Abstract
Music educators commonly use microphones for live and recorded sound applications. To achieve optimal results in each application, a basic understanding of microphones is necessary. This article discusses each application’s challenges and recommends the best mic to use for optimum sound. Recommendations for further learning are included.
Each year, music technology carves deeper inroads into formal music education settings. This makes it essential that music educators keep abreast of innovative advances in music technology and continue to learn more about current music technology. Microphones serve as a prime example. Invented in the late-19th and early-20th centuries, they are among the most used and critical implementations of music technology. In this column, I offer music educators insights into live and recorded sound—the two most common applications for which microphones are used. I discuss the challenges each application presents, suggest microphone types for various situations, and offer other remedies for common sonic problems related to microphone use. In summary, I list attributes of three different types of microphones that will enable music educators to make informed decisions about their use of microphones for their specific settings.
Mics for Live Sound
Selecting appropriate microphones to amplify sound for a live audience needs special attention. Many variables exist in live situations that can cause problems and lead to a less than satisfactory, or even unhealthy, listening experience for performers and audience members.
One set of variables is the structural factors of a room or staging area. In schools, the two areas that most frequently serve as performance spaces are the gymnasium/cafeteria and the theater/auditorium: two very different spaces with respect to sound. Gymnasiums are typically large spaces with hard surfaces that send sound waves bouncing in every direction and accentuate unwanted low frequencies, making feedback and “boominess” a constant challenge. Stages in gymnasiums tend to be shallow—meaning the distance between the stage front and back wall is generally small—and contain hard surfaces that reflect sound back into microphones, creating the dreaded feedback squeal. In contrast, a school’s theater typically contains padded seats, soft walls, and heavy stage curtains. This “soft” material makes the room sound “dry” compared with a gymnasium’s “wet” sound.
The number of performers and types of instruments needing to be amplified is a second set of variables influencing microphone selection. The potential for sound problems increases when more than one microphone is used. If a vocal group uses eight microphones, with one singer per microphone, microphone selection—along with careful consideration of the distance between the microphones and their placement—will be crucial in minimizing problems. If three or more microphones are used to amplify a piano and other instruments, the potential for problems increases further.
A third set of variables is decisions about microphones, including audience size and atmospheric conditions of the venue. The sound of a particular space can change drastically after the audience arrives. Human bodies absorb rather than reflect sound, thus decreasing the amount of sound waves reflected off walls and other hard surfaces. Human bodies, however, also “swallow” high frequencies. Even the atmospheric conditions within a particular room make a difference in sound! I have heard music educators say, “The mixer is now set; nobody touch anything before tomorrow’s concert.” The next day happens to be a rainy, moist day, changing how sound waves move within the space, and the teacher is shocked to find that the mix has to be changed because the humidity in the room changed overnight.
Variables that include structural factors of the room or stage, the number of singers, types of instruments, the audience size, and the room’s atmospheric conditions—and their various interactions—are important considerations for microphone selection for a particular space. With these variables in mind, what follows are microphone recommendations that, because of their inherent properties, will prove as suitable choices when wishing to put your best mic forward.
Microphones are transducers; they convert one form of energy (sound waves) into another form of energy (an electrical signal). Of the three distinct types of microphones—condenser, dynamic, and ribbon—the first choice for vocalist in live sound applications is a dynamic microphone. In a dynamic microphone, sound waves strike the microphone’s diaphragm, which, suspended in a magnetic field, generates a tiny electrical signal. This electrical signal is then boosted to a higher level that can be used by a mixer, a more powerful amplifier, and speakers.
Several characteristics of dynamic microphones make them especially suitable for use in live sound applications and particularly with singers 1 :
Dynamic microphones can have rugged construction, making them capable of surviving hard use and the bumps and accidents that accompany such use.
Dynamic microphones, again because of the nature of their construction, can often handle very high “sound pressure levels”; they can be used to mic very loud sound sources without distorting the signal they produce.
Dynamic microphones generate a very low level of “self-noise” (the “hiss” generated by the more complex type of electronic circuitry found in condenser-type microphones).
Dynamic microphones are relatively inefficient and insensitive, making them less prone to unwanted sounds entering or reentering the microphone (e.g., the sound of a nearby instrument, or particularly strong frequencies that could begin a feedback loop).
