jbulman's blog

Sound is delivered in many ways. One of the most commonly seen deliveries of sound come through the sound amplification of a microphone. Microphones are used primarily to address large crowds without raising one’s voice. The microphone detects the vibrations of the noise and produce an electronic signal that corresponds with the vibrations. The electronic signal is then sent through to the speaker, which translates the electronic signals back into sound vibrations, which are considerably more amplified. The types of microphones that used most commonly are dynamic, ribbon, and condenser microphones.

The general structure of a dynamic microphone Is a pressure sensitive metal coil wrapped around a magnet. When the vibrations of sound hit the coil, it moves back and forth across the magnet. Through the generator effect, the motion is then translated into voltage which travels through wires to an amplifier. The amplifier in turn translates the voltage back a dynamic loudspeaker. The dynamic loudspeaker then uses the voltage to produce a magnetic field that moves the coil to produce sound vibration. Dynamic microphones are generally the cheapest and easiest type of microphone to make.

A ribbon microphone uses a similar idea to produce an electronic message out of vibrations. Vibrations in the air move an incomplete circle of metallic ribbon with a magnet in the middle. Similarly to the dynamic microphone, the movement of the metallic ribbon is translated into a voltage. The voltage is then sent to an amplifier and translated back into louder sound vibrations through a speaker. Ribbon microphones most effectively produce very warm sounding low frequencies.

A condenser microphone produces the highest overall frequency response which translates into the highest quality of sound. Two thin metallic filaments are attached parallel to each other held at either end by charged plates. One of the plates is given a negative charge by an external battery. As vibrations move through the air between the filaments, the filaments move. The changing distance between the filaments causes a change in the charge of the plates. The change in charge produces an individual electric current reflecting the vibration. The current is sent through an amplifier and retranslated into vibrations.

One of the key factors that affect musical performance is the surrounding that it is performed in. Whether it be live music in a concert arena, an open air theater, or an enclosed recording studio the environment or acoustics of the room effects the sound and quality of the music. Acoustics is a broad term defined as the interdisciplinary science that deals with the study of all mechanical waves in gases, liquids, and solids including vibrations, sound, ultrasound and infra-sound . All acoustic actions have the same five steps that they share; there is a 1. Cause, 2. Generating mechanism, 3. Acoustic wave propagation, 4. Reception, and 5. Effect.

The knowledge of acoustics has been around for many centuries. Ancient Romans are well known for their open air theatres that allowed for many people to hear performances without the use of microphones. Over the centuries, people have refined and perfected the technique of building theatres or auditoriums. A good auditorium will effectively project sound so that people at a far distance will not experience sound loss. The sound loss is caused by the Inverse Square Law, which states  that any physical law stating that a specified physical quantity or strength is inversely proportional to the square of the distance from the source of that physical quantity.

In addition to good projection to fight the inverse square law, high ceilings that reflect sound will also improve sound quality. The clarity of the sound is also another factor that is taken into consideration. An auditorium that echoes can diminish clarity, so it is important to limit the amount of objects that block direct sound waves. For more even sound dispersion, box shaped rooms should not be used because they create “flutter echoes”. Rather angled side walls better at achieving even dispersion.

Music is enjoyed around the world in many different ways. It is played in public settings, at home, and on personal music players. One of the factors that makes all this possible are speakers. Speakers are an electro-transducer that converts electrical signals from an audio input into sounds that are loud enough to be heard from a distance. Speakers are a modern marvel and have a lot of physics behind them.

There are a wide variety of speakers, ranging in different sizes and shapes to different music quality. However, most all speakers work on the same principles. Speakers receive an electrical signal from an audio input; this can be an mp3 player, a microphone, etc. Once the signal is received it is translated into sound by an electromagnet. The electromagnet is a thin coil that has an electric current running through it; it acts like a magnet as long as there is electricity running through it. Also, by reversing the current the poles on the electromagnet will flip. This is helpful because it allows the speaker to move back and forth. Next to the electromagnet is a permanent magnet that stays in place. When an electric charge goes through the electromagnetic coil, the coil will go in and out based on the attraction and repulsion of the permanent magnet. The coil is attached to a cone made of various materials, depending on the quality of the speaker, which amplifies the vibrations. This is what creates the vibrations that produce sound from the speakers. The cone will move very fast, usually about 40-50 times a second depending on the type of music you are listening to. The cone size also contributes to the sound quality. Many times high quality speakers will have numerous cones of different sizes to compliment different types of music. Smaller cones are used for high frequency music and larger cones are used for low frequency music.

Speakers are a simple yet effective piece of technology that help share the gift of music whether in a public place or personal enjoyment they play a key role in music.

