figuring that out. :duh:

Here's a picture of one of my RL-p18's in a trial piece of MDF next to my super fancy circle jig that works great with a finishing nail.


I purchased a Carvin HD1800 to supply 900 wpc into 2ohms. Each sub will have its own channel and I have a Art Clean Box ready to go also.

I have a few concerns though:

(1) I want to try using the sub out on my Yammy receiver but it's crossover is 110Hz. I hope that's not too high?

(2) Should I run a 20amp dedicated circuit for the Carvin? My breaker box is full now and actually my last project forced me to use an ultraslim double breaker to free up more room. I guess I can do that again, but I'm thinking about just trying it as is first as I doubt I'll really use 900 wpc very often. Is this poor logic?

(3) Can I really fit these boxes behind my screen...no just kidding...I measured several times and I know they will fit, yeah, that's the ticket.:bigsmile: They are getting very heavy though! I'm definitely gonna need help lifting them through the screen wall.

-Tom A.
 

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Discussion Starter #12
And you have a great looking theatre by the way.
Here's a shot of the den before it was converted to the theater. This photo was taken from the same spot as the one above. You should have seen my neighbor's confused looks when they saw my dad and I removing the 6 foot sliding door to the backyard and covering it with vinyl siding.:rofl:

-Tom A.
 

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Wow... that is a significant change in that room... :T

110Hz may be a little high truthfully, but you'll just have to try it and see to start with. I don't think you'll have any problems with the amp, not to a point of necessarily needing a dedicated circuit.
 

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Wow... that is a significant change in that room... :T
Yeah, and that's only a small part of what I had to do to get my dedicated theater room. The house is only 1400 square feet and there is no basement. I don't really have enough property to add on to the house and building up would be prohibitively expensive so I and my reluctant wife decided to convert the den into the theater. But since I closed off the only entrance to the backyard I had to remove the window in the kitchen, which is directly behind the theater, and put a door there. The den (now the theater) had an open floor plan with a pass through thingie that you could put stools up near and a large entranceway to the kitchen and an open area to the adjacent living room. That had to all be sealed off and a door added. I also had to remove the hall closet (now my equipment closet) and move the door to the garage around into the adjacent living room. Since the kitchen was now entirely sealed off from the rest of the house, dad and I knocked out the corner pantry closet and that became our entranceway. It was quite an endeavour and while my wife couldn't quite see my grandiose vision beforehand, she likes the setup now since we actually use all of the space in our house. Before, the living room was never used, now it's the new den.

Are there any options other than trashing the Yammy receiver if the 110Hz crossover on the receiver is too high?

-Tom A.
 

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Your option would be to get something like the Behringer CX2310... about the least expensive crossover I know of. But like Steve suggest, it may not be a big deal.

Is the 110Hz the LFE crossover or is it also the high pass for your mains?
 

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Discussion Starter #17
...If you don't go for a new circuit, what will the Carvin be sharing power with, and on a 15 or 20amp circuit?
The Carvin would be sharing a 15amp circuit with my popcorn machine. The kettle and light would NEVER be on during movie time.:neener: but the 50 watt tray warmer would be. IIRC, the only other possible draw on the circuit would be the 3 plate amps for my Def Tech 2002's and the center channel 8" sub. I don't even know if I will need these plate amps on for the Def Tech's once the LLT is built. IOW, I don't know what the low pass is to the subs. I'll have to play with that.

-Tom A.
 

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Discussion Starter #18
Is the 110Hz the LFE crossover or is it also the high pass for your mains?
Well, I lied to you guys...sorry. I browsed thru the Yammy manual a few weeks ago and I could have sworn it said 110Hz. I re-read it again and it said the high pass is 90Hz. This should be better, right?

It also made a statement that the LFE channel has frequencies below 120Hz. Is this a Dolby/DTS thing or is that just how Yammy handles LFE? This is more confusing to me than it should be.:dizzy:

It looks like I can assign the LFE channel to the sub output, the mains or both. Would it be best to have the LFE go to my LLTs and set all other speakers to small so that the frequencies below 90Hz for the left, center, right and surrounds go to the LLT as well?

-Tom A.
 

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The LFE channel range goes up o 120hz, so that is the correct setting in your processor. Some older receivers will incorrectly lowpass the LFE channel at the same frequency your redirected bass crossover is set to, but the goodones keep the LFE channel independent of that, full range up to 120hz. I'd send the LFE only to the sub.

Just to make it clear, the redirected bass from your speakers below 90hz will go to the sub as well as the full LFE channel, which is 120hz on down.
 

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I'd say give it a listen both ways. Not that I have any suspicion that you'll be lacking in bass output, but it might integrate better with the mains playing low as well. then again, maybe you'll be getting the distortion back in the BPs, which you don't want, so you would go with just the LFE chan. I wish my Denon could cut off my mains at around 40Hz, so they would save on power trying to play really low, but still play low enough to blend well, unfortunately, 80Hz is my lowest crossover point. I think in my setup I like it better using the Main+LFE setting.
 
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