How Big Can the Enclosure Be?
Do you want to take up all the available space inside your
Tech Tips
car/truck/van/sport-utility? Or are you looking for something that is
Measure the available
compact enough to be removed easily when necessary? These are
space in your vehicle,
important questions you must answer before beginning your project.
making sure to draw
First, measure out the area you re interested in placing the subwoofer
out your design first,
enclosure. Use a good-quality measuring tape (not your mom s cloth
and ensure the
tape from her sewing kit) to determine the MAXIMUM height, width,
enclosure will fit
and depth of your area. Height is the measurement up-and-down, width
through any openings.
is the measurement from side-to-side, and depth is the measurement
Things to Remember
back-to-front. (We ll assume you re using English standards (inches,
feet, yards) when measuring, and our example calculations will be done
There are no special size limits.
using these standards.)
(You do, however, want to avoid
long, round enclosures in excess
Once you ve determined your maximum external dimensions, it is a
of 72" - if the airspace in the
good idea to start drawing out your enclosure on paper. If you make a
enclosure is long and stretched
mistake, you can simply erase it and start again, versus cutting the wood
out, the woofer cannot couple to
right away and discovering you have just made something resembling a
all of the air. When this happens,
large toy box.
the air at the end of the enclosure
becomes its own separate moving
Since you know what the external dimensions can be, we ll move to the
mass and can mistune the
next step!
enclosure dramatically.)
Re-measure the area you re
loading the enclosure into, and
make sure the box will fit in
through any openings. Nothing is
more frustrating than building the
perfect enclosure only to find it
won t fit through the trunk
opening.
www.rockfordfosgate.com/rftech RFTECH: ENCLOSURE 1
How Do You Figure the Dimensions?
It is extremely important to know the internal volume necessary for the
Tech Tips
subwoofer you re using (also known as box size ). Most manufacturers
will tell you what the ideal-sized enclosure is for their woofers, and
Use the volume formula,
we re no exception. Since not all subwoofers require the same amount of
(H X W X D) ÷ 1,728
to determine your enclo- airspace, different lines of the same brand of woofer can have
sure s internal volume, completely different enclosure size requirements. As a general rule of
allowing for displace- thumb, making the enclosure too small will result in a lack of low-end
ments of wood, woofer,
bass response, and if it s too large, you won t have as much output as
port(s), and bracing
you could and the woofer s power handling will suffer. (If you re unsure
when applicable. (Use
of the recommended enclosure size for your Rockford Fosgate woofers,
the manufacturer s
please visit the library section at www.rockfordfosgate.com.)
recommended enclosure
Calculating the correct box size is easy if you just remember a few
size.)
simple formulas and calculations. The key to calculating internal box
dimensions is a basic understanding of volume: Cubic volume is derived
by multiplying each of an object s dimensions (height, width, depth) by
each other.
For example: If you measure the internal dimensions of a rectangular
object (like a subwoofer box) and its internal height is 12", its width is
12"
24", and its depth is 12", and then multiply those dimensions together
24"
(12" X 24" X 12"), then you come up with a volume of 3,456 cubic
12"
inches. (See Figure A)
Enclosure volumes are never listed in cubic inches, so it is necessary to
12 x 12 x 24 = 3456
convert from cubic inches to cubic feet. (A cubic foot is no more than
3456 ÷ 1728 = 2.0 cu.ft.
12" X 12" X 12" or 1,728 cubic inches.) So, to convert from cubic
Figure A volume of an
inches to cubic feet, simply divide the volume in cubic inches by 1,728.
enclosure
In the case of our example above, this would be 3,456 divided by 1,728,
or 2.0 cubic feet internal volume.
