Philippe,
Sounds like you are 83-84 years old, great reading your recollections of an exciting period!
Art
to steph- my age and others.
hi Steph,
your calculations are quite wrong. !
if i was 24 years when korn and macway were 68 years,therefore, i just had my birthday of 66 years now.and i look 10 years less.
furthermore, i wrote that i am a musician for hobby, and i am a tremendous rock -blues guitarist, (satriani-steve vai- clapton- garry noore style).and i blow up all the "young " guys who are 35 years.
and when people ask me how i play ?, i have to answer "what do you think? i play guitar since 54 years !"
i do not know where this "force" to play that kind of music comes from (old guys plays jazz) , but ,surely Mr Macway force was an inspiration for me.
This guy was taking his car in brussels, and going to see a client in germany, then was coming back to brussels and continue to Paris to see another client during the same day !! and the morning after, he was in my house at 7 h in the morning to wake me up, because "we had to be at the factory before the workers".
This said, it was a very exiting period.
i can tell you some anecdotes:
for example, i met Steve Jobs when i went to New york to find a distributer, and he proposed me to have the distribution of Apple for the Benelux.
As I had an electronic factory, i could make the service of the computers, and i knew only one programer in belgium. (all that was super new), but Steve jobs was asking one million dollars to give me the representation, and i did not have it.
at these times, Belgium, and Europe, were in deep depression.we had the permit to by 20 liters of gas(essence) per car per week, and 4 shops on 5 at the "galerie louise" were closed because they had no client.
So, to find money at that time was quite dificult.
i met the guy who took Apple representation some years after: he made a fortune!
Another opportunity that i had:
i had a proposal from Yamaha muscial instrument to have - for free- the representation of Yamaha musical instument for Europe.
At these times, japanese where making very bad organs for japanese music only, and i thought that they never would be able to understand the needs of occidentals . What a mistake !!!
and you will have noticed that we sold the factory to an american- (they allways invest-), not to a belgian.
the right place to make a business was california, where any money was available for any project.
nor Bill gates, nor Steve Jobs could have done the same from Belgium at these times
the question is to be the right guy at the right place at the right moment.
i was the right guy at the wrong place at the wrong moment.
The crisis in Europe is one of the reason why I moved to south america, having found there a possibility of business that i thought to have a phenomenal potential .
but, Argentina went soon after in default of payment, (what greece avoided now) and had a terrible financial crisis.
nobody here was believing in my vision of this business, and my nickname was "el belga loco" - "the crazy belgian".
due to the permanent financial crisis, it took me 8 years (and not 6 months, as i thought) to sale the business (once more to an american) , and make only 10 times my investment, 20 years ago.
but today this business has a value of 1.000 times my investment....
So, my vision was correct.
and Argentina is again in default of payement since 14 years.
i have now another business with colosal potential , but nobody finance anything here now.period.
so, i have been always the right guy at the wrong place at the wrong moment.
to have the vision is not enough.
it was as logical to make small hyper quality loudspeakers 40 years ago as it is now, but we were ahead on time.
It is only 20 years later that the all world bought small loudspeakers.
The same happend with my south american business.
that is why i do not move a finger to launch a new product if all the elements are not there:
the right vision of the necessity, the right people, the right time, the right moment, ( to have clients or finance).
I hope that things will change here, and that the moment will come.
i am 2 years younger than Korn and Macway were, when they started the factory with me, so, there is no problem.
best regards,
hi Steph,
your calculations are quite wrong. !
if i was 24 years when korn and macway were 68 years,therefore, i just had my birthday of 66 years now.and i look 10 years less.
furthermore, i wrote that i am a musician for hobby, and i am a tremendous rock -blues guitarist, (satriani-steve vai- clapton- garry noore style).and i blow up all the "young " guys who are 35 years.
and when people ask me how i play ?, i have to answer "what do you think? i play guitar since 54 years !"
i do not know where this "force" to play that kind of music comes from (old guys plays jazz) , but ,surely Mr Macway force was an inspiration for me.
