where to start? high efficiency a must

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This may be the wrong place to post my thread, but it seems I need more high-tech advice on the cabinet than the musical instrument "traditions."

I have a traynor YBA-4 bass combo that sits around for various reasons. For the Hi-Fi guys, this is essentialy a 50watt class AB tube power amp with a hammond transformer (8/4 and 4 ohm taps)

I want to re-engineer a cabinet for this amp to make the sound/weight ratio better. I like the idea of using horns, but I still want to keep this a combo amp/cabinet design. My size restrictions are due to my element's (car) cargo room, whether I am going to take my upright bass to the gig or not, and will it go up the stairs on the skid rails I plan to put on the cab.
my size restrictions are:
39" max. cabinet hight (to allow for amplifier on top) (990mm)
24 9/16" (623mm) min. inside cab width (in case I want to drop in a fender chassis some day) To max. overall width of 27" (685mm)
11" (280mm) min depth to 18" (475mm).

I was thinking about using two pioneer B20FU20-51FW 8" in folded horns. To use the other tap on my transformer either the pioneer A25GC40-51F-Q 10" or a Daton DVC SD270-88 10" in a two passive radiator small box. After reading about Fostex drivers and the available information on using them I am very open to them. Could I fit 4 horns in to my size? and get rid of the passive radiator idea?

As a bass player I need low-end emphasis, but the mids are more important than anything. I would like a working range down to 36 hz, but some times I play my fifth string bass (fundamental is 32htz I think) I would like this to be more than just a bass amp, an experiment into the relm of unknown and unconventional. Maybe I will build some other horn / Transmission line stuff in the future.

Any direction would be appreciated.
Look at tapped horns, they might not have the musical range you need though.

Also look up J-bins and Karlson slots.

I strongly recommend separating the amplifier in a separate box so you can carry it, I don't like the sound of sliding an amp down stairs on skid rails.
Thanks for the help! I have been looking at the Frugal horn page and getting ideas. I will look up these as well.
Traynor amps are built tough. There is documented "testing" that Pete Traynor dropped his amps off the roof of the music store he worked at and they still operated! Currently I play with a fender head and separate cabinets, but I am still a bit jealous of the guitarists who just plug in and play, not to mention the clean look. This project is a bit of a novelty, but I may end up taking your advice about seperating the amp. I was planning on shock mounting the chassis some how, since tubes don't really appreciate the low frequencies like I do.
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