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Want to build a big subwoofer but don’t want to get involved
with high quality cabinet work? Then have a look at this
design. Based on a readily available TV/VCR cabinet, it has
the looks and it has the grunt - using a 10-inch Soundstream
woofer rated at 250 watts.
Build
the
BASS CUBE
38 Silicon Chip
By JULIAN EDGAR
U
NLIKE OUR compact Bass
Barrel featured in the August 1997 issue of SILICON
CHIP, the Bass Cube is designed to
deliver high power. It will really liven
up the low bass in even the biggest
lounge rooms.
You won’t have to apologise for its
appearance either because it is based
on a readily available commercial
product.
Best of all, you won’t need to go far
to buy the enclosure – it’s available
for under $50 from all Big W stores,
where it masquerades as the Economy
Video/TV Cabinet!
OK , you still have to do some woodworking to convert it to the Bass Cube
but this is quite straightforward. And
because it’s based on a commercial
cabinet, you should have no problems
at all when it comes to obtaining a
high-quality finish.
The Bass Cube uses a Soundstream
Rubicon 10-inch (250mm) subwoofer
with a maximum continuous program
power rating of 250W. That’s a serious
amount of power in anybody’s lan-
guage so it will really deliver the grunt.
This driver uses a 4-layer voice coil
with a Kapton-epoxy former which
is 50mm (2 inches) in diameter. The
woofer has a vented pole-piece to
provide forced-air cooling, while
high emissivity coatings are used
on the steel plates to improve power
handling. The cone is made from
reinforced fibre pulp with a synthetic
rubber roll surround.
Installed in the Bass Cube enclosure,
the driver reproduces frequencies
down to about 30Hz, tapering off
below that.
In the lounge room it’s a real window rattler. We also tested the Bass
Cube in a car and while it’s really too
large for most vehicles, the results
were pretty impressive.
By the way, the total cost of materials used to make your Bass Cube
should be well under $300. Most of
that is spent on the driver.
Design
When designing a subwoofer, there
are numerous conflicting criteria to be
taken into account. The first thing that
needs to be considered is size.
A software program like BassBox
makes it easy to come up with a subwoofer that will provide thunderous
bass – if the enclosure is as big as
a fridge, that is! Getting good bass
response from a smaller enclosure is
much more difficult and in fact, can be
Loudspeaker
Parameters
General Information
Company: Soundstream
Model:
Rubicon 10
Mechanical Parameters
Fs
Qms
Vas
Cms
Mms
Rms
Xmax
Sd
Dia
=
=
=
=
=
=
=
=
=
34 Hertz
11.5
45.4 litres
0.209mm/N
104 grams
1.947 kg/sec
21mm
391 sq.cm
22.3cm
Electrical Parameters
Qes
Re
Le
Z
BL
Pe
Fig.1: the predicted frequency response of the Bass Cube shows that its
-3dB point is at 33.6Hz and that is has good efficiency.
=
=
=
=
=
=
0.450
3.6W
2.9mH
4W
13.4 N/A
250W
Combination Parameters
Qts
=
no
=
Sens =
0.430
0.341%
91dB (2.83V)
Vented Box Parameters
Fig.2: the predicted impedance plot of the design shows that the minimum
impedance seen by the amplifier is 4.8Ω.
Vb
Fb
F3
QL
Fill
Ports
Dv
Lv
=
=
=
=
=
=
=
=
40.00 litres
34.6 Hertz
33.6 Hertz
7.0
normal
1 (round)
8.6cm
28cm
April 1999 39
amplifier is 4.8Ω.
Fig.1 shows the predicted frequency
response, while Fig.2 plots the impedance curve. Before its response starts
to taper off, the subwoofer should
produce a sound pressure level (SPL)
of 91dB at 1W (at 1 metre with a
2.83V input). That is a relatively high
efficiency as far as subwoofers go. It is
suitable for use with amplifiers rated
from 50 to 250 watts.
Modifying the TV cabinet
At this stage the side pieces have been shortened, the black woodwork
assembled ‘dry’, and the bottom part of the internal frame loosely placed into
position. Resting the speaker and the port into position will show you where
you need to cut these holes in the baseplate.
impossible with some drivers.
Fortunately, car subwoofers have
boomed (pun intended) over the last
five years, so there are now lots of
high-power drivers available that are
suited to compact enclosures.
The Soundstream driver specified
here is rugged, comes with full specifications and is widely available from
Strathfield Car Radio stores and other
suppliers. At $199, it is also relatively
cheap for a driver of this quality.
Having selected the driver, the next
problem involved choosing a suitable
enclosure. There are three commonly
used enclosures: (1) sealed, (2) bass
reflex (sometimes called ported) and
(3) bandpass.
