What Is Microphone Frequency Response?
What is Microphone Frequency Response? Microphone frequency response is the range of frequencies that a microphone can capture. This includes both the low and high end of the spectrum.
Microphone frequency response is one of the most important factors to consider when choosing a microphone. In this article, we’ll discuss what is microphone frequency response, and how it affects the sound of a microphone.
Frequency response is measured in hertz (Hz), and is generally specified as a range, such as 20-20,000 Hz.
The frequency response of a microphone can affect the sound of the recording. For example, a microphone with a wider frequency response will be able to capture more of the audio spectrum, resulting in a richer, fuller sound. Conversely, a microphone with a narrower frequency response may produce a sharper, more focused sound.
What is microphone frequency response? It is a specification of a microphone that details the relative output levels of the sound/audio frequencies a mic is able to reproduce. Frequency responses are specified as frequency ranges and as comprehensive graphs/charts.
Frequency And Hertz (Hz)
The number of cycles per second, or Hertz (Hz), is the unit of frequency. It is commonly used in measuring the speed of sound, or the speed at which sound waves travel through a medium, such as air. Frequency is measured in cycles per second.
Calculating a frequency is done by dividing the number of cycles by the number of seconds.
For example, a song that has a frequency of 1,000 Hz plays once per second. If we have a song that has a frequency of 1,000 Hz, it should play for 1,000 seconds or one minute, one second, one millisecond (1,000,000,000 milliseconds) to get exactly a minute of sound.
For example, in this song, the frequency is 1,000 Hz. We can also use the following mathematical equation to calculate the frequency of a sound.
How To Read A Frequency Response Graph/Chart
So far, we’ve covered the definitions of microphone frequency response, and frequency and Hertz. We’ve also seen a couple of frequency response graphs.
With that knowledge, let’s dive deeper into how to read a frequency response graph or chart.
Microphone frequency response (FR) graphs are a great way to understand how your microphone responds to different frequencies. By reading the FR graph, you can get a rough idea of how well your microphone captures sounds above and below the targeted frequency. This is particularly helpful if you are recording vocals, as the FR graph will give you an indication of how well the microphone is capturing high and low frequencies.
Additionally, this information can be used to tweak your microphone settings if necessary. By plotting the amplitude of the response against frequency, you can learn how the mic responds to different frequencies, and identify any problems with sensitivity or frequency response. If a microphone is not responding properly to certain frequencies, it may be necessary to adjust the mic’s settings.
A microphone’s frequency response diagram has two axes:
- X-Axis: frequencies (Hz)
- Y-Axis: relative sensitivity (dB)
The X-axis
The X-axis of the graph represents frequency, ranging from 40 Hz to 15 kHz. The graph will start at a value of 0 (zero) for 40 Hz, then go to a positive value for the first frequency measurement, then a negative value for the next frequency measurement, and so on. If a graph includes a non-linear response line, like the SM57, there will be multiple measurements along the graph (usually 2 or 3).
The X-axis is very important because it tells us the frequency range that the mic is sensitive to. It also tells us where the microphone will be flat (at 0 dB), and where the mic’s sensitivity is at its maximum. The mic will be flat at the lowest frequency that the microphone is sensitive to, and it will be sensitive at its maximum sensitivity at the highest frequency that the mic is sensitive to.
The Y-axis
The Y-axis represent sensitivity and is depend on many factore like increase in sound waves and amplitude. The Y-axis of the frequency graph set up in 0 dB or 10 dB. Sensitivity increases above the 0 dB value and decreases below the 10 dB value. If a graph includes a non-linear response line, like the SM57, there will be multiple measurements along the graph (usually 2 or 3).
The Frequency Response Line
As we know the measurements along the X and Y-axes, we need a line to represent a microphone’s frequency response. The frequency response line matches frequencies to the relative output level of the microphone. This allows us to see the frequency-specific sensitivity of the microphone, or, in other words, the mic’s frequency response!
The Frequency Response Line (FRL) is a reference line that represents the relative sensitivity of the microphone. The horizontal line represents the minimum sensitivity of the mic. The vertical line represents the maximum sensitivity of the mic. The distance between the horizontal and vertical lines represents the relative sensitivity of the microphone.
The diagram below shows a frequency response graph of a high-sensitivity dynamic microphone. This microphone has its maximum sensitivity at the 0 dB point on the Y-axis.
As we’ve seen in the above examples, the FRL line shows a steady rise as the Y-axis moves toward lower frequencies.
