The purpose of my experiment was to see the effect of woofer orientation on bass response.  Bass response is determined by the amount of distortion and output at low frequencies.

My hypothesis was that the woofer output at low frequencies aimed forward would be better than when it is facing downward. The amount of distortion would be worse on my speaker rather than on the commercially produced woofers.

Constants

•  Size and shape of testing room
•  Distance form woofer to first reflective surface (whenever possible)
•  Same test signal, source, and amplifier
•  Same measurement equipment
•  Measurement equipment same distance from the speaker, 1 meter
•  Same distance from the wall, 10 cm

The manipulated variable was the orientation of the woofer, up or down.
The responding variable was the bass response, which is the woofer’s amount of distortion and the output at low frequencies.
To measure the responding variable I’m using a decibel meter, the Vernier TM Lab Pro and computer software, Logger Pro TM.

My results have caused me to accept my first hypothesis because the numbers were continuing to rise rather than fall on the graphs.
My results have caused me to reject my second hypothesis because my speaker was performing better than the other woofers.

If I would conduct this experiment again, I would use more speakers and design a speaker that could face up and down.

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The purpose of my experiment is to see the effect of woofer orientation on bass response.  Bass response is determined by the amount of distortion and output at low frequencies.

I became interested in this experiment when I wanted to find the best way to set up the stereo system in my room to enhance the sound produced.

The people who would care are people who want an answer to the question, is there any reason we cannot fire woofers up or down, and at what frequency does it become necessary to change to a tweeter facing us.

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My hypothesis is that the woofer output at low frequencies aimed forward will be better than when it is facing downward. The amount of distortion will be worse on my speaker rather than on the commercially produced woofers.

I base my hypothesis on the facts that the diaphragm will sag because of gravity when it is facing downward which will make it harder to pull back up.  Commercially produced woofers are designed to reduce the amount of distortion and since mine is an original design it may not perform as well.
 

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Constants

•  Size and shape of testing room
•  Distance form woofer to first reflective surface (whenever possible)
•  Same test signal, source, and amplifier
•  Same measurement equipment
•  Measurement equipment same distance from the speaker, 1 meter
•  Same distance from the wall, 10 cm

The manipulated variable is the orientation of the woofer, up or down.
The responding variable is the bass response, which is the woofer’s amount of distortion and the output at low frequencies.
To measure the responding variable I’m using a decibel meter, the Vernier TM Lab Pro and computer software, Logger Pro TM.
 

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•  Framing square
•  Saber saw
•  Power sander
•  Soldering Iron
•  Dry wall screws
•  Machine screws
•  Bolts
•  Flat washers
•  Lock washers
•  Drill
•  Drill bits
•  Plywood
•  Weather stripping
•  Glues
•  Cupboard carpet
•  Spray glue
•  Wire
•  Terminals
•  Other woofers
•  30 cm woofer
•  Decibel meter
•  Test CD
•  121.92 cm of PVC piping
•  Amplifier
•  Vernier “Lab Pro” TM microphone model MCA-TBA
•  Vernier “Logger Pro” TM version 2.1
•  Damping material
• 3 -20.5 cm length 1.5cm diameter pipes for the legs

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Speaker
     A speaker is a device that reproduces recorded sound.  The three main parts of all speakers are the voice coil, permanent magnet, and a diaphragm.  The voice coil is a coil of wire that is wrapped around the permanent magnet. As electric currents pass through the voice coil, they produce varying magnetic forces, which move the coil back and forth in rapid vibrations. The diaphragm is also attached to the voice coil, vibrates with it, and the vibrations of the diaphragm produce vibrations in the air.  The vibrations in the air are heard as sound waves.
     The sound systems that rely on the speaker are stereophonic sound systems, radios, cassette players, and television sets.  Also public address systems and equipment used to amplify sound created by musicians. Some of these systems use several speakers, each of which reproduces either lower-pitched or higher-pitched sounds. A woofer is a speaker that produces lower-pitched sounds, and a tweeter produces higher-pitched sound. Sound waves spread out from a woofer, but the ones from the tweeter are directional.
The combination of having a system of woofers and tweeters has a level of sound quality that couldn’t be achieved with just one speaker.

