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Build the JV60
Here’s your chance to build a modern high
performance loudspeaker using high quality
drivers made by Vifa of Denmark. This is a
tower design producing lots of bass. It uses two
170mm woofers and a 25mm aluminium dome
tweeter with a ferrofluid cooled voice coil.
By LEO SIMPSON
Handsome and well finished, the JV60
cabinets have a capacity of 50 litres
and only take up a modest amount of
space in your listening room.
T
HESE DAYS, you have two
main choices as to the type of
loudspeaker system to buy from
your hifi retailer.
The first is a compact bookshelf style
system and the second is a tall narrow cabinet generally referred to as a
“tower” style using two small woofers.
Now it might seem that the compact
bookshelf system is the one to go for if
you don’t have a lot of space or you are
on a budget. But you will always find
that the manufacturers recommend
that their compact systems be placed
in floor stands to give the best overall
performance.
Typical floor stands are about 400 to
500mm high and have a “foot print”
18 Silicon Chip
which is about 350mm square. So
while the loudspeaker cabinet might
be quite compact, its effective bulk and
the floor space it takes up are much
greater. If you can afford it, the tower
option is always the better choice.
You get a bigger cabinet and this almost always means better bass (cleaner
and more extended). And this is the
benefit provided by the tower speakers
presented here. By building the kits
you save money and thereby you can
afford a system that otherwise could
be out of reach. And if you can make
your own cabinets, you can save more
money into the bargain.
On the other hand, a big bonus of the
kit presented here is that the cabinets
themselves are supplied fully assembled. There is absolutely no carpentry
work to be done and the cabinets are
very professional in appearance. Virtually all you need to assemble these
fine loudspeakers is a Phillips head
screwdriver and a soldering iron. Nor
do you have to put the crossover network together since it is also supplied
fully assembled.
Dimensions of the JV60 system
are 895mm high, 260mm wide and
315mm deep, which includes the
thickness of the grille cloth frame.
Made of 16mm particle board and
internally braced, the cabinet has a
volume of close to 50 litres.
By the way, this design has been
produced exclusively for Jaycar Electronics by Australian Audio Consultants, PO Box 11, Southport, SA 5410.
The loudspeaker line-up is two
170mm woofers and a 25mm dome
tweeter but the system is not strictly
two-way.
A glance at the circuit of Fig.1 shows
that the crossover is a modified twoway system with one of the woofers
(W2) effectively handling bass and
midrange frequencies while the other
(W1) handles bass frequencies below
200Hz. This has been done to achieve
a strong and extended bass, as we shall
see. This system is geared particularly
to those people who love plenty of
bass, without the need for any boost
from the amplifier.
Ferrofluid cooled tweeter
The Vifa tweeter featured in this
system is the D25AG-35-06. It has a
couple of unusual features, not the
least being the fact that it has an aluminium dome tweeter instead of the
more usual Mylar or synthetic fabric
dome.
The 25mm aluminium dome is protected from prying fingers by a plastic
shield which is de
signed to avoid
phasing and beaming effects which
can occur with any sort of obstruction
in the beam of a tweeter. Also unusual
is the ferrofluid cooling of the tweeter’s
voice coil. This has been a feature of
high-quality tweeters for quite a few
years now but it has seldom, if ever,
been featured in a kit-built system
such as this.
Ferrofluid is a patented synthetic oil
mixture with suspended iron powder.
Loudspeaker System
These are the Vifa drivers, crossover network and rear terminal panel provided
for each speaker system. Also included in the kit are Innerbond filling and
mounting screws.
The suspended iron means that the oil
has no effect on the magnetic circuit
of the tweeter. It has two benefits for a
tweeter. First, it helps cool the tweeter
voice coil which can otherwise become very hot when operating at high
powers. This can be easily understood
since a tweeter voice coil is a very light
assembly and it is suspended in the
magnetic gap where air flow is very
slight. With the ferrofluid, the heat in
voice coil is conducted away to the
magnet and frame of the speaker where
it can be dissipated harmlessly.
The other benefit of ferrofluid is that
it applies a degree of damping to the
suspension of the tweeter and thereby
can help smooth the overall response.
Other specifications of the tweeter
include a nominal impedance of 6Ω,
a free air resonance of 850Hz and a
nominal power handling (IEC268-5)
of 100 watts.
Woofers
For the bass and midrange there
are two 170mm woofers, type
P17WJ-00-08. These units feature a
cast magnesium basket with a synthetic rubber surround. The cone material
is mineral filled polycarbonate. It has
a sensitivity of 88dB and a frequency
response usable to 4kHz.
