What are the pros and cons of parabolic microphones?
By Paul Terpstra
If you watch any NFL or college football game here in the United States, you are almost certain to see a few TV guys along the sidelines holding a large plastic dish. Those dishes are in fact some type of parabolic microphone, and the TV network puts them there in order to capture sounds from the playing field. Parabolic microphones are specialized microphones that are designed to capture sound from a distance by using a parabolic reflector to focus sound waves onto a sensitive microphone element. (Refer to our article “What is a parabolic microphone and how does it work?” to learn more specifics on parabolic mics.)
If parabolic mics are so good for football why don’t we see them used more often? Here are some of the pros and cons of using parabolic microphones:
Because the parabolic collector (dish) collects the sound energy from a large area and focuses that energy onto a single point, parabolic mics provide a great amount of mechanical amplification. This is a huge benefit as the amplification is natural or “mechanical,” meaning it’s not done electronically. This is significant because electronic amplification (such as turning up the gain on your recording device or amplifier) produces imperfections and “self-noise.” This is the faint hum or his that is produced by all types of electronic amplifiers, to some extent.
The larger the collector dish is, the more mechanical amplification it provides. This is because, when you double the diameter of the dish you quadruple the surface area that is being collected.
The amplification provided by the parabolic collector creates a microphone with great range. So what sort of range or distances are we talking about?
The 26-inch diameter KLOVER MiK 26 can capture a normal conversation from up to 500-600 feet away. The 9-inch diameter KLOVER MiK 09, one of the smallest available, can capture a normal volume conversation up to 30-50 feet away.
Note that range is always difficult to define because it depends on many factors such as how loud the sound source is and how much ambient noise there is at the location. If you’re out in the desert, you’ll be able to listen to things at a much further distance than if you’re recording in a packed-out football stadium. Even wind and humidity can affect the range of a microphone.
In most situations you want to capture the subject directly in front of the camera, not things off to the side or behind. For parabolic microphones, the frequency range of human voice will be captured and amplified between 20 and 30 degrees away from the centerline (up to 40 degrees depending on how low, or bass, the voice you want to capture is).
This is quite significant when you realize that very high-end shotgun microphones will capture that same frequency range between 70 and 80 degrees away from the centerline. So parabolic microphone pickup patterns are typically twice as narrow as those of a shotgun microphone.
Once again, the area that is being captured grows exponentially as you move away from the centerline of the mic. If the pickup pattern is expanded from 30 degrees away from the centerline, to 60 degrees away from the centerline, the width of the pickup pattern increases by 73% and the surface area within that pickup pattern is tripled. As you can see, tightening up the pickup angle creates a huge reduction in the amount of unwanted audio you will capture. This allows you to hear the players and not the screaming fans or coaches on the sidelines.
The highly directional nature of the parabolic microphone is due to 3 facts:
#1 Sounds from the side and behind the dish are blocked by the dish itself
#2 Sounds that are coming from “off-center” (not directly in front of the dish) hit the dish but are reflected away from the microphone receiver.
#3 Sounds directly in front are greatly amplified by the unique shape of the dish.
Parabolic mics have a frequency bias which can “color” the audio. This bias occurs because low frequencies are absorbed into the dish more than high frequencies. Alternatively, you could say the high frequency sounds reflect more efficiently than low frequencies. This results in the mic receiving sound which is amplified more strongly at higher frequencies than the lower ones.
Contrary to some myths, the resulting audio signal doesn’t sound like you’re in a “tin can”. Most non-experienced listeners will not be able to tell the difference, though audio engineers likely will.
While you won’t want to use them for music recording or for movie production, where you want the highest possible quality and the budget is no concern, smaller parabolics are used quite regularly on the news without viewers knowing. Additionally, since this problem is fairly linear, it can be compensated for with equalization in editing, should you so choose.
Again, the amplification increases exponentially when you increase the size of the dish. So if you want to hear from a greater distance, you need a bigger dish. Klover Products manufactures collector dishes ranging from 9 inches in diameter up to 26 inches in diameter.
Consequently, these dishes can get quite large depending on the desired amplification. This can make them difficult to work with depending on the use-case. However, if you’re not needing as much amplification, the smaller sizes are much easier to travel with.
If transportation is a concern, custom hard cases are available for even the largest parabolic microphones. It should be noted that modern parabolic microphones are quite durable when properly constructed. At Klover Products we form the dish from polycarbonate which is used to make bulletproof glass. The other components are constructed with carbon fiber or Kevlar reinforcement to increase strength while reducing weight.
Obviously how useful a parabolic mic would be for you depends on your unique situation. If you would like to discuss your particular needs in capturing long-range audio, use our Contact Us form to reach out. We love to help.
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