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# Can you guy's check my sub box calculations? And a 12" driver choice question... (1 Viewer)

#### Jim A. Banville

##### Supporting Actor
My sub box's internal dimensions are 13x23x22.5", which is 3.89 cubic ft. The port is 4" in diameter x 17" long, which is .12 cubic ft. The amp I will be getting (PE 250) is 9x9x2.5" (actually 3.25" deep, but subtract .75" for the thickness of the box's rear panel), which displaces .11 cubic ft. Now, I haven't decided exactly which 12" driver to use, but I assume it too will take up approx. .12 cubic ft. My first question is, do all these calculations look correct up to now? Second, I'm sure that I must subtract the space taken up by the driver and amp, but must the volume of the port also be subtracted from the raw internal volume of the box? If so, the actual internal volume of my box when it is completed (driver and amp installed) should be 3.54 cubic ft, correct? Now, I had planned on using the Shiva, but I am also considering the Dayton Titanic and the SVS ISD. Which would work best in this box?

thanks!

Jim

#### Cam S

##### Screenwriter
The Shiva would be awsome in that box, and I know this because the volume of the box I just built is the same as yours. I used a full length Adire FP4 port kit. This thing is unbelievable!! here's the pics of it.

#### Patrick Sun

Senior HTF Member
Don't forget to account for the bracing that take up volume inside the box.

#### Jim A. Banville

##### Supporting Actor
So is the answer YES to the question as to whether the volume taken up by the port should be subracted from the raw internal volume of the box?

#### Brian Bunge

Senior HTF Member
Jim,
YES!

#### Pete Mazz

##### Supporting Actor
I'm getting a tuning of 22 1/2 hz with that box and length tube. It will give you a slight bump in the response ~50hz, but all in all, a maximally flat tuning.

Pete

#### Jim A. Banville

##### Supporting Actor
Thanks Pete! Is that with the Shiva's spec's? Anything I can do to improve it?

thanks

Jim

#### Pete Mazz

##### Supporting Actor
Yea, Jim, that was a Shiva.

I personally prefer a low Q design. You lose some output but gain more low end protection and, I think, better sound quality.

If it's just for HT, then your design will give you more impact for those bass intensive effects. You may want to consider a rumble filter of some sort to protect against bottoming on those "silly bass" scenes.

Pete

#### Jim A. Banville

##### Supporting Actor
Thanks again Pete. What causes the bump at around 50Hz? I will be using a Patrs Express plate amp that may or may not already have the rumble filter/bass boost, or I may have to mod it. I haven't taken it apart to see what resistors it has.

Thanks!

Jim

#### Patrick Sun

Senior HTF Member
I wouldn't sweat the minor bump at 50Hz, your room will have more to say about that bump than the design.

#### Pete Mazz

##### Supporting Actor
What Pat said. It would resemble a sealed .8 Q FR curve. The "slight bump" is only ~.5dB.

Pete

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