Ok, I am going to apologize in advance for the thread necromancy here.
I don't know how things work here but I am assuming people would not appreciate me creating a new thread on a topic that already exists.
I happened upon this forum when googling "Thiele Cab design". The short version of my story is that I've been trying to neuter my Dual Rec to 'downside' the monstrous tone. I'm only doing this because I really enjoy having a massive sound in volume sensitive contexts i.e. playing for people who just can't deal with the fact that guitars are stinking LOUD!
The long version was that an amp builder here in the great white north (Gar Gilles of Garnet Amps) recommended that instead of buying a little class A amp, I use Yellow Jackets on my Dual Rectifier. As most of you know, tubes work on push pull circuits so you can technically yank out a rectifier tube and the inside or outside pair of the power tubes in a recto to run it at half power. With two yellow jackets, you can effectively downsize the amp to a 15 watt "Class A" circuit and run it with no averse affect to the amp or tubes, provided you rematch speaker load so the amp is properly loaded. (8 ohm output from amp has to be matched with 16 ohms of resistance for a correct match instead of 8 as it would be with four power tubes)
When I first tried this mod, my head didn't have enough power to drive my Standard Rectocab. Basically, it sounds closed and constipated because there isn't enough current for the speakers to respond correctly to the signal. I kind of put the yellow jackets away and didn't really use them again. One day, I had the head down at a local guitar store and for whatever reason, the yellow jackets were in it. The sales dude wanted to know what the red things in my amp did so I showed him. I plugged into a Marshall 1960AX cab and my jaw hit the floor. The looser speakers sounded incredible when pushed by the twin el84 tubes! I then bought my friend's PEAVEY 1 x 12 and swapped the sheffield speaker for a Celestion G12m - 25. It just didn't sound the same as the 4 x 12. It was very tinny with an annoying frequency peak in the low treble area. I've put up with this thing for awhile, convinced that you NEED a 4 x 12 to have a huge sound, but my brother suggested that maybe the Peavey 1 x 12 is what sucks (duh) and that I should do a cab build project. He told me I should try a bunch of different cabs and then 'reverse engineer' the one I like the best.
Since then I tested a few 1 x 12s and 2 x 12s and I decided I really like the Dr Z 2 x 12 Theile cab which is appropriately christened "Z Best Cab." I managed to find the dimensions of the 2 x 12 online but I only realized when I saw a picture of the cab opened from the back that it was ported at the front and it had a shelf under the baffle. I'm trying to come up with some plans to build a similar speaker enclosure but I really don't know where to start. Dr Z's cab has a Celestion v30 and G12H - 30 (heritage greenback) but I want to use a G12m heritage paired with the v30 instead. (I know most people in this thread dislike Celestions but I happen to like them. Preference and all that)
I'm wondering if anyone would mind to provide a bit of guidance here?
i)Basically, I want to know how large the port should be i.e. height and length of the shelving in relation to the rest of the interior. I'm assuming the dimensions of the cab should work and I should be able to figure out the size of the baffle and internal volume based on the dimensions given if I assume the cab is built with 3/4 inch ply. (Keep in mind that the G12H has a more pronounced bass response than a G12m) There are some people here that really understand well how Thiele principles work so I'm hoping that this knowledge can help clarify some design specifications. I understand the concepts but I don't get the math at this point.
ii)I haven't ever built a cab before so one picture of the back of a cabinet with the cover off doesn't give me the best idea of where to start. I know I need to reinforce the box and that the back cover should fit snugly and screw into the bracing. I also know that the baffle must secure to something. In this case, the port is at the bottom of the cab when placed on the wide side. There are two crossbeams made from plywood, the shelf rests on this but doesn't extend to the back of the cab like the crossbeams do. The baffle is at the front of the cab and is situated above the shelf. What I want to know is what goes in front of the baffle? Is that more structural support? Is that what the baffle mounts onto? (I PM someone the picture but I'm leery to post it here since it is not of my cab since I do not own a Dr Z cab)
iii) Lastly, I know a grillscreen mounts on a separate frame. I am not sure of how to mount this and secure it onto the cab. I wish to install it with piping but I don't know quite where to begin. I am going to partially disassemble my 4 x 12 to see how Mesa approaches the build process but any input here will help me greatly.
The wood I'll be using is high grade maple plywood without any knots in it. It is ideal for making kitchen cupboards and won't warp. It also will look fantastic stained. Since my father in law is a carpenter, the build quality will be fine. I just have to design the cab appropriately ahead of time.
http://www.tulsaband.com/store/product.php?productid=16712"The "Z Best"
The Z Best 2x12 closed back cab is an animal all its own. We have utilized a Theile Ported design which allows us to dial in the full frequency range of the guitar. Low end is determined by the port thickness, Mid response by the shelf depth, and Top end by choice of speakers. Placed vertically, the Z Best delivers a tuned focused sound. yet has the airy qualities associated with open back cabs. When placed horizontally, you pick a bit more low end as the port is then coupled with the floor. This is a long throw cabinet that will get the sound to the back of the room. Standard speaker configuration is a Celestion Vintage 30 and Celestion G12H30. Other Celestion speakers are available on request.
Weight: 60 lbs Dimensions: 28 ¼” H, 19 ¼” W, 13 ¾” D"