Things to Remember
Since we know that the woofer will take up space in our enclosure, we
All dimensions you calculate are
will need to add for that volume, called its displacement. Woofers, ports,
interior dimensions, unless you
and internal bracing (covered in the Advanced section of our Enclosure
specifically include the
pages) will all have a certain amount of volume they will take up in the
displacement of the wood used.
enclosure. Their displacement will need to be accounted for in the
Allow extra airspace for internal
bracing, ports, and the speaker enclosure, or the enclosure might not sound as good as it can.
itself (called displacements ).
www.rockfordfosgate.com/rftech RFTECH: ENCLOSURE 2
Rockford Fosgate carefully measures the total volume of all of the
woofer s components (magnet, basket, cone, etc.) that displace air when
loaded into an enclosure. This volume, called Speaker Displacement,
Square
is included in your owner s manual or at www.rockfordfosgate.com.
This volume will need to be considered when designing your enclosure
if you want it to sound right, as it takes away from the available airspace
you have in the enclosure. If you simply make the enclosure larger, it
Rectangle
will compensate for how much volume the woofer takes up, and the
enclosure will sound exactly the way it was meant to!
Using our example of 2.0 cubic feet, if we load the woofer into the
enclosure it won t be 2.0 cubic feet anymore. Using our handy Rockford
Wedge
Fosgate Subwoofer Displacement Chart (See Woofer Displacement
Formula Section), we can see that the Punch Power 12" DVC subwoofer
displaces 0.21 cubic feet, so we subtract 0.21 cubic feet from the 2.0
cubic feet we have, and the enclosure is now 1.79 cubic feet. Since the
Trapezoid
recommended sealed enclosure for the Punch Power 12" DVC
subwoofer is 1.25 cubic feet to 1.75 cubic feet, we re just about right on
with the enclosure! However, if we were trying to make a ported
enclosure that was 2.0 cubic feet, we ll need to make the enclosure
slightly larger to accommodate for displacements of the woofer and the
Triangle
port! Simply adjust the dimensions of the enclosure (either Height,
Width, or Depth) until you have reached the ideal size you re trying to
achieve.
Parallelogram
Calculating more complicated enclosures with triangular, circular, or
wedge dimensions is simply a matter of breaking the dimensions of the
enclosure down into basic formulas for calculation. These calculations
can be found in Enclosure Calculation Guide.
Cylinder
Enclosure types
www.rockfordfosgate.com/rftech RFTECH: ENCLOSURE 3
How Do I Build The Enclosure?
Once the dimensions of the box are decided, and you know the enclosure
Tech Tips
will work well for you, the materials need to be selected. The following is
a list of common enclosure construction materials:
Use 3/4" Medium Density
Fiberboard (MDF), mea-
Particle Board: Very inexpensive, however this board tends to come
sure out your wood com-
apart under the high stress of subwoofers, and is very susceptible to water
pletely before cutting,
damage! Not suitable for very large enclosures unless a great deal of
glue & screw all joints,
internal bracing is added for extra rigidity.
and seal all joints with a
silicone caulk to make the Medium or High Density Fiber Board (MDF): The best overall
enclosure airtight.
material for speaker enclosures, fiberboard is extremely rigid, and will not
come apart at even the highest pressure levels. However, fiberboard is hard
to cut (requiring a carbide blade), and is not readily available in smaller
Enclosure exterior
stores.
Plywood (all types): A poor choice for car stereo subwoofer
enclosures, as plywood tends to de-laminate under heat and weather ranges
found in cars. It can also buzz at low frequencies when played at high
volume.
Strips
Birch, Maple, Walnut (and other dense, natural woods):
Very good for all enclosures, although it is quite expensive.
The choice of materials should be made considering cost, availability, and
3/4"
the type of finish the box will eventually have, so don t spend the money
Figure B Butt Joint Example
for natural wood if you intend to cover it up with carpet! The thickness of
material for the enclosure is governed by the overall size of the enclosure.
Enclosure exterior
The smallest of enclosures (1.0 cu ft or less) can use 5/8" or 1/2" material.
Average size enclosures (1.0 cu ft to 4.0 cu ft) should use 3/4". Very large
enclosures (over 4.0 cu ft) should use 1" material with braces to prevent
enclosure flex.
