1 Live Sound Reinforcement Microphones. 2 Live Sound Reinforcement A microphone is a transducer that changes sound waves into electrical signals and there

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Live Sound Reinforcement

Microphones

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A microphone is a transducer that changes sound waves into electrical signals and there are several ways of doing this.

Microphones take the incoming sound pressure and use a diaphragm that expands and contracts (compression and rarefaction of the air wave) this causes fluctuations in a charged field which is transferred into voltage.

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Below is a diagram showing the construction of a dynamic microphone, notice the diaphragm, it works in the opposite way of a speaker cone.

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There are four basic microphone types:

1. DYNAMIC2. CONDENSER 3. RIBBON4. PIEZO ELECTRIC

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The dynamic microphone has a magnet and a moving coil that moves in response to sound pressure across a diaphragm which in turn creates a small voltage.

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Dynamic microphones are the most widely manufactured and commonly used microphones.

The design of these microphones makes them very durable and cost effective.

The dynamic microphone can range in quality from low budget to high quality.

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Condenser microphones work on the electrostatic principle and requires power known as phantom power.

FOR THOSE OF YOU WHO HAVE BEEN THROUGH SEMICONDUCTORS YOU SHOULD BE ABLE TO IDENTIFY THE CIRCUIT SYMBOL THAT IS CIRCLED.

THIS IS A SCHEMATIC OF A CONDENSER MICROPHONE

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The condenser mics require 9VDC to 52VDC to operate, however the 48VDC power offered by mixers is the standard.

The condenser mic uses circuitry that incorporates a small amplifier and uses a gold plated diaphragm and a gold plated back plane, as the diagphram moves it creates a capacitance that is then amplified.

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Condenser mics are considered to be extremely high quality and can be fairly expensive ($200.00+).

They are also known for their ability to accurately reproduce the audio spectrum and have a very high frequency response.

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Ribbon microphones use a thin electrically conductive ribbon which vibrates within a magnetic field to initiate an audio signal.

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Ribbon mics can provide very high quality however they can be very sensitive to physical shock from dropping it and can be easily damaged with excessively loud sounds.

Ribbon mics are typically used in studios and are sometimes referred to as velocity mics.

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Piezo electric microphones are sometimes referred to crystal or ceramic mics.

A small crystal is connected to a diaphragm, as the diaphragm vibrates it causes the crystal to deform which in turn creates a voltage known as a piezo electric voltage.

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Piezo electric mics are considered to be of poor quality but are a very strong utility microphone.

Piezo electric microphones (contact pickup) are used in telephones.

CONTACT PICK UP

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Microphones can be further classified by how they are used;

Handheld micsShotgun mics- musical productionsParabolic mics- sporting eventsLavaliere mics- hands free, attached to clothingContact pickup mics- usually attached to instruments

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Another important means of classifying microphones is the way the transducer responds to sounds from different directions, this is referred to as the pickup pattern or directional pattern.

The sensitivity of a microphone to sounds coming from different angles determines it directional pattern, this pattern can be plotted and has a three dimensional characteristic.

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Microphones are usually classified as being either omni-directional or uni-directional.

Omni-directional microphones pick up sounds within a 360 degree pattern.

Uni-directional microphones pick up sounds from a single direction.

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Omni-directional mics are best suited for studio use where there is no other sounds present.

Uni-directional mics are typically used by performers on stage.OMNI-DIRECTIONAL MIC UNI-DIRECTIONAL MIC

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The uni-directional mics are called cardioid because of the heart shaped pickup pattern.

This pickup pattern can be narrowed to produce a hyper cardioid and further narrowing of the pickup pattern produces a super cardioid pattern.

CARDIOID OMNI-DIRECTIONAL BI-DIRECTIONAL

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Here are the various cardioid patterns, notice that shotgun mics are very directional, these types of mics are used in stage productions like the Jay Leno show or the David Letterman show.

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Here is a side by side comparison of the different pickup patterns used in mic designs.

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The frequency response curves for mics can vary depending on the applications of the microphones.

An ideal "flat" frequency response means that the microphone is equally sensitive to all frequencies.

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In this case, no frequencies would be exaggerated or reduced (the chart below would show a flat line), resulting in a more accurate representation of the original sound, we therefore say that a flat frequency response produces the purest audio.

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In the real world a perfectly flat response is not possible and even the best "flat response" microphones have some deviation.

More importantly, it should be noted that a flat frequency response is not always the most desirable option.

For example, a response pattern designed to emphasis the frequencies in a human voice would be well suited to picking up speech in an environment with lots of low-frequency background noise.

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The main thing is to avoid response patterns which emphasize the wrong frequencies.

For example, a vocal mic is a poor choice for picking up the low frequencies of a bass drum.

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Wireless mics are also available for live sound however they find their use in speech reinforcement more than music reinforcement.

Wireless mics require a transmitter and a receiver and operate on either the VHF or UHF frequencies.

These mics can be lavaliere types or hand held mics with built in transmitters.

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As you can see from these charts the VHF and UHF bands are allocated for TV and could cause interference.

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The bottom line is that a good quality microphone can greatly affect the output of the sound quality of any live sound reinforcement system.

Documents

1 Live Sound Reinforcement Microphones. 2 Live Sound Reinforcement A microphone is a transducer that changes sound waves into electrical signals and there