This is about the microphones themselves.
For their use in recording, see Audio.
In comparative tables, model numbers in italics
indicate specialized microphones (e.g., percussions).
(2017-05-25) Sound in air
Reversible local oscillations.
(2014-06-05) Classification of Microphones
Exploiting the variation with pressure of another physica; variable.
Historically, the problem of converting sound into an electrical signal was
first solved by devising a resistor sensitive to sound (this dominated
the telephone industry for 60 years). Now, most microphones are
based on the variation with sound pressure of either an inductance or a capacitance.
Alternative possibilities include piezoelectric microphones,
which rely on the voltages generated by varying pressure in certain solids.
Unlike all of the above, optical microphones can measure the variation of air pressure
directly, without the help of any kind of moving membrane, but they're not yet commonplace.
Here's a complete classification of the different types of microphones:
Resistive microphones, using liquids, powders or granules:
Transforming one physical quantity into another is called transducing.
Ultimately, all microphones are transducers of sound waves into electrical signals
(mostly, variations in voltage).
To do this, various intermediary techniques can be employed.
In some condenser microphones, for example, the sound-sensitive capacity of the capsule
is part of a low-noise radio-frequency (RF) circuit.
That way, sound modulates the frequency of the
primary circuit, which is then demodulated to retrieve the signal.
I'm told that Sennheiser's MKH series works this way,
including the legendary MKH 416. (That's called RF biasing.)
(2014-06-05) Unified Description of the Two Main Microphone Types
Condenser (varying capacitor) and dynamic (varying inductor).
Here, we'll focus only on capacitive and inductive microphones
(condenser microphones and dynamic microphones) which are currently
the most commonly used in audio applications.
They are electrical duals of each other and it's enlightening
to discuss them in parallel...
An ideal capacitor (resp. inductor)
is a two-lead component characterized by two parameters,
an electrical one and a geometrical one:
voltage U and capacitance C
(resp. current I and inductance L)
whose product is equal to an extensive electromagnetic
quantity stored by rhe device: the electric charge
q (resp. the magnetic flux F).
In the absence of external electromagnetic fields, we have:
q = C U
F = L I
Differentiating this with respect to time, we obtain:
I = C' U + C U'
U = L' I + L I'
As mechanically-induced motion causes C (resp. L) to vary,
a signal is generated which is proportional to the mechanical speeds
involved. If the geometry is tied to the position of a mechanical
membrane, that dynamical position is easily retrieved by integration...
The above analysis is fairly realistic for capacitive (condenser) microphones but is utterly inadequate
for inductive microphones which rely heavily on strong magnetic fields
(which dwarf the magnetic field induced by the circuit itself).
If we make the assumption (which is a valid one for ribbon microphones)
that the only part of the circuit which can move does so in a plane orthogonal to a constant
magnetic field and call S the apparent area of the circuit "seen" by that field, then
the following expression for the flux enclosed by the circuit holds:
F =
F0 + L I + B S
The first of those three terms is an irrelevant constant and the second term is dwarved by the third.
Therefore, in the main:
U = F' =
B S'
Between two strong neodymium magnets
(e.g., BX044-N52)
the magnetic field B can be about 1 T.
Longitudinally, a corrugated aluminum strip behaves essentially like a ribbon with a very low
Young modulus YC
(this depends on the thickness of the material and the shape of the corrugation but, paradoxically, not on its scale).
Transversally, it's virtually impossible for the ribbon to bend. So,
a corrugated ribbon behaves like a membrane whose mean curvature
H is half the
longitudinal curvature of the ribbon
(as the transversal curvature is utterly negligible).
The pressure difference between the two sides of the membrane is given by the
Young-Laplace equation:
(2018-01-25) Rating the Sensitivities of Microphones
Sensitivity is the ratio of voltage output to sound pressure input.
The sensitivity of a microphone is defined as the ratio of the
variation in its electromotive force output
(i.e., the open-circuit voltage it produces) to the corresponding
variation in sound pressure input.
When neither is too large, that's a constant.
In engineering terms, it's useful to think of it as the ratio of two
time-derivatives.
