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GENERAL AND SPECIFIC PROJECT OBJECTIVES:
To be able to design and construct a 2-way speaker system with ported boxenclosure.
To be able to test if the constructed speaker systems meet the expected outputbased on the design.
PROJECT DESCRIPTION:
There are four kinds of speaker enclosures in general use: closed boxes, ported boxes,
labyrinths and their variations, and horns. The first two types, closed boxes and ported boxes are
used for the great majority of stereo speaker systems.
Ported Box Enclosures Speaker System
The ported box or bass reflex is a tuned circuit in which a mass resonates against
compliance. The box with the hole in it acts as a resonator, properly called Helmholtz resonator,
after the nineteenth-century German physicist who first described the behavior of tuned
acoustical resonators. The frequency of resonance for any Helmholtz resonator is determined by
the compliance of the air in the container and the mass of the air in the port. At the Helmholtz
frequency of resonance, the air in the port vibrates easily, compressing and decompressing the air
in the box.
When a speaker is installed in a ported box and is coupled closely to the tuned circuit ofthe box, the original speaker resonance is replaced by two new resonances, one at a higher
frequency than the original, and the other at a lower frequency figure 1 below. At the upper
resonance, the air in the port moves in phase with the cone, but because this frequency is well
above that of the box resonance, the damping action is reduced. This is the frequency at which
some reflex systems produce too much output, particularly small enclosures whose upper
resonance peaks occur within the frequency the frequency of the male voice.
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Figure 1
If the box is properly tuned, the vibrating air piston works in phase with the cone over a
selected band of frequencies to reinforce bass output. This action is most effective at theHelmholtz frequency.
To tune a ported box, change the area or the length of the port/s. compact ported boxes
usually are tuned by a ducted port because the use a duct increases the mass of the vibrating air,
tuning the box to a lower frequency. One of the peculiarities of a reflex system is that port
radiation does not vary with the size of the port. A small port will radiate just as much sound as a
large port, but at higher velocity. If the port is too small, it can produce unmusical noises by its
high air velocity.
Importance
The most important advantage of the ported box is its damping control on the speaker. It
also offers more efficiency by permitting a more efficient woofer. A woofer designed for a
ported box does not have to have as heavy a cone or as long a voice coil as a sealed box woofer,
so it can have more extended mid-range response. This makes a 2-way woofer-Tweeter system a
practical possibility.
The disadvantage of the reflex is the complexity of speaker-to-box relationships,
requiring careful design for good performance.
An example of ported speaker enclosure
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Figure 2
Speaker Characteristics and Type
Subwoofer Speaker
A typical woofer will have an excursion of +/-8mm, push it further and it will still work
but introduce non-linear distortion due to the voice coil not being fully inserted in the magnetic
field of the magnet. Non-linear distortion obviously is unwanted, as it introduces harmonics inthe reproduction which were not in the original recording. But of course you cannot simply keep
increasing the cone diameter either, as the cone needs to remain stiff and move as a whole, rather
than the center piece being driven and the edges trailing behind it. Obviously larger cones are
also heavier requiring more powerful magnets and voice coils to drive them. Realistically 15" is
about the limit where conventional materials and engineering can be used to construct a properfunctioning woofer. In our case 10" and 12" woofers offer a good balance between accuracy,
effective cone area and maximum sound pressure level (spl).
Figure 3 image of a typical Subwoofer Speaker
http://www.hardwareanalysis.com/content/image/11490/http://www.hardwareanalysis.com/content/image/11489/http://www.hardwareanalysis.com/content/image/11490/http://www.hardwareanalysis.com/content/image/11489/http://www.hardwareanalysis.com/content/image/11490/http://www.hardwareanalysis.com/content/image/11489/7/29/2019 speaker design.docx
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Actual image of the Subwoofer speaker used for the project shows below
Selecting the right 10" or 12" woofer is not easy though. So before we make a list of
criteria for the woofer it is important to set a few design requirements for the subwoofer as that
will largely determine what specifications the woofer will need to have. These design
requirements are listed below and selected from personal and professional experience from the
author.
1. Compact design, with about 30-litre effective volume.
2. Closed, vented or passive radiator box.3. Active system with amplifier equalization and active filters.
4. Usable frequency response down to 20 Hz at max spl above 100 dB.
5. Total price
The 10" or 12" woofer we are looking for has a large excursion, allowing it to move lots
of air, but is also equipped with a powerful enough voice coil and magnet system so sensitivity is
not affected. It also needs to have a low resonance frequency (fs), a low equivalent volume
(VAS) and a low Q factor (Qts) so it can be mounted in a small box and still be able to offer
accurate and deep bass reproduction.
A closed box is not best suited for low frequency reproduction as the roll-off can be as
low as 12dB/oct. below the -3dB point (F3, fsb), which means that the sound pressure level
drops rapidly below the -3dB point. However actual roll-off is largely determined by theenclosure volume in conjunction with the Q factor of the loudspeaker, the lower the Q factor the
lower the roll-off. A closed box has a few advantages though which are quite suitable for our
design. For example a woofer with a low Q factor offers a very fast and accurate response in
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small closed box. Furthermore the air inside the closed box will limit the excursion of the woofer
at low frequencies.
Types of Tweeter Speaker
A tweeter loudspeaker is used for high-frequency sounds, typically those sounds used torepel animals or to produce high-frequency noises in songs, movies and other audio. There aremany tweeter speakers, such as the cone speaker, which has a small and fast cone and looks like
a woofer. The dome tweeter is formed like a dome, has larger voice coils than most other
tweeter speakers and is normally used for high-quality systems. A ribbon tweeter uses a rapidlymoving ribbon that is lightweight, but it typically this needs more power than the other tweeters
to make high-frequency sounds. Air motion transfer (AMT) systems use air to create high-
frequency sounds, and they tend to have fewer parts but can be difficult for designers to create.
