General microphone placement for good audio

Achieving good microphone placement is a surprisingly straightforward process and one grounded in physics and engineering concepts. Technical aspects like the microphone type directly influence the design, sensitivity, sound and directionality. Adapting these concepts makes capturing good audio for video a lot easier and more consistent.

The article uses a blend of real-world applications, understanding the different microphone types and understanding the basic theory behind how different designs work. All of this information proves overwhelming. However, given time, it is no different than playing a game once you learn the rules. It becomes second nature.

Proximity to sound source

When it comes to microphone placement, you need to reduce the distance to a sound source. Close miking is placing microphones within 12 inches of the source. If you place the mic too close, there is the risk of distorting and muddying the captured sound. A microphone set up too far causes the source to sound weak or washed out. Condensers lend themselves better to distances.

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Common microphone placement for typical situations

An important consideration to contend with for microphone placement is the microphone’s footprint. A cardioid pattern is a suitable choice for all of the examples below. However, this works with several cardioid packaging options: mounted/handheld, lavalier, shotgun.

Interview

There is a reason lavalier mics are synonymous with interviews. They are easy to use, tend to stay put once mounted and you don’t have to worry about holding or moving them. The tricky thing about lavalier microphone placement is they often sit visibly on the talent’s clothing. It is important to place the microphone and the cables strategically so that they don’t distract from the speaker.

The Rode VideoMic is purpose-built for this. It features a camera-mountable design, condenser capsule, super-cardioid pattern and camera-friendly 3.5mm output. Just don’t forget the 9-volt battery or things might get a little quiet.

The integrated approach has the added benefit of not having to sync the audio and video later, just make sure that your frame and sample rates are correct. At least 48KH for the audio track, frame rate can vary by application, but 24fps is suitable for online streaming and 27.97d for NTSC.

Before getting started, do your best to approximate your setup beforehand, and find the desired camera position while keeping in mind that this will also be your sound pickup point. Positioning is important — the more distant the camera and microphone are from the source, the less direct it sounds and the more gain needed. Being a condenser, the VideoMic is friendlier to use at longer distances and does not need to be directly in front. Meaning that six feet away won’t have world-ending consequences for your audio.

Try it for yourself in a variety of environments ranging from less to more reflective. It is all part of the larger experience of learning your equipment and getting the most from it.

Narrative

Good quality narrative relies on a quiet space free of ambient sound. This can be a sound booth or similar to the broadcast and streaming setups that are commonly seen. A cardioid microphone is the easy and suitable choice, pick a flavor of microphone that suits the purpose but also your talent’s voice. A popular choice for voiceovers is the Electro-Voice (EV) RE20. It is a large-diaphragm cardioid microphone, which makes it good for close proximities and handles lower frequencies well. Most importantly, it sounds good.

If you are in need of a more accessible microphone, the AT2020 is an amazing value-for-money condenser great for getting started it. Tonally it presents a good example of what to expect from a condenser. It has a good presence and frequency response that lends itself well to singers and narrators alike!

The setup considerations should consider whether the talent is standing or seated. This helps with breathing, projection, and comfort. Position the microphone about 12 inches from the source, try moving it within that distance and adjust to taste. Make height adjustments around the talent’s position and based on whether they tilt their head at all when addressing the microphone.

Live event

Focus on reducing and rejecting ambient sounds to help clean up the noise floor. This helps reduce the potential for feedback, bleed and just makes for a much cleaner sound. The lengths you go to will vary depending on the type of live event. Speaking events will require less mitigation than something larger and noisier like a concert.

A mounted dynamic condenser microphone is an excellent starting point. Provided this meets the sensitivity needs without requiring too much gain and risking feedback you are on your way. Typical placement scenarios include a static microphone stand for a standing speaker, a mounted stand for podiums or taking the handheld approach. The core principle is to take advantage of the directional cardioid pattern.

Stay behind the speakers where possible as this massively reduces the possibility of feedback. Noise gates make an excellent buffer by cutting audio below a set threshold, especially loud ambient sounds. Work with the talent beforehand and provide a few basic tips. The worst thing they can do is get too far away or address or not address the mic at all.

