Review: Magnet LS-621
2-way loudspeakers
The magnet LS-621 loudspeakers are a
compact bass reflex system which will
fit well into most lounge rooms.
Magnet will be a loudspeaker brand
name new to most Australians. It is
a company based in Thailand which
makes loudspeakers designed by engineers from Holland. The European
link is claimed to give the speakers a
natural sound which otherwise might
not be there if they had been designed
in the East.
The LS-621 system we reviewed
is a compact 2-way system based
on a 165mm polypropylene woofer
and a 25mm tweeter. The bass reflex
enclosure is wedge-shaped, tapering
from the bottom to the top to angle the
front baffle in such a way as to give
some time-correction to the tweeter.
That and the small frontal dimensions
of the speaker combine to make it
quite unobtrusive in appearance. Its
dimensions are as follows: 435mm
high, 206mm wide, 312mm deep at
the base and 275mm deep at the top,
with the grille cloth frame. Actually,
the cabinet is also slightly tapered at
the front which makes it look slightly
smaller than its measurements suggest.
Internal volume is 15 litres.
The enclosure is ported with a
tube of 55mm internal diameter and
surprisingly long at 220mm. That is
probably part of the reason why the
enclosure is tapered, to allow a long
port without making the box too deep
overall. The cabinets are finished in
simulated walnut veneer with a black
grille cloth.
We removed the woofer to have
a look at the internal details of the
enclosure and found that, surprise,
surprise, the woofer is not of Asian
origin at all but made by Peerless of
Denmark, although we don’t know the
model number. It is a well-made unit
with a large magnet and a neoprene
rubber roll surround for the polyprop
ylene cone.
And having revealed that the woofer
is of European origin, the ferrofluid-cooled 25mm soft dome tweeter is
too, made by Philips of Belgium. The
two drivers are coupled together via
quite a complex crossover network and
this has an air-cored inductor wound
with heavy gauge enamelled copper
wire and uses wirewound resistors and
a mixture of plastic and non-polarised
electrolytic capacitors. The system is
bi-wired so you can drive the tweeter
and woofer with separate amplifiers,
if you wish.
The enclosure
The enclosure is lined with bonded acetate fibre or a similar material
and interestingly, there is an internal
sloped shelf which undoubtedly adds
to cabinet rigidity but we don’t know
if it serves any other purpose. The four
terminal posts are deeply recessed in a
panel at the rear of the enclosure. This
makes it quite difficult to make wire
connections to the terminals unless
you have the wires fitted with jacks.
The terminal panels are so deeply
recessed that the terminal posts do
not protrude at all and this means you
could set the cabinets right up flush to
a wall, if desired.
Frequency response of the enclosure
is quoted as being from 40Hz to 22kHz
within 1dB and -6dB. We do not have
access to an anechoic chamber so we
continued on page 93
28 Silicon Chip
Several other computation functions are provided, such as mean value
of phase or line voltage and mean value
of phase current. An integration option
is available, allowing measurement of
amp-hours or watt-hours to an accuracy of ±0.2% + 1 digit up to a period
of 999 hours. A further option allows
frequency measurement over the range
of 20Hz to 200kHz with an accuracy
of ±0.1 % + 1 digit.
GPIB and RS232C options are
provided, allowing the 2533E to be
remotely controlled and output data
to be transferred to a PC.
For further information, contact
Tony Richardson, Yokogawa Australia
Pty Ltd, Centrecourt D3, 25-27 Paul St
North, North Ryde, NSW 2113. Phone
(02) 805 0699.
Economy soldering
irons from Scope
Two new low cost 25W and 40W
utility irons for electronic work have
been released by Scope Laboratories.
These mains voltage irons feature
long-life iron-plated tips that operate
at around 380°C, a stainless steel
barrel, a non-rolling impact-resistant
handle and four tip shapes.
For further information, contact
Scope Laboratories by phone on (03)
338 1566.
LS621 Loudspeakers – continued from page 28
are unable to verify this claim although
the response is quite smooth overall.
At the bass end there is usable response down to below 45Hz although
if pushed hard, the woofer does tend
to frequency double. At the high end,
the tweeter is a little prominent in the
region of 7- 8kHz and then tapers off a
little above that although it is smooth
right to the limits of audibility.
Efficiency is quoted as 87.5dB at
one watt and one metre and the unit
is claimed to be suitable for amplifiers
rated from 15 watts to 150 watts. Our
impressions were that you would need
an amplifier of at least 40 to 50 watts
and that anything much over 100 watts
on program would be too much. That
is backed up by the stated maximum
SPL (sound pressure level) of 106dB.
On music, the Magnet LS-621s give
a good account of themselves although
the tweeter seems a little muted for our
tastes. We found that they sound rather better with the grille cloth frames
off and we think most people would
listen to them in this way. On voice,
they sound very natural without any
tendency to chestiness or emphasis
of sibilants.
Our overall impression was that
they were very satisfying on classical
music, especially chamber works, and
they give a good account of themselves
on jazz material. If you are a heavy rock
fan, you will want bigger guns and it
would not be fair to expect them to
do the job.
Recommended retail price of the
Magnet LS-621s is $1150 a pair and
they are available from A-One Electronics, 432-434 Kent St, Sydney,
NSW 2000. They have recently fitted
out a sound lounge and to introduce
the Magnets they have them on sale at
$950 a pair, so get in quickly. Phone
A-One Electronics on (02) 267 4819.
(L.D.S.)
SC
FM Wireless Microphone – continued from page 67
it and set the operating frequency. For
this you need an FM radio. Connect
the 9V battery and turn on your FM
radio. Now tune across the band until
the speaker squeals.
The frequency on your dial is now
the operating frequency of the circuit.
Now if you want to adjust the frequency of operation, you reverse the process. Tune your radio to a vacant part
of the band. Let’s say this frequency
is 99MHz.
All you should be getting is hiss
from the loudspeaker of the radio. Now
adjust the slug of coil L1 until you get
a continuous squeal from the radio.
That’s it, the job is complete.
In more detail, the tuning range of
the wireless microphone can be adjusted upwards by removing the 1pF
capacitor. With this capacitor in circuit, the tuning range of L1 will be in
the lower region of the FM band: from
This close-up view shows how the on/
off switch is fitted to the end-plate at
one end of the tube.
below 88MHz to about 102MHz. With
the 1pF capacitor in circuit, the tuning
range will be from about 95MHz. You
have to decide which portion of the
band you want your circuit to operate
in and then pull the capacitor out or
leave it in. You then adjust the slug of
L1 as described above.
After you have adjusted coil L1 to
your satisfaction, move the microphone well away from the radio so
that the acoustic feedback squeal and
distortion is no longer apparent. You
should now be able to speak into the
microphone and your voice should
come from the radio with clean reproduction.
You can now complete the construction of your microphone by wiring up
the on-off switch and then installing
the board and battery inside the anodised aluminium tube. They are held
in place by pieces of foam plastic.
The PC board is positioned so that the
electret protrudes slightly from the
end of the tube, after which the foam
plastic windshield is fitted. The slide
switch is attached to an endplate with
epoxy adhesive and then the end plate
itself is glued into the tube with the
same epoxy.
SC
October 1993 93
