Frequency response (along with polar response) is the most important specification of any given microphone. The characteristic sound of any given mic is explained largely by frequency response.
What is microphone frequency response? Microphone frequency response is the frequency-specific output sensitivity of a microphone. It 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.
In this complete guide, we’ll discuss microphone frequency response in great depth. Frequency response is a critical specification to comprehend if we are to fully understand microphones. My goal here is to answer any questions you may have about microphone frequency response.
Be sure to check out My New Microphone’s article How Do Microphones Work? (The Ultimate Illustrated Guide)!
Related articles: What Is Headphone Frequency Response & What Is A Good Range?
Table Of Contents
- What Is Microphone Frequency Response?
- Decibel And Hertz: The Measuring Blocks Of Frequency Response.
- How To Read A Frequency Response Graph/Chart.
- Flat Vs. Coloured Microphone Frequency Responses.
- The Frequency Response Microphone Specification.
- Choosing The Microphone With The Proper Frequency Response.
- How Do Microphones Pick Up Different Frequencies?
- The Determining Factors Of Microphone Frequency Response.
- The Frequency Response Of The Human Ear.
- What Are Frequency Bands?
- How Is Frequency Response Measured In Microphones?
- The Proximity Effect On Frequency Response.
- Methods To Change A Microphone’s Frequency Response.
- Frequency Response Generalizations Of The 4 Main Microphone Types.
- Related Questions.
What Is Microphone Frequency Response?
As the name suggests, microphone frequency response is the microphone’s response to frequencies. More specifically, frequency response is a microphone’s frequency-specific sensitivity to sound frequencies.
Microphones respond to sound waves (mechanical wave energy) at their diaphragms, converting the waves into audio signals (electrical energy).
Sound waves are complex and are typically made of a range of frequencies with a range of amplitudes. These sound waves have a frequency range of 20 Hz – 20,000 Hz.
The frequency response of a microphone represents the range the mic is sensitive to within the audible sound frequencies. The microphone could effectively recreate the entire audible sound range from 20 Hz to 20 kHz or it could limited to a smaller band within the audible frequency spectrum.
Within that pickup range, a mic’s frequency response also represents the frequencies the mic is more sensitive to and those frequencies it is less sensitive to.
Let’s look at an example to help illustrate.
In this example, we’ll look at the frequency response specs for the famous Shure SM57 dynamic microphone (link to compare prices on Amazon and select retailers).
The specifications sheet of the Shure SM57 microphone tells us that the microphone’s frequency response is 40 Hz – 15 kHz.
This means that the SM57 will effectively recreate sounds in the range of 40 Hz to 15,000 Hz. The mic will be capable of outputting these frequencies in its mic signal.
However, this is not the full story. The SM57 does not simply start recreating sound at 40 Hz and stop at 15,000 Hz. Nor does it recreate all the frequencies within this range equally.
To get the full story, we must take a look at the SM57’s frequency response graph:
In the above graph, we see a frequency response line that denotes the SM57’s frequency-specific sensitivity.
Although the frequency response range of the SM57 states it recreates sound down to 40 Hz, we see that, at 40 Hz, the microphone is 12 dB less sensitive than its average line (denoted by 0 dB on the Y-Axis).
Similarly in the upper range, the SM57 has decreased sensitivity of about 8 dB at 15,000 Hz.
Within the range of 40 Hz – 15 kHz, we also see a slight dip in response around 400 Hz and a large boost in response between 2 kHz and 12 kHz.
This is to show that the frequency response range is a sometimes misleading specification. It is better to rely on the frequency response graph to truly understand a microphone’s frequency response.
Decibel And Hertz: The Measuring Blocks Of Frequency Response
Before we get too deep into our discussion of microphone frequency response, it’s essential that we understand the units of frequency and relative levels.
- Frequency is measured in Hertz or Hz (cycles per second).
- Relative microphone output levels are measured in decibels or dB.
Frequency And Hertz (Hz)
The frequency of a sound wave or audio signal represents the number of times that sound waves repeats itself per second.
Frequency is inversely proportional to a sound wave’s wavelength, and the two are related by the following equation:
f = ν/λ or λ = ν/f
• f = frequency
• λ = wavelength
• ν = velocity of sound (assumed constant 343 m/s or 1,125 ft/s)
Frequency is measured in Hertz (Hz), which means cycles/second.
In terms of pitch, doubling a sound wave’s frequency results in a pitch exactly one octave above. For this reason, frequencies are best represented logarithmically rather than linearly. We see this on the X-Axis of frequency response graphs.
Relative Levels And Decibels (dB)
As discusses, frequency response is the microphone’s frequency-dependent sensitivity along the range of audible frequencies.
In order to convey the differences of a microphone’s output level between frequencies, we use the decibel (dB).
Decibels, like frequency, are also logarithmic and are standard units of measurement for both sound waves and audio signals.
Decibels are units that compare the intensity of sound or the power of an electrical signal to a given level on a logarithmic scale.
In the context of a frequency response graph, relative mic signal power is measured along the Y-Axis and is noted in decibels.
The frequency response graph will have a 0 dB reference point (horizontal line). The frequency response line will tell us the microphone output level at frequencies along the audible spectrum relative to this 0 dB reference point (horizontal line).
Take note of the following generalities about how we hear changes in decibels:
- A 1 dB difference is only barely noticeable by most people.
- A 6 dB difference is considered to be about twice (or half) the amplitude (perceived volume).
- A 12 dB difference is considered to be about 4 times (or quarter) the amplitude (perceived volume).
How To Read A Frequency Response Graph/Chart
So far we’ve covered the definitions of microphone frequency response; frequency and Hertz; and relative levels and decibels. 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.
A microphone’s frequency response diagram has two axes:
- X-Axis: frequencies (Hz)
- Y-Axis: relative sensitivity (dB)
Let’s take another look at the aforementioned Shure SM57 dynamic microphone’s frequency response graph. I’ve explicitly added arrows to represent the X-Axis (frequencies) and Y-Axis (relative sensitivity).
The X-axis of a frequency response graph shows the frequencies in Hertz (Hz).
