| Purpose | |
| Experiment Design | |
| Procedures | |
| Results | |
| Bibliography |
The purpose of this experiment was to determine the amount of sound absorbed by different brands of acoustical foams. I chose this project because I thought it might benefit people who are designing recording studios, concert halls, auditoriums, and speaker designers. Knowing the information provided by this project, people using any one of these products might get the best possible results. I also chose to do this project because I am interested in learning about the mechanics of sound.
My hypothesis was that the Sonex brand acoustical foam that was an open cell Melamine base foam would absorb the greatest amount of sound emitted from the speaker at the higher frequencies. I hypothesized this based on research from the Illbruck-Sonex web site. I predicted that the standard bed foam would absorb the least amount of sound at any frequency. I hypothesized this because this type of foam is not designed for sound absorption; it’s designed for sleeping on. I also tested sonex brand acoustical foam that was made of urethane. I tested this because I wanted to get a broad range of product. During my experiment I had to take into account that all objects have a resonant frequency, or a frequency at which the object best vibrates. I also had to recognize that acoustical foams are designed to absorb mostly higher frequencies.
Manipulated variable: The
type of acoustical foam
Responding variable: The
amount of sound that is absorbed by the acoustical foam at different frequencies.
The loudness of sound will be measured in decibels using an analog dB meter
and 1/3 octave bands of noise.
Constants:
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Construction for Test Tube:
1. Paint 1m PVC piping with any color desired
with aerosol spray paint
2. Slide threaded PVC adapter on to one end
3. Drill hole 1cm in diameter for wires 4.5cm
from opposite end of PVC adapter
4. Drill hole to mount tweeter 7.62cm inside
tube
5. Mount tweeter inside tube using bracket
6. Thread wires for tweeter through whole, connect
to tweeter
7. Drill hole 2.54cm in diameter for dB tester
as close as possible to threaded PVC adapter
8. Drill four screw holes in end opposite of
PVC adapter in order to mount woofer
9. Apply generous amount of silicon sealant to
end of tube all around the end
10. Place Woofer on end of test tube pushing
firmly in silicon sealant
11. Drill the four screws into pilot wholes and
let set for 24 hours
12. After sealant dries use wires for tweeter
and strip back their cover
13. Attach Capacitor to one wire using sadder
14. Solder both wires from tweeter to woofer,
connecting one to positive and one to negative
15. Solder long cable capable of being connected
to amplifier to woofer
16. Test Tube Complete
Complete Test Tube (Shortened for
Display Purposes) Shown with Acoustical Foams
Experiment procedures:
1. Make spread sheet with all frequencies to
be tested listed on one side
2. Hookup woofer and tweeter to receiver
3. Place test CD into CD player
4. Leave test tube empty
5. Set dB tester into predrilled hole
6. Press play on CD player
7. Record dB level every ten seconds on data
sheet under “Empty Test Tube Test 1”
8. When test one is completed unscrew end cap
and place test foam number 1 into tube and screw end cap back on
9. Run the same test on foam 1 and record on
datasheet under “Foam 1 Test 1”
10. Run the same test until you finish testing
foam number 3
11. After completing test 1 on foams and blank
tube run the same test on all four again to ensure accuracy
12. After test set number 2
13. Run a third test on just the blank test
Introduction
This project was designed to inform people with
information concerning acoustical foams. Understanding the information
provided by this project will allow people who are designing recording
rooms, conference rooms, offices and other places where sound is an issue
towards productivity and comfort. Acoustical foams are being used
more and more in today’s society, so this project will hopefully provide
insight to their use.
Sound
Sound is around us all the time; sound is anything
that you can hear. The vibrating of an object produces sound.
The vibration goes out in all directions, it enters the ear, and the brain
interprets it. Sound most commonly travels through the air, but it can
also travel through solid objects. When an object vibrates, the outward
motion causes the molecules of the medium around the object to become more
compact this is called condensation. When the object that’s vibrating
moves inward, it causes the molecules of the medium to become less compact
this is called rarefaction. Each time this cycle is repeated it creates
one wave. These waves make up frequencies. Frequencies are the number
of condensations and rarefactions that occur in one second. Higher
frequency sound waves travel closer together because the object is vibrating
faster this causes the waves to being given of at a faster rate. Low frequency
waves are the opposite because the object is vibrating slower so the waves
are given off at a slower rate.
