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03-01-2010 Post does not mapped to Knowledge Tree
cv
Derby, United Kingdom
Posts 173
Joined on 09-15-2004

Post #: 81
Post ID: 13050
Reply to: 13042
More on the field coil damping - and an easy way to adjust it
fiogf49gjkf0d
Hello chaps,

Firstly, something I forgot before was that the high impedance coil will have more turns... so the DCR etc will be stepped down as seen by the voice coil. My guess is that overall it will still provide slightly less damping, due to imperfect transformer action and perhaps a lower copper/insulation ratio with the high voltage wire, but don't hold me to that.

Romy - I'm not sure a tapped coil is the way to go; there's only one optimal design and you may not get the flux required without full turns utilisation. But there's an easier way of varying the damping - which I'll get to in a moment.

Bud - high current CCS are a bit more difficult but shouldn't be a problem - a simple single mosfet based one should suffice. Doesn't need to have spectacularly high impedance of 200M across the audio band after all! That said, say we have a CCS (or series inductor), we can make the damping variable by putting a variable resistor across the field coil, with DC blocking capacitor in series. You could even play with the damping at different frequencies (EQ the damping network), which I'm sure only Romy would have the patience to explore and master.

Another way to do it is to undamp the amplifier - have some unbypassed cathode resistance on the output tube to raise the output plate impedance...
This will give you more predictable "undamping" across the bandwidth compared to the less predictable behaviour of a speaker motor masquerading as a transformer...


03-01-2010 Post does not mapped to Knowledge Tree
Romy the Cat


Boston, MA
Posts 9,540
Joined on 05-28-2004

Post #: 82
Post ID: 13054
Reply to: 13050
The field-coil loading vs. plate loading.
fiogf49gjkf0d
Yes, CV, I thought about it myself and I fine that this might be VERY interesting to play with. Unfortunately, or fortunately, I am months away from the position when I will be able to do it. The subject is devilishly interesting however.

I think it would be possible to tap field-coil by tapping off external layers. This would keep the filling of the magnetizing surface even but juts reduce the turn/ampere ration. I will not break my mind on it as I do not know how it needs to be engendered properly. I will ask the people who know how it need to be done and I am sure if it doable then it will be done.

I do feel that in the end the plate loading and sort of speaking the field-coil loading will have different effect. The plate loading give to us harmonics vs. transients balance but I think the field-coil loading will firm just transients character with less influence to harmonics. I however do feel that by acceleration of transients by field-coil we would consider to load the plates harder with all obvious advantages. Of course the validity of this presumption and how it might be used practically will be possible to assess only during the practical experiments.

The caT


"I wish I could score everything for horns." - Richard Wagner. "Our writing equipment takes part in the forming of our thoughts." - Friedrich Nietzsche
07-26-2010 Post does not mapped to Knowledge Tree
audiofilofine
Posts 29
Joined on 02-26-2010

Post #: 83
Post ID: 14113
Reply to: 13054
Another driver
fiogf49gjkf0d

altec 806
DSCI0150.JPG

07-26-2010 Post does not mapped to Knowledge Tree
Romy the Cat


Boston, MA
Posts 9,540
Joined on 05-28-2004

Post #: 84
Post ID: 14115
Reply to: 14113
I do not like those drivers.
fiogf49gjkf0d
audiofilofine,

I do not like when they just remove the magnet and to replace it with electromagnet coil. I do feel that in this configuration the coil is not vented well and either the driver has too much thermal stress or it will run only at very low magnetic force. The last one is not a problem for Altec 806 as it has reduced magnet side compare to Altec 808/802. What I would like those people who do conversions to do is to cut some sluts across the driver back path allowing the coil to breathe in open air. Or preplans to have own custom-made naked cylinder back path, the way how Cogent do.

The caT


"I wish I could score everything for horns." - Richard Wagner. "Our writing equipment takes part in the forming of our thoughts." - Friedrich Nietzsche
07-26-2010 Post does not mapped to Knowledge Tree
audiofilofine
Posts 29
Joined on 02-26-2010

Post #: 85
Post ID: 14117
Reply to: 14115
806
fiogf49gjkf0d


DSCI0197.JPG

I have not made any measurements on these drivers, I've just heard. at 100 volts the sound is similar to the original Alnico magnet, at 130 volts instead of the original seems to be more shrill and personally I find it more pù piacevole.sembra dettagliato.li I tried with horns altec 811 to have a reference with a that are well remembered. The next test will be made on mounting them with trumpets tactrix profile internal law as these  trumpets of the photo. unfortunately the time is little evidence to do ee endless. as the cooling coil do not think is a problem, even after several hours of high-volume sheet and the driver then I do not think the coil may be damaged. The idea is to get as high as possible frequency response (I am using diaphragms of 902) in order to use a system only 2 streets. this work is just fun to make my sound, without any claim to do extraordinary things.
07-04-2011 Post does not mapped to Knowledge Tree
Romy the Cat


