Nick, I'm using TAD 11" alnico magnet woofers in my current speakers.
Those woofers are now unobtainium. I was told today that a pair sold for $1500 on ebay recently; they're going up faster than gasoline. When my stash is gone, if I don't have a replacement I'll be up the proverbial creek sans paddle, at least as far as that product line goes. I know of one other manufacturer who's in pretty much the same boat, up the same creek.
So while there may not be a huge market for specialty woofers such as alnico or field coil Lambdas, if it's economical for A&E on a small scale that would be of major interest to some of us little speaker manufacturers alongside the DIY community.
Duke
Those woofers are now unobtainium. I was told today that a pair sold for $1500 on ebay recently; they're going up faster than gasoline. When my stash is gone, if I don't have a replacement I'll be up the proverbial creek sans paddle, at least as far as that product line goes. I know of one other manufacturer who's in pretty much the same boat, up the same creek.
So while there may not be a huge market for specialty woofers such as alnico or field coil Lambdas, if it's economical for A&E on a small scale that would be of major interest to some of us little speaker manufacturers alongside the DIY community.
Duke
Re: Re: Yowza
Well not PM'ed.. but,
-somewhere back in this thread there is 18 Sound's article on this, but its also here as a pdf link (from a pop-up link to the left of the page under "AIC paper"):
http://www.eighteensound.com/
Starting with page 3 last paragraph..
18 Sound places 2 positive and negative terminals for versatility, but when its "doing its thing" is with the coils in *parallel* - so you could just tie the coils together and provide only one pair of terminals.
Again, what I find attractive is not its distortion reduction but rather the significant reduction in resonance induced back emf that "fights" with the amplifier, something that shorting/thermal-exchange rings do not significantly address.
Anyway, its just an idea that I believe warrants at least *some* additional thought in the pantheon of driver improvements.
(..btw, I wouldn't be at all surprised if the Dayton Reference drivers utilized this technique, sans quad terminals.)
nickmckinney said:
Well not PM'ed.. but,
-somewhere back in this thread there is 18 Sound's article on this, but its also here as a pdf link (from a pop-up link to the left of the page under "AIC paper"):
http://www.eighteensound.com/
Starting with page 3 last paragraph..
18 Sound places 2 positive and negative terminals for versatility, but when its "doing its thing" is with the coils in *parallel* - so you could just tie the coils together and provide only one pair of terminals.
Again, what I find attractive is not its distortion reduction but rather the significant reduction in resonance induced back emf that "fights" with the amplifier, something that shorting/thermal-exchange rings do not significantly address.
Anyway, its just an idea that I believe warrants at least *some* additional thought in the pantheon of driver improvements.
(..btw, I wouldn't be at all surprised if the Dayton Reference drivers utilized this technique, sans quad terminals.)
audiokinesis said:
Duke is being modest here - I think that's his style. But it's not mine.
The HF of the AudioKinesis was excellent, but the bass and midbass was outright beautiful, right up there with exotica like the Feastrex - actually, I preferred it to the Feastrex, which was right down the hall from Duke's room. I had to ask which woofer was doing all this magic - and was very dismayed to find it was a TAD Alnico woofer that was going out of production.
I'm not convinced there's much subjective difference between Alnico and field-coil speakers - both share a tonal delicacy that is much more rare in ceramic-magnet speakers. Whenever I have a "what was that" reaction, on further research, it seems that most of the time the magnet is Alnico or a field-coil.
I can't easily describe this quality except to say it is more beautiful-sounding - and the kind of thing that is noticeable before you walk into the room. Not the sort of stupid audiophile thing where you scrunch up your face and listen as hard as you can for a little bitty difference - not like that at all. Instead, you are much more aware of the emotional qualities of the performance, and pay less attention to the "hifi" aspect of the sound. More music, more beauty.
In terms of Alnico vs field coil, I think a lot of people will be tempted with a field-coil speaker to turn up the power so high that the gap begins to saturate, which is plenty expensive to do with an Alnico magnet (although Lowthers have done this for years). So if Lambda travels down the field-coil route, I'd make sure there is plenty of power-handling reserve in the field coil, since the urge to tinker with the power setting will be irresistible for most users.
