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Discussion Starter · #1 ·
As some of you may have seen in my other thread. I have one of these mammoth 18's that somehow survived the beating that UPS gave it. It's time for me to put it to use and I need help deciding what to do. It will be used in a 4000+ cu ft room that has a stairwell and 2 doorways to other rooms. It will be used for about 50/50 HT/music. I will be powering it with 1 of my CE4000's and I'll be using a DCX2496 and/or a Rane PE-17 to tweak it. I'll be comissioning a local woodworking shop to build the enclosure for me, once I decide what I want to do. Here are the TSP's

Electrical Q Value -Qes: 0.68
Mechanical Q Value -Qms: 2.82
Total Speaker Q Value -Qts: 0.55
Free Air Resonance -Fs: 15.60 Hz
Equivalent Compliance -Vas: 482.0 liters
One-Way, Linear Excursion -Xmax: 54 mm
Efficiency -SPL 1W/1m: 86.20 dB SPL
Effective Piston Area -Sd: 1210 cm^2
DC Resistance -Re: 4.2 ohm
Nominal Impedance -Znom: Dual 2 ohm
Thermal Power Handling -Pe: 2000 W
Force Factor -Bl: 18.16

I've got a few ideas about what I want to go with, but wanted to see what everybody else would do. What would you do with this driver if you had it?
 

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Interesting, I will model this unit once home. One thing is sure,to get the most out of this unit you need a LARGE cabinet.
 

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Discussion Starter · #4 ·
Steve,
Did you see the UPS destroys the precious thread? Lots of pics and other details there. I payed $710:whistling:and unfortunately I can't pull off an IB type system:no:. Otherwise I'd go with a pair of them in a giant box tuned below 10hz:coocoo:.

I did hook it up free-air to one of the CE4000's bridged & lowpassed and played some music with strong sustained 25-30hz bass. I gradually turned it up until the amp clipped and then backed off the amp gain 1 click. I left it at that level with the song on repeat for about 30mins. It took it like a champ and asked for more, barely even got warm. It is a HAUS!
 

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Discussion Starter · #5 ·
Here's what I'm thinking...I either go sealed with it in about 310L... or... I get crazy and go 25ft vented, tuned to about 11hz and use the Polk Power Port vent system to get a 10" vent in there with that tuning. I think it will work, but the difficulty level goes way up to do it.

Here is a couple of graphs comparing 310L sealed to a 300L ported SDX15 tuned to 15hz and dual ED 190V2's in 310L sealed. FR.JPG
 

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I don't know how you will be able to get away with a 10" port with that low of tuning - what is the Polk Power Vent system?

How about two heavily flared 6" diameter ports (equivalent of a single 8.5" diameter port) that are each 32" long for a ~13hz tuning? Even at 1600 watts the air speed doesn't get to be too bad.
 

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Discussion Starter · #8 ·
It was a port system that Polk patented that can make a smaller and shorter port equivalent to a much larger and longer one. It is used in their subs and speakers. There was also a write up of it in the 1996 Audio magazine. They would give you an Excel calculator for it if you asked, that could be used for strictly personal(DIY) use. It seems to be well proven and there was a guy at AVS that modified his TC2K's to have a 10.5hz tune with it. Basically it uses a heavily flared port and an inner flow guide that conforms on both ends of the port to the flares, to slow the air speed down and increase the mass. I'm no expert on this by the way. I will post more info when I get on my cpu where I have the Excel calculator. Since I'm Guinea pigging with this driver I may as well try out some other relatively unused/unknown port tech with it.
 

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It seems to be well proven and there was a guy at AVS that modified his TC2K's to have a 10.5hz tune with it.
Link?

To me it doesn't look like anything special... It just lowers the tune by cutting down the cross sectional area and by making the port a little bit longer.
 

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Discussion Starter · #12 ·
It was Video. He was the guy who bottomed out his TC2000 15's and dented the cones out ward. He modified his ports to this kind of design.

I agree that it does obviously decrease the actual port area by virtue of the center flow guide. I also agree that it seems like the decrease in port area would take an 8" and make it closer to 6" in useable area, plus slightly lengthen due to the flow guides and consequently drop the tune. However why go to all of this trouble if you could just go with a normal 6" port to begin with? I don't think Polk would use it, bother to patent it, create the calculation sheet, get the huge technical write up in Audio and offer it to DIYer's if it did not do something of obvious benefit.

