How The Use Of Different Materials Affects The
Bass Response
Of A Speaker
Here is a picture of my
display board at the Mid Columbia Science Fair.
Abstract:
The purpose of this experiment is to show how using different
materials for a speaker enclosure affects the speaker’s bass response.
My hypothesis is that enclosures made of rigid, dense materials
will produce better bass response than weaker, less dense materials.
For my experiment I tested the bass response of 3 speakers that
were identical except for the material used for the enclosure. I used a dB
meter and test CD to find and compare the bass response of these speakers.
This experiment was meant to show how using certain materials
for a speaker enclosure affects the bass response of that particular speaker.
This is important because your choice of material could drastically affect your
sound quality
To increase validity of the
experiment I checked the dB readings twice ensuring correct readings. I also
conducted the experiment in an open room with few windows and doors, which give
off resonant frequencies altering the speaker’s sound.
The limitations of my experiment were resonant frequencies that
alter dB levels, and not using a digital dB meter.
My conclusion is that the type of material does affect a
speaker’s bass response. The test results showed that the enclosures made of
MDF produced better bass response than the other materials. This is useful because
it shows that your material choice has an affect on the sound from your
speaker. The next logical steps for investigation would be to build an
enclosure made of cement, because it would be very dense and rigid.
The purpose of this experiment is to determine how the use of
different materials for speaker enclosures affects the bass response of that
speaker. I became interested in this idea after reading a number of web pages
that all recommended a different type of material to use for a speaker
enclosure. I wanted to know if the material used from the enclosure would
noticeably alter the sound quality (i.e. bass response) The information gained
from this experiment could help audio companies and people who are interested
in building or buying speaker boxes determine what type of material creates the
best bass response for a speaker.
My hypothesis is that the speaker enclosure made of MDF will
create the best bass response out of the materials tested. I base my hypothesis
on information gained from my science teacher Mr. McMillen, encyclopedias, and
audio related web pages (see bibliography). All of these sources stated that
lower “bass” frequencies tend to produce a large amount of resonant
frequencies. The denser and more rigid materials will not only have a tendency
to not vibrate producing unwanted sound, but also they will tend to have a
lower natural frequency, making it less noticeable to the human ear.
The manipulative variable in my experiment is the material used
for the speaker enclosure.
The responding variable is the bass response put out by the
driver when installed in identical boxes of different materials.
The constants in my experiment were:
· Driver
· Interior box
volume
· Location of
testing
· Weather
stripping
· Chalking
· Temperature
· Location of dB
meter relative to speaker
· CD
· dB meter
· Watts
· Glue
The control group for my experiment is the MDF enclosure. MDF is
typically the standard material used for building speaker enclosures. In this
experiment I will measure the decibels (dB) or how loud the three speakers are
over a range of different frequencies. I will be using an analog dB meter 1
meter directly in front of the driver. I will be using dB for my metric unit.
Quantity
½ sheet ½ sheet ½ sheet 1 180cm 1 tube 1 package 1 bottle 1 1 1 1 1 1 1 8 1 |
Item
MDF Plywood OSB 8’’ woofer speaker wire silicon chalking ¼’’ adhesive weather stripping wood glue dB meter test CD CD player (capable of powering 8’’ woofer) table saw drill drill bit jig saw wood screws (at least 2cm long) tape measure |
1
Construct 3 boxes (one out of MDF, one out of Plywood, and one
out of OSB) with an interior dimension of 29.5cm by 19.7cm by 49.2cm
2
After glue has dried, on front of the enclosure, mark ½ of the
width, and 1/3 of the height.
3
Draw a circle with a radius of 18.1cm going out from the mark
made on front of enclosure.
4
Drill a hole inside of the circle.
5
Use a jig saw to cut out circle.
6
Repeat steps 2-5 for other 2 boxes.
7
Apply a thin bead of silicon chalk to the seams of the inside of
the enclosures to ensure they are airtight.
8
Place woofer in hole and mark spots for the screws.
9
Remove woofer and drill the screw holes.
10
Run a strip of weather stripping along the edge of the hole for
the speaker.
11
Drill a hole in the back of the enclosure, make it just big
enough to get the speaker wire threw.
12
Run speaker wire threw hole in back of enclosure.
13
Chalk around wire to prevent a leak.
14
Repeat steps 8-12 with other 2 enclosures.
15
Wait until chalk is dry.
16
Install the woofer in one of the enclosures.
17
Hook speaker up to CD player.
18
Arrange dB meter one meter directly in front of the woofer,
elevated so it is the same height of the center of the cone.
19
Turn dB meter on and start test CD.
20
Record readings at 25Hz, 31.5Hz, 40Hz, 50Hz, 63Hz, 80Hz, 100Hz,
125Hz, 160Hz, 200Hz, 250Hz, 315Hz, 400Hz, 500Hz, 630Hz, 800Hz, and 1kHz.
21
Place one of the other enclosures exactly were the first
enclosure was.
22
Run test again and record data.
23
Place third and final enclosure in the spot were the other two
enclosures were tested.
24
Run test again and record data.
INTRODUCTION:
I chose to do my project on comparing how the use of different
materials for a speaker enclosure affects the bass response from the speaker.
This research report will discuss the nature of sound, speaker enclosures,
types of typical materials used for speaker enclosures, and how the use of
these different materials affect the bass response from a speaker.
