Making a Parabolic Microphone

Materials needed to make the parabolic microphone

· Parabolic dish/Reflector Dish

· Microphone

· Audio Receiver

· A rod to hold the microphone in place

How to make a Parabolic Microphone

Point the dish towards the target and adjust the position of the microphone, ensuring that it is pointed directly to the focal point. When then volume and sound quality is at its best, that position of the microphone would be at the focal point. Attach the rod to hold the microphone in its place so that it will not lose its position at the focal point. Preferably use coat hanger wires or metal rods as they are easy to adjust and do not affect the sound quality much. Attach an amplifier to the microphone and connect it with a headphone. The parabolic microphone is done.

Considerations to take into account when making the equipment

If the size of the disc is increased, the amount of sound waves collected is also increased. Large parabolic dishes collect more sound. For instance, if the size is double, the amplification is the square of the difference in size. For example, a two-metre diameter dish will capture four times as much sound as a one-metre diameter dish.

For a clearer sound, the focal length is vital. The focal length represents the distance from the center of the dish to the focus point. With a longer focal length, the signal is less disrupted and more specific.

However there is one flaw in the designs of parabolic sound dishes. To focus a specific sound wave, the wave length of that wave has to be much smaller than the diameter of the dish itself. Because of this, most parabolic dishes have to sacrifice certain types of sounds to be more manageable in size.

Sound waves travel at 342 m/s through the air. In order to obtain an accurate sound (down to 20 Hz), one would require a parabola with a diameter of at least 17 meters (= 342 m/s / 20 Hz). 20Hz is the lowest sound in which human ears can detect.

Hence, in order to make a suitable parabolic microphone that can be adjusted easily according to the target, it cannot be too big. Most birds produce sounds with at least 500Hz to beyond 8000Hz. Hence, the ideal size for the microphone, such that it is easy to move around is around 34cm (342m/s/1000Hz)

How a Parabolic Microphone Works

A parabolic microphone involves the attaching of an end of a handle to a small audio receiver at the focus. The audio receiver is connected to an amplifier circuit, which is used by the user to listen to the amplified sounds with ear phones. If the user were to place his head near to the focus, so that he can listen to the sounds being amplified, his head would block the sound waves. The sound waves would not be able to reflect the waves into the focus to be amplified and hence would not work, thus the need of a small audio receiver.

The user looks at his target from a distance and points the sound dish at it. Unfortunately, the long distance from the target might result in the parabolic microphone amplifying the wrong sounds as it did not catch the sound waves produced by the target, but by the bird. Hence, the user must use his own hearing, ensuring that the microphone is properly locked on the target.

Concepts about sounds and how it works

When we produce sounds, they travel through the air in sound waves. Sound itself is energy; therefore it tends to spread all around. The direction of sound waves is generally omnidirectional, which means they travel in all directions. However, no matter how they travel, they preserve their variations of pressure for the sound it is producing.

Ever wondered why we hear persistent echoes in an enclosed room when we make a sound? This phenomenon is due to the ability of sound waves to reflect against surfaces. Because there is no other way for the pressure to escape, the echoes are actually reflections of the waves of the walls in another direction. This is known as reverberation.

If a sound wave hits an uneven surface, the angles of reflection varies with the angle of the surface. If a sound wave hits a completely straight surface, the angles of reflection will just rebound in the exact opposite direction.

However, if it was to bounce off a parabolic disc, all of the sound waves will reflect towards a designated location, which is the focus. This property is extremely important because the refocusing of the wave can amplify the signal. For example, if a faint sound wave hits a parabolic disc, all of the waves will be reunited at the focus and amplified. Because the sound waves preserve their pressure configuration, the signal will turn out to be uniform and clear.

Proposed real world situation

Hello there!

Here is our proposed real world situation.

One's hobby is bird watching and listening. Thus he uses parabolic microphone to listen to the sounds made by the birds from a distance because as mentioned above, parabolic microphone can amplify a sound from a distance. If the person goes too near to the bird, he might scare the bird away. Hence, he uses a parabolic microphone which can be used to amplify the bird's sounds for him to listen, without him having to move near the bird.

Constraint: Weight and size of parabolic microphone must be movable and convenient to move around, distance from the birds, size of audio receiver

Variable: Diameter of the parabolic microphone