Dynamic microphones are good choices for live applications (especially with singers) because they can be manufactured with a “unidirectional” polar pattern.
There are three fundamental polar patterns that microphones exhibit—omnidirectional, unidirectional, and bidirectional:
Omnidirectional: The microphone is (more or less) equally sensitive to sounds arriving from the sides, rear, and front of the microphone.
Unidirectional: The microphone is most sensitive to sounds arriving from the front of the microphone (“on-axis”), and sounds coming from the sides or rear of the microphone are minimized or rejected.
Bidirectional: The microphone is equally sensitive to sounds coming from the front and rear, but minimizes sound from the sides (see Figure 1).
From left to right: the omnidirectional polar pattern; the cardioid patterns: cardioid, hypercardioid, supercardioid, and shotgun; the bidirectional pattern
A unidirectional microphone can be manufactured with various degrees of pickup and rejection. The most common of the unidirectional patterns is the “cardiod” pattern, so named because its shape on a polar response graph resembles a human heart. “Supercardioid,” “hypercardioid,” and “shotgun” polar patterns are variations of the unidirectional pattern, with each type having a narrower angle of pickup in front of the microphone. Therefore, a dynamic microphone with a unidirectional polar pattern is well suited for live sound applications because it is most sensitive to the sound coming from in front of it and rejects sounds from its the sides and rear. Because of this, feedback and other sound problems can be minimized at their point of origin: the microphone itself.
Ways to eliminate sound problems when using dynamic microphones in live applications include the following:
Roll off the bass. Some dynamic microphones have switches to decrease low frequencies, thereby eliminating “room rumble” and “boom.” These are commonly termed “bass roll off switches.”
Use a wind screen. Wind screens are balls of foam or coverings of fur-like material that minimize the “plosive effect” caused by consonants during speech production (“p”s and “b”s, and sometimes “d”s and “t”s).
Use a shock mount. A shock mount—an accessory for a microphone stand that isolates the microphone from physical vibrations—can minimize the sounds of feet tapping or a pianist’s forceful use of the sustenuto pedal.
Carefully place microphones around monitors. Moving a microphone a mere 4 inches can sometimes eliminate a stubborn feedback problem. No matter the type of situation or microphone being used, microphone placement is crucial for optimal sound results.
Mics for Recording Sound
Essentially, there are three levels of making a live or critical music recording. The first is setting one or two microphones on microphone stands, pointing them at the sound source, making level adjustments on the recording device, and pushing record. This might be termed the “hope-the-recording-turns-out-well” method and requires little or no formal knowledge about microphones or the recording process. The second is purchasing a handheld digital recorder with two microphones built on to the unit. Depending on the quality of the recorder’s circuitry and built-in microphones, the results with such a device can sound quite good. If, however, one wants to make a good critical musical recording, one must know the basics of how to select and use microphones for that purpose. In this portion of the article, I will discuss the challenges of making a critical recording, offer two microphone recommendations, and mention other remedies that will assist in making successful recordings.
In any given critical recording situation, there are several considerations when selecting microphones and for methods of use. One consideration is how much of the “ambient sound” (i.e., the “room sound”) is wanted in the recording. Selecting an omnidirectional polar pattern—a polar pattern that receives sound from every direction—will result in more “room sound” in the recording; selecting a cardioid polar pattern—a pattern that “rejects” sound from the sides and rear of the microphone—will result in a recording with less “room sound.” In addition to the microphones’ response pattern, the distance the microphone is placed from the sound source will affect the ratio of the sound source and the room’s sound in the recording.
A second consideration in selecting a microphone for recording is the nature of the sound source. Over the course of a century, professional engineers have developed numerous preferences. Brass instruments and choral groups, for example, can sound glorious recorded with a ribbon microphone, because a ribbon microphone’s naturally “smooth sound” lends warmth and smoothness to recordings. Although experienced recording engineers have developed such preferences, in the final analysis, experimenting with various microphones is the best way to discover, confirm, or reject such preferences.
A third consideration is a nexus of three factors: a microphone’s “self-noise” level, its ability to handle high sound pressure levels before distorting, and the quality of the microphone preamplifier with which the microphone is paired. While at least two of the considerations border on the esoteric—few educators, for example, have a $2,000 microphone preamplifier to use or the budget to purchase one—these considerations are consequential to making a high-quality critical recording.
