|History: 25 Years CD||Ortofon, Garrard, Decca, Tannoy||The Sound of Tubes and Transistors|
|Your Desert Island Discs||Lp Cleaning & DIY Cleaning Formula||Elisabeth Lugt Soprano|
|Turntable & Cartridge Adjustment||Marie-Claire Alain, Organist|
|The Universal Stabilizing Ring||SACD: Upsampling & Noiseshaping||Decca London Ribbon HF Loudspeaker|
|DIY: Turntable Weight/Clamp||The Joy of Well Positioned Speakers|
|URSR: Review in HiFi World||LP Records for Sale||Vintage Equipment|
|URSR: Picture Gallery||The Long Playing Record Guide|
|The TD124 page||The SP10 Page|
|Joachim Bung: Swiss Precision||Stefano Pasini: German Perfection|
|Mengelberg's St. Matthew Passion||Plinth for Technics SP-10 mk2||Record Shops in Amsterdam|
|Paris Jazz||The Sound of The Turntable Mat||Acoustic Revive R77 Generator|
|CLASSIQUE 777 Lp Record Covers||The Treasure Trove||How to Correct WARPED Records|
|Klaas A. Posthuma - Remembered||Ernst Lumpe: Allegro-Royale Pseudonyms||Nostalgia: Violinists on 7" 45 rpm|
|Steinway-Lyngdorf Model D||Infinity KAPPA 7 A Loudspeaker Systems||DIY - Draaitafelconstructie - in Dutch|
|The Turntable Mat - Page in Russian||Ajuste de un giradiscos||NOTES: The Belt Drive Turntable|
|Phono Cartridge-Headshell-Plinth||Porgy and Bess||Active Loudspeaker System|
|Phono Cartridge Optimizing||Gold for Bernard Haitink||Rabco SL-8E Tangential Tonearm|
|Mercury Living Presence Records||HiFi Tunes: DAS KLASSIKERBUCH||DIY:Tonearm Building|
|The Bullet Plug||Violinist/Violist Paul Godwin||The Remington Site|
|Mercury Recordings on Fontana||CINERAMA and Trinaural microphone Placement||Concert Hall - Musical Masterpiece Society|
|Cook-Livingston Binaural Recording System||Willem Mengelberg and his orchestra filmed in Epinay in 1931-||Contemporary Records - Lester Koenig-|
CHOOSE A SUBJECT
Building an active loudspeaker system involves various ingredients and a number of choices:
The availability and choice of a suitable electronic crossover unit
2. The determination of how to divide the frequency band (the number of ways per channel).
3. The choice of the appropriate loudspeaker units in relation to efficiency, frequency response (bandwidth) and linearity.
4. The choice and availability of power amplifiers
Units, cabinets, electronic crossover and amplifiers, all these are interrelated. So we have to deal with many variables which make the road to harmony, excellent transient response and efficiency a difficult one.
1. The main advantage of an active system is that the loudspeaker units are directly connected to the amplifiers without the use of filter sections with capacitors, coils and resistors. Especially the omittance of coils used in passive filters (which are placed in series with the voice coil of the loudspeaker unit), make the units do their job in an optimum manner. Coils in series with the voice coil generally deteriorate the behavior of the unit. That is why designers often use coils with a ferrite core or a specific transformer in order to keep the resistance value of the coil low.
There is another advantage. When filtering with a 12 dB slope, there will be no capacitor in parallel needed which has a high value when choosing a low crossover frequency, let's say between 300 and 600 Hz. And for 18 dB the total of uF will be even higher. Capacitors store energy. That is a bad thing in loudspeaker filters. Omitting capacitors as well does mean that the units are working better.
A disadvantage of building an active system is that units have to be well chosen. Units with relatively linear frequency responses are to be prefered.
The objective is to avoid passive components which are generally used to linearize the frequency responses and the impedance curve.
Remember: most electronic crossovers have slopes of 6, 12, 18 and only in some cases 24 dB per octave. That's it. No 9 dB or 16 dB. The correction of the impedance of the units in an active system is of course possible by inserting a well calculated network in parallel (a capacitor, a resistance and sometimes a coil). The effect of such a correction is that the high end of the curve is less free sounding. That is why it is better to choose a unit which has an impedance curve which comes close to a straight line, far into the high end of the curve.