Bandpass enclosures allow very
high efficiency (big acoustic power out
for not much input) but they only cover a narrow frequency range; eg, from
30-90Hz, or less than two octaves. In
this type of design, the driver radiates
via two ports rather than directly from
the enclosure.
Unfortunately, it requires very long
tuning ports if we want good response
at low frequencies. In fact, if the ports
are made large enough in diameter so
that “chuffing” noises don’t occur, they
may need to be metres long to correctly
tune the enclosure!
The Bose Cannon is a classic exam40 Silicon Chip
ple of this approach and it is 4 metres
long! We want something a bit smaller
than that, please!
A small, high-efficiency bandpass
enclosure therefore has major drawbacks when it comes to port design.
In case you’re wondering, the previous
Bass Barrel bandpass design overcame
some of these problems by using
two speakers mounted in an isobaric
configuration. However, using two
Soundstream drivers would make this
project just too expensive.
Sealed enclosures are the easiest
to make and they have a predictable
response. However, the bass roll-off
(gentle as it is) starts very early and so
extended low frequency response from
small sealed enclosures requires a substantial bass boost; ie, lots of power.
The efficiency of sealed enclosures is
also lower than ported designs.
Finally, there are the bass reflex
enclosures. These augment the bass
response by coupling the output from
the rear of the speaker cone via a tuned
port. Fortunately, the tuned port can
be made reasonably short, even with
a relatively small enclosure.
The Bass Cube design uses the bass
reflex approach.
The final design uses a 40-litre enclosure. Its -3dB point is 33.6Hz and
the minimum impedance seen by the
Now that we had the basic design,
we started looking at suitable enclosures. To make construction as simple
(and economical) as possible, we
wanted a commercial enclosure that
could be modified to suit.
We found nothing really suitable
until we started looking “outside the
box”. If there was nothing available
designed for the purpose, what about
something designed for another purpose?
That's when we spotted a Video/
TV cabinet in the local Big W store.
Eureka!
This cabinet is very suitable for this
application. It is made from relatively hefty 16mm black plastic veneer
chipboard, screws together tightly and
needs only a few minor modifications
to turn it into a subwoofer enclosure.
The big advantage for the home constructor is that all exposed edges are
finished, the panels are all cut square
and the design is modern. What more
could you want?
Oh, you do have to put the cabinet
together. Did we mention that before?
It comes as flat-pack kit.
As well as the materials provided
with the cabinet, you will need all the
materials listed in the accompanying
panel.
You will also need a drill, an electric
jigsaw and preferably a circular saw. If
you don’t have the latter, a hardware
store can probably do the very few cuts
required or you can make the straight
cuts by running the jigsaw against a
clamped straight edge.
The first step is to unpack the cabinet. Incidentally, if you can’t find it
at Big W, contact the Victorian makers
direct (they are listed at the end of
this article).
With the pieces of the cabinet laid
out, you will see that it comprises a
large base, two sides, a smaller top
and a shelf.
Fig.3, reproduced from the manufac-
Fig.3: the assembly
instructions for the TV/Video
cabinet include this diagram.
In the Bass Cube application, shelf (D)
becomes the new front panel, with the side
panels (C) shortened to match.
turer’s assembly instructions, shows
the general layout.
In the Bass Cube configuration, shelf
(D) becomes the front panel, while the
side panels (C) are reduced in height
to suit.
It’s a good idea to first loosely assemble the cabinet (ie, don’t fully tighten
up the screws), so you can be sure how
it all goes together. The action of the
“cam lock” fasteners, for example, may
not be clear until you do this.
Cutting the panels
The two side panels (C) should
be cut to 337mm (high) by trimming
their bottom edges. You will need to
take special care to avoid chipping the
black plastic veneer along the cutting
edge. There are several things you can
do to minimise this problem.
First, use a sharp, fine-toothed saw.
We’re assuming that you’ll be using a
circular saw, by the way, and that you
will probably use it in conjunction
with a straight edge guide to ensure
a nice straight cut. Of course, there
is nothing to stop you from using a
hand saw.
Second, use a sharp Stanley knife
to deeply score along both sides of the
cut; ie, the width of the saw blade. In
this way, the plastic is cut before the
saw blade touches the material.
Also note that the blade will always
tend to chip the material more on the
underside of the cut. So it is a good
idea to make sure that the underside
is the side that won’t be seen when the
unit is ultimately assembled. On the
other hand, you need to take care that
the baseplate of the saw does not mar
the material as it slides along.
If the saw does happen to leave
minor blemishes in the plastic veneer,
fill these with black paint.
Once you have shortened the side
panels, redrill the pilot holes in the
base of each piece. You can see where
these need to go by checking the locations of the holes in the pieces that
April 1999 41
driver is improved and (3) the cabinet
looks neater.
