1. Microphones
One of the most important decisions you will make for your sound is choosing the right microphone. With so many different microphones available, this choice can be a chore unless you know what to look for.

Types of Microphones: Dynamic and Condenser
Dynamic microphones are the most popular and widely used as they are economical, hardwearing, and supply their own power. They are proven all-purpose microphones with exceptional performance.

Condenser (or Electret) microphones are well known for their high sensitivity to sound making them preferable for high quality studio recordings and special applications such as speech, music or overhead choir installations. These microphones also require power from an outside source such as batteries or a mixing console to operate-this power is known as phantom power. Unlike the dynamic microphone, a condenser mike does not make its own voltage and will not work without phantom power.

What is Phantom Power?
Phantom Power is a method of power for condenser microphone circuitry. This power adds a phantom voltage (usually +48V) generated from mixing consoles, mic preamplifiers, batteries, or in-line phantom power supplies. You may use any one of these depending on which one your condenser microphone requires.

Microphone Pickup Patterns
A Microphone Pickup Pattern identifies how your microphone picks up sound for amplification. The figure below illustrates some of the more popularly applied pickup patterns being used.

Microphone Frequency Response
A frequency response measures how well a microphone picks up different sound frequencies. Most provide a wide-ranging response that allows the microphone to respond well with most any application.

Wired Microphone Connectors (Cables)
There are two ways to connect a microphone to your equipment: either an unbalanced line (¼" jack or 3.5mm plug), or balanced line (usually XLR).

When connecting microphones and sound equipment together, make sure the inputs and outputs have a matching voltage level. There are two important voltage levels to remember; microphone level and line level.

Microphone level - This is the output voltage of microphones. It is a very small voltage of one millivolt (.001 volt). A microphone level output must be routed to a microphone level input.

Line level - This is the interconnecting voltage level of devices such as CD players, tape decks, audio mixers, and most all other non-microphone audio equipment. This voltage is one volt (1 volt). A device that is not a microphone uses a line level connection. Line level inputs and outputs are also called auxiliary inputs and outputs. A line level output MUST be routed to a line level input!

IMPORTANT! - Speaker output should never be confused with mic or line level. Speaker output levels can be very high, so ONLY connect speaker inputs to a speaker output!

Microphone and Line Level Mixing
An audio mixer will usually have both microphone level and line level inputs. This is how Microphone level and line level devices may be combined into a single audio signal. A mixer allows the level of each input to be controlled individually.

2. Amplifier (or Powered Mixer)
A chain is only as strong as its weakest link. Without a doubt, the most crucial link in the chain of any sound system is the power amplifier. An amplifier boosts sound for your un-amplified voice or instrument giving it strength enough to drive one or several loudspeakers at once. Amplifiers have ratings for the same characteristics that speakers have (expressed as ohms=W or watts). They are designed to drive a particular impedance, and they put out a certain amount of power.

Another kind of amplifier is one you find already built-in a mixer, also called a powered mixer. Most small box-style units with 4 to 16 channels will have a power amplifier built-in. The much larger mixing consoles with 8 to 40 channels usually are not powered and receive external power from an amplifier in order to send signals to the speakers.

For large sound installations, it's a good idea to have your amplifier installed as a separate component. However, for smaller installations and portability, a powered mixer is an easy, cost-effective solution.

Amplifiers are built for long-term, permanent installations where reliable sound amplification is required. They are specifically built with protection schemes that prevent damage to either the amplifier or your speakers. For instance, "spikes" or "surges" in power, thermal protection against overheating, signal suppression and filters to automatically turn down a signal that is too high (to keep it from clipping) or remove low frequencies that waste power.

Power and Cooling Requirements
Excessive heat is one of the main reasons that any sound system component will fail. As impressive as electronic technology can be, it cannot overcome one fact: Where there is power, there is heat. Power amplifiers still need air to keep cool. This means the vents should never be blocked and that sufficient room be allowed above, below and behind your amp. This is especially important for rack-mounted equipment where this is a close proximity of several heat-generating devices.

Amplifiers generate large amounts of heat with normal operation and or the most likely component of a sound system to succumb to heat. Most have sensing circuitry or built-in fans that protect the amp if internal temperatures exceed a certain level.