Whether it is advisable to apply these corrections depends on the configuration and also can be a matter of personal judgment. And of course what you hear.
Best System: Two-Way
The best loudspeaker system is a 2-way system, whether it is a passive or an active system.
In a 2-way
system a wide frequency band is reproduced by a low-mid unit, starting
at the fundamental frequency up to about 3000 or 4000 Hz. (or sometimes
So keep the lower end integer as much as possible. The ear is most sensitive to irregularities in the low and mid frequency band up to at least 2000 Hz.
That is why the best system is a 2-way system. That is also why in olden days the best 3-way systems left lows and mid frequencies in tact and filtered at around 600 (and sometimes at 900, 1500 or even at 2000 Hz.). You could encounter a 3-way system with crossover frequencies of 2000 and 6000 for example. Even 7000 Hz. was chosen if the crossover point between woofer and mid band unit was relatively high. Then specific tweeters could be used like the Decca Super Tweeter and Fostex Ring Radiators. Such high crossover frequencies guarantee a harmonious build up in the low and lower mid sections and keep the midband open and whole.
So your active system could well be a 2-way system with one or two 7, 8, or 10 inch woofer/midrange unit(s) plus a tweeter. The determination of the crossover frequency depends on the capabilities of the chosen tweeter (linearity and power handling) as well as the technical specifications of the low-mid unit and especially the linearity of the frequency curve. In this way you will avoid all the pitfalls which present themselves when constructing a three-way system with three amplifiers and three different units for low, mid and high frequencies.
The choice of units for an active 2-way system can be inspired by existing DIY sets or projects that do not use complicated filters but serial filters or simple sections with 12 or 6 dB slopes or combinations.
an existing DIY design from a shop is chosen as a basis of your active
system, see to it that the volume for the woofer/low-mid range unit
is recalculated as you leave out the passive filter section with the
coil in series. The internal volume should be less.
you want to go active by just adding a subwoofer to a pair of satellite
speakers, you can start by using existing 2-way systems and combine
these with just one subwoofer, home built or manufactured commercially.
This is the most common configuration. There are many options.
The advantage of the band pass system is that it sounds like a closed box system with a continuously decreasing excursion. These systems do need woofers with strong magnets and these are of course expensive. That is why so many designers use the cheaper units in bass reflex systems.
disadvantage of bass reflex (ported) enclosures is that they
have an irregular excursion curve with a dip in the 60 to 80
Hz. region. There the excursion is minimal and in fact not logical.
Back loaded horns do not go deep and if you want to reproduce low frequencies through a horn, the mouth of the horn should be extremely large and the way the sound travels has to be rather long. Even if your listening room in your house permits, these horns can occupy the entire back wall of the listening room.
line systems suffer from the same phase shift as bass reflex systems.
And again the cone excursion is restricted in that area. There the sound
is slender if compared to a big unit in a closed box. In many transmission
lines the lowest frequencies are emphasized and are slow.
There are also designs for open baffles. But the side panels have to be very large (as in the case of the horns). And there are various dipole designs too.
Each and every box, baffle, column or screen has to reproduce sounds which in real life are produced by large instruments (organ, longest and thick strings of the grand piano, big drum, large orchestra), or by instruments with a entirely different shape (violin, cello, flute, etc.), it certainly is no mean task to get a loudspeaker system "right". In this context the question that is often repeated is: Can a large electostatic loudspeaker reproduce a violin sound?
To Boost Or Not To Boost
and audiophiles use 24 dB Linkwitz filters to separate the woofer
completely from the transducers for the mid and high frequencies. It
is up to you if you want to opt for such steep filter slopes. It may
be that when gaining more experience while assembling an active system
you will find out that less steep slopes may result in better phase
and a more harmonic and lively sound.
are free to use electronics that help you correct the frequency curve
of the unit in the subwoofer enclosure, and can boost the lowest frequencies
as some designers do propagate. This is however a method which I personally
do not like at all. Better is to give the unit its appropriate volume
and curve, as the parameters enable you to calculate.
