AKG C451 EB by John Eppstein
This is the original, vintage C451 which is discontinued, not the current mic with a similar model number.
The mic is a system consisting of a preamp body and various capsules, pads, and accessories. The configuration this review primarily pertains to is the body with the CK1 cardioid capsule and 10 and 20 dB screw-in pads. The pads are attacked between the capsule and body as needed. In this configuration (the most common) the mic is a typical professional quality SDC conderser mic, front address, pencil form factor. It's commonly used on anything where good definition of high frequencies is desired, such as overheads, strings, snare drum (with a pad installed), piano, etc.
However, with the addition of some of the accessories this mic becomes extremely versatile. In addition to the various interchangeable capsules (omni, cardiod, hypercardiod, and shotgun) and the pads, accessories include a pop filter for use as a vocal mic (that makes it look like a ball mic), and extender (non-flexible gooseneck) tubes for use on lecterns, over choirs, and many other applications. There are photos of The Beatles using 451s with the gooseneck and pop filter on vocals. If you've seen a pic of Paul singing into a ball windscreen mounted on a very long, thin tube with an approximately 45 degree angle about 2/3 of the way toward the head and wondered "What the heck is THAT???", now you know. There are also, of course, the usual shock mounts and clips available. Here is a website that shows pic of many of the capsules, as well as many other vintage AKG mics.
The 451 stuff starts at the bottom of the page and continues on the next.
Back when I worked for Bill Graham's FM Productions we had a flight case about the size of a guitar case that contained a matched pair of C451Es along with the full set of accessories. Very impressive and cool.
The 451EB is the slightly newer model of the 451E - both take the same interchangeable accessories. Discontinued in 1984.