Distance from source

Width of source

Large Diaphragm

Narrow

Small to Medium

Diaphragm

Wide

Single Capsule

Far

Dual Capsule

Near

Less than 12" from very loud source?

Dynamic Condenser

Yes No

Source has abundant high mid to

high frequencies?

Brighter response

Flatter response or ribbon dynamic

Yes No

Width of source

Medium to Large

Diaphragm

Narrow

Small Diaphragm

Wide

Source has abundant high mid to

high frequencies?

Brighter responseFlatter response

Yes No

Source has abundant high mid to

high frequencies?

Brighter response

Flatter response or ribbon dynamic

Yes No

How to choose a microphone for (almost) any application!

Less than 12” from very loud source? Dynamic microphones.

Dynamic mics are capable of withstanding very high sound pressure levels without distorting because they are passive devices, containing only the dynamic capsule and a transformer. (The internal preamplifier of a condenser mic can be overloaded to the point of distortion). Ribbon dynamic elements also have higher mass than condenser diaphragms and are designed to move with greater excursion. When placing a microphone very close (less than 12 inches) to a very loud sound source (instrument amplifiers, drums, trumpet, etc.) the choice of a moving coil or ribbon dynamic microphone can prevent distortion at the microphone output.

The higher mass of a dynamic mic capsule also results in a high frequency response that starts to attenuate at a lower frequency than a typical condenser. Take a look at the frequency response chart for a Shure sm57 dynamic (top) compared to a Neumann km184 condenser (bottom):

You can clearly see the more extended high frequency response of the km184 condenser. Both of these microphones were designed with an intentional high frequency boost, and you can see that this boost is “bumpier” in the dynamic. This is due to the inherent “ringing” resonance of the heavy dynamic diaphragm and coil compared to the extremely low mass condenser diaphragm. Microphone designers have more control of the frequency response when designing condensers as opposed to dynamics. The KM184 was designed with a smooth and subtle high frequency boost.

Source has an abundance of high mid to high frequencies? Flatter or brighter response.

Instruments that have robust energy in the high-mid to high frequencies (3kHz - 20kHz) may sound too bright when recorded with microphones that boost these frequencies. Instruments that have little high-mid to high frequency energy may sound too dark and dull when recorded with microphones that have a flatter response in this frequency range. These darker instruments may become hard to hear in the mix because the human ear is more sensitive to high-mid frequencies than lower frequencies. Instruments that have an abundance of low frequencies might sound too boomy or muddy when recorded with microphones that have a pronounced proximity effect or a significant bump in the low frequency response. For example, a very bright and loud trumpet might sound best through a flatter response ribbon mic, or even one that attenuates the high-mids and highs, such as the Royer R-101:

Whereas a darker source like a bass guitar amplifier might sound more present in the mix when recorded with a mic that has a high mid boost and a bit of low frequency roll off, such as the Sennheiser MD421:

! ! !

NOT Less than 12” from very loud source? Condenser microphones.

When placed too close to a very loud source it is possible to overload a condenser microphone’s internal preamplifier, which produces distortion at the microphone output.Condenser microphone diaphragms are very sensitive due to their very low mass. This high sensitivity gives them an extended high frequency response and good signal to noise ratio. They are therefore a good choice when recording quieter sound sources or sources that produce desirable high frequencies. Condenser mics are widely used for voice, drum overheads (drum sets are loud but the overheads are a few feet away from the source), brass, woodwinds, acoustic instruments (acoustic guitar, cello, piano, etc.), and acoustic ensembles. They are by far the best choice when very far from the source, as when one records a classical ensemble or a thunderstorm.

Distance from sound source, far or near? Single verses dual capsule.

The AKG C 451 B is a single capsule condenser microphone. It has a fixed cardioid polar pattern.

The AKG C 414 XLS is a dual capsule condenser microphone with two cardioid capsules mounted back to back.

The five possible polar patterns are selected by a switch on the mic which combines the two cardioid signals, altering the amplitude and polarity of the rear capsule. For example, adding the front and rear cardioid patterns creates an omnidirectional pattern. Inverting the polarity of the rear capsule and adding it to the front capsule creates a figure eight polar pattern. Doing this while attenuating the rear capsule creates the hyper cardioid pattern, and turning off the rear capsule results in a cardioid pattern.

Dual capsule condenser microphones tend to become more omnidirectional at lower frequencies, and you can see this in the two polar pattern diagrams below.