This guy was taking his car in brussels, and going to see a client in germany, then was coming back to brussels and continue to Paris to see another client during the same day !! and the morning after, he was in my house at 7 h in the morning to wake me up, because "we had to be at the factory before the workers".
This said, it was a very exiting period.
i can tell you some anecdotes:
for example, i met Steve Jobs when i went to New york to find a distributer, and he proposed me to have the distribution of Apple for the Benelux.
As I had an electronic factory, i could make the service of the computers, and i knew only one programer in belgium. (all that was super new), but Steve jobs was asking one million dollars to give me the representation, and i did not have it.
at these times, Belgium, and Europe, were in deep depression.we had the permit to by 20 liters of gas(essence) per car per week, and 4 shops on 5 at the "galerie louise" were closed because they had no client.
So, to find money at that time was quite dificult.
i met the guy who took Apple representation some years after: he made a fortune!
Another opportunity that i had:
i had a proposal from Yamaha muscial instrument to have - for free- the representation of Yamaha musical instument for Europe.
At these times, japanese where making very bad organs for japanese music only, and i thought that they never would be able to understand the needs of occidentals . What a mistake !!!
and you will have noticed that we sold the factory to an american- (they allways invest-), not to a belgian.
the right place to make a business was california, where any money was available for any project.
nor Bill gates, nor Steve Jobs could have done the same from Belgium at these times
the question is to be the right guy at the right place at the right moment.
i was the right guy at the wrong place at the wrong moment.
The crisis in Europe is one of the reason why I moved to south america, having found there a possibility of business that i thought to have a phenomenal potential .
but, Argentina went soon after in default of payment, (what greece avoided now) and had a terrible financial crisis.
nobody here was believing in my vision of this business, and my nickname was "el belga loco" - "the crazy belgian".
due to the permanent financial crisis, it took me 8 years (and not 6 months, as i thought) to sale the business (once more to an american) , and make only 10 times my investment, 20 years ago.
but today this business has a value of 1.000 times my investment....
So, my vision was correct.
and Argentina is again in default of payement since 14 years.
i have now another business with colosal potential , but nobody finance anything here now.period.
so, i have been always the right guy at the wrong place at the wrong moment.
to have the vision is not enough.
it was as logical to make small hyper quality loudspeakers 40 years ago as it is now, but we were ahead on time.
It is only 20 years later that the all world bought small loudspeakers.
The same happend with my south american business.
that is why i do not move a finger to launch a new product if all the elements are not there:
the right vision of the necessity, the right people, the right time, the right moment, ( to have clients or finance).
I hope that things will change here, and that the moment will come.
i am 2 years younger than Korn and Macway were, when they started the factory with me, so, there is no problem.
best regards,
At least you moved to a sunnier/warmer climate hi, Zero D.
i will write a last coment , a bit more funny, about what one get get with electronics:
as said, i went o Brasil to make an agreement to manufacture my loudspeakers there.
So, In february, full winter, whit snow and -13 degrees C in brussels, I took a plane to Rio de Janiero with a pair of KM 50 under the arms.
when i came in to the airport, i nearly vanished due to the heath! and this despite the fact that i was 27 years old.
and when i went out of the aiprort, i realized that it was air conditioned.
outside it was around 45 degrees with 95% humidity!. it is like to put your head in a hoven .
of course, it was full summer there !
the owner of the brasilian factory, who spoke fluently french, told me exactly:
"listen, you are the only guy in the world which is Crasy enough to come to Rio de Janeiro the first day of the Carnival".!
So, i came withy the 2 nicest brown girl (mulatas) of Rio de janeiro, and you can have this one, or the other one, or both ! and we go now directly to the beach!
Carnaval in Rio, you can imagine.....
I staid a month in Rio, to "make the agreement", and was phoning to my old polish partners, saying that "the agreement is very hard ", looking at all the girls.
So, you are wright , i sold the factory, not only for money, but for the sun. (and the rest).
but now, maried with children, I live in Buenos aires, argentina, which is not a hot country. We are now in winter, it was freezing cold during a month, and now it rains more than in Belgium.
Life drives you in unexpected ways or places.
