Both mics are characterised by sound quality and reliable performance; however, there are differences that suit specific applications.

Our technical team here at Shure UK are regularly asked to describe the difference between our classic SM58 and its closely related cousin, the Beta58. Firstly, let's be clear: this is not a question of better or worse – both microphones are characterised by outstanding sound and performance. However, each model has key fundamental strengths suitable for different applications. Here are some of the key differences to bear in mind...
 

Polar Pattern:
Perhaps the most obvious difference is the microphone polar pattern. The SM58 has a cardioid polar pickup pattern, while the Beta 58A is a supercardioid. The polar pattern subsequently affects how you should use the microphone and where it would be most appropriate.

As you can see from the diagrams, a cardioid microphone will reject best from the back while a supercardioid microphone will reject better from the sides. Both microphones pick up sound best from the front, but a supercardioid polar pattern has the added advantage of being more directional and therefore less susceptible to feedback when using correctly placed stage monitors.
 

Output Level:
Due to its neodymium magnet, the Beta 58A has greater sensitivity and a 4dB hotter output than the SM58
 

Frequency Response:
The Beta58 has an extended low-end and high-end compared to the SM58. This does not necessarily mean the Beta58 is better, and depending on the style/tonal characteristic of your voice, you may or may not benefit from the extended frequency response.
 

Handling Noise:
The Beta 58A is quieter than the SM58 due to its advanced pneumatic shock mount system
 

Grille:
The Beta 58A has a hardened grille, which makes it more difficult to dent.

Summary