Several inSync readers have inquired about the differences between large and small diaphragm microphones and why such a big deal is made about that.
Easily the most critical component in any microphone for determining the sound of the mic is the diaphragm (see WFTD Diaphragm). The diaphragm’s ability to move accurately with the sound pressure waves that hit it is determined by a combination of its size, mass, rigidity, and the enclosure around it. Much science has been devoted over the years to perfecting diaphragm materials and construction techniques in search of the perfect diaphragm that can produce all audio without any distortion. Today microphone manufacturers are still left with a litany of compromises that must be made between cost, durability, and sound quality against the immutable laws of physics in producing high quality microphones. I shall not begin to attempt to offer an in depth description of microphone design and construction as it is way beyond the scope of inSync.
A good general rule of thumb is that small diaphragm microphones (usually considered to have diaphragm diameters of less than .75 inches) tend to do a better job of catching transients and other high frequency information. They will tend to have a bit more “air” (subjective audio term #143) to their sound and often have less coloration than large diaphragm microphones. Most of this is due to the reduced mass of the smaller diaphragm which allows it to more closely follow any air disturbances it is subjected to. Other factors are that the smaller diameter diaphragm can be more rigid which can prevent other types of distortion, and greater sensitivity because it takes less sound pressure to set it in motion due to the low mass. Small diaphragm mics are often used on woodwinds and other delicate orchestral instruments, acoustic guitars, cymbals, hi-hat, small percussion instruments or anything where a lot of detail needs to be captured.
Large diaphragm microphones (usually considered to have a diameter greater than .75 inches) tend to do a better job of capturing the depth of very low frequency sounds (though some would argue this). At least they subjectively sound better on low frequency sounds to most engineer’s ears. In general they have a “big” sound (subjective audio term #49) to them that many people have found very pleasing over the years – particularly on the human voice. To accommodate the larger diameter they are probably going to have a thicker diaphragm which will tend to make them more durable in high SPL (see WFTD archive “Sound Pressure Level“) situations. Large diaphragm microphones tend to be used on things where a certain amount of coloration or a big sound is desired. Things like: Vocals, guitar or bass amps, drums, acoustic guitar, and some big brass instruments.
Most studios will have a compliment of both kinds of microphones to choose from in order to capture the best qualities of any instrument being recorded. One will be better than the other only in the context of the job at hand and the subjective preferences of the artists doing the sound.