I'd also like to strongly discourage the idea of making a high-voltage field coil. True, in the old days the field coil was used as the primary (and only) choke for the B+ power supply, but that was done purely as a cost-saving measure - it's the reason that old Thirties-era radios had a noticeable hum as they warmed up, and always had some background hum, thanks to the sharing of the field coil and the filtering of the B+ supply. A genuine high-fidelity radio of that era had separate power-supply chokes and field coils, and the resistance value of the field coil could be optimized for the loudspeaker.
The biggest problem with the high-voltage field coil is the difficulty of transporting high voltages across interconnects in a safe way. I did this in the Karna amplifier, and the aviation-grade Amphenol connectors were not cheap, and certainly not attractive. The B+ cabling is exotic transmitter-grade coaxial cable, rated for 4X the intended voltage, and is neither cheap nor user friendly (any failure results in a serious safety hazard). Transporting B+ voltages any distance at all is expensive and gets into serious safety issues very quickly - if something as simple as trampling on a cable results in a safety hazard, why do it at all?
By contrast, 12 volts DC is no big deal, and is readily available from off-the-shelf SLA battery packs, computer power supplies, and fancy dedicated audiophile-quality supplies. One difference between now and the "old days" of field coil speakers is that we now have inexpensive low-voltage DC rectification - this simply didn't exist in the Thirties, when the only way to rectify low-voltage DC were expensive, extremely inefficient, and very hot "Tungar" rectifiers. That's why consumer-level products used either AC heating for filaments and rectifiers, batteries, or even occasionally motor-generators for mobile applications.
LineSource said:
Here's another vote for smth like this
That above, with high power handling and decent xmax -- just count me in. Just let the (hard] choice be btw Alnico, Neodymium magnet with counter-wound coil (ala 18Sound "active impedance" -- even more "bragging rights" for low inductance - and proven to work) or 12V field coils....
That kind of driver seems to have great potential of a scaled down version of what Lynn is currently doing (for those of us w/o "concert hall" sized room in the basement):
That 10'' XOed at 1500 cycles to a CD+WG (EQed to taste) and an indep powered bass unit below (e.g. Brian -- from rythmik fame -- Direct Servo tech and the matching 12''ers from GR research look really great).
As of today best candidates seem to be 10NDA520 with BMS4540ND in a DDS ENG 1-90 WG (or the more costly WG that magnetar found).
hear, hear. Not so sure about how noisy they are though...
LineSource said:
Although not Alnico or neo, the TD10M can easily cover this range already. A little over 94dB 1W and quite flat up to over 2KHz. I use a pair of them in this monitor from 50Hz up to just under 2KHz where they are mated to the fountek NeoPro5i:
This was the initial design and the ports caused a lot of diffraction issues with the tweeter. The final design has ports above and below the woofers. A little taller and slightly less deep. With 6mm Xmax It can manage continuous levels upwards of 120dB 1m everywhere above 50hz and distortion is extremely low at average listening levels.
We do definitely have plans to add Alnico motors to the mix in the future. It will be interesting to see the difference once we can do this. As Nick had mentioned way back, the TD woofers with the full copper sleeve behave much like an alnico motor. The difference being the shorting ring keeps the flux from moving with the ceramic magnets as the coil moves and the Alnico itself is more "resistive" to the flux moving to begin with.
John
John_E_Janowitz said:
John, not to diminish the merit of your drivers in any way (haven't had the pleasure to hear any) but judging from the T/S params for the TD10M (posted earlier in this very thread) it seems very similar to the aforementioned 10NDA520 -- with the notable exception of Xmax (but at the expense of 30% more Mms).
OTOH the 10NDA520 has that AIC with its 10 fold decrease in inductance...
I've read (with interest) your current experiments with IB15 "lite" (aka OB15) and an (upcoming ?) OB version of the TD12M.
Something similar for the TD10M should be very interesting to several -- higher Qts (according to the posted specs the TD10M should start rolling off at around 200Hz -- the F3 on IB is 166Hz) plus some goodies to make it more apealing than the 10NDA520 (field coil ? Alnico ? second coil i.e. AIC-like low inductance ?).
That -- and, like josh, I'll put my wallet where my mouth is.
CLS said:
The original speaker/music boxes back in the day did just that as it was the most economical design. The field coil did double duty as both a B+ choke and a speaker magnetizer. However I wonder how many people really want high voltage lines running to their speakers and/or mounting a high voltage power supply into the cabinet. I myself don't but its not really that much extra for us to make 2 coil options.