My mother language is french, i actually think in Spanish, and write in English.
best regards.
i will write a last coment , a bit more funny, about what one get get with electronics:
as said, i went o Brasil to make an agreement to manufacture my loudspeakers there.
So, In february, full winter, whit snow and -13 degrees C in brussels, I took a plane to Rio de Janiero with a pair of KM 50 under the arms.
when i came in to the airport, i nearly vanished due to the heath! and this despite the fact that i was 27 years old.
and when i went out of the aiprort, i realized that it was air conditioned.
outside it was around 45 degrees with 95% humidity!. it is like to put your head in a hoven .
of course, it was full summer there !
the owner of the brasilian factory, who spoke fluently french, told me exactly:
"listen, you are the only guy in the world which is Crasy enough to come to Rio de Janeiro the first day of the Carnival".!
So, i came withy the 2 nicest brown girl (mulatas) of Rio de janeiro, and you can have this one, or the other one, or both ! and we go now directly to the beach!
Carnaval in Rio, you can imagine.....
I staid a month in Rio, to "make the agreement", and was phoning to my old polish partners, saying that "the agreement is very hard ", looking at all the girls.
So, you are wright , i sold the factory, not only for money, but for the sun. (and the rest).
but now, maried with children, I live in Buenos aires, argentina, which is not a hot country. We are now in winter, it was freezing cold during a month, and now it rains more than in Belgium.
Life drives you in unexpected ways or places.
My mother language is french, i actually think in Spanish, and write in English.
best regards.
Hello Philippe,
Do you confirm in bold, that APSS/APLD had something to do with Korn (electronics, magnetic recording) and Macway (mechanics) ?
Do you confirm in bold, that Korn (and possibly Macway) worked on the APSS/APLD before it got patented by STAAR s.a. before it got licenced to SHARP and some other japanese companies ?
If so, one may imagine that Gustave Staar made a secret deal with Korn (and possibly Macway). The jackpot money never hit Servo-Sound, and never hit Korn & Macway Laboratories. Possibly the jackpot money hit some bank account, located in some distant country, possibly Japan. Consequently, Korn (and possibly Macway) earned part of the APSS/APLD licensing fortune, not taxed in Belgium, thanks to Gustave Staar, and this allowed Korn (and possibly Macway) to terminate Servo-Sound, and prepare the termination of Korn & Macway Laboratories. If the two men combined all this in secret with Gustave Staar, while you were far away in Rio, again you will say "wrong time, wrong place" (joking).
I hear from you, that the Servo-Sound "blackbox" deriving from the Motional Feedback patent is a "fake". I'm assuming that when you say "fake", you actually mean "this is a passive device". Thus, the power supply pin of the "blackbox" connects to nothing. Okay. I remember there was a press article saying the same in a lazy way. But wait a minute. The audio signal must pass though the "blackbox", otherwise there is no feedback, and the whole "servo-sound" conception becomes also a "fake". Thus, my little finger tells me that there could be a small audio transformer inside the "blackbox", acting as difference amplifier, outputting the voltage difference between the "voltage branch" and the "current branch". Can you please comment on this, precisely ?
Now about the "Korn & Macway Laboratories" saga.
1. Could it be that Prof. Korn had to rush, adding a passive radiator, because nobody produced anymore the long-throw elliptical fullrange speaker (double cone) that he relied on all the Servo-Sound speakers (SL15, SL20, etc ..) ? IMO, the disappearance of one component, caused the extinction of a whole generation.
2. Do you have memories, about how Korn and Macway designed their first passive radiators ? Are you aware that some are truly funny ?
p.s.
Are you still in Brussels, at the moment ?
Cheers,
Steph
Hi Philippe,
I guess you are talking about the Servo-Sound SL15 active speaker (available from 1968), comparing it with the Philips RH532 MFB speaker (available from 1973).
The 600% more cost incurred by Philips doesn't come from their MFB system. It comes from the fact that the Philips RH532 MFB speaker was a 3-way system (woofer, medium, tweeter) relying on a generous power supply (three diode bridges in parallel), a 2-way active crossover (woofer/medium), a power amplifier for the bass (full silicon, differential input stage, Darlington power transistors), a power amplifier for the medium and highs (full silicon, Darlington power transistors), and a passive 2-way crossover (medium/tweeter). Possibly this was somewhat overkill, by the time. Philips had to prove something. Philips had to prove that their MFB implementation could fit the high-end league.
