alnico/ferrite drivers

[Figge]

ok! this has probably been nagged about before but here we go!

i was just wondering about the diffrences between the 2421 (alnico) and say the 2425 (ferrite) sound?. the cores i mean.
should i expect higher performance with the 2425 core?

i heard the diffrence between the 116a alnico in l-19 and the 116h in 4301b. it was like day and night. ok not the exact same cabinets but...

[Mr. Widget]

I am also curious about this. Maybe someone out there could compare a LE85/2420 motor with a 2425 motor using the same diaphragms. It would also be interesting to compare the 375/2440 or 2441 motor with the 2445 motor sharing diaphragms. I don't know if anyone has done this, but it would be great if someone could do these comparisons both subjectively (listening) and objectively by measurement.

Widget

[Don McRitchie]

There shouldn't be a significant difference, if any, assuming that the throat and phase plug geometry is the same in both the ferrite and Alnico versions. I believe this is the case with the 2420/2425 and 2440/2445, but this is worth checking. Of course the big issue that will have to be checked is whether an Alnico, used for comparison, still meets the factory specs for flux density.

In bass drivers, there is a difference is sonic character because of differences in flux modulation and temperature curves of the different magnetic materials. In a compression driver, the coils are generally underhung so that flux modulation is mitigated to low levels. The lower power handling of compression drivers results in lower operating temperatures so that the temperature curve difference has minimal effect. Nonetheless, I would be interested in the results of any experiments.

[Figge]

ok since i now have both the 2421A:s and the 2425H:s i could step up to task of testing this. diaphragm that gonna be used is new 8ohm titanium.

one question though: the 2421 are pretty old and alnico, can it have gotten demagnitized?


widget: its only gonna be a listening test so far, as i have no messuring equipment.

the 2425:s are mounted now and im gonna listen to them for a while, get to know them. and then swap, and listen for a while.

a while = couple of days? weeks? idunno.

[Maron Horonzakz]

I have a pair of LE 85 drivers with Ti diaphrams . The units were sent back to JBl for gap rework & remagnetizing. They sound fine. I dont know what the units would sound like if I would put the aluminum diaphrams back in . the gaps are now different.

[Earl K]

the gaps are now different.

Really ? Someone at JBL told you this ? Did they say what they now are ?

<. Earl K

[scott fitlin]

I say you can hear differences between different magnetic material! My latest exploration of this was the TAD 4001 ( alnico ) vs the TAD 4002 ( neodymium ) and both use the exact same diaphragm, but sound so very different from each other!

The JBL 2441 vs the JBL 2445! Another buisiness down here that has big sound used the 2441J and switched to the 2445J. Ron didnt care for them, and put the 2441 diaphragms in the 45,s! Still they didnt sound like the 2441,s! I heard it, he heard it, and his sound engineer heard it!

The JBL 2402,s! I have some alnico 2402,s and when I got them had them rediaphragmed, and sent em to JBL for a remag! I have A/B,d them against my 2402H and can hear difference between the two types! The alnico bullet seems to have a finer sounding top end, more jingly and airy, while the ferrite 2402 has that raspier sound, Tss Tss Tss! But i can always hear a difference between the two types! Im not saying you cant get ferrite drivers to sound good, they can sound great, but I can hear a difference between the magnet types!

[Mr. Widget]

Hi Scott,

I really doubt that the magnetic material itself is the cause of the differences you are hearing.

In the case of the TAD 4001 vs. the TAD 4002 you are correct that they both use the same diaphragm, but they have different phase plugs and different throats. TAD also makes the 4003 with neodymium and I think it is slightly better than the alnico 4001. It is a completely different driver though so it isn't a proper comparison.

In the case of the 2441 vs. the 2445, I believe they have different throats and different phase plugs so once again a direct comparison isn't possible. I do find it interesting that with the same 2441 diaphragm, the 2441 driver is preferred. I have not made this comparison, but would like to at some point.

I can't think of any reason that different magnetic materials by themselves should make a difference sonically in a HF device. I haven't noticed a sonic difference when comparing alnico 077s and ferrite 2405Hs. When dealing with these minute details the power of suggestion can be huge. Have you tried your comparisons in a blind or double blind scenario?

Widget

[Maron Horonzakz]

Earl K.......Well they shure the hell sent me a bill for for that service.

[Maron Horonzakz]

Widget.... If you look at the cutaway drawings in the TAD catalog The 4001 & 4002 Have the same diaphram & the same phaze plug design. Its the magnets that are different plus the flux levels are different.

