What is a Parabolic Mic and How Does it Work?

Have you ever wondered what the TV guys are holding on the sidelines of a football game? Or… have you heard the term parabolic microphone and wondered exactly what that was or how it works?

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.

‍So what is a parabolic microphone?  

A parabolic microphone is a combination of two separate items.  1) a parabolic collector and 2) a microphone.  

Let’s begin with the microphone.

A microphone is an electronic device that converts sound pressure into an electrical signal.  That electronic signal is then amplified so the original sound can be listened to, recorded, or transmitted.  We will be creating a number of articles on the details of microphones themselves, so be sure to check out our other articles on our Learning Page.

Now let’s talk about the parabolic collector.

A parabolic collector is anything with the shape of a parabolic curve.  A parabola is a bowl shaped curve defined by a mathematical equation discovered by Menaechmus in the fourth century B.C.  One mathematical definition of a parabola is the set of points that are all the same distance from a fixed point called the focus and a line called the directrix.

The special feature of this curve is its ability to focus energy coming straight at it, onto a single point.  Satellites, radar, and cell phone towers all use this special ability to focus electromagnetic energy from a large area onto a receiver.  Huge radio telescopes use it to collect faint signals from outer space.

Sunlight reflected off of a shiny parabolic collector is intense enough to light a cigarette, or heat a meal.  It can even create steam for an electric generator.

Interestingly, the curve can be used in reverse.  The light from a flashbulb inside a parabolic curve will be reflected outward in a straight line.  Parabolic reflectors were used by photographers and videographers for many years.

Sound energy can be collected in the same way and focused onto a single point.  When you cup your hand around your ear you are creating an imperfect parabolic collector.  Owls have parabolic shaped faces that allow them to collect faint sounds of their prey.

One of the first widespread uses of this ability to capture faint sounds was detecting aircraft.  The British developed a network of “sound mirrors” that were used from World War I through World War II.  

The sound mirrors were normally rotated so the angle, or direction producing the loudest sounds could be determined.  Using two sound mirrors at different positions generated two different bearings allowing the location of the sound source to be triangulated.  Some large, stationery audio collectors are still standing today near the English Channel.

Acoustic aircraft location was critical once aircraft came into common use but was ultimately replaced by radar.  The systems in these photos were developed by the Dutch in the 1930s.

Whether it was intentional or an accident, many buildings have “whisper chambers” where the shape of a wall forms a parabolic collector.  A person standing at the focus point of the parabolic wall can hear faint conversations from considerable distances.

Why is the shape of a parabolic collector so important?

If the reflector is not a true parabolic shape the energy will not be focused on one point.  The reflected energy will be scattered about instead.  The images on the right show how the hemispherical shape reflects the energy but that energy is not focused onto a single focus point.

Think of how a magnifying glass must focus the sun’s energy precisely if you want to burn your initials into a block of wood.  If the light is not focused you just have a bright spot.

In the same way, using a bowl of some type that is NOT a true parabolic shape will provide sound that is not focused and will have much less amplification.

So, how does a parabolic microphone work?

As we’ve discussed, all the sound energy entering directly in front of a parabolic collector will be focused onto a single point.  The focusing of the sounds from a relatively large area onto one single point provides a significant “mechanical” amplification. When an electronic microphone is placed at that focus point the sound pressure acting on the sensing element has already been amplified before any electronic amplification is added to the signal.

So, why would I use a parabolic microphone?

The first reason is the mechanical amplification we just discussed.

The second, is a parabolic microphone’s ability to focus in on sounds from one direction.  While the sound from the front of the collector is being amplified, a large portion of the the sounds from the rear of the collector, or from the side, are reflected away.  This allows a parabolic microphone to focus on sounds from one direction.  You can think of this as blinders for the microphone.

How are parabolic microphones used?

Obviously parabolic mics are used by television producers to focus in on the sounds of the game during sporting events.  Unfortunately, many people think that is the ONLY use for parabolic microphones.

Parabolic microphones are used by law enforcement and military personnel to listen for sounds and voices from considerable distances.  Search and rescue teams use them to triangulate the position of people lost in the wild.

They are used in industrial environments to listen for unwanted noises such as arcs or leaks.

Nature enthusiasts use parabolic microphones to get sounds that are as focused as the visuals their long lenses can supply.

Small parabolic microphones allow vloggers to record their voice without being confined to a certain location, or worrying about a wireless mic.  We use a small parabolic mic for online meetings so we can move about, turn our head, and use the keyboard without dealing with a microphone in our face.

Conclusion

So to recap, a parabolic microphone is a combination of a parabolic collector and a microphone, or sensor.

The parabolic collector collects the sound energy from a large area and focuses that energy onto a single point.  The microphone is placed at the focus point to generate an electronic signal from the already amplified sound.

Parabolic microphones can be used whenever a sound source is too faint to be captured with a typical microphone, or when the sounds from a certain area need to be pulled out from surrounding sounds.

Obviously how useful a parabolic mic would be for you depends on your particular needs.  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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