Above: Garth Brooks wears a Crown CM331A head-worn microphone.
Wikimedia Commons

One of the primary advantages of a head-worn microphone is that it moves with the speaker's head and maintains a very constant distance to the source of the sound. Another advantage is that although the microphone is in plain sight, the smallest of them are small enough to disappear from view at a distance or on video if they are worn properly. To this end, most of the small models are available in a variety of colors to match different skin tones. Also, to the end of allowing the microphone to disappear from view, the microphone can be worn in such a style as to allow natural shadow lines along the jaw to camouflage the microphone. To make such camouflage effective the microphone must lay on or very close to the skin (within 1/4 inch or less). Otherwise, shadows and highlights from ordinary lighting give the microphone away, even accentuating its visibility.

Sometimes a head-worn microphone is used mainly to fight feedback. If this is the case, the best place to locate the microphone capsule is about 1/2 inch back from a smile and in line with the speaker's lips.

Above: George Washington Carver and George Washington are
each wearing a head-worn microphone in the ideal location for
picking up the maximum signal practical, thus giving the
maximum gain possible before feedback sets in.
Wikimedia Commons and Wikimedia Commons (both marked up)

Usually maximization of gain-before-feedback is not needed. Furthermore, head-worn microphones are typically extremely sensitive to plosives. If the microphone is any closer to the lips than is shown above then distortion of plosives becomes a possibility.

Usually, it is best to position the microphone to achieve camouflage rather than to minimize feedback. There is a natural shadow-line on the front of the jaw. If the microphone is located as if to extend this shadow-line all the way back to underneath the earlobe, the eye of the viewer will overlook the microphone. If a shirt is worn with an open collar, be sure the microphone is not so low on the jaw as to possibly rub on the collar. Even at this location, the microphone is just a few inches from the speaker's mouth and a good strong signal is available.

Above: George Washington Carver and George Washington are
each wearing a head-worn microphone in the ideal location to
camouflage it, giving the microphone the least visibility.
Wikimedia Commons and Wikimedia Commons (both marked up)

Sometimes the speaker has difficulty getting the microphone to fit well. In this case the mic may hang in mid-air an inch or more from the speaker's face. Distance between the mic and the face causes the microphone to become distractingly visible against the background. Ideally the sound technician should work with the speaker to get the microphone placed well so that the speaker is comfortable with the microphone and does not have to fiddle with it during the worship service and so that the microphone is mounted optimally for the needs of the situation.

Above: George Washington Carver and George Washington have
been given no help from the sound tech. Although this location
for the microphone seems intuitive, it optimizes nothing.
Wikimedia Commons and Wikimedia Commons (both marked up)

If you have a choice of colors for the microphone, choosing a color that is slightly darker than the speaker's face will disguise the microphone better than choosing a color that is slightly too light. This works best because the lighting on the podium will typically cause a few spots of glare or specular reflection from the microphone. A slightly darker color will offset the glare and give a better overall color match.

Above: Head-worn microphones are often available in a variety of colors.
Product photo, MM-PSM Pro Series, fair use.

Head-worn microphones tend to be fragile. To make them small and nearly invisible the boom of the microphone and all the other parts are made of the thinnest possible materials. Whereas a handheld microphone might have a useful life of twenty years or more, most head-worn microphones seem to have a useful life of less than three years. They are nearly a "consumable" quantity. When budgeting for a head-worn microphone, plan on purchasing and keeping on hand a spare microphone. The day will inevitably come when you need to make a fast replacement.

Three factors that are unique to head-worn microphones contribute to their fragility. 1.) They get bent. To provide a comfortable and effective fit it is necessary to bend the boom and ear-loops of the microphone. Eventually the metals fatigue and crack and then the microphone will need to be replaced. 2.) The wire gets flexed a lot. The wire that leads from the microphone also gets bent with every turn of the speaker's head. Considering also that the wire has been made as thin as possible, this wire has a limited lifespan. Some head-worn microphones can be ordered with different options for the wire: a thin option for invisibility and a thicker option for durability. 3.) The capsule of a head-worn microphone is unusually vulnerable to any dirt that might enter the front of the microphone. Especially if the microphone is used in an environment where food may be present there is the possibility that the microphone will be handled by fingers that have food residue on them. This residue can be accidentally introduced into the front of the mic. Once dirt enters, it muffles the signal. This type of dirt is difficult to clean out. Some microphones have specific instructions for cleaning, usually involving rinsing with distilled or deionized water and drying under specific conditions. But these procedures do not always work. Some dirt is insoluble.

The wire that leads from the head-worn microphone to the bodypack tends to pull the microphone out of position. To prevent this, a clip should be used to fasten the wire to some clothing. There should be a enough of a loop of wire between the head-worn mic and the clip to accommodate the full range of turning of the head from side-to-side. Typically, the clip can be fastened to a collar on the back of a shirt or blouse. Then the clip should be about nine or ten inches down the wire from the back of the microphone. As you follow the wire from the microphone to the clip, the wire should enter the clip on the opposite side from where the microphone is, as illustrated below. This causes the loop of wire to fall on the person's back. If the wire is lead the other way through the clip, then the loop has an unsightly tendency to fall over the person's shoulder instead.

Above: The wire leading to the microphone should be clipped to clothing.
As the wire exits the clip on its way to the mic it should face away from the microphone so that the loop of wire falls on the center of the person's back.
Pexels stock photo marked up

Jewelry, especially earrings, can occasionally rattle against a head-worn mic causing considerable noise and distraction in the signal. In certain cases it may be better to resort to a lavalier or stand-mounted microphone.

This ends the discussion of miniaturization of microphones. In order from largest to smallest, studio, stand-mounted, installed, handheld, boundary, lavalier, and head-worn microphones have been discussed. The smaller the microphone is, the harder it is to make it directional and high-fidelity.

2.) Directionality (vs. miniaturization and fidelity)

It is relatively easy to make a microphone that is not at all sensitive to the direction of the sound as the sound approaches the microphone. As the sensitivity of the microphone to the direction of the approach of the sound waves is increased the microphone becomes increasingly difficult to miniaturize and it becomes more difficult to maintain high-fidelity audio reproduction.

A microphone that to some extend is insensitive to sounds from the sides and/or the back of the microphone is said to to be directional. In a narrow technical and mathematical sense, it is helpful to think of the amount of directionality as the relative sensitivity to sounds arriving on-axis compared to the sensitivity (or better, the in-sensitivity!) of sounds arriving perpendicular to the axis. A perfectly directional microphone rejects sounds arriving at a 90° angle to its axis. Notice that nothing has been said in this definition about rejection from the rear of the microphone. That's a bit counterintuitive, but that is the mathematical way to think of it. Of course, in practice, whatever directional pattern works is what we will use, even if in the technical-mathematical sense it might not be the most directional microphone that could be chosen. Microphones with near perfect rejection from the back are common, but these are somewhat sensitive to sounds from 90° off axis. Even though these are not the mathematically most directional microphones, we like them!

A microphone that is completely insensitive to directionality is said to be omnidirectional. The next step in increasing the directionality of the microphone results more in a microphone that rejects sounds from the back. This type of microphone accepts sounds from lots of directions, except directly from the back side, from which it is designed to reject sound. This type is called cardioid. The next step of increased directionality has a goal of narrowing the angle of acceptance of sound as a higher priority than rejecting sound from the back of the microphone. This is a super-cardioid, also known as an hyper-cardioid microphone. Continuing to make the microphone more directional eventually results in a microphone that completely rejects sounds from the sides (from 90° off axis) but accepts sounds equally well from the front or back. This is a bi-directional microphone, also known as a figure-of-eight microphone. Finally, microphones that are designed to be more sensitive to on-axis sounds than sounds from the sides and the rear are the shotgun or parabolic microphones.

