Was wondering if any one knows much about these cabs?

I can' give you many specifics but here is what I know. Ampeg makes instrument amplifiers, especially well known for bass guitar. The V4B was an amp built earliest in the 60's (exact dates unknown). Big old tube thing, louder than all get-out. If you have a sub for it, it is most likely a bass guitar cabinet and loaded with very efficient MI speakers (somewhere in the 95-100dB range). The trade-off for all that efficiency is size and low end response. They aren't really intended to be hifi speakers, as a matter of fact probably don't have very flat response.

a quick edit: Is this the honkin' big 2x15 folded horn?

It's the 2X15 horn loaded cab that went with the Ampeg V4B. I do not have one, but two skating rinks near where I live have four each. One is actually using them whle the other is not.

I can't find much on this before '71.My "Ampeg-The story behind the sound" book says the V4-B timeline as '71 thru '80. Loaded with two Altec 421A drivers,and later with two EV 15".Ampeg ripped out the reverb from the V-4 to make the V-4B.They said was 25 feet before it really developed.Sounds like the people in the back heard these enough to induce bowel movements,but you couldn't hear as much onstage while playing.I missed the chance to buy one of these rigs a while back w/ EV drivers and a '71 Jazz Bass for 900 bucks.I settled for a used Ampeg B15-S with the Altec driver,which was introduced the same year.I still run it daily. The book says-Yes,folded horn. So I'm thinkin 97-99 DB,with response to 5k or so.

I know where eight of those cabs are. They are both at two skating rinks one where I live and one in Macon which is immediately north of me. The one in Warner Robins still uses the subs in conjunction with eight Peavey SP-1 speakers which need crossover repairs while the one in Macon does not use them and IIRC also had at one time eight Yamaha horns and eight Altec? (at least that's what they look like) speakers.