you decide not to add a subwoofer to satellites but you want to assemble
a full blooded 3-way system you will have to make your choice with
care. There are several x-over units on the market. There are units
made especially for studios and for PA purposes.
Try to find a high quality module for real high fidelity application.
Three-way modules do not have the adjustable phase control for the
subwoofer. In that case you have to find/calculate the best position
of the units in relation to each other as you would do when designing
a 3-way passive system with stepped/recessed baffles. You may even
look for a vintage unit on eBay or Audiogon.
myself use a vintage crossover unit: the LuxKit 2003 from Luxman which
was a present from one of my mentors, Mr. W. de Haan, well-known icon
of the hifi-history of the Netherlands, not only because he imported
for a long time Tandberg and later the Mission and Cyrus products,
and Cabasse loudspeakersystems, but also because he was above all
a first rate technician.
Luxman Crossover (LuxKit 2003) was available in the nineteen seventies.
It has 8 tubes of the type 12AU7 (ECC82). This unit has slopes of
6 and 12 dB.
turnover (crossover) frequencies can be chosen. It suffice to insert
a small circuit board with the appropriate capacitors with the values
indicated in the manual.
are 5 positions to the left and 5 positions to the right of the zero
point (0 = the chosen frequency). Each step to the left represents
a difference of 1/8 of an octave.
example. You choose for the low pass for the woofer or subwoofer (the
section at far left) a cross-over frequency of 200 Hz. This means
that 1 octave is 100 Hz. That means that every step down if 1/8th
of 100 Hz. is 12.5 Hz. At position -1 the frequency is 200 minus 12.5
Hz make 187.5 Hz. at position minus 2 the frequency is 175 Hz. And
the knob to position +1 gives a different frequency. The octave of
200 Hz. is 400 Hz. That octave has to be devided in 8 parts. Only
5 are usable. Each section adds 25 Hz to the frequency chosen for
Initially the Marchand electronic crossovers were designed with 24
dB or even steeper slopes and they use 12AX7 tubes. The steep slopes
are not to everybody's taste. However, now the website says that 6,
12, and 18 dB slopes can also be used by inserting appropriate circuit
the Lux Kit works with circuit boards, but the advantage of the Lux
Kit is that switching from one crossover frequency to another, and
from 6 dB to 12 dB, is possible without changing a circuit board.
This means that the effect of a different crossover frequency can
be heard and measured immediately and helps to determine the best
crossover points for the loudspeaker units and the final values of
capacitors on the circuit boards. It is even possible to overlap crossover
points. This versatility is a great asset and is tempting. However
building this crossover from scratch is no minor task. Only experienced
hobbyists can do that.
configurations are possible. As said the simplest is in fact a 2-way
active system consisting of a subwoofer and two satellite speakers.
Satellites can be full range speakers or 2-way, 3-way and even more
experience and a good ear is necessary to establish an active 3-way
system where all three transducers have to be adjusted: frequency,
power level, and phase.
visitor of my pages wondered if a combination of a 3-way active system
could work together with a separate 2-way active crossover and subwoofer.
That is of course possible. But the success depends on the quality
of the electronic crossover units, and again the knowledge and perception
of the hobbyist. The more adjustments will have to be made, the more
difficult it is to optimize such a system. No active system will be
assembled overnight, not even the simple 2-way configuration, let
alone such a complicated system using two active crossover units.
HARMONICS, CHASSIS, RESONANCES
with all cabinets and chassis, also the Luxman shows some microphony
when tapping on the housing.
The level depends on the way the chassis is built (weight of the material,
strength and sturdiness of the
construction), on how tight the tubes fit in the sockets, and were
the crossover is located.
I have heard tube amplifiers constructed by hobbyists and manufacturers
alike which were too heavy and placed the mechanical resonance (resonant
frequency of the unit) too low and made the sound muddy to such an
extent that they began to sound like bad solid state amplifiers.
schematics of the LuxKit do not prescribe the way the x-over cabinet
should be built. So it is up to the hobbyist to decide what housing
he will build and how he will go about it.
I myself am against too heavy housings for tube amplifiers. I myself
am against the silicone tube rings or whatever rings are often used
to suppress resonances. They not only dampen the resonance, but do
make the sound un-tube-like and less harmonious. But I must emphasize
that these opinions/findings are strictly my personal preferences.
tube amplifiers of today sound neat but are too heavy in the lower
region and specifically in the bottom.
One of the features of good constructions is the airiness of the sound,
specifically provided by tube amplifiers, mosfet amplifiers, and naturally
valve crossovers. It is wise to seek the best construction and weight
of the housing of any amplifier and especially the Luxman Electronic
Crossover filter (Lux Kit).