For example, at 40 Hz, the SM57 is not very sensitive (-12 dB). However, from 40 Hz to just under 200 Hz, the sensitivity of the SM57 increases at about 6 dB per octave. There is also a slight dip in sensitivity around 400.
Flat Vs. Colored Microphone Frequency Responses
Flat Frequency Response With Mcrophone Examples
We’ve already discussed the SM57, which is the example of flat frequency response microphone. It has a flat frequency response line from 20Hz to 20kHz. It’s very reasonably priced and can easily be found at any good microphone store.
The A-370 is another flat frequency response microphone. Its frequency response line is also flat from 20Hz to 20kHz. It’s a very reasonably priced microphone. The Earthworks M50 is another flat frequency response microphone. Its frequency response line is also flat from 20Hz to 20kHz. It’s a very reasonably priced microphone.
The AKG C 414 XLII
The AKG C 414 XLII (link to check price on Amazon) is a large-diaphragm condenser microphone with a flat frequency response.Notice that the C 414 XLII frequency response line is not necessarily flat, though the microphone is often considered to have a flat frequency response.
The C 414 XLII has a very flat frequency response from about 100 Hz to 20,000 Hz, with only a slight boost in the brilliance range around 8,000 Hz. This is a great mic to use for recording vocals and doubling up as a stereo or surround mic as well.
Colored Frequency Response With Microphone Examples
- The Neumann KM 184
- The Shure Beta 52A
- The Shure SM57
The Neumann KM 184
The Neumann KM 184 is a small-diaphragm cardioid microphone that, in addition to a flat frequency response, also has a high-pass filter (to eliminate the low-end).This high-pass filter is also known as a notch filter. Most high-pass filters are around 20 Hz to 20,000 Hz.
This high-pass filter is great for recording any type of music. It can help eliminate unwanted low frequencies as well as the possible added hiss or distortion that can occur when recording at low volumes.
The Neumann KM 184’s frequency response line is certainly not flat. It rolls off quite heavily below around 4,000 Hz. However, the high-pass filter (notch filter) is an excellent addition to the flatness of the KM 184.
The Shure Beta 52A
The Shure Beta 52A is a moving-coil dynamic microphone with a colourised frequency response. It yields a relatively flat frequency response from 20 Hz to 20 kHz. At higher frequencies, however, there is a ±1 dB variation in the mic’s response.
The Shure SM57
The Shure SM57.5 is a high-quality cardioid dynamic microphone with a flat frequency response from about 100 Hz to 20 kHz. This is a high-quality microphone marketed as a ±flat’ microphone. The sound quality of the SM57.5 is not really flat. But, from about 100 Hz to 18 kHz, the frequency response variation is only about ±2 dB. The frequency response line of the Shure SM57.5 is far from flat. But, it does not exhibit extreme highs or lows.
The SM57.5 is a great mic for recording vocals, but I would not call it flat. The Shure SM57.5 is one of My New Microphone’s Top 10 Best Condenser Microphones Of All Time (With Alternate Versions & Clones).
The Determining Factors Of Microphone Frequency Response
The Weight Of The Diaphragm
The weight of the diaphragm is one of the most influential factors in the frequency response of a dynamic microphone. The greater the diaphragm’s mass, the lower the frequency of the resonance. The larger the diaphragm, the smaller the frequency of the resonance.
With a larger diaphragm, the diaphragm will have a greater mass and will resonate at a lower frequency. The frequency response is a strong function of the diaphragm’s mass. The following chart shows the frequency response of a dynamic microphone with various diaphragm masses.
The Size Of The Diaphragm
The Shape Of The Diaphragm
The shape of the diaphragm is also a key factor in the frequency response. The shape of the diaphragm affects the frequency response. The larger the diaphragm, the less it will be affected by the shape. If the diaphragm is small, it will be affected by the shape of the enclosure and how it is placed in the space.
A circle, square, rectangle or oval shape have different resonance characteristics than a circular diaphragm, and so have different frequency responses.
The resonant frequency of a diaphragm is more dependent on shape and thickness than on material properties such as density or mass. The diaphragm is thicker in response to high frequency sound, so a circle is a good shape for condenser microphones, while an oval produces a more even response.
Tension Of The Diaphragm
The tension of a diaphragm is the force that keeps the diaphragm from collapsing. The greater the tension, the more rigid the diaphragm is. The greater the diaphragm rigidity, the better the microphone’s high-frequency response is.
