Of all the parts and designs that go into creating a microphone, the capsule is the most critical element.
What is a microphone capsule? A mic capsule is the part responsible for the conversion of sound waves into mic signals. Capsules (or baffles when referring to ribbon mics) always feature diaphragm(s) and the housing for those diaphragms. Different transducer types have varying additional parts that complete their capsule design.
In this article, we’ll dive deeper into the inner workings of capsules from various microphone types and take a look at the 3 most popular capsules (and their variants).
What Does A Microphone Capsule Do?
Microphones are transducers that convert mechanical wave energy (sound waves) into electrical energy (mic signals). Simply put, it is the capsule of the microphone that actually changes one form of energy to the other.
How does a capsule do this? It all starts with the diaphragm.
The diaphragm of a microphone is a thin membrane that vibrates in reaction to the sound waves around it. Both condenser and dynamic (moving-coil and ribbon) microphone types utilize diaphragms to start the energy conversion process.
So the diaphragm plays a crucial role in allowing the capsule to act as a transducer. The method in which a capsule converts energy, however, is dependent on the microphone’s transducer type.
For more information on microphone diaphragms, check out my article What Is A Microphone Diaphragm?
The capsule of a microphone is critical to the microphone’s character and sound. The capsule design is responsible for the following specs:
Let’s look at the rest of the parts that go into the capsules of each type of microphone transducer.
Anatomy Of A Microphone Capsule
So the anatomy of a microphone capsule depends on the type of microphone in question. In general, there are 2 primary transducer types:
- Condenser microphones: condenser microphones have capacitor-like capsules and are generally denoted as being either small-diaphragm or large-diaphragm.
- Dynamic microphones: dynamic mics include moving-coil dynamic mics (with robust moving-coil capsules) and ribbon dynamic mics (with ribbon “capsule” better known as baffles).
For more information on the condenser and dynamic microphone types, check out my article Microphone Types: The 2 Primary Transducer Types + 5 Subtypes.
Let’s dive into the inner workings of each capsule type:
- Condenser microphone capsules.
- Moving-coil dynamic microphone capsules.
- Ribbon dynamic microphone baffles.
Condenser Microphone Capsules
When musicians, engineers, and audiophiles discuss capsules, they’re typically talking about condenser microphone capsules. More specifically, they’re usually talking about large-diaphragm condenser microphone capsules.
Condenser microphone capsules transduce energy via electrostatic principles. The basic condenser microphone capsule is designed as a circular parallel-plate capacitor.
The two key components of any condenser capsule are the movable diaphragm (frontplate) and the stationary backplate. A tensioning ring is incorporated into the capsule’s housing and holds the thin diaphragm in place while providing the proper tension on the diaphragm. There is a chamber within the housing with the appropriate space between the parallel plates. Finally, electrodes are attached to the diaphragm and backplate to extract what would be the mic signal.
So all together, the anatomy of the condenser microphone capsule includes:
- Diaphragm (frontplate)
- Stationary backplate
- Tensioning Ring
Assuming there is charge between the plates, as the diaphragm moves in accordance with the sound pressure around it, the capacitance will change between the plates. With a constant charge, a varying capacitance with yield and inversely proportional variance in voltage. This AC voltage is ultimately the microphone’s signal.
Condenser microphone signals can be calculate via the following electrostatic principle formulas:
V = Q / C
Where V is voltage (mic signal)
Q is charge (practically constant)
C is capacitance
C = ε · A/d
Where C is capacitance
ε is the permittivity of the dielectric material (constant)
A is the area of the circular diaphragm and backplate (constant)
d is the distance between the parallel plates
Important Distinctions Between Different Types Of Condenser Microphone Capsules
- Large vs. Small diaphragm
- Pressure vs. Pressure-gradient
- Electret vs. Non-electret
- Edge-terminated vs. Centre-terminated
- Single-diaphragm vs. Dual-diaphragm
Large Vs. Small Diaphragm Condenser Microphone Capsules
The loose distinction between large-diaphragm condensers (LDCs) and small-diaphragm condensers (SDCs) is this: LDC generally have a diaphragm diameter of 1 inch (25.4 mm) or greater while SDC generally have a diaphragm diameter of 1/2″ (12.7 mm) or less.
What about those mics with diaphragm diameters between 1/2″ and 1″? Throughout the history of microphones, ingrained design protocols have made it so there aren’t many outliers within this range. For the mics that do find themselves in no-man’s land, they usually act like an LDC is they’re closer to 1″ or an SDC if they’re closer to 1/2″.
