There are many ways to describe microphones and many ways in which mics differ from one another. Whether qualitatively or quantitatively, a microphone’s important differentiators and characteristics are listed in a manufacturer-made document called a microphone specifications sheet or data sheet.
What is a microphone specifications sheet and how do we read one? A microphone “spec sheet” or “data sheet” is a written document that manufacturers create to complement and explain the technical details of a given microphone. Every microphone has its own spec sheet and in order to properly read a spec sheet, we must know what the data indicates.
Note that, for this article, I’ll use the terms “spec sheet” and “data sheet” interchangeably.
This article will provide an excellent overview of what to expect on a microphone specifications sheet and what each of the specifications actually tells us about the microphone!
Table Of Contents
- The Microphone Specifications Sheet.
- The Sections Of A Specifications Sheet.
- Full List Of Microphone Specifications.
- Important Specifications For Each Microphone Transducer Type.
- Related Questions.
The Microphone Specifications Sheet
There’s no exact standard for mic manufacturers to follow when putting together their spec sheets. Some specifications are more important to certain manufacturers than others. Similarly, some specs are more applicable to certain microphones than others.
Some manufacturers keep their data sheets short and to the point, providing only the essential information. Others provide an in-depth rundown, covering all the technical details of their mics.
Data sheets can be found by themselves; in microphone owner’s manuals; on manufacturer websites; and elsewhere online.
Spec sheets will most often relay both general data and technical stats about the microphone. They are:
- Very useful to browse when researching a potential purchase.
- Handy to read prior to and even during the use of a microphone.
- Important to consider when choosing the right microphone for a specific application.
But the spec sheets are only ever truly useful if we are able to effectively read and understand what is written, which is that main focus of this article.
Before getting into the meaning of each individual specifications, let’s quickly go over the sections of a typical microphone spec sheet.
The Sections Of A Specifications Sheet
Although the specs that are included on a spec sheet are largely dependent on the manufacturer and the microphone, there are some sections that are common. They include:
- Full Title And A Picture Of The Microphone.
- Included Accessories.
- Optional Accessories.
- Replacement Parts.
- Operation/User Tips.
- Specifications & Diagrams.
Note that these are simply the common sections found on data sheets. Different spec sheets may expand or consolidate these sections. Different manufacturers may add or remove certain sections in their data sheets.
Full Title And Picture
You’ll always find the full model number and the manufacturer’s name at the top of a spec sheet.
This is sometimes labelled “key message,” “overview,” “general description,” or other names. It depends on the manufacturer.
This gives us a general description of the microphone. The description will typically tell us big picture details of the microphone, like:
- If it’s a dynamic or condenser.
- What its polar pattern(s) is/are.
- If it has a small or large diaphragm.
- Its general frequency characteristics.
Features are very similar to the specifications, except that the information is broader than precise specification measurements. Features are often stated with more colourful language than the cut-and-dry specifications section.
The features section is often in point form and quickly puts forth the important characteristics of the mic without being overly technical. Some common, notable, features include:
- Frequency response characteristics.
- Polar response (qualitative).
- Diaphragm size and material.
- How the featured accessories make the microphone perform better.
- Self-Noise, Max SPL, and Dynamic Range data.
- Switchable options.
- And many other selling points!
Included Accessories/ Optional Accessories/ Replacement Parts
These are all pretty self-explanatory, but worth noting that specific models of accessories are sometimes needed to go with specific microphones!
Some manufacturers recommend applications for their microphones (often this will be included in the “features” section). Some mics are even known for their specific uses and are often marketed as such
This section is sometimes included to help users get the most out of their microphone. Operation/User Tips could include:
- How to position the mic for optimal performance.
- How to properly gain stage the microphone.
- If phantom power will damage the microphone.
- Notes on durability, temperature, and humidity.
- General “how to” on caring for the microphone to help increase its longevity.
The List Of Specifications & Diagrams
From reading through many spec sheets during my research for this article, I’ve found that many of the following are commonplace microphone specifications.
I also found that different manufacturers give out different information and different microphone types warrant different data.
So without further ado, I present to you the full list of microphone specifications!
Full List Of Microphone Specifications
- Type Of Transducer.
- Diaphragm Design / Capsule Size.
- Address Type.
- Acoustic Principle.
- Frequency Response.
- Polar Pattern.
- Off-Axis Rejection.
- Output Sensitivity.
- Maximum Sound Pressure Level.
- Maximum Output Voltage.
- Hum Pickup Level.
- Signal-To-Noise Ratio.
- Dynamic Range.
- Output Impedance.
- Rated Load Impedance.
- Output Connection.
- Supply Voltage.
- Current Consumption.
- Switchable Options.
- Sample Rate (USB).
- Bit Depth (USB).
- Headphone Amplifier Specs (USB).
- System Requirements (USB).
- Net Weight.
- Shipping Weight.
- Wiring Diagram.
- Temperature Range.
- Relative Humidity.
Wow, there are a lot of potential microphone specifications! Without going into too much detail, this article will explain what each of these specs is and how they describe a given microphone.