Re: Re: Re: Re: Re: Yowza
Yeah with everything being modular designed its not an issue. I talked with John quite a bit today about the Alnico design, we are waiting for available Alnico sizes to be sent back to us so I can start the napkin drawings.
Both the Alnico and field coils have magnetic field that are not sensitive to the magnet field the voice coil generates. As John stated incorporating Faraday rings helps to keep the magnet field stable. The closer to the gap the better (which is why I stick a thick tube of copper in the gap)
I am sure people will have all sorts of fun figuring out the best amp output for the field coil. Lower amps will give higher Qts and vice versa. The coils will be able to handle pretty much whatever you throw at them. There will be a "knee" in the magnetization curve where adding more current does little to nothing.
Yeah I am in this boat myself as I have 3 rooms that need small cabinet sound. The napkin drawings have started on both the wide band 8" and a small Alnico "small horn" tweeter.
Oops - just sent it.
Yeah that was another thought of mine, being able to use batteries for testing at least.
Give it a few months, it will happen. Designing the motor is easy actually, however we are also trying to design it so the specs come out near the same as the ceramic magnet versions. It will use the same everything else.
audiokinesis said:
Yeah with everything being modular designed its not an issue. I talked with John quite a bit today about the Alnico design, we are waiting for available Alnico sizes to be sent back to us so I can start the napkin drawings.
Lynn Olson said:
Both the Alnico and field coils have magnetic field that are not sensitive to the magnet field the voice coil generates. As John stated incorporating Faraday rings helps to keep the magnet field stable. The closer to the gap the better (which is why I stick a thick tube of copper in the gap)
I am sure people will have all sorts of fun figuring out the best amp output for the field coil. Lower amps will give higher Qts and vice versa. The coils will be able to handle pretty much whatever you throw at them. There will be a "knee" in the magnetization curve where adding more current does little to nothing.
FlorianO said:
Here's another vote for smth like this
That above, with high power handling and decent xmax -- just count me in. Just let the (hard] choice be btw Alnico, Neodymium magnet with counter-wound coil (ala 18Sound "active impedance" -- even more "bragging rights" for low inductance - and proven to work) or 12V field coils....
That kind of driver seems to have great potential of a scaled down version of what Lynn is currently doing (for those of us w/o "concert hall" sized room in the basement):
Yeah I am in this boat myself as I have 3 rooms that need small cabinet sound. The napkin drawings have started on both the wide band 8" and a small Alnico "small horn" tweeter.
chrismercurio said:
Oops - just sent it.
Magnetar said:
Yeah that was another thought of mine, being able to use batteries for testing at least.
JoshK said:
Give it a few months, it will happen. Designing the motor is easy actually, however we are also trying to design it so the specs come out near the same as the ceramic magnet versions. It will use the same everything else.
This all sounds good. I think there will be a lot of interest in top-quality 12" and 15" midbass drivers - for premium studio-monitor applications, as well as various dipole/horn projects.
Now that TAD/Pioneer are walking away from the their traditional high-efficiency monitors (their latest $60,000 flagship product is a beryllium-diaphragm Uni-Q with 90 dB/metre efficiency), there's a real gap in the market for top-quality high-efficiency drivers. And it's not like there is a glut of high-quality, high-efficiency loudspeaker systems - these are still very thin on the ground, 15 years after the low-powered triode amplifiers started to appear on the market.
I would vote for efficiencies a bit higher than 94 dB/metre - that's just on the doorstep of true high efficiency. 97 dB/metre and higher is more like it, and what I'm aiming for. The sonics do change as the efficiency goes up, and for the better - more headroom, but also better microdynamics as well.
I don't know why, but high-efficiency speakers sound surprisingly good when they're playing at background-music levels, while by contrast audiophile-efficiency speakers (85 to 88 dB/metre) only seem to "come alive" within a rather narrow range of playback levels - they can "go dead" if the playback level is too low.
I've heard this a number of times, particularly with boutique-priced high-end speakers - the sound just completely comes apart at background-music levels. I've been struck how a $200,000 hifi system can be completely unsuitable for playing background music, and a table radio with a single 5" paper-cone speaker will sound more natural and less "processed" sounding.