The following table lists the generalities between LDC capsules vs. SDC capsules:
|Lower self-noise||Higher self-noise|
|Fuller sound across|
|Less consistent polar pattern||More consistent polar pattern|
|Slower transient response||Faster transient response|
|Typically positioned as|
|Typically positioned as|
Pressure Vs. Pressure-Gradient Condenser Microphone Capsules
Pressure and pressure-gradient are the 2 acoustic principles that govern microphone capsules.
Pressure microphones have diaphragms that are only open to external sound pressure (sound waves) on one side. The rear side of a pressure mic diaphragms is subjected to constant pressure within a fixed pressure chamber within the mic capsule.
Pressure-gradient microphones have diaphragms that are open to external sound pressure on both sides. The diaphragms move not only in reaction to the sound pressure changes on their front sides, but also the pressure changes on their rear sides.
Pressure-gradient capsules have perforated backplates and acoustic pathways built into their housing in order to allow sound pressure to act upon the rear of their diaphragms.
The following table lists the generalities between pressure capsules vs. pressure-gradient capsules:
|Pressure capsules||Pressure-gradient capsules|
|Omnidirectional polar pattern||Directional polar patterns|
Used in multi-pattern mics to
achieve all polar patterns
|Practically immune to plosives||Sensitive to plosives|
|No proximity effect||Exhibit proximity effect|
backplates and housing
Electret Vs. Non-Electret Condenser Microphone Capsules
Non-electret microphones require external power to operate their internal amps/impedance converters and to polarize their capsules. Electret microphones, on the other hand, do not require external power to polarize their capsules.
Electret mic capsules, as the name suggests, achieve this with electret material. There are three main types of electret microphone capsules:
- Foil/diaphragm electret: the diaphragm is made of the electret film. This is the cheapest, most common, but lowest quality type of electret. Electret film does not make a particularly good mic diaphragm.
- Back electret: the electret film is applied to the stationary backplate of the mic capsule. The diaphragm is then free of any electret material.
- Front electret: the traditional backplate is removed from the capsule design and is replaced simply by the inside surface of the capsule. An electret film is applied to the rear side of the diaphragm.
Electret microphone technology has gotten to a point where there really isn’t a whole lot of difference between the sound of an electret and non-electret condenser mic. The main difference being, of course, the presence of electret material in the capsule versus the absence of electret material in the capsule.
That being said, many top-end manufacturers (I’m looking at you, Neumann) continue to stay “true” to externally polarized (non-electret) condenser capsules.
Edge-Terminated Vs. Centre-Terminated Condenser Microphone Capsules
The termination of a condenser capsule refers to the connection of the lead wire (electrode) that carried the AC voltage (mic signal) from the capsule to the rest of the microphone circuitry.
Edge-terminated condenser capsules have an electrode attached to the edge of the capsule while centre-terminated capsule have their electrode attached in the centre of the diaphragm membrane.
The following table lists the generalities between edge-terminated capsules vs. centre-terminated capsules:
|Edge-terminated capsules||Centre-terminated capsules|
|More pronounced high-end|
|Higher low-end frequency|
|Lower low-end frequency|
|Sensitive to plosives||Less sensitive to plosives|
|Sensitive to low-end rumble||Less sensitive to low-end rumble|
Single-Diaphragm Vs. Dual-Diaphragm Condenser Microphone Capsules
Single-diaphragm condenser microphone capsules are simple. They have one diaphragm, one backplate, housing, and termination. Their differences are in the distinctions stated above.
Single-diaphragm condenser capsules are limited to omnidirectional and unidirectional polar patterns. True bidirectional patterns are not achievable due to the nature of the capsule backplates.
Dual-diaphragm condenser microphone capsules can be built with shared or separate backplates. Shared backplates require equal tuning of each diaphragm.
It’s important to note that dual-diaphragm capsules only work in side-address microphones.
Dual-diaphragm condenser capsules allow for multi-pattern microphones, which make up a great amount of high-end and popular condenser microphones.
2 Standout Condenser Microphone Capsules
- The Bock Audio 507 Elliptical Capsule
- Ehrlund EHR-M Triangular Diaphragm
Moving-Coil Dynamic Microphone Capsules
Moving-coil dynamic microphones also have capsules that [typically] feature circular diaphragms. Because they are dynamic mics, their capsules work on the principle of electromagnetism. More specifically, they convert energy via electromagnetic induction.