Type Of Transducer
This spec will also be labelled as “type,” “element,” “transducer principle,” element type,” “cartridge type,” and other names.
My one [albeit long] sentence to describe microphones is this:
“A microphone is a transducer that converts mechanical wave energy (sound waves) into electrical energy (audio signal) by means of a movable diaphragm.”
A transducer is any device that convert one form of energy to another.
With microphones, there is always a vibrating diaphragm that reacts to external sound waves. However, there are two general methods for microphones to convert sound waves to mic signals.
In other words, there are two general types of microphone transducers:
- The dynamic microphone transducer.
- The condenser microphone transducer.
This is perhaps the biggest differentiating factor of microphones.
The Dynamic Microphone Transducer
A dynamic microphone converts energy via electromagnetic induction.
Electromagnetic induction refers to the voltage created across a conductive material as that material is subjected to a changing magnetic field. With dynamic mics, the diaphragm element is conductive and moves back and forth within a permanent magnetic field, effectively creating a voltage (mic signal) that coincides with the movement of the diaphragm.
There are two popular types of dynamic microphones on the market:
- Moving-coil dynamic microphone.
- Ribbon dynamic microphone.
Moving-Coil Dynamic Microphones
The diaphragm of the typical moving-coil dynamic mic is not, itself, conductive. Rather, a small induction coil is attached to the movable diaphragm.
The coil fits in a space between permanent magnets and is, therefore, in a magnetic field.
As sound pressure moves the diaphragm, the conductive coil moves along with it and electromagnetic induction creates a mic signal!
General Characteristics Of A Dynamic Microphone:
Although not cut-and-dry, dynamic microphones typically have the following characteristics (some of which will be described through other specs):
- Simple design/economical.
- Passive circuitry (does not require power).
- No self-noise.
- Robust build.
- Humidity resistant.
- Low sensitivity.
- Very high maximum sound pressure levels.
- Shaped/coloured frequency response.
- Slow transient response.
For more information on moving coil dynamic microphones, check out my article “Dynamic Moving Coil Microphones: The In-depth Guide“
The Ribbon Microphone
When discussing the main types of microphones, we often break them down into dynamic (referring to moving-coil), condenser, and ribbon mics. However, the ribbon microphone is actually a dynamic microphone.
The diaphragm (aka ribbon) of the typical ribbon microphone is made of a very thin conductive metal. The diaphragm is often corrugated and resembles a ribbon (hence the name).
The ribbon is attached at two points at its ends (length-wise) and sits within a baffle with magnets all around its perimeter.
As sound pressure moves the conductive ribbon diaphragm, electromagnetic induction creates a coinciding mic signal!
General Characteristics Of A Ribbon Microphone:
Once again, these are only typical of a ribbon microphone and are not set in stone:
- Less robust than a moving coil.
- More expensive than a moving coil.
- Lower sensitivity rating than a moving coil (unless active).
- Shaped frequency response.
- Gentle “natural” sounding high-end roll-off.
- Faster transient response than a moving coil.
Note that some modern ribbon mics are active, which means that have active circuitry and require power in order to function. These active ribbon mics will have specs like Self-Noise and Supply Voltage whereas the typical passive ribbon mic will not.
For more information on ribbon microphones, check out my article “Ribbon Dynamic Microphones: The In-depth Guide.“
The Condenser Microphone Transducer
A condenser microphone converts energy via electrostatic principles. The capsule of a condenser microphone is effectively a large parallel plate capacitor.
Here’s how a condenser capsule is designed:
There are two plates that form the capsule’s capacitor. One plate is the diaphragm, which moves according to exterior sound waves. The other plate is fixed and is called the backplate.
When the capsule/capacitor of a condenser microphones has a fixed charged (either permanently or by an external polarizing voltage), the mic will function properly.
The fixed charge makes it so that the variation in voltage across the plates (the mic signal) is inversely proportionate to the capacitance of the capsule. This is shown simply in the following equation:
V = Q / C
Where V = voltage (the variance of which is the mic signal)
Q = charge (fixed/constant)
C = capacitance (changes as the diaphragm moves)
Condenser mics are also known as capacitor mics (which is a more suitable name, in my opinion).
General Characteristics Of A Condenser Microphone:
- Complex design/More expensive.
- Active circuitry.
- Less robust than dynamic microphones.
- Higher sensitivity.
- Lower maximum sound pressure level.
- Flat frequency response.
- Fast transient response.
As mentioned, the capsule of a condenser microphone can be permanently charged or charged via an external polarizing voltage.
- Electret condenser microphones: These mics have electret material in their capsules that gives the capsule a permanent charge.
- True condenser microphones: These mics do not have permanently charged capsules and therefore require an external polarizing voltage.
Electret microphone capsules are often referred to as pre-polarized capsules on specifications sheets.
Regardless of whether a condenser microphone is electret or not, all condensers are active. This means that they all require external power in order to function properly.
There are various methods of supplying this power which include: phantom power, DC bias, USB power, and more. The external DC voltage of these powering methods goes toward powering the impedance converters and internal amplifiers of the active condenser microphones.