Boston, MA
Posts 9,540
Joined on 05-28-2004

Post #: 86
Post ID: 16632
Reply to: 1929
Continuing the debate….
fiogf49gjkf0d

Somebody from AA was asking about electromagnet. The subject pup up here from time to time but this time Bruce Edgar uploaded an interesting comment. Bruce is not a typical AA Moron and if he says “inaccurate things” then it is not due to ignorance but rather because of business interests. Well, he is with his constitutional rights to say whatever he wish but I think  some commentary about his deposition need to be made:

http://www.audioasylum.com/forums/hug/messages/15/156766.html

  Bruce Edgar wrote:
The first experience was that FC drivers out trump many horn problems. In my Subwoofer horn, the bass sometimes was lacking any response below 35, depending whether you had a wood or concrete floor or lacked the proper boundary setup. My living room wood floor was a real problem for me compared to the concrete floor in my sound rooms at my industrial site. But when the 18" FC driver was installed instead of the JBL 2241 ferrite driver that I formally used, the bass low end went all the way to 20-25 Hz instead of wimping out at 35-40Hz with the ferrite driver. The low end of my midrange horns was also improved with FC compression divers.

Ok, let not to be overly excited here. JBL 2241 is a driver with primary resonance of 35Hz.  Bruce’s Subwoofer horn is 1/8 hyperbolic 35Hz horn(it might get lower in a given room by the fact the it loaded to boundary). Loaded to the horn the 2241 probably drops to mid 20Ha and Bruce driver it back to 35Hz with back chamber. I do not argue that implementation of electromagnet might drop the resonance frequency. Warn you that the resonance frequency change NOT because of use electromagnet but become they built the driver differently. I did make the experiment and I can testify that with the same driver (no other modifications) and the identical amount of flux the resonance frequency was slightly HIGHER with electromagnet. To have identical Fs with Alnico and electromagnet I was forces to drive my filled coil with lower current that created lower flux in the gap, lower then permanent magnet did. I think Bruce does disservice to true explaining the drop of Fs by use of different magnet type. If the primary resonance was dropped then it happen because other reasons, not because the contribution of electromagnet. The most important part: the Bruce’s Subwoofer horn is 35Hz horn, how the drop of Fs was able to benefit it if the month high pass 35Hz. Sorry, Bruce, what you are reporting violates whatever you taught us and what I experienced. I do insist that driving over any horn the frequency that is lower then what a horn can pass unavoidably worsen Sound, making it boomy, homogenized and mudding the entire horn articulation. That is why I ALWAYS high-pass any of my horns just below the horn rate, always.

  Bruce Edgar wrote:
The explanation for the differences in low end response characteristics is that horn low end response is limited by horn mouth size, flare frequency, horn flare type (i.e. hyperbolic, exponential, conical or tractrix) and reflections. Given that your design is designed well, reflections are the big restriction. Mouth or floor reflections can come back to the cone and try to push the cone back in spite of the input audio trying to push the cone forward, resulting in VC interactions and cancelations. The FC speaker has better control of the VC in the gap because of the stiff power supply and thus can resist the push back of refected waves.

Sorry, I do not buy the whole reflections idea in THIS case. The Bruce’s Subwoofer horn is floor firing design with very low clearing from the floor. It has of cause huge acoustic reflection back to the driver but this reflection is permanent and this reflection has been factored into the sizing of back chamber. This type of horn does not pick new room reflections and if it does then it happen to a degree that is negligible to mass of diagrams of a bass driver. This is why Bruce’s Subwoofer horn does not need the back chamber tuning in respect to a different room – the clearing between the mouth and floor is permanent and the reflectors are permanent.

  Bruce Edgar wrote:
Steve Schell gave me the genesis of the following explanation. A ferrite or alnico speaker magnet can be thought of a storage battery of magnetic energy. When a battery reaches the limit of its current capacity, it just gives up. In the case of a FC, a stiff DC power supply will look like an infinite capacity storage battery, i.e. a flashlight cell compared to a large marine storage battery. In the case of FC magnets the magnetic field in the gap is always in control of the VC and thus reflections can not cancel out the low end response.