The majority of time, the X-axis shows the frequencies across the audible range of sound (20 Hz – 20,000 Hz) even if the microphone does not have a response across the entire range. This is shown above in the SM57’s graph.
Other times manufacturers may extend their X-axes to include frequencies in the infrasound (below 20 Hz) and ultrasound (above 20 kHz) ranges.
Let’s look at some examples:
- Earthworks M50 measurement mic (link to compare prices at select retailers)
- DPA 4006A omnidirectional mic (link to compare prices at select retailers)
As mentioned, sound frequencies are heard logarithmically. In other words, we hear every doubling of a frequency as an octave above the original.
A 1 Hz difference results in a greater pitch difference in the low frequencies than in the higher frequencies.
Therefore, the X-axis is set up as a logarithmic scale.
Each octave (every doubling of frequency) takes up the same length along the X-axis. You can see this in each of the frequency response graphs mentioned in this article.
In other words, the space between one frequency value and the next frequency value get smaller and smaller as you move from the left to the right on the graph.
The Y-axis of a frequency response graph shows the relative sensitivity in decibels (dB).
Frequency response graphs usually have their Y-axes set up in 1, 5 or 10 dB intervals. In our above examples:
- Shure SM57 frequency response Y-axis has 5 dB intervals on grid.
- DPA 4006A frequency response Y-axis has 5 dB intervals on grid.
- Earthworks M50 frequency response Y-axis has 2 dB intervals on grid.
It’s critical to note that the decibel values along the Y-axis are noted linearly. However, as we’ve discussed, decibels, themselves, are a logarithmic ratio.
Let’s recap the generalities about how we hear level changes in decibels:
- A 1 dB difference is slightly noticeable by most people.
- A 6 dB difference is considered to be about twice (or half) the amplitude (perceived volume).
- A 12 dB difference is considered to be about 4 times (or quarter) the amplitude (perceived volume).
So frequency response graphs have a set 0 dB point on their Y-axis. This provides a set 0 dB horizontal reference line across the graph.
- Markings above the 0 dB point represent an increase in sensitivity.
- Markings below the 0 dB point represent a decrease in sensitivity.
Remember that the Y-axis represents relative sensitivity. The absolute output of a microphone depends on many other other factors, including the amplitude and frequencies of the sound waves it is subjected to.
The Frequency Response Line
So we know the measurements along to X and Y-axes. In order to complete the diagram, though, we need a line to actually represent a microphone’s frequency response.
The frequency response line matches frequencies to the relative output level of the microphone. It gives us a solid idea of the frequency-specific sensitivity of the microphone, or, in other words, the mic’s frequency response!
Let’s bring back the Shure SM57’s frequency response graph to have a look at the frequency response line. Recall that the frequency response range of the SM57 is from 40 Hz to 15,000 Hz.
- At 40 Hz, the SM57 is not very sensitive (-12 dB).
- From 40 Hz to just under 200 Hz, the sensitivity of the SM57 ramps up at about 6 dB per octave.
- There is a slight dip in sensitivity around 400 Hz (2 dB).
- There’s a upward ramp in sensitivity from 2 kHz to about 6 kHz, where the mic becomes 7 dB more sensitive.
- Past 6 kHz, the microphone has non-linear peaks and valleys in sensitivity until about 12 kHz.
- There is a sharp high-end roll off from 12 kHz to 15 kHz (the upper end of the SM57’s frequency response range).
Note that sometimes there will be multiple response lines drawn on the graph. Typically these will relate to one or more of the following:
- High-pass filter options.
- Off-axis response.
To illustrate this, let’s take a look at the frequency responses of 2 new mics:
- AKG C 414 XLII (link to compare prices on Amazon and select retailers)
- Electro-Voice RE20 (link to compare prices on Amazon and select retailers)
The AKG C 414 XLII has three selectable high-pass filter options (at 40 Hz, 80 Hz, and 160 Hz). The above frequency response graph shows us that the 40 and 80 Hz options filter out more steeply at -12 dB/octave while the 160 Hz option filters out at a gentler -6 dB/octave.
For more information on microphone high-pass filters, check out my article What Is A Microphone High-Pass Filter And Why Use One?
The above RE20 frequency response graph shows us the response of the mic with and without its high-pass filter engaged. It also shows us the response directly to the microphone’s rear (180° off-axis).
The RE20 is a cardioid microphone and so it has maximum rejection at 180°. The graph tells us that there’s roughly 16 dB attentuation to the rear of the microphone across its entire frequency response.
For more on the cardioid microphone polar pattern, check out my article What Is A Cardioid Microphone? (Polar Pattern + Mic Examples).
Reading A Frequency Response Graph
Let’s recap. When reading a microphone’s frequency response graph, we will see the following:
- The low-end roll-off of the microphone within the audible frequencies (if applicable).
- The high-end roll of the microphone within the audible frequencies (if applicable).
- The frequencies where the mic is most sensitive.
- The frequencies where the mic is least sensitive.
- How flat (or coloured) the mic’s frequency response is.
- Various lines to represent high-pass filters (if applicable).
- Various lines to represent other EQ boosts or cuts (if applicable).
- Various lines to represent proximity effect at various distances from the mic (some manufacturers add this to their directional mics).
- Various lines to represent the rear pick up of directional mics (some manufacturers add this).
With a trained eye, we may look at a series of microphone frequency response diagrams and know how to maximize their potential.
However, even with a trained eye, it’s difficult know whether or not you’ll subjectively enjoy the character and coloration of a microphone in a certain situation until you actually put the microphone in that situation. After all, there are many other specifications that affect a mic’s sound.
Flat Vs. Coloured Microphone Frequency Responses
To quickly describe a microphone’s frequency response, we can put a microphone into one of two groups:
- Flat frequency response: the microphone is equally sensitive to all the frequencies across the audible frequency spectrum. It could also mean that microphone is equally sensitive to all frequencies within its range (though there will be low-end and/or high-end roll-offs). The mic has a flat frequency response line in it graph.
- Coloured frequency response: the microphone is more sensitive to some frequencies and less sensitive to others. A coloured mic will often have a low-end roll-off, high-end roll-off, or both. The mic has a a non-flat frequency response line.
A perfectly flat microphone frequency response is difficult to create. “Flat microphones” will generally have some variation in their frequency-specific sensitivities.