Diaphragm Design / Capsule Size
This spec, often in the general description section of the spec sheet, tells us how big the microphone’s diaphragm is and what it’s made of.
This specification, if at least qualitatively, is a fairly standard one to see on data sheets.
It is not overly critical with moving-coil dynamic microphones. However, with the more sensitive condenser and ribbon mics, differences in the diaphragm, capsule, or element design could alter the sound of the mic.
Therefore, diaphragm design / capsule size is an important specification for condenser and ribbon mics.
- Condenser microphones fall mostly into large-diaphragm and small-diaphragm model. As we’ll see, there are distinct differences between the two.
- Ribbon microphone diaphragms are very sensitive. Their dimensions (including thinness), material, and corrugation specs are important to know.
Large Diaphragm Vs. Small Diaphragm Condenser Mics
Sometimes the exact diameter of a condenser mic’s diaphragm will not be specified. Instead, the diaphragm will be labelled as either small or large. What exactly does that mean?
Well, there’s no exact definition, but in general small and large diaphragm mean the following:
- Small diaphragm ≤ ½ inch (12.7 mm or less).
- Large diaphragm ≥ 1 inch (25.4 mm or more).
So what if the diaphragm diameter is between a half inch and an inch? Although it doesn’t happen often, the manufacturer will typically give the measurement if their microphone diaphragm falls in this grey area.
It’s also worth noting that the diaphragm size is usually reflected in the overall design of the microphone. Small diaphragm mics are usually “pencil” shaped and top-address, while large diaphragm mics are usually bulky and side-address (more on address type later).
Let’s look at some characteristics of “small” and “large” diaphragms.
Note that, although we’ll be discussing condenser microphones in this small vs. large diaphragm sections, the points here apply (though not as much) to moving-coil dynamic diaphragms as well.
Small Diaphragm Microphones
If I could describe small diaphragm microphones in one word, the word would be “consistent.” Other descriptive words include “uncoloured, accurate, and true.”
Small diaphragms are more reactive to sound pressure and “snap back” to resting position a bit faster than their large diaphragm counterparts.
The main con is this makes them a bit more susceptible to the noise of their active electronics (we’re talking condenser mics here). In other words, SDCs have typically higher self-noise specs.
However, the advantages that small diaphragm microphones have will often outweigh the slight bit more noise they inherently have.
Small diaphragm microphones, generally speaking, have the following advantages over large diaphragm mics:
- Better transient response.
- Clearer high-frequency response (oftentimes the roll-off happens well above 20 kHz).
- Much more consistency in the polar pattern at low and high frequencies.
Large Diaphragm Microphones
Large diaphragm condenser microphones typically have better noise performance than small diaphragm condensers. This means less self-noise and a better signal-to-noise ratio.
However, as we mentioned when discussing the small diaphragm microphone, large diaphragms will typically have:
- Slower transient response.
- Lower point of high frequency attenuation (poorer frequency response).
- Less consistent polar pattern across all frequencies.
- Less proximity effect.
Ribbon Microphone Diaphragms
Often this spec will be given as “generating element” or “transducer element” since the ribbon acts as both the diaphragm and conductor in a dynamic ribbon microphone.
Ribbon diaphragms are made from conductive metal (typically aluminum). They are often corrugated and their thinness is measured in microns (millionths of a meter). Generally, the thinner the ribbon, the better it will react as a diaphragm. The thinness of ribbons also makes them very fragile!
This spec will only ever apply to dynamic transducers.
From my research, rare earth neodymium seems to be the preferred magnetic material used in dynamic mics.
This, to me is a type of “quality control” spec. Some manufacturers explicitly tell you they use good magnets, and others don’t.
As we discussed earlier in the diaphragm design / capsule size section, there are two basic address types:
- Top address (also known as end address, front address, top fire, end fire, or front fire).
- Side address (also known as side fire).
Top address is when the diaphragm’s central axis (where it points) is at the top or end of the microphone. This is typical of small diaphragm “pencil” shaped microphones.
Side address is when the diaphragm “points” through the side of the microphone. This is typical of large diaphragm and bulky microphones.
Some manufacturers add address type in their spec sheets so we know how and where the microphone picks up sound.
However, it’s often easy to guess whether a mic is side address or top address.
This spec will sometimes be labelled as “principle of operation.”
There are two basic acoustic principles that microphones work on:
- Pressure principle: one side of the mic diaphragm is open and the other is closed.
- Pressure-gradient principle: both sides of the mic diaphragm are open.
The acoustic principle of a microphone is related to the mic’s polar pattern:
- Pressure Principle = omnidirectional polar pattern.
- Pressure Gradient Principle = any other polar pattern (plus the possibility of omnidirectional if two diaphragms are summed together, as with multi-directional microphones).
The pressure principle operates with a diaphragm that is “open” on one side and “closed” on the other side.
The open side reacts to varying external air pressure caused by sound waves, while the other side is closed in a column of air at a fixed pressure.