That much is clear at the outset when
designing a microphone.
Voltage is unrelated to static pressure.
That sensitivity is most commonly expressed in mV/Pa
(millivolt per pascal) assuming a standard sinusoidal sound signal of 1 Pascal amplitude (94 dB SPL)
at 1 kHz.
When decibels are used,
the dBV/Pa scale is usually understood.
Thus, the stated dB sensitivity rating is 20 times
the decimal logarithm
of the sensitivity expressed in V/Pa
(which is the standard SI unit for sensitivity).
Sensitivity of 35.5 mV/Pa is -29 dB (re: 1 V at 1 Pa).
Indeed, we have: 20 log (0.0355 V/Pa) = -28.99543... dBV/Pa
A microphone is said to be loud when its sensitivity is high
(the opposite of loud is soft).
Normally, the louder the better, because of a lesser need for amplification
(as a signal is amplified, so is the accompanying noise).
However, there's such a thing as too much of a good thing: If a microphone is too loud,
it may generate unexpectedly high voltages at the input of the next circuits
(preamplifiers).
That won't damage them but they'll saturate or clip
(same thing) which will introduce unacceptable distortion.
Today, microphones are rarely designed with a sensitivity exceeding 50 mV/Pa
(that's -26 dBV/Pa). The discontinued predecessor of the
aforementioned BP4071 was the AT4071a which had a nominal sensitivity of
89.1 mV/Pa (that was -21 dB). This is considered
way too loud by today's standards for general-purpose use
(although bird lovers still like this kind of sensitivity in a directional microphone).
The sensitivity rating of a microphone is always stated for on-axis sound
(coming from the preferred direction of the microphone, which gives the maximum sensitivity).
Polar patterns are charts giving relative sensitivity as a function of direction
by reference to that basic sensitivity
(de facto, the 0 dB level for a particular microphone).
Warning :
An older decibel scale for microphone sensitivity is still floating around which differs from the modern
one by 20 db. In that obsolete scale, the aforementioned BP4071
would have been quoted as having a sensitivity of -49 dB (which could be misinterpreted as quite low).
The discrepancy comes from the former use in acoustics of the units of pressure still preferred by
many meteorologists. When meteorologists in France and elsewhere were criticized for issuing TV reports
expressed in millibars (1 mb = 100 Pa) instead of
a proper SI unit, they didn't change their numbers
but started using the SI-equivalent hectopascal
(which is correct albeit arguably somewhat weird).
In the old days, audio engineers were routinely using the microbar (0.1 Pa)
as their unit of pressure (this was an alternate name for the official unit of pressure
in the CGS system, namely the dyne per square centimeter).
This made the volt per microbar (10 V/Pa)
their unit for microphone sensitivity. Using that unit, the
numerical values of sensitivities are ten times smaller than the values in V/Pa.
Expressed in decibels, they're thus 20 dB lower, as advertised!
In Numericana, microphone sensitivities are only given in mV/Pa.
Not only does this avoid the aforementioned ambiguity of decibels,
but it also serves as a constant reminder of what sensitivity is all about.
Unit conversions is a known source of distress.
NASA once crashed a spacecraft on Mars because of that.
As I was looking for data relevant to this page,
I came across a
discussion between audio afficionados
where the above 20 dB offset is mistaken for real substance.
Electromotive force vs. measured voltage :
Microphone sensitivities are best expressed in terms of open-circuit voltages
(the common name given to electromotive forces).
So defined, sensitivity depends only on the microphone itself,
not on whatever load it may have to drive (usually, the input impedance R of some preamplifier).
Nevertheless, some manufacturers give the actual voltage V that would be observed
per unit of sound pressure into a load of specified impedance within the range they recommend
(e.g., A = 1 kW).
That number is slightly smaller than the aforementioned intrinsic sensitivity U.
The relation between the two is obtained by observing that the microphone's output current is equal to
the preamplifier's input current.
Let z be the microphone's output impedance and Z be the preamp's
input impedance:
i = U / (Z+z) = V / Z
(at 1 Pa). Therefore:
U = ( 1 + z/Z ) V
For example, if a 200 W microphone is said to yield
10 mV/Pa into a 1 kW load,
then we just quote its intrinsic sensitivity U as 12 mV/Pa.
