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Dual RL-p18 LLT begun

34K views 110 replies 18 participants last post by  Scott S 
#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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#86 ·
Nice project sir:hail:. Gave me alot of ideas for what I might be gettting into this summer. I've been considering doing a LLT sono tube with the RLP18. Heheh. and furthermore:




hehehehe :rofl:
 
#87 ·
Plots

Well Sidi_UC, I hope AsianCat approves of the following plots. :R

My listening position is about 13-14 feet from the subs and the SPL meter is just behind my primary seating position at about ear level. My Yammy receiver's XO is 90Hz. I have no BFD at this point. I removed the Clean Box as recommended.

Here's the most important plot, the listening position:

Green Text Line Plot Slope


Should I be concerned with the dip at 60Hz?

Just in case I cut off the plot at the wrong point, here it is again with the unbelievable lower frequencies shown:

Text Green Line Plot Slope



Here's a near field plot. I placed the SPL meter about 12" from the right sub:

Text Blue White Line Pattern


It appears that the subs have no trouble with 60Hz, but my room does. Thoughts?

Same plot with the lower unbelievable frequencies shown:

Text Blue Line Plot Pattern


Here is a plot with the SPL meter about 8" from the right hand sub's port:

Text Green Line Slope Plot



..and of course the same plot with unbelievably low frequencies:

Text Green Line Slope Plot


Am I correct thinking that my "real world" tune is about 13Hz??


I have played with the subs a little, mostly with music as I cannot watch movies yet because my screen is still down...I hope to finish that up this weekend or the next at the latest and my projector is still off for repair. I sent it in under warranty to have what appeared to be two smudges during dark scenes removed. First they told me they couldn't duplicate the problem but then they had the "head service tech" look at it and he determined the DMD chip was bad. I was glad that they found the problem but of course they (Optoma) doesn't stock the TI chips because "they never go bad"....hmm...oh well that just gives me more time to procrastinate on the screen. Once I get the projector back, I'll live with it for a little while and attack the rattles that I get in the kitchen. I think the pictures on the kitchen wall (shared with theater wall) will have to be velcroed to the wall. :devil:

So, do you guys think a BFD could help me?

I want to thank everyone for their input and coercing me to press on with this, my first DIY sub/speaker project. I will probably build some new L,C,R's next. :bigsmile:


-Tom A.
 
#88 ·
Congratulations dude!!

your FR is marvellous, the Dip is not too much of a concern for me. If you want to do something about it, I would suggest either boosting 3-4 db at that Dip, or using a nice Housecurve would to reduce it, or maybe a combination of both!! You would need a BFD then!

But I think that even witout doing anything, that Dip will not be so noticeable.

You cannot know exactly the tune with FRs at listening position, but a nearfield (very close to the woofer) sweep would inform better about the tune. for ex. the sweep at 12" from the right woofer shows approx. the tune. But I would even go closer to the woofer to minimize room interction.

What was the initial design tune?

B Rgds
 
#89 ·
What was the initial design tune?
Well, originally I was wanting to go about 13-13.5Hz with 600L effective for each box but I scaled that back to 550L effective with a tune of 14.65Hz according to Unibox. If my natural tune is 13Hz, I could live with that. :bigsmile:

BTW, I'll be following your massive project. :T

-Tom A.
 
#90 ·
I think Blaser is correct about the near field driver FR showing the tune. The peak output of the port will actually be a couple of Hz below the tuning frequency, so it looks like you hit your target of ~14.5 pretty well.

Looks like a smashing success either way!
 
#91 ·
Hey! Do you know/guess how much each of these monsters weigh? How did you move them:dumbcrazy:
 
#92 ·
#95 ·
The response at the listening position, is that with the mains in the loop or no?
My original intention was to test just the sub by shutting the front speakers off at the Yammy receiver but I forgot to do so. I re-did one of the sweeps but I didn't notice a change. The Yammy receiver has an "A" and "B" speaker on/off switch but perhaps you cannot shut both speakers off at once? Or, maybe if both are switched off, everything is passed thru the sub? I didn't really spend much time with it, I guess if I wanted to get a true sub only plot, I would have to disconnect the front's at the terminals.

