Perhaps you've been recording with a smartphone or a handheld recorder for some time now and
you'd like to up your game.
One of the best things you can do to improve the front end of your system is to attach
a directional microphone.
For wildlife recording, two types of directional mics are commonly used.
The parabolic reflector system, or parabola for short, and the shotgun microphone.
In this session we'll talk about the parabolic reflector.
Specifically we'll talk about four things.
Why use a parabola.
How it functions.
How to aim a parabola.
And the Pro and Cons of using one.
So let's get into why you'd use a parabola.
Any sound can be electronically amplified, but electronic amplification comes with a
cost.
Noise, often described as hiss.
As one increases the level of amplification, the electronic and environmental background
noise get louder and louder.
Just as the signal of interest does.
A parabolic reflector is a noise free, mechanical amplifier.
In the most basic terms, using a parabolic reflector is like cupping your hand behind
your ear to make a sound louder, only much more effective, due to the parabolic curve.
So how does it function?
A parabola is based upon a geometric curve.
Sound pressure waves arriving perpendicular to the parabolic curve are reflected back
to the focal point.
The distance traveled by sound pressure passing through any point of the plane of the parabola's
rim and then reflecting off the inside surface, to the focal point, is the same distance.
The geometric curve directs the sound energy to the parabola's focal point and that in
combination with the parabola's surface area, thereby amplifies the signal.
In contrast, sound pressure waves arriving off-axis of the parabola reflect off of the
dish, but are not reflected back to the focal point and therefore are not amplified.
Using a parabola requires precise aiming.
Wherever you point that parabola with its narrow angle of acceptance, that's what's
going to be tremendously amplified.
While an animal is vocalizing by methodically moving the parabola across the horizontal
axis, listening for the point at which the animal sounds the loudest, and then doing
the same for the vertical axis, you can quickly and efficiently locate a sound source that
you're unable to see.
For field recording, a parabolic curve with a focal point at or close to the rim of the
dish is desirable.
It provides protection against wind and is easier to carry in the field than a reflector
with a focal point outside the rim.
You need one more thing to properly aim the parabola.
You need a good pair of headphones that allows you to hear that dramatic increase of the
loudness of the signal, and the great detail you're going to hear when you're aimed directly
at the subject.
So what are the cons of using a parabolic reflector?
One, that the diameter of the dish determines the lowest frequency you can record.
Any sound frequency wavelength that's longer than the dish is wide, won't be reflected
off the dish, and therefore there's no amplification at those frequencies.
The second is that the diameter of the dish makes it a little awkward to carry through
dense undergrowth.
Another con is that the parabola accentuates higher frequencies and therefore alters the
sound that you're recording.
So what are the positive aspects of using a parabola?
One is it gives you tremendous reach.
If you're trying to record a bird that's up in a tree, using a parabola is going to give
you a sound that it appears the bird is sitting right on your shoulder vocalizing.
Another is that a parabola will allow you to achieve a high signal to noise ratio.
Its amplification property help you overcome noisy situations where there may be a lot
of other acoustic activity in the area.
Because of its great directionality and amplification property, it lifts that sound out of the
sound scape for you.
In short, using a parabola is going to give you a better signal to noise ratio, in any
given situation, and allow you to operate at a greater distance from an animal than
you would be able to with any other type of microphone.