CHAPTER 1

There are several ways to capture and listen to sounds at a distance. Obviously, it could always set microphones at a location of interest, and transmit the sounds by wire or radio to certain position. However, that is not always convenient or practical in certain cases of surveillance, or when dealing with bird calls or animal sounds. Another option is to use a sensitive, directional microphone similar to those used in network TV broadcasts of football or other sporting events. Such microphones typically have parabolic reflectors for focusing sound onto them which is perfect for long-distance monitoring or surveillance (Blackwell, 2012).
A parabolic microphone uses a parabolic reflector (or dish) that will collect and focus sound waves onto a microphone receiver, in much the same way that a parabolic antenna (e.g. satellite dish) does with radio waves. A parabolic reflector will focus a parallel wave of sound onto a specific point, allowing a very weak sound to be more easily heard. Such reflectors are used in parabolic microphones to collect sound from a distant source or to choose a location from which sound is to be observed and then focus it onto a microphone (Matos, 2012).
A parabolic microphone works much like a satellite dish. A parabolic dish reflects the sound waves from a larger area down to a small point, so using a parabolic dish with an attached microphone can allow a person to listen to unclear sounds at a great distance. When looking for a parabolic dish to be the base for the sound collector, materials similar to a flattened bowl or a satellite dish should be utilize (Wood, 2013). The collector portion of the microphone used in the project was made from an inexpensive material such as umbrella hat.

Theoretical Framework

Sound energy is a very exciting starting point for exploring and observing natural phenomena. The sound waves that can hear with the ears are but a very limited range of the total audio spectrum. The perception of sound allows to "hear" only the narrow slice of energy between 20 Hz and 15 KHz on this spectrum. In fact a whole range of audio exists both above and below the range of what can perceive, which is in fact very interesting to explore (Norderval, 2012).
Sound Mirror. Figure 1 shows a sound mirror, known as the "listening ears", consist of three large concrete reflectors built in the 1920s–1930s. This experimental nature can be discerned by the different shapes of each of the three reflectors: one is a long, curved wall about 5m high by 70m long, while the other two are dish-shaped constructions approximately 4–5m in diameter. Aeroplanes flying across the channel could be heard by observers positioned near these "ears".

Figure 1. Sound Mirror
A sound mirror is a passive device used to reflect and perhaps to focus sound waves. Prior to World War II and the invention of radar, acoustic mirrors were built as early warning devices around the coasts of Great Britain, with the aim of detecting incoming enemy aircraft by the sound of their engines.
Parabolic microphones depend on a parabolic dish to reflect sound coming from a specific direction into the microphone placed at the focus. Because of their small, portable size, they can easily be used in the same manner as sound mirrors for detection and direction finding of distant noise sources (Wikipedia, 2013).
Parabolic Reflector. A parabolic (or paraboloid) reflector (or dish or mirror) is a reflective surface used to collect or project energy such as light, sound, or radio waves. Its shape is part of a circular parabolic, that is, the surface generated by a parabola revolving around its axis.

Figure 2. Parabolic Mirror
The dimensions of a symmetrical paraboloidal dish, as shown in figure 2, are related by the equation: 4FD=R where F is the focal length, D is the depth of the dish (measured along the axis of symmetry from the vertex to the plane of the rim), and R is the radius of the rim. Of course, they must all be in the same units. If two of these three quantities are known, this equation can be used to calculate the third.
A more complex calculation is needed to find the diameter of the dish measured along its surface. This is sometimes called the "linear diameter", and equals the diameter of a flat, circular sheet of material, usually metal, which is the right size to be cut and bent to make the dish. Two intermediate results are useful in the calculation: P=2F (or the equivalent: P=R22D and
Q=P2+R2, where F, D, and R are defined in figure 2. The diameter of the dish, measured along the surface, is then given by
RQP+PlnR+QP, where lnx means the natural logarithm of x, (i.e. its logarithm to base "e").
The parabolic reflector functions due to the geometric properties of the paraboloidal shape shows that in any incoming ray that is parallel to the axis of the dish will be reflected to a central point, or "focus". Because many types of energy can be reflected in this way, parabolic reflectors can be used to collect and concentrate energy entering the reflector at a particular angle (Binarywolf, 2012).
Microphone. A microphone, as shown in figure 3, is a transducer that converts sound waves into electrical signals proportional to the strength of the sound. The microphone output can be recorded or transmitted.

