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.
I 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, but also because he is 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. The turnover (crossover) frequencies can be adjusted
easily by inserting small circuit boards with high quality capacitors.
Even then the turnover frequency can be adjusted in 5 steps of 1/8th
of an octave of that frequency. This means that each step is 1/8
of twice the chosen basic frequency or 1/8 of half that frequency.
In other words: 5 steps of 1/8th of an octave which makes the Luxman
2003 crossover unit extremely versatile and lets you immediately
know what happens if you change the crossover frequency and the
level of one or more sections. No other crossover has these flexible
adjustments for fine tuning in order to produce beautiful harmonics.
See for schematics and details at the end of this page.
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
Lux Kit also 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 immediately and helps to determine the best crossover points
for the loudspeaker units and the final values of capacitors on
the circuit boards.
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 solid state amplifiers.
The schematics of the LuxKit do not prescribe the way the 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.
Many 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 tube amplifiers and 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. At right
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 be accidently use
a less performing one. But the quality measurement does not say
all. You will have to experimently 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 during
you should decide on what configuration you are going to make: just
add a subwoofer to existing satellites or design a real active loudspeaker
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)
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.
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.
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
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
it is important to find an upper -3dB frequency situated around
100 Hz. to go with it.
in all cases the curve should be as linear as possible 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?
There 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. In Hartikainen's program you can alter the system's resonance
frequency and come up with a different port length and characteristic.
This all helps to 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 integration.