Physics tells us that pressure in gas (sound pressure in air) pushes equally in all directions at any given point. And since pressure microphones only measure sound pressure at one single point (plane) in space (the open side of the diaphragm), they respond uniformly to sound pressure from all directions. They are, therefore, omnidirectional in nature!
The pressure-gradient principle operates with a diaphragm that is “open” at both sides.
It is the difference in pressure between the two sides of the diaphragm that causes the diaphragm to move.
The most basic form of a pressure gradient microphone yields a figure-8 polar response (which we’ll get to shortly).
This is because the maximum difference in pressure between the front and back of the diaphragm happens when a sound source is hitting either the front or the back directly.
Similarly, if the sound source is directly to the side of the diaphragm, it will apply equal pressure to both the front and back, which creates no difference and no movement.
With different designs in the microphone structure and diaphragm housing, we can, in theory, build any polar pattern. Manufacturers use the pressure-gradient principle in conjunction with clever capsule design to achieve polar patterns in their microphones.
Pressure gradient microphones, by nature, exhibit the proximity effect and are sensitive to vocal plosives.
This spec will also be labelled as “frequency range.”
Frequency response on a spec sheet will be stated in two ways:
- Range (the microphone picks up sound from frequency-A to frequency-B).
- Frequency response chart (a visual representation of frequency-specific sensitivity along the audible frequency spectrum).
Let’s relate frequency response to humans.
Humans can hear in the range of 20 Hz – 20,000 Hz, but that’s not the whole story. We’re not particularly sensitive to low frequencies or high frequencies but we’re very sensitive to the frequencies in the 2 kHz – 5 kHz range (where speech intelligibility resides).
Similarly, a microphone may indeed pick up frequency in the range of 20 Hz – 20,000 Hz but could be more sensitive to certain frequencies and less sensitive to others within that range.
Microphone frequency response is often categorized into two camps:
- Flat response: the microphone is practically equally sensitive to all frequencies along the spectrum.
- Coloured/shaped response: the microphone is more sensitive to some frequencies than others and may be completely insensitive to some other frequencies at the low or high end.
If a microphone has an ideal flat frequency response, it is equally sensitive to all frequencies in its range. On the frequency response graph, the response line will be horizontal (flat).
Small diaphragm condenser microphones generally have wider and flatter frequency responses than other microphones.
If a microphone has a coloured/shaped frequency response, it will not be drawn flat on the chart. Instead, these microphones have bands of increased or decreased sensitivity within their frequency ranges.
Large diameter dynamic microphones are generally more coloured than other microphones and have narrower frequency ranges.
Flatter Isn’t Always Better
Sometimes we want a wide, flat frequency response in a microphone. Some practical applications of these “neutral” microphones include the capture of:
- Ambience or room sound.
- Pianos, harps, and other wide range instruments.
- Sound effects or foley.
- Anything that requires an accurate capture of the original sound.
That being said, there are also advantages of using shaped-response microphones.
If a microphone is less sensitive in the low frequencies, it will pick up less handling noise (good for lavaliers) and less hum or rumble from the environment.
Oftentimes the colouration of the mid-frequencies yields a desirable “EQ.” A common example of this is a boost in the 3 kHz – 6 kHz range that adds clarity and presence to vocals.
The attenuation of high frequencies in a shaped-response microphone is also wanted in many cases. Firstly, it produces a less “harshness” in the sound. Secondly, it may help with noise rejection, (for example a kick drum microphone rejecting the noise from the cymbals on a drum kit).
This spec will also be labelled as “directional pattern” or” polar response pattern.”
A microphone’s polar pattern spec shows us how sensitive a microphone is to sound sources at all angles relative to its central axis (where the microphone “points”).
Let’s briefly go over the common polar patterns of microphones:
- Omnidirectional: picks up sound equally from all angles.
- Figure-8: picks up audio from the front and back while rejecting the sides.
- Cardioid: Picks up the most from the front, half as much from the sides, and none from the back.
- Supercardioid: More directional to the front than cardioid. Less pick up from the side, but a rear lobe of sensitivity.
- Hypercardioid: More directional to the front than supercardioid. Less pick up from the side, but a bigger rear lobe of sensitivity.
- Shotgun/Lobar: Extremely directional to the front. Small lobes to the sides and to the rear.
This is a spec that, like frequency response, often comes with a diagram.
Polar pattern diagrams show us a 2-dimensional representation of how a microphone will react to sound sources at all angles relative to its on-axis response. It will also, oftentimes, show us the directionality of the microphone at different audio frequencies, which is important.
Some microphones are even multi-pattern, which means that they can switch between multiple polar patterns.
For more information on polar patterns, please consider reading my article The Complete Guide To Microphone Polar Patterns.
This is typically assumed in the polar pattern spec. Sometimes manufacturers will include an off-axis rejection stat if their microphone has particularly good rejection.
The only manufacturer that adds this spec on their sheets that I’ve found is Audix. What off-axis rejection really means, though, is vague and I don’t think it’s a very important spec. All the information can be found on the polar pattern diagram(s).
This spec will also be labelled as “output sensitivity,” “output level,” “open circuit sensitivity,” “AF sensitivity,” “transfer factor,” or some derivation of these titles.