Figure 3. Microphones
Although there are various types of microphones, the operating principal is the same. A diaphragm, either metal or plastic, vibrates in response to a sound wave and transmits the movement to an electrical component causing an induction of an electrical current. Microphones can be classified according to the way the diaphragm transmits sound or the way they pick up the sounds.
Based on the way the sound is transmitted, there are five groups of microphones: carbon, dynamic, ribbon, condenser and crystal. Each of these microphones can be made to pick up sounds from various directions. There are omnidirectional, bidirectional, cardioid, hypercardioid, supercardioid and parabolic microphones. Omnidirectional microphones pick up sounds from the entire surrounding area (360°). In contrast, bidirectional devices have only a 90° pickup arc. The various cardioid microphones pick up sounds from a 105–131° arc. Parabolic microphones are the most unidirectional microphones, therefore, they have to be pointed directly at the source of sound. Their name comes from the fact the microphone itself (for example, omnidirectional) is surrounded by a parabolic dish. This dish gathers sounds and, by directing it to the microphone, also amplifies it.
None of the different types of microphones is superior to the other. They are all suited for different purposes. Important factors in selecting a microphone include the sensitivity, quality of sound, overload characteristics, and especially for surveillance and intelligence purposes is the size of the microphone.
The sensitivity of the microphone is measured by an amount of current produced. The currents produced by the microphones are very small and a signal has to be amplified before it can be used. However, amplification is not selective. Not only are the sounds amplified, but also any noise that was produced by an instrument itself. Sounds that are too loud or bad placement of a microphone can lead to distortion of the diaphragm known as an overload.
In any surveillance operation, placement of the microphone is crucial, not just for the quality of sound, but also for remaining inconspicuous. Microphones can also be carried by people to provide continuous surveillance or rapid identification and response. Such microphones are often combined with a transmitter or a recorder to send or record conversations (Lichanska, 2013).
Condenser Microphone. Electret or condenser microphone is the type of microphone used in the project. It was invented in the late 1910's to deal with problems of signal to noise ratio and frequency response found in the previously popular carbon microphones. E.E. Wente at Bell Labs was the first to develop the 394 condenser microphone, shortly followed by the RCA 4AA. Since then the condenser microphone has been refined to include various pickup patterns, such as omnidirectional capabilities, switchable pickup patterns and more durable diaphragms to accommodate more diverse applications.
The use of the term condenser is actually not appropriate, as it uses a capacitor to convert an acoustic signal to electrical energy. This is why a condenser microphone is sometimes referred to as a capacitor microphone. The condenser microphone, as shown in figure 4, is made up of two plates: a front plate and a back plate. The front plate is known as a diaphragm and is made of a very light material. As acoustic energy hits the diaphragm it vibrates, thus reducing and increasing the distance between the two plates. When the plates are close, capacitance, or the change of current, increases and when the plates are farther apart, it decreases. This current is sent through a battery to increase its voltage and then sent through the output. Since a power is required to boost the electrical signal, a condenser microphone requires either a battery or power from an external source, such as a mixer or audio interface, known as phantom power.