Sound
    The study of sound goes as far back as 500 BC in Greece, with the philosopher Pythagoras, who conducted experiments on the sounds produced by vibrating strings.  Then in about 400 BC Archytas, another Greek philosopher, theorized that sound was produced when one object struck another object.  50 years later, Aristotle said that sound was carried to our ears by the movement of air.
     The theory of sound waves began in the early 1600’s with Galileo.  He demonstrated that frequency determines pitch by scraping a chisel across a brass plate, which produced a screech, he then related the grooves on the chisel to the pitch of the screech.  Then in the 1640’s Martin Mersenne obtained the first measurement of the speed of sound in air.  20 years later, Robert Boyle showed that sound must through a medium.  Then Sir Isaac Newton formed the connection between density and compressibility and the speed of sound in a medium.  Between 1750 and 1850, three men, Daniel Bernoulli, Jean Baptiste Fourier, and Hermann von Helmholtz all made steps forward in understanding sound waves.
     The book The Theory of Sound by Lord Rayleigh has established much of the modern acoustic principles. The science of acoustics has expanded much since the publication of the book in 1878.  In the 1940’s Georg von Mekesy showed through his experiments how the ear distinguishes between sounds.  The most rapid expansion of environmental acoustics took place in the 1960’s because of the concern over the psychological and physical effects of noise pollution.  In the 1970’s, better ultrasound equipment was being developed and new uses were discovered.  Then in the 1980’s, computers were developed to reproduce and understand human speech.
    Sound is produced when an object vibrates.  The vibrations of the object cause the surrounding air to vibrate.  The air vibrations are known as sound waves.  Sound doesn’t just move through air, it can move through any material.  As an object vibrates the sound waves move outward it condenses the surrounding air which produces a region of compression known as condensation. When the object moves inward the air expands into the area that the object had formally occupied.  The region of expansion is called rarefraction.   Sound waves consist of condensations and rarefractions.  There is no sound in space because there is no medium for sound waves to move through.
     Frequency is described as the number of condensations or rarefractions produced each second by a vibrating object.  Rapidly vibrating objects produce a higher frequency.  The unit hertz is used to measure frequency.  One hertz is equal to one vibration or cycle per second.  The distance between any point on one wave and the same point on the next wave is the wavelength.  As the frequency of sound waves increases, the wavelength decreases.  Normal people can hear sounds between 20 and 20,000 hertz.  Pitch is determined by the frequency of a sound.  Pitch is the highness or lowness of a sound as perceived by a listener.
     How intense a sound seems to a listener depends on the amplitude of the vibrations producing the waves.  The distance a vibrating object moves from its at rest position as it vibrates is amplitude.  Intensity is also directly related to the amount of energy in sound waves.  The more intense the sound, the larger the amplitude of vibration.  The stronger the sound seems is the loudness of the sound.  The more intense a sound is at a given frequency, the louder id seems when it strikes our ears.  Sound waves lose intensity as they move outward form the vibrating object.
     Sound waves travel at different speeds through different mediums.  The properties that determine the speed of sound are density and compressibility.  Density is defined as the amount of matter in a unit volume of a substance.  Compressibility measures how easily a unit volume of a substance can be crushed into a smaller volume.  The denser and the more compressionable a substance is, the slower the sound waves travel.  Sound travels a lot faster through brick than through air.
     Reflection is also known as an echo.  An echo results when sound waves traveling through a substance, like air, strike a large object of another substance, like a concrete wall.  Not all of the sound waves are reflected though, some enter and pass through the new substance.  What determines the amount of reflection is the speed of sound in the two substances.  If the difference in density and speed in the two substances is a lot, then most of the sound waves will be reflected.  But if there is very little difference between the two substances, most of the sound waves will pass into the new substance.
     The sound waves that aren’t reflected when they leave one substance and enter a new one are changed in the direction that they were traveling in. What really affects the direction that the sound waves take is the speed that they travel at in the new substance, and this is known as refraction.  If the sound waves travel faster in the new substance, then they will be refracted away from the normal.  The normal is an imaginary line perpendicular to the boundaries between the substances.  If the sound waves travel slower in the second substance, then they will be refracted toward the normal.  Another way sound can be refracted is if the speed of the sound waves changes according to their position in the substance.
     When sound waves pass through an opening or along the edge of an object, they spread out. This is commonly known as diffraction.  The reason why you can hear sounds from around a corner is because of diffraction.  It occurs whenever sound waves encounter an opening or obstacle.
     A small repeated force produces larger and larger vibrations in an object, which reinforces the sound.  This is known as resonance.  A repeated force produces resonance with the same frequency as the resonance frequency of the object.  Resonance frequency is about the frequency that an object would vibrate naturally is it was disturbed in some way.
     If you were to produce two tones of slightly different frequencies at the same time, you would hear a sound that got louder and softer at regular intervals and these periodic variations in sound are called beats.  They are produced because the two tone’s sound waves overlap and interfere with one another.  There are two types of interference, constructive and destructive.  Constructive interference occurs when condensations coincide with condensations and rarefractions coincide with rarefractions, which produces a louder sound.  The interference is destructive if condensations meet rarefractions.  This creates a weaker sound or silence.  If you have periods of constructive and destructive interference alternating, then the loudness of the sound increases and decreases producing beats.
     To measure sound scientists use a unit called a decibel to measure the intensity of the sound.  The weakest sound that the human ear can hear is a 3,000-hertz tone of zero decibels and the threshold of pain is 140 decibels.  The threshold of pain is where you feel pain rather than hear.    To measure the loudness level of tones you use a unit called a phon. The loudness level in phons of any tone is the intensity level in decibels of a 1,000-hertz tone that seems equally loud.
     Acoustics is the science of sound and its affects on humans.  One of the major fields of acoustics is environmental acoustics, which is the control of noise pollution.  Major sources of noise pollution are airplanes, construction and industrial plants.  People can suffer permanent loss of hearing if they are exposed to loud noises for a long time.   Also loud noises of short duration, like fireworks and other explosions, can cause hearing loss.  Constant noise has been shown to cause fatigue, headaches, hearing loss, and tension.  Another major field of acoustics is providing good conditions for producing and listening to speech and music in such places as concert halls and movie theaters.  One thing acoustical engineers have to deal with is reverberation, the bouncing back and forth of sound waves in an auditorium or hall.  They don’t have to totally eliminate reverberation because some is needed to produce pleasing sounds, but also too much of it can blur the sound of an instrument or a speaker.  To control reverberation, the acoustical engineers use carpets, draperies, and upholstered furniture to absorb the sound.
      Many different fields of science use sound to find minerals, underwater objects, and disorders of the body.  Sonar uses sound waves to find underwater objects, like submarines and schools of fish.  To find brain tumors, gallstones, and liver diseases, physicians use ultrasound.  Ultrasound is sound that is above the range of human hearing, approximately 150 decibels.