So long as the microphone portrays a mostly horizontal frequency response line, we can call its frequency response “flat.” Of course, this is subjective.
Let’s look at some examples in order to better understand flat and coloured frequency responses.
Flat Frequency Response Microphone Examples
Flat microphones provide consistent sensitivity across the frequency spectrum.
These are often condenser microphones (both small and large diaphragm). The specifics of condenser capsule and diaphragm design make flat frequency response relatively easy to achieve.
Mics with flat frequency responses are chosen for their accurate and detailed recreation of sound.
Example microphones with flat frequency responses:
- Neumann KM 184.
- AKG C 414 XLII.
- DPA 4006A.
Neumann KM 184
The Neumann KM 184 (link to compare prices on Amazon and select retailers) is a small-diaphragm cardioid condenser microphone with a flat frequency response.
Here is the KM 184 frequency response graph:
Notice that the KM 184 frequency response line is not necessarily flat, though the microphone is often considered to have a flat frequency response.
From about 100 Hz to 20,000 Hz, the response is very flat, straying only ±2 dB and only having a slight boost in the brilliance range around 8,000 Hz.
The KM 184 also has a gentle low-end roll-off starting around 200 Hz, but that doesn’t overly colour the mic signal.
This is to show that, although the graph is not perfect, the KM 184 is considered to have a flat frequency response.
AKG C 414 XLII
The AKG C 414 XLII is a large-diaphragm multi-pattern microphone.
Each of its polar patterns has a slightly different, but flat, frequency response graph. Pictured below is the cardioid option’s frequency response graph:
Like the aforementioned Neumann KM 184, the AKG C 414 XLII is not perfectly flat. However, it is certainly arguable that the C 414 has a flatter frequency response than the KM 184.
With no high-pass filters engaged, we see only the slightest low-end roll-off. This is followed by an almost perfectly flat response until about 1,000 Hz.
Above 1 kHz, there are slight variations (no more than ±3 dB) in sensitivity.
The AKG C 414 XLII is an excellent example of a flat microphone.
The DPA 4006A is a small-diaphragm cardioid microphone that has an extremely flat frequency response.
Note that the DPA 4006A frequency response graph goes up to 40 kHz on the X-axis (rather than the typical 20 kHz).
For 20 Hz to about 5,000 Hz, the frequency response of the 4006A is completely flat.
The upper frequency response depends on if the sound source is on-axis (where the microphone is pointing) or diffuse (off-axis or reflecting around the acoustic space).
On-axis sounds are subjected to a gentle boosts in the upper frequency range while diffuse sounds are gently rolled-off.
Flat/Coloured Frequency Response Microphone Examples
Some microphones fall into the middle ground between “flat” and “coloured.”
Ribbon microphones often fall into this grey area. They sound very accurate and natural, even though they do not typically portray overly flat frequency responses.
These microphones yield a fairly natural sound but will have some jaggedness in their frequency response line. Often times these “flat/coloured” mics have significant high-end and/or low-end roll-offs.
Mics with flat/coloured frequency responses are often chosen for their character while accurately and naturally capturing sound.
Example microphones with flat/coloured frequency responses:
- Electro-Voice RE20.
- AEA R84.
The Electro-Voice RE20 is a moving-coil cardioid dynamic microphone with a relatively flat frequency response (compared to other moving-coil dynamic mics).
The frequency response line of the Electro-Voice RE20 is far from a flat line. However, from about 70 Hz to 14 kHz, there is really only a ±2 dB variation in the mic’s response.
The low-end and high-end roll-offs certainly play into the colouration of the RE20 along with the jaggedness of the response line.
So the Electro-Voice could be considered both flat and coloured. It is certainly flat relative to many other moving-coil dynamics, but is definitely coloured if compared to the above condenser microphones.
The AEA R84 (link to compare prices at select online retailers) is a bidirectional ribbon microphone with a frequency response typical of high-end ribbon mics.
Ribbon microphones are cherished for their natural sound, especially when recording digital audio.
The gentle high-end roll offs of ribbon mics (like the AEA R84) cause them to approximate how we naturally hear sound.
The frequency response line of the AEA R84 is far from flat, but the microphone sounds incredibly natural and picks up sound accurately.
I would not call the R84’s frequency response flat. However, by the definitions of flat and coloured mics, it may very well fit in the grey area.
To learn more about ribbon mics and the bidirectional polar pattern, check out my articles The Complete Guide To Ribbon Microphones (With Mic Examples) and What Is A Bidirectional/Figure-8 Microphone? (With Mic Examples), respectively.
Coloured Frequency Response
Coloured microphone exhibits peaks and valleys within their frequency responses.
Due to their rugged and heavy nature, many moving-coil dynamic microphones have coloured frequency responses brought on by resonant frequencies and inertia within their diaphragms and capsules/cartridges.
Coloured microphones are often chosen to accentuate the important frequencies of their intended sound sources while suppressing the not-so-important or competitive frequencies.
Example microphones with coloured frequency responses:
- Shure Beta 52A.
- Shure SM57.
Shure Beta 52A
The Shure Beta 52A (link to compare prices on Amazon and other select retailers) is a moving-coil dynamic microphone with a supercardioid polar pattern and extremely coloured frequency response.
Here is the Shure Beta 52A frequency response graph:
The peaks and valleys in the Beta 52A are vast.
The microphone heavily accentuates 4 kHz and is very sensitive to low-end frequencies (particularly at close distances due to the proximity effect). There is also a very sharp high-end roll-off between the peak at 4 kHz and the upper point of the 52A’s frequency response at 10 kHz.
The extreme colouration of the Beta 52A make it a specialty microphone that is marketed as a kick drum mic.
In fact, the Shure Beta 52A is my top recommendation in my Best Kick Drum Microphones article.
The Shure SM57 is a moving-coil dynamic microphone with a cardioid polar pattern and coloured frequency response.
As we can see, the SM57 is definitely coloured.
The coloured frequency response of the SM57 make it an excellent choice for vocals and other instruments, particularly in live situations.
- The low-end roll-off improves noise cancellation and gain-before-feedback.
- The peak at 6 kHz improves speech intelligibility and accentuates many instruments.