NATURE OF SOUND:
Sound is a form of waves that are caused by a vibration. These waves produce a
series of compression and rarefaction’s that travel threw a solid, liquid, or
gas and stimulate our sense of hearing. The loudness of a sound is measured in
decibels (dB). The pitch of a sound is how high, or low it’s frequency is. The
fast the sound waves move the higher the frequency, causing the sound to be
higher pitched. Low frequency sounds have large waves, and produce low-pitched
sounds, Frequency is measured in hertz (Hz). Which equals on cycle per second.
In humans. Hearing takes place whenever vibrations of frequencies between 15
and 20,000 Hz reach the inner ear. These vibrations reach the inner ear when
they are transmitted through the air, and the term sound is something
restricted to such airborne vibrational waves. All things have a frequency at
which they like to vibrate naturally. This means a driver can cause the
enclosure to vibrate at a different frequency than what is intended. Of course
this is bad because it changes the pitch of whatever you are listening to from
your speaker. Usually if the frequencies are higher than 20,000 Hz they are
called ultrasonic and can not be herd by the human ear. The distance at which a
sound can be herd depends on it’s intensity, which is the average rate of flow
of energy per unit area perpendicular to the direction of proportion. IN
propagation of sound through the atmosphere, changes in the physical properties
of the air, such as temperature, pressure and humidity, produce damping and
scattering of the directed sound waves, so that the inversesquare law generally
is not applicable in direct measurements of sound intensity.
SPEAKER ENCLOSURES:
Today there are many kinds of speakers and speaker enclosures.
There are two main types of enclosures, sealed, and ported. In my experiment I
only tested the sealed type enclosure because they are easier to construct and
have fewer variables that could alter bass response. The bass response of a
speaker is how well it can produce the same decibel level at different
frequencies. In a sealed enclosure the box is air tight so when the driver’s
cone moves back and forward the trapped air acts like a spring. The air spring
enables a smaller enclosure to produce a very deep bass sound. Unfortunately
sealed enclosures also tend to be less efficient than a ported enclosure,
meaning a more powerful amplifier is required. Ideally the speaker enclosure
should be made of something very rigid and dense. This is so the vibrations
given off by the driver will be less likely to produce a resonant frequency,
which results in poor bass response.
TYPES OF MATERIALS:
MDF
MDF stands for “medium density fiberboard.” MDF is the most
commonly used material for speaker enclosures. MDF is produced by mixing
refined rubberwood chips with resin and wax. After this mixture has dried, it
is heated to a high temperature and is compressed for an extended amount of
time until it is dried. MDF is the most dense of the 3 materials being tested,
but is not as rigid as plywood.
PLYWOOD
Plywood is a material commonly used in construction of homes and buildings. It
is made by gluing multiple thin sheets of wood together with their grain at
right angles of each other for added strength. Plywood is sometimes but not
commonly used for speaker enclosures. It is the most rigid of the 3 materials
being tested but is also the least dense.
OSB
OSB stands for “oriented strand board.” It is commonly used in
residential construction. OSB is made by bonding cross-aligned strands of small
wood with a bonging agent and applying heat and pressure. OSB is slightly more
dense than plywood but not as rigid. It is more rigid, but not nearly as dense
as MDF.
CONCLUCION:
The speaker enclosure is a very important element in a good
sounding speaker. If the enclosure is not dense and rigid, the driver will not
be able to function as it was designed to, and the enclosure may also produce
enough resonant frequencies to cause poor bass response.
In this experiment my goal was to determine how the use of
different materials for a speaker enclosure effects the bass response from that
speaker. My results show that the type of material used for a speaker enclosure
does affect the bass response from the speaker, Typically all three enclosures
were within 1 to 3 dB of each other. The enclosure made with MDF has the
smoothest and flattest graph. The enclosure made of OSB and plywood have graphs
that are very similar to each other but the plywood enclosure’s graph is
somewhat smoother and flatter than that of the OSB.
Analysis and
Conclusions:
From my results you can see that using different types of
materials for a speaker enclosure does affect the bass response produced from
the speaker. My hypothesis was that the speaker enclosure made out of MDF would
produce the best bass response of the tested materials. My results show that
the rigid and dense materials produce better bass response than weaker less
dense materials, therefore I believe my hypothesis should be accepted. After
having completed the experiment, I wonder how much the bass response can still
be improved, by the use of materials even more dense and rigid than MDF.
Some possible sources of scientific error could be resonant noise
from objects in the room were I tested the speakers. Also, the use of the
analog dB meter might have given data not as accurate as a digital meter might
have. If I repeated this experiment I would try using a digital dB meter. I
would also try to conduct the test in a room with lots of sound absorbent
material to help reduce resonant frequencies. Finally I would build an
enclosure out of cement, which is very dense and very rigid, to see how much it
would improve the bass response compared to the enclosure made of MDF.
hi-fi playground, [online] Available http://www.hi-fi.com/diy/,
December 24, 2000
Ishtek Speaker Design Basics, [online] Available http://www.ishtek.com/spkr_basiccs.htm,
December 24, 2000
Johnson, Kenneth W./Walker C., The Science Of Hi-Fidelity,
Dubuque, Iowa, Kendall/Hunt, 1977
“Loudspeaker,” Microsoft Encarta 98 Encyclopedia, 1998a
OSB Information, [online] Available http://www.sba-osb.com/sba.osb.info/sba.osbinfo.1.html,
January 12, 2001
Pohlmann, Ken C., “Speaker,” The World Book Encyclopedia, 1999
Robin MDF, [online] Available http://www.robinmdf.com.sg/production.html,
January 12, 2001