The Servo-Sound SL15 and SL20 active speakers were much simpler, 1-way system featuring a long-throw oval speaker having a dual cone, aka the "mechanical tweeter" that you'll read inside the brochure. One power supply, one pre-equalizer, one power amplifier, and you are done ! Minimalism is the name of the game.
The Servo-Sound SL15 and SL20 active speakers relied on heavy electronic equalization, aiming at linearizing the response curve, not only in the bass, but also in the highs.
As consequence, the polar radiation diagram in the highs was far from ideal.
A better contender is the Philips RH541 MFB speaker available from 1976. This is a 2-way system (woofer, tweeter) relying on a power supply and a power amplifier (full silicon, Darlington power transistors).
If you look into an electronics spare parts catalog, you'll read that the same Philips AD8067 woofer was available, with or without the MFB suffix. The one with the MFB suffix had the PXE accelerometer inside. The listed price was not extravagant, compared to the "regular" one. The premium that Philips asked, was something like 40%. The 8-inch AD8067 MFB speaker driver was thus costing slightly more than a regular 10-inch speaker. The 8-inch Philips AD8067 MFB speaker driver was available from established electronics parts shops here in Brussels, like Cotubex. Albeit not extravagant, the price of the Philips AD8067 MFB speaker driver repelled many hobbyists. Apart from the Sept. 1981 article in Wireless World (De Greef), I know no DIY-made MFB speakers, relying on the Philips AD8067 MFB speaker driver.
What's regarding the speaker driver equipping the Servo-Sound SL15 and SL20 active speakers, that's a completely different story. This was a long-throw oval speaker driver, equipped with a special magnetic circuit and a special peripheral suspension, all supported by a beautiful aluminium injected casing. Philippe, do you remember the name of the supplier of such beautiful speaker driver ? IMO, such speaker was not available from established electronics parts shops. IMO, this was not a mass-produced speaker. There was a special treatment applied on the membrane. There was a special treatment applied on the peripheral suspension (IMO, latex compound). Was it done in-house at Servo-Sound or Korn & Macway Laboratories ?I guess that the purchase cost of such speaker driver, was higher that the purchase cost of the Philips AD8067 MFB speaker driver. Luckily for Servo-Sound, the heavy costs of a tweeter and a passive crossover could be avoided, by electronically equalizing the highs - doing so, it only costs a few resistors and capacitors.
So, in a nutshell, the Servo-Sound / Philips competition was not about Motional Feedback. It was about 1-way against 2-way.
One could compare the Servo-sound / Philips MFB systems, by looking at the required speaker drivers and electronic circuits :
- Servo-Sound MFB requires a current-sensing resistor (impossible to implement in case the power amp uses a bridge-tied-load), and a voltage difference amplifier (for computing the difference between the voltage branch signal, and the current branch signal)
- Philips MFB requires a special engineered speaker driver containing an accelerometer glued on the membrane, and two (or more) wires (moving wires), and two (ore more) binding posts on the chassis.
Today, it is difficult to find a long-throw speaker driver that you can use as 1-way speaker, just like Servo-Sound did back in 1968. What would you suggest ? Some Alpine, Blaupunkt, or JBL car audio speaker that comes equipped with a coaxial tweeter ? Any idea welcome ! I would like to hear the equivalent of a Servo-Sound SL15 or SL20 active speaker, equipped with a power amplifier IC (say a LM3886) and a dual audio-opamp (say a NE5532). And possibly, a 1:4 audio transformer for elaborating the Motional Feedback voltage.
Since 1976, Philips had passive speaker enclosures like RH457, AH467, AH487.
Regarding the Korn & Macway Laboratories saga, and the resulting passive radiators speakers like KM30 and KM50, I'm still doubtful about the benefits from a technical point of view, when adding the Servo-Sound MFB to it.