One of the best aspects of using
Vifa drivers is their consistency. The
drivers were measured using the
Loudspeaker Measurement System
(LMS) and these measurements were
compared with the manufacturer’s
published data. To some extent,
driver parameters will vary on the
production line, even within a batch.
A manufacturer who is consistent
manages to maintain these variations
in such a way that the repercussions
August 1995 19
RED
P2
RDE245A
C5
0.1
POLYESTER
P1
RDE070A
C3
6.8
BP
INPUT FROM
AMPLIFIER
YELLOW
TWEETER
D25AG
L3
0.22mH
BLACK
L2
0.39mH
BLUE
R2
5. 6
5W
C6
0.1
POLYESTER
W2
WOOFER
P17W1
C2
10
BP
L1
4mH
RED
R1
5. 6
5W
C7
0.1
POLYESTER
C1
33
BP
W1
WOOFER
P17W1
JV60 SPEAKER SYSTEM
Fig.1: the JV60 is a modified two-way bass reflex system with
one of the woofers (W1) only handling bass frequencies below
200Hz.
are negligible. All driver parameters
are related and if one group are a little
high then another grouping should be
a little low, counteracting any change.
Vifa seem to manage this effortlessly.
The 50-litre enclosure has two
66mm ports 197mm long. The internal brace is an essential feature of the
cabinet and is placed underneath the
topmost woofer. A shelf brace should
never be placed in the centre of an
enclosure. This method of bracing
carries out several functions, the first
of which is to connect adjoining panels and help to dissipate vibrations.
A shelf brace also divides panels
into smaller segments, thus moving
resonances to higher frequencies and
Solder the wires to the rear terminal panel, before fitting it into place.
20 Silicon Chip
lowering vibrational energy.
Constructors who wish to build
their own cabinets may use the drawing of Fig.2 as a guide. Increasing wall
thickness to 18mm will have very
little effect, although increasing it to
25 or 32mm will be a considerable
advantage (but make it much heavi
er). Ensure that the internal volume
remains the same, even allowing for
the increased brace thickness.
The cabinet is tuned for a corner
frequency of about 35Hz (-3dB point)
and, as such, it produces copious
amounts of bass. Before we look at
the crossover network, let’s take a
quick look at contemporary design
techniques in this area.
In the past crossovers were designed
by placing textbook components into
the cir
cuit and assuming that they
would do the job. However, this does
not take into consideration several
factors, the two principal ones being
(a) the drivers’ natural roll off slopes
and (b) the interaction between the
drivers’ motor system (ie, magnet,
voice coil and suspension) and other
components.
Nowadays, CAD packages such as
the Loudspeaker Enclosure Analysis
Program (LEAP) allow a designer to
check and recheck systems at every
stage of development. Computer optimization allows one to consider all
variables when designing crossovers.
Crossover design
The crossover design is unusual, as
can be seen from the diagram of Fig.1.
It is based on a second order (12dB
slope/octave) Linkwitz-Riley filter.
The tweeter section uses a 0.22mH inductor and a 6.8µF capacitor operating
at nominally 3.5kHz, well above the
free air resonance of 850Hz.
As noted above, the two woofers
have separate crossover networks.
Woofer W2 can be regarded as the
main woofer as it handles the mid
range frequencies as well. Its associated inductor L2, 0.39mH, provides a
roll-off of 12dB octave above 3kHz by
virtue of the inductor’s impedance and
the driver’s natural roll-off characteristics. R2 and C2 provide impedance
equalisation so that the woofer “looks”
like a resistor as far as the inductor is
concerned.
L1 is a 4mH inductor and rolls off
the second bass driver W1 at 6dB per
octave above 200Hz. In effect, the
second woofer is there to provide a
Fig.2: use this diagram as
a guide if you are building
the cabinets yourself. The
dimensions may be varied
slightly but the capacity should
still be close to 50 litres and the
shelf brace must be included.
808
A
B
253
655
507.5
895
(863)
C
BRACE MOUNTED 9 BELOW
THE BOTTOM OF HOLE B
360
D
227
INTERNAL BRACE
4 HOLES 80 x 80 SPACED 23
APART ABOUT BRACE CENTRE
207
E
MATERIAL: 16 PARTICLE BOARD
CL
HOLE SIZES: A AND E : 76 DIA.
B AND D : 146 DIA.
C : 74 DIA.
DIMENSIONS IN BRACKETS
ARE INTERNAL
* ENCLOSURE BACK INSET
11 FROM REAR EDGE
296 *
(253)
259
(227)
DIMENSIONS IN MILLIMETRES
JV60 SPEAKER ENCLOSURE
August 1995 21
The crossover is mounted on the rear panel of the cabinet, beneath the terminal
panel. Identify all the wires first before installing the crossover.
3dB boost to frequencies below 200Hz.