[Earl K]

Hi Maron

I'm just curious . I certainly believe JBL "regapped" the le85(s) , along with remagnetizing them . But to me, "regapping" is essentially "recentering" all the top-plate parts to achieve the best symmetry for the 2 circles. Somewhat "simplistically" like having a car engine "blueprinted" .

This process shouldn't preclude the use of older diaphragms - unless I'm missing something here .

regards <. Earl K:)

[Maron Horonzakz]

Earl k......I guess I could replace the diaphram in one LE 85 to the old unit to see if it drops in output a skoshe. I just assumed it would. If its only a db I won,t hear it. I dont know if a rat shack meter could show this.

[Mr. Widget]

Originally posted by Maron Horonzakz
Widget.... If you look at the cutaway drawings in the TAD catalog The 4001 & 4002 Have the same diaphram & the same phaze plug design. Its the magnets that are different plus the flux levels are different.

I just took another look at the catalog, and I can't be sure the phase plug or throat are the same or not. Are you certain they are the same?

The 4002 is a "low cost" alternative to the 4001. It seems strange that if the goal was to recreate the 4001 at a lower price point, using the same diaphragm, phase plug, and throat dimensions, that they would change the flux density. It certainly could be the same as the 4001 if they wanted it to be. I did notice from looking at the drawings that the rear chamber of the 4002 does seem smaller than the 4001. This would affect performance.

Other than looking at the catalog I have no experience with the 4002 driver so I can't say anything about it's sound, but for their top of the line driver they chose to once again use neodymium and from my experience it does indeed surpass the alnico 4001.

Slightly off topic, JBL has used alnico for their top of the line 1500AL woofer and yet gone with neodymium for it's companion mid and HF drivers. Further off topic even further still for JBL's slightly more cost effective alternative drivers to the beryllium diaphragmed 435Be and 045Be, they went with aluminum instead of Ti.

If anyone has a theory or an actual explanation as to why they think alnico may be superior to Fe or neodymium, I am all ears.

Widget

[Earl K]

Hi Maron

If you're not comfortable with recentering replacement diaphragms ( you need some test gear ) then I wouldn't recommend you mess about with what you got back from JBL . On the other hand, if swapping diaphragms in & out of magnet structures is second nature to you - then it would be interesting to hear about your impressions, of old versus new.

regards <. Earl K

[scott fitlin]

Originally posted by Mr. Widget
Hi Scott,

I really doubt that the magnetic material itself is the cause of the differences you are hearing.

In the case of the TAD 4001 vs. the TAD 4002 you are correct that they both use the same diaphragm, but they have different phase plugs and different throats. TAD also makes the 4003 with neodymium and I think it is slightly better than the alnico 4001. It is a completely different driver though so it isn't a proper comparison.

In the case of the 2441 vs. the 2445, I believe they have different throats and different phase plugs so once again a direct comparison isn't possible. I do find it interesting that with the same 2441 diaphragm, the 2441 driver is preferred. I have not made this comparison, but would like to at some point.

I can't think of any reason that different magnetic materials by themselves should make a difference sonically in a HF device. I haven't noticed a sonic difference when comparing alnico 077s and ferrite 2405Hs. When dealing with these minute details the power of suggestion can be huge. Have you tried your comparisons in a blind or double blind scenario?

Widget In the case of TAD I was able to borrow two 4001,s and I could hear distinct difference between the 4002 and 4001. I preferred the 4001, better upper midrange! But still i prefer the sound of the JBL 2441!

For the tweeters, I had one day, about three years ago while my dad was still running things with me, put up one cluster of four that I have with all four tweeters in that array being 2402 alnico bullets! The other three arrays were our 2402H. I played music for a bit, and about an hour into this my dad comes into the place, and said system sounds pretty good! he aksed me if I had his Yanni CD, which I did, and I played stuff from it for him. And he comes over to me, and asks me how come the tweeters over there sound better than the rest? I ask him, what do you mean? he tells me those sound better, cleaner, more top end, sounds like they go up higher than the others, and the others are kind of raspy! I say cant be! But I hadnt told him anything, or that those werent OUR bullets. I play more music, he keeps telling me Those sound better! Finally I tell him those are different ones, not ours! Same basic tweeter, same diaphragm, different magnet. He didnt know they were different, but he heard something different. This would be, to me, about as double blind as you get!


The TAD 4002! heard em at a show, heard em in a pro rig, wasnt sure if i wanted the 4001,s or 4002,s! TAD wholeheartedly recommended the 4002 OVER the 4001, other pro sound guys also recommended the 4002! I bought six! Installed them, didnt like em, did everything, EQ, change amps, crossovers, crossover slope and points, just couldnt get what I wanted or expected from them! The 4001 is a superior sounding driver compared to the 4002, IMHO! Went back to my JBL 2441, and It sounds good. You know I really wanted to love the 4002, after spending THAT much money its hard to swallow that I made a mistake! But I did! I glad I held on to my JBL 2441,s though!