! ! C 414 XLS ! ! ! ! C451B

When your dual diaphragm mic is close to the sound source this is not a problem because the source is so much closer to the mic than the sound arriving from behind the mic (wall reflections or other instruments). The source is much louder at the mic position than the reflected sound due to the inverse square law, so you won’t hear much of the low frequency omnidirectionality of the mic. However when the mic is far from the source the inverse square law dictates that the direct and reflected sound will be closer to the same amplitude, so you may tend to hear a muddiness in the sound as the low frequency omnidirectionality becomes more audible.

When single diaphragm mics are far from the source they do not exhibit this increased low frequency omnidirectionality, however the do start to pick up excess low frequencies when they get close to the source.

For more detail on this topic read the paper: Unique Directional Properties of Dual-Diaphragm Microphones by Guy Torio and Jeff Segota, Shure Brothers Department of Acoustical Development. In the mean time you will have more accurate low frequency response if you choose dual diaphragm mics for close placement and single diaphragm mics for distant placement.

Is the source wide or narrow? Large verses medium or small diaphragm.

Some sound sources are narrow, like a singer’s mouth or a speaker in a guitar amplifier. It is easy to place a mic for these sources because all you have to do is point the mic at the source and you can be relatively confident that you are picking up all the sound. Wide sound sources might include a grand piano, a marimba, a chorus, or an orchestra. With these sources it is important to select a microphone (or microphones) that will pick up good sound from off to the sides as well as from directly in front of the mic.

We refer to microphone diaphragms with a diameter of approximately 1 inch as “large diaphragm” mics. The Neumann M147 is an example of a “large” diaphragm condenser microphone. Microphone diaphragms closer to 1/2 inch are called “small diaphragm” mics. The diaphragm in an AKG C451 has a diameter close to 1/2 inch. Microphones such as the Neumann KM184 and the Sennheiser mkh40 have diaphragm diameters closer to 3/4 inch, but are often referred to as “small diaphragm” mics.

Large Diaphragm (M147) Small Diaphragm (KM184)

The diameter of the diaphragm alters the high frequency response of the microphone for sounds that do not arrive from 0 degrees (directly in front of the mic). We refer to

sounds that arrive from 0 degrees as “on axis” and sounds that arrive from off to the sides as getting progressively more “off axis”. Consider a high frequency sound that arrives at a 1 inch diaphragm capsule from 90 degrees. If the frequency of the sound is 14kHz then its wavelength is approximately 1 inch, the same as the diameter of the capsule. Therefore the compressions and rarefactions of the sound are affecting the diaphragm at the same time, with the compressions pushing the diaphragm while the rarefactions are pulling. Therefore, at 14kHz the 1” capsule will not produce an output signal! This attenuation lessens as the angle of the sound source gets closer to 0 degrees, or as the frequency gets lower. If the diaphragm has a diameter of 1/2 inch then the attenuation happens one octave higher, so it is not as noticeable.

If your sound source is wide, or any time you do want good high frequency response from off axis then a smaller diaphragm is better. For example, singers and saxophones are narrow sound sources but drum sets are much wider, as are pianos, marimbas, harps, and orchestras. However if you need to place one mic each on 4 singers who are standing shoulder to shoulder then large diaphragm mics will help attenuate high frequency leakage between the singers.

Source has an abundance of high mid to high frequencies? Flatter or brighter response.

From the section above under Dynamic Microphones:

Instruments that have robust energy in the high-mid to high frequencies (3kHz - 20kHz) may sound too bright when recorded with microphones that boost these frequencies. Instruments that have little high-mid to high frequency energy may sound too dark and dull when recorded with microphones that have a flatter

response in this frequency range. These darker instruments may become hard to hear in the mix because the human ear is more sensitive to high-mid frequencies than lower frequencies. Instruments that have an abundance of low frequencies might sound too boomy or muddy when recorded with microphones that have a pronounced proximity effect or a significant bump in the low frequency response.

An ensemble of trumpets and trombones can be very bright and may sound best recorded with a mic (or mics) like the Sennheiser mkh40, which has a perfectly flat frequency response.

However an acoustic bass has an abundance of low frequencies and a relative lack of high frequencies, so a mic that rolls off some lows and boosts higher frequencies might be best. Here is the frequency response of the Neumann M147:

The re-appearance of the ribbon dynamic at the bottom of the chart.

I have included the ribbon dynamic mic as a possible alternative to condensers for narrow sound sources both far and near. Most ribbon mics have a figure eight (or bidirectional) polar pattern, which is not the best for off axis pickup. They also tend to have a rather low output amplitude, so they might not work very well for quieter instruments at a distance. However they do tend to have smoother and more extended high frequency response than moving coil dynamic mics, so they are worth a try under these circumstances.