One of the top microphone myths that many people believe is that all shotgun microphones have very tight pickup patterns and can capture audio over a long distance. This misconception is addressed by Shure microphones as follows: “The reality is that microphones do not reach out and grab the sound from a distance. They merely measure pressure variations right at the diaphragm itself.” This leads us to understand that the one specification of a microphone that loosely corresponds to the concept of reach or distance is directionality or the microphone’s polar pattern.
So, Why Use a Shotgun Microphone?
First, all shotgun mics employ a standard directional capsule, but with a long, hollow, slotted interference tube attached to its front surface. The interference tube design is so the wanted on-axis sound passes straight down the length of the tube to the capsule diaphragm unimpeded, but the unwanted off-axis sound from the sides reaches the diaphragm by entering the side slots. This design has its drawbacks, though, because different frequencies have different wavelengths and each frequency is affected differently. So, coloration for off-axis sounds of the original waveform are attenuated differently, according to frequency. In addition, the interference tube does not provide any amplification. It is attempting to block off-axis sounds (side noise). Any amplification comes from an electronic amplifier built into the shotgun microphone itself. More amplification means more electronic noise. These mics sound their best at no more the 3.5 to 4' with an ideal height of 2 to 3' above the sound source, and are great for interview applications.
Then Why Use a Parabolic Mic?
A parabolic microphone provides a natural mechanical amplification of about six times, due to the characteristics of the collector dish. The special shape of the parabolic dish collects the incoming pressures (sound waves) and focuses them onto a single point (the microphone). The microphone is usually an omnidirectional or a cardioid pickup pattern placed inside the dish, but this depends on the size of the dish, as well. The level of amplification is consistent over the entire area of the parabolic dish. The microphone will pick up some ambient noise from the rear of the mic, but the amplification provided by the dish makes the non-amplified sounds, coming from the back side of the mic, insignificant. The peripheral sounds outside the dish are not amplified and are blocked by the dish itself. This provides the directionality of the parabolic microphone.
Additionally, only parabolic mics can deliver directional sound pickup at great distances such as hundreds of feet. They effectively amplify low SPLs (sound pressure levels) from long-distance sources while at the same time reduce ambient sounds. So, sporting events, surveillance, nature documentaries, sound library collections, search and rescue, wedding shoots, and videography are common applications for parabolic mics.
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