Also Motional Feedback circuits do hamper transient response. The correction generated by the feed back takes the tops of the pulses of the woofer and other reproducers that are corrected this way. And as the lows are the basis on which the harmonics of the entire system are build, naturally the feedback correction can be heard in the rest of the frequency band, can be heard in the total sound picture. The reproduction may sound clean, but has a less realistic character.
An ingenious solution which gives a strong and well controlled bass reproduction is that of The Boffle which was designed by H.A. Hartley. I read the discription of The Boffle in one of the old 1950s issues of The Gramophone. The author of the article promised high quality sound.
Hartley said about it: "I suppose I am an old-fogey purist, but it does seem to me that as a speaker in its enclosure has to make an attempt to reproduce every kind of musical noise, it must have no "personality" of its own. It must be absolutely unbiased; it must add nothing and take nothing away."
And that is exactly what The Boffle can do. Of course the music making depends on what unit you choose.
The Boffle is in fact a cube with an edge of say 50 or 60 cm. My version had a Philips dual cone loudspeaker unit in it. It was a full range unit with a stiff suspension (corrugated surround). There was no separate high frequency unit connected to this speaker. So no extra reproducer for the highs, connected with a capacitor in series. In olden days full range units were often used and were a pleasure to listen to as there was no phase shift (which means no time delay) as was often experienced in 2 or 3-way systems if the design of the filter and the position of the units on the baffle were not correct. Being used as a teen ager to my boffle, I was not pleased when I heard a 2-way or 3-way system even from a renown manufacturer.
Any speaker system which uses a full range driver will give you insight of what coherent sound is. Open baffles are more appropriate for mid range reproduction and for a woofer/subwoofer The Boffle is a very good choice.
The Boffle as seen below was drawn from memory by me. The compartments are separated by sheets or panels of 5 mm felt. The original plan stressed that the holes in the felt should vary the way the drawing shows. The holes directly behind the unit should be large in order not to obstruct the flow of air. Also a too small hole at a is not advised. The second half of the boffle (between a and back panel b) also has variations to work correctly. This how I built The Boffle and never adjusted the holes of one or more of the panels.
Boffle uses felt panels. Felt was not readily available at the time
and had to be ordered. It was also expensive. So in my system I used
sheets of soft board. That was practical because the holes could easily
be cut out and the panels could be replaced if necessary. On top of
that they were easily fixed to the wooden bars. Knowing from years of
experience what damping materials do and how to apply them, I suspect
that soft board which is a "harder", less absorbent material,
gave a very good low mid register, especially the sound of the grand
piano had tangeability.
A high level of quality can be achieved when using commercially manufactured 3-way systems connected to an active crossover filter. The better quality is specifically attained with satellite three-way systems which are equipped with rather large woofers, preferably 12" or 10" woofers in parallel, and placed vertically in the enclosue or mounted in individual enclosures that are stacked and if you have a large listening room you can place them horizontally.
discovered that large woofers for the lower mid section do follow
up the frequency band of the subwoofer in a much better way than
small sized units do. Large woofers provide a far more realistic sound.
of crossover frequency will generally be around 100 Hz. Such a system
can later be updated by adding a second subwoofer.
Another option is to go active with the small satellite 2-way systems and omit the specific subwoofer, but combine 2-way satellites with large woofers as in a full blooded 3 way system. These woofers have to have their appropriate (well calculated) cabinets, one for the left and one for the right channel. The satellite 2-way systems can be home built and optimized in relation to the woofer. The appropriate turnover-frequency should be determined in practice but could be situated in the region from 350 to 600 Hz.. Such a system has the advantage that it leaves at least three octaves of the fundamentals intact.
The most original and most difficult option for assembling/constructing an active loudspeaker system is not to use existing 2- or 3-way satellites with subwoofers, but to calculate and build the cabinets for the low, the mid and the high frequency bands oneself.
the choice is for incorporating a subwoofer or not, the midrange units
must have the ability to perform well up to round and about 3000 or
4000 Hz. As said earlier, a very musical system can consist of a 12"
woofer, one 5" or 7" midrange unit and a quality unit for
the high frequencies. Crossover frequencies could be 600 and 3000 Hz.
in case of a dome-tweeter or horn loaded ribbon tweeter. In the event
a ring radiator like one manufactured by Fostex is chosen, the crossover
frequency for the treble should be 7000 Hz. With such a system a very
harmonious and lifelike reproduction can be achieved especially if you
choose high efficiency units. That is the classic way.