- The high-end roll-off reduces harshness while improving gain-before-feedback.
For a more in-depth read on flat and coloured microphone frequency responses, check out my article What Are Coloured And Flat Microphone Frequency Responses?
The Frequency Response Microphone Specification
Frequency response is a critical specification for microphone manufacturers to put on their mic spec sheets.
For more information on microphone specifications and the most important mic specs, check out my articles Top 5 Microphone Specifications You Need To Understand and Full List Of Microphone Specifications (How To Read A Spec Sheet).
As we’ve discussed, there are two general ways of expressing microphone frequency response:
- The range of frequencies a microphone will reasonably reproduce. This will often be expressed with a measure of tolerance.
- A graph showing the relative sensitivity of a microphone to frequencies within its “range.”
The range of frequency response is not overly helpful (even with a measure of tolerance).
For example, a 20 Hz – 20,000 Hz frequency response range tells us a mic will effectively output frequencies across the audible range, but we have no idea if the mic will boost or cut any particular frequencies within this range.
20 Hz – 20,000 Hz ±3 dB tells us that the mic frequency response is at least fairly consistent and flat. However, we’re still guess at the frequencies where the mic is 3 dB more sensitive and where it is 3 dB less sensitive.
By far the best way to convey microphone frequency response is with a graph.
Frequency Response Specification Example: Shure Beta 52A
The Shure Beta 52A has a frequency response specification of 20 Hz – 10,000 Hz. Shure also provides the following frequency response graph.
As you can see, the graph yields so much information that “20 Hz – 10,000 Hz” cannot convey.
Choosing The Microphone With The Proper Frequency Response
There are many different microphones on the market with many different frequency responses.
We’ve discussed flat and coloured frequency responses and how a microphone’s frequency response makes up the mic’s characteristic sound.
So how do we choose the right microphone with the right frequency response for the right purpose?
There are a few things to ask ourselves.
- What sound source(s) are we miking?
- In what acoustic situation are we miking the sound source(s)?
- How are we miking the sound source(s)?
In other words, we should ideally understand the sound and frequency profile of the source and the acoustics of the space. We should then optimally choose a mic with a frequency that enhances the sound of the source, taking into consideration the technique(s) we’ll be using to place the microphone in order to capture the source.
Let’s look at some examples:
Choosing A Mic Frequency Response For Voiceover
Voiceovers are ideally recorded solo in sound proof isolation booths. These acoustic spaces have as little room sound and reflections as possible.
This allows us to position the microphone optimally for the room and the voiceover performer.
So we have an ideal recording environment and we’re recording the human voice. In this situation a microphone with a flat frequency response would be ideal.
A flat frequency response will pick up the voiceover with as little colouration as possible.
A popular voiceover microphone example found in professional studios around the world is the famous Neumann U87 (link to compare price on Amazon and select retailers):
The Neumann U 87 AI has 3 selectable polar patterns and a high-pass filter.
Here are the frequency response graphs for each of the polar patterns (omnidirectional, cardioid, and bidirectional):
Although any of the above polar pattern would work well on voiceovers in isolation booths, the cardioid pattern is the most popular.
As we see in the graph above, the U 87 cardioid mode is wonderfully flat between about 70 Hz and 5,500 Hz. This is what we want in a voiceover microphone.
The slight low-end roll-off helps to eliminate noise in the signal.
If we really need extra low-end, the cardioid mode does exhibit proximity effect, so we can easily move the performer and mic closer together. Conversely, if there’s too much low-end or the proximity effect is too much, there is a high-pass filter.
The 2-3 dB bump in sensitivity between 6 kHz and 12 kHz adds a bit of sparkle to a voiceover.
The slight high-end roll-off helps to reduce the harshness or brightness of the voiceover. This is particularly helpful in digital audio, which is sometimes too clean/bright.
To read more about choosing a microphone for voiceovers, check out my article Best Voiceover Microphones.
• Top 11 Best Microphones For Recording Vocals
• Top 12 Best Microphones Under $1,000 for Recording Vocals
• Top 10 Best Microphones Under $500 for Recording Vocals
• Top 12 Best Microphones Under $150 For Recording Vocals
Choosing A Mic Frequency Response For Live Vocals
In most situations, live vocals are performed on relatively noisy stages. Even in small ensembles and venues, there will likely be other instrumentation, crowd noise, room noise, and the PA system that will also be entering the mic designated for the vocals.
For this reason, live vocal mics are positioned as close as possible to the vocalists. This makes for the best isolation of the vocal performance possible.
Typically, they also have cardioid polar patterns and point away from loudspeakers. This is to increase gain-before-feedback and yield a cleaner, clearer vocal signal.
The above two points tell us that the typical live vocal mic will exhibit proximity effect.
Because the stage will likely be noisy and there will be significant bass boost due to the proximity effect, a microphone with a low-end roll-off in its response is preferred for live vocals.
A high-end roll-off is also nice to have in order to filter out any harshness in the signal due to cymbals and high-frequency sound sources.
These roll-offs also help to reduce the likelihood of microphone feedback.
For more information on microphone feedback, check out my article 12 Methods To Prevent & Eliminate Microphone/Audio Feedback.
Additionally, because the environment will probably be noisy, a boost in the speech intelligibility range (roughly 2 kHz – 6 kHz) will allow the vocals to cut through the mix a bit more without the need for equalization after the fact.
The most popular live vocal microphone in the world is the Shure SM58 (link to compare prices on Amazon and select retailers):
The Shure SM58 is a moving-coil dynamic microphone with a cardioid polar pattern.
Here is the frequency response of the Shure SM58:
The Shure SM58 has a frequency response that lends itself extremely well to live vocals.
The low-end roll-off effectively filters out low-end rumble for electrical mains and stage vibration.
However, because the mic is directional, the proximity effect will effectively flatten out the lower frequency response, assuming the vocalist will be very close to the mic.
From about 100 Hz to 2,000 Hz, the SM58’s frequency response is flat. This allows it to capture the bulk of the vocals very accurately.
The boost in the presence range (3 kHz – 10 kHz) allows the intelligibility of vocal performance to cut through the mix.
The high-end roll-off filters out any excessive brilliance from the voice or environment.