Such a microphone would drive a 2.5 kW load with
12 / (1 + 200 /2500) = 11.111 mV/Pa.
At a given audio frequency, the electromotive force and the
output impedance of a microphone can be deduced from electrical measurements
(current, voltage and phase difference between the two) under just two different load.
There's no need for acoustic calibration (we do need such a calibration
to establish the sensitivity though).
The electric noise of a dynamic microphone depends entirely on
the how its impedance as a function of frequency (to that should be added
the acoustic thermal noise at a prescribed tem[erature and pressure,
which depends mostly on the size of the diaphragm).
(2018-02-05) Microphone directionality. Polar pickup patterns.
Omnidirectional, bidirectional, cardioid, etc.
(2018-02-05) Dual-Diaphragm Microphones for variable pickup patterns.
A cardioid is the sum of omnidirectional and bidirectional patterns.
Multi-pattern and variable pickup pattern:
Mixing equal parts of an omnidirectional pickup pattern and a bidirectional one
(figure-8) yields a cardioid pattern.
Other proportions in this type of mixing also yields the other traditional
microphone pickup patterns:
Subcardioid pattern (between omnidirectional and cardioid).
Supercardioid pattern (between cardioid and figure-of-eight).
The above five patterns and the four intermediate ones between them yield a palette of nine patterns, which
are commonly available at the flip of a switch in somemulti-pattern microphones.
The term hypercardioid is sometimes applied to any such mix but it's most
often reserved to patterns with a wide cone of silence up to
(but excluding)
the bidirectional figure-of-eight itself (90° angle of silence).
Variable-pattern microphones (e.g., CAD Audio M179) even allow you
the freedom to dial anything in-between.
Note that a two-diaphragm microphone which is capable of recording at least two
pickup patterns from the above standard family can also be used to reconstruct
any of them in post-production. For example, if the omnidirectional signal is on the
left channel and the figure-8 bidirectional signal is on the right channel,
Then, you obtain a forward cardioid by adding the two channels and a backward cardioid by subtracting
them (opamps were originally intended do perform exactly this
sort of operations).
This way, you can choose the pickup pattern after recording.
Any dual-diaphragm microphone could be modified into a pseudo-stereo microphone capable
of recording the two separate phase-tracks just described.
Two products offer this capability straight out-of-the-box:
The Lewitt LCT 640 TS microphone (TS stands for twin system)
whose secondary output is on a mini-XLR connector (sideways).
The
MS
("Mid Side") attachment for the 10-pin connector of Zoom recorders
(H5, H6, F1, F4, F8)
records separately the signals from two capsules: Forward cardioid and
sideways bidirectional.
Other multiple-diaphragm configurations would provide other capabilities.
Multi-pattern dual-diaphragm microphones (data is for cardioid pattern)
(2018-05-08) Multiple-capsule microphones
Putting several very different microphone capsules in the sams housing.
Driven by professional demand, some manufacturers have put several capsules
using different technologies behind the same grille
(e.g., a condenser mic and a dynamic mic next to each other).
This allows an adjustable frequency response but there are complicated phase issues
at high-frequency, which restrict such compound microphones to specialized applications
(e.g., kick drum).
Compound microphones (including more than one capsule)
Most prosumer measuring microphones have a ¼'' capsule (6 mm diaphragm).
Professionals sometimes use smaller membranes (3 mm)
which are more accurate in the upper-part of the audio spectrum.
They tend to prefer expensive low-noise ½'' units for general use.
Acoustic Calibrators (1 kHz, 94 dB SPL) :
By convention, absolute calibration of a sound-measuring instrument
is always done at 1000 Hz. For that purpose, standard sound sources
are available which deliver precisely
94 dB SPL into a force-fit
microphone port allowing cylindrical microphone heads up to 1'' in diameter
(sometimes only ½'').
Smaller microphones require adapters which may or may not be included with calibrating units.
Below is a list of current models of such acoustical calibrators.