R1 and C1 again provide impedance
equalisation for the woofer. The only
capacitors not mentioned so far, C6 &
C7, are included to improve the power
factor of the bipolar electrolytic cap
acitors and thereby improve the sound
quality.
Two levels of overdrive protection
are provided by Polyswitches. Poly
switches are special low resistance
thermistors with a positive temperature coefficient. Normally they have
a very low resistance and thus have
minimal effect on the signal fed to the
drivers. But when the signal current
exceeds a critical level, the Poly
switches suddenly switch to a high
resistance state which effectively removes the drive signal. After a period
which depends on the initial overload,
they revert to their low resistance state
and the signal can pass once more.
The important aspect of Poly
switch
es is that they are in
tended
as insurance against damage. The
speakers should not be repeatedly
overdriven otherwise the characteristics of the Polyswitches will alter
and thus their future performance can
be prejudiced.
Two polyswitches are included in
this design, one to protect the whole
system and the other to protect the
tweeter which is the driver most likely
to be damaged if an amplifier is driven
heavily into clipping.
This JV60 system can be used with
amplifiers capable of 20-100 watts.
Assembly
As already noted, the JV60 cabinets
are supplied ready-built so there is
no carpentry required. The first task
is to fit the crossover network inside
the enclosure. As can be seen from
the photos this is hand-wired on a
piece of medium density fibre board.
It should be attached to the rear panel
Take care when fitting the drivers
not to damage the cones. They are
well made but if you are ham-fisted
you could damage them.
22 Silicon Chip
AUDIO PRECISION
50
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ALEX
IMPEDANCE (OHMS) vs FREQUENCY (Hz)
The UV People
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10k
20k
Fig.3: this is the impedance plot for the JV60 loudspeakers.
with a couple of screws, just above the
terminal panel. Before you do mount
the crossover network, you need to
identify all the wires on it so that you
can make the correct connections to
the various drivers.
First, identify the two input wires.
The red wire connected via the large
yellow Polyswitch is the hot (+) input
wire. All black wires go to the negative
terminals of the drivers.
The positive terminal of each
loudspeaker driver is marked with
an adjacent spot of red paint. The red
wire connected via the small yellow
Polyswitch goes to the tweeter and
the blue wire goes to the main woofer
(W2). The remaining red wire goes to
the second woofer (W1).
Having mounted the crossover on
the rear panel, connect and solder the
two input wires to the rear terminal
panel, then screw it into place. Install
the two plastic port tubes and screw
them into place. Connect and solder
the two wires to the tweeter and then
screw it into its central position on
the baffle.
Next, connect the two wires to each
of the two woofers. The main woofer
(W2) mounts at the top of the cabinet
while the second woofer is mounted at
the bottom. Before fixing the woofers
into place on the baffle, you need to
insert the Innerbond wadding into the
enclosure. For two cabinets you will
be supplied with a little over a metre
of 900mm wide Innerbond. Half this
should be placed in each enclosure.
You will need to place about a third
of it in the top section and the other
two thirds in the bottom section. Just
pack it in loosely and then place the
woofers in position on the baffle and
screw them down.
Note that it is important not to
over-tighten the screws otherwise they
will strip their holes. If this happens,
drill pilot holes in a slightly different
position and re-fasten the screws.
Listening tests
When you have finished one loudspeaker system, hook it up to your
amplifier and have a listen. If all
is well, go ahead and assemble the
other loudspeaker. If the sound is not
quite right, make sure that you have
connected all the speakers correctly.
If the phasing is wrong, the speakers
can sound quite strange. If the woofers
are out of phase with each other, the
bass will be practically nonexistent.
Kits for the JV60 loudspeakers are
available from all Jaycar Electronics
stores and their dealers. Prices are as
follows: (1) Speaker kit – includes four
woofers, two tweeters, two crossover
networks, two rear terminal panels,
Innerbond and mounting screws,
$579.00; (2) Cabinet kit – includes a
pair of cabinets finished in blackwood
veneer and two grille cloth frames with
SC
grille cloth fitted, $299.00.
✸ AUSTRALIA’S NO.1 STOCKIST ✸
K
ALEX
40 Wallis Ave, East Ivanhoe 3079.
Phone (03) 9497 3422, Fax (03) 9499 2381
TRANSFORMERS
• TOROIDAL
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• POWER • OUTPUT
• CURRENT • INVERTER
• PLUGPACKS
• CHOKES
STOCK RANGE TOROIDALS
BEST PRICES
APPROVED TO AS 3108-1990
SPECIALS DESIGNED & MADE
15VA to 7.5kVA
Tortech Pty Ltd
24/31 Wentworth St, Greenacre 2190
Phone (02) 642 6003 Fax (02) 642 6127
August 1995 23
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