Adjust your approach to the suit the event and talent. Not all presenters have the same skill or mic control, they might need coaching on how and where to hold it, and speaking distance. A podium presentation can be similar to a narrative voice over or entirely different if the presenter tends to move on and off axis. Compression helps smooth out peaks and valleys but doesn’t entirely eliminate them.

Wedding

When it comes to microphone placement, this is by far the most discrete setting used. Wireless lavaliers are a known quantity in this space and also come in cardioid flavors. In most cases, it’s not practical to mic the bride. The aesthetics alone make it a challenge, as well as the technical, and time considerations. Unless everyone is willing to take the time and space concessions to disguise a wireless pack and hide a lavalier, never say never!

More specifically we are going to be using two supercardioid Shure WL184 lavaliers to illustrate and take advantage of the directional cardioid pattern. Use two lavaliers, one on the groom and the other on the caller. We are aiming to dial in the gain so that the bride is sufficiently audible through both mics combined. This is based on the assumption that everyone is standing in the standard triangular arrangement roughly three feet apart.

Microphone Directionality

Another consideration when thinking about microphone placement is directionality. Directionality is depicted using polar patterns that use a 360° axis to illustrate the shape and strength of a microphone’s pickup. Keep in mind that these are 2D representations, but in reality, they are 3D bubbles of sorts. On-axis refers to front address, where off-axis is anything but the intended direction.

Cardioid vs Hyper cardioid

These two polar patterns are synonymous with microphone directionality and for a very good reason. The cardioid pattern forms the basis for this as the other patterns are extensions of the design. Directionality is created by allowing sound waves to flow in from other directions. This does need to be both subtle and measure as not just a matter of letting in some sound through the back door. The types of openings used are called ports and rely on complex channels that carry the sound through to the diaphragm while keeping it in phase. Rear-facing pickup is useless if the sound waves cancel each other out.

The difference between a cardioid and its super and hyper siblings is the amount of sound permitted. Hyper cardioids are the most permissive iteration and bear a slight resemblance to a figure-8 or bi-directional pattern.

Cardioid polar pattern.
Hypercardioid polar pattern, note the additional pick up at rear or 180°.

Microphone types

A microphone’s design plays a major part in its sound and microphone placement. The types below utilize different designs, offer different levels of sensitivity, and each has its uses. All of these designs are a means of generating an electrical current that forms the basis of the signal supplied to the mic preamps. The ability to choose the most suitable tool is powerful!

Each of the following sections explains the characteristics of the design before providing a technical overview of how they work.

Dynamic

The passive nature of a dynamic microphone design tends to make them less sensitive overall, more so in the higher frequencies. This also has the effect of making them capable of taking higher sound levels. When it comes to tone, dynamic microphones are on the darker and warmer side. They can be used on everything from vocals, guitars, drums, and are ideal for close miking.

Dynamic microphone capsule. Notice the moveable diaphragm and voice coil layout.

Dynamic microphones operate through the principle of electromagnetic induction, which is when a conductive metal moves within a magnetic field, thus generating a current. The conductive material is the voice coil and the main moving element is the diaphragm. Acoustic pressure in the form of the sound waves moves the membrane in proportion to the sound’s amplitude and frequency. The mylar diaphragm then moves the attached voice coil, in turn inducing a current. Now we have a signal!

To be clear, dynamic microphones do not require any supplemental power to function. Besides the standard microphone preamps already used. This is an important difference between dynamic and condenser microphones. This also means that dynamic microphones are less sensitive, which is advantageous when dealing with louder sources.

Notable dynamic microphones: Shure SM57, Sennheiser MD 421-II

An aluminum ribbon suspended in a permanent magnetic field.

Ribbon

Today’s ribbon microphones see much more varied use, owing to years of design iterations. Traditionally they had a place in broadcast because of how good the human voice came across. What many refer to as “air” or presence.

Ribbon and dynamic microphones use the same electromagnetic induction method. They differ through the design and materials used for the diaphragm. Early designs used a thin aluminum ribbon, just 2 microns thick, suspended a strong magnetic field. The conductive aluminum strip moves due to sound pressure. As earlier, conductive metals moving in a magnetic produces a current and again signal.