Stereophonic Sound System

     A stereophonic sound system, or simply a stereo, is equipment that reproduces sounds like music that seems to come from many directions and has depth.
     The stereophonic phonographs first came on the market in the late 1950’s. Before that the phonographs were monophonic, they only produced sound from one channel.  The first radio station was established in 1961.  In the mid-1980’s compact disks and tapes came on the market, but before then phonographs were the most common reproducing sound systems.
     There are many types of stereo systems but they can be divided into four categories component systems, rack systems, portable systems and home theater systems.  Component systems are individual parts that are purchased separately and connected by the consumer to best fit their particular needs. This system has the best sound quality. Rack systems are systems that the manufacturer assembles and that cannot be taken apart, some are small systems that can fit on a desk or tabletop and generally have poor sound quality. Portable systems consist of a CD or cassette player and headphones that can be carried in a pocket. There are larger systems, boom boxes, which are powered by batteries and have small speakers.  Home theater systems combine picture playback with high-quality sound. The components in this system are connected to a television set and the sound and picture come from the videocassette player or videodisk player.
     There are three main parts to all stereo systems, a program source, an amplifier, and speakers. The program source produces electric signals the represent sound waves.  An example of a program source is a compact disk player.
    A compact disk player is a device that produces sound that has been recorded on a small disc in digital code. The disc, which is made of plastic, has a metal coating that a laser beam shines on as it spins and the light bounces off as pulses of light. The CD player uses the code on the disc and the pulses of light to create a signal.
     An amplifier is a device that strengthens the signal from the CD player.  There are many options for what an amplifier can do to make the sound produced better.  Some amplifiers have controls, which enable the operator to change the levels of bass, treble, and midrange.
    The speaker is the actual device that produces the sound from the program source. It receives the signals from the amplifier and converts them into vibrations or sound waves. Stereos require at least two speakers, one for each channel of recorded sound.  High quality systems have three speakers, one for bass, (a woofer) one for midrange, and one for treble (a tweeter).  Speakers in component systems are generally mounted in wooden or plastic cabinets. The size and shape of the cabinets can effect the quality of sound that is produced.

Summary
     These sections were compiled for the study of how a hand built speaker can compare to manufactured speakers.  The information in the sections, Speaker, Sound, and Stereophonic Sound System, were to inform the reader about the properties of sound and the components in speaker.
 