Shotgun and parabolic microphones tend to be the largest and lowest-fidelity microphones. Every compromise possible has been made to enhance directionality. In contrast, at the other end of the directionality spectrum, omnidirectional microphones will be the easiest to miniaturize and will tend to deliver the highest fidelity because nothing needs to be compromised to promote directionality.

Before explaining each of the different types of directional microphones it is helpful to understand how the direction of a sound wave is evident to a microphone. Sound waves are longitudinal waves. They are created by the motion of air molecules. In the illustrations below, each black dot represents an air molecule. Sound causes these molecules to vibrate in a pattern that creates compression zones (a higher density of molecules) and rarefaction zones (lower density of air molecules) that form in lines. These lines move in a continuous direction—the direction in which the sound is traveling. In the caption below the first illustration there is a link to a web page that includes an animation of the illustration below. The animation is valuable for visualizing how sound moves through air in a particular direction.

The first illustration below is valid for a source of sound far away, say three feet or more away. The illustration that includes a vocalist shows how the lines of compression and rarefaction in a sound wave are curved and spherical at their source and that they get weaker as they expand outward. Whereas the groupings of compression and rarefaction move outward from the source, the air molecules just bounce back-and-forth for an ordinary sound wave. This can be most clearly seen in the first animated illustration linked below. Not illustrated here is a plosive soundwave, in which there is a sudden addition of air molecules at the source creating a puff of wind in addition to the longitudinal waves. Pronunciation of letters p, b, t and some others create some plosive sound as well as longitudinal sound.

Above: A visualization of sound in air. Please check out the
animation of the above illustration.

Above: A visualization of sound in air close to the source.
Longitudinal waves have a spherical shape close to the source and their intensity
fades as they radiate outward. Pixabay (edited).

These characteristics of how sound travels through air are important in understanding how microphones are made directional and how to make best use of directional microphones.

Omnidirectional

• All directional, rather "musical" to most ears.
• Resistant to wind noise and plosives in speech
• Simple construction leads to high-accuracy sound pick-up
• Keep omnidirectional mics close to sound sources in live-sound applications, else feedback.

Above: The arrow shows the direction of sound waves.
The blue box represents an omnidirectional microphone. The small portion at the top senses the pressure at that point. Illustration by Prof. dDB.

Above: The direction of the sound does not matter. Even if the direction was completely reversed, or turned to any angle, the pressure changes at the sensitive point of the microphone are equally easily sensed. Illustration by Prof. dDB.

Omnidirectional microphones are somewhat insensitive to wind noise (e.g. outdoors) and plosives from "p," "b," "s," and "t" sounds. This is because wind (air velocity) does not correspond directly to waves of pressure or rarefaction. This is an important advantage of omnidirectional microphones. Wind rushing over the housing of the microphone can produce turbulence that can create some pressure-waves thus inducing some wind noise, so wind screening is still appropriate in many situations, but in general, omnidirectional microphones resist wind noise better than directional microphones.

The directional pattern of a microphone can be expressed as a polar plot of gain relative to on-axis gain. In the plot below, the "0" degree mark (where 3 o'clock would be on an analog clock face) represents the ability of the microphone to pick up sounds on-axis. (The ability to pick up sounds with the microphone pointed directly at the sound.) On all polar patterns, this has a unit of "1" or 100%, meaning that for sounds approaching the microphone from this angle (zero degrees) relative to the axis, 100% or 1.0 units of the sound will be picked up. For an omnidirectional microphone the plot is uninteresting because, as the heavy (blue) line indicates, the microphone picks up 100% of the sound when it arrives at any angle. The plot is shown here mainly for comparison to the plots for directional microphones.

Above: The ideal omnidirectional pattern. The numbers around the outside of the plot show the angle, in degrees, from which a sound may arrive. The numbers between 0 and 1 on the radius to the right of 90 degrees label the fractional amount of sound that might be picked up relative to an on-axis arrival. If you multiply this number by 100 you get the percentage of sound that might be picked up relative to an on-axis arrival. The heavy (blue) circle around the outside indicates that an omnidirectional microphone picks up sound equally well from any angle. Illustration by Prof. dDB.

Most omnidirectional microphones have a directional pattern very close to the ideal pattern shown above for frequencies below 5 kHz. Considering that the highest note on a piano is about 4 kHz, this covers all the fundamental frequencies and even some harmonics of voices and most musical instruments. However not everything is so perfect. Most omnidirectional microphones, especially those in larger housings, show some slight lack of sensitivity from the rear as frequencies go above 5 kHz. This will matter mostly for miking high-frequency instruments such as a piccolo or cymbals, tambourines, etc. The plot below shows a pattern that is more typical of an actual omnidirectional microphone at about 8 kHz.

Above: An achievable practical omnidirectional pattern for high frequencies. This plot could be typical of 8 kHz sounds. The numbers around the outside of the plot show the angle, in degrees, from which a sound may arrive. The numbers between 0 and 1 on the radius to the right of 90 degrees label the fractional amount of sound picked up relative to an on-axis arrival. The heavy (blue) nearly circular line indicates that a practical omnidirectional microphone picks up a little less high-frequency sound from the rear. Illustration by Prof. dDB.

The slight directional effect of omnidirectional microphones is usually so minimal as to be negligible for all except a few applications, and even then, omnidirectional microphones handle off-axis sounds with less distortion than any directional microphone. For acoustic instruments on a quiet stage (no other nearby competing instruments or voices) omnidirectional microphones typically produce especially pleasing results relative to equally expensive directional microphones. But a quiet stage is a seriously restrictive qualifier in most live-sound environments, unless perhaps there is a solo instrument. Omnidirectional microphones are more common in a studio environment for recorded sound. Omnidirectional microphones in live-sound house-of-worship applications are mostly limited to lavalier and ear-set microphones where their ability to be miniaturized matters.

Omnidirectional microphones are also inherently superior to directional microphones of equivalent cost when uniformly accurate and smooth high-fidelity low-frequency response is needed. Pianos (the low notes extend down to 27 Hz), Pipe organs (some go down to 16 Hz), bass violins, contrabassoons, and electric bass cabinets can sometimes benefit from using an omnidirectional microphone because of the inherent low-frequency advantage of this design. Not all omnidirectional microphones achieve such excellent low-frequency response, so be sure to check the datasheet before purchasing. However due to feedback concerns in live-sound, omnidirectional microphones are not a common choice, even when good low-frequency response is helpful.

If omnidirectional microphones are used in live-sound reinforcement their ability to pick up sound from all angles means they are more open to picking up feedback. This is a serious strike against the routine use of omnidirectional microphones in live-sound reinforcement. This disadvantage may be overcome by keeping the microphone very close to the sound source, which is exactly what ear-set and lavalier microphones do. (Also, whenever possible keep the mic behind the loudspeaker so that the directional pattern of the loudspeaker directs amplified sound away from the microphone.)

Within the category of omnidirectional microphones there is a category of microphones called "measurement" microphones or "reference" microphones. These use standard XLR connections and look like any microphone, and superficially they act like any microphone. But they are optimized for use with spectrum analyzers for scientific laboratory work, not audio mixing boards. It is not impossible to use this type of microphone in a house-of-worship application, but it is unlikely to be your best choice for the money in this application. Many of them have restricted dynamic range. They overload easily and they might have higher background noise than a normal microphone. What they do have is ultra-flat frequency response. It is usually best not to order one of these for live-sound house-of-worship reinforcement.

Figure-of-eight

• Bi-directional. Rejects sounds from the sides.
• Especially sensitive to wind noise and plosives in speech
• Strong proximity effect.

Above: The arrow shows the direction of sound waves.
The blue area represents the capsule of a figure-of-eight microphone. As the air-molecules move against the diaphragm (thin red line) the diaphragm follows their motion, creating a signal. Illustration by Prof. dDB.

Above: The direction of the sound matters. If the sound arrives perpendicular to the axis of the capsule, as shown, then it creates no motion of the diaphragm, and there is no signal. Illustration by Prof. dDB.