To read more about choosing a microphone for live vocals, check out my article Best Microphones For Live Vocal Performances.
Choosing A Mic Frequency Response For A Snare Drum In A Drum Kit
Miking a drum kit can be as simple as placing an overhead or room mic, or it can be as involved as close-miking every single drum. In most situations (when equipment allows), drum kits are miked with two overhead mics, a dedicated kick drum mic, and a dedicated snare drum mic.
Snare drums typically have a strong fundamental frequency in the low-mid range (100 Hz – 250 Hz). Above the fundamental, there’s really no rhyme or reason to the frequencies. However, snare drums usually have another peak in the upper mid range between 3-6 kHz.
Selecting a mic with a frequency response that boosts around the fundamental and upper mid range peak of the snare drum will help accentuate the character of the snare.
The acoustic environment of a snare drum (or any other drum within a drum kit) is noisy to say the least. Isolating the snare is impossible, but we still strive to do so.
In attempting to isolate the snare, we generally mic it very closely with a directional microphone. This means that the proximity effect will be a factor to account for.
Choosing a mic with a low-end roll-off in its frequency response will help filter out low-end rumble; the sound of the kick drum; and combat the proximity effect.
A high-end roll-off is also preferable in order to effectively filter out the brilliance of the drum kit’s cymbals.
A go-to for miking snare drums has already been mentioned several times in this article. It is the famous Shure SM57:
The Shure SM57 is a moving-coil dynamic microphone with a cardioid polar pattern.
Here is the frequency response graph of the Shure SM57:
We see in the above graph that the SM57 has a frequency response that suits the typical snare drum quite nicely.
Its low-end roll-off help filter out the other drums in the kit. However, the proximity effect will still allow the mic to pick up the low-end of the snare, assuming we are close-miking the snare.
The upper-midrange boost helps to accentuate the snap and character of the snare drum.
The high-end roll-off of the SM57 helps filter out the sound of the drum kit’s cymbals.
To read more about choosing a microphone for snare drums, check out my article Best Snare Drum Microphones.
Choosing A Mic Frequency Response For A Grand Piano
The grand piano is a huge instrument with a huge range.
Multiple microphones positioned at different spots around the instrument and acoustic space are often used in order to capture the best sound of a grand piano.
Flat, extended frequency response are ideal to capture the truest sound of the beautiful grand piano.
A common environment to mic up a grand piano would be in a concert hall. The audience noise is typically negligible in these large reverberant rooms, but the mics will definitely pick up reflections of sound around the acoustic space. This is perfectly fine and generally wanted.
Omnidirectional mics with flat frequency responses, in general, sound the most natural. And so, grand pianos are typically recorded with these mics!
A recommended mic for capturing the sounds of a grand piano if the AKG C 414 XLS (link to compare prices on Amazon and select retailers):
The AKG C 414 XLS is a large-diaphragm multi-pattern condenser microphone.
Although the AKG C 414 XLS has 9 selectable polar patterns, we’ll be focusing in on the omnidirectional pattern.
Here is the frequency response of the C 414 in omni mode:
The flat nature of the AKG C 414 XLS frequency response allows it to capture the true sound of the grand piano and the reverberations of the acoustic space.
If there is too much low-end rumble in the mic signal, try engaging one of the 3 selectable high-pass filters.
To read more about choosing a microphone for grand piano, check out my article Best Microphones For Grand Piano.
Choosing a microphone with a complimentary frequency response comes with the practice of recording various instruments. To recap, a solid strategy includes just 3 steps:
- Understand the frequency range (fundamentals and harmonics) of an instrument.
- Choose a microphone with a frequency response that enhances the important frequencies of that instrument.
- Be aware of mic placement; the nearby extraneous noise; and the proximity effect.
How Do Microphones Pick Up Different Frequencies?
Different sound frequencies vibrate the air at different rates. Frequency is measured in Hertz (Hz), as we’ve discussed, which is cycles or vibrations per second.
Sound vibrations in the air are caused along longitudinal waves (sound waves). These waves have peaks (max compression) and troughs (max rarefaction) just like other waves.
The wavelength of these longitudinal waves is inversely proportional to the frequency (assuming a constant speed of sound).
Lower frequencies naturally have a greater amplitude (a fundamental frequency of an instrument, for example, has a greater amplitude than its harmonics).
These “quieter” harmonics are added to the overall vibration of the air, resulting in all sorts of interesting wave forms. So we have slower moving waves (low frequencies) and faster moving waves (higher frequencies) effectively summed together to vibrate the air in complicated ways.
Our ears pick up on this and send an electrical signal to our brains.
Microphone diaphragms are very similar!
A microphone’s diaphragm will vibrate according to the sound waves it is exposed to.
Microphone diaphragms, capsules/cartridges, and overall bodies have natural resonant frequencies that affect the peaks and valleys within their overall frequency response. This is particularly relevant in the relatively heavy diaphragms of moving-coil dynamic mics.
The Determining Factors Of Microphone Frequency Response
Frequency response is the most significant determinant of a microphone’s characteristic sound. It is a function of many variables both inside and outside the microphone itself.
The frequency response of a microphone is influenced by the following factors:
- Weight of the diaphragm.
- Size of the diaphragm.
- Shape of the diaphragm.
- Tension of the diaphragm.
- Size and shape of the capsule/baffle/cartridge.
- Directionality of the capsule.
- Resonant frequencies of the microphone body.
- Distance Between The Sound Source The Microphone.
- Output impedance versus load impedance between mic and preamp.
The Weight Of The Diaphragm
The weight of the microphone diaphragm is a limiting factor on the high-frequency response.
The inertia of a heavy diaphragm makes it less sensitive to smaller wavelengths of sound (higher frequencies). For this reason, the relatively heavy moving-coil diaphragms have poorer high-frequency sensitivity than their lighter condenser and ribbon counterparts.
The Size Of The Diaphragm
The diameter of a circular diaphragm plays a big role in determining its microphone’s high-frequency response.
If a sound wave has a wavelength equal to the diameter of a diaphragm, it will apply equal amounts of both positive and negative pressure, effectively cancelling itself out.
