Monkey see, monkey do... two RL-P18s for me too! - Page 2 - Home Theater Forum and Systems - HomeTheaterShack.com

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post #11 of 151 Old 10-03-07, 02:09 AM
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Re: Monkey see, monkey do... two RL-P18s for me too!

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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 noticeable. 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.
Yeah, I gotta say I am in total agreement with Steve here. (whats new? ) If you could possibly go with a tiny bit bigger cab then I would go for it. In the long run you wont run into such hazards as the port resonance gets really close to audible with such long tubes. I was really pushing it with my design. They are about 35-36 inches each and I have yet to hear any effects. Although, I have my xover @ 60hz so maybe I just lucked out.

Also, going with the 8" port will allow for a slightly lower tune and thats always nice. *nods*

Just something to consider if its a doable option for you.
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post #12 of 151 Old 10-03-07, 10:22 AM Thread Starter
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Re: Monkey see, monkey do... two RL-P18s for me too!

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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.
So at 15 ft^3 you were recommending 16.5 Hz tune but at 20 ft^3 you'd recommend 13.3 Hz? Running the sim both ways, and at several places inbetween, there are significant but not huge differences. Some people seem very concerned with air velocity in the port, but since the 8" port has been used by so many people with good results, I would have to conclude that port velocities well over 17 m/s (and as high as 25 m/s) down in the 12-14 Hz range are not a problem.

I guess I'll chew on all this some more and try to wrap my head around it, so to speak. No matter what, I will not use a port length greater than 35" (193 Hz resonance).

Thanks for the input. I respect the experience you bring to the table and your strong convictions.
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post #13 of 151 Old 10-03-07, 05:21 PM
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Re: Monkey see, monkey do... two RL-P18s for me too!

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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.
Congrats on your decision! Those RLP18's are definitely awesome and somehow I don't think you'll miss your deftechs. I was a bit concerned about using fiberglass insulation as well. I thought maybe fine particles would fly out of the port and that it may not perform as well as other materials. When budget and accessibility became a factor I decided to use some R-13 and have not been sorry. It's easy to find, cheap, easy to install and it's actually a great sound absorber. In fact when people soundproof rooms they often use double thick walls with more insulation. I've never noticed any dust or particles flying out of my tubes and I couldn't be happier with the sound. Good luck with the build and keep us informed!


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post #14 of 151 Old 10-04-07, 12:54 AM Thread Starter
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Re: Monkey see, monkey do... two RL-P18s for me too!

Nothing new to report tonight... but I thought I would post the mandatory picture of the newly arrived RL-P18s! For reference, next to them is a (blown) 15" driver out of one of the Def Tech PF15TL+ subs I just sold.



Just puts a smile on my face every time I look at them.
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post #15 of 151 Old 10-04-07, 02:27 AM
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Re: Monkey see, monkey do... two RL-P18s for me too!

That looks like a 12" sitting next to those 18's.

I'm looking forward to some build pics...
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post #16 of 151 Old 10-04-07, 12:43 PM
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Re: Monkey see, monkey do... two RL-P18s for me too!

While working with the fiberglass, handling and cutting...there were some floating particles. I had an opened side to my boxes until I closed them. By then I had dusted and vacuumed the extra particles out. Ive played all sorts of loudness outta them inroom and there is no fiberglass floating around in the room. And for the first month I had the ports pointed INTO the room. So no, fiberglass will not be blowing particles around the room.

Love the pic of the dual 18's next to the whimpy Def Tech.
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post #17 of 151 Old 10-06-07, 01:18 AM
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Re: Monkey see, monkey do... two RL-P18s for me too!

Man you're in for a treat, I just built my single 18" SS, and yes I used an 8" port, you can pick them up at Lowes in the concrete section, massive port for a massive speaker, make sure you have everything nailed down when you crank those babys up and enjoy!
Oh yeah, the QSC is an excellent choice, I'm running a RMX 1450, a little over halfway shakes the house.


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post #18 of 151 Old 10-07-07, 12:27 AM Thread Starter
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Got MDF?

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Mongrel714 wrote: View Post
Man you're in for a treat, I just built my single 18" SS, and yes I used an 8" port, you can pick them up at Lowes in the concrete section, massive port for a massive speaker, make sure you have everything nailed down when you crank those babys up and enjoy!
Oh yeah, the QSC is an excellent choice, I'm running a RMX 1450, a little over halfway shakes the house.
I was actually over at Lowes today picking up the MDF and I took a look at the concrete form tubes. They only had two 8" tubes left and they were significantly different in size. It says "8 inch nominal" with plus or minus .5 inch variation, obviously so they can slip one tube inside the other for saving space and lowering shipping costs. Anyway, I hit Home Depot and picked up some Sakrete brand tubes. Cherry picked two identical tubes, which are about 8.25" inner diameter. They're not what I'd call robust, though. I have a feeling genuine Sonotube brand tubes are probably stronger.

Anyway, found somebody helpful with half a brain to cut up the MDF for me so it would fit into my car. He did a pretty good job, accurate to within a 16th of an inch. I felt pretty silly loading 450+ pounds of MDF into the back of my Audi.



I also picked up this used table saw today with a newly installed Biesemeyer rip fence. Should be pretty nice for this project!



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post #19 of 151 Old 10-07-07, 01:35 AM
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Re: Monkey see, monkey do... two RL-P18s for me too!

Swwwweeeeeeetttt!



You're on your way to bass heaven.
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post #20 of 151 Old 10-07-07, 10:49 AM
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Re: Monkey see, monkey do... two RL-P18s for me too!

HEHEHEHEH, The Audi looks like a fine vehicle to haul MDF to me! The sakrete tubes are a little flimsy wouldnt use them for a main enclosure, but for a port that will be braced it works well what ever sound deadning material you use to line the interior walls with, be sure to wrap the port in also,Good Luck!!


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