Microphone Response Curves

This week, in part 3 of our Understanding Microphones series, we are taking a look at microphone response curves. As we did last time, we are looking at the Shure SM57 Cardioid Dynamic Microphone. Go ahead and download the specification sheet for it from this link. We are going to be looking at the  diagrams at the bottom of the page.

What is a microphone Frequency Response Curve?

Without going into huge detail, a frequency response table is a graph to help you understand how the microphone will sound to the human ear.

The horizontal axis is the frequencies that can be heard by the human ear. Notice the vertical lines aren’t evenly spaced. This is a logarithmic scale that mirrors how the human ear hears sound so the significance of the actual curve is easier to understand.

The vertical axis is centered at 0dB in the middle. A microphone that picks up everything evenly would have a response curve that was a straight horizontal line at 0dB. However, there is no microphone that can do that perfectly, so you will see a curve that wanders above and below the 0dB line. Above the 0dB line shows frequencies that the microphone is more sensitive to, while below the 0dB line are frequencies that the microphone is less sensitive.

Let’s look  at 2 actual microphone response curves, Shure’s SM81 and SM57.Question: Which is the best microphone?

A microphone with a flat response like the SM81 would be better than a microphone with large variations in its curve because it would be a better representation of the original sound, right?

Not always.

The Shure SM57 has what is called a Shaped response curve. The variations in the high and low areas are completely intentional.

The SM57 is intended as a vocal microphone. It’s response drops off around 2000hz which helps eliminate handling noise and boominess that is not really part of the human voice (the blue area). The response is reasonably flat through most of the vocal range so voices sound normal. The green area is where the frequencies are that give that bright presence in a voice. The SM57 has a nice rise in that band so voices sound great. In the red area, response falls off sharply to help eliminate feedback and squealing.

The flat response of the SM81 is great for acoustic instruments like acoustic guitars, flutes, and percussion while the shaped response of the SM57 is great for vocals in front of a band, reducing stray low frequencies from instruments like drums and bass, while making the voice pop.

So back to our question, Which is the best microphone? The answer is………… it depends.

Next week we will closer at microphone types like large diaphragm condensers, boundary layer mics, shotguns, and more!

In Part 1, we talked about the basic types of microphones.

In Part 2, we looked at microphone polar pickup patterns to understand where mics accept and reject sound.