Sound waves shorter than this wavelength get quite “phasey,” especially when both sides of the diaphragm are exposed to external sound pressure. This further reduces the clarity of the high-frequency response.
The shorter the wavelength, the higher the frequency, and so smaller diaphragms are physically able to reproduce higher frequencies than large diaphragms.
The Shape Of The Diaphragm
The shape of the diaphragm is one factor in the resonant frequencies of the microphone.
Typical moving-coil and condenser diaphragms are circular and therefore are susceptible to resonant frequencies (think standing waves).
A wavelength having exactly twice the length of the diaphragm diameter causes a sort of standing wave on the diaphragm, where the nature of the diaphragm shape slightly accentuates this wavelength’s frequency. Integer multiples of the wavelength behave interestingly on the diaphragm, causing either self-cancellation or resonant standing waves.
Ribbon microphones are different. Their long, corrugated ribbon diaphragms typically do not have strong resonant frequencies due to their irregular shape!
Moving-coil diaphragms often have leaf slots and indents where the coil attaches. This irregular shape also affects the microphone’s frequency response.
The Tension Of The Diaphragm
The tension of a diaphragm affects the inertia of the diaphragm and the frequency response of the microphone.
Think of tuning a snare drum. The tighter we stretch the skin, the higher the resonant frequency of the snare drum. Similarly, the tighter a microphone diaphragm, the higher its resonance frequency due to tension. Just don’t hit microphone diaphragms with drumsticks!
In small diaphragm condenser microphones, this tension may cause resonance way above the audible range of human hearing.
Large diaphragm condensers will usually have a high-frequency boost due to diaphragm tension.
Ribbon diaphragms are often loose enough for their resonant frequency (due to tension) to be in the sub-bass region or even below the audible range of human hearing.
For more information on microphone diaphragms, check out my article What Is A Microphone Diaphragm?
The Damping Material And Space Around The Capsule
Microphones typically have protective grilles around their capsules. Within the grille and around the capsule there is often dampening acoustic foam. There is a space between the grille, foam, and capsule.
The damping material dampens help protect the capsule from plosives while damping higher frequencies.
The space within the mic has the potential to promote short standing waves.
Although minor and terribly complicated, these seemingly small factors are all serious parts of microphone design and frequency response.
Generally speaking, diaphragms are damped at −6 dB per octave in order to produce a natural sounding frequency response.
Directionality Of The Capsule
Yes, even the directionality of a microphone affect its frequency response. This is particularly true when moving off-axis from directional microphones.
In a directional microphone, the capsule is designed with a specific “path” that sound must travel to get from the front of the diaphragm to the back of the diaphragm. This distance affects the high-frequency roll-off of microphones.
The frequency roll-off starts at a peak point: At a frequency with a wavelength twice that of the path length from front to back of the diaphragm. At this frequency, there is a maximal pressure difference between the two sides of the diaphragm, causing a peak in frequency response.
The pressure difference above this cut-off frequency will get smaller and smaller. The amplitude difference will also get smaller with higher frequencies. These both cause a decrease in frequency response.
Note that microphones are more directional at high frequencies and become increasingly omnidirectional at low frequencies.
Therefore, the off-axis frequency response of a directional microphone will have relatively less highs and more lows compared to the on-axis response. As we move the sound source further off-axis, the microphone becomes worse at reproducing high-frequencies.
For more information on microphone directionality, off-axis response, and polar patterns, check out my article The Complete Guide To Microphone Polar Patterns.
Resonant Frequencies Of The Microphone Body
All physical objects have resonant frequencies (think tuning forks). Microphones are no different.
Quality microphone bodies are designed with this in mind and special care is taken to minimize the presence of resonant frequencies. But the fact remains that these resonant frequencies of the microphone body will affect the frequency response.
Distance Between The Sound Source The Microphone
Though not a part of the microphone anatomy, sound source distance plays a role on the frequency response of directional microphones. Specifically on the low-end. This is due to the proximity effect,which we’ll discuss in more detail later.
The closer the sound source is to a microphone, the more low frequencies the microphone will reproduce.
Output Impedance Versus Load Impedance
Voltage transfer between microphone and preamp increases as the load impedance increases compared to the mic output impedance. A load impedance at least 5 times that of the output impedance is preferable.
However, a microphone’s output impedance is frequency specific and is often much greater at low frequencies. Therefore, low load impedances may cause a loss of low-frequency response.
At the impedance converters (whether step-up transformers or circuitry), high frequencies can be lost due to the increase in the mic signal impedance.
For more information on microphone impedance, check out my articles Microphone Impedance: What Is It And Why Is It Important? and What Is A Good Microphone Output Impedance Rating?
The Frequency Response Of The Human Ear
Yes, our ears also have a frequency response!
The outer limits of human hearing, as we’ve discussed, are 20 Hz on the low end, and 20,000 Hz on the high end.
We’ve evolved to have a sensitivity between 2,000 Hz and 5,000 Hz. This is range of speech intelligibility in the human voice. As we discussed earlier, vocal microphones benefit from a boost in this range.
As we get lower on the spectrum, heading toward 20 Hz, we become less and less sensitive to SPL levels.
We actually feel these sub-bass frequencies (20 Hz – 60 Hz) frequencies more than we hear them.
On the higher end of the spectrum, we slowly lose sensitivity as we get older and repeatedly damage our hearing.
For example, from spending so much time playing music in loud bands and attending loud shows, I personally have a hard time hearing anything above 16,500 Hz… Protect your ears!
To better understand the complicated frequency response of human hearing, check out the Fletcher-Munson curves:
The above curves show us, generally speaking, the relative frequency-specific sensitivities of human hearing.
On the above graph, you’ll find several lines related to different phon values.
A phon is a level of perceived loudness. You’ll see that the lower the “phon” line, the less sound pressure level is needed for us to hear a frequency.
- 0 phon is the threshold of hearing.
- 120 phon is the threshold of pain.
At the low-end (20 Hz), we see that it would take a great sound pressure level for us to actually hear a sound. However, at a frequency of 4 kHz, we are very sensitive to sound pressure variations.
What Are Frequency Bands?
Before we move on, I’d like to give a bit more information on the frequency bands (ranges) and how we hear them:
Note that these ranges are simply rough guidelines. There is no standard here.