Directional microphones, and especially Figure-of-eight microphones are sensitive to wind and especially the turbulence of any breeze that might flow past the capsule. This makes them especially sensitive to plosives such as "b," "p,", "s," and "t" in speech. These microphones will emphasize these sounds if the microphone is close enough to the source. The effect starts to become noticeable within a foot or so of the person speaking and can become obnoxious if the microphone is very close and has no windscreen. For speech and vocal reinforcement wind screening becomes essential with these microphones.

The directional pattern of a figure-of-eight microphone is shown below. Notice that the sound is equally well received from the rear as well as from the front, but at an angle perpendicular to the axis the microphone is totally insensitive. Thinking of directionality as being the ability of the microphone to reject sound from the side—from 90 degrees off-axis—the figure-of-eight pattern is the most directional pattern possible. In theory at least, it achieves perfect directionality in this conception of directionality.

Above: The ideal figure-of-eight pattern. The numbers around the outside of the plot show the angle, in degrees, from which a sound may arrive. The numbers between 0 and 1 on the radius to the right of 90 degrees label the fractional amount of sound that might be picked up relative to an on-axis arrival. If you multiply this number by 100 you get the percentage of sound that might be picked up relative to an on-axis arrival. Maximum rejection of sound is at angles perpendicular to the axis of the microphone. Illustration by Prof. dDB.

Figure-of-eight microphones are essentially sensitive to the velocity of the moving air molecules in a longitudinal sound wave. In contrast, an omnidirectional microphone is essentially sensitive to the pressure variations (density of air molecules) in a sound wave. Recall the animation which shows the two different aspects of a longitudinal sound wave. In this animation a figure-of-eight microphone is sensitive to the motion of the "particle" and an omnidirectional microphone is sensitive to the "wave." Thus, an omnidirectional microphone is said to be responsive to pressure and a figure-of-eight microphone is sensitive to velocity. (Velocity sensitivity is also known as pressure gradient sensitivity. Mathematically, a gradient is a directional derivative. Velocity is the gradient of position. For sound in air, a pressure gradient is proportional to the velocity of air molecules.)

Figure-of-eight microphones, when placed very close to a source of sound (usually within one foot or closer) give exaggerated bass (low frequency) response. This is called the proximity effect. It is caused by the curvature of the sound waves near the source. As the waves radiate outward from the source the circumference of each wave-front increases resulting in weaker pressure gradients (weaker sound) being associated with the further wavefronts. Moving a microphone from one inch away from a source to four inches away, a motion of three inches, makes a big difference in the strength of the sound at the microphone. However if the microphone is moved from thirty-one inches to thirty-four inches away—an identical three inch movement— there is hardly any difference in the strength of the sound at the microphone because the waves at those greater distances are hardly curved at all.

If a figure-of-eight microphone is very close to the source of sound, the sound at the side opposite of the sound source, say the rear side of the microphone, is just a little bit weaker than the sound at the front because the back side of the microphone is just a little further from the source then the front side of the microphone. (Or the sound has to travel just a little further to get to the back side of the diaphragm of the capsule.) Some of this difference depends on the size and geometry of the microphone capsule, the diaphragm, and the structural elements (which may block some sound waves) required to support the diaphragm. This means that some microphones have larger proximity effects for a given distance to the sound-source than others. In a counterintuitive way, weaker sound at the back of the diaphragm reduces the overall sensitivity of the diaphragm. However, as the frequency of the sound gets lower its wavelength gets longer which means that the distance the waves have to travel is less important. Thus, lower frequency sounds get picked up better than higher-frequency sounds when the sound waves are curved.

Proximity effect is inherent in any velocity-sensitive microphone. Fundamentally, some proximity effect will always be inherent to achieving directionality. Although in a technical sense the proximity effect is distortion, most people find that a small or moderate amount of it sounds pleasing, adding a sensation of closeness or authority. This is true for both male and female voices. The lack of proximity effect in omnidirectional microphones is one reason why they are not so frequently used for speech and vocals. However for musical instruments the proximity effect can sometimes be obnoxious, causing certain low notes to ring out obtrusively. If directional microphones are used for musical instruments that have low notes, e.g. piano, cello, bass violine, etc. it is important to keep the microphone at least several inches from the sound-producing parts of the instrument, such as the sound-board or the strings. (Unless you are deliberately trying for a honky kind of sound, say for a special effect.)

Of all the directional microphone designs, figure-of-eight microphones display the strongest proximity effects. Only omnidirectional microphones are completely free of the proximity effect because they sample the sound at a single point. Click here for a demonstration of proximity effect. (Headphones or earbuds with good low-frequency response will help you hear the demonstration accurately.) One may also note that directional microphones eliminate most room resonances from the sound, mainly because room resonances arrive from all directions, making an omnidirectional microphone especially sensitive to them.

An equation can be used to describe the directionality of a microphone. In the equation below, θ is the angle of arrival of the sound. If θ = 0 then the sound is arriving on axis, directly into the front of the microphone. If θ = 90° then the sound is arriving at a perpendicular angle directly into the side of the microphone. And if θ = 180° then the sound is arriving directly from the rear of the microphone. Also in this equation the variable d represents the directionality of the microphone. The variable d can range from zero to unity. If d = 0 then the microphone is not directional, it is omnidirectional. If d = 1 then the microphone is fully directional, it is a figure-of-eight microphone. Finally, S(θ) represents the amount of sensitivity of the microphone at angle θ. The sensitivity, S(θ) will always be 1 (or 100%) for θ = 0. At other angles it can vary from 1 down to 0, zero being completely insensitive.

S(θ) = |(1 – d) + dcos(θ)|

The above equation is the equation that was used to generate the figures illustrating the directionality of omnidirectional (d = 0) and figure-of-eight (d = 1) microphones. But the directionality amount, d does not have to be exactly zero (0) or exactly unity (1). It can be any amount in between those limits. This equation nicely illustrates that omnidirectional microphones and figure-of-eight microphones represent two extremes of a continuum. Other patterns such as cardioid, and super-cardioid, are achieved with different directionality factors, d.

Cardioid

• Easily understood pickup pattern—picks up from front, rejects from back.
• Can help reduce feedback problems
• Pleasant and mild proximity effect
• Sounds entering from the rear or sides can be distorted.

Above: The ideal cardioid pattern. The numbers around the outside of the plot show the angle, in degrees, from which a sound may arrive. The numbers between 0 and 1 on the radius to the right of 90 degrees label the fractional amount of sound that might be picked up relative to an on-axis arrival. If you multiply this number by 100 you get the percentage of sound that might be picked up relative to an on-axis arrival. Maximum rejection of sound is at an angle of 180°, the rearward direction of the microphone. Illustration by Prof. dDB.

A cardioid pattern is usually created by partially occluding the back side of the diaphragm of the cartridge. The phase between the velocity and the pressure is offset from each other by 90 degrees. With a partial occlusion, the pressure in the chamber behind the diaphragm can be delayed an additional 90 degrees causing the two effects to reinforce each other when the sound arrives from the front. However, if the sound arrives from the back the phase of the velocity wave is delayed relative to the pressure wave and now the two effects cancel. The partial occlusion is referred to by manufacturers as a port or a labyrinth or as a baffle or as a pad or possibly with other language. In other words, the word is not standardized.

Above: The arrow shows the direction of sound waves.
The blue area represents the capsule of a cardioid microphone. As the air-molecules move against the diaphragm (thin red line) the diaphragm follows their motion, creating a signal. Illustration by Prof. dDB.

Above: The direction of the sound matters. If the sound arrives from the rear of the capsule, as shown, then just enough of it passes through the occlusion to cause the diaphragm to experience no net force. Then there is no signal. Illustration by Prof. dDB.