Microphone sensitivity answers the following questions:
- How efficient is the microphone transducer at converting mechanical wave energy into electrical energy?
- What’s the relationship between sound pressure level applied to the microphone diaphragm and the output voltage?
Sensitivity ratings are given as dBV or mV per Pa or 94 dB SPL.
dBV = decibels relative to 1 volt (mic signal strength)
mV = millivolts (mic signal strength)
Pa = 1 Pascal (sound pressure).
94 dB SPL = sound pressure level equal to 1 Pascal.
Microphones with higher sensitivity will output stronger mic signals when subjected to the same sound pressure.
It’s important to note that sensitivity rating are also typically given according to a mic’s response to a 1 kHz tone. It’s also worth noting that, typically, sensitivity is measured in an open circuit. Though not real world applications, these testing parameters yield accurate results.
Typical sensitivity specs for dynamic microphones are:
- 1 to 4 mV/Pa @ 1 kHz
- -60 to -48 dBV/Pa @ 1 kHz
Ribbon microphones are typically less sensitive and have outputs closer to the 1 mV/Pa or -60 dBV/Pa end while moving-coil microphones typically have sensitivity rating near the 4 mV/Pa or -48 dBV/Pa end.
Note that active ribbon mics will generally have much higher sensitivity ratings than those listed above due to their internal amplifiers.
Typical sensitivity specs for condenser microphones are:
- 8 to 32 mV/Pa @ 1 kHz
- -42 to -30 dBV/Pa @ 1 kHz
This is due to the internal amplifiers found in condenser microphones.
Maximum Sound Pressure Level
This spec will often be shortened to “max SPL,” and will also be labelled as “maximum input sound level.“
The maximum SPL rating is the threshold at which a microphone will begin to distort its signal. It is the point at which a certain amount (usually 0.5%) of total harmonic distortion happens to the signal.
Total harmonic distortion (THD) is the ratio of the [sum of the powers of all harmonic frequencies above the fundamental frequency] to the [power of the tone at the fundamental frequency].
Manufacturers generally use a 1 kHz tone to test the point at which THD begins to happen, and, therefore, to measure max SPL.
So what causes a microphone to “max out?”
Although it is physically possible to overload microphone diaphragms, it’s very unlikely.
Ribbon diaphragms are the most susceptible to overloading due to their thinness, but even then, sound pressure level alone would be tremendously high to cause that. Ribbon tear is generally causes by gusts of wind or physical trauma rather than SPL.
The max SPL of a microphone, then, is an overloading of the microphone circuitry. It is the point at which the actual mic signal starts distorting rather than the point at which the diaphragm begins acting non-linearly.
For that reason, the following points are true:
- Passive microphones have very high max SPL values: oftentimes dynamic mics will not even have max SPL ratings because they are so high and impractical to test for. Moving-coil and passive ribbon dynamic mics typically have high max SPL values.
- Active microphones have lower max SPL values: the circuitry and amplifiers in active mics may be overloaded when a high SPL causes a strong mic signal. Condenser and active ribbon mics will typically have calculated max SPL values.
Just for reference, here’s a quick bullet list of typical dB SPL scenarios:
- 0 dB SPL – Threshold of hearing. Anything below 0 dB is not perceivable to human ears.
- 20 dB SPL – Bedroom when no one’s home.
- 40 dB SPL – Refrigerator hum.
- 60 dB SPL – Normal conversation.
- 65 dB SPL – Business Office.
- 85 dB SPL – Average City Traffic.
- 100 dB SPL – Jackhammer.
- 110 dB SPL – Chainsaw or Rock Concert.
- 120 dB SPL – Ambulance Siren.
- 125 dB SPL – Jet Engine from 100 meters away.
- 140 dB SPL – Threshold of pain. Anything this loud or louder will cause immediate hearing damage and will be very painful.
Maximum Output Voltage
Similar to max SPL, maximum output voltage is the maximum signal that a microphone can output before distorting.
The max output voltage is the threshold at which a certain THD becomes present in the signal. The THD threshold is typically 0.5% or 1% just like with the max SPL.
In other words, the maximum output voltage coincides with the maximum sound pressure level of a microphone!
This spec will also be labelled as “equivalent noise level,” or simply as “noise.”
Self-Noise is only a specification for active microphones since they contain active circuitry that inherently produces noise.
Self-noise is typically given in dBA units (decibels “A-weighted”).
The dBA Scale
dBA is very similar to dB SPL but is different in that it takes into account and is based on the sensitivity of human hearing (we’re less sensitive to the low and high-end frequencies of the 20 Hz to 20,000 Hz range of human hearing).
This, in theory, is a better measurement for the “noise” we’ll hear from a microphone. It also yields smaller, more marketable numbers for a specification about noise!
Large diaphragm condensers typically have a self-noise rating of less than 15 dBA, which is most often indiscernible from the ambient noise of even sound-proof recording rooms.
