1. How does a microphone work?
  2. What's the difference between a dynamic and a condenser mic?
  3. What are polar patterns (cardioid, omni, etc.)?
  4. Why are some mics better for vocals and others are better for instruments?
  5. What kind of cables do microphones use?
  6. What is a mic pre, and do I need one?
  7. What is phantom power?
  8. How does a wireless mic or wireless instrument system work?
  9. What is "True Diversity" on wireless systems?
  10. Why use a wireless system?
  11. Which is better for wireless: UHF or VHF?
  12. How do I know what frequency to select for my wireless system?
  13. How far away can I go from the receiver?
  14. What do I do if I am getting interference?
  15. What are some other common problems that affect wireless systems?
1) How does a microphone work?
A microphone is a transducer. That means that like a speaker in reverse, its job is to change acoustic energy (sound in the air) to electrical energy. While different types of microphones use different ways to accomplish this, every microphone uses a diaphragm... a thin membrane that can respond to varying pressure waves in the air and, along with the mic's electronics, convert them into varying electrical signals. The diaphragm in a microphone works on precisely the same acoustic principal as the eardrum in your ear.

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2) What's the difference between a dynamic and a condenser mic?
The two main categories of microphones are dynamic and condenser mics. A dynamic mic is the most rugged type of mic, and requires no external power, since it generates its signal with electromagnet effects. Similar to the way a guitar pickup works, the diaphragm in a dynamic mic moves a magnet or a coil when sound waves hit the diaphragm, and the movement creates a small current. Dynamic mics can handle louder sources (guitar amps, drums, etc.) than condenser mics, which are more sensitive.

Condenser mics allow the movement of the diaphragm to be registered by the plates of a capacitor, creating an electrical signal that must then be amplified with a built-in amplifier. This means that the condenser mic must receive external power, usually through Phantom Power or via its own special power supply. Condenser mics are often chosen for their sensitivity, and resulting ability to capture a high level of detail for critical applications like studio vocal recording.

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3) What are polar patterns (cardioid, omni, etc.)?
Polar patterns shows how the microphone will respond directionally. There are only four main types of polar patterns:

Cardioid: A standard pattern for most mics. It has a slight amount of directionality toward one direction of the mic, which means it will sound louder from that direction and quieter from other directions.

Omni: An omni pattern picks up sound equally from all directions of the mic's diaphragm.

Hypercardioid: A super directional mic used in situations where you want to avoid having a mic mistakenly pick up other sounds surrounding the intended source.

Figure 8: Like the name implies, it picks up sound equally in the front and back direction (while canceling out sounds from the side directions).

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4) Why are some mics better for vocals and others are better for instruments?
Microphones are designed for specific applications based on two main factors: the dynamic range (degrees of loud and quiet the mic needs to reproduce) and the frequency response (the way the mic responds to low frequency bassy sounds versus high frequency trebly sounds). Therefore, mics can be "voiced" to best represent the sonic requirements of a voice versus a guitar or bass.

Mics for vocals also have features like built-in windscreens in the ball area that helps prevent the mic from popping from loud "p" and "b" sounds.

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5) What kind of cables do microphones use?
Most professional dynamic microphones use a cable called an XLR, with a corresponding connector on the bottom of the mic. The connectors and cables use a 3-pin configuration, which may be connected on the opposite end to PA systems, mixers, recorders, and other professional audio tools.

Some mics that require an external power supply may use special cables that carry the power to the mic. In those cases, the special cable is usually provided with the microphone.

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6) What is a mic pre, and do I need one?
A "mic pre" is short for "microphone preamplifier", and yes, you do require one. The electrical signal coming from your microphone is still very small, and a mic preamp is required for that signal to be loud enough for recording, or for further amplification into a PA system.

Luckily, many recording tools and PA systems have built-in mic preamps, so it may not be necessary for you to get a mic pre as a separate piece of gear. However, the quality of the mic preamp will have a big effect on the sound of the mic, and for a high-quality system, it's a good idea to have at least two channels of high-quality preamplification for important purposes like recording lead vocals.

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7) What is phantom power?
As discussed above, condenser microphones require power for functionality. Often, this power can be accessed via the normal XLR cable that connects the mic to a preamplifier, mixer, or other tool that provides +48V of power for the mic, called phantom power.

IMPORTANT NOTE: Dynamic mics (like most Digital Reference mics) DO NOT require phantom power, and sending phantom power to ANY dynamic mic could result in damaging the mic. Be sure that phantom power is not inadvertently turned on while a dynamic mic is plugged in.

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8) How does a wireless mic or wireless instrument system work?
Instead of using a cable to transmit signals, a wireless system uses radio transmission to accomplish the same purpose. Operating like a tiny FM radio station, your wireless mic has a miniature radio transmitter and a radio receiver. Unlike your car radio, your receiver is designed to only get one radio frequency (from the matching transmitter).For wireless lavalier mics and instruments, a body pack that clips on the a belt on in a pocket contains the transmitter.

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9) What is "True Diversity" on wireless systems?
True Diversity is a technology for wireless systems that uses two spaced antennas and two receiver channels tuned to the same frequency. The system automatically switches to the channel with the stronger signal, virtually eliminating dropouts and other signal loss problems.

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10) Why use a wireless system?
There are three main situations in which a wireless system is preferable over the use of a cabled instrument or microphone.

