microphone research document

8/8/2019 Microphone Research Document

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Microphone Research Document

Before we go recording on location its good to look at the microphones that we are going to

use and study the specifications to learn the advantages and disadvantages of microphone.

Here Im going to explain each specification of the microphones, to help understand them and

use them at the full potential

There are three types of microphones; Dynamic, Condensers, and Ribbons. Heres adescriptions of each.

DynamicA dynamic microphones works by using a magnet surrounded by a coil of wire thatssuspended in a magnetic field, if disrupted it causes an analogue electrical signal. A thin

diaphragm is attacked to the coil, so when a change in air pressure hits it at its certain

frequency it then disrupts the magnet field as the coil moves, then that air pressure becomes

changes in voltage. (David Miles, 116-117)

In the diagram above you can see the coil, magnet and the diaphragm. You can see the sound

wave hitting the diaphragm which the moves the coil. Its a good example of what I wasexplaining.

RibbonA ribbon microphone works similar to the dynamic, but instead of a coil it has two magnets

around an extremely thin piece of aluminium that is suspended between the two magnets. If

the aluminium moves, it disrupts the magnetic field which creates an electrical signal, but its

so weak a transformer is used in the microphone to boost it. Here is a diagram of ribbon

microphone. (David Miles,117)


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CondensersCondensers use electrostatic rather than electromagnet like the dynamic and the ribbon

microphones. A condenser has a movable diaphragm which is one of two small plates. The

plates have an electrical charge going through them from a battery inside the microphone.

When acoustic energy hits the front plate it moves it and the distance between the front and

back plate moves too and creates a charge that its then turned to electrical signal. Thecondenser needs phantom power to power (48volts). (David Miles,119)

Polar Patterns

A polar pattern is when a microphone detects changes in air pressure. With polar patterns you

determine the response of the microphone by its sensitive it of the polar pattern. (David Miles,

123)

Omni Directional polar pattern is a 360 degree pick up, as in any sound made anywhere will

be picked up by the microphone. Omni makes a more natural sounding pick up as will also

pick up reflections made by the sound. (Homerecording.about.com)

Cardioid is pattern that picks up from the front, also picks up a narrower side compared to

Omni directional, and the from the rear of the microphone there is no pick up, so the pattern isa heart shaped. The cardioid pattern is very commonly used, used for live, vocals and many

other applications. Because of its front pick up and no rear pick up its good for picking up

sounds from the front. (Homerecording.about.com)


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Cardioid microphones use a rear port, paced at the right distance away from the diaphragm to

create a delay or a acoustic labyrinth. This puts sounds from the rear out phase and for when it

hits the front of that diaphragm. (David Miles,125)

Hypercardioid is similar to cardioid polar pattern, except that the sides of the pattern are much

narrower and doesnt pick up around 120 degrees from the back. This pattern is commonlyused in live performances because they help preventing feedback.

(Homerecording.about.com)

Figure of eight or bio directional, this polar pattern picks up from the front and from

the back equally. The polar pattern has a no pick up from the sides; its just front and

back. Ribbon microphones commonly use figure of eight for their pick up, and the

figure of eight is commonly used for stereo techniques and micing up acoustic

instruments. (Homerecording.about.com)

Pressure gradient is a term used for pickups of a microphones that show directional properties.

This is happens when different pressures effect the front, sides and back of the diaphragm.

Figure of eight is pressure gradient, the pressure hitting at 180 degrees at the rear will be out

phase with an equal on axis signal. Phase cancelation will take effect if sounds hit off axis and

are opposite pressures at the front and rear of the pressure gradient polar pattern. (David Mile

124)

Frequency response

Frequency response is essentially what the microphone can hear. Frequency response isdifferent for each model of microphone but is always plotted in a graph from 20hz to 20KHz.

A flat response is what is expected from microphones this is so all frequencies are all

balanced but microphones have different frequency responses which could mean there better

at picking up bass or high frequencies.


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You can see in this frequency response that the microphone has a drop at 0-20hz, and drops

and sudden boosts between 1kHz to 20kHz. Now you can determine where and how to use

this microphone because you know what frequencies it can pick up.

Decibels

Decibels are used as units to describe a the maximum or the minimum volume of sound. As

sound increases in density the louder it becomes, we measure between 0dB to 140dB, 140dB

being the peak of humans pain tolerance. Calculate decibels we have to use a non-linear scale,

or the logarithm scale. The two units are involved the decibel which uses units of ten and

Pascal's which will be the reference number. (Francis Rumsey, 15)

dB= 20*log (Pa1/Pa2)

reference = 0.00002 (1dB)

Pascal = 6

6/0.00002 = 30 000

* Logarithmic

= 5.5

* 20

= 109dB

This sum show the calculation for working out decibels and the increase of decibels. it is

relevant because if volume is doubled it isn't twice as loud because 60dB + 60dB = 66dB not120dB because of the dB uses non-linear scale.


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AKG C414

Specifications of the AKG C414, form AKG.com

The Polar Patterns the AKG C414 has are Omnidirectional, cardioid, wide cardioid,

hypercardioid, and figure of eight, see above for information these polar patterns

MAX SPL, is essential how much this microphone can take before distortion starts to take

effect.

Pre-attenuation pad is used when a sound source is loud

Stereo Microphone techniques


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Reference

Fig.1.http://www.totalvenue.com.au/articles/microphones/mic-dynamic.gif

Fig.2.http://www.acoustics.salford.ac.uk/acoustics_info/microphones/microphones_fil

es/image030.jpg

Fig.3.http://www.totalvenue.com.au/articles/microphones/mic-condenser.gif

Fig.4.http://soundslive.files.wordpress.com/2009/04/polar_pattern_omnidirectional.pn

g?w=300&h=300

Fig.5.http://upload.wikimedia.org/wikipedia/commons/6/6d/Polar_pattern_cardioid.p

ng

Fig.6.http://upload.wikimedia.org/wikipedia/commons/8/80/Polar_pattern_hypercardi

oid.png

Fig.7.http://upload.wikimedia.org/wikipedia/commons/archive/8/8f/20070425174735!

Polar_pattern_figure_eight_thumb.png

Fig.8. http://www.hometheaterhifi.com/volume_7_3/images/perpetual-technologies-

frequency-response-apex.jpg

Fig.9. http://www.glossopdale.net/images/akgc414.jpg

http://www.akg.com/site/products/powerslave,id,781,pid,781,nodeid,2,_language,EN,

view,specs.html

http://homerecording.about.com/od/microphones101/bb/Mic_Patterns.htm
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