The total weight of the original Luxman is about 6 kg. which is some
13 pounds. Weighing the parts (transformer, circuit boards, components,
capacitors, potentiometers, etc.) and subtracting this from the 6
kg. can give some indication about the weight to be chosen for the
cabinet of the X-over.
the Luxkit has 8 tubes, and brands and quality of tubes are not the
same, it is important to know what tubes to get and if the quality
is right. Testing tubes is necessary to find out if your Chinese and
Russian tubes deliver what they promise and if old Philips, RCA, Telefunken,
etc. specimen are still working well.
you see the EMC 213 tube tester which I use. It is a simple
to handle, very practical and effective unit to measure the quality
of tubes. And you will be surprised how often newly manufactured tubes
perform badly. Throw the bad tubes away so you will not accidently
use a less performing one. But the quality measurement does not say
all. You will have to experiment to find the best sound by rearranging
the tubes in the crossover. Always of course after listening tests
and evaluating each section of the audio band. Before you rearrange
make sure the tube crossover is switched off and cooled down for several
you should decide on what configuration you are going to make: just
add a subwoofer to existing satellites or design a real multi-way
active loudspeaker system.
us start with the subwoofer. There are many subwoofers on the market.
When surfing on the world wide web you will encounter many different
propositions and plans to build a subwoofer yourself. Read these plans
carefully and find out about efficiency, power handling, frequency
band, linearity and size of the cabinet, and then decide what way
to go. If you are into classical music and into jazz and the refined
reproduction of analog material, I advise not to use any electronic
bass boost. You just should strive to select a bass unit and construct
the appropriate cabinet so that low frequencies will be reproduced
without any artificial compensation. That is only if you have rather
sensitive ears. If so, you may have heard that boosting and correcting
the low frequencies (as in Motional Feedback systems for example applied
by Philips and also by Cabasse years ago) yields to a completely different
(unnatural) low frequency reproduction.
planning to build a subwoofer you should look for 12" or even
15" speaker units that have a low resonance frequency and the
appropriate Qts for functioning in a closed compartment. Try to find
units that do not have a foam suspension which will deteriorate in
time. The unit should have a rubber roll surround which can stand
the test of time. Yes, they are expensive. I was lucky to buy a pair
of second hand 1976 Goodmans 3-way systems which had 12" woofers
in a volume of 53 liters. The suspension of the woofers is rather
stiff, but as I could hear before I bought them, the resonance frequency
seemed relatively low. The units weigh some 10 lb. each. Since the
basket is of steel most of the weight goes into the magnet.
Vas = 199 l
Fs = 31 Hz.
Re = 7.19
Le = 3.93
Qms = 1.83
Qes = 0.36
Spl = 90 dB
Bl = 13
Diameter = 26.4 cm
Sd = 0.550 cm2
Pe = 75 Watt
Z = 8 Ohm
are speaker units which are especially suitable to be used in band
pass enclosures I wanted to see if these Goodmans woofers could do
the job as well. A friend measured both units and came up with interesting
parameters and to my surprise the resonance frequency was 31 Hz. and
the QTS had a nice value of 0.30. I would have welcomed a slightly
higher QTS and a lower Fs though. In order to calculate a bandpass
system I used
Hartikainen's valuable WinISD beta-program which you can download
from the web. It is a rather simple but effective program which also
can calculate closed boxes and vented enclosures.
program makes it possible to determine the desired frequency response
by altering and adjusting the volumes of the front and rear chambers
just by moving the mouse over the drawing. Since a computer program
is infatigable one can go on calculating and by trial and error come
up with many possible solutions. Also by changing the frequency of
the system. The aim is threefold.
First: it is important to change volumes in order to come up with
a low -3dB frequency which is situated around 30 Hz. or possibly lower.
it is important to find an upper -3dB frequency situated around 100
Hz. to go with it.
initially the curve should be linear and at the same time the impulse
should be the best you can get. If the configuration you calculate
shows a bad impulse and a frequency characteristic with the shape
of a saddle, than calculate again and again.
subwoofer designers choose a frequency curve which is linear within
3 dB. This is all right if you have a large listening room. In small
rooms the long wavelengths of low frequencies cannot establish themselves.
So what is the use of reproducing 20 or 30 Hz. when you have to sit
in the kitchen or in the hall in order to hear them properly?
is a second problem. When adding a subwoofer to a satellite system
there is a possible side effect and that is that the sound in the
vicinity of the crossover frequency gets a slender character, especially
in cases a satellite with a relatively small bass-midrange unit is
used. To avoid this one has to doctor around and find the best integration
without changing the strength around the crossover frequency.
Hartikainen's program you can easily alter the system's resonance
frequency and come up with a different port length and characteristic.
This all helps to gradually find out what the best rear and front
volumes are. The final adjustment of the port length should be done
when setting up the system in practice. I calculated a volume of 29
liter for the front and 58 liters for the rear volume. The volumes
were actually 30 and 60 liter because the bracing and the woofer's
baffle take up some of the volume,
decided to position the units on oblique baffles. This would help
minimizing standing waves. It would also position the coils somewhat
farther towards the front of the box for better alignment with the
other units. The Goodmans woofers only have four holes for fixing.
Four clamps were added for rigid fixing of the units. The box is well
braced using metal strips glued and screwed on wooden sticks to minimize
panel resonances. The unit is braced as well by means of a beam supporting
the magnet. The front of the box is detachable so the unit can be
screwed on the baffle and damping material can be adjusted. Each subwoofer
has 2 vents which can be adjusted as well in order to achieve a seamless