The first is freedom of movement. With a wireless instrument transmitter, for example, you don't have to worry about tripping over a cable that's become wrapped around your legs as you move about onstage. A wireless microphone gives you the ability to be a more dynamic performer, alleviating the need to be tethered to a certain spot. The possibility of a cable becoming disconnected, with the resulting panicky run back to re-plug your mic or instrument, is removed entirely.

The second reason for wireless is visual appeal. From coffeehouse gigs to theatrical performances, the aesthetic messiness of cables strewn around a stage is completely eliminated.

The third situation that calls for a wireless system is simple practicality and logistics. If you're on a particularly large stage, using an extremely long cable can cause your audio quality to denigrate with the added possibility of interference or cable damage. Other situations that involve the need to remotely access the signal can mean that a cable simply won't work as a functional solution.

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11) Which is better for wireless: UHF or VHF?
Like many choices in life, there's not a clear-cut "better or worse" decision when considering a UHF versus a VHF wireless system. As those of you who remember the days before cable and satellite transmission, UHF (Ultra High Frequency) and VHF (Very High Frequency) are frequency ranges used in television broadcasting. As they relate to wireless transmission of audio signals, both have inherent and respective advantages and disadvantages.

Most of the higher-end wireless systems function within the UHF frequency range, since UHF means that there is less chance of interference because of more available frequency spectrum. Also, the possibility of interference on a UHF system is somewhat lessened because there are fewer transmitters operating on UHF frequencies. Also, UHF is less likely to get noise interference from digital devices and computers.

On the downside, UHF wireless equipment almost always costs more than VHF, since more parts and more expensive construction is required for UHF systems to operate. UHF also has a lower battery life than VHF wireless systems, so you'll need to factor in the cost of battery replacement over the course of time. In a situation where you have a relatively low interference environment (and don't plan on traveling with your wireless system into different environments), VHF can provide a fine solution.

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12) How do I know what frequency to select for my wireless system?
On more advanced wireless systems, multiple frequency channels are available. The reason is simple: you want to use a frequency that no one else is using. Since a wireless system works on the same principles as a radio, you can imagine what would happen if two stations were broadcasting on the same frequency... sonic chaos.

The same thing applies to wireless systems. If a band's singer, backup singers and guitar player are on the same frequency, the signal from each respective source will be picked up by each of the receivers... the guitar will be coming through the PA, the vocals through the guitar amp, and so on. Even if the frequencies are not precisely the same, frequencies that are close together will cause interference.

To avoid this nightmare, the more advanced wireless systems allow you to select between several frequency choices so that each signal is only transmitted to the appropriate receiver. That way, the singer, background singers, and guitar player can each maintain their own signal integrity.

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13) How far away can I go from the receiver?
There are many factors that influence the functional distance between the transmitter and receiver.

One factor is that the government puts strict regulations on wireless systems, which include the maximum transmitter power. Why? Since there are only a certain number of frequencies to work with, a system that's too powerful could overwhelm TV or radio broadcasting in the area. More importantly, it could interfere with the transmission of public safety signals as used by police, emergency medical teams and so on.

Environmental factors also heavily affect the distance you can be from your receiver. In a crowded indoor situation, the signal from your transmitter needs to find its way to the receiver through many obstacles, and you may have less than 100 feet in which operation is practical. The same wireless system in an open outdoor environment may work as much as 1000 feet away.

Finally, the amount and type of interference from radio, TV, computers, digital equipment and other sources can become more prevalent the further away you move from the receiver. It's best to test out the distance while in a non-crucial situation, like a sound check. Simply take your wireless mic or instrument pack and play while walking away from the receiver, noting where you are when the signal starts to cut or become distorted. Keep in mind that when the room fills with people, you will have less range to work with.

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14) What do I do if I am getting interference?
The first thing to do is see if you can isolate the cause of the interference and eliminate it. However, this is often impractical, since the source may not be in your local vicinity.

If you have a multi-channel wireless system, try selecting a different operating frequency. Since the interference is likely to be isolated to a particular frequency (or small frequency range), it's likely that this will automatically solve the problem.

If you don't have a multi-channel system, another method is to move closer to your receiver. Unless the interfering signal is of much greater strength than your own transmission, the receiver will likely pick up the signal with the closest proximity.

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15) What are some other common problems that affect wireless systems?
One issue that may seem obvious is that if there's not a clear open-air path between the transmitter and the antennae of the receiver, the signal will not be received well (or at all, in extreme cases). Make sure the receiver is placed so that there's a direct line of sight to your transmitter at all times.

The most common problem that affects wireless systems may also seem obvious, but is frequently overlooked. If the batteries in your transmitter are weak or worn-out, you will experience poor performance that will range from distorted audio and interference through complete failure. Always have extra batteries with you when you perform with any wireless system, and make sure the batteries are fresh. You should only use high-quality alkaline batteries, since most other types of batteries won't last as long and may cause other problems as well.

Since your wireless microphone gives you the freedom to move about a stage, don't forget that walking in front of speakers will probably cause feedback.

Finally, a brief safety note: the power output of wireless mics and instrument systems is very low and completely safe under normal circumstances. However, people who have cardiac pacemakers and similar medical devices need to be cautious about using wireless systems in the same way they are about being around other electronic devices like microwave ovens. Never place a body-pack transmitter adjacent to such a medical device.

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