Hearing
Scientists use a unit called the hertz to measure
the frequency. One hertz is equal to one cycle. A humans voice
can put off frequencies from 85 to 1,100 hertz, the human ear can hear
receive frequencies from 20 to 20,000 hertz. Scientists use a unit
called the decibel to measure the degree of loudness of sound. Sound is
very important to humans because it’s the way we communicate, and also
the way we get our news and information.
Acoustics
Acoustics are a science that deals with production,
control, transmission, reception, and effects of sound. Acoustics
originated from the study of mechanical vibration and the radiation of
these vibrations. Acoustics are very important to the arts, mostly in music
and the designing different instruments. The knowledge we have about
acoustic has come greatly from long experimentation by different artists,
these experiments turned into theories. What information we have
currently concerning architectural acoustics has been gained through centuries
of trial and error testing. These experiments have provided good
information but have only recently been considered real science.
Sound Control
Sound controlling methods are used all the time.
Some of these methods include: containing noise with barrier materials
and enclosures, absorbing noise with panels, baffles and other types of
acoustical foams, and finally by canceling the noise by introducing sound
frequencies that interact with the offending sound. This project
deals with the sound absorption method. Acoustical foams are used
in all different places; it is most commonly used in industrial environments
such as recording rooms, conference rooms, and speaker designers.
These are just a few of the real world uses for acoustical foams, there
are many more.
Foam
Acoustical foams are made from all different
kind of ingredients. Since the companies cannot disclose what is
used in there foam. The two Sonex acoustical foams used in this project
were made of Urethane and Melamine. To make the foams all the ingredients
are first combined. After the substances are combined they are put in a
large micro waving machine. After micro waving the foam is in the
shape of a cube. The foam is then shipped to the United States where it
is cut into panels. Finally the product is shipped to the consumer.
Summary
After reading this background report hopefully
you will have a better understanding of the mechanics behind sound.
Also an understanding of how sound is controlled and its impact on today’s
society.
In this experiment I hoped to compare several
different types of acoustical foams. By using an acoustical test
tube I was able to test and determine if there was a difference.
My data showed results that I didn’t expect at
all. It turns out that there wasn’t really much of a difference between
all three foam. There was however quite a difference in comparing
an empty tube to one that has foam in it. So the acoustical foam
does definitely reduce the decibel level.
.
My original hypothesis was that the acoustical
foam made of Melamine would have the best rate of sound reduction.
After completing experimentation I have to accept and reject my hypothesis.
I say this because the Melamine foam didn’t completely dominate the sound
reduction rate. At some levels it did better, but at others
it did worse. The bed foam performed quite well because it was the
same and sometimes a little better then the rest of the acoustical foams.
Since I wanted a broad range of product, I tested the Urethane foam. It
performed as well if not a little better then the other foams especially
in the middle frequencies.
After completing my experimentation I wondered
if my tests would have been more accurate if I had used a digital dB tester.
I would also try the experiment at different temperatures and humilities.
If I were to repeat my experiment, I would definitely
use more accurate equipment to test the results. I would specifically
get a better decibel tester because during testing the needle moved a lot,
so I had to average its position.
Test Results from First Test
TOP
After completing my testing I observed that the
bed foam absorbed almost the same amount of sound as the acoustical foams.
The only place where the acoustical foam totally out did the bed foam was
in the high frequencies because acoustical foams are designed to absorb
high frequencies. Knowing this information the average consumer wanting
a room with acoustical foam on the walls possibly for a band or other applications
can turn to standard bed foam for what they’re wanting to do.
My original hypothesis was that the acoustical
foam made of Melamine would have the best rate of sound reduction.
After completing experimentation I have to accept and reject my hypothesis.
I say this because the Melamine foam didn’t completely dominate the sound
reduction rate. At some levels it did better, but at others
it did worse. The bed foam performed quite well because it was the
same and sometimes a little better then the rest of the acoustical foams.
Since I wanted a broad range of product, I tested the Urethane foam. It
performed as well if not a little better then the other foams especially
in the middle frequencies.
After completing my experimentation I wondered
if my tests would have been more accurate if I had used a digital dB tester.
I would also try the experiment at different temperatures and humilities.
If I were to repeat my experiment, I would definitely
use more accurate equipment to test the results. I would specifically
get a better decibel tester because during testing the needle moved a lot,
so I had to average its position.