Dynamic microphone capsules are often referred to as “cartridges.”
The anatomy of the moving-coil dynamic microphone features the following pieces:
- Conductive coil (attached to the diaphragm)
- Magnets and pole pieces
- Tensioning ring
- Electrical lead wires
Generally speaking, the “moving-coil” of conductive wire is attached to the rear side of the non-conductive diaphragm. The diaphragm is tensioned properly and attached to the capsule housing via the tensioning ring.
The cylindrical conductive moving-coil is suspended in a small gap with magnets to its exterior and interior. The peculiar shape of the magnet is achieved with pole pieces. An electrical lead wire is attached to each end of the conductive coil.
As the diaphragm moves according to sound waves, so too does the moving-coil. As the conductive coil oscillates within the magnetic field, an AC voltage is produced across it via electromagnetic induction. The two lead wire take this AC voltage as the mic signal.
Dynamic microphone signals can be calculated via electromagnetic induction with the following formula:
Ɛ = – dΦB/dt
Where Ɛ is the electromotive force or voltage (mic signal)
dΦB is the change in magnetic flux
dt is the change in time
As with the aforementioned condenser capsules, the moving-coil dynamic capsule can be pressure or pressure-gradient as well as large or small-diaphragm (though the diaphragm size is not as big of a factor with moving-coil dynamic mics.
For more information on dynamic mics, check out my article Moving Coil Dynamic Microphones: The In-Depth Guide
Ribbon Microphone Baffles
Ribbon microphones do not technically have capsules. Rather, the mechanism that converts sound waves to mic signals in a ribbon mic is referred to as a baffle.
Sometimes the baffle is called an element, however this gets confusing since the ribbon diaphragm itself is also often called an element. For this article, I’ll refer to the ribbon “capsule” as a baffle.
Because the ribbon mic doesn’t have a capsule, I’ll run through it quickly.
The anatomy of the ribbon baffle is made of the following:
- Conductive ribbon diaphragm
- Magnets and pole pieces
- Ribbon attachments
- Signal lead wires
There is no outer shell for the overall baffle of a ribbon mic. This is the reason why it is not referred to as a “capsule.”
The thin ribbon diaphragm is suspended length-wise between two magnets with opposite poles and attached at its ends to the housing/magnetic structure.
The ribbon diaphragm is itself the conductor, so as it moves within the magnetic field, a voltage is produced across it via electromagnetic induction. The signal lead wires at either end of the ribbon effectively take the mic signal.
For more information on ribbon mics, check out my article Dynamic Ribbon Microphones: The In-Depth Guide.
The Top 3 Most Popular Microphone Capsules
As mentioned, when speaking of microphone capsules, we’re typically talking about large-diaphragm condenser microphone capsules. This is where most of the capsule technology has been concentrated and where the little variations make the most difference.
The variation in dynamic microphone capsules makes it difficult to see a “most popular” capsule. I suppose the Shure SM57 and SM58 capsules are the most replicated since these microphones are the most cloned.
Similarly, small-diaphragm condenser microphone capsules are not as popular or specialized.
So, of all the large-diaphragm microphone condenser microphone capsules in the world, many are either originals, replicas, or inspired by 3 legendary capsules:
- AKG’s CK12: dual backplate, dual membrane. First introduced in 1953.
- Neumann’s K47 (variant/improvement upon the Neumann M7): single backplate, dual membrane. First introduced in 1958.
- Neumann’s K67: dual backplate, dual membrane. First introduced in 1960.
The AKG CK12
The AKG CK12 was developed in 1951 and saw its first release as part of AKG’s legendary C12 in 1953. This capsule has since been replicated and revamped numerous times by numerous microphone manufacturers.
The CK12 is a large-diaphragm condenser microphone capsule. CK12s feature dual diaphragms and are therefore multi-pattern-capable. In fact, many microphones that utilize the CK12 capsule have 9 selectable polar patterns including the common omnidirectional, cardioid, and bidirectional patterns.
The diaphragms are edge-terminated, which means their electrode or “lead” comes out of the side rather than the centre of the membrane. Edge-terminated capsules, like the CK12, benefit from improved low-end due to a lower low-frequency cutoff. The tradeoff is increased sensitivity to vocal plosives and low-end rumble.
Though each manufacturer may do things differently, the CK12 diaphragms were originally 10-micron Stryoflex plastic and have changed over the years to become 6-micron Mylar. Each diaphragm measures 1″ in diameter and is fully metallized with gold.
