With many of my early years spent in music retail and later representing Shure in New Zealand, one regular question was "what's the difference between the industry standard Shure SM58 and its bigger brother the Shure Beta58".
So here's the answers:
1. Other than the blue ring around the ball grill, the Beta58 has an extra layer of foam for the pop filtering inside the ball grill. Good for calming down your P's and B's.
2. The Beta58 has a lower impedance. The SM58 has an actual impedance of 300ohms, where the Beta58 has an impedance of 150ohms. This means the Beta58 has a higher gain output (in dummy language, more signal at the mixing desk).
3. Polar Pattern - the SM58 has a Cardioid pickup pattern where the Beta58 has a Super-cardioid pickup pattern (explanation about microphone polar patterns below).
4. Microphone frequency response: (Frequency response refers to the way a microphone responds to different frequencies over its specified operating range).
One of the key differences is in the low mid's and bottom end of the Beta58. You can see based on the graph that the Beta58 starts to roll off at 300Hz, where the Sm58 is flat till 100Hz, (most voices don't go below 100Hz). This may or may not suit your voice. Warning - The SM58 could make you sound like a radio DJ or Barry White!
You will note that in the Beta58 graph it has dotted lines from 1000Hz downwards with measurements assigned to each of the 3 lines. This is representing what's called the Proximity effect. The Proximity effect is common on all single coil dynamic microphones where the closer your mouth is to the microphone capsule the greater the bass response of the microphone. While Shure are not showing this on the SM58 graph this increase in bass response vs distance to the capsule will also be true for the SM58.
I mentioned above the polar pattern, so for those of you who might be new to these terms here's an explanation;
Cardioid - As you can see in the SM58 specs above, the Cardioid pattern is a bit like a heart shape. If you can picture putting a microphone down on its side, with the top of the ball grill at the 0 point of the polar pattern, then you get an idea of its pattern related to frequency. Generally speaking, a Cardioid mic picks up sound from the front, a bit on the sides, and as you get to the back where you hold the microphone, it rejects sound, known as a null.
Super-cardioid - Again, imagine lying the microphone down at the 0 point and getting an idea of its pickup pattern related to frequency. Generally, super-cardioid picks up the most sound at the front, but is narrower in the front zone compared to a cardioid mic. As a result of this narrowing you get a bump at the back of the microphone where sound is picked up. There a 2 null points with this pattern 120 degrees apart or 60 degrees either side of the center line.
One of the major advantages of the super-cardioid pattern is the narrow frontal pickup, which for a vocalist mean less stage bleed through the microphone of the band behind you!
You can take advantage of the null zones of the microphone when placing your floor monitors to increase the systems gain (Sound Level) before feedback - in other words have louder, cleaner monitors before you have feedback issues.
If you are using a Shure SM58 or any cardioid microphone place your monitor right in front of the microphone, so the back of the microphone is facing the monitor. Now the null zone of the mic is rejecting a lot of the sound coming out of your floor monitor.
If you are using the Shure Beta58 or any Super-cardioid microphone place you monitor or monitors 60 degrees of axis on either side of the microphone again the monitors are now facing the null zones of the microphone reducing the likely-hood of feedback!
If you have any questions about Shure Microphones or microphones in general please contact me.