Thanks guys for your responses. Again having no professional experience, and my only background was reading an old radio shack book "building speaker enclosures". I wanted to be an audio engineer, and build or design speaker cabinets, but life took me in a different direction, so now (at age 50) I settle for this as a passionate hobby. It never dawned on me that there would be such a thing as capacitance delay, which would slow down in time, the point where the PR
would pull in when the active pushed out. This seems then to be a critical factor when building either a tuned port or PR
design cabinet, correct? As the internal cabinet air volume increases (starting from a theoretical zero), the time at which the PR
would pull in vs the active driver pushes out will increase. So this means I think you would want to pick an idea cabinet size that causes both active driver and PR
to move in or out at roughly the same time. What I don’t' know, and maybe you an answer, is if, in a practical size cabinet, in this case for a subwoofer only cabinet, whether 1 - it is possible to achieve this without having the cabinet be the size of a refrigerator. And 2 - If it is possible with a "normal " size cube design, then perhaps it is critical to design the amount of movable air inside the cabinet to be exact, since if you are even a little bigger than optimal, you start to go the other way, and make the active driver and PR
out of phase again.
And all this is frequency based I gather. Meaning at 1.5 times the frequency (60 hz as opposed to 40 Hz) maybe it all acts different? What I am realizing is that there's an awful lot of theory that goes into the deisgn of a speaker cabinet, especially at the lower frequencies, and there's likely often a tradeoff between theory, and how it actually sounds, given the materials you are using, that might mean certain theoretical formulas can be overlooked or left out of the design because another design factor is 3-5 times more prominent that affects the final listening experience.
I am all amped up again recently, because I am about to upgrade my home theater sound system, and found that the most expensive and critical piece is the subwoofer. With my home theater and my desires, I need to buy a sub that goes for $1,000 minimum, but I don’t have that kind of money. It’s been a while since I built my last enclosure, and it dawned on me that I might build my own powered subwoofer. I looked on Amazon, and can buy a JBL dual voice coil 1400 watt peak subwoofer driver for only $150. I also can buy a matching barebones amp for about $100. It would appear one could make their own 15 inch 1,000 watt powered subwoofer with a honking JBL driver, for around $250 + wood + wires/connectors, that should roughly compare to subs costing $1,000 or more easily.
Can any of you point me to any reference material that will help me design a cube or rectangular cabinet for a tune port design for a 15 inch subwoofer driver. I’d like to take a stab at this for my next cabinet making project, and looking to start designing right away. I think at this point I can way too easily get lost on all the theory around individual design elements, and how each one can affect sound adversely. It would be nice if someone in a book somewhere spelled out, from most important, to least important, the considerations for making a bass cabinet sound good, as opposed to books where 100 different points in theory are described for your understanding, leaving you without a clue as to which elements are actually important to the final listening experience for your intended deliverable as a cabinet.
My other way of going about this would be to try to check out in person other 15 inch powered sub cabinets with tuned ports, and start with the port dimensions that someone already used for a retail design. Of course, I understand I have no way of knowing what the inside of the cabinet looks like, if they used filler wood as part of the capacitance and to tweak the air volume design, and I heard that tune ports often have “cones” rather than just an open box hole, that contribute to the tuning point (length of cone, shape, etc). While it seems it’s advanced calculus to exactly design ANY enclosure to theoretical perfection, my HOPE is that me as a proud individual enthusiast, and maybe my close family and friends, listening to my home theater home made mega subwoofer, might find that it sounds nothing less than spectacular, even if I miss a key element or two in the design. My other question is, are there any inexpensive TOOLS I can buy to analyze the sound, and give a visual representation on the tuning and frequency response, so that I can make tweaks to the original design even post construct?