Shure SM51
A lavalier built for the rigors of broadcast — machined steel, a recessed grille, and a snap-in mount that went on in an instant.
Overview
The SM51 is a wearable lavalier that Shure built with a seriousness most lapel mics of its day never got. The company's own catalog copy calls it a "versatile omnidirectional dynamic microphone" designed specifically for radio, TV, and motion pictures, and it was pitched to match in sound with stand- or desk-mounted units — meaning a talent wearing an SM51 could cut in and out of the same mix as a studio desk mic without the tonal mismatch that plagues cheaper lavaliers.
The physical build is where the SM51 separates itself. Shure describes a smoothly-contoured, machined-steel case with a recessed grille — that recess is the whole point, because a lavalier lives clipped to a lapel or tie where fabric rustles against the capsule constantly. Recessing the grille is a direct attack on clothing noise, and it's the kind of detail that tells you the designers had actually worn one. The mounting is Shure's "Positive Lock" system: the mic snaps into its lavalier clip in an instant and then adjusts position without noise, so a talent can reposition it mid-broadcast without the audience hearing a thing.
That snap-in convenience is easy to undersell. On most lavaliers of the period, repositioning meant fumbling with a clip while the mic stayed live — every touch a potential thump. Shure's answer was a mounting that holds securely but releases cleanly, and the catalog makes a point of the "greater convenience, security" of the arrangement. The cable got the same treatment: extra-flexible, kink-free rubber, and — critically — easily replaceable. Lavalier cables are the first thing to fail on any body mic, and a field-replaceable cable is the difference between a repair and a replacement.
Shure built the SM51 as part of a broader lavalier ecosystem rather than a one-off. The company's accessory catalog lists two lavalier assemblies that fit it: the A51L in plastic and the A57L in rubber, both also shared with the 570, 570S, and 571 microphones. A swivel adapter, the A57E in black, is listed for the SM51 alongside the 570, 571, SM76, SM85, and SM87. That shared accessory line means an SM51 owner today has a slightly wider path to replacement clips and mounts than the model's age would suggest.
Contemporary Shure advertising placed the SM51 at the bottom of a page otherwise devoted to the SM60 omnidirectional dynamic, and the pairing is telling — the SM60 was the rugged hand-held, the SM51 the wearable. The same 1967-era ad copy that boasted the SM60 could be dropped on its nose without internal damage introduced the SM51 as the lapel option "specifically designed for radio, TV and motion pictures." The SM51's own catalog page carries a 1967 Shure Brothers copyright, which is the firmest date anchor available for the model.
The mic's long tail in the studio is worth noting. EQ Magazine (March 2009, p.43) found the SM51 still in working rotation decades later — an engineer interviewed there lists it alongside the Shure SM81 and AKG C451 as hi-hat options in a modern drum-tracking setup. A dynamic lavalier turning up as a hi-hat mic in 2009 is not the fate Shure designed it for, but it's a familiar one: a small, tough, omnidirectional dynamic with a recessed grille is exactly the kind of thing that survives the broadcast career and gets pressed into service wherever a close, uncolored pickup is wanted.
What the record does not give is the hard data collectors want. No frequency response, impedance, sensitivity, weight, or original price for the SM51 appears in the available documentation — the period listings that do exist, in Studio Sound (January 1975, p.35), quote figures for the SM60 and SM76 but not the SM51. Buyers should treat any published SM51 spec sheet with suspicion until a Shure data sheet for the exact model surfaces. The 1967 catalog copy and the accessory listings are solid; the numbers are not.
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