Dynamic Microphones

Dynamic microphones work on the “moving coil” principle. A small diameter of thin aluminum or Mylar diaphragm is connected to a coil of very thin hair like wire that is suspended in a strong magnetic field. As the acoustic sound waves hit this diaphragm, the coil of wire vibrates in the magnetic field causing an electrical signal to be produced. The electrical signal is the same frequency as the original sound wave. Tremendous mechanical durability, lower cost, no external power requirement and very high input SPL (Sound Pressure Level) capability were always the advantages of dynamic microphones. They are ideal for live events and concerts, in front of electric guitar cabinets, loud instruments (trombones, trumpets) and the like. They are ideal where rough treatment, such as at a school or church, is expected. Their lower cost makes it possible to own more mics so this is a big benefit to sound companies as well. Typical dynamic microphone transducers are less than one” in diameter. They have acoustical properties yielding frequency responses with peaks and dips in the wrong places, causing programs to sound either nasal or muddy or both. Excess equalization always had to be applied to electrically “fix” these poorly designed dynamic elements. The number one audio rule: You Can’t Fix Acoustical Problems With Electronic “Fixes”!

Condenser Microphones

Condenser microphones are typically found in the studio. The element is made up of a thin film coated with a conductive material such as silver or gold suspended over a polarized (powered) backplate. This condenser diaphragm is part of an electrical circuit that changes voltage with movement and this voltage becomes the output of the microphone. Sensitivity, wide frequency response and transient response were always the performance advantages of condenser microphones over ribbons, dynamics and all other types of microphones.

Unlike dynamics or ribbons, condensers require a power source to operate. This power is typically delivered via an external “power supply” or something called “phantom power”. Phantom power is a dc voltage fed back through the microphone cable from the console or mic preamplifier to the microphone to run its internal electronics. The term “phantom” was coined because there is no additional wiring or connections to carry the dc power from the console to the microphone. Most all consoles or mic preamps have a built-in 48 volt phantom supply that can be sent to the condenser mic up the mic cable.

Electret Microphones

An Electret microphone is a small version of a large diameter condenser. Using an internal Field Effect Transistor, the Electret can usually be powered from an internal battery or phantom (console supplied) power. Their primary advantage has been size and you will find them on the lapels of TV anchors and news folk. They do not exhibit the extreme sensitivity of the large diaphragm studio condenser but they are still vulnerable when placed in and around high SPL situations. Care in handling the delicate Electret has to be taken since they do have sub miniature internal electronic components. They are best at voice, but expensive versions can offer wider response and wider applications.

Ribbon Microphones

The ribbon microphone was popular in the early days of audio back in the 1930s, ’40s and ’50s. Using a metal bifurcated ribbon stretched between two poles of a large heavy permanent magnet, these microphones were noted for their wonderful midrange, warm tone and great bass response. Unfortunately they are very fragile and cannot take loud sounds (high SPL). The ribbon is easily broken if dropped or mishandled. Even blowing into them (“Hey, “whoooof” is this on?”) would often fracture early ribbons. The other issue with ribbons was very low output. Special high gain mic preamps were employed to get sufficient gain from the microphones. Ribbon technology was stagnant for many years but a few companies have brought some new technology back into this arena lately. The durability has increased and output has improved but these mics remain best at recording applications.

- From Microphones 101, taught by the master himself, Bob Heil