I should probably acknowledge the fact that I am playing fast and loose with the whole letter X part of this post but there was always going to be some awkward letters, can we just ignore the 'B" and move on?
Spring reverb! Guitarists love it in all its zoingy glory but in studio applications it is associated with poor man's reverb for those of us who couldn't afford plates or digital reverbs. The Great British Spring Reverb was one such device, this popular but always rather "built in a shed" unit resembled a length of drainpipe and although remembered fondly by some, I'm not sure many users of this device would have turned down even the most basic digital reverb from today.
The same couldn't be said of plate reverbs and AKG made some of the few truly professional spring reverb units which could occupy the same space as a plate. The biggest was the BX20.
In this video Review, Russ looks at the BX20 and finds it rich, dark and distinctly different in character from a conventional algorithmic reverb or a plate.
As part of Black Fortnight, until November 30th the AKG BX20 is discounted to £75 (usually £150). If you want a reverb with a distinctive character then the BX20 might be the one.