Hmmmm. It is not a secret that Steve Schell loves electromagnets but his love of it shall not blur the reality. There is no “infinite capacity” and there is no “current capacity”. There is no continuing discharge in magnets of loudspeaker driver. The only sagging of magnetizing force is possible due to the flux modulation from voice coil. If voice coil cares a high current transient then it creates a transient magnetic field that sags the flux created by magnet. So, the claim is that electromagnet while creating the same magnetic force is able to buffer the flux modulation better. Possible BUT there are a few problems with it. First: not one ever published data of flux modulation in the SAME driver with perm and electro magnets. It is not hard to do and if I am manufacture who would like people to buy my electromagnet driver then by measuring the flux modulation differences I would objectively closed the subject. Did you wonder why no one did it? By presumption is that because there is no difference. In horns we use compression driver, even the bass drivers we use as they are compression drivers. Compression drivers do not take a lot of current and they are driver very gently. That 18” driver in the Bruce’s Subwoofer horn practically does not move and has in operational mode a few mm of excursion, it take very little current from amp. If Bruce make high excursion bass speakers for stadiums with 1000W power handling and 30Hz response, and particularly ported enclosures then of cause the flux modulations would be a huge subject but I do not think that we are near to that. I am sure there are plenty of Bruce subwoofer horn users who drive then with 2A3 or 300B, come of what king current they drive across that voice coil? Second: are you sure that the polls for electromagnet and perm magnet are the same sixe and the same material? It highly unlikely that they are the same as with electromagnet there is a need to dissipate heat and therefore the core under the field coil is always much larger. So we basically are talking not about the electro vs. perm magnet about about the driver with different magnetic stricture. If you in Alnico driver change the type of Alnico magnet then it changes sound. So, in electromagnet you very much change the magnetic stricture by incorporation a core from different material.

Anyhow,  I can go on and on. I do not insist that flux modulation is not the subject in home use horns BUT if someone repost that change the bass driver from perm to electromagnet did make ”improvement” and if this ”improvement” is not imaginary (which is the case most of the time) then it happened because it was factually different driver, not because it used electromagnet. I am not against better driver or against electromagnets. I am against the methodological dishonesty.

  Bruce Edgar wrote:
You could improve the performance of regular loudspeakers with additional magnets, but manufacturers generally won't do it because magnets cost money and add to material costs. But I have observed exceptions. I have tried the early JBL Neo compression driver (I don't remember the model number) which used a stack of Ne0 slugs in its design. I didn't notice any difference in performance between it and my favorite 2441 driver. Several horn customers wanted to use their new JBL small "hockey puck) Neo compression drivers. I was able compare them to my standard 2441 driver in listening tests. The 2441 was clearly better. Part of the difference may be due to the minimal Neo magnet (which actually measured better than the 2441 in response tests).

Well, if anybody compares Altec 806 and 808 then they have seen how “could improve the performance of regular loudspeakers with additional magnets”.  I do not believe that by adding more magnet performance might be improved. A properly designed driver use as much magnets as necessary and it’s suspension, cone damping and many other parameters are based upon the given amount of magnetic force.

Rgs, Romy the Cat


"I wish I could score everything for horns." - Richard Wagner. "Our writing equipment takes part in the forming of our thoughts." - Friedrich Nietzsche
07-05-2011 Post does not mapped to Knowledge Tree
decoud
United Kingdom
Posts 241
Joined on 03-01-2008

Post #: 87
Post ID: 16635
Reply to: 16632
Signal-driven field modulation
fiogf49gjkf0d

If a magnetic field is static, who cares how it is created? Isn't the main potential advantage of electromagnets one that no one has explored at all - the possibility of modulating the field strength in direct response to the audio signal? So, one extracts some parameter of the signal in parallel - say instantaneous frequency power - and adjusts the field strength on-line. 
07-05-2011 Post does not mapped to Knowledge Tree
Romy the Cat


Boston, MA
Posts 9,540
Joined on 05-28-2004

Post #: 88
Post ID: 16636
Reply to: 16635
The active flux recuperation
fiogf49gjkf0d
 decoud wrote:
If a magnetic field is static, who cares how it is created? Isn't the main potential advantage of electromagnets one that no one has explored at all - the possibility of modulating the field strength in direct response to the audio signal? So, one extracts some parameter of the signal in parallel - say instantaneous frequency power - and adjusts the field strength on-line. 

