Apps Tech Tip #245R: SM58 Arcana…Happy 60th!

Each month features an updated reprise of a Tech Tip from ten years ago because many past Tips are well worth review. Also, some will benefit from updating. Enjoy the sixty-third monthly Tech Tip reprise.

September 2026 is the 60^th anniversary of the Unidyne III SM58 debut. Here are twenty-five tidbits about this iconic microphone.

1. The original SM58 handle was two-toned, a dark gray field with darker gray flecks.
2. SM = Studio Microphone. The intended market was radio and television broadcast studios. We were wrong.
3. The SM58 was nearly discontinued circa 1970 because the radio/television market did not embrace it.
4. Add a meshed ball grille to the SM57 and you have an SM58.
5. It is nearly impossible to overload the SM58 with sound pressure level.
6. The original SM58 handle had a “step” near the XLR connector where the handle diameter suddenly decreased in size.
7. The original SM58 featured selectable dual low impedance: 50 ohms and 150 ohms.
8. The SM58 has been used aboard the International Space Station.
9. Ernie Seeler, the Unidyne III development engineer, disliked rock music.
10. The industrial design of the SM58 was never patented.
11. When operating, the SM58 diaphragm moves only millionths of an inch.
12. The length of SM58 voice coil wire is nearly 40 feet.
13. The air trapped within the handle of the SM58 is key to the vibration isolation mechanism.
14. The SM58 has survived a 200-foot drop from a helicopter; being run over by cars, buses, trucks; being underwater for weeks after a hurricane; being buried for one year; being slapped-shot by pro hockey players; and suffering even worse treatment in karaoke bars.
15. The SM58 grille is designed to dent when dropped to absorb energy, like a crumple-zone on an automotive body.
16. A dented SM58 grille can be reshaped by placing the rounded end of a wooden file handle inside the grille, then lightly tapping the grille surface with a small hammer.
17. The model PE86 was an SM58 with a different paint job.
18. The model PE50SP was an SM58 with an on/off switch.
19. The SM58 is the most widely used mic element for wireless handheld transmitters.
20. The internal acoustic network of the SM58 can be traced back to the Unidyne Model 55 introduced in 1939.
21. The model number “SM58” is a Shure trademark.
22. The one millionth SM58 was manufactured in the 1990s. It is housed in the Shure archive.
23. The original SM58 had a threaded hole near the handle bottom where a setscrew could be employed to firmly secure the XLR connector.
24. Duning the 1970s/80s, Shure sold SM58 mic elements to wireless mic manufacturers as their customers demanded the SM58 sound.
25. When Shure re-entered the wireless microphone market in 1986/87, we ceased selling our SM58 mic element to other manufacturers. They were not happy.

Related links: SM58 in custom colors

Self-noise of the SM58

The English band T. Rex

Arcana – mysterious or specialized knowledge

Unidyne III indicates the transducer type, “the engine,” inside the SM58. Other Unidyne III models include the 545, 565, SM5, SM7, SM56, and SM57. The Unidyne III element is the grandchild of the Unidyne I Model 55 launched in 1939.

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The Shure logo used for the SM58 before 1982 has become known as the “Porsche logo” because of the unique font with wide capital letters. Porsche employs a similar font.

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Why were the digits “58” added after SM? Your author’s historical research has not uncovered the marketing reason beyond that 58 follows 57 and 56, i.e., SM58 introduced in 1966; SM57 in 1965; SM56 in 1964. The number 55 was already in use for the Unidyne II in 1951 and the Unidyne I in 1939.

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Occam’s razor states all things being equal, the simplest solution tends to be the best one.
Thus, 58 follows 57 follows 56 follows 55.

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Hanlon’s razor states never attribute to malice that which can be adequately explained by stupidity.

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The number “5” as the first digit in a Shure microphone model often indicates a moving coil element. This began with the Unidyne I Model 55 in 1939 but is not a “hard and fast” rule as our Model 50, also from 1939, was a moving conductor (ribbon) element.