Built this subwoofer a few years ago.   Have been relatively happy with it, but just doesn't seem to hit as hard as it should.   Parts Express box (1" MDF.....not 3/4"), 12" Dayton DVC, 250 Watt amp.   The whole thing is very heavy, since the MDF is 1" thick.    Box is approx 19 3/4" square.

Anyway, thinking if I put some type of port in it, it will really come alive.   What size port should I install in it?   Where would I cut the hole in the enclosure?  

Thank you.

http://www.carstereo.com/help/Articles.cfm?id=31

Not home audio but should work the same.

You should also be able to reduce the gain a bit on that amp and still get a louder bass with a ported Box.

3in tube 8 in long port on top

Part of the equation is "what frequency that you need to tune your vent to."    What number do I enter in for that?

That is not the best tuning frequency for that box since the the subsonic filter on that amp is set at 20hz.

That sub really shines in a 4.5 cubic foot box with a 4" port tuned to 20hz.  I've used that same amp/driver combination for both sealed and ported enclosures.

A 19. 3/4 square box gives you a gross internal volume of 5591.4 cubic inches.  There are 1728 inches in each cubic foot.  That gives you a goss internal volume of 3.24 cubic feet.  Subtract the volume that the sub frame, magnet, amp parts and cone take up and you can estimate about a net internal volume of 3 cubic feet.

For a 20hz tuning in a box of that size you need a 3" port (white PVC) that is 13.6" long.  You don't have to be exact so a little over 13 and 1/2" will work fine.  Go to Wal-Mart and buy a cheap pillow or 3 to stuff in there as well.  Put the port on the side.  There is no room on the side or bottom because of the amp and driver mounting locations.  Putting it on top (suggested earlier) allows things to be dropped into the box which will land directly on the driver.

I forgot to ask - Is that amp the one with the bass boost or without?

No base boost on amp.

Thank you for all the hard calculations and efforts.    It is such a well built (all precut from PartsExpress) and stout box, I didn't want to just start cutting holes in in and just slapping a sewer pipe in it for a port.

But I am surprised you said the subwoofer actually likes a BIGGER box?    Really?    This box is HUGE!!!!

Again, thank you for your time and effort.

Huge? Really? I already have plans for a pair of 5 cubic foot boxes for my 15's, an 8 cubic foot box for my 18 and an 11,cubic foot box for my 21.  The guys over at AVS Forum are building refrigerator sized boxes for the new Stereo Integrity 24 inch sub.....Huge is a relative term.

Even retail subs are getting bigger.

250 watts per channel is not a lot for a sub, in my truck I use 1100 watts of class ab power for a single jl 13w7 and ad home I use a QSC4050 at 2200 watts into the 1.5 ohm load

Depends on the efficiency of the driver, xmax of the driver and the enclosure that it is in.  The Dayton DVC 12" is a very low Qts driver (loose suspension) and in a 1.5 cubic foot box a 275w amp will push it to full excursion (approximately 15mm) at 20hz.  I'm surprised that the OP hasn't bottomed out the driver in such a large, sealed box.

I run a Powerbass 1000w class D amp in my car that powers a custom built 12" driver from Pink Star Industries.

Forced perspective from the camera operator........sub boxes are really probably about the size of shoe boxes.  

But yeah, I stand corrected.    lol

Here's a couple more pics.   The only "stuffing" is foam that I had glued to a couple sides of the box.  

Gonna head to home depot tomorrow and see if they have any 3" pvc.  

here's a better view of the amp.    where should I have the dials set for best results?

All of these recommendations assume you use the bass management of your Audio/Video receiver (aka AVR).  Phase should be at zero (all the way left).  Crossover should be at 180 (all the way right).  Start with the level at the 1/2 point (the line pointing up).

What type of AVR do you have?  Does it have any automatic calibration system?  Pioneer has MCACC where you put a microphone in your listening position (I use a tri-pod so it is at ear level) and you just run the auto calibration setup.  I tweak the settings after that.  In your case you may have to adjust the sub's level dial depending on what the final results are.  If you don't have an AVR with auto calibration then we have to do a manual one which takes time to explain.

http://www.mobileinformationlabs.com/HowTo-1Woofer-Box-CAL%20Port%20lenth%201.htm

I used WinISD for my sonosub

http://www.linearteam.dk/default.aspx?download=winisd

I use Unibox for my sub designs.  Years ago, Dan Wiggins posted at one of the many audio forums I frequent that it is more accurate than WinISD.  He compared both results to his professional software and actual results.  In fact, when you put the Le1 and Le2 values into Unibox, it is spot on.  The simulated frequency graph was almost exactly to what I measured and graphed.

Probably
I built my SonoSub in 2003  

I need to build another larger one for the new media room, so thanks for the link.

I'm STILL using an old Yamaha DSP-E492.   The only reason I'm still using it, is because I just can't yet part with my Yamaha M80 amp and C80 preamp.   I have yet to find an upgrade to the 492.    

From time to time I think about ditching all my old gear, but having bought it brand new in the mid 80's, it's just hard to part with.   Would be nice to have a high end receiver.

I'm not familiar with that Yamaha so I'm giving you generic instructions.  Set the sub crossover to 80hz.  I like to route all of my bass to the sub instead of just the LFE channel so I set my speakers to "small" even though they are tuned to 35hz.  

Now you need to calibrate without any automatic tools.  Set your distance with a tape measure.  I sat my wife down in my spot and measured the distance from her head to each speaker.  I then entered it into the receiver.  What does that do?  It assures you that the sounds get to your ears at the exact same time despite the different distances between speakers.  Set your levels with an SPL meter.  Don't have one?  Download an app for your phone.  It doesn't have to be set to 85db, they just need to be set all the same.  For my cousin, I spent 5 minutes with his receiver and the internal test tones and it was done.

If you want to get even more detailed, let me know.  I run a digital parametric equalizer on my sub so that my in-room response is + or - 3db from 100hz to 17hz with significant output down to 12hz.  That sounds like a lot but the EQ is less than $100 and it made a HUGE difference in my bass.

A quality HT receiver should have an internal 80Hz cutoff for the LFE channel.
I understand setting the sub's amp's cutoff at 180 is to allow the receiver to do the work and make sure you don't accidentally cutoff a portion of the spectrum.

I believe the HT receiver's cutoff is digital, at exactly 80Hz.  
This appears to be an analog control so you'd have some roll off using the amp's setting.

I use the small setting for the fronts as well.

Thread derail, but I was wondering what you guys were running for receivers.

Pioneer VSX-1114.  Yes it is an older model but it was the last one to use the Pioneer Premier amp section in the lower price line.  Because of that, I can easily drive 4 ohm speakers which I do.