Bracing the enclosure
With the holes cut for the speaker and port (and the mounting holes drilled for
the speaker), the black woodwork can be assembled using PVA glue.
have just been cut off.
If you look at the inside faces of
the side panels you’ll see more holes
drilled to take the shelf-locating cam
pins. These holes remain unused –
instead, new pilot holes need to be
drilled to hold the shelf in its new
location as the front panel. We recessed the front panel by 4mm so that
it matched the appearance of the rest
of the cabinet.
Be careful when drilling these holes
that you don’t drill right through the
panel. If you do, you will spoil the
appearance of the finished job.
Once all the holes have been drilled,
you’re ready for a trial assembly. Don’t
use glue or screw anything fully home
at this stage – just make sure that it
all goes together in Bass Cube form
without any problems. If all goes
well, you’re ready to add the internal
framework before fitting the back, the
speaker and the port.
Internal framework
As shown in the photos, the speaker
is mounted face downwards inside
the enclosure and “fires” through a
hole cut in the baseplate. The port
also vents through this bottom panel.
However, because the Bass Cube sits
up on the integral feet provided with
the cabinet, there’s plenty of room for
the sound to escape, although if you
place the Cube on deep pile carpet, you
should extend the feet or possibly fit
furniture casters.
Taking the bottom-firing approach
has a number of advantages: (1) the
driver is protected without the need
for a grille, (2) the air-loading of the
The Materials Required
PVA glue and a tube of Liquid Nails (or a similar adhesive)
One MDF panel about 443 x 335 x 18mm
5 metres of 20 x 20mm DAR pine, Meranti or similar timber
28cm of 90mm plastic stormwater pipe
50 6G x 30mm self-drilling plasterboard screws
12 6g x 35mm (or 40mm) self-drilling plasterboard screws
8 nuts, bolts and washers to suit the speaker mounting
1 speaker terminal and heavy-duty speaker wire
1 square metre of quilt wadding.
42 Silicon Chip
An internal framework braces each
of the panel joins of the enclosure.
This stiffens the box, provides added
insurance against air leaks and locates
the new rear panel. The framework is
made from 20 x 20mm DAR (dressed
all round) pine and is screwed and
glued into place.
The exact dimensions of the
framework will be determined by the
amount that you recess the front panel.
Assuming that it’s recessed by 4mm,
the long pieces of timber bracing will
be 445mm long and the short pieces
296mm long. The accompanying
photographs show the layout of this
framework. We used butt joints since
they’re easy to make.
After cutting the four pieces, temporarily position them on the bottom
panel. When you’ve done this, it will
be apparent that there’s only just
enough room for the speaker to fit.
When you add the port dimensions,
it becomes clear that the driver needs
to go at one side of the bottom panel
and the port at the other! Mark the
holes for the speaker and port on the
baseplate, then cut them out with a
jigsaw.
Once this has been done, you can
glue the Bass Cube together. We suggest that you use white PVA woodworking glue for the initial assembly.
This can easily be wiped off with a
wet rag and also dries clear, so any
bits that you forget to wipe away are
not visible.
Begin by assembling all the black
panels, ie; the base, the two side panels, the top and the front panel. The
front and side panels are also secured
to the base using screws.
Let the PVA glue dry for a few hours
before installing the internal pine
framework. This should be glued into
place using generous applications of
Liquid Nails. Pick the water-soluble
type of Liquid Nails so that it’s easy
to clean up and be sure to choose a
well-ventilated area when applying
the glue, to avoid inhaling the fumes.
In addition to the glue, we used two
or three 6G x 30mm self-drilling plasterboard screws (inserted from each
direction) to hold every piece of the
framework firmly in position.
When inserting the screws, be sure
to drill pilot holes to avoid splitting
The internal framework is screwed and glued into position using chipboard
or plasterboard screws and copious quantities of Liquid Nails. Note the use of
a brace across the front panel (seen at back of picture). There is also another
hidden piece across the underside of the top panel.
the timber. We also stiffened the large
front and top panels with additional
lengths of 20 x 20mm pine, as shown
in the photos.
When the glue dries you should
have a stiff, well-sealed enclosure –
apart from the open back, of course.
against the internal framework, with
its outer edge flush with the rear of
the Cube.
The back is held in place by 12 6G
x 35mm screws but don’t put them in
just yet! First, you need to mount the
rear terminal block (we used one from
Dick Smith Electronics) and wire the
speaker to it.
Soundstream state that the leads
should not be soldered to the speaker
(and may not honour a warranty claim
if they are), so we used push-on spade
terminals. Make sure that the positive
and negative terminals on the driver
are wired to the corresponding terminals on the rear panel terminal and use
heavy-gauge speaker wire for this job.
Now cut some quilt wadding and
glue it into place on the inside surfaces
of the enclosure, not forgetting the
inside of the back panel.
