511Bs are... controversial.
Had a pair here for a while (which I acquired quite inexpensively) and I did spend some quality time with them. They're long gone, though.
Besides the ringiness, which is legendary
,
albeit somewhat tame-able, I think most of the issue with the 511B (even more than the 811B, which I find aurally acceptable -- though many don't) is that long, skinny,
pinched throat.
I will say this -- fiddlin' with the 511Bs got me attuned to the notion of using far lower XOs from "woofer" to treble driver/horn (that, and the counsel of some regional horn luminaries).
I far prefer the multicell Altecs, but NO WAY can I afford a pair.
I make due with EMILAR EH500-2, which are... well... quite nice really.
Way more cost-effective than a pair of 1505s at this point in time.