There are many options and many possibilities and also many pitfalls. But you can begin by adding a subwoofer and crossover to an existing system. And that can give you already increased listening pleasure, a lot of fun and it is a learning school for gaining knowledge. After some time you can continue from there and expand your active system. Or not. It is up to you.
It takes a lot of calculation and experimentation to find the best units for a three way system with crossover frequencies of 100 Hz. and, say, 4000 Hz. as the mid band speaker should well be able to reproduce the most important section of 100 to 200 Hz. as well as the higher frequencies.
CHOOSE ANOTHER SUBJECT
already have experience in constructing tube amplifiers, tube pre-amplifiers,
etc. you should have enough knowledge and have had practice to construct
the Luxkit a2003 Crossover Unit.
people who ask for the manual do already have the Luxkt crossover.
They just want to repair it or improve the performance.
with the Luxkit asks for patience and the will to learn and to get
experience in the long run. At the same time while making the construction
and working with it, you will develop your perception of what sound
and reproduction is all about: dynamics, frequency band, about phase
(time coherence), and with it width, depth, and even height of the
sound image. Much is determined by the choice of amplifiers, of loudspeaker
units, of size and shape of cabinets, and by finding the best crossover
points, plus that you will be striving for linearity and good dynamics
and avoid coloration.
The original manual includes the schematic of just one section that you will have to repeat 6 times (3 sections and these for left and right channel to obtain stereo). Included are the real size images of circuit boards for low, mid and high filter sections, and of course the schematic and image of the circuit board for the Power Supply. They are included also as real size black and white images of these boards on a CDROM.
Each filter section has its own print board on which the tubes are located in their individual sockets. There are three tubes (sockets) for the low section, three tubes (sockets) for the mid section and 2 tubes (sockets) for the high section.
In addition there is the circuit board for the power supply with the values for the transformer and the capictors. The transformer should be manufactured. You should look for a specil factury where the transformer can be made to the given parameters.
All boards indicate the positions of the components (and their values) which are to be soldered on the print boards.
there are the small print boards (circuit boards) for the individual
x-over frequencies of your choice. These small boards with capacitors
can be made for practically every frequency. The manual gives the
values for the small film capacitors (if not available you will chose
another quality). Overlapping and combining 6 dB slopes with 12 dB
slopes for the various sections is possible.
CHOOSE ANOTHER SUBJECT
Subwoofer and Electronic X-Over
Subwoofers have existed since the early days of high fidelity. Even before World War II (according to Jean Hiraga in his excellent book 'Les hautparleurs' - Editions Fréquences. Paris, 1980) a man named Olney proposed a loudspeaker specifically designed for the reproduction of the low frequencies. Mr. Olney used a labyrinth (which was later tapered by Dr. Baily and became known as the 'transmission line' loudspeaker).
In the very first issue of High Fidelity Magazine, published in the Summer of 1951 (Vol.I, No. 1), is a description of another low frequency system: the 'air coupler', which is a long slim cabinet with a loudspeaker mounted on the back panel, radiating into it and just above the speaker unit is a wide port.
The cabinet is 6 feet tall (long). The Air-coupler is meant to reproduce the frequencies from 20 Hz. up to around 350 Hz. The cabinet was complemented by a two way speaker or a dual concentric or a loudspeaker unit like a Goodmans Twinax or some similar construction.
Both air-coupler and full range cabinet had their individual low pass, respectively high pass filters. I have scanned the drawing from my (rare) copy of the first issue of High Fidelity magazine (summer 1951) and have put the drawing on another page. Just click on the drawing above. Maybe it could inspire you to build an air coupler and find the best crossover frequency.
In the nineteen fifties Kelton designed a system which was further developed by Hitachi. This idea became the basis for the bandpass subwoofer of today.
