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Understanding Studio Microphone Specs

Understanding published technical specifications for studio microphones will not guarantee you'll like the sound you get but it will help you understand some of why you might prefer one mic over another. When making the decision to buy, it will also help narrow the field of choices and improve the odds you will like what you hear.

Frequency Response
While the sensitivity of microphones over frequency are all unique there are some common "attributes":
  • Notice the 3-10 kHz "peaking" in many of the LCMs? At least a portion of this is related to the natural resonance of the capsule's diaphragm.
  • Notice the steep "roll-off" most have above 20 kHz? The physical diaphragms of mics are too thick to respond to high frequencies and are too far from capsule resonance so sensitivity drops -- but it doesn't matter as the average human ear cannot hear these frequencies anyway.
  • Notice the gradual roll-off below 50-300 Hz of most LCMs? Most LCMs operate in a cardioid pattern and respond to pressure gradients between the two sides of the diaphragm. As the frequency drops below 100 Hz there is less and less phase difference between the sides and so the sensitivity drops with frequency.
  • Notice multiple "bumps" in some response curves? These are generally a result of multiple mechanical resonances of the diaphragm, capsule housing and headbasket. For a given size, style and configuration it is valid to assume the manufacturer has done their best to minimizes these -- for the price they are asking.
  • Notice how most all these curves are generally "smooth"? All makers publish "typical averaged" response curves which "hide" the nuances of most sharp resonances. It's mostly marketing, but don't obsess over this "distortion" or "masking" of the details. Remember that the curves are only "typical" and the variances between mics of the same model# from the same manufacturer are all different and they generally do not publish the range of this variation. Neumann's mics are apparently +/- 2dB of the published typical curves which is at the human threshold of hearing the difference. It would be fair to assume that all other makers are worse.
Polar Plots
Most mics have polar plots to show their "on-axis" (which way the mic capsule is pointed) sensitivity curves with direction away from center. Some things to look for:
  • Symmetry: Generally cardioid mics have symmetrical patters around the "on-axis" center. If the plot looks perfect, it is probably averaged to make it seem that way. If the pattern is symmetrical but rotated toward one side of center, that will indicate some bias toward one side to be aware of when positioning.
  • Normalized: Most polar pattern data has been normalized to show all frequency plots with the same sensitivity. This is not wrong, it is just assumed that you know to look at the frequency response plot to get the sensitivity difference between frequencies.
  • Directionality: Cardioid mics will show a distinctive one-sided sensitivity curve where the "back side" lobe is much much smaller (or even zero) compared with the main forward lobe. This is the result of phase cancellation between the front and back as the acoustic wave is delayed hitting the back. Just be aware that this is frequency dependent so will not be as effective at all frequencies. This is why there are multiple curves plotted on most polar charts.
Transient Response
Much has been written comparing microphones using descriptive terms like 'warmth', 'smooth', etc. but little is provided about another important measure -- the response of the mic to impulse energy. While much of the audio energy processed by a mic is not of a pressure impulse, knowing how the mic responds to an impulse is a means for analyzing how it behaves with respect to time. Time response differences are a major factor in how a sound is 'colored' by the mic capsule, basket and internal pre-amp if any. This needs much more research.

Two equivalent values are listed for each mic. The higher the (mV/Pa) value (and less negative the (dB) value), the greater the sensitivity. The 'dB' scale is logarithmic so changing the (mV/Pa) value by 2x, or 1/2, is a 6dB change. As a simple "rule of thumb", the human ear cannot easily detect less than about a 2-3 dB difference. Typical numbers where 1Pa equals a 94dB SPL are shown below. Note that at -40 dB sensitivity, it requires 40 dB of external gain to achieve 0 dB on the mixing level meter.

 Type Sensitivity (dB)
 Sensitivity (mVrms/Pa)
 Ribbon -59 1.1
 Dynamic -54 2.0
 Condenser -40 10
 High-Output Condenser
 -32 25

Self Noise
This is the total, averaged noise level produced by the electronics within the microphone. A lower number is better. The important concept here is that the external mic gain amplifies both the signal AND the noise. Ideally you want low noise and high sensitivity. However, since these mics are all very quiet (low noise), if the rest of the system is quiet, background noise in recordings should not normally be an issue. In fact, system "hum" is frequently a much, much bigger issue than mic noise..

Maximum Sound Pressure Level before distortion -- usual 1-2% (5% would sound really terrible)(distortion roughly doubles for every additional 6dB in SPL). This should never be an issue in a recording studio as the Max SPL of these mics would be deafening if the average source were that loud, but it's good the values are all high to prevent distortion on random transient peaks from instruments. Rarely do voices achieve more than 120 dB SPL and most of the LCMs below have at least 130 dB MAX SPL. It should be noted that the most famous and trusted all-purpose LCM, the Neumann u87, only has a max SPL of 117 dB. This is a big clue.

This is the "dynamic resistance" of the mic output drive level. All of these mics are low (600 ohms or lower) so can easily "drive" the high impedance inputs of most all mic preamps.

Dimensions (mm)
Millimeters are commonly used in technical specs. 1 inch is 25.4 mm.

Weight (g)
Weight in grams (g) is common in technical specs. 1 pound is 453.6 grams.