Microphones (assignment for Coursera class)
Week 1 Assignment
Hi, I am Denis Martynkin, from Moscow, Russia, This lesson is for week 1 of Introduction To Music Production at Coursera.org. I will be teaching you different types of microphones which were not described in the short lectures provided by Coursera.
So, as you can remember, two types of microphones we were dealing with were dynamic microphones and condenser (aka capacitor) microphones. Let’s start from the very first microphones in history and then move forward.
Let’s get a bit back, to the 1870s, where David Edward Hughes invents a carbon microphone (first type to discuss). How did it work? It used loosely packed carbon granules – the varying pressure exerted on the granules by the diaphragm from the acoustic waves caused the resistance of the carbon to vary proportionally, allowing a relatively accurate electrical reproduction of the sound signal. The carbon microphones are not used anymore, still, they are direct prototypes of today’s microphones and were critical in the development of telephony, broadcasting and the recording industries.
Another old-timer is liquid microphone or water microphone (second type). Early microphones did not produce intelligible speech, until Alexander Graham Bell made improvements including a variable-resistance microphone/transmitter. Bell’s liquid transmitter consisted of a metal cup filled with water with a small amount of sulfuric acid added. A sound wave caused the diaphragm to move, forcing a needle to move up and down in the water. The electrical resistance between the wire and the cup was then inversely proportional to the size of the water meniscus around the submerged needle. These were the first working microphones, but they were not practical for commercial application. The famous first phone conversation between Bell and Watson took place using a liquid microphone.
image taken from ssstudio.ca
So, what are the (third type) dynamic microphones?
A lightweight diaphragm, usually made of plastic film, is attached to a very small coil of wire suspended in the field of a permanent magnet. When a sound causes the diaphragm to vibrate, the whole assembly works as a miniature electricity generator, and a minute electric current is produced. Dynamic microphones have the advantages of being relatively inexpensive and hard-wearing, and they don’t need a power supply or batteries to make them operate.
But why aren’t they used everywhere? What are their disadvantages?
Dynamic microphones fail to reproduce very high frequencies accurately. In some applications, this isn’t too serious, but if you’re working with an instrument where a lot of tonal detail is contained in the upper harmonics, a dynamic mic is unlikely to bring out the best in that instrument.
Another side-effect of the finite mass of the diaphragm/coil assembly is that the dynamic microphone is not particularly efficient – a lot of amplification has to be used to make the signal usefully large, and the more gain you use, the more noise you add to the signal, so if you’re trying to capture a quiet or very distant sound, then a dynamic mic isn’t likely to produce good results.
There is an alternative evolution branch of dynamic microphones which is called (fourth type) ribbon microphones - this is a type of microphone that uses a thin aluminum, duraluminum or nanofilm of electrically conductive ribbon placed between the poles of a magnet to produce a voltage by electromagnetic induction.
(image taken from Wikipedia, the free Encyclopaedia)
The advantage of the ribbon microphone when introduced was that the light ribbon had a much higher natural resonant frequency than diaphragms in existing microphones, above hearing range, so it had flatter response at high frequencies. Ribbon microphones were once delicate and expensive, but modern materials make certain present-day ribbon microphones very durable, and so they may be used for loud rock music and stage work. They are prized for their ability to capture high-frequency detail, comparing very favorably with condenser microphones.
So, let’s move to another big branch of the microphones - condenser microphones (type five) also known as capacitor microphones. Here, the diaphragm acts as one plate of a capacitor, and the vibrations produce changes in the distance between the plates. Condenser microphones span the range from telephone transmitters through inexpensive karaoke microphones to high-fidelity recording microphones. They generally produce a high-quality audio signal and are now the popular choice in laboratory and recording studio applications. The inherent suitability of this technology is due to the very small mass that must be moved by the incident sound wave, unlike other microphone types that require the sound wave to do more work. They require a power source, provided either via microphone inputs on equipment as phantom power or from a small battery.
For those with the love for the old-school sound, there are some special condenser mics: valve microphones (sixth type). A valve microphone is, simply put, a condenser microphone which uses a valve amplifier, as opposed to a transistor circuit. There are many reasons why valve microphones have become so important in today’s recording and home studios, partly they are fashionable due to their early use by influential composers and musicians such as The Beatles, Pink Floyd, The Rolling Stones, etc. but also because the sound quality they reproduce has pleasing sonic qualities even though more technically perfect reproduction is possible by transistor microphones which have less self-noise.
Not widely used but still alive are (seventh type) piezo microphones. A crystal microphone or piezo microphone uses the phenomenon of piezoelectricity—the ability of some materials to produce a voltage when subjected to pressure—to convert vibrations into an electrical signal. They are mostly used as contact microphones to amplify sound from acoustic musical instruments, to sense drum hits, for triggering electronic samples, and to record sound in challenging environments, such as underwater under high pressure. Saddle-mounted pickups on acoustic guitars are generally piezoelectric devices that contact the strings passing over the saddle. This type of microphone is different from magnetic coil pickups commonly visible on typical electric guitars, which use magnetic induction, rather than mechanical coupling, to pick up vibration.
There is kinda standalone pretty exotic microphone type - fiber optic microphone (number eight). A fiber optic microphone converts acoustic waves into electrical signals by sensing changes in light intensity, instead of sensing changes in capacitance or magnetic fields as with conventional microphones. Fiber optic microphones are used in very specific application areas such as for infrasound monitoring and noise-canceling. Medical equipment, industrial monitoring, high-fidelity equipment, you name it.
Thank you very much for reading my compilation. I hope you liked it and it helped you to gather some additional knowledge, which may be of some help to you if you decide to dive deep into the music production.