I fear that the need for adding a passive radiator mat have emerged, because of the unavailability of the traditional long-throw oval speaker (see above). Philippe, do you have thoughts or memories, in such context ? Were the two old men worried ? Were there comparative tests done in the lab, between the SL20 (KM22), and the KM30 and KM50 ? Can you describe them ? What other speakers were confronted ? B&W, Celestion, IMF, JBL, KEF, Philips, Wharfedale ?
Cheers,
Steph
"Servo-Sound" got incorporated in 1967, right ?
Obviously, some fundamental guidance was missing in such company, for promoting the "full silicon" conception and for promoting the "2-way" conception. Still in 1973-1974, Servo-Sound was relying on germanium transistors in the audio output stage (power stage), and relying on "1-way" so-called "fullrange" speaker drivers. Albeit famous back in 1967-1968, Servo-Sound credibility fell rapidly. And sales fell accordingly.
Is it true that Rolls-Royce raised a legal complain, pretending that the Servo-Sound SL15 SL20 speakers metal grill graphic design was infringing the Rolls-Royce patented graphic design ? Was it a hoax arranged by Servo-Sound ? If so, why ?
"Korn & Macway Laboratories" got incorporated in 1973, right ?
Same year Philips marketed their RH532 MFB loudspeaker.
Back in 1973, in the middle of the oil crisis (no cars allowed to run on Sundays in Belgium), you were 24 years old, and you've got hired by "Korn & Macway Laboratories".
Was it your first job ?
How did you reach the place ?
Not the first time you had contact with Prof. Korn ? And Macway ?
You've got involved into the development of the KM50, hitting the market as soon as 1974. The KM50 was "Full silicon" and "2-way".
IMO, brutally said, the passive radiator of the KM50 was a marketing gimmick, allowing the KM50 to compete as "3-way MFB Speaker", with the Philips RH532 MFB speaker.
The passive radiator technique delivers advantages, however for attaining the huge efficiency boost below the active speaker resonance frequency, that was claimed by T.S. Korn, you need a passive radiator that's able to move more air than the active radiator (bigger diameter, bigger throw).
Viewing the various KM50 iterations that came on the market, I feel that "Korn & Macway Laboratories" faced problems in such area. Their intention was to implement the passive radiator using raw material like an aluminium disk surrounded by rubber, glued on the speaker cabinet, controlled by a flexible copper arm acting as spring. Hence no frame required. Hence a very low production cost. This was the trick. Actually, they failed. They ended up mounting a passive radiator produced by Audax, 7 inch in diameter. They could have mounted passive radiators produced by Philips, the ones equipping the Philips RH457, AH467, AH487 enclosures. The Philips AD8001 was the 8 inch one. The Philips AD1200 was the 12 inch one. Clearly, "Korn & Macway Laboratories" selected the smallest passive radiator that was available. That's a scoop, isn't ?
IMO, the dreamed "Korn & Macway Laboratories" speaker was a 2-way speaker cabinet exhibiting controlled flexibility, some panels being assembled using rubber joints, those panels playing the role of passive radiators. Unfortunately, back in those times, the panels were too heavy for acting properly. One should try carbon fiber panels, today. Their rigidity/mass ratio may fit.
Cheers,
Steph
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Hello Philippe,
From what I understand, years 1974-1975 acted as big hinge in T.S. Korn life :
- retirement from ULB
- termination of "Servo-Sound"
- incorporation of "Korn & Macway Laboratories"
- development of the KM50 with you
Do you remember the names of some colleagues at "Korn & Macway Laboratories" ? What were the departments ? Who was heading what ? How many people ?
What's regarding the "Korn & Macway Laboratories" R&D lab, can you please tell if :
- most measurements were made at the ULB
- most measurements were made on site, on equipment inherited from "Servo-Sound"
- most measurements were made onsite, on new equipment purchased by "Korn & Macway Laboratories"
- can you please describe the equipment populating the R&D lab (Bruel & Kjaer I guess ...)
- was it relying on FFT analysis, Narrow Band Noise, or Sine Sweep
Upon developing the 2-way KM50 speaker system, was the KM50 crossover designed according to the Linkwitz-Riley rule stating that it is better to ensure a synchronous phase (woofer and tweeter remaining closely in phase in the overlap region), at the expense of distorting the global phase (allpass behavior).
