Some microphones look the same, some look wildly different. Reading each manufacturer’s product description leaves you with the impression that every mic is the best for everything. Microphones in the sub-$100 range are often described the same way as mics in the territory of several thousand dollars. So, how do you determine what sets them apart? You can get your first clue in those ultra-boring and seemingly pointless specifications. I know it would be much more fun to just try all the mics, but that’s not possible, is it? As you dive into the following details about microphones and their various characteristics, please bear in mind the fact that establishing what sounds “best” is subjective.
The transducer is what converts the acoustic energy or sound pressure waves into an electrical signal. The most common types of transducers are dynamic moving coil, dynamic ribbon, condenser (tube and solid-state), and electret condenser. Although detailing the physical differences between them is not discussed in this article, you should understand that each transducer has different inherent properties.
- Dynamic moving-coil mics typically have the least-accurate frequency response and the slowest transient response, but the highest maximum SPL and greatest off-axis rejection.
- Dynamic ribbons tend to have the lowest maximum SPL, great rejection from the sides while picking up sound from the front and back, and more accurate frequency and transient response.
- Electret condensers usually have even more accurate frequency and transient response, with max SPLs between moving-coil and ribbon mics.
- Tube and solid-state condensers usually have the most accurate frequency and transient response, max SPLs comparable to or greater than those of ribbon and electret condenser mics. However, they tend to pick up more ambient sound than the other mic types.
The polar pattern details if and how the microphone picks up sound differently, based upon the direction of the incoming sound waves. Operating principles—pressure gradient and pressure operated—influence what polar patterns are possible. Pressure operated means that the capsule picks up sound evenly from all directions. Omnidirectional is a pressure operated polar pattern. Pressure gradient means that the capsule picks up sound differently from different directions. There are several pressure gradient polar patterns such as cardioid, hypercardioid, supercardioid, figure 8, and other intermediary ones. When you want to capture more room ambience or signal regardless of the microphone’s direction, use omnidirectional mics. Use directional patterns such as variations of cardioid to reject more sound from the off-axis areas (the sides and back). Polar pattern diagrams indicate the directionality of microphones by showing the level and frequency of sound rejection from different directions.
A microphone’s frequency response, measured in Hertz (Hz) tells you how accurately it converts the frequencies of an input signal. It’s common to see specs such as 30 Hz to 18 kHz. This means that it can transduce frequencies in that range with a certain degree of accuracy. According to those numbers, frequencies outside of that range, such as 20 Hz or 19 kHz will not be output from the mic. However, the frequency range tells a very limited portion of the truth. It’s important to know the degree of accuracy, expressed as a +/- decibel variation. 20 Hz to 20 kHz (+/- 20 dB) means that there could be 20 dB differences between the input and output signals at certain frequencies. 20 Hz to 20 kHz (+/- 3 dB) means that there would only be a maximum of 3 dB differences between the input and output signals at certain frequencies. The latter is obviously more accurate.
Even more telling is a frequency response chart, which displays the decibel variations across the frequency spectrum. Such a chart allows you to see exactly where the mic will attenuate or boost frequencies and by how much. Frequency response charts indicate how the mic will change the tone of the input signal. Think of it as the mic’s equalization curve.
Keep in mind that more accurate doesn’t necessarily mean better. When miking a kick drum, a mic with a low-end boost may sound better to you than an ultra-accurate mic.
This indicates the highest input level the microphone can handle before a certain amount of distortion is produced. Think of it as the loudest sound you can capture “cleanly.” Mics with high maximum SPLs are beneficial when close-miking loud sources, such as drums.
Sensitivity, usually measured in decibels, describes the level of output produced from a given input level. If the same input level is passed through a low-sensitivity mic and a high-sensitivity mic, the low-sensitivity mic will yield a lower output level than the high-sensitivity mic. Thus, low-sensitivity microphones require more preamp gain than high-sensitivity mics do. However, high-sensitivity mics will usually yield lower maximum SPLs.
The impedance is the level of resistance to the flow of electrical signal and is measured in Ohms. High impedance microphones present a stronger resistance than low impedance mics do. Thus, they compromise frequency response and pick up more noise over long cable runs.
This is the level of noise produced by the microphone even with no input signal. The lower the value, the less “hiss” the mic produces. Mics with high levels of self-noise tend to be problematic for dialogue production scenarios (think TV, film/video, podcasting, voice-over, etc.) because the noise will be much more audible than in music production where it may be masked by the presence of other instruments.
This value, measured in decibels, shows the difference between the minimum possible signal level (the self-noise) and the maximum possible signal level before overloading. The dynamic range represents theoretical performance and doesn’t factor-in real-world issues like noise from air conditioners, which raises the ambient noise level of a room. Rank this as a low-priority consideration.
Often abbreviated SNR and always expressed in decibels, it is the difference between the nominal (not maximum) signal level and the noise floor. The higher the number, the less perceivable the noise floor will be in relation to the ideal signal level.
THD is an abbreviation for Total Harmonic Distortion, which is the level of distortion produced based upon a given input signal. Assuming you’re after clean signal reproduction, lower THD values are preferred. Since THD is measured as a percentage, 0.005% would be preferred over 0.05%.
This details what power source, if any, is required for the microphone to operate. Some mics require batteries, others such as tube mics require dedicated external power supplies, some require phantom power (DC voltage typically sent from a mic preamp), and others require nothing! The power requirement is not necessarily an indicator of audio quality, but it will obviously affect the mic’s ability to function.
I hope this helps you make sense of those terms and numbers that mic manufacturers provide. Remember, the factors that most significantly affect the resulting sound are mic type, polar pattern, and frequency response. Don’t just look at the numbers; check out the charts! Investigate further and feel welcome to share helpful mic research experiences you’ve had!