Small diaphragm condensers generally have more self-noise than their large diaphragm counterparts. A good small diaphragm condenser mic should have a self-noise of under 20 dBA. This noise may be heard in quiet recordings, but gets lost in a mix pretty quickly.
Between 20-23 dBA, the self-noise is evident but usually fine for recording loud sources. Anything above 23 dBA is generally viewed as “unfit” for studio recordings.
For everything you’d want to know about self-noise in active microphones, check out my article What is Microphone Self-Noise? (Equivalent Noise Level).
Hum Pickup Level
This is a specification I’ve only ever found on Electro-Voice microphone data sheets.
I suppose hum pickup level is like “self-noise for the dynamic microphone.”
Although this specification is rare to see on a data sheet, the hum pickup of dynamic mics is not such a rare issue, especially when recording quiet sources with less-than-ideal preamps.
This spec will often be shortened to “S/N Ratio.”
This is yet another way microphone manufacturers let us know how much noise is inherent in their mics.
The signal-to-noise ratio is measured in dB, a relative unit of measurement.
When stating the S/N ratio, manufacturers once again use the standard of a 1 kHz tone at 94 dB SPL (1 Pascal).
The standard signal-to-noise ratio is equal to the difference between the 94 dB tone and the self-noise of the microphone. The dB SPL (as with the tone) and dBA (as with the self-noise) are treated as the same units in this calculation.
If the standard is not followed for the S/N ratio spec, it is up to the manufacturer to specify otherwise.
The dynamic range of a microphone is not usually specified on a spec sheet since it is easily calculated with two other, more common specs.
The dynamic range of a microphone is the difference between its max SPL and its min SPL (the self-noise of the active microphone). In other words, the range of SPL the microphone can recreate cleanly.
Dynamic range, self-noise, signal-to-noise ratio, and max SPL are all related to one another.
Dynamic microphones rarely have a dynamic range spec since their max SPL ratings are typically very high and, since they have passive electronics, their noise floor is very low.
Condenser microphones, however, have lower max SPL ratings and higher self-noise. Therefore, dynamic range is worth considering and worth noting on spec sheets.
Note that self-noise is typically given in dBA while max SPL is given in dB SPL. From my research, the dynamic range is still [max SPL – self-noise] even though the units of measurement are slightly different!
This spec will also be labelled simply as “impedance,” “rated impedance,” “nominal impedance,” or “electrical impedance.
Impedance to AC circuitry (like audio signals) is like resistance to DC circuitry.
Basically, the lower the impedance, the “easier” it is for the audio signal to travel from the microphone output to the following input.
We want the output impedance of our microphones to be low in order for the mic signal to travel properly as intended. Generally speaking, any output impedance below 600 ohms is considered “low.”
All professional microphones are deemed "low impedance." A good percentage of them are even less than 300 ohms!
This essentially allows them to “push” their audio signal through long runs of cable without that signal being degraded. After all, a microphone is pretty well useless without its signal path and recording and/or playback device.
In theory, the lower the output impedance, the cleaner the signal. But it all depends on where the signal is going.
The preamp or audio device “next-in-line” after the microphone must have a high enough input impedance for the signal to be transferred effectively, which brings us to our next point.
Rated Load Impedance
This spec will also be labelled simply as “load impedance,” “minimum terminating impedance,” or “minimum load impedance.”
Although rated load impedance is not a characteristic of the microphone itself, it’s important nonetheless.
The rated load impedance is the minimum input impedance an audio device must have if it is to go inline directly after the microphone.
This minimum load impedance must be met (ideally exceeded) in order for the microphone to function properly and the mic signal to be tranferred as intended. It must also be met or exceeded for all the data in the spec sheet to hold true!
Examples of “audio devices inline directly after the microphone” could be:
- Microphone preamplifiers.
- Powered speakers.
- Audio mixing consoles.
- Computer Audio Interfaces.
- Anything that you could plug your mic into!
Sometimes this piece of data is specified and sometimes it isn’t. The general rule of thumb is that the rated load impedance should be at the very least 5 times that of the microphone output impedance. Though 10 times or more is great to be safe.
Note that standard professional mic inputs are built with more than enough input impedance to effectively take in signals from typical professional microphones.
For a thorough examination of both output impedance and rated load impedance, click through to my article Microphone Impedance: What is it and Why is it Important?
Polarity is oftentimes consolidated into the output connection specification.
Most single diaphragm professional microphones have an XLR output, and so polarity most often refers to the 3 pins of the XLR connector. However, there are also many mics that have Tuchel, Mini-XLR, or other connections and so polarity would apply to those connections as well.
Balanced mic signals require three separate wires inside the cable, which XLR provides (we call them “pins”):
- Pin 1 is the ground shield and carries no audio signal (instead it “shields” the audio on pins 2 and 3).
- Pin 2 carries the audio signal in “positive polarity.”
- Pin 3 carries the audio signal in “negative polarity.”
The AC circuit needed to send the audio from the microphone to the preamp is created through pins 2 and 3.
Typically this spec will tell us that positive pressure on the diaphragm produces positive voltage on pin 2 with respect to pin 3. That’s it!