Older ribbon microphones have some drawbacks. For example, the fragile ribbon material is susceptible to damage from high sound levels and rough handling. There is also the problem of accidentally applying +48v phantom power, resulting in the instant death of the thin aluminum strip. Lastly, the signal levels in ribbons struggle to compete with their dynamic cousins. That is why ribbons require an additional step-up transformer.

Modern Day Ribbon

The conventional and practical packaging of the Beyerdynamic M160. A new type of ribbon with a cardioid pattern.

Fortunately, modern improvements like miniaturization and stronger materials have made ribbon microphones more rugged and flexible. Corrugated aluminum ribbons provide increased strength.

Printed ribbon microphones use a polyester film with an aluminum ribbon printed on it. Ring magnets sit at the front and back of the diaphragm. The M160 is one such example.

Royer designed a flagship ribbon microphone for the 21st century by beefing up the internals and making the R121 capable of holding up to close-miking guitars and drums alike; all while retaining the signature Figure-8 polar pattern.

SE Electronics VR2 active ribbon microphone, a new perspective on an older design with a built in transformer and high frequency range.


There is one final type of ribbon microphone in need of mentioning, active ribbon microphones. Take the SE Electronics VR2, which uses an in-house design that packages the transformer internally and allows for higher output levels. Combined with SE’s ribbon design and the result is a powerful, versatile, and responsive ribbon mic. Combined with a 20Hz to 20KHz frequency response makes the VR2 all the more impressive.

Worthy mentions: Royer R121, Beyerdynamic M160, SE VR2

Condenser

The most sensitive microphone type around, condensers lend themselves well to higher frequencies and don’t come far behind the sound level ceilings of dynamic microphones. If anything this has only got better over the years. Condensers offer a good choice when looking for more sensitivity in the higher ranges and bringing more presence to a recording. They can be used in close or room miking arrangements.

A condenser microphone capsule, note the movable top plate and fixed back plate.

Condensers rely on the electrostatic principle to capture sound waves and produce a signal, they are essentially capacitors. Even the word condenser means capacitor.

This section will explain the details of operating a condenser microphone while staying fairly light on the technical details. Condenser microphones require an additional power source. Today, this comes standard as a switchable +48v phantom power on all interfaces and recorders.

The microphone capsule consists of two plates, a movable top plate and a fixed back plate. Once powered and both plates have reached an equal charge the unit becomes a microphone.

Sound waves impact the top plate and causing it to move, which in turn causes the overall charge or capacitance to change. Ignoring for a second the microphone impedance characteristics at play. It is this change in voltage, when captured, that produces a usable signal that is sent to the preamp.

Famous condensers: Audio Technica AT2020, AKG C214

References

  • General microphone theory
    • Modern Recording Techniques, 6th Edition. David Miles Huber; Robert E. Runstein
  • Cardioid polar pattern
    • https://upload.wikimedia.org/wikipedia/commons/9/93/Polar_pattern_cardioid.svg
  • Hypercardioid polar pattern
    • https://upload.wikimedia.org/wikipedia/commons/f/f3/Polar_pattern_hypercardioid.svg
  • Dynamic and Condenser diagrams
    • https://service.shure.com/Service/s/article/difference-between-a-dynamic-and-condenser-microphone?language=en_US
  • Ribbon microphone diagram
    • https://upload.wikimedia.org/wikipedia/commons/2/29/B%C3%A4ndchenmikrofon.svg
  • RE EV20
    • https://products.electrovoice.com/na/en/re20
  • Shure SM57
    • https://www.shure.com/en-GB/products/microphones/sm57
  • Sennheiser MD 421-II
    • https://en-uk.sennheiser.com/recording-microphone-broadcasting-applications-md-421-ii
  • Royer R121
    • https://royerlabs.com/r-121/
  • Beyerdynamic M160
    • https://europe.beyerdynamic.com/m-160.html
  • Shure WL184
  • Audio Technica AT2020
  • AKG C214
    • https://www.akg.com/Microphones/Condenser%20Microphones/C214.html?dwvar_C214_color=Black-GLOBAL-Current&cgid=Condenser%20Microphones#start=1
  • SE Electronics VR2
  • Rode VideoMic
    • http://www.rode.com/microphones/videomic

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Blag Ivanov
Blag spends his time between DevOps and audio. He works at a software company and is a contributing editor at Videomaker where he mainly focuses on, you guessed it, audio!