I'd make sure to test with the mains in the loop and experimenting with different distance values in the processor before even considering a BFD, as that may make the dip at 60hz go away by itself.
Good tip, thanks. I'll have to try that. I am currently on hold as I am still awaiting the return of my projector and believe it or not, I still don't have my screen totally rebuilt and up yet. It's a little hard to get motivated when I have no projector to throw images anyway. The metal frame is all done, the screen wall has been tweaked to accommodate the new frame and I have removed the screen material from the old frame and put velcro on it. I just need to put the mating velcro on the metal frame and pull it tight, and re-pull it to I am happy. Then I need to get a buddy to help me set the completed screen frame in the screen wall. I was able to lift the old wood frame in by myself but don't think I will attempt to do the same with the new much heavier metal frame.

You'll also want to play around with opening and closing various doors.
Nope, can't do that, light would enter into the dark abyss. The room is a dedicated theater room with one entrance and no windows. The fire marshal might not approve but it makes for very good movie watching. 12 noon looks just like 12 pm. :R

-Tom A.
 
#98 ·
Thanks thxgoon. I had a build thread over at AVS but it is over 3 yrs. old and I cannot find it anymore. I have some gallery photos of the build over at AVS if you would like to look at them. My user name is the same as here, tjambro. The material on the walls is GOM (Guilford of Maine). It is a sonically transparent fire resistant fabric. I am very happy with it. I have 1" thick insulation behind the fabric from the chair rail down to the floor. Above the chair rail is polyester batting. This has improved the acoustics in my room and I would definitely do it again.

-Tom A.
 
#104 ·
tjambro,

I will go offtopic a bit because I don't know where I will post that. I think you ar using a projector, don't you have any problems with vibration?...I know your room will be seriously vibrating at high SPL:bigsmile:
 
#105 ·
I will go offtopic a bit because I don't know where I will post that. I think you ar using a projector, don't you have any problems with vibration?...I know your room will be seriously vibrating at high SPL:bigsmile:
Wow, this is very old but I just noticed it, sorry Blaser. Yes I was using a projector and the projector did not vibrate. I put a piece of closed cell foam that I had left over from the project under the projector mounts. That seemed to stop the vibrations. I should say that I THINK it stopped the vibrations because once while watching the ice crack at the beginning of "The Day after Tomorrow" something vibrated, either the projector or the screen. I personally think it was the screen as it was not attached to the ceiling above due to a pan or vaulted ceiling.

I am ashamed (or proud:devil:) to say that the subs did knock a picture off the NEIGHBOR'S wall...oops...

If I remember correctly, you have some fairly strong bass capability yourself. :whistling:

-Tom A.
 
#106 ·
FREE: Dual RL-p18 LLT boxes

Well guys, this project is no more. I sold my single level ranch in June and moved to a similar sized house that has a full basement! Yes, the whole right side of the basement will be converted into a theater, lobby, etc.

This time around, I think I am going to try a very large sealed box/IB behind the screen area. I want to go with 4 18" drivers. Although I already have 2 SS RL-p18's, if I buy 2 more, the combined VAS is going to be larger than I am willing to dedicate to the enclosure to achieve 10X total VAS, so I plan on selling those...see the Classified Section if interested...but I am giving away my boxes if anyone wants them.

The boxes are exactly as they are in this thread. They are not pretty but I thought they worked very well behind the screen in my previous theater. I cannot ship them due to size and weight, but they are free to anyone who wants to come and pick them up in Evansville IN 47715.

You can have one or both...just let me know.

-Tom A.
 
#108 ·
Re: FREE: Dual RL-p18 LLT boxes

Well guys, this project is no more. I sold my single level ranch in June and moved to a similar sized house that has a full basement! Yes, the whole right side of the basement will be converted into a theater, lobby, etc.

This time around, I think I am going to try a very large sealed box/IB behind the screen area. I want to go with 4 18" drivers. Although I already have 2 SS RL-p18's, if I buy 2 more, the combined VAS is going to be larger than I am willing to dedicate to the enclosure to achieve 10X total VAS, so I plan on selling those...see the Classified Section if interested...but I am giving away my boxes if anyone wants them.

-Tom A.
You could still use them with very good results in an IB if you get another pair. While most shoot for 10x VAS you do not necessarily need the full 10x VAS. That's just the optimal number. IIRC, you can even go with 4x VAS and still get great performance. In fact, I doubt there would be any change in Qtc.
 
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