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In this experiment I wanted to see If the orientation of a woofer effect its base response.

In the 42 tests that I conducted it seems that the commercially produced woofers had more distortion than mine did because the graphs should have had square waves but none of them had anything close to a square wave. In the output tests, there was a noticeable difference in the upright tests (.1-. 3) and the downward tests (.4-. 5). On my woofer, there was no difference because I could only test it downward.

See the graphs and charts below.

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Data Table for the Guitar Amplifier Tests  Hertz     Decibel  Level     Level  25     63 54 55 57 1/3   55 55 60 56 2/3 31.5  73 65 64 67 1/3   60 62 68 63 1/3 40     78 75 75 76        65 70 70 68 1/3 50     81 84 82 82 1/3   75 78 77 76 2/3 63     88 88 88 88         88 85 84 85 2/3 80     87 90 90 89           89 88 89 88 2/3 100   86 86 86 86           89 89 84 87 1/3 125   88 88 88 88           89 89 86 88 160   95 95 96 95 1/3     90 90 92 90 2/3 200   96 96 96 96         96 92 92 93 1/3 250   98 96 96 96 2/3     98 97 96 97 315   99 98 98 98 1/3     96 99 99 98 400   98 98 98 98            96 96 96 96 500   104 102 102 1022/3 96 94 94 94 2/3 630   104 101 101 102     92 94 94 93 1/3 Test # 1.1  1.2 1.3 average 1.4 1.5 1.6 average  Facing Up                        Facing Down

Data Table for the Pyramid Tests    25 74 74 74 74 73 72 73 72 2/3 31.5 82 76 76 78 76 76 76 76 40 84 83 83 83 1/3 83 82 83 82 2/3 50 90 84 82 85 1/3 87 84 86 85 2/3 63 89 90 90 89 2/3 90 90 91 90 1/3 80 84 89 89 87 1/3 91 91 90 90 2/3 100 80 82 83 81 2/3 82 82 82 82 125 78 80 80 79 1/3 83 83 82 82 2/3 160 82 79 78 79 2/3 84 84 84 84 200 82 84 83 83 86 83 82 83 2/3 250 82 83 82 82 1/3 78 76 77 77 315 82 81 81 81 1/3 76 78 78 77 1/3 400 78 78 79 78 1/3 74 75 74 74 1/3 500 77 78 78 77 2/3 75 74 75 74 2/3 630 82 82 83 82 1/3 84 86 84 84 2/3 Test # 2.1 2.2 2.3 average 2.4 2.5 2.6 average        Facing Up                   Facing Down

Data Table for My Woofer Tests  Hertz Level Decibel Level  25     76 76 76     76 31.5  78 78 78     78 40     84 84 84     84 50     86 86 86     86 63     91 91 91     91 80     90 90 90     90 100   86 86 86     86 125   81 82 82     81 2/3 160   88 88 90     88 2/3 200   84 85 84     84 1/3 250   82 82 83     82 1/3 315   83 84 82     83 400   84 82 83     83 500   83 83 84     83 1/3 630   83 84 85     83         3.1 3.2 3.3 average  Facing Down

Data Table for the Floor Woofer Tests  Hertz Level Decibel Level  25    77  77 77  77         78 78 79    78 1/3 31.5 82  82 83  82 1/3    84 83 84   83 2/3 40    82  83 82  82 1/3    86 86 86   86 50    90  91 91   90 2/3   93 92 92   92 1/3 63    94  93  94   93 2/3  94 94 94   94 80    91   91 91   91        90 90 90    90 100   82   83 83 82 2/3   90 89 89    89 1/3 125   77   77 80   78       91 91 91   91 160   79   78 77    78      87 87 88    87 1/3 200   76   77 77   76 2/3  76 77 77    76 2/3 250   68   70 69   69        74 72 73    73 315   67   66 66   66 1/3  70 69 70    69 2/3 400   62   62 64   62 2/3   64 64 65   64 1/3 500   62   62 62   62         60 62 62    61 1/3 630   60   60 61   60 1/3   59 60 60    59 2/3 Test # 4.1 4.2 4.3 average 4.4 4.5 4.6 average

 