Although there are many different ways to join the edges of enclosures
Strips
together, the basic butt joint or the 45-degree miter joint are more than
adequate for subwoofer enclosures (See Figure B & C). When joined with
carpenters glue such as Titebond or Elmer s wood glue and screws, the
3/4"
joints become stronger than the wood itself. Further strength can be added
by using corner bracing made out of 1" strips at every inside edge. This
Figure C Miter Joint Example
will also ensure an air tight seal. The easiest way to put a enclosure
together is to glue and screw it. (See Figure D & E)
Things to Remember
Measure twice, cut once!
www.rockfordfosgate.com/rftech RFTECH: ENCLOSURE 4
Top Panel
Left-Hand
Rear Panel
Side Panel
Braces
Window
Brace
Assembly
Right-Hand
Side Panel
Bottom Panel
Braces
Front Panel
Figure D Parts and Assembly of Enclosure
Figure E Corner Bracing Example
www.rockfordfosgate.com/rftech RFTECH: ENCLOSURE 5
Simple Enclosure Building Instructions
" Cut all of the enclosure sides and inner braces.
" Pre-drill and countersink the sides where they will attach to the braces.
" Lay a bead of glue on the brace and line it up with the appropriate
edge.
" Screw one edge of the brace to a side, making sure that the edges line
up. Remember to pre-drill your screw holes so the wood doesn t split
when you put the screw in.
" Screw the opposite edge to the side, again making sure that the edges
line up, then continue with the balance of the holes (screws should be
placed at 3" intervals).
" Attach the rest of the braces.
" Apply a bead of glue to the edge of the brace and one side.
" Line up the attaching side and screw together the two pieces starting
with the far edge.
" Continue with each screw in line, making sure that the edges stay flush.
(This will take any warp out of the wood.)
" Continue the rest of the enclosure. In addition to the corner braces, it
may be necessary to brace the enclosure from side-to-side, or top-to-
bottom. In the case of such large surface areas, enclosures will tend to
flex at the lower frequencies. This can cause distortion, a boomy box
sound, and wastes energy that could be used to attain higher output
levels. Anytime that you have an area larger than 1' X 2', you should
put a brace in the middle. (see window brace in Figure D)
" Finally, remember to keep your enclosures airtight, even in the case of
a vented system. All subwoofer systems can be mis-tuned dramatically
from small amounts of leakage, so using a high-quality silicone (not
latex) sealant from GE or DAP to seal all joints will make your
enclosure work just right. The speaker itself may be sealed to the
enclosure with foam gasket material or rope caulk to assist in
preventing air leaks. Make sure to caulk around the holes cut for the
ports as well, if your enclosure uses them.
www.rockfordfosgate.com/rftech RFTECH: ENCLOSURE 6
Damping Enclosures
Adding damping material, such as lambs wool, fiberglass, or Dacron
polyester (pillow stuffing like Poly-Fil) to your subwoofer enclosure
helps cancel any standing waves or resonances that form in the enclosure
because of its particular dimensions. We recommend adding stuffing
only if you need to, and only to sealed enclosures. It won t make up for a
poorly-constructed enclosure or an enclosure that s built too small, but it
can help make the enclosure play low frequencies with added emphasis.
It is possible to make your speaker think that it is in a larger box than it
actually is by adding extra damping material, up to 75% of the entire
enclosure volume. The general rule here is to add 1 pound of fill material
(R-19 fiberglass, Dacron, or lamb s wool) per cubic foot of enclosure
volume.
Naturally, you can vary the amount of fill you use to fit your personal
taste. If you want to gradually change the way a sealed box sounds, add
damping material to the enclosure beginning with about 10% fill, and
adding up to 75% of the total enclosure volume according to the way
you want the enclosure to sound. Don t compress the material, just
loosely add fill to the enclosure. This works because the fibers of the
material cause the sound waves to bend around them, slowing the waves
down and taking longer to reach the enclosure s sides. As much as a 15%
change in box volume/response can be achieved by this method.
