anyone got designs for a double 18" push pull sub bass cab?

I've built nothing but push-pull subs for the last 20 years or so. Dual and quad 12s, dual 18s, and lots and lots of dual 15s. 

None were clamshell, that is a waste of time, money, efficiency, and output.

The box design must be specific to the T/S parameters of the driver you want to use.

Kind of like this:

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=7339275215&category=47094&rd=1 - http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=73392 75215&category=47094&rd=1

This was a box EV came out with after I talked with one of their engineers at a trade show about 20 years ago.

EV showed me the light in 1974 with the Interface A, an SBB4 alignment with a Q=2 filter ahead of the amplifier, so it became a B6.

All my best vented designs were assisted B6 or C6 after that.

Around 1980 a friend of mine that was a FOH engineer with dB Sound turned me on to the (then) unreleased MTL4 design. I thought it was cool, but didn't like the short x-max 18s (I don't like 18s in general), and didn't want to have to use a fork lift to move it.

I built a half-height design with two 15s facing each other on a narrow slot. On one of the pair I mounted the drivers push-pull (the reversed driver hooked up out-of-phase electrically).

This sounded so different I thought it sounded funny (at first).

It sounded funny because it had no distortion. It made a large 40hz bass horn sound distorted in comparison. I had Eminence custom make me a large x-max 15 that had the same volume displacement as a good 18 (and went lower).

Now, of course, we see push-pull boxes from EAW, TAD, etc, although I have not seen any exactly the same as the ones I made.

I took an engineering type job (doing L-band RF stuff for the military) about seven years ago and haven't really made anything much since then. I've been thinking it may be time for another production run as some of my old used boxes are trading hands for more than I sold them for new.

I was looking for designs for somthing like these :-

http://www.smartsounddirect.com/content/ProductDetails.asp?ProductID=SSD1013 - http://www.smartsounddirect.com/content/ProductDetails.asp?P roductID=SSD1013

"The two drivers are loaded by a cavity (resonance) which might make for some interresting effects a little higher up the frequency spectrum."

It does limit the useable HF response. The EV MTL4 has a huge (6dB) cavity resonance at 160hz, they EQ it out in the dedicated electronic crossover.

With careful design I can get mine to where you can cross them at 250hz without a peak.

smartsounddirect.com looks like an EAW clone. Simple to design and build.

hey i was thinking of puting some jbl 2226s into a push and pull cab as subs. idealy i want a flat responce right down low and a high sensitivity (im shure thats all designers dream). i think they will be used for smaller spaces so i dont think horns will be good for this? 

im fairly new to speaker design. i built some bass reflex cabs and they sounded good so i have some experience. im studying as an engineer so i have ability in involved calculations so i would like to get right in to it all tho time is scarce right now

can anyone suggest how i might go about tackeling this design? or info on this sort of design?

billy 

You won't get high sensitivity from compound loading. In reality,you won't do a whole lot better than 6th order bandpass. The only reason you would want to compound load is if you needed REALLY small boxes. If you can make a pair of 6th order cabs(space wise) you will get as much output as possible.You would even do ok from large ported boxes.

The compound cab might be able to get a little lower but at the expense of output(power divided by 2 drivers and you can only 'hear' one). If you were to build a large compound cab,driver control(excursion) would be a little limited and you will run out of cone travel early with low power(and output)