What's regarding the "Korn & Macway Laboratories" product strategy :
- upon designing the KM50, have you tried feeding a regular speaker enclosure (say a Philips RH457, AH467, or AH487) using a "Servo-Sound" amplifier ?
- were you aware of Louis W. Erath (in USA) active speakers ?
- have you considered joining the Louis W. Erath bandwagon, manufacturing a preamplifier equipped with a tailor-made "electronic cartridge" enabling to drive a speaker using a controlled (negative) impedance and equalization, kind of Yamaha AST-A10 amplifier 15 years ahead ?
Who was responsible at "Korn & Macway Laboratories", what's regarding the product strategy ?
Back in the seventies, was it impossible to introduce a "Korn" system and licence to be paid by millions of customers each year, for adapting the power amplifier to the speaker ?
Just like the "Dolby" system and licence, paid by millions of customers each year, for adapting the tape dynamic to the audio message.
Back in the seventies, was it impossible to introduce a "Korn" system and licence to be paid by millions of customers each year, for adapting the progressive loudness correction to the speaker sensitivity and listening room absorption ?
What's regarding DIY audio, why don't we still have access to all this ? Is it because DIY audio people :
- don't master the required technical base ?
- don't want to rely on a measuring mike ?
- don't want to rely on a dual-channel FFT analyzer?
- can't sacrifice a speaker driver (immobilizing the coil in the magnetic gap) for optimizing the MFB transfer function ?
- are not aware that they can keep their beloved power amplifier blocks, albeit replacing their preamp by a "Korn" preamp ?
What would be the cost of developing such preamp, right now ?
Cheers,
Steph
Can you please list some ? You had success ? Fun ? Flops ?
Do you know people having got T.S. Korn as professor in ULB ? Each year, there were students preparing a thesis. Among them, a proportion should be under the supervision of Prof. T.S. Korn. Who are the students having lead to the incorporation of "Servo-Sound" ? What material can we expect to have survived ? Company incorporation documents ? Students thesis ? T.S. Korn teaching notes or labs ? Students notes ?
From what I understand, years 1974-1975 acted as big hinge in T.S. Korn life :
- retirement from ULB
- termination of "Servo-Sound"
- incorporation of "Korn & Macway Laboratories"
- development of the KM50 with you
Do you remember the names of some colleagues at "Korn & Macway Laboratories" ? What were the departments ? Who was heading what ? How many people ?
What's regarding the "Korn & Macway Laboratories" R&D lab, can you please tell if :
- most measurements were made at the ULB
- most measurements were made on site, on equipment inherited from "Servo-Sound"
- most measurements were made onsite, on new equipment purchased by "Korn & Macway Laboratories"
- can you please describe the equipment populating the R&D lab (Bruel & Kjaer I guess ...)
- was it relying on FFT analysis, Narrow Band Noise, or Sine Sweep
Upon developing the 2-way KM50 speaker system, was the KM50 crossover designed according to the Linkwitz-Riley rule stating that it is better to ensure a synchronous phase (woofer and tweeter remaining closely in phase in the overlap region), at the expense of distorting the global phase (allpass behavior).
What's regarding the "Korn & Macway Laboratories" product strategy :
- upon designing the KM50, have you tried feeding a regular speaker enclosure (say a Philips RH457, AH467, or AH487) using a "Servo-Sound" amplifier ?
- were you aware of Louis W. Erath (in USA) active speakers ?
- have you considered joining the Louis W. Erath bandwagon, manufacturing a preamplifier equipped with a tailor-made "electronic cartridge" enabling to drive a speaker using a controlled (negative) impedance and equalization, kind of Yamaha AST-A10 amplifier 15 years ahead ?
Who was responsible at "Korn & Macway Laboratories", what's regarding the product strategy ?
Back in the seventies, was it impossible to introduce a "Korn" system and licence to be paid by millions of customers each year, for adapting the power amplifier to the speaker ?
Just like the "Dolby" system and licence, paid by millions of customers each year, for adapting the tape dynamic to the audio message.