The frequency ranges are:
- ≤ 60 Hz = Sub Bass.
- 60 Hz – 250 Hz = Bass.
- 250 Hz – 500 Hz = Low Mids.
- 500 Hz – 2 kHz = Midrange.
- 2 kHz – 4 kHz = High Mids.
- 4 kHz – 6 kHz = Presence.
- ≥ 6 kHz = Brilliance.
≤ 60 Hz = Sub Bass
This frequency band is felt more than it’s heard (check out the Fletcher-Munson curves). Most instruments and sounds lack information in this range.
Pay special attention to the sub bass frequency response in the microphones for kick drums, bass guitar amplifiers, and tubas.
60 Hz – 250 Hz = Bass
This is where most of the “musical” bass information is. The fundamental frequencies of many instruments are in this range including the fundamental frequency of most human voices!
250 Hz – 500 Hz = Low Mids
This range contains the stronger harmonics of the bass instruments and the fundamentals of some higher pitched instruments. To much response in this band may cause the microphone to sound “muddy.” Not enough response in this band may cause the mic to sound too thin.
500 Hz – 2 kHz = Midrange
The human ear starts getting more sensitive in this range. This range contains weaker harmonics from bass instruments and stronger harmonics from higher pitched instruments.
2 kHz – 4 kHz = High Mids
The human ear is the most sensitive in this range. A microphone that has a substantial boost or cut in this band will not recreate the timbre of a sound very accurately.
4 kHz – 6 kHz = Presence
If a microphone is sensitive in this range, it may add more presence to the sound, or it may sound harsh. There’s a fine line.
If there’s a dip in a microphone’s frequency response in this band, it can make the source sound transparent or further away than it actually is.
≥ 6 kHz = Brilliance
Many dynamic microphones drop off somewhere in the “brilliance” frequency band (even though they may be rated to capture up to 20 kHz).
This band is part of the reason why condenser microphones, in general, sound more “hi-fi” than their dynamic counterparts. Condenser microphones typically do a great job at picking up frequencies in this range, which encompasses all the upper harmonics of sounds as well as the “air” and “sparkle” of a sound (those are my technical terms).
Ribbon microphones tend to gently roll-off in the brilliance band, therefore reproducing a “warm” sound.
To learn about how musical notes fit into the audible frequency spectrum, check out my article Fundamental Frequencies Of Musical Notes In A=432 & A=440 Hz.
How Is Frequency Response Measured In Microphones?
The process of properly calculating a microphone’s frequency response is simple to conceptualize. However, microphone manufacturers need expensive equipment in order to actually measure correctly. This equipment includes:
- An anechoic chamber.
- A perfectly calibrated loudspeaker.
An anechoic chamber is absolutely acoustically dead. There is no ambient noise in an anechoic chamber nor are there any reflective surfaces in the room itself. It’s not uncommon to have negative dBA values when measuring the room noise of an anechoic chamber. This is incredible!
Next, a perfectly calibrated loudspeaker is needed. This loudspeaker needs a flat frequency response and must able to output 20 Hz to 20,000 Hz evenly. Like the anechoic chamber, a truly incredible amount of design detail must go into this loudspeaker.
The microphone in question is placed in front of the loudspeaker, connected via XLR to a calibrated spectrum analyzer, and the test is ready to take place.
Pink noise is played through this loudspeaker and captured by the microphone.
Pink noise is used because it has equal energy across all octaves in the human range of hearing. And so if the resulting frequency response diagram is not flat, it has something to do with the microphone’s response to particular frequencies.
The microphone signal is routed into a spectrum analyzer and a frequency response chart is then produced.
This sounds expensive, and it is!
An Alternative Way To Measure Frequency Response In Microphones
Instead of using all of this expensive equipment to produce an accurate frequency response, manufacturers (and audio enthusiasts alike) compare against a known reference.
By analyzing the microphone in question against another mic with a known frequency response, we calculate the differences and deduce a frequency response for the unknown microphone!
In this option, we need to ensure that everything but the microphones are the same in both tests:
- The room.
- Everything in the room.
- The position of the microphones.
- Distance to the speaker.
- The same pink noise is to be used and at the same volume.
This is a cheaper option. The room doesn’t need to be anechoic since both microphones will be subjected to the same stimulus. Though acoustically dead rooms are better since reflections of sound within the room will give a skewed result.
Also, the loudspeaker doesn’t need to be perfect, but should be calibrated so we know the pink noise is as flat as it can be.
We find the differences in frequency response between the two microphones using frequency analyzers. From that, we chart out a new frequency response diagram based on the known diagram.
Even that sounds tedious…
And it is, but it’s worth having for a spec sheet to better serve the customer.
However, some manufacturers do more “guesswork” than others when it comes to their frequency response charts. So sometimes the frequency response diagram isn’t necessarily accurate.
Another way these charts lack accuracy is in the scale of the graph. Oftentimes the response line is smooth and sums the average sensitivity (rather than being very precise and jagged). This is fine to purvey a general sense of where the mic naturally boosts and cuts in the frequency spectrum but lacks the true detail of the real frequency response.
So basically there are 3 ways of measuring a microphone’s frequency response:
- An anechoic chamber with a calibrated loudspeaker.
- Comparison to a known microphone.
Wow, the precision really dropped off quick!
The Proximity Effect On Frequency Response
The proximity effect is a microphone phenomenon in which moving a mic closer to a sound source actually boosts its sensitivity to low-end frequencies.
A microphone’s frequency response, therefore, changes depending on its proximity to the source it is capturing.
Here is a graphical representation of the proximity effect in the Shure Beta 57A microphone (link to compare prices on Amazon and select retailers):
How can this be?
First, there are two kinds of microphone principles: the pressure principle and pressure-gradient principle.
The proximity effect only affects pressure-gradient microphones. Pressure-gradient microphones are directional (cardioid and figure-8 polar patterns and all the variations thereof).
Because the pressure difference between the back and front plates is what causes the signal, and the difference is physically greater in high frequencies than it is in low frequencies (due to phase differences in shorter wavelengths). Microphones dampen the diaphragm to help balance out the signal and capture a “flatter” frequency response.