All of these can work either at 94 db
or 114 dB (the latter setting is helpful in a noisy environment).
Now, the calibrators themselves drift out of calibration and have to be recalibrated yearly
by the manufacturer. Most people will only trust Brüel &
Kjær (or possibly Cirrus) for that follow-up.
Sound Meters, Measurement Microphones :
Measurement microphones are designed to be as linear as possible,
They have a flat frequency response throughout the audio range and
deviations must be carefully documented (see example below).
Tiny diaphragms help keep resonant frequencies safely outside of the audio domain.
Many uncalibrated consumer models are just intended for the analysis of room acoustics
and cannot be trusted beyond a precision of 2 dB or 3 dB.
The following models are thus not recommended for scientific applications:
$299:
Audix TM-1 (uncalibrated version of the Audix TM1-Plus).
A much better precision is offered at a similar cost with any of the models listed below.
Each such unit comes with an individual calibration curve made with a professional instrument.
The resulting on-axis frequency response is typically made available
online (tied to the serial number of every microphone)
in a digital form suitable for audio-analysis software.
Sonarworks also provides an off-axis curve.
Some measurement microphones which come with individual calibration curves :
With a street price of $50 (I just got mine on sale for $40) the EMM6 is the most
affordable of the above. Packed with each unit is a dated plot of its frequency response.
The corresponding data is also available online (tied to the serial number)
in the form of a tab-separated text file
(ready to import into Excel or other specialized software). That file contains
measurements at a precision of 0.1 dB for 256 frequencies
whose logarithms are evenly spaced, from
20 Hz (n = 0) to 20000 Hz (n = 255). That's to say:
fn = (20 Hz) 10 n/85 (for n between 0 and 255 = 3 x 85)
The values are given in decibels relative to the level at frequency f145 = 1016.0436 Hz
which is given tersely in absolute terms (in dBV/Pa) on the first line of the data which reads,
in the example of my own unit:
*1000Hz -39.6
This misleading header actually indicates that the sensitivity of this particular microphone is
-39.6 dBV/Pa (i.e., about 10.47 mV/Pa) at precisely 1016.04 Hz (not 1000 Hz).
The blow-up at right shows the frequency-response near 1 kHz of my own EMM6.
Each black square is precisely a single data-point (it covers exactly one pixel in the
full graph shown below, where the height of each pixel is just 0.1 dBV/Pa.)
To obtain a very precise value of the sensitivity at exactly 1 kHz (which is the usual standard)
we remark that 1000 Hz = fn when
The data for my own unit says that the sensitivity for
f144 is 0.2 dB above the level for the aforementioned ad hoc
reference frequency (f145 ).
Thus, the response at 1000 Hz is best obtained by linear interpolation:
Now, all of the above are based on actual voltage measurements performed by Dayton into a load
of 1000 W (precisely so, hopefully).
As the nominal impedance of the EMM6 is 200 W,
its intrinsic sensitivity is obtained after a correction
of 20% (i.e., 1.58 dB). Before rounding, we obtain:
(2018-02-09) Input Attenuator (Pad)
A switchable input pad allows a microphone to record louder sounds.
Such a pad is a network of resistors placed just after the microphone capsule
to prevent the subsequent active electronics from
saturating ("clipping").
(2018-02-09) Low Cut Filter = High Pass Filter (HPF)
Filtering out the lowest audio frequencies.
On many microphones, a switchable low cut filter is provided
to get rid of the low-audio and sub-audio hum and rumble.
Typically, a corner frequency of 80 Hz is used.
Most manufacturers are content with a simple
first-order filter (6 dB/octave) which
provides a modest 12 dB attenuation at 20 Hz.
Others, like Audio-Technica
will do more and they should be commended for it.
If you need low-cut in an urban environment, the more attenuation the better.
Even in their entry-level AT2035, the low-cut filter
they provide is second-order (12 dB/octave)
for a 24 dB attenuation at 20 Hz.
On Audio-Technica shotgun microphones
(AT897, BP4073, BP4071) the switchable low-cut filter is third-order
(18 dB per octave) and provides an attenuation of 36 dB at 20 Hz
(that's 12 dB at 50 Hz).
