Some Basic Concepts
FIGURE 1: Example of a Multi-microphone Sound System
The Basic Sound System
| Why Condenser Microphones
| Why Unidirectional Microphones
The Basic Sound System
The sound system begins at the microphones where acoustic sound is converted into an electrical signal. Our example below has four microphones - one for the podium, one for the piano and two for the choir (Fig. 1). The microphones are connected to an audio mixer where their input signals are amplified, adjusted and combined to produce a single output signal. (Note that if an auxiliary phantom power source for the mics is required, it must be placed between the microphones and the mixer.)
From the mixer, the output signal is sent to a power amplifier. The amplifier strengthens the signal further, making it powerful enough to drive loudspeakers, which convert the microphone signals back into acoustic sound.
Why Condenser Microphones
One way microphones are classified is by how they convert sound energy to an electrical signal. The most common types are "dynamic" and "condenser." In a place of worship, condenser microphones offer a number of advantages over dynamics. First, condenser microphones can be made much smaller (and less conspicuous) than dynamics without compromising performance. They also have higher sensitivity for excellent pickup, even at the distances required by hanging choir mics. They have lower handling noise than dynamics, and their extended frequency response provides a crisper, more accurate reproduction of sound. Finally, condenser mics have superior "transient response" for accurately reproducing sudden sonic impulses such as those produced by voice, piano and percussion.
Condenser microphones require a power source for their internal electronics. Some models can receive power from an internal battery. Others may be "phantom" or "remote" powered. Phantom power supplies, built into some mixers and also available as Audio-Technica accessories, deliver low DC voltage to the microphone over the same 2-conductor shielded cable used to carry the microphone's output signal. Phantom power has no effect on the sound of the system.
FIGURE 2 & 3: Omnidirectional Microphone (left) and Unidirectional (Cardioid) Microphone (right)
Why Unidirectional Microphones
Another way to identify microphones is by their directional properties, that is, how much sound they pick up from various directions.
"Omnidirectional" microphones pick up sound almost equally well from all directions (Fig. 2). While they must be used close to the sound source wherever feedback is a possibility, "omnis" offer reduced sensitivity to handling noise and breath blasts, making them ideal for many clip-on mic applications.
In a place of worship, however, most applications are better served by unidirectional types of microphones described as "cardioid" (Fig. 3). These microphones pick up sound best within a 120° conical area at their front called the "acceptance angle." Outside the acceptance angle, microphone sensitivity is reduced. A sound source located at a 90° angle to the side of the microphone will seem to be twice the distance away as the same source located directly in front. And, when the same source is directly to the rear of the microphone (at the angle of minimum sensitivity, or "null"), it will seem to be about 10 times as far away.
By pointing the microphone directly at the desired sound source, with the null of the microphone facing any unwanted sound (such as a sound reinforcement loudspeaker), problems with feedback and echo will be reduced. The result is improved intelligibility of speech at a greater "working distance."
FIGURE 4: Basic Polar Patterns
Hypercardioid models extend the working distance farther, with their 100° acceptance angle providing greater rejection of sound from the sides. Even more side cancellation is offered by A-T MicroLineŽ models. Their narrow 90° acceptance angle and higher output make them a good choice for more distant pickup of sound. They also improve clarity in reverberant or otherwise noisy environments. Figure 4 summarizes the performance of different pickup patterns.
Continue to the next section (Specific Applications)
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