It is difficult to cause the partial occlusion to operate uniformly at all frequencies. This causes the directional pattern to vary with frequency. This variation is the main disadvantage of a cardioid microphone. The directional pattern is optimized for mid frequencies. Most cardioid microphones have a good uniform cardioid pattern across a range from about 300 Hz to 5 kHz. However very high or very low frequencies may have more of an omnidirectional (typical of lower frequencies) or a figure-of-eight pattern (typical of higher frequencies). This means that most cardioid microphones are a little more directional at high frequencies than at low frequencies.

Above: A typical practical cardioid pattern. Each line represents the pattern at a different frequency. Generally, the patterns that are more toward the inside of the concentric pattern correspond to higher frequencies and the patterns on the outside correspond to lower frequencies. Illustration by Prof. dDB. The frequency sensitivity of the Shure SM-58 cardioid microphone can be seen by clicking the next link and scrolling about 3/4 of the way down the page to the "Typical Polar Pattern."

The sensitivity of the microphone's frequency response to direction means that sounds picked up from the sides (especially) or the rear of the microphone usually are not very high-fidelity. In the above plot notice that the pattern-lines are fairly near each other and orderly (this is good) for angles up to about 60 degrees off-axis, but for angles more than about 120 degrees off-axis (up to 180 degrees off-axis) the pattern gets further separated and some even cross over the others (near angles around 150 degrees). These widely separated and crossing lines will result in bad sound. As the microphone is turned away from the source, before the sound fades it also starts to sound hollow and distorted, especially for sounds coming in from the back of the microphone. This dependency of the directional pattern on frequency is the most serious disadvantage of a cardioid microphone. This video on Directionality and Proximity Effect will allow you to hear the hollow and distorted sound that is picked up when the microphone is not aimed at the source of sound. Listen with good headphones or earbuds at 1:35 to 1:45. Especially listen to the sound of the actor's voice saying, "and I'm trying to maintain." In this phrase, while the microphone is not quite pointed directly away from the source of sound, the distortion is strong.

A minor disadvantage of a cardioid microphone is that it is more difficult to miniaturize because the rear-ports (which give it directionality) need some physical separation from the front of the microphone. But for a handheld or stand-mounted microphone miniaturization is not needed, so this disadvantage does not matter.

A third disadvantage of a cardioid microphone is that it is intrinsically a bit more sensitive to plosives than an omnidirectional microphone, but it is not as sensitive as a figure-of-eight microphone. Good wind screening can mitigate this problem, but again at the expense of the size of the microphone since good wind screening requires some space. Generally, wind screening of a cardioid microphone is more important than for an omnidirectional microphone, and not very hard to achieve.

The advantages of a cardioid microphone are several, but probably the main advantage is that this microphone pattern just does what people naturally expect a microphone to do. It picks up sound when it is aimed at the source and not when it is aimed away from the source. All other microphone patterns are harder for the general public to understand.

When it comes to preventing feedback, a cardioid microphone has a strong advantage. If the loudspeaker(s) are placed in front of the sound sources, and if they are aimed away from the microphones, then the cardiod pattern also helps avoid picking up feedback. This arrangement usually provides very good gain-before-feedback, even if the microphone might be only a few feet from (but in back of) the loudspeakers. Also, if stage monitors (loudspeakers on the floor aimed back at vocalists, guitarists, etc.) are used, cardioid microphones can be aimed to avoid feedback from the monitor loudspeakers if the monitor loudspeakers are placed several feet out in front of the vocalists, guitarists, etc. (And not at the feet of the performer or behind the performer.)

Another advantage is that the proximity effect, so strong in figure-of-eight microphones, is moderated in a cardioid pattern. This moderate proximity effect is usually more pleasing than a strong proximity effect, and again, the general public seems to naturally prefer about the amount of proximity effect that a cardioid microphone typically has.

In a house-of-worship the disadvantages of a cardioid microphone (distortion of off-axis sounds, difficult to miniaturize) are minor or even negligible. The advantage of the intuitive directional pattern and the resulting feedback reduction is huge. For this reason, most houses-of-worship use cardioid microphones almost exclusively except for a few niche situations (primarily lavalier and ear-set microphones that need miniaturization). All the microphones at Covenant church are cardioid except the pastor's ear-set microphone (which is omnidirectional).

Super cardioid

• Picks up from directly in front, rejects from about 120°, some rear sensitivity.
• Can help reduce feedback problems when floor-wedge monitors are used.
• Proximity effect can be fairly strong
• Sounds entering from the rear or sides can be distorted.

Above: The ideal super cardioid pattern. The numbers around the outside of the plot show the angle, in degrees, from which a sound may arrive. The numbers between 0 and 1 on the radius to the right of 90 degrees label the fractional amount of sound that might be picked up relative to an on-axis arrival. If you multiply this number by 100 you get the percentage of sound that might be picked up relative to an on-axis arrival. Maximum rejection of sound is at an angle of 120°. There is some pickup of sounds arriving from the direct rearward end the microphone. Illustration by Prof. dDB.

An exemplary application of a super cardioid microphone is a vocal microphone with a floor-wedge monitor speaker near the base of the microphone stand. There are two reasons why it is important to arrange the monitor speaker and microphone so that the microphone can reject the sound arriving from the monitor speaker. First, sound arriving from the rear of any microphone except an omnidirectional microphone is likely to be distorted and hollow sounding to the extent that the microphone picks it up. Secondly, if there is enough pickup from the monitor speaker feedback howl will ensue. In most cases a cardioid microphone can do an adequate job of rejecting sounds from floor-wedge monitors if the monitors are set five or six feet beyond the microphone stand toward the congregation. However, if the monitor can be brought closer to the vocalist it will not have to be driven as hard to make it adequately loud at the vocalist's ears. But as the monitor is moved closer to the microphone the angle of sound arrival encourages more sound to be picked up if a cardioid microphone is used. In contrast, if a super-cardioid microphone is used, then the monitor can be moved into a position closer to the angle of maximum rejection from the microphone. In a case such as illustrated below where the monitor speakers need to be close to the base of the microphone stand then a super cardioid microphone will be a better choice than a cardioid microphone.

Above: A super cardioid microphone is used along with floor-wedge monitors. The green lines illustrate the approximate angles of sensitivity. The red lines illustrate the approximate angles of rejection. The monitors are placed relative to the microphone to achieve strong rejection. Wikimedia Commons (modified).

The reader might wonder why a super cardioid pattern is not generally better than a cardioid pattern for house-of-worship situations. The philosophical answer is that you should never expect a free lunch. Super cardioid microphones come with a set of issues that are hard to work with. The angle of high-fidelity acceptance is usually so narrow that most vocalists will not be able to completely stay within that desirable angle, especially if the microphone is hand-held. The result will be that the tonal quality of the sound will vary as the performer moves around. Additionally, the proximity effect is usually more pronounced, giving the microphone a heavy sort of tone whenever it is close to the sound source. In this video at 3:30 to about 4:00 you can hear the typical sound of a super cardioid microphone including the strong proximity effect and a slight variation in tonal quality as the microphone is moved around. A performer using a super cardioid microphone needs to be aware of these difficulties and needs to stay properly positioned relative to the microphone to get good results.

Overall, for house-of-worship situations a super cardioid microphone may on occasion be used to advantage, especially with regard to the use of floor-wedge monitors, but in most situations a cardioid microphone will give more optimal results overall.

A microphone that is similar to a super cardioid is a hyper cardioid microphone. One must really consult the manufacturer's specifications to see how far the cardioid pattern has been compromised over toward that of a figure-of-eight since there is no official standard for the pickup pattern of these microphones, but usually "hyper" signifies that the microphone is closer to a figure-of-eight microphone with an angle of maximum rejection of perhaps 100° to 110° whereas a super-cardioid microphone is usually about a 33-67 compromise between a cardioid and a figure-of-eight pattern with a maximum rejection angle of about 120°

Shotgun and Parabolic Microphones

• Extra sensitivity for higher-pitched sounds arriving from directly in front.
• Main advantage is the ability to be placed far from the sound source.
• Low-frequency sounds entering from the rear or sides can be badly distorted.
• Consider rolling off low frequency sounds, using another mic to pick those up.