Figure 4. Condenser Microphone
The condenser microphone is known for its sensitive signal which allows it to capture the details of a sound source with low self-noise. Coupled with a need for an external source of power, condenser microphones are most frequently used in a studio setting to record a diverse array of instruments and vocal performances. It is rare to see a condenser microphone used in a live setting because of their sensitivity. A shotgun microphone, used for film and broadcasting, is a type of condenser microphone that is both extremely directional and made of more durable material than other condenser microphones for use in unconventional settings.
The condenser microphone is built to be sensitive to its sound source and is different from other microphones. A dynamic microphone, for instance, is known for its durability and performance even with loud sound signals. It also does not require phantom power to work which makes it the most popular choice for live performances. A dynamic microphone is not able to pick up the same nuance of sound as a condenser microphone, which is more likely to produce the warm sound needed for studio recordings. Though they work differently, ribbon microphones perhaps come the closest to the sound of a condenser microphone, though they do differ. Condenser microphones are designed to accentuate certain frequencies, depending on their presumed use. Ribbon microphones, on the other hand, provide a much flatter frequency response and do not need phantom power to boost their signal (Hoffmann, 2011).
Parabolic Microphones. It only focuses on waves that are smaller than the diameter of the parabola. Since sound waves travel at a speed of 300 m/s through the air, a parabolas would have to have a diameter larger than 15 meters (300 m/s = 20 Hz = 15 meters), in order to reach the standard of high-fidelity sound to the human ear, which is at least 20 Hz. However, often parabolic microphones give up high fidelity sound in order to allow the microphone to be a more convenient size (Ryleymath, 2013).
Amplifier. The purpose of an amplifier is to pick up a weak signal coming from the parabolic microphone and converts it into a strong one. It is widely used in several devices to boost electrical signals. In the case of a pre-amplifier the signal must be amplified enough to be accepted by a power amplifier. In the case of a power amplifier, the signal must be enlarged much more, enough to power a loudspeaker (Altunian, 2013).
Serial Port. A serial port is an interface on a computer system with which information is transferred in or out one bit at a time. An interface is a connection between two subsystems. In this case, it is an electrical connector built into a computer into which another external connector can be easily inserted (and removed) by a user to allow data to be transferred to or from peripheral devices (e.g., display units, keyboards, mice, printers and scanners). The advantage is that the cable is very small, thin, light and cheap (Jponbac,2013).
Line-in and Line-out. The line in or line-in is a port found on computer sound cards that enables a user to connect an external audio device such as a cassette tape player, disc player, audio mixer, additional microphones, etc. to record or otherwise manipulate the incoming audio. Figure 5 shows the back of the sound card. With this sound card the line-in port is blue and is represented as an arrow pointing into sound waves.

Figure 5. Sound Card
While in sound out, the line-out is a port found on computer sound cards that allow external speakers, headphones, or other output devices to be connected to the computer, which enables computer generated sound and audio can be heard. With this example sound card, there are three line out port, ports that are green, black, and orange each represented with an arrow pointing out of sound waves, as shown in figure 5. With most computers, there will only have one sound out connector that will be green (Jargon, 2013).

Conceptual Framework

High Power Amplifier
Pre-Amplifier
Parabolic Microphone

Sound
(Input)
(Input Device)
External Speaker
PC

(Output Device) (Interfaced)
Figure 6. Block Diagram of the Parabolic Microphone
The parabolic microphone takes the sound input and focuses sound waves. It is generally not used for standard recording application since it tends to have poor low-frequency response. A pre-amplifier will be used to increase the low-level signal coming from the parabolic microphone. The high power amplifier will boost the resulting signal strength to energy the sound input without degrading the signal to noise proportion. It will be then interfaced in a computer where sound can be analyzed and recorded. This sound can be heard using either a speaker embedded in the computer or an external speaker.

Software Specification

Operating System: * Windows XP * Windows Vista * Windows 7 ( 32bit or 64 bit)
Application:
* LibZPlay (Win32)
Version 2.02
This is multimedia library for playing mp3, mp2, mp1, ogg, flac, ac3, aac, oga, wav and pcm files and streams.
New: version 2.02 can also record sound from soundcard and encode into disk file with mp3, ogg, flac, aac or wav encoder.

Other Specification: * 2GB RAM * Intel Core i3-2120 CPU or higher * Monitor - 1366 x 768 resolution * com Port * Speaker * Keyboard * Mouse

Computer Interface

Figure 7. Parabolic Microphone Application

The designed software will receive a sound which is amplified by pre-amplifier and high power amplifier. Figure 7 shows a parabolic microphone application developed in this project. With parabolic microphone application, it can record, play, and analyze the sound spotted by the parabolic microphone. The file(s) that has been recorded can be retrieved and replay. It also displays the changes in frequency range and the noise level coming from the sound input.

Definition of Terms
The following key terms are herein defined for better understanding of the study:

Amplifier. A device that increases the power of a signal,
Audio Spectrum. It is a representation of a sound, usually a short sample of a sound, in terms of the amount of vibration at each individual frequency. It is usually presented as a graph of either power or pressure as a function of frequency. The power or pressure is usually measured in decibels and the frequency is measured in vibrations per second (or hertz, abbreviation Hz) or thousands of vibrations per second (kilohertz, abbreviation kHz).
Bell Labs. It is one of the most popular scientific laboratories in the world.
Bidirectional. Moving in two usually opposite directions.
Carbon Microphone. A microphone in which a diaphragm, vibrated by sound waves, applies a varying pressure to a container packed with carbon granules, altering the resistance of the carbon. A current flowing through the carbon is thus modulated at the frequency of the sound waves.
Capacitance. The ability of an object or a system of objects to store an electric charge.
Capacitor. To store energy, in an electric field between separated charges.