(2017-11-22) Characteristics of Full-Size Wired Microphones
Condenser type (varying capacitor) or dynamic type (varying inductor).
Microphones currently being produced range in price from $1.67 to
thousands of dollars
(the AKG C12 VR sells for &5999).
Used vintage Neuman U67 tube
LDC microphones are typically sold for $9000-$16000, depending on condition.
At least part of that madness is due to a nostalgia for the particular type
of distortion introduced by
tube (or valve) circuits.
For some obscure reason, tube amplifiers tend to distort a waveform symmetrically,
which is another way to say that they introduce more evenharmonics than odd ones.
The type of sound so produced is normally associated with female voices
(it would seem that Adam's apple
on a male voice box
is responsible for producing asymmetrical waveforms rich in odd harmonics).
Whatever the exact reason may be, this is just one example of an acquired taste
among audiophiles which has little or nothing to do with high-fidelity.
If anything, modern semiconductor circuits have better fidelity qualities,
quantitatively speaking.
The good news is that those high-price instruments are not a necessary part
of high-fidelity home recording.
Designing microphones is an art form in itself.
Microphones are a crucial tool for musicians and an object of worship for countless
audiophiles.
Just enumerating the main aspects on which that subculture is based will serve to
demonstrate that we can only scratch the surface here
(focusing, as usual, on nontrivial numerical aspects besides cost).
All these aspects are interrelated:
Price, cost of ownership.
Options and customizability.
Look, feel and durability.
Size and weight.
Possible mounts (handheld, tabletop, lapel, stand, arm, boom).
Sensitivity at various frequencies (bandwidth & microstructure).
Impedance magnitude and phase shift (as functions of frequency).
Directivity (polar pattern) at various frequencies.
Proximity effect at various frequencies.
Noise figure, noise floor (hiss).
The previously introduced concept of sensitivity
influences greatly overall noise performance because lower sensitivity
demands greater subsequent amplification, which magnifies hiss just as much as the useful signal.
The self-noise (or equivalent noise level,
henceforth tabulated as hiss)
of a microphone is the loudness of the signal it produces by itself in an isolated soundproof enclosure
(it would be cheating to report only the electric noise of the apparatus without the microphone capsule).
The same figure of merit is sometimes reported as a
signal-to-noise ratio (SNR) assuming a 1 kHz
sinusoidal standard soundwave of
1 Pa amplitude (94 dB SPL):
SNR = 94 dB - (self-noise, dB)
The dynamic range of a microphone is defined as
the decibel difference between the aforementioned self-noise
and the top loudness it can record, with less than 1% THD
(total harmonic distortion).
The nominal output impedance is expressed in ohms (W).
A microphone is normally plugged into a
preamplifier whose input impedance shouldn't be lower than whatever
is specified by the microphone manufacturer
On the other hand, it shouldn't be too high either because high impedance breeds noise.
A time-honored rule of thumb is to load a microphone with five to ten times its own output impedance.
Some compact microphones sold with on-camera mounts :
(2018-02-01) Acoustical Properties of Large Circular Diaphragms
Resonant frequencies and frequency-dependence of pickup patterns.
The diaphragm of a condenser microphone consists of a thin circular membrane whose rim is
attached under tension to a rigid hollow cylinder.
In the so-called center terminated variant,
the diaphragm is also anchored by a small screw at the center,
where it can neither move nor tilt...
That method is used, in particular, in good ½''measurement microphones.
It presents three major advantages:
The center point can be used for electrical contact.
Resonances are suppressed if the center isn't a node.
Resonances are suppressed if the gradient at the center is nonzero.
Those last two properties eliminate the lowest resonant frequencies for a
circular membrane of prescribed size, areal weight and tension.
That helps remove all resonant frequencies away from the audio range.
However, the central contact restricts the amplitude of the diaphragm's motion at lower frequencies
and thus reduces the basic sensitivity of the microphone.
A condenser microphone is formed by the varying capacitor consisting of one such diaphragm
opposite a rigid backplate (polarized by an external voltage and/or an
electret).
