2. Introduction to The Microphone
Decent microphones are an essential part of the videographer’s kit, and in many ways we take them for granted. We throw them into our camera bags (although of course we shouldn’t!) and drag them out whenever we need them, relying on them to produce crystal clear sound time after time.
Still, even a good microphone can produce poor results when it is used in the wrong context or environment, so it is essential that the videographer knows what different types of microphone are available and why some perform better in particular situations than others.
A microphone is an instrument, or transducer, that changes one form of energy into another form of energy; in this case, sound pressure waves into electrical signals. The microphone is usually the first device in the recording chain on route to your camera or audio recorder and that chain can include a variety of items, such as mixers, transmitters and receivers, noise gates and limiters, graphic equalisers, digital enhancers and effects boxes and, of course, your computer. Therefore, it makes sense to remember that the overall quality of your sound recordings will be no better than the weakest link in the path your audio signal travels. A poor or unsuitable microphone at the head of the chain will ruin your programme.
The quality of your recordings will vary according to the environment you are in. Elements such as the design of the microphone, its placement, the acoustics of the location (which contribute to colouration), ambient noise and weather will all have an effect.
Microphone manufacturing technology has steadily improved over the years, resulting in better quality microphones being more affordable. However, many classic high-quality microphone deigns, still highly sought after today, were first introduced over 25 years ago. And unlike video technology, where no-one would choose to use a 25 year old camera, good quality microphones of any age are worthy of consideration for inclusion in your sound kit.
2.1 Dynamic Microphones
| The Dynamic microphone is the most widely manufactured and used of all the types of microphone. The design employs a moving-coil diaphragm, which is simply a loudspeaker in reverse. They can be very durable and immensely cost effective, since they employ no internal electronics and require no external power to operate. They vary in price from the low budget mass-produced item, which can often sound terrible, through to the expensive virtually hand-built item that has incredible sound quality.
Dynamic microphones are able to cope with extremely high sound pressure levels at short distances and are often used for close up work on drum kits. They are also helpful when used close up to the face for vocal work in noisy environments, particularly at live music venues. Whenever you turn up at a location to shoot, remember that dynamic microphones respond best to being close to the sound source that you are recording, in that they can deal effectively with high levels of sound pressure and that they are robust. Knock a Dynamic microphone over and you can, more often that not, just pick it up and use it again. That said, it is best to treat all your microphones as delicate instruments and treat them with care. Treated with due respect, a good microphone is an investment that will far outlive any video camera. |
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2.2 Condenser Microphones
The Condenser microphone works on an electrostatic principle rather than the electromagnetic principle employed in the Dynamic microphone, with the diaphragm acting as one half of a condenser (or capacitor, as they’re also known). It has no moving coil attached to the diaphragm, making it lighter and more responsive at higher frequencies. As a result it can produce an extremely high quality output. However, this comes at a price as Condenser microphones are not as robust as their Dynamic cousins, and they require a power supply to operate.
There are two sub-groups of condenser microphones.
1 – Conventional Condenser
In a conventional condenser microphone, the diaphragm is charged via circuitry in the microphone body, usually requiring power from an external source.
2 – Electret Condenser
In an electret (condenser) microphone, the diaphragm is made of a special “electret” material which is pre-charged for its lifetime. Very little additional circuitry is required, giving the option of powering the microphone from an internal battery. In general, electret mics are cheaper to produce than the equivalent size “true” condenser, and are of lower sonic quality, although the difference has narrowed since their introduction due to improved manufacturing techniques.
One exception is in the category of small personal mics (lavaliers), where it is impractical to make non-electret condenser mics, and the electret principle works well. However, even here there is a potential downside, faced by all electrets, in that over time the electrostatic charge on the diaphragm can dissipate, after which the microphone will no longer work, irrespective of the state of the battery.
When the microphone requires external power, it can be supplied via the microphone cable. There are two types of powering system that you might encounter. T-Power (or 12V A-B powering) was the first system used for battery powering microphones for location filming, but has effectively been replaced by Phantom Power, which is more versatile and less prone to causing damage when connected to a non-condenser microphone. The default voltage for Phantom Power is 48V (often abbreviated to P48) although some microphones can work on a range of voltages anywhere in the range from 9V to 48V.
The actual power source can be an external battery box or built into the recording device or mixer. Most onboard camera microphones are of the P48 condenser variety and receive their power via the camera. If you are using a microphone mixer, it is best to obtain one that provides phantom power as standard, or better still get one that does both.
Knock over a Condenser microphone and you will, most probably, have to buy a new one. Condenser microphones usually produce a higher quality recording and, as a result, are the microphone type of choice for manufacturers of video cameras for their on-board microphones – as well as being the most common external microphone in use by videographers. As long as care is taken not to overload them, they are an essential, if relatively expensive, part of your kit.
2.3 Ribbon and Piezoelectric Microphones
There are two other main types of microphone, the Ribbon and the Piezo-electric – neither of which is commonly used for location sound recording.
Ribbon microphones are similar in some degree to their Dynamic cousins, but while they can produce excellent sound quality, they are sensitive to shock and you must be careful when handling them or overloading them with excessive sound pressure. Piezoelectric mics are traditionally strongly constructed utility microphones, but of poor sound quality. They are typically used in telephones. There are a few notable exceptions, such as when Piezoelectric microphones are fastened to the vibrating side or plate of a musical instrument, as with a guitar or stringed instrument. In this instance they can produce a very high quality audio signal.