Table of Contents
When purchasing or reading about microphones, you will often come across the term ‘frequency response’, but do you know exactly what it is?
Most people will get intimated by the word and its complexities at first glance. Seeing this jargon and a graph full of lines and numbers can be scary, especially for beginners. Fear not though, in this guide, we will define and explain what frequency response is and all its related elements in the simplest way possible.
Frequency response is perhaps one of the most important specifications of a microphone, regardless of the type. It is through the frequency response that we can determine the characteristic sound that a microphone may be able to emit or produce.
In that case, frequency response is the frequency-specific output sensitivity of the microphone. Simply put, this is the microphone’s response to frequencies. It is through the frequency response we can determine the sound signature or characteristic of a microphone as frequencies will vary depending on its output or response to a sound within a certain range. It measures the output of a device when given an input signal.
The frequency responses of a microphone can be further specified as frequency ranges and these can be read through frequency response graphs and charts. A bode plot can show the frequency changes in magnitude and phase while the time-domain data will show the changes in signal.
The two most common frequency response types are flat frequency response and shaped frequency response.
If a microphone has a flat frequency, then this means it is equally sensitive to all frequency ranges. It has the ability to reproduce the sound source exactly the way it is, with no added variation. In a frequency response graph, the frequency response curves of a flat response microphone are straight or flat lines.
A perfectly flat frequency response microphone is good for recording musical instruments, sound effects, and sources where you want the finished output to sound exactly the same as the original source. However, it may not be ideal for recording vocals or voices as you won’t hear any variation. A flat response curve may sound too lacking for listeners.
If a microphone has a shaped frequency response, then this means it is more sensitive to a certain range of frequencies. Microphones with a shaped frequency response are less sensitive to low frequencies, which makes them good at reducing noise from microphone handling or when situated in a mic stand. In frequency response graphs, the response curves of shaped response microphones will have peaks and valleys.
Since a shaped response microphone can typically boost in the upper mid-range, it has the ability to do a ‘presence rise’ wherein the audio or sound will be enhanced and you will hear that the sound reproduced will have a certain punch. This makes it ideal for recording voices, vocals, and instruments.
Since frequencies respond differently over a specified range of audible frequencies, they will emit response curves. These curves are represented in a graph to show how an output signal can affect the overall sound timbre or characteristic of a microphone.
In a graph, the curve can be seen by looking at the y-axis, which will have the frequencies (Hz), and the x-axis, which will have the relative sensitivity (dB). Depending on the frequency range or response specification provided by the microphone manufacturer, the graph will stay within the defined range.
The following table graph shown above is an example of what two different response curves look like. The microphones used in the example are; Top: Oktava 319 and Bottom: Shure SM58. The adjustable curves make use of digital signal processing.
A microphone is an audio device that converts sound waves into an electrical signal. As the signal reaches one of the end frequencies, the signal strength will change. If the audio system or audio equipment device reaches its limit in the range, it may have a voltage gain or loss. This all contributes to whether the specs of a microphone can give high frequencies or low frequencies.
In the frequency spectrum, 50 Hz is the low end while 20,000 Hz is the high end. If the specs have a “-”, “+”, or “+/-”, then that would mean “-” for loss or “+” for gain. On the other hand, the 1dB is the amplitude that shows the amount of gain or loss. Ideally, the audio system will produce the same amplitude across frequency points so that the output signal will be equal to the input signal. However, that is not always the case for other systems.
If your audio equipment or device has a low-frequency response, then it is designed to pick up low-frequency sounds that may be too low for the typical human ear to hear. An example of where microphones or speakers with a low-frequency response will come in handy is when you intend on monitoring subwoofer signals and levels in a PA system or recording bass instruments as they tend to be low in the musical notes.
A condenser microphone is a good example of what microphone to use when picking up low-frequency sounds. Just make sure that the system you are using can handle high sound pressure levels so that the microphone won’t distort or clip the sound. It’s also good to note that the microphone or speakers system you will be using have a good bass response.
The highest frequencies will range above 20 kHz. Professional recording studios and live sound applications often have this frequency response specification, which means microphones and the speakers system needed for these applications need to have tolerance for such a system’s response and frequency domain.
Additionally, a microphone or a speaker that is intended for high-frequency applications will need to have a smaller diaphragm. This allows the speaker or device to respond faster to changes in pressure while maintaining accuracy. Take note that high frequencies usually mean a higher maximum SPL so make sure that your mic or speaker has the tolerance for it otherwise the audio will be distorted and will not function properly.
With all that said, the measure of which frequency response to use will vary depending on the function of your mic and intended application. For miking and recording low sounds, it’s better to use a low-frequency response mic. For miking and recording high and loud sounds, then opt for a high-frequency response mic.
Now that you know the basic fundamental frequency response definitions and explanations, you can now follow discussions and give your input about it in audiophile and consumer audio circles.
The frequency range is also known as a frequency band. This is the interval between the upper limiting frequency and the lower limiting frequency.
In the frequency domain, the following are the rough frequency ranges of a microphone:
Modern amplifiers have a frequency response that will range from 20Hz up to 20 kHz, which allows no change of amplitude and accuracy in producing sounds. However, there are amplifiers that may go above 100kHz, or even beyond a maximum deviation of 200kHz. This is not a good idea as it may open up to radio frequency interferences and a nonlinear frequency response can mush down an audio band. Generally, a frequency of 5Hz-50kHz or 20Hz-20kHz is a good input.