Back in the seventies, was it impossible to introduce a "Korn" system and licence to be paid by millions of customers each year, for adapting the progressive loudness correction to the speaker sensitivity and listening room absorption ?
What's regarding DIY audio, why don't we still have access to all this ? Is it because DIY audio people :
- don't master the required technical base ?
- don't want to rely on a measuring mike ?
- don't want to rely on a dual-channel FFT analyzer?
- can't sacrifice a speaker driver (immobilizing the coil in the magnetic gap) for optimizing the MFB transfer function ?
- are not aware that they can keep their beloved power amplifier blocks, albeit replacing their preamp by a "Korn" preamp ?
What would be the cost of developing such preamp, right now ?
Cheers,
Steph
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A series resistor in all cases. Followed by circuitry computing the instantaneous cone velocity. You need more than the instantaneous coil current for doing this. You also need the instantaneous coil voltage. Hence the need for a difference amplifier. A bridge may do this. In our case, there is no such bridge. Try a 1:4 audio transformer as difference amplifier. Transformer primary terminal A connecting to the shunt resistor (this is a low-impedance voltage acting as instantaneous current image). Transformer primary terminal B connecting to the output of a 300 ohm voltage divider fed by the coil voltage. Applying the right voltage division factor here and applying some RC filtering (compensating the coil inductance) are the key factors. One should add a buffer on such terminal for lowering the impedance before feeding the transformer. Not required in practice. The voltage A - B applied to the transformer primary roughly equates the required difference. Grab the voltage showing at the transformer secondary, that you reference to the signal ground. Such difference voltage, you need to blend it carefully with the audio input, before the power amp. Please note, such difference voltage represents speed instead of acceleration (acoustic pressure). For transforming speed into acceleration you need to blend using a capacitor instead of a resistor. It's that simple. On top of this, you better not try blending the highs, because MFB doesn't work reliably past 2 kHz (uncertainty in the coil inductance modelization). You will thus add a resistance in series with the blending capacitor. In case you don't modify the local feedback network of your power amplifier (need to boost the deep bass gain by 12 dB or so), you need an inverting opamp as blender, whose feedback network is providing the required 12 dB gain in the deep bass. As I said previously, the only way to setup all this correctly is to verify that the MFB signal (transformer secondary voltage) stays close to nihil when you apply a 5 V rms pink noise voltage on the voice coil, while maintaining the coil immobile. Guess how to do this ? You need to sacrifice a speaker driver, gluing the coil inside the magnetic gap. Are you ready to pay for this, knowing that the driver that you will mount after the sacrificial setup, may not be the exact same ? Haha ! Ask yourself this, before spending time (and money).
Try embedding a pink noise generator, a 2-channel FFT analyzer, a few variable computer-driven R and C for continuously tuning the system, while it is playing, while it is heating, while it is wearing. The algorithm and convergence are tricky as you can't rely on coil immobility. It is great fun to simulate all this using LTspice, Flowstone or LabVIEW.
From an industrial viewpoint, such advance only makes sense if in return, your digital monitoring system helps keeping the speaker within its physical limits, without distorting and without overheating. Consequently, it is mandatory to apply a variable highpass filter on the audio input for maintaining the speaker within its physical limits, whatever the content, whatever the volume. That's fundamental from an industrial viewpoint.
Let's do the math what's regarding industry. Say the added hardware complexity is costing 3 dollars. Industry may consider such advance, in case speakers costing only 5 dollars, appear to deliver significantly better results than speakers costing 10 dollars.
The equation may not be the same for DIY audio.
p.s.
You may have noticed, the "Korn" feedback is same as Louis W. Erath "Electronic Suspension". Both can be seen as derivatives of the Voigt bridge.
Regards,
Steph
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Hi Philippe,
I have an Audio Linear Turntable TD 4001 with the KM Logo on the base.
Serial # 15044947. I purchased it in the year 1981 in Canada from Pro Acoustics Inc.
Yesterday the Dust cover got broken. This equipment is one of my most treasured for its design, elegance, performance and the good memories.
I would appreciate help in sourcing a new dust cover replacement, regardless of cost.