Average Chart for All Data  Hertz Level Decibel Level  25            57 1/3     56 2/3       74       72 2/3      76          77       78 1/3 31.5         67 1/3     63 1/3       78         76         78       82 1/3    83 2/3 40               76        68 1/3    83 1/3     82 2/3     84       82 1/3       86 50           82 1/3      76 2/3    85 1/3    85 2/3       86      90 2/3     92 1/3 63              88         85 2/3     89 2/3    90 1/3       91     93 2/3        94 80               89        88 2/3    87 1/3    90 2/3         90        91           90 100             86        87 1/3    81 2/3       82            86     82 2/3     89 1/3 125             88            88      79 1/3    82 2/3      81 2/3     78            91 160          95 1/3     90 2/3    79 2/3       84         88 2/3     78         87 1/3 200              96       93 1/3     83          83 2/3      84 1/3   76 2/3     76 2/3 250           96 2/3    97        82 1/3        77           82 1/3    69            73 315           98 1/3    98        81 1/3       77 1/3       83      66 1/3      69 2/3 400           98          96       78 1/3        74 1/3       83      62 2/3      64 1/3 500          102 2/3  94 2/3   77 2/3       74 2/3    83 1/3      62         61 1/3 630           102       93 1/3   82 1/3        84 2/3   72 2/3    60 1/3      59 2/3 Averages 1.1-1.3   1.4-1.6   2.1-2.3    2.4-2.6   3.1-3.3   4.1-4.3   4.4-4.6

My hypothesis was that the woofer output at low frequencies aimed forward would be better than when it is facing downward. The amount of distortion was worse on my speaker rather than on the commercially produced woofers.

My results have caused me to accept my first hypothesis because they were continuing to rise rather than fall on the graphs.
My results have caused me to reject my second hypothesis because my speaker was performing better than the other woofers.

A question that has been raised from my experiment is do larger woofers perform better than smaller woofers?

Possible sources of error are the fact that the floor woofer (4) could only go up to 200 hertz and I tested it to 630 hertz.  Also my woofer could only be tested facing downward.

If I would conduct this experiment again, I would use more speakers and design a speaker that could face up and down.

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Coppens, Alan B. and James V. Sanders. “Sound”. World Book Encyclopedia. 1999 Ed.

Dzurko, Mike. “Subwoofer Primer” Audio Concepts Inc.
 http://audioc.com/informaion/subwoo.htm
(November 29, 2001)

Dzurko, Mike. “Subwoofer Primer” Audio Concepts Inc.
http://audioc.com/information/sub_manual.htm#Intro
(November 29, 2001)

“How to Create a Speaker”
http://xsspl.tripod.com/Audio/Sound1.htm
(November 29, 2001)

Pohlmann, Ken C. “Speaker”. World Book Encyclopedia. 1999 Ed.

Pohlmann, Ken C. “Stereophonic Sound System.” World Book Encyclopedia. 1999 Ed.

"Sound," Microsoft® Encarta® Online Encyclopedia 2001
http://encarta.msn.com
© 1997-2000 Microsoft Corporation. All Rights Reserved. (November 30, 2001)

"Sound Recording and Reproduction," Microsoft® Encarta® Online Encyclopedia 2001
http://encarta.msn.com
© 1997-2000 Microsoft Corporation. All Rights Reserved. (November 30, 2001)

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Acoustics is the science of sound and of its effects on people.

Bass response is the amount of distortion and the output at low frequiencies.

Beats are periodic variations in the loudness of a sound.  Beats are heard when two tones of slightly different frequencies are sounded at the same time.

Condensation is a region of compression in a sound wave.

Decibel is the unit used to measure the intensity level of a sound.  A 3,000-hertz tone of zero decibels is the weakest sound that the normal human ear can hear.

Frequency of sound waves refers to the number of condensations or rarefractions produced by a vibrating object each second.

Hertz is the unit used to measure frequency.  One hertz equals one cycle (vibration) per second.

Infrasound is sound with frequencies below the range of human hearing.

Intensity of a sound is related to the amount of energy flowing in the sound waves.

Phon is a unit of ten used to measure the loudness level of tones.  The loudness level in phons of any tone is the intensity level in decibels of a 1,000-hertz tone that seems equally loud.

Pitch is the degree of highness or loudness of a sound as perceived by a listener.

Rarefraction is a region of expansion in a sound wave.

Resonance Frequency is approximately the frequency at which an object would vibrate naturally if disturbed in some way.

Sound Quality also called timbre, is a characteristic of musical sounds.  Sound quality distinguishes between notes of the same frequency and intensity produced by different musical instruments.

Ultrasound is sound with frequencies above the range of human hearing.

Woofer a speaker that produces low frequency sound.
 

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