If the spec sheet doesn’t explicitly state this, it can be safely assumed.
If the reverse is true, there may be an issue when double miking a sound source with a “regular polarity” microphone and a “reverse polarity” microphone. If the two mics are placed at the same point, they will effectively cancel each other out. But this is a rare case indeed!
For more info on microphone audio signals, check out my article What Is A Microphone Audio Signal, Electrically Speaking?
To learn more about polarity in balanced professional mics and consumer unbalanced mics, check out my article Do Microphones Output Balanced Or Unbalanced Audio?
This spec will also be labelled simply as “connector,” or “matching connector.”
The XLR connection is the most popular for professional microphones (this includes the standard 3-pin; the 5-pin for stereo mics; and the mini-XLR to miniature lav/lapel mics).
However, there are many output connections on the market, including Tuchel and multi-pin connections for tube microphones.
As was mentioned in the section on polarity, the polarity is sometimes included in a general output connection spec.
Other types of connections include:
- USB microphones will typically have a microUSB or USB out.
- Consumer microphones may have TRS outs (or even a cable attached to them).
- Professional Stereo microphones will have 5-pin XLR outputs (like the Rode NT4).
- Tube microphones may have specialty multi-pin connectors for audio, powering, and grounding.
- Miniature lavs have all sorts of output connection types including mini-XLR and Tuchel.
- Headsets or mic/headphone combos have all sorts of specialty multi-pin connections.
To read more about microphones and the XLR connection, check out article Why Do Microphones Use XLR Cables?
This spec will also be labelled as “power supply,” “power requirement,” “phantom power requirements,” “powering,” or some variation of these terms.
Active microphones require external power in order to function properly. There are many powering methods, all of which are specified as DC voltages.
Microphones require a supply voltage to power the following elements:
- Impedance converters.
- Internal amplifier.
- Condenser capsule (in non-electret condenser mics).
- Tube electronics.
- Other active electronics such as on-air lights, analog-to-digital-converters, and internal headphone amps.
The following microphones will need power and, therefore, will have a supply voltage specification:
- Condenser microphones (true, electret, and tube varieties).
- Active dynamic microphones (some modern ribbon mics are active).
- USB microphones.
This spec will also be labelled as “supply current.”
Some manufacturers will tell us how much current the microphone will draw when supplied with proper power.
All active mics will draw a certain amount of current based on their individual needs.
Options are always nice! There are plenty of microphones that offer various modes of operation.
Switchable options on a microphone could be:
- Attenuation Pads: attenuation switches or “pads” on microphones effectively reduce the amount of signal a microphone outputs (usually by -10dB or -20 dB).
For more detail, please consider reading my article What Is A Microphone Attenuation Pad And What Does It Do?
- Filters: filters will alter the frequency response of the microphone and typically filter out low-end frequencies. Engaging a mic’s high-pass filter can reduce low-end rumble; handling noise; plosives and wind energy; AC hum; and other low-frequency sound sources.
For more detail, please read through my article titled What Is A Microphone High-Pass Filter And Why Use One?
- Polar Pattern Switches: multi-pattern microphones come with polar pattern options. Some multi-pattern mics even have continuously variable polar pattern “switches.”
For an in-depth look into microphone polar patterns and multi-pattern microphones, please check out my article The Complete Guide To Microphone Polar Patterns.
The Neumann U 87 AI (pictured below) has all 3 switchable options mentioned above: a 10 dB attenuation pad, a high-pass filter, and variable polar patterns (omnidirectional, bidirectional, and cardioid).
Ah the art of the upsell!
All marketing aside, the listed accessories can really enhance the microphone’s performance and the user experience.
Oftentimes the listed accessories are part of the purchase of the microphone. Other times, the accessories are mentioned, but sold separately.
I’ll list some common accessories I see on spec sheets and touch a bit more on those that I feel need some more explanation:
- Interchangeable capsules.
- Threaded stand mount and threaded adapter (microphone clip).
- Shock mount.
- Protective case (soft or hard).
- Pop filter.
- Battery supply unit.
- Power supply unit.
- Replacement grille.
- Compatible cable.
Some microphone amplifiers have interchangeable capsules that you can swap in and out change the microphone’s polar response and overall sound.
When it comes to studio application, a shock mount plays a big role. Shock mounts help to minimize handling noise and noise from low frequency rumbling.
To read more about microphone shock mounts, check out my article What Is A Microphone Shock Mount And Why Is It Important?
When it comes to outdoor application, windscreens save us a lot of grief. If you’re going to be using a microphone outdoors, I’d suggest getting a good windscreen!
For a better discussion on microphone windscreens, blimps, deadcats, and more, check out my article What Are Dead Cats And Why Are Outdoor Microphones Furry?
Power Supply Unit
Because sometimes you need an external source in order to properly power your microphone.
USB microphones will always come with a USB adapter.
Professional “analog” microphones often don’t come with an XLR cable, but it’s nice when they do.
Stereo microphones often have a 5-pin XLR output. And so they often come with a 5-pin (female) to dual 3 pin XLR (male) Y-cable.