Supposedly, the phase plug is the same in both the 4001 and 4002, yes the throat is different, and this could be what I hear, but to me the 4002 reminded me somewhat of the JBL 2450J, also not on my LIKE list! Beryllium diaphragms being the same, a major difference in tonality!

These days I say specs, schmecks, I use my ears! if I like it, I like it, and I dont care WHAT makes it do what I like as long as I like it!

I say we can hear difference between magnets! All of them can be made to sound good, but we can hear difference!

[scott fitlin]

I have no experience with the TAD 4003! I only know what you tell me, and that others say its good as well!

[Mr. Widget]

Originally posted by scott fitlin
... preferred the 4001, better upper midrange! But still i prefer the sound of the JBL 2441!



These days I say specs, schmecks, I use my ears! if I like it, I like it, and I dont care WHAT makes it do what I like as long as I like it!




I too have compared the 4001 and 2441 both on the same horn in the same room through the same system and came to the opposite conclusion! :hmm: To my ears both drivers had a smooth sound, but there was just more detail from the TAD.

I agree completely the specs are frequently irrelevant.

Widget

[scott fitlin]

Originally posted by Mr. Widget
I too have compared the 4001 and 2441 both on the same horn in the same room through the same system and came to the opposite conclusion! :hmm: To my ears both drivers had a smooth sound, but there was just more detail from the TAD.

I agree completely the specs are frequently irrelevant.

Widget What horn are you using the drivers on? I tend to agree the TAD has an extremely high resolving capablity, but, for one reason or another, I find the JBL 2441 more fun to listen to.

Another thing Ive noticed, and Ill probably get shot down for this, but, I also feel the 2441 exhibits a coloration, albeit a musical sounding coloration, but a coloration nonetheless, that I find pleasing to listen to!

I definitely LIKED the sound of the 4001,s but I am not about to go out and spend that much on those drivers. I definitely DID NOT prefer the sound of the 4002. The 2441, well, yeah, there may be better, but from a musical point, they do something thats nice, IMHO.

On a side note, I have been playing around with some better cabling, and I am at a loss for how to explain why I hear differences. This one particular set of cables a freind of mine made for me and sent me from Japan, well, they bring out these minute details. The JBL 2441 holds up well, even today, and even one of my co-workers asked me if I had done anything to the system, he said he was hearing things in the recordings he never heard before! But I am able to get things out of the 2441 that surprises even me!

Believe this, when I purchased the TAD 4002,s I had EVERY intention of selling my 2441,s! Upgrade, top flight, top shelf. I was moving into the 21st century. I was quite unhappy over the fact that the 4002 wasnt what I anticipated it to be!

I will be selling off my TAD drivers this winter. If they fetch me back 80% of what they cost me, that will be the best sound the 4002,s ever made to me! :eek:

[Maron Horonzakz]

Has anybody figured out how the 5 slit phaze plug in the TAD 4003 works? The slits are straight although of diffrent length. The TD 2002 3 slit is the same design. Where as the JBL 475nd and 2450 phaze plug have a lazy S curve slit shape called coherent wave to keep things in phaze. It does,nt seem the TAD 4003 & 2002 keeps in step.

[Mr. Widget]

Originally posted by scott fitlin
What horn are you using the drivers on? I tend to agree the TAD has an extremely high resolving capablity, but, for one reason or another, I find the JBL 2441 more fun to listen to.


That would be this one.

All drivers have some coloration. While the TAD 4001 and the JBL 2441 are very low in their coloration, they each have a flavor.

I can certainly understand why you might like one flavor over another, however after one EQs the system to remove most of the coloration/character as I do, the one with the most detail really shines through.

Widget

[Mr. Widget]

Originally posted by Maron Horonzakz
Has anybody figured out how the 5 slit phaze plug in the TAD 4003 works? The slits are straight although of diffrent length. The TD 2002 3 slit is the same design. Where as the JBL 475nd and 2450 phaze plug have a lazy S curve slit shape called coherent wave to keep things in phaze. It does,nt seem the TAD 4003 & 2002 keeps in step.
I am currently listening to the 4003 on the TH-4003 horn. This combination is scary flat in on axis response. It is plus or minus 1dB from 2KHz to 10KHz. This is what I measured in my room with no external EQ and this is similar to what others have measured in their systems. If there were phase plug issues I doubt the response would be that flat.

That said, I have no idea what TAD is doing with their "subtle improvements to the shape and material" of their phase plug.

I hope to try out this driver on my horn pictured above. I have to finish my 1.5" throat adapter first.

