Question: What do microphone specifications mean?
Answer: Determining how microphones differ from each other, along with finding which microphone will best suit your needs, may be a challenge for some. Microphones are designed to capture sound. Sound is subjective and some characteristics of a microphone should be gauged by personal preference, with the measurement tool being your own ears. But sound also has characteristics that can be measured absolutely. These characteristics of a microphone are referred to as specifications, and may be found on the product pages of each microphone. These specifications, however, are often misunderstood.
The frequency response of a microphone, commonly represented by a number (“frequency range”) as well as a graph (“frequency response graph”) in the specifications, is a measurement of how the microphone responds to a range of frequencies. In the graph, the X axis (horizontal) represents the frequency range and the Y axis (vertical) represents the fluctuation of voltage (volume). This means that as you follow the line from left to right, you will see which frequencies cause a slight variance in the response. An experienced user may be able to look at a frequency response graph and get an accurate idea of what the microphone will sound like. Some frequency responses may look very odd on paper, but they have been intentionally designed with a specific purpose in mind. This is commonly the case with drum microphones like the ATM230 where the high frequencies are intentionally rolled off. This is when you let your ears decide which microphone to choose.
The impedance specification is also a commonly misunderstood measurement. To understand this specification, you should know that all electrical circuits and devices create some resistance to an AC signal. The amount of this opposition and reactance to the signal as it passes through the microphone is called impedance. It is not unlike a water valve that provides resistance to a connected water source. Microphones are often low impedance devices (“Lo-Z”), with output ranges typically between 50 and 1,000 ohms. High impedance devices (“Hi-Z”) have an input or output impedance rating that is approximately 5,000 ohms.
Sensitivity of transducers, such as microphones, refers to the amount of output for a given input. A standard sensitivity measurement is calculated using a 1 kHz tone at 94 dB. The reference of the 94 dB is equal to 1 Pascal (“Pa”), which is the same as 1V. Microphone output is measured in millivolts (“mV”) and is also listed to the equivalent dB level.
The noise floor, signal to noise, dynamic range, and maximum input sound level specifications are other measurements that seem to have a lot of people confounded. The noise floor is the calculated sum of all the noise sources in a given system or space. Microphone noise floor is often referred to as “self-noise.” All circuits create a small amount of noise, and the self-noise of a microphone in relation to the signal being captured by the microphone is the signal-to-noise ratio. The maximum input sound level of a microphone is the highest dB level that the microphone can handle from a sound source without experiencing problems from total harmonic distortion (“T.H.D.”). This is most commonly a specification for active circuits such as condenser and phantom-powered ribbon microphones. Dynamic microphones do not commonly have a maximum input sound level due to the design of the element. Lastly, since the measurements in this group are interrelated, the dynamic range can be determined by subtracting the self-noise from the maximum input sound level.
Additional common listings that are found in microphone specifications include the type of element used (dynamic, condenser, or ribbon) and the microphone pickup polar pattern (directional or omnidirectional.) Also, if the microphone has switches, there may be a specification listing to identify these (low cut and roll off, stereo configurations, etc.). Other specifications listed may be the weight, dimensions, case style, and included accessories.
While there is a lot of information crammed into this single blog post, hopefully it has given you a general idea of what microphone specifications mean. Again, use these absolute measurements along with the relative measurements you get from your ears when judging microphones. And, of course, feel free to contact the Audio Solutions Department for assistance with determining which Audio-Technica microphone will best suit your needs.