Above: A typical shotgun or parabolic directional pattern, usually valid only for high frequencies such as 2 kHz and up. Many variations with different numbers of lobes and nulls are possible. Not shown: at low frequencies the pattern is more similar to a supercardioid pattern. The numbers around the outside of the plot show the angle, in degrees, from which a sound may arrive. The numbers between 0 and 1 on the radius to the right of 90 degrees label the fractional amount of sound that might be picked up relative to an on-axis arrival. If you multiply this number by 100 you get the percentage of sound that might be picked up relative to an on-axis arrival.
Illustration by Prof. dDB.

I have arranged this discussion of directionality to show that as more sound is admitted to the back side of the diaphragm of the capsule (via appropriate baffling and/or labyrinths) the microphone becomes more directional (in the sense of rejecting sound from the sides). But opening the back of the capsule is not the only thing that can be done to create directionality. One can also manipulate how the sound gets to the front of the capsule. This is the technique of shotgun and parabolic microphones.

In a parabolic microphone usually an omnidirectional or cardioid basic design is chosen for the capsule. To this, a parabolic reflector is added, and the front of the capsule is placed at the focal point of the parabola and aimed into the parabola. The back of the capsule is aimed toward the sound source. The parabola reflects the sound into the front of the capsule. The large diameter of the parabola relative to the capsule's diaphragm provides a type of acoustic amplification resulting in the ability to pick up sounds far away from the parabolic reflector. Sounds that arrive off-axis are also reflected by the parabola, but the off-axis angle causes these sounds to be focused away from the capsule, so they are not picked up very well. The parabola is not totally opaque to sounds arriving from the back of the parabola, especially low-frequency sounds, so these sounds get through to the front of the capsule. The result is that there is some sensitivity to sounds arriving from the back of the parabola, especially low frequencies. These sounds from the back side often sound hollow or boxy (as if emanating from a box) due to their non-uniform frequency response.

In a shotgun microphone usually a supercardioid or occasionally a cardioid basic capsule design is chosen. An interference tube is placed in front of the capsule and is aimed at the sound source. The interference tube is a tube of about the same diameter as the capsule's diaphragm and typically about a foot long. It has carefully placed slots or holes or screens in it to allow a fraction of the sounds arriving from off-axis to enter the tube and ricochet down the tube finally arriving at the front of the capsule. When off-axis pressure waves arrive at the diaphragm they are at random phases due to the variety of different path lengths they have traveled down the interference tube. Thus, they cancel each other out and the diaphragm does not respond well to them. Meanwhile, on-axis sounds shoot coherently straight down the interference tube and do not cancel each other out. A large amount of electronic amplification then further extends the range of this frontal pick-up, and unfortunately simultaneously amplifies the leakage into the signal of sounds from off-axis. This combination of acoustic wave cancelation for off-axis sounds and electronic amplification (of all the output of the capsule) narrows the angle of acceptance of sound in the main lobe of the directional pattern and extends the distance over which the microphone can pick up on-axis sound.

The above descriptions of how parabolic and shotgun microphones work may seem convincing, but there is a problem. To be an effective reflector a parabola needs to be at least a wavelength in diameter. An effective interference tube needs to be at least a half-wavelength long. To put this in perspective consider that the wavelength of a pipe-organ note is about twice the length of the pipe (for a pipe that is open at the top). The wavelength of middle C (also known as C₄) is about four feet! (The organ pipe will be about 2 feet long.) So an effective parabolic reflector for this pitch would have to be at least 4 feet in diameter and an effective interference tube would have to be at least 2 feet long. Most parabolic and shotgun microphones are not this big. This means that the highly directional character of parabolic and shotgun microphones is typically limited to frequencies above 500 Hz or even 1000 Hz. (Above about the first or second C above middle C, C₅ or C₆.)

Obviously, a larger diameter parabola or a longer interference tube is better. But such big microphones are unsightly and awkward. Compromises are made. Most parabolic microphones are between one foot and three feet in diameter. Most interference tubes are between 4 inches and 18 inches long. At the smaller dimensions these microphones offer a pattern with a good enhancement of directionality only at very high frequencies. Small parabolic and shotgun microphones are successful in the marketplace mostly based on marketing hype and uninformed customers or literally as toys. On the other hand, an 18-inch-long interference tube can be quite effective at frequencies above about 300 Hz, which will include most human speech sounds. (Probably the longest shotgun microphone ever made for commercial sale was the Electro-Voice model 643 at 7 feet long!)

For the spoken word, sibilant sounds (e.g. the hissy part of many "s" sounds) add much to the ability to understand the speech and distinguish words like "sea" from "tea," "key," and "me." The frequencies of these sibilant sounds are mostly above 1000 Hz and so a reasonably large parabolic or shotgun microphone can be quite effective in picking these sounds up. These microphones might not be natural sounding, but speech clarity is improved. For musical vocals, excessive sibilance is distracting and un-musical sounding.

Using a parabolic or shotgun microphone can be even more complicated than the above considerations might suggest. Making an interference tube that works effectively and uniformly across a wide range of frequencies is challenging. In practice, the effectiveness of the tube varies with frequency, even for frequencies for which the tube is long enough to have an effect. Similarly, making a good parabolic reflector for sound that does not itself vibrate with the sound (like a speaker cone) and thus distort the reflection is difficult. Consequently, the directional pattern of parabolic and shotgun microphone(s) vary a lot with frequency. The number of side-lobes in the pattern and the number of nulls (angles from which sounds are practically eliminated) changes as the frequency changes. This has the effect of making the off-axis sounds that do manage to leak into the signal sound very low-fidelity. This low-fidelity sound might be characterized as sounding muffled or nasally or screechy depending on the angle of arrival. If the microphone or sound source are moving relative to each other, these off-axis sounds can change character obnoxiously as time passes.

With all these limitations, you might be wondering how a parabolic or shotgun microphone might be used to good advantage. The big advantage of these microphones is the greater sensitivity of the front or main lobe of the directional pattern. The rejection from the sides is not much of an advantage because they are not really as good at rejecting from the sides as you might think. The distortion given to sounds that leak through from the sides makes these sounds more prominent and obvious than desired.

In those rare cases where shotgun microphones are used in house-of-worship applications, they are usually used in combination with other microphones. For example, one or two shotgun microphones might be used to pick up congregational singing. Understanding that the low-frequency sounds from these microphones might be poor-sounding, it is common to severely roll off the low frequency sounds (say from 300 Hz on down) from these shotgun microphones. To make up for this low-frequency roll off, some other microphones such as some cardioid or omnidirectional microphones might be mixed in to provide low-frequency support. Then the shotgun microphones support the intelligibility of singing and the other microphones support the rhythm and bass parts of the music. The resulting mix might not be true to the original sound in the room, but it can have pleasing bass along with intelligible vocals. Sometimes, when getting a microphone close to a choir is not practical, this same technique is used for picking up a choir. In any case, getting a cardioid microphone or super-cardioid microphone closer to the sound source is usually a better-sounding choice than resorting to a shotgun microphone at a distance.

Above: A parbolic microphone in use at a football game.
Wikimedia Commons (modified).

There are applications where the advantages of parabolic and shotgun microphones really shine. Parabolic microphones are often used to pick up field sounds in the televising of sporting events. (The crack of the ball on a baseball bat, the sound of teams clashing in football, etc.) In studio-based video recording work and in live news-gathering events, such as a press conference, a shotgun microphone can be a good choice when it is desired to keep the microphone outside of the video frame or when being able to reach over a crowd is an advantage. Shotgun microphones are also occasionally used in live theatre performances to unobtrusively pick up signals for hearing-assistance systems. Shotgun microphones can be hidden above the stage or in the wings of the stage. In these applications feedback is not possible so distorted off-axis sounds are not as serious an issue, whereas in live sound relying on the non-uniform directionality of a shotgun microphone is often a formula for feedback.