Recommended Reading
Loudspeaker Design Cookbook, Old Colony Sound Labs
Post Office Box 243
5th Edition
Peterborough, New Hampshire
Vance Dickason
03458-0243 U.S.A.
Building Speaker Systems, Master Publishing
14 Canyon Creek Village MS31
2nd Edition
Richardson, Texas 75080 U.S.A.
Gordon McComb, Alvis J. Evans,
214-907-8938
Eric J. Evans
Radio Shack part #62-1087
Advanced Speaker Systems Master Publishing
14 Canyon Creek Village MS31
Ray Alden
Richardson, Texas 75080 U.S.A.
Radio Shack part #62-2317
214-907-8938
www.rockfordfosgate.com/rftech RFTECH: ENCLOSURE 7
Enclosure Calculation Guide
TERMS Enclosure Type Calculation for Cubic Feet
H = Height
Square (H X W X D) ÷ 1,728
W = Width
Rectangle (H X W X D) ÷ 1,728
D = Depth
Wedge ((D1 + D2) X 0.5 X H X W) ÷ 1,728
D1 = Top Depth
D2 = Bottom Depth
Trapezoid ((D1 + D2) X 0.5 X H X W) ÷ 1,728
B = Base
Triangle ((0.5 X B) X H X W) ÷ 1,728
L = Length
Parallelogram (H X W X D) ÷ 1,728
r = Radius
Cylinder ((3.14 X r X r) X L) ÷ 1,728
Woofer Displacement Formulas
Due to different manufacturing designs and materials used, the formula
for calculating speaker displacement is not perfect but at least it works
?
better than dipping the speaker into a bucket of water.
Speaker Displacement = 4 X 0.33 X 3.14 X the distance from the back
of the mounting lip to the rear of the magnet ^ 3 X 0.5 X 0.6.
Figure F Speaker Displacement
For example: using a Punch Power 12" DVC woofer, which has 6.03"
inches from the back of the mounting lip to the rear of the magnet (see
Figure F).
4 X 0.33 X 3.14 X 6.03 ^ 3 X 0.5 X 0.6 = 273 cubic inches (0.16 cubic
feet) displacement
CAUTION: Using this formula can result in up to 25% tolerance
difference. For precise figures, please refer to the pre-calculated
Subwoofer Displacement Chart in your Rockford Fosgate owner s
manual or use the handy chart on the next page.
www.rockfordfosgate.com/rftech RFTECH: ENCLOSURE 8
Woofer Displacement Chart
Model Displacement
Model Displacement
Model Displacement
Model Displacement
(cubic feet)
(cubic feet)
(cubic feet) (cubic feet)
Punch Power HX2
Punch HX2
Punch RFZ Punch HE
RFR 3110 .11
RFD 1208 .041
RFZ 2408/2808 .05 RFP 3408/3808 .035
RFR 3112 .12
RFD 1210 .055
RFZ 2410/2810 .06 RFP 3410/3810 .060
RFR 3115 .19
RFD 1212 .069
RFZ 2412/2812 .09 RFP 3412/3812 .085
RFD 1215 .109
RFZ 2415/2815 .113 RFP 3415/3815 .135
Punch Power
RFD 2208 .041
RFZ 3408/3808 .05 RFP 3406/3806 .018
RFR2210 .12
RFD 2210 .055
RFZ 3410/3810 .06
RFR2212 .21
RFD 2212 .069
RFZ 3412/3812 .09 Punch XLC
RFR2215 .25
RFD 2215 .109
RFZ 3415/3815 .11 RFP 2408/2808 .05
RFD 1218 .300
RFZ 1408/1808 .05 RFP 2410/2810 .06
RFD 2218 .300
RFZ 1410/1810 .06 RFP 2412/2812 .09
RFD 3118 .244
RFZ 1412/1812 .09 RFP 2415/2815 .113
RFD 3218 .244
RFZ 1415/1815 .113 RFP 2418/2818 .19
RFD 2110 .055
RFD 2112 .069
RFD 2115 .109
Punch HE2
RFP 3208 .031
RFP 2208 .031
RFP 2210 .050
RFP 3210 .050
RFP 2212 .066
RFP 3212 .066
RFP 2215 .103
RFP 3215 .103
Punch DVC
RFP 1208 .035
RFP 1210 .06
RFP 1212 .085
RFP 1215 .135
www.rockfordfosgate.com/rftech RFTECH: ENCLOSURE 9
Vent Displacement Formulas
The formula for figuring displacement of a vent is as follows:
Vent Displacement = (1/2 the outside diameter X 2) X 3.14 X length of
the vent
For example, a 4" port, 5" long would figure like this: (a typical 4" port
has an outside diameter of 4.5"): 2.25 X 2.25 X 3.14 X 5.0 = 78.46
cubic inches of displacement!