All in all, the smooth low-end of the CK12 overrides its increased sensitivity.
Additionally, each diaphragm has its own backplate. These CK12 backplates are separate, asymmetrical resonant plates which yield a beautifully flat midrange as well as a nice 10-12 kHz bump in sensitivity.
Microphones With CK12 Capsule Or CK12-Variant:
- AKG Acoustics C 12
- AKG Acoustics C 12 VR
- AKG Acoustics C 214
- AKG Acoustics C 414 B-TL II
- AKG Acoustics C 414 B-XL II
- AKG Acoustics C 414 B-XLS
- AKG Acoustics C 414 EB
- AKG Acoustics C 414 EB P48
- AKG Acoustics C 414 LTD
- AKG Acoustics C 414 XL II
- AKG Acoustics C 414 XLS
- AKG Acoustics C 426 B
- Blackspade Acoustics UM25
- Bock Audio 151
- Bock Audio 241
- Bock Audio 251
- Cathedral Microphones C12 CG
- FLEA 12
- InnerTUBE Audio MM-2006
- Josephson Engineering C700A
- Josephson Engineering C700S
- Josephson Engineering C716
- Lawson Inc L251
- Lucas Engineering CS-1
- Manley Laboratories Reference Gold
- Peluso Microphone Lab P12
- Peluso Microphone Lab 22 251
- Rowsell Pro Audio Colares
- Soundelux Elux251
- Telefunken Elektroakustik C-12
- Telefunken Elektroakustik Ela M 14
- Telefunken Elektroakustik Ela M 250
- Telefunken Elektroakustik Ela M 250 E
- Telefunken Elektroakustik Ela M 251
- Telefunken Elektroakustik Ela M 251 E
- Telefunken Elektroakustik Ela M 251 T
- Telefunken Elektroakustik Ela M 270
- Wunder Audio CM12
The Neumann K47
The Neumann K47 was developed in 1958 as a replacement for the PVC-heavy M7 capsule in many of Neumann’s mics (most notably the U47). This large-diaphragm condenser microphone capsule has since risen to fame, being copied over and over by many mic brands and used in plenty of microphones.
The K47 design features 2 gold-coated Mylar diaphragms 6 microns. These diaphragm make the K67 multi-pattern-capable. Most microphones that use the K47 capsule have omnidirectional, cardioid, and bidirectional polar pattern options. The diaphragm membranes measure 1″ in diameter and are metallized to 0.9″.
Unlike the aforementioned CK12, the K47 is centre-terminated. This means its electrical lead is mounted to the centre of the membrane. This centre-termination yields higher and more complex high-end resonances along with a higher low-end frequency cutoff.
As opposed to the other two most popular capsules, the K47 features a shared backplate for both its diaphragms. However, this presented tuning challenges. If the diaphragms were not tensioned equally, the capsule’s figure-of-8 and omnidirectional patterns would be negatively affected. This simply increased the labour and testing of these otherwise high-quality mic capsules.
The K47 is cherished for its smooth low-mids and relative lack of a high-end peak.
Microphones With K47 Capsule Or K47-Variant:
- ADK Berlin 47-Au
- ADK Berlin 47-T
- ADK Frankfurt 49-T
- Advanced Audio Microphones CM47 FET
- Advanced Audio Microphones CM48 FET
- Bock Audio iFET
- Bock Audio 407
- Horch Audio RM4
- Kel Audio HM-7U
- Neumann M 147 Tube
- Neumann M 149 Tube
- Neumann M 249
- Neumann M 49
- Neumann TLM 49
- Neumann U47
- Neumann U47 FET
- Neumann U47 FET Collector’s Edition
- Neumann U 497
- Pearlman Microphones TM-47
- RMS Audioworks RMS47
- Ronin Applied Sciences Pegasus
- Rowsell Pro Audio Mini K47
- Soundelux E47
- Soundelux E47C
- Soundelux iFET7
- Soundelux U95S
- Telefunken Elektroakustik U47
- Violet Design Garnet
- Violet Design Globe Vintage
- Wunder Audio CM7
- Wunder Audio CM7 FET
The Neumann K67
The K67 was developed by Neumann in 1960 as a dual-backplate improvement upon its successful K47 (mentioned earlier). This large-diaphragm condenser microphone capsule is the most commonly copied microphone capsule in the world (in low and high-quality mics alike).