This works great at a fair distance.
However, when the sound source gets close to the capsule, things change. Let’s say there’s a distance D between the front and back of a mic’s diaphragm and the sound source is a distance D from the front of the diaphragm.
This means the source is 2D from the back and therefore the SPL is four times louder at the front than it is at the back.
At these distances, the difference in pressure between the front and the back is barely dependant on frequency and much more dependent on amplitude.
And so the dampening actually boosts the bass frequencies rather than equalizing them. This boost results in a variation of the frequency response in the low end of a microphone and is known as the proximity effect!
For more information on microphone proximity effect, check out my article What Is Microphone Proximity Effect And What Causes It?
Methods To Change A Microphone’s Frequency Response
How do I change a microphone’s frequency response? Although an innate characteristic of a microphone, frequency response can be altered by the following:
- Proximity effect.
- Moving the sound source off-axis.
- Cupping the microphone.
- Introducing or removing grilles and acoustic foam.
- Supplying varying amounts of phantom power (to active microphones).
- Changing the load impedance.
- Engaging filters.
- Switching polar patterns.
As we’ve touched on earlier, the proximity effect states that as a directional microphone moves closer to a sound source, the bass response the mic is increased.
Moving The Sound Source Off-Axis
Microphones naturally become more omnidirectional at lower frequencies and more directional at higher frequencies. Therefore, moving a sound source off-axis will effectively reduce the high-frequency response of the mic.
Cupping The Microphone
By cupping the microphone, we introduce more standing waves around the microphone diaphragm. This causes alterations to the mic frequency response.
Introducing Or Removing Grilles And Acoustic Foam
Any time we add or take away material from around a microphone diaphragm, we risk altering the way sound affects the diaphragm. In doing so, we alter the frequency response.
Related article: Why Do Microphones Have Screens? (Pop Filter, Grille, Windscreen)
Supplying Varying Amounts Of Phantom Power
Some active microphones that require phantom power are capable of running on a range of DC voltages and not only the standard +48 volts.
However, many of these mics will have limited functionality with less voltage. One of the ways this decreased functionality shows itself is in a decreased high-frequency response.
Related article: What Is Phantom Power And How Does It Work With Microphones?
Changing The Load Impedance
Varying the load impedance of a microphone will affect the signal flow.
There are variable impedance preamps on the market that can be used to alter the sound of the microphone. These preamps are best known and paired with ribbon microphones.
Engaging high-pass filters and frequency boosts (presence boosts, etc.) will directly effect a microphone’s frequency response.
Switching Polar Patterns
In multi-pattern microphones, changing the polar pattern will often alter the frequency response ever-so-slightly.
Related article: The Complete Guide To Microphone Polar Patterns
Frequency Response Generalizations Of The 4 Main Microphone Types
Let’s talk about some generalities of various microphone types and their frequency response characteristics.
There are 4 main types of professional microphones:
- Dynamic moving-coil microphones.
- Dynamic ribbon microphones.
- Small diaphragm condenser microphones.
- Large diaphragm condenser microphones.
I’ll include links to online retailers of each mic examples for more information and price points.
Dynamic Moving-Coil Microphone Frequency Response Generalities
Example microphone: Shure SM58
Moving-coil dynamic mics often have the following frequency response characteristics:
- Coloured response.
- High-end roll-off within the audible spectrum.
- Significant resonant frequencies.
For more on moving-coil dynamic microphones, check out the following My New Microphone articles:
• The Complete Guide To Moving-Coil Dynamic Microphones
• Top 11 Best Dynamic Microphones On The Market
Dynamic Ribbon Microphone Frequency Response Generalities
Example microphone: Royer R-121 (link to compare prices on Amazon and select retailers)
Ribbon dynamic microphones often portray the following frequency response traits:
- Relatively flat response in the mid frequencies.
- Gentle roll-off of high-end frequencies.
- No significant resonant frequencies within the audible range.
For more on ribbon microphones, check out the following My New Microphone articles:
• The Complete Guide To Ribbon Microphones (With Mic Examples)
• Top 12 Best Passive Ribbon Microphones On The Market
• Top 11 Best Active Ribbon Microphones On The Market
Small Diaphragm Condenser Microphone Frequency Response Generalities
Example microphone: DPA 4006A
Small diaphragm condenser microphones generally exhibit the following frequency response characteristics:
- Flat frequency response across the entire audible frequency range.
- Extended high-end response above the audible range.
For more on small-diaphragm condenser microphones, check out the following My New Microphone articles:
• Large-Diaphragm Vs. Small-Diaphragm Condenser Microphones
• 11 Best Small-Diaphragm Condenser Microphones Under $500
Large Diaphragm Condenser Microphone Frequency Response Generalities
Example microphone: Neumann TLM 102 (link to compare prices on Amazon and select retailers)
Large-diaphragm condensers often yield the following frequency response qualities:
- Relatively flat frequency responses across the audible range.
- A gentle low-end roll-off.
- A boost in sensitivity in the upper-mid and/or high-end frequencies with a slight high-end roll-off within the audible range.
For more on large-diaphragm condenser microphones, check out the following My New Microphone articles:
• 11 Best Large-Diaphragm Condenser Microphones Under $1000
• 12 Best Large-Diaphragm Condenser Microphones Under $500
For an in-depth but different approach to understanding microphone “types,” check out my article Microphone Types: The 2 Primary Transducer Types + 5 Subtypes.
Do speakers and headphones have a frequency response? Speakers and headphones, like microphones, have frequency responses. The frequency response of an audio output device is determined mostly by the size of the speaker(s), transducer type, circuitry, and resonant frequencies.
Related article: What Is Headphone Frequency Response & What Is A Good Range?
What is microphone sensitivity? Microphone sensitivity is defined as the output signal strength of a mic (mV or dBV) relative to the sound pressure level the mic is experiencing (measured with a 94 dB SPL or 1 Pascal 1 kHz tone). The sensitivity rating of a mic has to do with the signal output rather than the reactivity to sound.
Related article: What Is Microphone Sensitivity? An In-Depth Description
For information on all the possible microphone specification, please continue to my article Full List Of Microphone Specifications (How To Read A Spec Sheet).