Thank you,
Tej.
I have an Audio Linear Turntable TD 4001 with the KM Logo on the base.
Serial # 15044947. I purchased it in the year 1981 in Canada from Pro Acoustics Inc.
Yesterday the Dust cover got broken. This equipment is one of my most treasured for its design, elegance, performance and the good memories.
I would appreciate help in sourcing a new dust cover replacement, regardless of cost.
Thank you,
Tej.
I bought K&M at one point
Working with another American who later purportedly closed the deal to purchase K&M, I was the first person to recognize a way to purchase the company and keep it alive. I met with Mssrs Korn and McWay at the factory in Waterloo in the late 70s, and it was clear they wanted someone to take over the business.
I do recall a preamplifier, which had some of Korn's ideas about canceling out-of-phase information that he felt was inherent in multi-mike recording. The results were weird and stunning — a kind of unprocessing of multi-miking.
K&M also had some nifty patents for cathedral sound reinforcement speakers which used a bucket brigade to create a virtual 'look-down' image for the speakers, so they could be tight against a column but act acoustically as if they were tilted out over a cathedral floor.
Working with another American who later purportedly closed the deal to purchase K&M, I was the first person to recognize a way to purchase the company and keep it alive. I met with Mssrs Korn and McWay at the factory in Waterloo in the late 70s, and it was clear they wanted someone to take over the business.
I do recall a preamplifier, which had some of Korn's ideas about canceling out-of-phase information that he felt was inherent in multi-mike recording. The results were weird and stunning — a kind of unprocessing of multi-miking.
K&M also had some nifty patents for cathedral sound reinforcement speakers which used a bucket brigade to create a virtual 'look-down' image for the speakers, so they could be tight against a column but act acoustically as if they were tilted out over a cathedral floor.
KM A.I.R. system
I just posted over at Audiokarma to try and get some help on how I can use this Korn and Macway component I have. I have no clue what to do with this thing! Is anyone here familiar with the K&M A.I.R. system?
This is the only info I could find on the web:
From http://www.soundfountain.com/lyngdorf/steinwaylyngdorf.html:
Belgian professor T.S. Korn of Servo Sound devised a system of preamplifier and small loudspeaker boxes with integrated amplifier. The boxes were servo controlled. His name is also connected to the firm Korn & Macway when he went a step further by introducing A.I.R. which means Acoustic Inter-modulation Reduction. His electronics were analog of course and no RoomPerfect calibration existed. Similar applications of corrections in loudspeakers were incorporated in the Motional Feedback (MFB) systems of Philips in the 1970s, and later also adopted by Cabasse in the Galion and Albatros designs. The Cabasse active loudspeakers had a very high efficiency and could easily attain a sound level of 120 dB. Whatever the make, these speakers behaved extremely well but they were somewhat robbed of their spontaneity, depending of course how severely the feedback signal was calibrated. Large excursions were restrained and measurements showed that the sinus was topped off, so to speak.
I just posted over at Audiokarma to try and get some help on how I can use this Korn and Macway component I have. I have no clue what to do with this thing! Is anyone here familiar with the K&M A.I.R. system?
This is the only info I could find on the web:
From http://www.soundfountain.com/lyngdorf/steinwaylyngdorf.html:
Belgian professor T.S. Korn of Servo Sound devised a system of preamplifier and small loudspeaker boxes with integrated amplifier. The boxes were servo controlled. His name is also connected to the firm Korn & Macway when he went a step further by introducing A.I.R. which means Acoustic Inter-modulation Reduction. His electronics were analog of course and no RoomPerfect calibration existed. Similar applications of corrections in loudspeakers were incorporated in the Motional Feedback (MFB) systems of Philips in the 1970s, and later also adopted by Cabasse in the Galion and Albatros designs. The Cabasse active loudspeakers had a very high efficiency and could easily attain a sound level of 120 dB. Whatever the make, these speakers behaved extremely well but they were somewhat robbed of their spontaneity, depending of course how severely the feedback signal was calibrated. Large excursions were restrained and measurements showed that the sinus was topped off, so to speak.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
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