Already in 1970 John Marovskis from the Bronx (New York) designed his extraordinary Janis W-1 subwoofer. The story goes that he made some 50 cabinets before he arrived at the excellent sonic performance of his system which has a flat frequency response from 30 to 100 Hz. (-3dB).
an electronic crossover module with a 60 Watt amplifier to go with the
handsomely finished cabinet. He called this elelctronic crossover unit
with amplifier, Janis Interphase with a fixed crossover frequency
of 100 Hz. Both low pass and high pass sections were filtered with 18
designed a smaller Janis W-2 to add to his catalog, and also another
version of the Interphase. The crossover frequency was fixed at 100
Hz. This Janis Interphase, type 3A, filtered the low pass section (Janis
W1 or smaller W2) and the high pass section (satellites) also with slopes
of 18 dB per octave.
most important feature of the Interphase modules was the continuous
variable phase adjustment of the subwoofer (0-180º) in order to
achieve a seamless and harmonious integration of subwoofer and satellites,
independent of the subwoofer's position in the room.
Dutch importer Jan Endenburg told in an interview in 1986 that he had read about the Janis W-1 system in 1970 in an article written by Bert Whyte (published in AUDIO) and when he was in New York he called John Marovskis asking where he could hear the Janis subwoofer. Marovskis asked Jan Endenburg where he was calling from. "I am in New York", Endenburg said. John Marovskis invited him to his home and demonstrated the systems set up with Quad ESL loudspeakers.
That is how Endenburg's firm Engasound became the importer for the Netherlands already in the early 1970s. It was Jan Endenburg who explained to me the importance of phase and he pointed out to me that optimum phase coherence could also be obtained by using a 12dB low pass for the Janis W1 and a 6dB high pass filter for the satellite speaker as was achieved by the than cherished and famous Symmetry Electronic Crossover. But I found that the 18 dB slopes were much cleaner and also the Symmetry did not have this variable phase.
JANIS INTERPHASE + SUBWOOFER
Once in a while you read a rather negative review about the Janis subs. But these are always written by people who do not know how to use the Janis sub woofers. They make the mistake of using high current amplifiers (NAD, Rotel, Bryston, etc.) that get their power out of the large toroidal transformer instead of large capacitors. Toroidal transformers cannot deliver enough current and are soon exhausted because they need to deliver current directly out of the AC mains.
the past I have tried a Tandberg TPA 3003 power amplifier for the satellites.
They did not match at all. The sound of the Janis Woofers became realistically
impressive only when using amplifiers that really go with the nature
of the Janis Interphase. For instance when an Amcron power amplifier
was used to furnish the power to the satellites. The Janis worked also
perfectly well with mono blocks from French manufacturer Elipson which
were actually designed by Setton. Just to mention some historical units.
If you combine the Janis Interphase with the right amplification for
the satellites, the music will get its impact and slam. Not only when
playing Tchaikovsky's 1812, but any record from your collection.
In recording studios in Hilversum (The Netherlands) Janis Subs were used in the nineteen seventies en eighties.
Below the frequency response curve of the Janis W-1 apparently non filtered. (From the literature provided by John Marovskis.)
Another favorite bass system from the past was the Hartley sub woofer which was combined with de Decca Ribbon high frequency unit and the Quad Electrostatic Loudspeakers (ESL). Impressive as well. (See: The Decca London Ribbon Horn Tweeter.)
last 15 years many well known manufacturers of expensive subwoofers
have forgotten about the importance of the continuous variable phase
feature or just do not realize its importance and only adorn their modules
with a phase-switch with the two positions of 0º and 180º.
Most people think that a boom is what it is all about. This British manufacturer certainly has not done his homework. I have witnessed the horrible sound produced by expensive Avalon loudspeakers (and other high-end loudspeaker systems) in various living rooms because the electronics of the expensive subwoofer(s) did not have the continuous variable phase control. Disconnecting the subwoofer brought back the harmonious sound and the slam of the Avalons. Even today, many years after my conversation, these subwoofers still do not have the variable phase control but just a phase switch.