Yes, I had this idea a few years back: to drive electromagnet with current that is synchronized with signal strength. Then I realized that on compression drivers there is no such a thing as flax modulation as the flux is too strong and the current in VC are too low.  If you have voice coil that care let say 1000W and very loose magnetic field at 1.2T then the magnetic file of such voice coil do stress the gap’s flux. In compression drivers we deal with very low currents. My own MF driver run at 250mV, which makes 0.25W/15R=16mA if I am not mistaken with my math. If I turn a coil and will drive across it 16mA then with my gauss meter n micro-Tesla mode I will not be able to read something but this something will be at the level of background noise. From another side the magnetic force in gap of compression drivers is huge. My driver has 1.7T and some of the drivers have 2.4Tesla. The 2.4T is huge magnetic force. The medical magnetic imaging resonance systems create 3T magnetic field. Do you know the force of that magnetic strength? This magnetic force reportedly wipes out memory from human mind and a technician who work with those machines and who go into the gap to serve MRI machines told me that he writes a note to himself what to do in the gap as when he in then he will not remember why he went there. So, if somebody tell me that a magnetic force of 2T can be in any way upset /demodulated by a current from few dozen milliampere then I would be very suspicions.

Again, somebody who feels that flax demodulation is a factor in compression driver – publish the data of flux transient drop during loud play of the compression driver. It would very indicative and very honest: here is the driver that at given instance out this signal, this is the graph of VC current and this is the graph of gap’s magnetic force. On graph indicating that with perm magnet the flux sagging and another graph indicating that with electromagnet of the same force and the same magnetizing surface the sagging does not take place. That will be no BS explanation but you know why no one did it so far? I presume that it is because it never happened in reality.

The Cat


"I wish I could score everything for horns." - Richard Wagner. "Our writing equipment takes part in the forming of our thoughts." - Friedrich Nietzsche
07-05-2011 Post does not mapped to Knowledge Tree
Paul S
San Diego, California, USA
Posts 2,145
Joined on 10-12-2006

Post #: 89
Post ID: 16637
Reply to: 16635
Bingo
fiogf49gjkf0d
Decoud, this is certainly the evolutionary idea, all right, that I have been turning over in my head for a while now.  However, even to start with, if nothing else, there is with FC the opportunity to "dial in" flux by ear.

I cannot remember when, but I have read contradictory "reports" on various magnet materials and how they behave, both in stasis and with the VC working in the flux.  The latter, of course, is what we are interested in.  One "finding" that stuck was that Ferrite magnets hold stronger (per measured unit), then let go more dramatically, while AlNiCo lets go more quickly but also more "gracefully".  So, Ferrite is SS, and AlNiCo is tubes?  If to take anything from this, perhaps AlNiCo is the way to go if one plans to push the driver?  Some bass guitarists say that, other factors being equal, they get deeper better with Ferrite.

As far as I know there have been no truly rigorous attempts to correlate fluxion and sound, by any measure, in either static or dynamic conditions, except everyone seems to agree that poor flux management = poor sound.  Still, even AlNiCo is not a "given", since there are so many factors at work here.

Best regards,
Paul S
07-05-2011 Post does not mapped to Knowledge Tree
decoud
United Kingdom
Posts 241
Joined on 03-01-2008

Post #: 90
Post ID: 16638
Reply to: 16637
Positive dynamic modulation
fiogf49gjkf0d
Yes, I think we are all agreed that flux demodulation is not the issue here, and that simulating different permanent magnet materials statically may be interesting but is unlikely to be revolutionary. But if FCs have a unique advantage it has to be the ability to change flux on the fly, not so as to counter signal-driven disturbances in the field, but *positively* to modulate the interaction between the magnet and coil in a new way that might be beneficial to sound. At the most basic level, might you not get an improvement in dynamic range if flux changed in relation to the signal power envelope?
07-05-2011 Post does not mapped to Knowledge Tree
Romy the Cat


Boston, MA
Posts 9,540
Joined on 05-28-2004

Post #: 91
Post ID: 16639
Reply to: 16638
I am still on a fence with all of it.
fiogf49gjkf0d
Decoud,