Above: Shotgun microphones (both with additional windscreens) used for news gathering.Wikimedia Commons

In good applications of shotgun and parabolic microphones getting intelligible spoken-voice pickup (or other mid- and high-frequency sounds) from a microphone that is far away from the sound source is the goal and the low-frequency sounds are often rolled off because they sound ugly. Rejection of sounds from the side and rear is not a strength of these microphones because distortion makes these sounds more obvious and objectionable.

Because a shotgun microphone is highly directional it will be especially sensitive to wind noise. Usually, a shotgun microphone is placed far from the person speaking so plosives are not a problem, but if outdoors, a good windscreen is needed. Similarly, the capsule of a parabolic microphone should be well windscreened when used outdoors.

Directionality Summary
Microphones can be sensitive to either the absolute pressure vibrations in the air that create sound, or they can be sensitive to the velocity of the air molecules that are moving to create pressure vibrations and sound, or they can be sensitive to some combination of both. Microphones sensitive to pressure variations only are theoretically omnidirectional. Microphones sensitive to velocity variations only theoretically have a figure-of-eight directional pattern, with the pickup from the rear being out-of-phase compared to the pickup from the front. By using a combination of pressure and velocity sensitivity the pickup pattern can be varied. In theory, a 50-50 combination of pressure and velocity sensitivity gives a pattern called cardioid. A 33% pressure, 67% velocity combination of pressure and velocity gives a pattern called super cardioid. Microphones with 25%-75% combinations are also available. Sometimes these are called hyper cardioid microphones. By adding an interference tube or a parabolic dish in front of the capsule a super cardioid or cardioid microphone can be made more directional yet, especially at high frequencies.

It is hard to keep the ratio of pressure and velocity sensitivity uniform across all frequencies, and even harder to make an interference tube or parabolic dish that acts uniformly at all frequencies. This means that omnidirectional and figure-of-eight microphones tend to give flatter frequency responses for off-axis arriving sounds. Other microphones tend to not only attenuate sounds arriving from null angles, they also tend to give these sounds arriving from near-null angles a hollow coloration, sort of like an old telephone. Of course, some microphones have less coloration of off-axis sounds than others.

Plosive sounds in vocals, such as "p,", "b," "s," and "t" sounds are not purely from the vibrations and pressure waves of air. Some parts of these sounds are from an explosive addition of air molecules emanating from the sound source. Velocity-sensitive microphones are very sensitive to these sounds. In a non-amplified environment people are not close enough to hear the plosive content of plosive sounds, but a microphone held close to a plosive source such as a vocalist might pick up these unpleasant sounds. Thus a velocity sensitive microphone needs wind screening to attenuate plosive sounds. Although this effect is especially strong with a velocity sensitive microphone, the turbulence of airflow around a capsule can leave an omnidirectional microphone with some slight sensitivity to plosives as well. For most speakers or vocalists (except experienced professional vocalists) supplementary windscreening around a microphone capsule is good insurance that any near and prominent plosives get attenuated to normal proportions. This is especially important with the more directional patterns; it is also valid even for an omnidirectional microphone.

Close to a sound source the sound waves are curved. This makes no difference for a pressure-sensitive microphone, but it does matter for a velocity sensitive microphone. This gives every velocity-sensitive microphone a proximity effect. A figure-of-eight microphone has a strong proximity effect because it is totally velocity sensitive. The effect is so strong that usually all sources are kept at least three or even six inches from the capsule. Omnidirectional microphones have no proximity effect. That, in combination with a lack of coloration of off-axis arriving sounds gives these microphones a natural advantage in high-fidelity pickup. A little proximity effect tends to be flattering to most vocals, both masculine and feminine. This, plus the intuitive notion that the microphone ought to reject sounds from the rear, plus the feedback rejection that results from a controlled use of the directionality of a microphone, makes cardioid microphones the most popular overall choice for house-of-worship microphone applications.

A demonstration of microphone pick-up patterns can be found at the video-link in this sentence. See especially the part from 7:30 to 9:10. Listen to the hollow character of the sound of the voice when the sound is arriving from an angle that should cause rejection. In addition to the attenuation of the sound, the character of the sound is ugly when it arrives off-axis. The microphone being demonstrated here is a very expensive and high-quality model, yet this coloration is still audible. Also listen to the room echo that the omnidirectional microphone picks up, and which is rejected to varying degrees by the other patterns. This room-echo may be used to very pleasing effect in a studio environment, but it is usually out-of-control in a live-sound environment, mainly making feedback more likely.

Directionality exists on a continuum from no directionality at all—that being an omnidirectional pattern—to maximum directionality—a figure-of-eight pattern and then beyond that, a parabolic or shotgun pattern. By placing a labyrinth or a baffle at the back of the capsule's diaphragm increasing sensitivity to velocity and decreased sensitivity to pressure can be achieved and this adds directionality to the microphone's pickup pattern. Adding an interference tube to the front of the capsule further increases directionality. Omnidirectional microphones are the easiest to miniaturize and the easiest to design for high-fidelity. Highly directional microphones such as figure-of-eight microphones and shotgun microphones tend to compromise fidelity or size and weight or both.

3.) Audio Fidelity (vs. miniaturization and directionality)

Obviously, some microphones sound better than others. Can this be measured and numerically quantified? Can this be qualitatively heard? Does a microphone that measures best (using technical instruments and some sort of theory of what is best) always qualitatively sound best to the listener? These matters are debatable. Can a microphone make a vocalist or acoustic guitar or other acoustic musical instrument sound better than the pure acoustic sound it makes? What do we mean by saying, "make this guitar sound better?" There really are no definitive answers to these questions. "Beauty is in the eye of the beholder," we say. Or in this case, beautiful sound is in the ear of the listener.

On the other hand, the matter is not entirely a matter of undefinable qualitative statements. If a microphone reviewer states that, "The XYZZY microphone, delivers more top-end air, has a more liquid midrange, and has a tighter bottom end than the Shure SM-58 microphone." does that help you understand which microphone to use? The Shure SM-58 microphone is a de-facto industry standard in that it is a very popular choice even when money is plentiful. But here is a statement that in some particular circumstance the XYZZY microphone is a better choice than the SM-58. How can we evaluate the truth of that statement? Only by experience.

To the question of which microphone sounds best for which application there are some quantitatively definable concepts that are highly useful. Yet there are also qualitative qualities that are hard to describe. Although both quantitative and qualitative descriptions of microphones can be helpful, only quantitative descriptions have general usefulness. Qualitative descriptions are always tied to the particular application's context and the related equipment (mixer, windscreen, musical genre, etc.). Thus, qualitative descriptions have a narrow range of validity, comparing only one situation to a few others—qualitatively. Qualitative judgements mean the reviewer liked one total situation more than another. If people judge the sound to be inferior (a qualitative assessment) no degree of explaining technical specifications is likely to sway that opinion. In spite of the generality of quantitative knowledge about a microphone, we find that our choices always come down to qualitative judgements which are validated mostly by the acceptance of others of our choices.

What is important in the end is the qualitative judgement of most listeners that the sound is "good." But what is important in the beginning—in the design or set-up phase of the live-sound reinforcement—is quantitative knowledge of what technical specifications are needed to produce good sound.

For qualitative discussions about the use of microphones, one needs simply to experience them in different contexts, even virtually, such as by perusing YouTube for various comparisons and demonstrations of microphones. Then you need to make your own decisions. Is, "more air," (or "tight bass" or "liquid midrange" or any similar qualitative description) a good thing or a bad thing for the application you are contemplating? Only a consensus of opinions of people who hear the result can decide. That is the essence of a qualitative statement. What is "air" (or whatever) in the sound of a microphone anyway? These terms seem to mean different things to different people, but the use of such qualitative terms does not invalidate experience and comparisons.