When using a condenser microphone, the amount of noise (heard as “hiss”) the microphone’s electronic circuitry generates is sometimes so “loud” as to be audible on very soft passages of recorded music. This requires teachers to seek out a “quiet” microphone. (In specifications, these mics will have a self-noise of 10 dB to −16 dB; the lower the number, the better. A microphone generating 16 dB of noise is “louder” than one generating 12 dB.)
If the sound source you are recording is loud—such as a wind band or larger orchestra—be sure your microphone can handle a high sound pressure level. Bartlett and Bartlett (1992), in Practical Recording Techniques, note that a microphone with a maximum sound pressure level “. . . of 120 dB is good, 135 dB is very good, and 150 dB is excellent” (p. 118). To put this in some perspective, a typical human conversation from one foot away is about 70 dB, and a painfully loud sound is 120 dB.
The final factor—combined with a microphone’s self-noise and capability to withstand loud sound sources without distortion—is the preamplifier with which a microphone is paired. It should be noted that the microphone preamplifier specifications in most recently manufactured mixers is acceptable for making a very good recording. Thus, unless “the final degree of audio excellence” is needed and affordable, the preamplifiers in mixers will serve music educators quite adequately. Nonetheless, a high-quality microphone preamplifier can improve even the most basic microphone sound better than average or below-average microphone preamplifiers, which make it a worthy consideration.
Selecting and obtaining a high-quality microphone preamplifier is challenging, and this is not because of cost alone. Every high-quality microphone preamp sounds different; each “colors” the sound from the microphones differently. Even if the specifications on paper are nearly identical, differences in sound exist from one preamplifier to the next—especially to the musically trained ear. How, then, to know which preamplifier will suit a particular purpose, and work well with the microphones your school owns? This is an area where r-esearching your purchase “pays off” handsomely. Internet sites devoted to recording exist and often have professionals “chime in” and offer opinions. Additionally, professional audio dealers almost always offer return guarantees that allow the preamplifier to be returned if it does not meet your needs.
Ways to eliminate sound problems when using condenser microphones in critical recording applications include the following:
Turn off all heating and air conditioning systems, fans, and electric motors when recording. These systems are so omnipresent that they tend to be “invisible noise”—but microphones amplify the sound loud and clear.
Use a shock mount with condenser microphones. A shock mount is essential in critical recording situations.
Experiment and learn. Making a good sounding critical recording is a genuine accomplishment. If your first few attempts do not result in the sound you want, keep experimenting and learning.
Summary
A quality dynamic microphone is a good “first choice” option for singers, and often instrumentalists, in live applications. Dynamic microphones are typically built rugged and can handle high sound pressure levels. Having low sensitivity, dynamic microphones—especially those with a cardioid polar pattern—acceptably minimize annoying feedback in sound systems.
A ribbon microphone is bidirectional by nature and therefore receives sound from the front and back of the microphone. This polar pattern makes a ribbon microphone a fine choice when desiring to capture a room’s sound. In addition, a ribbon’s smooth high-frequency response minimizes harsh high harmonics, lending a beautiful “naturalness” to the sound it captures. Greater care is needed when handling and using ribbon microphones. A sudden large puff of air from a vocalist or a gust of wind outdoors can destroy the mic’s ribbon, requiring the ribbon to be replaced. Moreover, it is vital that the microphone preamplifier possesses a very low self-noise level, and be capable of boosting the microphone’s signal by 60 to 70 dB.
Condenser microphones are well regarded for their wide frequency response, their sensitivity, and the detailed sound they capture. An omnidirectional condenser has a near flat frequency response at the low and high ends of the audio spectrum, making such a microphone accurate for capturing low and high sounds. A unidirectional condenser is a fine choice for when a microphone with high sensitivity, detailed sound, and the ability to minimize sounds at the back and sides of the microphone is needed.
Equipped with the knowledge presented here, you are now on the path to putting your best mic forward, and ready to capture performances and recordings with success.
Footnotes
Declaration of Conflicting Interests
The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.
Funding
The author(s) received no financial support for the research, authorship, and/or publication of this article.