Woodwind instruments are another group of instruments that are categorized as an instrument that produces sound by a musician blowing air into a sharp angled mouth piece. Most of the woodwind instruments produce high pitch sounds however there are exceptions. Woodwind instruments are not always made of wood, some are made of plastic or metal. Examples of woodwind instruments are the flute, piccolo, oboe, clarinet, saxophone, recorder, and bagpipes. Woodwind instruments play an important role in an orchestra, but they sound just as good as a solo piece.

Woodwind instruments work when a musician blows into a sharp mouth piece or reed. This causes the air in the instrument to vibrate; the place where this vibrating column of air is held is usually called a resonator. In simple instruments such as a recorder, there are very few pieces involved and a straight basics resonator. In more complex instruments like a saxophone there are bends and curves which help give the saxophone such a wide range of pitch. The saxophone can span the entire range of woodwind instruments. Another unique feature of the saxophone is the conical air column. The conical air column will produce the same fundamental frequencies as an open cylinder (recorder).  Also the holes that are controlled by the musician create different sounds. When a hole is opened it creates a shorter air column which makes the sound a higher pitch. Inversely, when a hole is left closed the pitch will be lower.

Another unique instrument in the woodwind family is the piccolo. The piccolo has the highest pitch of all the woodwinds. The shape of the piccolo is what gives it its high pitch. It has a short length and controllable holes that allow for an even shorter air column. When it is played, even in an orchestra setting, it can usually be heard quite easily.

Percussion instruments are also very popular instruments and vary in shape, size and weight. There are many different types of percussion instruments such as the snare drum, bass drum, triangle, xylophone, cymbals, and bells.    What they all have in common is that they are played by being hit or struck to create the music. There are two categories of percussion instruments, definite and indefinite pitch instruments. Definite pitch instruments are simply percussion instruments that have a definite and constant pitch when played. Indefinite pitch instruments are the opposite; they have a range of pitches that can vary when the instrument is struck.  A definite pitch instrument would be a xylophone and an indefinite would be a snare drum.

Percussion instruments work through vibration and resonance, for example a drum is struck that causes the vibrations, the vibrations are then trapped in the hollow middle where the vibrations stay for a while. It is actually the air that is making the sound. Due to its circular shape, a snare drum has many modes of vibration. These modes of vibrations are waves that expand out in a circular shape. This is crucial to the sound of the instrument because the size affects how far the modes expand and the placement of the strike affects the sound also. All of these variables contribute to why a snare drum has indefinite pitch. Definite pitch instruments have fewer variables and are usually less mechanically complicated.

Auxiliary percussion is a subset type of percussion under indefinite pitch. Auxiliary percussion does not use air to make vibrations but rather other small objects such as beads. Maracas or rain sticks would be perfect examples, they are filled with numerous tiny beads that when shaken make the noise inside the instrument.

All sounds are vibrations that occur at different frequencies, amplitudes, wavelengths, and directions. Sounds can be quite random, which is why we have musical instruments. Musical instruments are made to produce a constant frequency making the vibration predictable and thus making a stable pitch. One of the simpler instrument families is the string instruments.
String instruments are a very popular instrument family and include instruments like the guitar, cello, and violin. All string instruments have tensioned strings that are plucked or hit in order to make sound. All non-electronic string instrument vibrations are produced by standing waves. Standing waves are when two waves travel in opposite directions.

These wave frequencies can be manipulated to create different sounds by changing the length, thickness, mass, and tension of the string. For example, long or thick string produces a lower tone and tight string produces a higher one.
Standing waves simultaneously produce harmonics and a fundamental frequency. Fundamental frequency is the relationship between the wave and the string. It says that the wavelength is twice the length of the string. Once you have the fundamental, there is the harmonics which is an integer multiple of the fundamental. Harmonics are measured by the number of nodes in the wave. The nodes are motionless points on the wavelength or where the two opposite waves meet.
One of the most popular string instruments is the guitar. The physical makeup of the guitar helps improve sound quality and amplification. The strings are usually made of steel or nylon and effect how the guitar sounds. In addition, there is a hole in the center of the body that acts as an amplifier and creates a cavity resonance. The cavity resonance strengths the sound because the air is forced to oscillate in and out at the same frequency, thus strengthening the sound.

Almost everyone enjoys music, whether it be as a musician or a listener most people enjoy at least one form of music. However most people overlook the physics involved in making the music; the vibrations from a violin or the electronic beat in a song. I will be exploring these concepts throughout the year and hope that you will be joining me in learning more about the physics of music.

http://en.wikipedia.org/wiki/Music

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