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I am building a 3300 cu foot (22' x 15' x 10') dedicated theater room, starting with the audio. I am planning my subs and wanted it loud and deep (who doesn't???).

I have also finished reading the excellent book by Floyd Toole (Sound Reproduction: The Acoustics and Psychoacoustics of Loudspeakers and Rooms ) and in the interest of good bass for as many as possible, have elected to position two subwoofer enclosures in the middle of the front and the middle of the back wall.

This places some constraints on my box size, notably the depth, which I want to keep at 18-20". I am planning to place 2 drivers in each vented enclosure and using Box Notes have arrived at a box that is 42" tall, 66" wide, and 20" deep with a working volume of 21.7 cu feet (615 liters). Here are the gory details (by the way the port is 8" diameter; the cursor makes it look like 18"):

So, I am getting to the heart of my question here. I have modeled this box tuned to 15 Hz with two ED 19Ov.2 and two SoundSplinter RL-p18 drivers using WinISD alpha.

Here are the SPL graphs without EQ assuming 125 W of system input power. The 19Ov.2 is in blue and the RL-p18 is in red:

Not exactly the flat response from 15-80 Hz that I am looking for.

If I apply parametric Eq (fc=15, Q=1, gain=4.5dB) to each system, then the curves look like this:

I am struck by the flatter curve of the RL-p18, but slightly deeper extension of the 19Ov.2, but let's face it, at this point I am over my head and really don't know too much about what I am doing. Can I flatten the 19Ov.2 curve with a lowpass filter or ??? I am hoping that some of you smart folks can help me optimize the situation and solidify my build plans.

Do note that the 190v.2 costs $245 shipped, while the RL-p18 is $440 shipped. I am cost conscious, so if I can get the 190v.2 to model flatter, then I will be convinced to go that direction, recognizing that this modeling gets you only so far what with the marked room influences that I see in some of the in room FR analyses that some of you all are posting...

Thanks in advance for your advice and engagement in my project and apologies for the loooooong post,

Geoff