To be of any general use, this discussion of "Audio Fidelity" will necessarily have to focus on quantitative measurements of a microphone's characteristics. Specifically, frequency response, dynamic range, and two types of distortion, harmonic and intermodulation distortion.. The reader will find that understanding these quantitative measures can give generally reliable suggestions on how the microphones will qualitatively perform in various applications.

Before reading much further, you might find it helpful to watch one of the many YouTube videos that have been published that qualitatively compare some microphones. There are so many of these it is hard to pick a "best" video on this topic, but here is one that will help give a surface-level qualitative understanding of the nature of the difference between a poor (cheap) microphone and a really good (expensive) one. The title of this video is: $22 Microphone Vs. $3600 Microphone. This video compares four microphones, the Newer NW-800 (~$22), the Shure SM-58 (~$100), the Shure SM-7 (~$400) and the Neumann U-87 ($3600). (You will need good-quality ear-buds or headphones to properly appreciate the video.)

Frequency Response

• Frequency response is best expressed as a graph.
• A flat horizontal line from 20 Hz to 20 kHz is the nominal ideal.
• The nominal ideal is usually compromised to achieve directionality, etc.
• If not a graph, then a frequency range with a decibel range is OK
        Nominal ideal: 20 Hz–20 kHz ±0 dB
        More typical example: 50 Hz–12 kHz ±4 dB
• If not a graph and missing a decibel range, it is a weak specification
        Example: 20 Hz–20 kHz (but how uniformly is this range is covered?)
• Interpreting frequency response gives insight to the best ways to use the mic.

Human hearing is said to cover the range of frequencies from 20 Hz to 20 kHz. But just as the sharpness of vision varies from person to person, so does the ability to hear the full spectrum of sound from 20 Hz to 20 kHz. Most young children do come close to being able to hear the full 20 Hz to 20 kHz spectrum, but even by the teenage years most people start losing high-frequency and low-frequency response. Regardless, a goal of a good sound reinforcement system should be to reinforce the full range of frequencies from 20 Hz to 20 kHz.

With typical program material (spoken voice, music, but not test tones) a variation in loudness of 3 dB is the smallest variation that will be reliably noticed by most people. With training, smaller variations may be noticeable, but for practical purposes, frequency response variations between two microphones of less than 3 dB are insignificant unless the sounds are carefully compared. Variations between 3 and 6 dB are noticeable, but still not objectionable to some listeners. Variations of 10 dB or more are usually obnoxious. However, if the source does not contain frequencies where the variations are the greatest, even 20 dB variations in the frequency response can go unnoticed.

Of course, no real microphone has a perfectly flat frequency response. The diaphragm of the capsule of a microphone has mass, damping, and elasticity to some degree so there are always resonances in even the most expensive microphones. The frequency response of any real microphone will depart from the ideal. (This is also true for the cone of a loudspeaker, the stylus of a phonograph, etc.) On the other hand, modern electronics are easily made to have quite ideal frequency responses. The mixer board and the power amplifier and any electronics like these have, for all practical purposes, ideal frequency responses (given professional level equipment). Thus, in a house-of-worship situation the choice of microphones is usually the single most influential factor in the overall frequency response of the sound system.

Suppose a microphone has almost no output below 50 Hz as shown by the frequency response. Then no amount of equalization will be able to accurately create the bass sounds that the microphone did not pick up in the first place. It is essential that the microphone has a reasonable response at the frequencies that it will need to pick up. But that said, small frequency response variations can often be practically corrected by using the equalizer of the mixer's channel strip.

Most microphones' frequency responses are optimized for particular purposes. Vocal microphones, for example, typically have a frequency response that avoids any loss of frequencies in the range of 2 kHz to 6 kHz because these frequencies are very important to the understandability and clarity of speech. Simultaneously, if the microphone is designed to be hand-held, it often rolls down the low frequency response because human voices, even the deepest bass voice, have little content below 80 Hz while the noise of the microphone wire flopping around and fingers moving on the microphone's body are mostly below 80 Hz. Thus, for clear vocals, a good choice is a microphone that suppress frequencies below 80 Hz and enhances the 2 kHz to 6 kHz frequency range by a few decibels. The Shure SM-58 microphone has been a big success in the marketplace, and it has such a frequency response. This is strong evidence that this type of frequency response is desirable for vocals. Even if it is not perfectly flat, it performs well at the frequencies of vocals and rejects handling noise.

Above: Frequency response of a Shure SM-58 microphone, popular for vocals. Note the approximately 5 dB rise at frequencies from 2 to 6 kHz (2000 to 6000 Hz). Also note the low-frequency roll-off (below 100 Hz) to suppress handling noise.
(Graph is from the Shure SM-58 User's Manual. Fair use.)

For an instrument microphone the first priority is usually a flat low-frequency response from about 80 Hz down as close to 20 Hz as possible. Instrument microphones with good low frequency response and a slight emphasis of high frequencies of about +3 dB from about 4 kHz and up as high as possible (to perhaps 20 kHz) tend to be popular. Comparing to a vocal microphone, the low frequency response is flatter and the boost in high frequencies, if any, is less in amplitude and happens at higher frequencies.

Above: Frequency response of a typical instrument microphone (Sennheiser MKH8020). Note the nearly flat response down past 20 Hz and the slight rise above 4 kHz. (Everything above 20 kHz is inaudible because it is supersonic.)
(Graph is from the Sennheiser MKH8020 User's Manual. Fair use.)

A reference microphone (also known as a measurement microphone) is designed to have as flat of a frequency response as the manufacturer can manage. Since all other aspects of the microphone may be compromised to achieve this flatness, these are usually not good choices for live sound reinforcement. Reference microphones tend to be omnidirectional, have a high noise floor, and have a low dynamic range. The intended application of a reference microphone is for spectrum analysis and setup of room equalization and similar technical purposes. Other than that there are almost always better choices of microphones for live-sound applications in houses-of-worship. A typical example of a reference microphone is the Earthworks M50.

Above: Frequency response of a typical reference microphone (Earthworks M50). Note the ruler-flat response down past 20 Hz and even above 20 kHz.
(Everything above 20 kHz is inaudible because it is supersonic.)
(Graph is from the Earthworks M50 User's Manual. Fair use.)

General-purpose studio microphones offer switches and sometimes interchangeable capsules and other accessories to tailor the frequency response and/or the directionality to different situations. The AKG C414XLS, Neumann U87Ai, and Shure SM-81, are examples. Most of these can be configured as vocal or instrument or reference microphones depending on how they are set up. Many of these types of microphones are impractical for live-sound use, mainly due to the complexity of setting them up advantageously for various situations. On the other hand, if you set up such a microphone more-or-less permanently for a dedicated purpose, they might be useful. An example would be a stereo pair used to mic a grand piano and always used in the same setup and positions. In a situation like that the sound operators do not need to spend time at each event considering the switch settings on the microphones and carefully searching for the best positions for them for each event. The technique can be the same at each event.

General-purpose studio microphones are mentioned here just to let you know that they exist and in case there is a particular application you have for them, but usually other microphones are going to routinely be more cost effective.

Some consumer-grade microphones have similar switching options to general-purpose studio microphones, but the overall quality is not in the same league. Their lower cost makes them popular for karaoke, podcasting, teleconferencing, and similar applications. A popular example of a consumer-grade general-purpose microphone is the Blue Yeti and its many variations. (The frequency response of any of the Blue Yeti models is nowhere near as flat as professional microphones can provide.) Usually, consumer-grade microphones are not good choices for live-sound house-of-worship applications even though they are great choices for their target applications.


Dynamic Range

• For every mic there is a maximum sound-pressure level (in dB-SPL) that it can
        accept without undue distortion.
  
• Every microphone generates slight self-noise. In the microphone's output,
        self-noise typically has a hissing or whooshing sound, as if it is something
      like wind, very soft. Others might describe it as the sound of brushing
      your hand through some long grass.
• The difference between the maximum acceptable SPL and the equivalent SPL of
        the self noise is the microphone's dynamic range.
• Sounds to be picked up by the microphone must have a loudness that fits well
        in the microphone's dynamic range.