When those two form a closed capsule, an omnidirectional
pickup pattern is obtained (at least at low frequencies).
A microphone capsule is never completely closed,
or else it could bend (or even pop) in response to slow changes
in atmospheric pressure. There are just tiny vents which allow air
to go in and out of the capsule fairly slowly, with little or no impact at audio frequencies.
The best designs will make the vents just large enough to cancel
hum just below the audio range (which is usually assumed to start at 20 Hz,
although that's definitely not audible).
The mathematical simplicity of the above configurations makes a complete
theoretical analysis possible, which may serve as a useful basis for experimental refinements
in the actual design of commercial microphones.
Another aspect amenable to pencil-and-paper analysis (barely so) is
the pickup pattern (sensitivity as a function of direction)
of a large-diaphragm for a sound having a wavelength commensurate with its size
(for much larger wavelengths, the pickup pattern is omnidirectional).
(2018-01-22) Large-Diaphragm Condenser Microphones (LDC)
Quintessential capacitive microphones. Every voiceover artist has one.
Most condenser microphones use the 48 V phantom power normally
found on XLR sockets (one more reason to get an
XLR1 audio adapter, if you shoot video with a Panasonic Lumix GH5).
What's the fuss about large diaphragms?
Well, the larger the diaphragm the quieter the microphone,
but too large a diaphragm will struggle with the upper part of the audio spectrum,
especially off-axis, as different parts of the membrane see different phases
of the soundwave (at 20 kHz the wavelength is only 17 mm).
Earthworks achieved the extreme bandwidth (30-33kHz) of their
SV33 flagship by limiting the diameter of the diaphragm to 14 mm.
The price they paid was a 15 dB noise-floor which is unimpressive
for a microphone at that price-point ($2499).
The membranes of more typical LDC microphones are about 1''
in diameter (25.4 mm).
One popular LDC microphone is the affordable
AT2020 from Audio-Technica
($99 bundle).
I went instead for its big brother, the
AT2035
($149 bundle)
because of a side-by-side sound comparison on YouTube.
Also, unlike the AT2020, the AT2035 has two desirable features:
Switchable 10 dB in-line attenuator ("pad")
whose effect is equivalent to tripling the distance from the sound source.
Switchable second-order high-pass filter
with 80 Hz corner frequency, which helps cut out hum and rumble in an urban environment.
(Other makes often provide only first-order.)
The AT2035 gets
rave reviews
as the best in its class (I wouldn't consider a higher class for home use,
following the law of diminishing returns).
That microphone comes with a soft pouch and a shockmount (including
a plastic thread adapter; 5/8''-27 male to 3/8''-16 female).
I got mine with a complimentary 10-ft XLR cable and Neewer® pop screen.
All for $149.
The shockmount by itself (AT8458) would sell for
$79.
(Third-party shockmounts go for
$10,
a short cable is about $9 and the pop shield is $7.)
The AT2035 was released in 2008.
It's built around a center-terminated 24.3 mm diaphragm (0.96").
It uses back electret polarization,
which helps accommodate a wide range of phantom voltages (from 11V to 52V).
Some purists still scoff at this approach, compared to what they call true
condenser microphones, in spite of the fact that the electret technology has been around
for more than 50 years and helps deliver superb performance.
To address such queasies within the Audio-Technica ladder, the AT2035
is bracketed by two condenser microphones which are purely DC-biased without electrets,
the AT2020 and the AT4040 (which both demand 48V phantom power).
The latter costs twice as much as the AT2035 without offering any improvement in self-noise.
(Since it's 1 dB more sensitive, it's technically just 1 dB quieter.)
This isn't the whole story, though:
The noise figure of the AT4040 was achieved in spite of the fact that it uses only
a smaller diaphragm of 20.4 mm (0.8'')
which helps with transient response.
Although my own ears couldn't detect those subtleties
(I'm now on the wrong side of sixty) I could easily see that the AT4040 grille is more transparent,
which can be acoustically desirable.
Røde's NT1-A still looks like a better upgrade,
as a true condenser microphone which is 8 dB quieter
than the AT2035 (for only $80 more).