Now that TAD/Pioneer are walking away from the their traditional high-efficiency monitors (their latest $60,000 flagship product is a beryllium-diaphragm Uni-Q with 90 dB/metre efficiency), there's a real gap in the market for top-quality high-efficiency drivers. And it's not like there is a glut of high-quality, high-efficiency loudspeaker systems - these are still very thin on the ground, 15 years after the low-powered triode amplifiers started to appear on the market.
I would vote for efficiencies a bit higher than 94 dB/metre - that's just on the doorstep of true high efficiency. 97 dB/metre and higher is more like it, and what I'm aiming for. The sonics do change as the efficiency goes up, and for the better - more headroom, but also better microdynamics as well.
I don't know why, but high-efficiency speakers sound surprisingly good when they're playing at background-music levels, while by contrast audiophile-efficiency speakers (85 to 88 dB/metre) only seem to "come alive" within a rather narrow range of playback levels - they can "go dead" if the playback level is too low.
I've heard this a number of times, particularly with boutique-priced high-end speakers - the sound just completely comes apart at background-music levels. I've been struck how a $200,000 hifi system can be completely unsuitable for playing background music, and a table radio with a single 5" paper-cone speaker will sound more natural and less "processed" sounding.
John_E_Janowitz said:
John and Nick,
The pro audio speaker companies have different design goals than diyAudio goal of ultimate home audio, and high efficiency is not a top design goal of Seas, Dayton. etc... New designs are necessary for high efficiency ultimate home audio.
The graph illustrates how a typical underhung motor can have a more linear BL vs. displacement than a typical overhung motor.
For a high efficiency midrange, low Mms is also very important.
Lambda TD10M = 44grams Mms
18 Sound 10NDA520 = 30 grams Mms
An underhung prototype using NdFeB and 30 gram Mms still looks like a candidate for the ultimate high efficiency midrange.
Paper comparing underhung and overhung motors...worth a read. Very loose summary.....
http://www.s-m-audio.com/underhung.pdf
For Bl <18 the claim that an underhung motor structure requires less magnet flux than an equivalent overhung structure was verified only under a qualified condition. The condition was that the total flux of the underhung motor must be at or below an operating point where the core and fringe energy losses are approximately the same as the gap magnetic energy. For flux levels below this operating point, the underhung magnet requirements are less than the overhung’s requirements. If the flux is higher, then the underhung motor requires more magnet than the overhung motor because it’s core losses are higher.
For high Bl ~22, the underhung motor requires 3x the magnetic flux and 2x the core metal volume compared to an overhung motor. However, because of the typically shorter coil on underhung motor designs, lower moving mass is possible on underhung than overhung motors. So, for the same SPL, underhung motors need about 2x the magnetic flux and 1.5x the core metal volume compared to an overhung motor. NdFeB and TC Sounds type thick-to-thin tapered pole steel can do this.
Attachments
LineSource said:
First thing - don't use a Bl only spec for anything as it means zero without including the Re of the voice coil.
Bl means 2X to me, without knowing what the X is you don't know anything about the real number it is specifying.
The problem with NdFeB and that TC tapered pole you are describing is that the TC pole is designed for a magnet on the outside of the pole. Not only is that a massive diameter of NeFeB, I can only imagine the magnet charger needed to zap it to life.
I only looked slightly at the paper but the first problem I saw was that he used a T pole and thin top plate (relative to coil length) to come to his conclusions. If he would have used an extended pole combined with a top plate where the voice coil overhang was less than the thickness of the top plate then his results would have been very different. Both that TC Sounds design and mine use the better ratio and pole height for overhung.
agent.5 said:
I can answer that and unless it's for an OEM project, we will never take money up front for something we don't at least have parts in stock for. The parts supply end of things is a continual nightmare it seems, especially being the little company. I'm still waiting on a final set of samples on aluminum cones for the AV series that should have been to market in October last year. If I had taken money up front with the proposed October delivery, I'd have some very upset customers by now. We do take money up front for the TD drivers as long as all parts are in stock because they are made to order, but they have only a 5 day lead time.
We have some thinking to do yet on the Alnico as there are several ways to do it. Solid slug of alnico in the pole, ring of alnico on the outside, combination of both, etc.
John