Recall that about 191 dB-SPL is the highest sound pressure level that is possible in a normal atmosphere and that 120 db-SPL is the threshold of pain (borderline discomfort). A microphone placed inside a kick drum might experience 150 dB-SPL. A microphone held up close to the lips of a person shouting as loud as possible might experience 130 dB-SPL. It is important that the microphone you choose can handle the loudest sounds. Most microphones have a maximum loudness limit that increases as frequency increases. Thus, a kick drum (lots of low frequency content) is a challenge for a microphone with a limited maximum SPL, but most other types of sources have such little low-frequency content that they are handled easily.

Some older (pre-1970's) models of condenser microphones had relatively low maximum SPL capabilities. Because of this, condenser microphones have developed a reputation of being unsuitable for loud sound sources such as drums and trumpets and even a loud vocalist. But this reputation is outdated now. Most modern condenser microphones, some very inexpensive ones excepted, have maximum SPL capabilities approaching those of popular dynamic microphones such as the Shure SM-58. Consequently maximum SPL capability is usually only an issue for drums and possibly trumpets, and then only if the microphone is very close to the instrument. For house-of-worship applications a maximum SPL capability of 125 dB or more should be enough, except for close-miking of drums when 140 dB-SPL or more would be better.

On the soft side of the dynamic range issue, every microphone generates some slight amount of self-noise. This self noise is created by the thermal motion of atoms of the atmosphere bouncing off the diaphragm. In addition, any preamplifier in the microphone will generate more self-noise due to thermal motion of electrons and other causes in the electronics. You can notice self-noise if you place the microphone in a quiet place (e.g. muffled tightly between pillows in a quiet room) and then, using headphones and with all loudspeakers turned off (so there can be no feedback) turn up the volume really high. You will hear a hissing sound. Some of this hiss is from the microphone itself. (Some more of it may be from the console you are using.)

If the sound you are attempting to pick up with the microphone is not loud enough, it cannot overcome the self-noise of the microphone. For example, if the sound you want to pick up is at a level of 55 dB-SPL and you want at least a 30 dB signal-to-noise ratio, then your microphone must have a self-noise level of 55 – 30 = 25 dB-SPL. Otherwise, when the sound is soft you will hear the hiss of the microphone's self-noise in the background. As you can imagine, the need to pick up such soft sounds is rarely a problem in a house-of-worship situation. If you hear hiss or think you are having a problem with a microphone's self-noise, check the gain trim on that channel first. Gain structure errors are more common and can produce hiss that sounds just like microphone self-noise.

Microphone self-noise is measured in comparison to a theoretically perfect microphone which has no self-noise at all. Imagine two rooms. One is perfectly silent--an anechoic chamber with no sound source in it. Put the microphone to be tested in this room. Measure the loudness of the signal that comes from the microphone. Since there is no acoustic signal in this room, all the signal from this microphone is self noise. Now in the second room--also an anechoic chamber--place an ideal noise-free microphone and also a source of "A weighted" (or CCIT weighted) noise. (This sounds hissy, like radio static between stations.) Turn up the level of the noise until the signal from the ideal microphone matches the strength of the signal from the microphone being tested. Measure, in dB-SPL, the loudness in the room that has the noise source. This is the level of self-noise in the microphone being tested. (Of course, there is no such ideal microphone to use for this test, so an actual test requires use of a calibrated and well-understood microphone with very low self-noise and some math to compensate for the self-noise of the nearly ideal microphone.)

Because self-noise is usually not an issue with a dynamic microphone, most specification sheets for dynamic microphones don't mention anything about it. Better condenser microphones will include self-noise on their specification sheets. For house-of-worship applications anything below about 25 dB-SPL A weighted is good enough. (Or anything below about 37 dB SPL CCIT weighted.)

Hum
Technically, hum is not self-noise. But this seems to be an appropriate place to discuss it. If you are having trouble with hum, the first thing to check is the microphone cable. A broken wire in the cable can reduce the cable's ability to shield the signal from hum. But aside from a defect like that, dynamic microphones are inherently slightly suceptible to hum pickup from nearby magnetic fields such as flourescent light balasts, motors, and sometimes just the wiring in the walls. Most dynamic microphones are designed assuming the microphone is used in a place free of stray magnetic fields (other than the Earth's natural magnetic field, which is not a problem anyway). Higher-quality dynamic microphones include a hum bucking coil to almost completely eliminate the slight suceptibility to stray magnetic fields. If a humbucking coil is present the microphone can be expected to have very little or no audible hum in its output in practically every circumstance.

Humbucking coils are also known as compensating coils—same thing. Condenser microphones never include humbucking coils because they are insensitive to magnetic fields in the first place. If a microphone includes a humbucking coil you can expect it to be mentioned in the user's manual or on the specifications sheet. If it does not include a humbucking coil usually there is no mention made of this omission. The popular Shure SM-58 and the AKG D5 are microphones that are susceptible to magnetic fields. The Electrovoice RE-20 and the Shure SM-7 are examples of microphones with hum-bucking coils.

In summary, the microphone you choose needs to have enough dynmaic range to accomodate the sound source. This means the maximum SPL specification of the mic must be greater than the maximum loudness of the sound or you will hear clipping distortion. The self-noise of the microphone must be many decibels (30dB or more) below the minimum loudness of the sound or you will hear hiss. A dynamic microphones without humbucking coil might have a slight hum in the background of the sound, meaning it should not be used for soft or delicate sounds. The DPA Microphone company has a good summary video: "Understanding dynamic range and the sound pressure level of the voice." Their video puts emphasis on the maximum SPL issue. Lewitt company also has a good video on this topic, this time with the emphasis on the self-noise issue. "Learn WHY Microphone Self-Noise matters."


Distortion

• Professional audio equipment, when properly applied, installed and adjusted,
        has been free of noticeable distortion issues since at least the 1950s.
• If a microphone distorts the signal, it is usually because the acoustic source is
        too loud. (dB-SPL is above the microphone's maximum rating)
• Other reasons for microphone distortion include water or dirt infiltration.
• One measure of audio fidelity is total harmonic distortion or THD
        (lower is better, less than 1% is good—the distortion will be inaudible.)
• Another measure of audio fidelity is intermodulation distortion.
• Clipping is still another type of distortion.

Total Harmonic Distortion (THD)
A microphone is supposed to covert air pressure variations plus air velocity variations into a voltage signal. Ideally, a doubling of air pressure variation should cause a doubling of voltage and similarly, a doubling of air velocity should cause a doubling of voltage. It does not have to be a doubling either. If one triples, the other should triple. Mathematically, the ideal distortion free response of a microphone is

v(t) = S_p1p(t) + S_w2w(t)

Where:
S_p1 = Pressure sensitivity transfer factor (V/Pa)
p(t) = Air pressure variation as a function of time
S_w1 = Air velocity variation sensitivity transfer factor (Vs/m)
w(t) = Velocity variation as a function of time

[Sidenote: The amount of directionality is d = S_w1/(S_w1 + S_w1)
Thus, if d ≠ 1 one has v(t) = S_p1[1/(1 - d)]p(t)
Where S_p1[1/(1 - d)] is the overall sensitivity of the microphone (in V/Pa).
For omnidirectional, d = 0;
cardioid, d = 0.5;
supercardioid, d ≈ 0.66;
bidirectional, d =1]

To be continued. . .

Planned for the future on this page:

--Capsule technologies
    * dynamic
    * condenser
    * electret
    * piezoelectric, a.k.a. crystal
    * ribbon
    * carbon
    * fiber-optic
    * laser
    * MEMS
    * Plasma
    * "Speaker in reverse" (kick drum mic)

Planned for the future on another page:
-Techniques for using microphones

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