I do reject any speculations about flux modulation in compression drivers as I do presume that it is absolutely negligible. It is like using a SS amp with ultra low output impedance, to drive a ribbon tweeter and to worry about return current from the tweeter. Yes, it will exist but the amplitude of this current will be zillion times lower of any practical level. I do not have knowledge about the amount of flux modulation but my guess that it is also negligible in compression MF driver. To convert my or my opponent gesso into fact it is necessary to put a separate coil into the gap and to measure it in real time. Be advised that it is not as simple as we care to measure only linear flux deviations from different magnets. However, there is very little linearity in the gap as most of the gaps are very close to saturation and at near saturation the change event are very non- linear.  This is the field where speculation of guesses shall not take place and it shall be data. For any resourceful company that sells electromagnets it would be not hard to make measurements, interpret results and to publish data.  If I care I would do it myself but I have no stimulus to do it. Do not format the same people who claim today that electromagnet is “better” because it buffers flux modulation 10 years ago claim that  electromagnet are “better” because they have more magnetic force and allow to manage the Q of driver in fly. Thankfully by the efforts of my criticism and a very few other people who do not buy into hype but stick with actual data and results not one repeat this stupidity anymore. Today they “invented” new concept – buffering flux modulations. I think in context of MF compression driver it is purely imaginary fight with wind mills. I do not say that there is no good electromagnet drivers but they are good or bad has very little to do with type of the magnet they use and has more to do with OTHER factors. Since so far I am the only one known to me public figure who did the methodologically clear experiment with identical driver with both perm and electro magnet and to publish the results I feel that I have reason to express doubts when I see methodologically non-kosher tests or purely BS statements.

The Cat


"I wish I could score everything for horns." - Richard Wagner. "Our writing equipment takes part in the forming of our thoughts." - Friedrich Nietzsche
07-05-2011 Post does not mapped to Knowledge Tree
Paul S
San Diego, California, USA
Posts 2,145
Joined on 10-12-2006

Post #: 92
Post ID: 16640
Reply to: 16639
Cutter Head/Servo
fiogf49gjkf0d

Too lazy to research it and, rather than mentally invent new technology, I keep thinking, "cutter heads", like the old, analog "lathes" that cut the metal masters.  This has to take some real force, perhaps analagous to a speaker coil, and I dimly recall that the cutter is not allowed to "fly off the handle" but it is somehow "controlled", coming and going, and according to signal strength, during the process.  I would not be surprised if someone reading here is prepared to illuminate this matter.  Or, someone who makes the rounds might put it to someone like Steve Hoffman and then get back, post a link, or...

Paul S

Page 5 of 5 (92 items) Select Pages:  « 1 2 3 4 5
   Target    Threads for related reading   Most recent post in related threads   Forum  Replies   Views   Started 
  »  New  Vitavox’s S2 Survival Guide...  A typical convention......  Horn-Loaded Speakers Forum     123  932438  07-16-2004
  »  New  Compression drivers saga..  Wet compression drivers dream....  Horn-Loaded Speakers Forum     2  31418  04-16-2005
  »  New  Gaussmeter wanted...  Re: Gaussmeter wanted....  Audio Discussions  Forum     4  19321  01-16-2006
  »  New  Satisfying result: the RMAF Show + Cogent..  A Subject for your post!...  Horn-Loaded Speakers Forum     22  198582  10-25-2006
  »  New  Vitavox S2 driver made in china..  What does it do right?...  Horn-Loaded Speakers Forum     36  182640  12-20-2006
  »  New  Maxonic drivers from Japan..  Large midwoofers...  Horn-Loaded Speakers Forum     6  61904  06-14-2007
  »  New  About cost of electromagnetic drivers...  About cost of electromagnetic drivers....  Horn-Loaded Speakers Forum     0  16622  07-08-2007
  »  New  Cogent+Electronluv+Acapella=Wretched What?..  The Cogent architectural problem or the Cogent++...  Horn-Loaded Speakers Forum     5  55853  09-04-2007
  »  New  The jump-start of loudspeaker economy..  Yep, you are right: the Grande Utopia...  Audio News Forum     17  116393  03-19-2008
  »  New  Vitavox S2 coupling..  Adaptor thickness etc....  Horn-Loaded Speakers Forum     18  55511  12-20-2008
  »  New  Another electromagnet driver: Great Vintage Loudspeaker..  An excellent question!...  Horn-Loaded Speakers Forum     17  107489  05-08-2009
  »  New  The African compression electromagnet drivers?..  OK. Thanks....  Horn-Loaded Speakers Forum     42  250584  08-17-2009
  »  New  The Evolution of Honk...  Horn-loading and compression had no direct relativity t...  Horn-Loaded Speakers Forum     2  19149  06-06-2010
  »  New  "O Vitavox, Vitavox! Wherefore art thou Vitavox?&q..  Niche...  Horn-Loaded Speakers Forum     22  140030  06-27-2011
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