Hello I’m Jacob Solomon from Nairobi, Kenya. This lesson is for Week 1 of Introduction To Music Production at Coursera.org. I will be teaching Microphone Basics. The focus is on Microphone Types.
A microphone is a transducer that changes air pressure variations into electric variations. Most microphones today use electromagnetic induction this means that a voltage is produced when it is exposed to a varying magnetic field. Remember that through this whole process the signal is still in analog for and needs to be converted to a digital signal.
Microphones are referred to by their transducer principle and their directional characteristics.
These microphones work through electromagnetic induction. a small movable induction coil is placed in the magnetic field of a permanent magnet attached to the diaphragm. When sound enters it moves the diaphragm and the coil. This movement creates a varying current.
Dynamic microphones are useful because they are durable and resistant to moisture and are also quite affordable.
Dynamic mics have an upper frequency response limit of 60kHz this means that they are not designed for high frequency sounds such as cymbals, bells and the upper harmonics of acoustic instruments such as the piano or the guitar. If you do record with them the top end of your recordings will sound transparent and flat.
Dynamic mics have a cardioid pick-up pattern (pick sound better from one-direction). A problem with this is what is known as the ‘proximity effect’, when the mic is close to the sound source the bass end frequencies increase considerably. To stop this the mics have been designed with a low-end roll-off frequency below 100Hz, the outcome is that if the mic is used more than a few inches away from the sound source the bass will be considerably light.
Another issue with dynamic microphones is that due to the coil/diaphragm assembly the signal has to be amplified to make it useful. The more gain you add the more noise you add to to the signal. This is only an issue if you want to record distant sounds.
Dynamic microphones have a restricted sensitivity. Sensitivity is the measure of how much electrical signal comes out of the microphone for a given level of audio input. The less sensitive a mic, the more amplification you need to get it to the right level.
In summary dynamic microphones are most effective when working with relatively loud sound sources that don’t contain a lot of very high-frequency detail.
They are also known as capacitor or electrostatic microphones. A condenser microphone is built with a pair of conducting plates, one fixed and the other in the form of a moving diaphragm. When the diaphragm vibrates the capacitance varies, and if an electrical charge is applied to the capacitor an electrical signal is produced that mirrors the diaphragm movement. The diaphragm is very light compared to that of a dynamic mic, that means its more efficient and can capture harmonics beyond the human hearing range. Furthermore when purchasing condenser microphones pay attention to the diaphragm size - a large diameter is chosen for vocals because of the warm sound, while a small diameter is chosen where high accuracy is needed, such as film recordings.
Like dynamic microphones, condenser mics electrical signal needs to be amplified. That is why they have a built in preamplifier, which is a factor to its high cost. Additionally, all capacitor mics need polarizing voltage power (phantom power). It is known as phantom power because the polarizing voltage is supplied via the signal leads of the microphone, no additional cabling needed. It is important to note all phantom powered microphones are balanced. Condenser microphones are generally used in studio settings, where it is quiet, due to its sensitivity. It is used for vocals, but can also be used for drum kit recording for a natural sound especially for jazz music where that is detrimental. Unlike dynamic mics which are humidity resistant, condenser microphones loose sensitivity, have intermittent noise and dulling of the high end frequencies. The only solution is to place the microphone somewhere warm it dries out.
In summary condenser mics work well in most situations and are sensitive enough to pick up quieter or more distant sounds.
Their weakness is the high cost, their reliance on external power and the susceptibility of some models to succumb to condensation
Piezoelectricity means electricity resulting from pressure. It is the accumulation of electrical charge in certain materials in response to applied mechanical stress.
The contact microphone in the image above is made of a thin piezoelectric ceramic round glued to a thin alloy metal disc. the centre disc is positive while the alloy disc is negative. If the centre disc gets scratched it won’t function at optimum sensitivity.
Piezo mics are generally used as contact mics to amplify sound from acoustic instruments. Contact microphones are designed to sense sound vibrations through solid objects. Contact mics are used to record sound in high pressures (underwater). Also most saddle mounted pickups on stringed instruments are piezoelectric devices that contact the strings passing over the saddle.
Experimenting with digital microphones - http://designingsound.org/2013/02/experiments-with-digital-microphones/
How to achieve ‘Million Dollar Sound’ without A Million Dollars - http://designingsound.org/2011/03/ric-viers-special-how-to-achieve-million-dollar-sound-without-a-million-dollars/
Extra Microphone Types - http://www.paformusic.info/mics.htm
Researching and compiling this lesson was really interesting to me. it was my first time learning it and I hope you learn as much as I did. An issue I had compiling this lesson was to the influx of microphone types. I restricted myself to microphone types used in the music recording process strictly. others such as the Shotgun microphones, used mostly for film were avoided. I also avoided delving into polar patterns as the lesson would not be on microphone types. I have clearly stated merits and demerits as well as application of the microphone types I have covered. as well as explain the key terms. Also if you want more information of what I have missed I have placed links under the ‘Extra Material Section’. I believe my subjective decision on microphone types could have been widened and placed under one page rather than linking away from the work. Furthermore I should have gone deeper into explaining subcategories of dynamic and condenser microphones.
Articlebase. (2008, June 15). Types of Microphones and their uses. Retrieved March 11, 2013, from Articlesbase: http://www.articlesbase.com/electronics-articles/types-of-microphones-and-their-uses-450020.html
PAforMusic. (2012, April 16). Microphone Types, selections and Use. Retrieved February 10, 2013, from PAforMusic: http://www.paformusic.info/mics.htm#Care of Microphones
SoundonSound. (1995, June). Choosing A Microphone: Types and Uses. Retrieved January 11, 2013, from SoundonSound: http://www.soundonsound.com/sos/1995_articles/jun95/microphones.html
SoundonSound. (1998, April). Mic Types and Characteristics. Retrieved March 11, 2013, from SoundonSound: http://www.soundonsound.com/sos/apr98/articles/mic_types.html