Sunday 18 August 2013

Dynamic Microphones

These are probably the most common and familiar microphones in general use today.
Used by vocalists, voice-over artists, drummers, guitarists on
their speaker cabinets, announcers, radio broadcasters, children's karaoke machines - the list is long and growing!
Depending on performance, specifications and construction
quality, prices can vary from $5.00 to several hundred dollars.  Some professional models, for use in public performances (on stage) can be configured with a neat attached radio transmitter, thus avoiding the need for an attached cable, and enabling flexibility of movement for the performer.  Maybe we'll discuss wireless systems on a later post.

So, how do they work?

Firstly, all dynamic microphones are termed "end address", because they point end-on to the sound source (vocalist, musical instrument, etc.).  Sounds are also picked up from the side of the capsule, but not to the same extent:  high frequency response is less, and also sensitivity. 
In addition, the design of dynamic mics means that, compared to some other microphones, they are relatively less sensitive overall, and more suited to placement quite near to the sound source, rather than at a distance.  This is why you will often see them employed in live performances of small bands and groups that use sound amplification for vocals and unamplified instruments.  A very useful side benefit is that sounds coming toward a dynamic mic from the opposite direction to which it is being pointed, and to a certain extent the sides also, will not be picked up well.  For example, the floor wedge-type speakers used for fold-back.
Without delving much into the physics of the above design, sound enters through the screen at the top of the mic. and causes a light but very stiff circular diaphragm which is attached to a small, fine coil of wire to move in sympathy with the sound waves, moving "up and down" within the field of a strong magnet assembly.  The net result is a small electric current is generated in the coil, the ends of which are attached to flexible wires:  sound has been transduced / transformed into an electrical signal!  Nearly always, in the main body of the microphone, a small transformer is connected to the capsule output wires so that the resulting signal is suitable for connection to the microphone inputs on various pieces of equipment, such as mixing desks, digital recording systems, public address amplifiers, etc., which can be at quite a distance from the microphone.  The little transformer ensures our microphone is therefor has a "low impedance" output, suitable for long cable runs and correct electrical matching to amplifying equipment.
This is a photo of the "business end" of a dynamic mic. with the wind-shield (the mesh ball) removed.  Notice the smooth, pinkish(!) diaphragm mounted in the centre.
The frequency response of dynamic mics is rarely smooth, or even.  It is often tailored, by design of the diaphragm assembly and the protective cover, etc., to make it suitable for clarity of speech or singing by emphasizing the upper mid-range and lower to mid treble sounds.

Dynamic type microphones are not able to respond to very small details in sound, and they are by design fairly to very insensitive.  But they are very popular, generally cost-effective, able to handle rough treatment and are the "go-to" mic. type for vocal performances and acoustic instruments in an amplified setting.  Believe it or not, Michael Jackson recorded his voice using a dynamic type mic. on an obscure album called "Thriller".  So you'll see them in studio settings quite commonly - vocals, drums, guitar cabinets:  the list is endless.

Next time:  Condenser Microphones.


1 comment:

  1. Worthwhile info if you're needing to purchase a microphone for a particular function. Sounds like the dynamic mic. is a choice that many musos go for use on their gigs. This post elaborates on great particulars about the above mentioned microphone.

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