Make sure that the wadding doesn’t
block the port though, because that
would seriously upset the performance
of the Bass Cube.
At this stage, it’s a good idea to
connect the subwoofer to an amplifier
and play some music, just to make
sure that the driver and your wiring
are OK. Keep the level reasonably
low for this test though, as the unit
is not yet sealed (the back isn’t on). If
everything seems fine, disconnect the
amplifier and then glue and screw the
back panel into place.
Again, be lavish with your use of
Liquid Nails – you don’t want any
air leaks at all. Once you have done
Mounting the speaker
The next step is to mount the 10inch woofer and the port tube. The
28cm long port is cut from plastic
stormwater pipe. It has a nominal outside diameter of 90mm and an internal
diameter of 86mm.
To mount the driver, first mark and
drill the eight mounting holes in the
base. Be sure to use the gasket provided
when installing the driver and tighten
its mounting bolts down evenly so that
the frame doesn’t distort. The port tube
can be glued into place using Liquid
nails, making sure that there are no air
leaks around its edge. The tube should
be located so that its end is flush with
the bottom surface of the base panel.
The rear panel is made from a 443
x 335mm piece of 18mm thick MDF
(medium density fibreboard). Note
that these were the dimensions used
on the prototype; it would be wise to
measure your own enclosure just in
case it is slightly different.
The thicker rear panel does not
require internal bracing. It should fit
neatly into the enclosure and nestle
The final steps before sealing the box are to glue quilt wadding on the inner
surfaces and wire up the terminal. Make sure that you use heavy-gauge cable
for this purpose.
April 1999 43
MAKING YOUR OWN BASS CUBE BOX
If you don’t want to buy the TV/
Video cabinet we modified for this
article, there’s nothing to stop you
constructing your own Bass Cube in
the conventional manner.
The diagram below shows how
this can be done using 18mm MDF.
With this thickness of timber, internal bracing should not be required
44 Silicon Chip
but all joins must be completely airtight.
The speaker baffle should be the
last panel fitted, following a similar
test procedure as outlined in the text.
Note that this enclosure is shown
upside down – like the enclosure
featured in this article, it is designed
to have the speaker and port aimed
at the floor.
Similarly, the enclosure will need
to be supported clear of the carpet –
and note the comments about shag
pile carpet in the text.
Incidentally, at 480 x 340 x 370mm,
this subwoofer is getting close to the
size seen in many large cars.
Yes, it’s big but the bass is amazing!
The completed subwoofer lying on its front face. This photo gives a good idea of
how all the pieces go together and the mounting positions for the speaker and
port. Note the large ‘feet’ – this size lifts the speaker baffle off the floor enough
for normal carpet but these would need to be even higher if the Bass Cube was
sitting on thick, shag-pile carpet.
that, let the adhesive harden before
launching into action.
Note that the rear panel should not
be glued, although some sort of sealant
should be used to avoid leaks.
Testing
The Bass Cube should be tested
alone first, without other speakers
playing. At this stage you want to
be able to hear just what the Cube is
doing – not have its sounds partially
drowned out by the rest of the system.
Play some music relatively quietly
through the sub and listen for buzzing
noises – they can be evidence of air
leaks. Moistening your fingers and
moving them along all of the joins will
also help you locate any leaks. These
leaks must be sealed if the subwoofer
is to perform well.
Perhaps the easiest way to seal leaks
is by smearing some PVA glue into the
join at the point where there is a leak
and say 50mm each side, then wiping
the excess off with a damp rag.
When the subwoofer is working
without buzzes, turn up the volume
– again with just the Bass Cube connected. Listen for distortion, clacking,
buzzes, whistles and the like. If there
aren’t any, turn up the volume a little
more.
If you have a powerful amplifier
(or more frequently, a small amplifier
that’s driven into distortion!) you
will clearly hear when the limits are
reached.
Except for a very brief time during
this testing, don’t ever drive the Bass
Cube into distortion. Note that this
may occur without being noticed when
the other speakers are connected and
playing – you have been warned!
Like all speakers, the frequency
response of the Bass Cube will be affected by its location within the room.
If it is placed against a wall or in a
corner, its bass will be augmented – but
will tend to be boomy or “muddy” as
well. If your listening situation allows
it, move the Cube around during testing until you find the most pleasing
location.
Remember also that if you wade
through the carpet at your place, you’ll
need to extend the Bass Cube’s feet to
lift the base panel above the shag pile.
Given its size and cost, we were
pretty pleased with the performance
of the Bass Cube. We are sure that you
will be too.
SC
WHERE TO BUY THE CABINET
The Economy Video/TV Cabinet
is available at any Big W store, or
failing that is manufactured by:
Koala Furniture International Pty Ltd
(03) 9878 3688
April 1999 45
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