Hand-held Speech Microphone
The desired sound source, for a hand-held micro-phone, is a speaking voice.
Undesired sounds may include loudspeakers, other talkers, ventilation noise, and other various ambient sounds.
Suitable microphone performance for this application can be provided by dynamics or condensers. Due to frequent handling and the potential for rough treatment, dynamic microphones are most often used, though durable condensers are also available.
The preferred frequency response is shaped with a presence rise for intelligibility and low roll-off for control of proximity effect and handling noise.
Handheld Mic
These microphones are typically unidirectional. A cardioid pattern is most common, while supercardioid and hypercardioid types may be used in difficult noise or feedback situations.
Balanced low-impedance output configuration is standard while sensitivity may be moderate-to-low due to the higher levels from close-up vocal sources.
Finally, the physical design is optimized for comfortable hand-held use, and generally includes an integral windscreen/pop filter and an internal shock mount. An on-off switch may be desirable in some situations.
Placement of hand-held microphones at a distance of four to twelve inches from the mouth, aimed towards it, will give good pickup of the voice, relative to other sources.
In addition, locating the microphone slightly off-center, but angled inward, will reduce breath noise.
With high levels of unwanted ambient noise, it may be necessary to hold the microphone closer. If the distance is very short, especially less than four inches, proximity effect will greatly increase the low frequency response.
Though this may be desirable for many voices, a low frequency roll-off may be needed to avoid a “boomy” or “muddy” sound. Additional pop filtering may also be required for very close use.
Use of rugged, flexible cables with reliable connectors is an absolute necessity with hand-held microphones.
A stand or holder should also be provided if it is desirable to use the microphone hands-free. Finally, the correct phantom power should be provided if a condenser microphone is used.
Good technique for hand-held microphone use includes:
• Do hold microphone at proper distance for balanced sound.
• Do aim microphone toward mouth and away from other sounds.
• Do use low frequency roll-off to control proximity effect.
• Do use pop filter to control breath noise.
• Don’t create noise by excessive handling.
• Do control loudness with voice rather than moving microphone.
Lavalier
The desired sound source, for a lavalier microphone, is a speaking voice.
Undesired sources include other talkers, clothing or “movement” noise, ambient sound, and loudspeakers.
A condenser lavalier microphone will give excellent performance in a very small package, though a dynamic may be used if phantom power is not available or if the size is not critical.
Lavalier microphones have a specially shaped frequency response to compensate for off-axis placement (loss of high frequencies), and sometimes for chest resonance (boost of middle frequencies) .
The most common polar pattern is omnidirectional, though unidirectional types may be used to control excessive ambient noise or severe feedback problems.
However, unidirectional types have inherently greater sensitivity to breath and handling noise.
Balanced low-impedance output is preferred as usual. Sensitivity can be moderate, due to the relatively close placement of the microphone. The physical design is optimized for body-worn use.
This may be done by means of a clip, a pin, or a neck cord. Small size is very desirable.
For a condenser, the necessary electronics are often housed in a separate small pack, also capable of being worn or placed in a pocket.
Lavalier Mic
Some condensers incorporate the electronics directly into the microphone connector. Provision must also be made for attaching or routing the cable to minimize interference with movement. Wireless versions simplify this task.
Placement of lavalier microphones should be as close to the mouth as is practical, usually a few inches below the neckline on a lapel, a tie, or a lanyard, or at the neckline in the case of a woman’s dress.
Omnidirectional types may be oriented in any convenient way, but a unidirectional type must be aimed in the direction of the mouth.
Avoid placing the microphone underneath layers of clothing or in a location where clothing or other objects may touch or rub against it.
This is especially critical with unidirectional types. Locate and attach the cable to minimize pull on the microphone and to allow walking without stepping or tripping on it.
A wireless lavalier system eliminates this problem and provides complete freedom of movement. Again, use only high quality cables, and provide phantom power if required.
Good technique for use of lavalier microphones includes:
• Do observe proper placement and orientation.
• Do use pop filter if needed, especially with unidirectional.
• Don’t breathe on or touch microphone or its cable.