Polk claims that a power port of the same size as a normal port, like 6" vs 6", the power port would be shorter, have much greater useable airflow(output before chuffing)even with diminished useable port area, and provide closer to predicted max output. For instance the port that I attached is claimed to be equivalent to a 14.87" diameter port! I can only assume that this is accomplished by slowing the airspeed exiting the port, allowing much greater airspeed to be useable before port compression /noises/etc., greater effective coupling of the port mouth to the room(maybe some kind of Quasi horn like effect?:dontknow:). I honestly don't know and I'm not vouching for the reality of these claims, but I may be willing to find out. Maybe this would be something worth checking out for yourself with an old 10 or 12 that you've got lieing around Illka and starting a thread in your test area?
 

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How will you go about sculpting the conical shape, and how do you plan on floating it a few inches away from the port openings? Though I'm skeptical of Polk's claims, I guess it's worth a shot if it doesn't become too labor intensive or costly.
 

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Discussion Starter · #14 ·
I can make the flow guides without too much trouble. I've got a secret weapon for that, but it will be a lot more labor intensive and a little more expensive to build one of these ports no matter what. I'll post an illustration of the way it would be mounted in the enclosure tomorrow. Basically the port mounts into the enclosure as normal and the bottom cone is mounted to a baseplate that is mounted at a distance like an older downfiring SVS, or a normal sonosub. Internally you mount the second flow cone to an internal brace the same way. I've even thought about using one of these in a sonosub, but then it gets trickier to mount the inner flow guide to something. I have some ideas about that too though. It's either try this, go with a huge slot port, severely underport it, or tune way higher. I may as well go sealed with it if I can't get a really low tune because it would be nearly impossible to use all of this drivers output with normal 15-19hz tune. Even bridged Crown CE4000 won't get it there.
 

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So you're saying this fixture would be mounted to a baseplate - does that mean the ports would be downfiring? You would need REALLY tall legs then to prevent any turbulent air flow.

To me, it still looks like two flared 6" diameter ports with a 13hz tuning works just fine. I wouldn't sweat it.
 

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Discussion Starter · #16 ·
Here is a view of what the port would be like in the enclosure. You are right it would be on a stand-off but it wouldn't be that much taller than a normal sonosub, in this case 3.25". This distance is a critical component of the way the port is supposed to work and is used in the calculations.
25ft ppp.JPG
 

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Discussion Starter · #17 ·
Not a single comment? LOL

I did figure out that the center flowguide from the current port design only chops the area of the port down from a 10" to the equivalent of a 9.36" port, which is not too bad imop.
 

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On the inside of the box would you need to make sure you had at least the same distance from the port to the walls as the diameter of the port? Seems that there wouldn't be a lot of air space between the two braces that hold each and it could cause turbulance if it was too close to a wall. Another thing "thinking out loud - and believe me I know nothing", could you move the support back from the end of the tube and use a dounut shape for the end of the tube (more than a flare) and allow more unobstructed are to be around the port opening?
 

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Discussion Starter · #19 ·
Actually the flow guide and the baffle spacing are integral parts of how this port is supposed to operate. The standard of needing 1 port diameter in all direction's would prevent the principles of this design from even being applied. Also that small space between those 2 inner baffles is actually 3.25" and that is a 10" vent. This is by no means anything ready to be built, I'm just brainstorming. It needs work!

One thing that I have figured out is that I believe the vent mouth is re-located on this kind of port among other things that are going on. It is not the area that is high-lighted green on this shot.
http://i241.photobucket.com/albums/ff260/Antikythera/vent1.jpg

It becomes this area high-lighted in green and red that wraps around the entire perimeter.
http://i241.photobucket.com/albums/ff260/Antikythera/vent2.jpg

This has an area equivalent to 173.5 sq inches. Compared to a regular 10" vent having an area of 78.5". This is why the calculation sheet claims that the vent mouth and exit are equivalent to a 14.87" port diameter. I still don't know if the port can handle an equivalent amount of air flow to a vent of that size. I assume that the air speed will be low upon entrance, high speed in the middle of the port and then slows again at the exit, due to the flow guides and expanding port area at the exits. It is claimed that this port would flow much more air without chuffing or overloading than a regular port of the same diameter.
 

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Discussion Starter · #20 ·
Looks like this thing is going to get built. I was hoping this would generate some discussion, or someone would talk me out of this madness! Guess I was wrong. :rolleyesno: Like trying to do stand-up comedy at a funeral.:thud:
 
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