For another $40, I find their NT1 even more tempting with its true-to-life
flat-response sound and praised shockmount (Rycote lyre).
Audio-Technica
reports that they incorporated into the AT2035 the honeycomb diaphragm design used in their own
$3000 AT5040
flagship, for increased surface area and enhanced performance.
In the following table, we give a wide selection of the medium-to-large condenser microphones
available today. All of those are single-diaphragm microphones
(we list separately dual diaphragm microphones featuring selectable
pickup patterns).
They're all cardioid microphones, except :
Earthworks SR40V (hypercardioid).
CAD Audio E100s, (supercardioid).
Some current LDC microphones (Data with all pads and filters disengaged.)
Because of its 4 dB sensitivity advantage,
Audio-Technica's AT2035 ends up being 12 dB less noisy than the AT2020
(or 18 dB less noisy than the multi-pattern Behringer C-3).
Likewise at the high-end, the AT5040 is 8 dB more sensitive and 15 dB
less noisy than the AT2035.
It's twice as sensitive and 4.7 dB less noisy than the Equitek E100s.
The Samson C01 mic gets mixed reviews; it's reportedly rather hissy.
(2017-11-22) Dynamic Microphones (French: bobine mobile)
Rugged inductive microphones, usually with limited bandwidth.
A moving-coil dynamic microphone functions exactly as an ordinary speaker. Actually,
a moving-coil speaker can be wired to work as a dynamic microphone, albeit a lousy one.
Because a dynamic microphone is a passive component, it generates no noise besides thermal
Johnson-Nyquist noise.
Unlike condenser microphones, dynamic microphones don't require
any outside polarization voltage to work.
There are two very different types of dynamic microphones:
As part of an old-school PA system I purchased years ago, I got the rugged
Radio-Shack 3303043 Super-cardioid Dynamic Microphone (RS catalog number 33-3043)
which is a perfect voice microphone in that capacity (great proximity effect).
That unit is still available new on eBay, between $25 and $50 or so
(it goes for less than $20 used).
It has the exact same look and feel as the legendaryShure SM58S
(SM58 with a mute switch). Both feature the exact same spherical grille (51 mm diameter).
The built quality is the same, except that the RadioShack body is a half-inch longer and has a black grille
coupling (which is silver on the Shure unit).
Some Dynamic Microphones (moving-coil microphones)
The 33-3043 microphone was manufactured by Shure specifically for RadioShack.
So were other dynamic microphones. All were made in Mexico and none
had any direct equivalent in the regular Shure line (they were typically loosely
related to more expensive Shure models sporting the same grille). Examples include:
(2018-02-04) Ribbon Microphones
A very special type of dynamic microphone.
The engine (or motor) of a ribbon microphone
is a very thin corrugated strip of metal (usually aluminum)
which fits tightly between very strong magnets without touching them
(today, neodymium magnets are used). The ribbon thus separates two
symmetrical cavities formed by the walls of the magnet.
As the ribbon moves in response to sound pressure,
a tiny electromotive force appears between its extremities which are
connected to the primary windings of a step-up audio transformer.
The natural acoustical symmetry of such microphones translate into a figure-8
directional pattern.
They pick up sound equally well from the front or the back and very little from the
perpendicular directions.
Ribbon microphones include legendary lip microphones like the
Coles 4104 for dramatic voice reporting in very loud environments.
Examples of Ribbon Microphones (special type of dynamic microphones)
(2018-02-02) Shotgun Microphones
Small-diaphragm condenser microphones with high directivity.
A shotgun microphone consists of a standard standar capsule monted at the rear
of a long interference tube with a number of slots on it.
On-axis sound passes through the tube unimpeded or theough the different slots in phase
(constructive interference). On the other hand,
destructive interference attenuates off-axis waves as they pass through the slots with
different phases.
Because of their natural cylindrical shape, shotgun microphones often
feature a compartment for a single AA battery to power them as
an alternative to phantom power
(units primarily intended for use with DSLR or
hybrid cameras don't even allow phantom power).