• Don’t turn head away from microphone.
• Do mute lavalier mic when using lectern or table microphone.
• Do speak in a clear and distinct voice.
Audience
The desired sound source is a group of talkers.
Undesired sound sources may include loudspeakers and various ambient sounds.
The use of audience microphones is governed, to some extent, by the intended destination of the sound.
In general, high level sound reinforcement of the audience in a meeting facility is not recommended.
In fact, it is impossible in most cases, unless the audience itself is acoustically isolated from the sound system loudspeakers.
Use of audience microphones to cover the same acoustic space as the sound system loudspeakers results in severe limitations on gain before feedback.
The absolute best that can be done in this circumstance is very low level reinforcement in the immediate audience area, and medium level reinforcement to distant areas, such as balconies or foyers.
Destinations such as isolated listening areas, recording equipment, or broadcast audiences, can receive higher levels because feedback is not a factor in these locations.
A condenser is the type of microphone most often used for audience applications.
Audience Mic
They are generally more capable of flat, wide-range frequency response. The most appropriate directional type is a unidirectional pattern, usually a cardioid.
A supercardioid or a hypercardioid may be used for slightly greater ambient sound rejection.
Balanced low-impedance output must be used exclusively and the sensitivity should be high because of the greater distance between the source and the microphone.
This higher sensitivity is also easier to obtain with a condenser design.
The physical design of a microphone for audience pickup should lend itself to some form of overhead mounting, typically hanging. It may be supported by its own cable or by some other mounting method.
Finally, it may be a full size microphone, or a miniature type for unobtrusive placement.
A particular method that is sometimes suggested for overhead placement is a ceiling-mounted microphone, usually a boundary microphone. This position should be used with caution, for two reasons.
First, it often places the microphone too far from the desired sound source, especially in the case of a high ceiling. Second, the ceiling, in buildings of modern construction, is often an extremely noisy location, due to air handling noise, lighting fixtures, and building vibration.
Remember that a microphone does not reach out and capture sound. It only responds to the sound that has travelled to it. If the background noise is as loud or louder at the microphone than the sound from the talker below, there is no hope of picking up a usable sound from a ceiling-mounted microphone.
Placement of audience microphones falls into the category known as area coverage. Rather than one microphone per sound source, the object is to pick up multiple sound sources with one (or more) microphone(s).
Obviously, this introduces the possibility of interference effects unless certain basic principles, such as the “3-to-1 rule”are followed.
For one microphone, picking up a typical audience, the suggested placement is a few feet in front of, and a few feet above, the heads of the first row. It should be centered in front of the audience and aimed at the last row.
In this configuration, a cardioid microphone can cover up to 20-30 talkers, arranged in a rectangular or wedge-shaped section.
For larger audiences, it may be necessary to use more than one microphone. Since the pickup angle of a microphone is a function of its directionality (approximately 130 degrees for a cardioid), broader coverage requires more distant placement.
As audience size increases, it will eventually violate the cardinal rule: place the microphone as close as practical to the sound source.
In order to determine the placement of multiple microphones for audience pickup, remember the following rules:
1) The microphone-to-microphone distance should be at least three times the source-to-microphone distance (3-to-1 rule).
2) Avoid picking up the same sound source with more than one microphone.
3) Use the minimum number of microphones necessary.
For multiple microphones, the objective is to divide the audience into sections that can each be covered by a single microphone. If the audience has any existing physical divisions (aisles or boxes), use these to define basic sections.
If the audience is a single large entity, and it becomes necessary to choose sections based solely on the coverage of the individual microphones, use the following spacing: one microphone for each lateral section of approximately 8 to 10 feet.
Microphone Positioning For Audience Pick-Up
If the audience is unusually deep (more than 6 or 8 rows), it may be divided into two vertical sections of several rows each, with aiming angles adjusted accordingly.
In any case, it is better to use too few microphones than too many.
Once hanging microphones are positioned, and the cables have been allowed to stretch out, they should be secured to prevent turning or other movement by air currents or temperature changes.
Fine thread or fishing line will accomplish this with minimum visual impact.
