improving my subwoofer enclosure

I have a few question regarding vented subwoofer enclosures. First of all, I am having trouble making sense out of the enclosure I currently have. Here is a link to the enclosure: http://www.diamondaudio.com/PDF/current/WiringEnclosures/Single10VentedEnclosure.pdf.Does the volume of the enclosure (as given by winisd) include the volume of the vent or is it only the volume where the back of the subwoofer is in? WinIsd seems to provide a pretty good response for my woofer ( D910D4) at a box volume of around 1.35 ft^3 and a tuning frequency of ~27Hz. Would this 1.35 ft^3 include the volume occupied by the vent?    I've tried calculating the volume of the box I currently have with and without the vent volume and I can't seem to match up the tuning frequency between WinIsd and the enclosure specs with the same vent (2" X 12" X 44"). Namely, when I include the vent volume I get a tuning frequency much lower (~33Hz) from WinIsd than what is specified on the specs. When I don't include the volume of the vent I get around 42Hz.   The volume of the box I have without the vent volume included (which gives me Fb~42Hz) is only about 0.8 ft^3. The response using WinIsd seems to be kind of peaky with that small of a volume so I'm thinking about building a different enclosure. I'm more into SQ and like my bass to be as deep as possible. I generally keep my Low Pass crossover on my amplifier at ~60Hz.    So, all of that for my main question: would it be worth it for me to build another box with a volume of 1.35 ft^3 tuned to 27 Hz?I know this is a rather subjective question, but please keep in mind that it's SQ and deep bass that I'm after.Here are a couple of plots from WinIsd. The first one is of the setup I am currently running and the second is of the setup I am considering changing to:

stevdart wrote: Read https://www.the12volt.com/installbay/forum_posts.asp~TID~104086~PN~2 Make sure you deduct the entire port structure as displacement, not just the port airspace.

Thanks for the link. I must have just missed that thread with it being so recent and all. So, I have calculated the box volume correctly for the first WinIsd graph displayed above. The main question still stands. Should I change enclosures?

Unless you're looking to build an SPL comp vehicle, the second graph will produce far more usable results.Support the12volt.com

Ok then, I will build a new enclosure ... eventually. I won't be able to do it until the end of summer when I go back home (where all my dad's woodworking tools are) from school. So that gives me a good amount of time to make plans for the enclosure. Here's another question: how much group delay is acceptable?

DYohn wrote: In general, you want to keep in-room or in-car group delay under 20 msec  at 20Hz and under 10 msec at 40 Hz.  Software will tell you the group delay based on the plotted frequency response and system phase but ths will change once the system is installed.

Question for you, DYohn:  can you just take it for granted that the group delay always gets worse, or can it actually get better in the installation than it shows in the modeling?  (You said it "will change".)

Do you just model for the best group delay that you can get and hope for the best when it's installed?  Or is it, in reality, a minor factor and of little concern in the modeling phase because it is known to change once installed?

(For these questions let's assume we have absolutely determined that the enclosure will be vented, not sealed.)

Build the box so that it performs well in the worst case scenario and, in return, it will reward you at all times.

Yes, it can get better in the car.  Group delay is determined by the phase delay at a specific frequency and in car (or in room) the phase delay will vary depending on the size and geometry of the space and how many reflections are generated.  In a car, which is relatively small, the group delay at higher frequencies tends to be worse and at lower frequencies tends to be pretty much what gets modelled, or can even be better than what's modeled because the space is too small for low frequency waves to fully develop.  Determine the standing wave frequency of the space as group delay at this frequency will be increased significantly and can lead to significant SPL nulls.  You want it to be as low as possible at and above the standing wave frequency even if it means lower frequencies are higher.  Indeed, it becomes harder and harder to hear group delay effects at frequencies below 40Hz, unless it is very severe.Support the12volt.com

Here's a plot of the group delay for the box I am currently modeling: It is a little above 20ms @ 20Hz and is below 10ms @ 40Hz. However, as you can see, there is a big spike at about 24Hz. Would this group delay be ok?

That's your port tuning frequency, right?  It is pretty severe, although I bet you won't be able to hear it.Support the12volt.com