Cardioid. Traced the path of a point on a circle as the circle rolls around a fixed circle of the same radius.
Crystal Microphone. A microphone in which sound waves vibrate a piezoelectric crystal that generates a varying voltage.
Condenser/Capacitor Microphone. It designed to capture the sounds with sensitivity and accuracy.
Diaphragm. A thin, flexible disk, especially in a microphone or telephone receiver that vibrates in response to sound waves to produce electrical signals, or that vibrates in response to electrical signals to produce sound waves.
Dynamic Microphone. A microphone in which the sound waves cause a movable wire or coil to vibrate in a magnetic field and thus induce a current.
Electric Current. It is the rate at which charge flows through a surface (the cross section of a wire).
High-Fidelity (HI-FI). A sound reproduction over the full range of audible frequencies with very little distortion of the original signal.
Hypercardioid. Records from the front, a lesser extent to the sides, and rejects everything around 120 degrees to the back of the microphone.
Linear Diameter. The distance between an object’s opposite sides.
Microphone. It detects sound signals and produces an electrical image of the sound. The most common microphones for musical use are dynamic, ribbon, or condenser microphones.
Omnidirectional. It is designed to receive signals in all direction.
Overload. To provide too much power to a circuit.
Parabolic Dish. It is a reflective surface used to collect energy such as sound. Its shape is part of a circular parabolic, the surface generated by a parabola revolving around its axis.
Parabolic Microphone. Unite sound waves toward a single point called the focus, giving it the ability to record sound from a great distance away, some even claim to pick up sound waves from as far as 50 yards away. It can determine the ideal microphone placement by calculating the focal point of the dish.
Phantom Power. A method for transmitting DC electric power through microphone cables to operate microphones that contain active electronic circuitry.
Radio Detection And Ranging (Radar). It is an object detection system which uses radio waves to determine the range, altitude, direction, or speed of objects. It can be used to detect aircraft, ships, and spacecraft. The radar dish or antenna transmits pulses of radio waves or microwaves which bounce off any object in their path.
Ribbon Microphone. Also known as a ribbon velocity microphone, is a type of microphone that uses a thin aluminum, duraluminum or nanofilm electrically conductive ribbon placed between the poles of a magnet to generate voltages by electromagnetic induction. It is typically bidirectional, meaning they pick up sounds equally well from either side of the microphone.
Satellite Dish. It is a parabolic shaped antenna used for data transmission and broadcasting. A dish antenna used to receive and transmit signals sent by satellite.
Sound Energy. It is the power produced by vibrating sound waves. An example of sound energy is the small amount of vibrations collected by the outer ear which let a person hear.
Sound Mirror. Also known as Acoustic Mirrors, Concrete Dishes or Listening Ears, are large concrete structures designed as an early warning system for Britain to detect enemy aircraft.
Sound Waves. It is the pattern of disturbance caused by the movement of energy traveling through a medium (such as air, water, or any other liquid or solid matter) as it propagates away from the source of the sound.
Supercardioid. A variation of the cardioid microphone that is most sensitive at the front while rejecting sounds entering 150° to the rear.
Surveillance. It is the monitoring of the behavior, activities, managing and directing.
Financial Statement Materials/Components | Quantity | Unit Price | Price | Resistor | 7 pcs. | ₱ 0.30 | ₱ 2.10 | Potentiometer | 2 pcs. | 10.00 | 20.00 | Capacitor (tantalum) | 2 pcs. | 8.50 | 17.00 | Capacitor (electrolytic) | 2 pcs. | 1.00 | 2.00 | Capacitor (disc) | 2 pcs. | 0.50 | 1.00 | Toggle Switch | 1 pc. | | 8.00 | Electret Microphone | 1 pc. | | 18.00 | 9-volt battery | 1 pc. | | 35.00 | Alligator Clip | 2 pcs. | 7.00 | 14.00 | PCB | 1 pc. | | 44.00 | UI LM386 | 1 pc. | | 22.00 | TL 084 | 1 pc | | 25.00 | Ferric Chloride | 1 pc. | | 25.00 | Wire | 1 meter | | 9.00 | Casing | 1 pc. | | 30.00 | Header Socket Male | 2 pc. | 5.00 | 10.00 | Soldering Lead | 3 meter | 10.00 | 30.00 | Umbrella Hat | 1 pc. | | 48.00 | Total Amount | ₱360.10 |