Microphones that use lesser known connectors will often come with properly wired cables and/or adapters.
This spec will also be labelled simply as “case,” or “materials/finish.”
The material that makes up the outer case of a microphone doesn’t change the way the microphone sounds and is more an aesthetic spec than anything else (sometimes microphones will have multiple versions with different finishes). As long as the case is made of durable material, it will serve its purpose of holding the mic together and protecting ints inner workings.
Sample Rate (USB)
The sample rate spec applies only to USB and digital microphones that have internal analog-to-digital converters and output digital audio.
In digital audio, the sample rate tells us how many times we “measure” the audio per second. We’re measuring the amplitude of the audio wave, and measuring it so often that is sounds smooth to our ears. Sample rates, like sound frequencies, are measured in Hertz (cycles per second, or in this case, samples per second).
Common sample rates for audio recording are in 10’s of thousands of Hertz and include:
- 44,100 Hz (44.1 kHz)
- 48,000 Hz (48 kHz)
- 88,200 Hz (88.2 kHz)
- 96,000 Hz (96 kHz)
For a deeper discussion about digital and USB microphones, please check out my article Are Microphones Analog Or Digital Devices? (Mic Output Designs).
Bit Depth (USB)
Bit depth is in close relation to sample rate. We’re still in the game of transferring digital data (1’s and 0’s). Thus, bit depth specs only apply to digital and USB mics.
Bit Depth refers to the number of possible amplitudes we can measure each time we sample digital audio. For every 1-bit increase, the number of possible amplitudes doubles.
The two most common bit depths a USB microphone outputs are:
- 16-bit (65,536 possible amplitudes).
- 24-bit (16,777,216 possible amplitude).
As you can see from this simple comparison, higher bit depths give a much more accurate digital replication of what we’re trying to capture in the real “analog” world.
Headphone Amplifier Specs (USB)
Some USB microphones come with their own headphone amplifier built-in. The reason for this is for zero-latency monitoring.
Latency happens in digital audio since it takes the recording device time to process all the data and play it back. We want low latency (typically under 5 milliseconds) so that we don’t hear the “digital echo” of our own performance when monitoring. Built-in headphone amps bypass the recording device altogether and provide zero-latency monitoring.
Typical specs you’d find about the headphone amp are:
- Output connector.
- Power output.
- Total harmonic distortion.
- Frequency response.
- Signal-to-noise ratio.
System Requirements (USB)
System requirements are typical of USB mics that plug into computers.
This tells us the minimum specs a computer must have in order for the microphone to work properly with it.
How much does the microphone weigh?
Sometimes manufacturers will give the weight of accessories separately as well.
How much do the microphone, the packaging, and the accessories weigh in total when shipped from the manufacturer?
Sometimes all dimensions will be given under one spec. Other times, the lengths and diameters will be given separately.
Width and Diameter are interchangeable here. They are both measured at the widest part of a given microphone.
This doesn’t happen too often, but it’s pretty cool to see a wiring diagram on a mic spec sheet.
The wiring diagram will show how the electrical circuitry is set up inside the microphone.
Microphones are pretty resilient to temperature differences, but there comes a point where their performance will suffer or they’ll fail. Though rare, some manufacturers add these temperature extremes to their spec sheets.
It’s always best practice to keep your microphones out of extreme temperatures (both hot and cold). This is especially critical with tube microphones.
Condensers and other active microphones will have decreased performance at high relative humidity due to their active circuitries.
Crackling and a decrease in frequency response are likely symptoms.
It’s always best to keep your studio dry and to store microphones in dry spaces (preferably with a desiccant).
Note that the simple and robust design of dynamic microphones make them much more resistant to humidity.
Important Specifications For Each Microphone Transducer Type
So we’ve gone through all the potential specifications that could show up on a microphone data sheets. However, some of these specs only apply to certain microphones transducer types.
To keep this article concise and at a reasonable length, I’ll add links to separate articles that list out all the specifications of each microphone type.
Before getting to the full lists, I’d like to present to you a similar read about the most important mic specs in general. You can read about that in my article Top 5 Microphone Specifications You Need To Understand.
With each of the following articles, I’ve added an example microphone to show real world specifications.
Links To Full Lists Of Microphone Specifications Per Microphone Type:
- Full List Of Dynamic Mic Specifications (With Shure SM58)
- Full List Of Ribbon Mic Specifications (With Royer R121)
- Full List Of Condenser Mic Specs (With Neumann U87 AI)
- Full List Of Electret Condenser Mic Specs (With Rode NT1-A)
- Full List Of USB Mic Specifications (With Blue Yeti)
What are good microphone specs? “Good” mic specs are generally application specific. Certain situations call for certain frequency, polar, and transient responses, sensitivity, and other important specs. Generally speaking, higher max SPL and lower self-noise specs make for better active microphones.
What microphones are best for singing? Cardioid dynamic and condenser mics are typically used for singing/vocals. The directionality, proximity effect, and isolation of the cardioid pattern make it a great choice. Dynamics are often used live (lower sensitivity) while condensers are typically used in studio (higher sensitivity).