Yet there are electronic crossover modules on the market for filtering the subwoofer and correcting the phase of the signal via the continuous variable control from 0º to 180º. Best known are those of Detonation and Mivoc (search with Google). Thommessen, also from Germany, used to make the Subway Active Crossover. But they have stopped the manufacture.
Dutch readers click here to download the Dutch PDF about John Marowskis Janis Subwoofer.
CHOOSE ANOTHER SUBJECT
Use of the Electronic X-Over
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.
I myself use a vintage crossover unit: the LuxKit a2003 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.
TUBES, HARMONICS, CHASSIS, RESONANCES
WIN ISD BETA
CHOOSE ANOTHER SUBJECT
A Suggestion for A Subwoofer
||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 the resonance frequency is relatively low from what I could hear. The unit weighs some 10 lb. Since the basket is of steel most of the weight is of the magnet.||
A friend measured the parameters and to my surprise the resonance frequency was 30 Hz. The speakers could be used in bandpass subwoofers. For calculation I used Juha Hartikainen's valuable WinISD beta-program which you can download.
|Juha Hartikainen's program makes it possible to determine the desired frequency response by altering and adjusting the volumes of the front and rear chambers. I choose a volume of 29 liter for the front and 58 liters for the rear volume.||
The volumes were actually 30 and 60 liter but because bracings and the woofer's baffle, the volumes were calculated slightly less: 29 and 58 liter respectively.
|I decided to position the units on oblique baffles. This would help in minimizing standing waves. It would also position the coils farther towards the front of the box for better alignment with the other units. The drawing shows the small difference according to the inclination.|
|These Goodmans units have only four holes for fixing. Four clamps were used for added rigidity.||
The box is well braced using metal strips glued on wooden beams to minimize panel resonances. The unit is braced as well.
The front of the box is detachable so the unit can be fixed to the baffle and damping material can be readjusted if necessary.
|The subwoofer has 2 vents and is mounted in an iron frame together with the units for mid and high frequencies.||
Qts = 0.30
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
Amplifiers, Units and Power
PHASE AND FREQUENCY RESPONSE
you use loudspeaker units with an efficiency of 85 to 88 dB and they
can handle enough power, it is advised to use power amplifiers with
a high power capability. That means not just Watts, but how these are
generated and eventually stored is important. Only amplifiers with large
capacitors for storage of lots of energy will do the job.
Amplifiers with large toroidal transformers and just two capacitors with low values do not pump enough power in 85 to 88 dB units. Yes, they generate power. But the power is mainly drawn from the big transformer, i.c. from the net. The effect of these amplifiers (most of which are in the non-clipping category) can not only be measured but can be heard as well. In heavy and loud, complex passages in classical symphonic music the attack of drums, brass and cymbals should be instantaneous and direct. In other words: if the conductor's baton says "now!", it means "now!" for all musicians involved.
When using low efficiency speakers with amplifiers which draw their energy from the transformer, such complex passages do not sound instantaneously but there is a small time delay which in commercial loudspeakers get larger and is really noticeable when complex passive, energy-absorbing filter sections are being used. Many times the sound of the kettle drum which needs more energy comes at a different time than the sound of a cymbal. So it is advised to use these amplifiers with big toroidal transformers in conjunction with relatively high efficiency speakers of 90 to 93 dB.
you use units with an efficiency of 95 dB and higher, you also should
choose your amplifiers with care. Especially high efficiency units make
it possible to use small power transistor amplifiers or valve (tube)
amplifiers which are fast. Power amplifiers with many hundreds of Watts
and large capacitors for energy storage, generally mean overkill for
most important criterion for choosing amplifiers for an active loudspeaker
system is that they should be of the same electronic design. A manufacturer
like Cabasse for instance, who have a long history of designing active
loudspeaker systems, may choose power amplifiers with different output
power for the low-, mid- and high frequencies. But what all these amplifiers
have in common is the same design philosophy. This results in phase
coherence of the amplifier throughout the entire system.
the best option is to choose the same type of amplifier for all loudspeaker
units. Most of the time you
will choose amplifiers from the same manufacturer and even with the
same reference number.