Figure G Vent Displacement
Port Diameter
Port Length 2.0" 2.5" 3.0" 4.0" 5.0" 6.0"
2.0" 0.007 0.009 0.011 0.015 0.018 0.022
2.5" 0.009 0.011 0.014 0.018 0.023 0.027
3.0" 0.011 0.014 0.016 0.022 0.027 0.033
3.5" 0.013 0.016 0.019 0.025 0.032 0.038
4.0" 0.015 0.018 0.022 0.029 0.036 0.044
4.5" 0.016 0.020 0.025 0.033 0.041 0.049
5.0" 0.018 0.023 0.027 0.036 0.045 0.055
5.5" 0.020 0.025 0.030 0.040 0.050 0.060
6.0" 0.022 0.027 0.033 0.044 0.055 0.065
6.5" 0.024 0.030 0.035 0.047 0.059 0.071
7.0" 0.025 0.032 0.038 0.051 0.064 0.076
7.5" 0.027 0.034 0.041 0.055 0.068 0.082
8.0" 0.029 0.036 0.044 0.058 0.073 0.087
8.5" 0.031 0.039 0.046 0.062 0.077 0.093
9.0" 0.033 0.041 0.049 0.065 0.082 0.098
9.5" 0.035 0.043 0.052 0.069 0.086 0.104
10.0" 0.036 0.045 0.055 0.073 0.091 0.109
10.5" 0.038 0.048 0.057 0.076 0.095 0.114
11.0" 0.040 0.050 0.060 0.080 0.100 0.120
11.5" 0.042 0.052 0.063 0.084 0.104 0.125
12.0" 0.044 0.055 0.065 0.087 0.109 0.131
12.5" 0.045 0.057 0.068 0.091 0.114 0.136
13.0" 0.047 0.059 0.071 0.094 0.118 0.142
13.5" 0.049 0.061 0.074 0.098 0.123 0.147
14.0" 0.051 0.064 0.076 0.102 0.127 0.153
14.5" 0.053 0.066 0.079 0.105 0.132 0.158
15.0" 0.055 0.068 0.082 0.109 0.136 0.164
15.5" 0.056 0.070 0.084 0.113 0.141 0.169
16.0" 0.058 0.073 0.087 0.116 0.145 0.174
www.rockfordfosgate.com/rftech RFTECH: ENCLOSURE 10
Wedge
D1
3-D
H H
Side Front
D2 W
Square
Side Front 3-D
H H
D W
Rectangle
Side Front
H H
3-D
D W
Trapezoid
D1
Side Front H
H
3-D
D2 W
Parallelogram
Side H Front H
3-D
D W
Triangle
H H
Side Front
3-D
D
W
Cylinder
r
Side Front
3-D
L
www.rockfordfosgate.com/rftech RFTECH: ENCLOSURE 11
Edited by: E.R. 7-2002
Created by: Z.S. / C.N. / E.R. 2-2000
Wyszukiwarka
Podobne podstrony:
HP BladeSystem c Class enclosuresenclosing floatsenclosureCabinets Bathtub EnclosureEnclosuresDance, Shield Modelling of sound ®elds in enclosed spaces with absorbent room surfaceswięcej podobnych podstron