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Discussion Starter #1
I currently have two RL-p15 in LLT tubes tuned to 13.5Hz. They are awesome, and really rattle my bones when I want them to.

But IF I were to use them for IB, how much would I lose in SPL and headroom?

They are D2s driven by an EP2500.
 

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You'd loose some headroom off the low end definately as you won't have the port assisting you anymore. You'd also possibly loose some SPL as the drivers will hit xmax easier.

The best way to answer this question would be to model both situations in Unibox or WinISD and compare. You can simulate an IB by making a sealed enclosure with a very large volume (like 9999L). Pay close attention to the FR and excursion graphs.
 

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Discussion Starter #3 (Edited)
I did. Seems the IB will hit Xmax at 18Hz, where the ported will reach around 12Hz. The IB is down 4dB at 20Hz, and around 7dB at 13Hz, where the ported drops off.
The group delay charts is pure art for the IB compared to the ported. Not sure how audible it is that low, but still.. It's peace of mind, anyway. :)

Edit: Just looked at the plots, and with a 2nd order hi-pass at 10Hz, I'm not hitting Xmax at all with my current amp, and still doing almost identical for SPL. The tradeoff is higher group delay, though, but muchmore even and shallower than ported.
All in all it looks really good on paper....
 

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I'm kinda suprised that with that much power they are hitting xmax at that low of a frequency. With the EP2500 they could be taking 1200 watts or so each. I know the RL-p15's are very capable, but I didn't think they were that capable!

If you are modelling in WinISD it should be easy to see the changes to group delay and excursion assuming you are boosting the low end to match the low-end performance of the ported subs. Doing this in Unibox is possible, but trickier.

Also, can someone else chime in about how the EP2500 performs in the teens of Hz's? I know most amps drop off.
 

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Here's the cone excursion and spl comparison graphs. Yellow is sealed and pink is what you have, 10.7 cu.ft. tuned to 13 hz. The sealed needs a SSF at 15hz and the ported at 13 hz to stay within maximun Xmax of 24.6 mm. Both models have an input power of 650 watts. There is a 9 db difference at 13 hz and a 5.5 db difference at 18 hz.

alt cone ex..JPG

alt spl.JPG
 

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And the group delay follow the excursion curve pretty closely, so no real benefit, really.
For maximum output, ported would be the way to go. But for "sound", I'm not so sure. I've personally never heard an IB, but the people who have them say it's the ultimate sound. There must be something to it. It would be nice to find someone who has had both and can say from first hand experience what an IB sounds like compared to a ported.
 

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Discussion Starter #11
And it looks like I can drive them a good bit safer with a HPF on there too. Right now I have NO idea how hard I've pushed them. They have never bottomed out, and it would be good to know that they were safe with a HPF. Is there a solution for a 10-15Hz HPF?
 

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You should experiment with how hard you want to push your system. If you're happy with the levels and the subs aren't bottoming out then a SSF isn't nessecary. If the subs do bottom out then the Reckhorn B1 from Creative Sound Solutions works well with pro amps. It has an adjustable SSF so you can tune it to your needs as well as a some other features.

http://www.creativesound.ca/details.php?model=B-1

Click on the "More Information" link and it will take you to the Reckhorn website and the manual.
 

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You can also add another 2 drivers. Ib's work a lot better the more drivers there are. 2 is the absolute minimum you can go.
 
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