It goes without saying that small listening rooms ask for small speakers with an efficiency around 88 dB and relatively small amplifiers. The sound generated by high efficiency units and big amplifiers does not fit in a small room. In very large rooms big units and amplifiers with a lot of energy are a necessity. In average rooms units with an efficiency of 90 to 93 dB will work wonders. These numbers are just an indication. Experience will tell you what the best system is for a given listening room.
CHOICE OF MODULE
Even if you have selected loudspeaker units with linear frequency curves, it is of the Utmost importance what X-Over unit you chose. If you just add subwoofers to existing loudspeaker systems, than the earlier mentioned Thommessen subwoofer crossover or the Detonation will do the job. But if you go for a 3-way system, than it is important to chose a quality unit which enables you to vary the crossover frequencies and the slopes. There are units with slopes of 6 and 12 dB like the Luxkit a2003 tube cross-over.
There are others which also sport 18 dB and sometimes even 24 dB (Linkwitz) filtering. The advantage of steep 24 dB slopes is that the unit just gets that part of the audio band which it is meant for and causes the least distortion. The sound becomes clean. But in my view too clean. I myself have always found that 24 dB is too steep a slope and makes it more difficult to build a harmonious sound pattern without leaving details out. Slopes of 18 and 12 dB, or 12 and 6 dB are better.
Using 6 dB and/or 12 dB slopes as these are provided by the Luxkit make attaining phase coherence much easier. Using just 24 dB slopes means that you have too choose the units with as much care but an electronic filter with only 24 dB slopes is not versatile at all and soon takes away the hobbyist's enthousiasm. Slopes of 6 dB/oct. mean that the phase is correct (coherent). It is still is necessary to find the correct vertical and horizontal distances between the cabinets and the best acoustic load for the mid range units. The X-over should be well designed and if possible have discrete circuitry or just have not too many operational amplifiers (opamps) and integrated circuits (ICs).
An important ingredient is the available budget. If the budget is low, the best thing is to start with relatively cheap power amplifiers with the same reference number of a given brand. Maybe you will find them in the second hand marketplace. If after some time when you become more experienced and more knowledgeable and your active system reaches a high level of quality, than more expensive power amplifiers may be chosen. Remember that cheap amplifiers will hardly be able to drive a subwoofer in the lowest register due to little capacitance in the power supply. Also I do not advise the use of high current amplifiers (large toroidal transformer and just two low value capacitors). When high dynamic levels are asked for the transients are smeared out and in fact can not be called transients!
Important is also the choice of cables: interconnects and loudspeaker cables. How many times did you read in threads or mailing lists that someone combined cables of different make and bi-wired a loudspeaker system? And how many times that person described how the sound benefited from this? If different cables and/or cables from different brands can be combined and give a correct sound, it is a chance of one in a hundred. In an active loudspeaker system the same type of loudspeaker cable has to be used for all sections. There may be some difference in internal wiring, connecting the binding posts with the unit inside the cabinets, but even then one has to choose wires which are from the same manufacturer. Using Cardas wire - as a suggestion - of different diameter for internal wiring of low, mid and high frequency unit, will lay the basis for smooth transition from one section to another.
The various amplifiers should also be connected with the same type of interconnect. Optimum slopes and crossover frequencies can only can be chosen if there is no influence brought about by different cables.
R.A.Bruil, October 10 2002
LUXKIT a2003 SCHEMATICS
The Luxkit a2003 Electronic Valve Crossover with 8 x 12AU7 (ECC82) is a fine unit and can certainly be built by the amateur with knowledge of electronics and experience in building valve components. The Luxkit a2003 is a 3-way crossover with many possibilities. The low pass and high pass crossover frequencies are variable and can be adjusted in relation to the qualities and behavior of each driver. This means that sections can be adjusted in such a way that they overlap each other or that a gap between two sections can be made in case of an irregular frequency curve of one or more units, combinations of 12 and 6 dB slopes can be made with minimal phase shift.
and Service Manual contains all schematic diagrams and values of
resisters and capacitors.
As an extra
I have edited the images so they can be used for etching the circuit
boards in case you would like to overhaul your unit or build
a unit from scratch. I have also added extra information about the
unit and how to make the prints for the selection of the crossover
frequencies. But you also can etch prints yourself or have them
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