The Recording Forums

Basic Home Recording X

Jim Goodman

Part 10 – Microphone Essentials

Microphones are an essential piece of the overall sound puzzle. In this installment we are going to look at the absolute basics of microphones and microphones and usage. This no-nonsense look at microphones will barely scratch the surface of what is available in microphone options, technologies and applications.

When doing home recording you need to be aware of equipment limitations. If your signal chain consists of a lot of low-dollar hardware and software then the best and most expensive microphones will give poor results (expensive is relative as studio microphones can go into the tens of thousands of dollars). The smart way to choose a microphone is found in our motto “begin with the end in mind.”

Most of us will be recording ourselves and will have a specific style of music to record. If we have that settled then we can begin thinking about mic selection, but before we get there lets get some basic understanding of microphone types and some key terms down.

The transducer is the device within a microphone that converts the analog sound of the voice or instrument to a voltage that can travel along the signal path. There are 3 types of transducers for microphones: dynamic, ribbon and condenser.

A dynamic microphone has a small diaphragm that is suspended in a capsule surrounded by a coil. When the sound enters the capsule the diaphragm vibrates moving the coil over a magnet to produce voltage. The dynamic mic is used most commonly as an instrument and performance vocal mics. 2 well know microphones of this type are the Shure SM-57 and SM-58. Dynamic mics are known for their durability and multi-purpose use.

                       
Shure SM-57                         Shure SM-58

Ribbon microphone works the same way except instead of a diaphragm it has a thin piece of foil material that is suspended in the capsule that vibrates within the magnetic field to produce its voltage. Ribbon mics are not durable, but are great for studio applications because they are warm and very smooth sounding. Mostly used for vocals and acoustic instruments but must be used with care as it is relatively easy to “blow-out” the ribbon.

Condenser microphones have no coil and require a power supply to operate the diaphragms to produce the output voltages. It can come from an internal battery (placed inside the microphone housing or an external phantom power source. Phantom power is +12 to +48 Vdc and can be supplied by either an external power module or from the mixing console. Many of the inline mic preamps we look at in a previous article have built in phantom power. Some condensers can run on as little as +3Vdc though not with practical results much better than a dynamic transducer. Condenser mics have a variety of uses and applications because of the external power needed examples would be vocal mics, studio mics, choir mics, lapel and headset mics, etc.

Diaphragm size generally will dictate a purpose of a particular condenser mic, but as you will learn in the studio there are no rules and what rules the experts write are written to be broken. Hear is a rule of thumb, the larger the diaphragm the more sound and frequencies it will capture and convert. Some sizes and uses would be a micro- diaphragm used in lapel and choir loft mics. Small diaphragms are generally used for acoustic instruments and cymbals. Medium to large diaphragms are used as vocal and ambient room mics.


Audio-Technica AT4045

The last item of importance in microphone essentials is polar pattern. Polar pattern is simply how the mic will receive sound relative to capsule position and distance. There are 2 patterns, omni-directional (picks up sound from all around 360degrees) and uni-directional (picks up sound from less than all around or less than 360 degrees. Uni-directional is broken down into 3 sub-types, cardioid, supercardioid, hypercardioid and bi-directional.

Most Common Patterns:

Omnidirectional          Cardioid               Hypercardioid 

          

The cardioid pattern is a heart shaped pattern will “reject” sound that comes in from behind. This pattern is great for studio use if you have offending noise in the studio you just point the mic in the opposite direction of the sound and it will reject that sound coming in from behind.

The supercardioid will has more isolation than a cardioid, meaning a greater rejection area off to the sides between 120 to150 degrees also 210 to 240 degrees ideal for stage micing.

The hypercardioid mic has the most side rejection of any uni-directional pattern over a greater area and distance also ideal for stage and live recording situations.

Finally bi-directional rejects sound on the sides but front and back have the same pick-up characteristics. You would see this mic in tabletop interview situations and in special situations or in duet vocal applications amongst others.

Here is an article on Shure’s website that can give some more information: http://shure.com/ProAudio/TechLibrary/EducationalArticles/index.htm . Almost all microphone manufacturers have some great articles and educational materials on their sites and Shure houses probably the best education and knowledge base section of all of them.

Next installment: How To Choose a Mic.