Capturing Sound Pt. I – Microphone Types

Before you manipulate sound with all the technical analogue and digital wizardry that studios can offer, it is useful to know how that sound is captured. I would like to think of this as a handy reference for any starting engineer and a pleasant refresher for the weathered music maker. If neither apply, then just enjoy my diagrams in all their artistic splendor.

How does one capture that which he cannot see?

“Microphones appear in an almost endless variety of shapes, sizes, and design types, but no matter what their physical attributes, their purpose is same – to convert acoustic vibrations (in the form of air pressure) to electrical energy so it can be amplified or recorded.” – Bobby Owsinski

If you think of microphones as ears on sticks, this becomes easier to understand (albeit the imagery is not the best). When a stringed instrument is plucked, it vibrates very quickly and travels through the air and into our ears to resonate with our ear drums – a very thin piece of tissue – and our brain interprets it as sound. Microphones do not have an ear drum, but rather a very thin and light piece of material called a diaphragm.The diaphragm varies slightly in purpose with different microphone types, but this is its fundamental role. Now that these sonic vibrations have been picked up, they have to be processed via a transducer – a device that converts the audio into an electrical signal that is sent along a cable to be replicated as sound once more. Finally, as these components are very fragile, a durable casing is needed that not only protects the microphone but can also affect its polar pattern (the way in which the microphone picks up audio, but more of that in Pt. II).

 

Different Microphone Types

I. Condenser

This microphone consists of two electrically charged plates; the one at the back is static (the backplate) and the other moves to act as a diaphragm. When sound reaches it, the diaphragm sinks down causing a change in the distance between itself and the backplate – this causes a change in capacitance and thus a change in voltage potential. This small change in voltage potential needs to be amplified by a vacuum tube or FET transistor – this means that phantom power or a power supply must be used to operate the microphone and run the pre-amp. A condenser microphone is more complicated than others so if it helps the physicist in you, a condenser operates much like a capacitor with a positively and negatively charged electrode and a gap of air in between (if this doesn’t help, here is a diagram).

 

Brilliant frequency response, especially in the highs.

–  Requires phantom power or external power source. Performance is affected by humidity and temperature.

 

II. Dynamic

The way in which a dynamic microphone functions is easier to digest than the condenser. There is a single metallic diaphragm that vibrates when subjected to sound waves causing the connected coil of wire to also vibrate. These two components are attached to each other and move within a permanent magnet that causes the current to flow. The amount of current generated is dependent on how fast the sound hits it, making this microphone velocity sensitive. As both the diaphragm and coil move this makes it relatively heavy compared to other microphone types – this means that it will not be as responsive to higher frequencies (typically around 10kHz). However, dynamic microphones do have a resonant frequency (an emphasised group of frequencies) of around 1-4kHz, making them very popular with vocalists as the human voice is normally situated around those frequencies.

 

Robust microphone, great for live. No external power supply. Is not affected my humidity. Usually relatively inexpensive.

– Weak high frequency response above 10kHz

 

III. Ribbon

From the most durable to one of the most fragile, the ribbon microphone functions similarly to the dynamic microphone but a transducer is used as a diaphragm to reduce the weight and thus provide a better response to higher frequencies. The transducer/diaphragm is a very thing piece of aluminium foil that is light enough to vibrate with sound waves but fragile enough to be damaged by phantom power, so make sure this is off before you use the ribbon. Although they are fragile (even a strong blast of air is enough to warp and damage the transducer) they have an excellent frequency response:

“While always fragile, ribbon mics still provide some of he sweetest sounds in recording, as most old-school engineers realized.” – Bobby Owsinski.

No external power needed. Generally flat frequency response.

– Very fragile – both in handling and operation. Can be expensive.

 

To conclude Part I.

It is my hope that with this understanding of how microphones work, your reasons in which you choose a microphone will be much more logical and hopefully you will achieve your desired tone. For further reading, pick up a copy of The Recording Engineer’s Handbook by Bobby Owsinski and never look back.

 

Any questions, just ask :] (unless it is about my artistic ability to draw diagrams)

Neil

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