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Discussion Starter · #1 ·
I've modeled the Soundsplinter RLP-15 in WinISD.
The picture shows the response for sealed and ported...as well as the T/S parameters I used. (Do my T/S parameters look correct?)

Question... Why would I want to used a sealed box when the ported one goes MUCH lower? I know the box is bigger, but its for my Home Theater, so size isn't important. I have a BFD for EQing. A ported box seams like a no brainer...

Am I missing something? :huh:

 

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Well, you're not missing anything really... what you're noticing is the advantage of a vented allignment over a sealed allignment. Sealed boxes have only 1 source of spl, being the driver. Vented speakers have two sources, 1 being the port, the other being the driver.

In some smaller rooms, it makes more sense to go with a sealed subwoofer because they generally(w/o highpass) exhibit a 2nd-order roll-off after Fb (tuning frequency or enclosure resonance). Vented systems have a 4th order roll-off after Fb and an increasing danger of exceeding xmax after the tuning frequency. Smaller rooms will help the sealed subwoofer in the lower frequencies with its own contribution to spl called room gain. Also, since the roll-off is more gradual with the sealed subwoofer it may mesh better with the room gain. Vented boxes roll-off twice as fast below the tuning frequency.

You'll need some sort of highpass protection to prevent the driver from over excursion with the vented speaker. If the sealed speaker is designed to be amp-limited (to simplify this), the air-spring inside of the sealed box will help prevent ever exceeding excursion.

In order to get the same or similar results from a sealed system one has to spend a lot more than a vented system. You'll simply need more power, more drivers, and a form of LinkwitzTransform (special eq to bring up the lower frequencies in a sealed system) to reach a ported system in outout with the same driver.
 

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You can get much better results with a ported sub than that. Exocer is right about the rolloffs meshing with room gain, but if you use a large enough enclosure with a low enough tune, you can create a FR that will have a shallow rolloff below ~30hz pushing the 4th order rolloff down into the low teens, and the shallow rolloff will mesh extremely well with typical room gain, better than a traditional sealed or ported, giving you solid extension down to the low teens.
 
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Discussion Starter · #6 ·
So ported it is...
How does this look? A 13.5cuft bot tuned to 22Hz. -3db @ 19.5HZ
Could someone check my TS parameters to see if they look right for a dual 4 ohm RLP15

 

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how about larger enclosure still ported with a lower tune. say somewhere between 11 and 15 hz so the roll off is nice and slow and that should take up for room gain.
 
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Discussion Starter · #9 ·
how about larger enclosure still ported with a lower tune. say somewhere between 11 and 15 hz so the roll off is nice and slow and that should take up for room gain.
13.5 cuft is about as big as I can go in the the room. I figure 20HZ was low enough. I certainly can't hear anything that low, although I can certainly feel it. The problem is port size. For a 22Hz tune, a single 4" port is only 2.15" long. That doesn't seem right to me. Two 4" ports need to be 7.23" long. A single 6" port need to be 7.04" long. Do these numbers seem right?

RLp15 D2 in 260 effective liters with a 6" port that is 30" long using a 3/4" roundover being fed by 600-900 watts. Proven performer :T
I'm stuck with a Dual 4 ohm sub due to my Amp. I would need 2 of the Dual 2's, which I dont want.


Do my T/S parameters look correct on post #1?
 
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Discussion Starter · #13 ·
RLp15 D2 in 260 effective liters with a 6" port that is 30" long using a 3/4" roundover being fed by 600-900 watts. Proven performer :T
I plugged that into WinISD and the reading looked awful. it showed -10db at about 23 hz...Is this right? I am sure I am reading something wrong or not using the program correctly, but every time I plug a driver into that thing (WinISD)...it looks like I will just be wasting my time. I was trying to attach a picture of the graph but I am not sure how to capture a screen shot.
 
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Discussion Starter · #15 ·
Yes you are doing somithing wrong. With 260l and a 30" long port I get -5 at 23hz
I cant get the screen shot loaded here. What Tuning Freq are you set at. Mine auto adjusted to approx 14hz. I am sure I am doing something wrong...every driver I have tried looks like it would be a waste of time. Ill check the tutorial again on WinIsd
 

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I cant get the screen shot loaded here. What Tuning Freq are you set at. Mine auto adjusted to approx 14hz. I am sure I am doing something wrong...every driver I have tried looks like it would be a waste of time. Ill check the tutorial again on WinIsd
Try the 15" TC-2000 SVC.

http://www.tcsounds.com/tc2000.htm

Make sure you're using the Pro version of WinISD. Try 320liters, with a 15Hz tune, and 900W.

That shouldn't look like a waste of time. :flex:
 
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Discussion Starter · #17 ·
Here is what I get with a 260L box tuned with a 6" port 20in long (15.38Hz). If you compare that to the box I'm thinking about (13.5cuft, 22Hz tune), I think the 13.5cuft box has a nicer looking curve atleast down to 17HZ.

Could someone check my T/S parameters...PLEASE?

 

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The response of the D2 in 260 liters with a 6" port that is 30" long is quite good. The high Le and medium Bl are what would be causing the -3db point to be reached early on in simulations, but in real life, the output is pretty **** flat. I think the published Le is a bit high.

mchorter, the design I mentioned is for a D2, you'll want to go bigger with a D4.....though I would personally stick to the D2.
 

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I'd definitely ignore that highish -3db point...In-room it'll probably be WAY lower than the simulations suggest with room gain and all.
 
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