Tension, or compression of a diaphragm, is a limiting factor in high-frequency response. The diaphragm is held taut at the edges by a frame or spring, but is completely free at the center. When sound waves strike the diaphragm, the positive and negative pressure creates a restoring force that keeps the diaphragm in its original shape.
The Damping Material And Space Around The Capsule
The material of a microphone’s capsule surrounds the diaphragm and defines the damping characteristics of the microphone. This material is normally referred to as the capsule’s “back plate.” The back plate is the “wall” of the microphone’s capsule. The material of the back plate, or damping material, is usually chosen to provide adequate damping while not affecting the frequency response of the microphone too much.
The damping material is usually a non-conductive material such as plastic, rubber, or other similar material. Some small diaphragm condenser microphones might use a metal back plate. These are commonly referred to as “ferrofluid” or “magnetic” microphones.
The space around the microphone’s capsule is often referred to as the “vacuum.” Most microphones have a vacuum between the back plate and the diaphragm.
Direction Of The Capsule
Microphones may have a directional cavity for reducing the amount of unwanted sound that reaches the capsule. This directional effect is most evident in dynamic mics.
The directional cavity can be used to a microphone’s advantage by pointing it in the direction of the desired sound. In small-diaphragm condensers, the directional cavity is a hole in the diaphragm that allows sound to enter the capsule. In large-diaphragm condensers, the directional cavity is often a dual-diaphragm configuration that can cancel unwanted sound waves.
Ribbon microphones have a directional cavity as well, but they are generally made for the purpose of reducing feedback, and not for improving frequency response.
Resonant Frequencies Of The Microphone Body
For the most part, microphones are designed to respond to frequencies between 0Hz and 10kHz. Above this frequency, the microphone becomes less sensitive and becomes directional, often much more so than below this frequency. Below 0Hz, the microphone can become highly directional.
If the microphone is intended to be used with an external speaker, how does the speaker effect the frequency response of the microphone? Many external speakers have a certain frequency response, and many do not. If the speaker’s response is too high or too low, it can be easily adjusted by changing the gain or frequency response of the amp or mixing board. The speaker’s frequency response can also be altered by using a different substitution for the speaker capsule or by placing a different speaker in the room.
Distance Between The Sound Source And The Microphone
Have you ever been in a room when a loud pop or sizzle was heard at a sudden volume increase? This is the effect of a microphone being placed too close to the sound source.
For a microphone to be a good match for the sound it is supposed to pick up, the distance between the microphone and the sound source should be roughly equal to half the wavelength of the highest frequency in the sound.
If the distance is too short, then the microphone will sound like it is picking up the high-frequency “pops” and “sizzle”, and if the distance is too long, it will sound like it is picking up the low-frequency “thumps” and “pans”,The distance between the microphone and the sound source is called the pickup distance.
It is not uncommon for microphones to be placed too close to their sound sources.
An Alternative Way To Measure Frequency Response In Microphones
The alternative way to measure frequency response is to use the following equation to calculate the frequency response of a microphone:
|x| = sound|x|/sound|0|
|x| = sound|x| = sound|x|/sound|0|
Now, as you know,
|X| = Sound|0|, so we can use this equation to calculate the frequencies of the microphone’s frequency response:
|X|/Sound|0| = Sound|X|/Sound|0|
where |X| is the sound wave’s amplitude, and SOUND|0| is the amplitude of the sound wave at the start of the microphone’s frequency response.
≤ The equation is based on a 20 Hz – 20,000 Hz spectrum.
Proximity Effect
Why Is There A Proximity Effect?
Methods To Change A Microphone's Frequency Response
Of course, the best way to test a microphone is to take it out of the box and measure it. However, that’s not practical for all of us so we have to rely on the data sheets and other manufacturer’s specifications. How do you go about testing the frequency response of a microphone?
So you have a microphone, perhaps a Shure SM7B that you want to test, but you don’t have the time to test it against a known frequency response. To make a long story short, there are two ways to do this:
- Take an audio analyzer, such as the Focusrite AudioFile SFDR1, and record the mic’s frequency response.
- Try to get the microphone’s frequency response from the manufacturer.
Conclusion
In this article, we covered what is microphone frequency response and how it affects the sound of the microphone. We looked at both the technical and practical side of frequency response and explained how to use it to your advantage when selecting a microphone.
We hope you found this article useful. If you have any questions, please don’t hesitate to ask in the comments section below.
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