Some Basic Concepts

The Basic Sound System | Condenser and Dynamic Microphones | Microphone Pickup Patterns | Protection from Radio Frequency Interference | About RFI

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.



Some Microphone Basics


Condenser and Dynamic 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 two-conductor shielded cable used to carry the microphone’s output signal. Phantom power has no effect on the sound of the system.

Dynamic microphones are renowned for their ruggedness and reliability. They can take quite a bit of abuse and need no batteries or external power supplies. They are capable of smooth, extended response, or are available with tailored response for special applications. Many have a small presence peak making them ideal for vocals that need to punch through a mix. Their output levels are high enough to work directly into most microphone inputs with an excellent signal-to-noise ratio. They need little or no regular maintenance, and with reasonable care will maintain their performance for many years.

Dynamic microphones are a great all around choice for hand held vocals, high SPL instruments such as drums and guitar amps as well as general communication applications. On the down side, because of their mechanical design, dynamic microphones are typically large. With this type of microphone, miniaturization results in reduced low-frequency response, overall loss of acoustic sensitivity and higher mechanical or handling noise. Dynamic mics can also be less sensitive to subtle nuances or small transients, and they may have frequency response limits in the higher frequencies due to their mechanical nature.

Microphone Pickup Patterns
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.



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 MicroLine® and UniLine® 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. A bidirectional or figure-of-8 microphone pattern, with two equal lobes 180 degrees apart, is equally sensitive to sound originating in front and back of the element. Figure 4 summarizes the performance of different pickup patterns.

Audio-Technica’s UniGuard® technology

Protection from Radio Frequency Interference
Maybe you hear RFI as a buzz. Or a crackle. Or even an uninvited voice from a nearby radio station. With the proliferation of cell phones, computers and other technology, the annoyance of Radio Frequency Interference in sound systems is more of a problem than ever before.

Audio-Technica has developed a design innovation–UniGuard®– that protects Engineered Sound® and UniPoint® microphones from interference. With UniGuard, it’s as if there’s an invisible shield guarding the microphones, creating a safe haven from RFI.

UniGuard comprises 13 individual Audio-Technica patents, a total system for RFI protection that impacts every aspect of the design and production of A-T’s Engineered Sound and UniPoint lines of installed-sound miniature condenser microphones.

Each UniGuard microphone is a completely shielded enclosure, offering paint free connection points as well as custom RFI-shielding and filtering on all input and output connectors. Audio-Technica has also improved each microphone’s shield termination to solve the pin 1 problem, a common cause of RF interference in condenser microphones.

About RFI
RFI sources run the gamut from cell phones and other wireless communication devices to AM, FM and television broadcasts, and radiated noise from lighting. Wireless communication devices are special culprits because they are typically used in close proximity to condenser microphones in installed-sound settings, and they operate on very short wavelengths that are particularly challenging to filter and shield.



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