Like the aforementioned CK12, the K67 has dual backplates (one for each of its diaphragms). The two symmetrical backplates of the K67 are made from solid brass (they’re not resonant chambers like those of the CK12). This gives the K67 a narrower high-frequency peak around 12-13 kHz (rather than the CK12’s wider 10-12 kHz peak).
Like the aforementioned K47, the K67 is centre-terminated. This smooths out the top-end and low-mids while rolling off some of the low-end of the capsule’s sound. The K67 is known for its signature peak around 5 kHz, which lends itself incredibly well to vocals.
The K67 Mylar diaphragms measure 1″ in diameter and are metallized with gold to 0.9″.
Microphones With K67 Capsule Or K67-Variant:
- ADK A-51 Mk 5.1
- AKG Acoustics Perception 200
- AKG Acoustics Perception 220
- Alesis AM51
- Apex Electronics 430
- Apex Electronics 435
- Apex Electronics 460
- Audix CX-111
- Behringer B-1
- Beijing 797 Audio CR998
- Blue Microphones Dragonfly
- Bock Audio 195
- Brauner VM1 KHE
- CAD Audio GXL3000
- CAD Audio GXL3000BP
- CAD Audio M9
- CAD Audio M179
- CAD Audio Trion 6000
- Cathedral Guitars U 67 CG
- Chameleon Labs TS-2
- CharterOak Acoustic Devices SA538
- Gauge Microphones ECM-87 Stealth
- Karma Audio Trinity
- Karma Audio Unity
- Kel Audio HM-2D
- Lewitt Audio LCT 540
- Lewitt Audio LCT 640
- Lewitt Audio LCT 640TS
- Lewitt Audio LCT 840
- Lewitt Audio LCT 940
- Manley Laboratories Reference Cardioid
- Miktek CV4
- Miktek C7
- Miktek MK300
- Mojave Audio MA-200
- Mojave Audio MA-300
- Monoprice 600850
- MXL CR-89
- MXL Revelation
- MXL V67G
- MXL V67GS
- MXL 2010
- MXL 2001
- MXL 2008
- MXL 3000
- MXL 4000
- MXL 5000
- MXL 890
- MXL 909
- MXL 920
- MXL 992
- Nady SCM-900
- Ningbo Alctron Electronics STM400
- Neumann M 269 C
- Neumann SM 69 fet
- Neumann TLM 67
- Neumann USM 69
- Neumann U 67
- Neumann U 87
- Neumann U 87 Ai
- Peluso Microphone Lab P-67
- RØDE NT1
- RØDE NT2
- Roswell Pro Audio Aurora
- Roswell Pro Audio Delphos
- Roswell Pro Audio RA-VO
- sE Electronics X1
- sE Electronics X1S
- SM Pro Audio MC03
- SM Pro Audio MC03 Mk 2
- Sontronics DM-1B
- Sontronics Saturn
- Soundelux U195
- Soundelux U99B
- Soyuz Microphones SU-017
- Soyuz Microphones SU-019
- Stellar Sounds CM-6
- Studio Projects C1
- Studio Projects C3
- Studio Projects LSM
- Studio Projects T3
- Telefunken Elektroakustik R-F-T AK47
- Telefunken Elektroakustik R-F-T AK47 Mk II
- Telefunken Elektroakustik R-F-T AR-51
- Telefunken Elektroakustik R-F-T CU-29
- Telefunken Elektroakustik R-F-T M16 Mk II
- Telefunken Elektroakustik R-F-T M216 Stereo
- Telefunken Elektroakustik R-F-T M216 Matrix
- Telefunken Elektroakustik R-F-T M216 X-Y
- t.bone SCT 1100
- t.bone SCT 700
- t.bone SCT 800
- Violet Design Amethyst Vintage
- Violet Design Globe Standard
- Wunder Audio CM67
What are condenser microphones used for? Condenser microphones are often used for recording vocals and voiceover in the studio and on film sets. They’re also used as room mics in the studio and for recording natural/ambient sound in the field. Additionally, condensers sound great in stereo miking techniques and in mono on most instruments.
What is the difference between a large-diaphragm and small-diaphragm condenser? SDCs (diameter <1/2″), generally speaking, have numerous benefits over LDCs including better transient response, extended high-frequency response, and more consistent polar patterns. LDCs (diameter >1″), generally speaking, have lower self-noise ratings and sound fuller than their SDC counterparts.