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Discussion Starter #1 (Edited)
Hello, I currently own a SVS 20-39PC+ that I bought 8 years ago. Was going to upgrade to another SVS, but got bit by the DIY bug. This DIY design will be used for both HT and music. Satellite speakers will be crossed over at 80 Hz, but LFE (.1) channel effects will go up to 120 Hz (brick wall filter). Accordingly, the sub will need to handle up to 120 Hz, though LFE content will likely be rolled off quite substantially by then.

I was hoping for a sanity check on the following design from some of the more experienced members here.

(2) Infinity REF1262W will be in a dual opposed config, wired 4-ohm, and powered by a Bash 500 from Parts Express.

Using WinISD, I came up with a 9 ft3 (net) vented enclosure tuned to 18 Hz. The Bash 500 will have its stock HPF changed to a Fc of 19 Hz and a Q of 1.4. Corresponding FR is +1,-3 dB from 17 (F3) to 120 Hz.

With this HPF change, a max excursion of 13 mm (xmax) occurs at 14 and 25 Hz with 224 W of system input power. At 224 W, apparent amp load power peaks at 350 W and occurs at 20 Hz. Port size is 6" and first port resonance is 312 Hz. Port velocity peaks at 25 m/s at 17 Hz at this same input power.

Exact project file is attached. Thanks . . .
 

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Discussion Starter #3
Thanks for the reply, Mike.

I have already started the build, so the tune and volume are fixed now. The only thing that can easily be changed at this point are the Q and Fc of the HPF.

Even so, I am interested why you would suggest a 16 Hz tune and stock HPF model.

When I model a stock HPF (Q 0.817, Fc 17.36) with a 16 Hz tune, SPL below 16 Hz and above 32 Hz is higher. However, the F3 is also higher at 26 Hz. My initial design, Q 1.4 and Fc 19 with an 18 Hz tune, shows more SPL from 16 to 32 Hz. Also, the F3 is lower at 17 Hz.

You did get me thinking, though. Q 1.4 is probably a bit too aggressive and may cause the enclosure to be underdamped and "boomy". Therefore, I think I am going to use Q 1.0 (and Fc 19). This will have the downside of increasing the F3 from 17 to 20 Hz, but it will also eliminate the bulge in the 20 - 40 Hz FR (underdamped area) that comes with Q 1.4.

Q 1.0 project file is attached. Thoughts?
 

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You did get me thinking, though. Q 1.4 is probably a bit too aggressive and may cause the enclosure to be underdamped and "boomy". Therefore, I think I am going to use Q 1.0 (and Fc 19). This will have the downside of increasing the F3 from 17 to 20 Hz, but it will also eliminate the bulge in the 20 - 40 Hz FR (underdamped area) that comes with Q 1.4.
You said this subwoofer will be used for movies and music, so depending upon how much of the latter you plan on doing you might want to rethink a Q of 1. For movies I suspect it would provide a satisfying experience, but the same probably can't be said of music (especially if your particular). You may find that something around .7-.8 would be a better overall compromise.
 

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Discussion Starter #6
Ideally, I would like a lower Q on the HPF, but FR starts to suffer badly.

Q 1.0

F3 20 Hz
F6 17 Hz
F10 15 Hz

Q 0.7

F3 27 Hz
F6 20 Hz
F10 16 Hz

Q 1.0 does still show a bump in the FR. However, it's very minor, starts at 35 Hz, and only results in a 0.21 dB peak at 55 Hz. I will also be using this sub with Audyssey MultEQ XT, so I'm hoping it will be able to help with this design limitation and any other FR anomalies due to the room itself.
 
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