According to the specifications of Røde and
other manufacturers, the battery must be
a 1.5V cell
(i.e., a single-use alkaline battery).
A rechargeable NiMH battery has a nominal voltage of only 1.2V,
which makes it unsuitable.
A well-conditoned fully-charged NiMH cell may work at first
(the initial voltage of a freshly-charged battery is about 1.46V) but it will
struggle and fail very soon. You've been warned.
The Audio-Technica models AT4071a and AT4073a are discontinued.
They've been superseded by the BP4071 and BP4073, respectively.
A few comments are needed about the bottom of that table, which lists low-end consumer product,
as the listed prices indicate:
The VidPro models (14-inch XM-88 and 10-inch XM-55)
come with plenty of accessories (each as a 13-piece kit in a molded case).
Their noise figures are undisclosed by the distributor. The audio quality is modest but
either microphone can be very cost-effective, as it can be plugged directly into the 3.5 mm socket
of a DSLR (cable included) running off its own internal AA battery. They can also use XLR phantom power.
The BY-PVM1000 is consistently reported to suffer from crackling noises when operated off 48V phantom power.
This problem is reported in some written reviews and can be heard even in
favorable video reviews.
That seems to be a design flaw present in all units
(it may be caused by capacitors with borderline voltage ratings).
Not recommended at all for use with 48V phantom power (and audio quality is downrated on battery power).
Could be OK with 24V phantom power, who knows?
The cheapest XLR shotgun microphone, sold as Marantz SG-5B, is just adequate for experimentations
and educational projects (dissecting a microphone).
It has been on sale at $16 or less.
Its restricted bandwitdth and high noise make it unsuitable for any type of video production.
(It's apparently not a fake; the official Marantz site does report the poor specs.)
For completenes, the Neewer bargain brand also sells short (10")
and long (14.37") shotgun microphones on the cheap
(for $23 and
$24,
respectively). They can't use phantom power and will work for up to 26 hours
off a single AA battery.
(2017-11-01) Lavalier Microphones (Lapel Mics) :
The best way to isolate a voice from ambient sound.
It's an unavoidable part of the physics of sound
that tiny microphones will produce more hiss than full-sized ones.
Lavalier mics are appealing in other ways. Draw your own conclusions.
All commercially available lapel mics are condenser mics which
need either their own battery or plug-in power
from the audio socket, typically from 2 V to 10 V
(more than 10 V may damage the mic and 48 V will fry it).
Properly taking sensitivities into account, the shocking truth which emerges from
the nonexhaustive table below is that the least noisy lavalier mics are the ME2 and the Giant Squid (the latter
being only 0.2 dB behind, which isn't significant).
The MKE2, which costs three times more than the former and eight times more than the latter,
is actually 2 dB worse than either!
The J 044 and the HQ-S are respectively 5 dB
and 10 dB worse than the ME2.
(I don't have data yet for the Purple Panda and the lowly Neewer.)
Noise is only part of the whole story and the less-than-stellar performance of the
expensive MKE2 in that department is entirely due to its tiny size.
The relatively low noise of the ME2 is partly due to its limited bandwidth.
Some Omni-Directional Lavalier Microphones (a.k.a. Lav mics, lapel mics)
Sennheiser's cost-no-object MKE2 is fairly bright (+4 dB at 10kHz) to compensate for the
fact that it's normally worn under a shirt. It comes with several caps to adjust its frequency response.
Sennheiser's mics come with locking plugs ("EW" = "Evolution Wireless").
JK's very popular Mic-J 044 (which may well be the best value for the money)
is available with many plugs to choose from (including Sennheiser's locking connector).
Usually, all others only have regular TRS and/or TRRS 3.5mm audio jacks.
The Neewer 0077 microphones are extremely cheap
(I just got three of them for a grand total of $4.99.)
You can't buy fewer than three at a time. They are essentially disposable microphones.
They are reportedly prone to failure
and are supposed to produce only junk boomy sound... However, they're certainly
not a total waste of money. They do sound better than
most on-camera mics. With low expectations, I was even
surprised to find the sound rather pleasant on my initial test!