A Power Rating states the power that unit will deliver to a specified load-at a specified distortion level, and over a specified frequency range. Sometimes termed RMS (Root Means Squared), which refers to a method for calculating average power. For stereo amps, a figure of watts power channel is given.

Frequency Response measures how accurately the output of the device reproduces the input across the frequency spectrum-an important specification for devices in all points of the sound chain.

Power Bandwidth is the measure of an amplifier to produce high output power over a wide frequency range and thus complements the standard power specification, which tells more about performance. It is frequency related-sometimes given as a numerical bandwidth.

Matching Amplifiers to Loudspeakers
It is important to be sure that your power rating is not too low; otherwise the full SPL (Sound Pressure Level = dB) potential of your loudspeakers will not be fully utilized. The amplifier must also be able to handle the load that loudspeakers present. You need to know the impedance of each individual loudspeaker and calculate the net load impedance. Improper matching can result in excessive power use, distortion, and even noise problems.

Impedance calculations-the load impedance on an amplifier should never be less than 4 ohms (ohms = W).

Mixer Inputs
Inputs: The most common type of mixer inputs are 1/4" phone jacks and XLR female connectors. Most mixers designate 1/4" phone jacks as high impedance inputs, while XLR connectors are used for low impedance.

Sources: The XLR jack is usually a balanced input. The 1/4" input could be balanced if a tip/ring/sleeve (TRS) jack is used, but they are usually unbalanced. When selecting a mixer you must know how many sources you need to accommodate. Always get a few extra inputs for surprise needs. Another consideration is how many Aux sends you will need for stage monitors, effects, recording and feeds. We recommend four to accommodate most needs.

Outputs: Outputs, like inputs, use 1/4" jacks and XLR connectors and are almost always low impedance. Typically the 1/4" jacks will be unbalanced and the XLR connectors will be balanced. A powered mixer will also have 1/4" jacks for speaker outputs. Only speakers should be plugged into these outputs (unshielded cable should be used).

3. Speakers
Speakers have two important characteristics, the amount of power they can handle (shown as watts) and their impedance (listed as ohms = W). The factor that relates amplifier to power to sound pressure level for a given loudspeaker is the loudspeaker's sensitivity rating, otherwise specified in dB. Choose a loudspeaker with the highest sensitivity.

Speakers for house sound reinforcement are designed to handle larger signals and offer more control over where the sound output is directed. They are usually designed with the ability to mount them on a tripod speaker stand or fly-mounted from supports above.

Most sound system speakers feature a two-way design where one speaker driver handles the low frequencies, while the other drives the higher frequencies. When a speaker has this two-way design, a fuller spectrum of low and high frequencies will be more accurately reproduced.

Dividing up the entire audio spectrum with more than one speaker of the proper size and design, to reproduce the correct frequencies within their limits, allows for clearer sound and lets you drive the speakers a little bit harder.

Series or Parallel Speaker Connection?
Connecting speakers in a series raises the impedance while a parallel connection lowers the impedance. Parallel connections are generally preferred for sound reinforcement systems because if one of the speakers stops working or "blows," the other speakers won't fall victim as well.

Preventing Feedback
Feedback is an undesirable condition that occurs when amplified sound (usually from a speaker) is reintroduced into the microphone. The amplifier then tries to re-amplify the audio and it gets amplified over and over until all you hear is a loud squealing sound coming from the speakers. Careful placement of microphones and speakers can reduce feedback problems to a minimum.

First, always keep stage microphones behind the main house speakers, with the speakers directed out toward the audience. When a microphone moves in front of a speaker, it will pick up the sound being amplified and then "feed" that sound "back" through the amplifier, causing feedback.

Another feedback risk is placement and volume level of any on-stage floor monitors. Monitors help performers hear themselves, however, they are still speakers. Make any performer-requested level adjustments slowly and with caution while they are testing their microphone. With proper placement and level adjustment, you'll keep feedback to a minimum.

When feedback occurs, or begins to occur, NEVER place your hand over the top of the microphone. It's a natural reaction, however, this makes feedback worse. The fastest way to stop feedback once it starts is either turn the main level down, or better yet, turn down the level of the offending microphone. Then, you can gradually raise your levels and begin troubleshooting to find a suitable level adjustment.

Copyright © 2005 by Long's Electronics. All rights reserved.