Use only high quality cables and connectors, particularly if miniature types are specified.
Many older meeting facilities are very reverberant spaces, which provide natural, acoustic reinforcement for the audience, though sometimes at the expense of speech intelligibility.
In spaces like this, it is often very difficult to install a successful sound system as the acoustics of the space work against the system.
Most well-designed modern architecture has been engineered for a less reverberant space, both for greater speech intelligibility, and to accommodate modern forms of multimedia presentations. This results in a greater reliance on electronic reinforcement.
The use of audience microphones is normally exclusively for recording, broadcast, and other isolated destinations. It is almost never intended to be mixed into the sound system for local reinforcement.
If it is desired to loudly reinforce an individual member of the audience, it can only be done successfully with an individual microphone placed amid the meeting participants: a stand-mounted type that the member can approach or a hand-held type (wired or wireless) that can be passed to the member.
Good technique for use of audience microphones includes:
• Do place the microphones properly.
• Do use minimum the number of microphones.
• Do turn down unused microphones.
• Don’t attempt to “over-amplify” the audience.
• Do speak in a strong and natural voice
Non-Meeting Applications
Today, the life of meeting facilities extends far beyond just meetings, to include classes, plays, and social events.
Sound systems can play an important role in all of these situations.
While it is not possible to detail microphone techniques for every application, a few examples will show how to use some of the ideas already presented.
Though most classrooms are not large enough to require the use of a sound system, it is sometimes necessary to record a class, or to hold a very large class in an auditorium.
In these cases, it is suggested that the teacher wear a wireless lavalier microphone to allow freedom of movement and to maintain consistent sound quality.
If it is desired to pick up the responses of students, it is possible to use area microphones in a recording application, but not with a sound system.
A better technique is for questions to be presented at a fixed stand microphone, or to pass a wireless microphone to the student.
Microphone use for plays and other theatrical events involves both individual and area coverage. Professional productions usually employ wireless microphones for all the principal actors.
This requires a complete system (microphone, transmitter, receiver) for each person, and the frequencies must be selected so that all systems will work together without interference.
While it is possible to purchase or rent a large number of wireless systems, it is often more economical to combine just a few wireless systems with area microphones for the rest of the players.
Use unidirectional boundary microphones for “downstage” (front) pickup, and use unidirectional hanging micro-phones for “upstage” (rear) pickup. Always use a center microphone, because most stage action occurs at center stage.
Use flanking microphones to cover side areas but observe the 3-to-1 rule and avoid overlapping coverage. Turn up microphones only as needed.
Social events, such as dances, generally require only public address coverage. Use unidirectional, hand-held or stand mounted microphones. Dynamic types are excellent choices, because of their rugged design.
The microphone should be equipped with an on-off switch if it is not possible to turn down the microphone channel on the sound system. In any case, turn up the microphone(s) only as needed.
Outdoor use of microphones is, in some ways, less difficult than indoor. Sound outdoors is not reflected by walls and ceilings so that reverberation is not present. Without reflected sound, the potential for feedback is also reduced.
However, the elements of nature must be considered: wind, sun, and rain. Because of these factors, dynamic types are most often used, especially in the likelihood of rain. In any case, adequate windscreens are a must.
Microphone principles are the same outdoors, so unidirectional patterns are still preferred. Finally, because of frequent long cable runs outdoors, balanced low-impedance models are required.
Conclusion
Though it is one of the smallest links in the audio chain, the microphone is perhaps the most important.
As it is the connection between sound source and the sound system, it must interact efficiently with each. Choosing this link successfully requires knowledge of sound and sound systems, microphones, and the actual application.
This article has included the basic principles not only of microphones but also of sound and sound systems.
Through the examples given, the correct selection and use of microphones for a variety of meeting facility sound requirements has been indicated. Applying these basic principles will assist in many additional situations.
The subject of microphone selection and application for meeting facility sound systems is ever changing, as new needs are found and as microphone designs develop to meet them.
However, the basic principles of sound sources, sound systems, and the microphone that links them remain the same, and should prove useful for any future application.