Cone tweeter speakers normally look circular on the outside, but there is a small cone
inside that is built from stiff or soft material, or both. Stiff material, such as ceramic, is more
durable; softer materials such as fabric have a better dampening effect. When a high-frequencysound is in the audio, the cone rapidly moves to produce the noise. While these are cheap and
easy to produce, they are uncommon because they cannot disperse sound as well as other
tweeters.
Dome tweeter speakers are usually larger than other tweeters, and they also have a longer
voice coil. The voice coil, which is usually 1.5 inches (3.8 centimeters), is hidden behind a soft
or somewhat soft material, such as thin metal mesh or fabric. This dome protects the voice coil,and the softness of the dome makes it easier for high-frequency sounds to be produced. They are
normally good at dispersing high-frequency sounds, so dome tweeters are commonly used.
Ribbon tweeter speakers require a thin and lightweight ribbon wire to produce high-frequency sounds. These tweeters tend to use much more power than other tweeters to make the
wire move quickly enough; otherwise, the ribbon will not be able to function properly. High-
powered ribbon tweeters have higher dispersion rates and can be stacked together for powerfulresults.
AMT tweeter speakers function by using air and pushing it through a mesh. Air isresponsible for making the high-frequency sounds, so these tweeters have fewer moving parts
and tend to be more durable. They are typically only made as high-end equipment, so these
tweeters are generally expensive and can be difficult for designers to create without interrupting
the high-frequency sound production.
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Figure 4 dome tweeter use for the project
Figure shows Front View and Back View Of the 2 way ported enclosure
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Figure 5 shows the Left and Right Side View
Figure 6 shows the Top and Bottom View
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Figure 7 shows the different side and disassembled plywood and assembled one w/ the used of
Computer Aided Design
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Fs = Resonance frequency of the driver. In free-air, the driver's impedance will peak at this
frequency.
Pe = Thermal capacity of the driver, in Watts. If continuously driven above its rated Pe, the
driver may prematurely burn out and fail.
Qes = Electrical Q of the driver at Fs. Qes is a measure of the driver's tendency to resonate at
Fs, based on its electrical characteristics, e.g. magnet strength, magnetic circuit
characteristics, etc.). The driver's overall resonance characteristics are usually
dominated by Qes.
Qes=Qms/Ro-1
Qms = Mechanical Q of the driver at Fs. Qms is a measure of the driver's tendency to resonate
at Fs, based on its mechanical characteristics, e.g. surround compliance, the compliance
of the spider, weight of the cone, etc.
Qms
Qts = Total Q of the driver at Fs. Qts is a measure of the driver's tendency to resonate at Fs,
based on its overall characteristics. Qts can be calculated using the equation:
Qts= Qms*Qes/(Qms+Qes))
Re = DC resistance of the driver's voice coil. Re is less than the driver's rated impedance
(normally 4 or 8 ohms).
Sd = Effective surface area of the driver. Roughly equal to the area of the cone plus 1/3rd of
the surround.Vas = Equivalent air compliance. The volume of air that has the same compliance
("springiness") as the driver's suspension. Because less air is more "springy" than moreair, a large Vas represents a "loose" suspension
Vb = The net box volume
Zmax = Impedance value at frequency of resonance Fs.
Ro = Computed resistance in terms of Zmax and Re
Ro
Konzert Subwoofer Specifications:
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Fs= 30 Hz
F1= 25 Hz
F2= 35 Hz
Re= 7.8
Zmax= 60
Max. Power Rating= 300watts
SPL= 93 dB
Rs= 8
Dia=10 inches
Plywood Board= inches
To Compute for Ro,Qms, Qes, Qts
Ro= Zmax/Re =60/7.8
Ro=7.692307692
Qms
=
Qms=8.320502943
Qes=Qms/Ro-1
=8.320502943/ (7.692307692 -1)
Qes=1.243293543
Qts= Qms*Qes/(Qms+Qes))
= (8.320502943*1.243293543)/ (8.320502943+1.243293543)
Qts=1.081665383
Vas external dimensions
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Height=62.5 cm.
Width=36.5 cm.
Length=31.0 cm.
Vas= LxWxH
Vas= 31cm. x 36.5 cm. x 62.5 cm.
Vas= 4315.522903 cubic inches
Vas= 2.497409087 cubic feet
Vas internal volume
H= 24.60629921 inches- 1.5 inches
H= 23.10629921
W=14.37007874-1.5
W= 12.87007874
L= 12.20472441-1.5
L=10.70472441
Vas internal= L*W*H
Vas= 3183.36977 cubic inches
Vas= 1.842227876 cubic feet
Port Displacement
Diameter= 2.75 inches
Subwoofer 10 diameter
Approximate cone area= 50 sq. inch.
Minimum port area= 3.5 sq. inch.
Minimum pipe diameter= 3 inch.
Computation on Crossover Network
Cut Off Frequency= 2000 Hz
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Xc = 8 ohms @ fH
XL = 8 ohms @ fL
For High Frequency: Capacitor Value
Xc = 8 ohms @ fH
C = 1/2x2000x8
C= 9.94718943 uF
Use 10 uF---Commercial Value of Capacitor
For Low Frequency: Inductor Value
L=8/2(2000)
L= 636.6197724 uH
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