Widget

[Maron Horonzakz]

AAAhhhhhhhhhh......A Smith horn 2397 variant. The sound of paradice. Didnt some one on this FORUM interview SMITH ?

[still4given]

Ooooooooooooooo, I really want to build a pair of those wooden horns. Does anyone know if there are plans for those?

Blessings, Terry

[boputnam]

Hey, Terry...

Since you weren't around for that period, here's a Link to Widget's Wooden Horns (http://audioheritage.csdco.com/vbulletin/showthread.php?s=&threadid=695&highlight=wooden+horns)

They are beauties, and sound even better than they look. :yes:

[Maron Horonzakz]

You can buy them from WIDGET.. He makes them usung the finest woods. Just dont beg or grovvle.

[scott fitlin]

Originally posted by Mr. Widget
That would be this one.

All drivers have some coloration. While the TAD 4001 and the JBL 2441 are very low in their coloration, they each have a flavor.

I can certainly understand why you might like one flavor over another, however after one EQs the system to remove most of the coloration/character as I do, the one with the most detail really shines through.

Widget You see i happen to agree with you, Mr. Widget, the 4001 on those 2397+ horns are actually superior!

But on my 2395,s I prefer the 2441! To both the 4001 and definitely the 4002!

Your wood work and choice of wood for constructing these beauts, is second to none, although I would never take a horn as fine as yours and put them into my commercial system! That would be a crime on my part, rather your horns are for serious studio or home Hi Fi critical listening!

But on that horn of your I can understand one preferring the TAD 4001. :yes:

[still4given]

Originally posted by boputnam
Hey, Terry...

Since you weren't around for that period, here's a Link to Widget's Wooden Horns (http://audioheritage.csdco.com/vbulletin/showthread.php?s=&threadid=695&highlight=wooden+horns)

They are beauties, and sound even better than they look. :yes:

Thanks bo,

Those are beautiful


You can buy them from WIDGET.. He makes them usung the finest woods. Just dont beg or grovvle.

What I'm actually interested in is plans for them. I would like to do the woodworking myself.

I'm sure they are worth every penny the Mr Widget is selling them for but at that price I will never own any. Besides, I love to build stuff. :D

Blessings, Terry

[Don McRitchie]

Originally posted by Maron Horonzakz
Has anybody figured out how the 5 slit phaze plug in the TAD 4003 works? The slits are straight although of diffrent length. The TD 2002 3 slit is the same design. Where as the JBL 475nd and 2450 phaze plug have a lazy S curve slit shape called coherent wave to keep things in phaze. It does,nt seem the TAD 4003 & 2002 keeps in step.

The coherent wave phase plug was never really used to its design potential. It was developed with the intent of ultimately using a berylium diaphragm with these drivers. However, such a diaphragm was never put into production.

Differences in path length causes the wavefront to be recombined out of phase that can result in response anomalies at the highest frequencies. However, this is only noticable if the diaphragm is acting pistonically. If the diaphragm is in breakup mode, as most are at their HF limits, then the phase discrepancies caused by this mask any anomalies caused by differing path lengths. However, with since berylium diaphragms can be made to act pistonically to near the limits of audibility, the phase plug design again becomes an issue. In the 435Be, the smaller diameter phase plug means that even a straight path does not introduce differences in path length great enough to be an issue within their bandwidth. However, if JBL ever decided to develop a 4" berylium driver, they may look at this again.

With regards to TAD, I don't believe that their design specifically addresses this issue. I'm not sure if this is because they do not believe it is significant, or if JBL's patent prevents them from doing so. If I had to guess, it would probably be the former.

[Oldmics]

"Differences in path length causes the wavefront to be recombined out of phase that can result in response anomalies at the highest frequencies"


Enter the waveguide design of the L"Acoustics products.

In minimalist terms of explanation, a 1.5 horn entrance that wraps back upon it itself (similiar to a compression drivers phase plug) engineered to produce a phase coherent,flat response in the hi frequency realm.

Used in the V-dosc line array system.

Might be another path to travel-Engineering of the expulsion horn to work with the driver and all of the drivers characterists both positive and not so good to create the ultimate combination hi frequency reproduction device.

Way beyond the scope of my toolshed! But I"d like to be on the team.

Oldmics

[Maron Horonzakz]

DON...... If the 475.....2450 type drivers using coherent wave phazing plugs were really designed for Be .... Why the odd 2450SL powder coat aquaplas diaphram as used in the JBL K2 95000 ? What was that coating supposed to do. And why the smooth coat rather than the ribbed pattern?

[Don McRitchie]

The aquaplas coating is intended to damp resonances within the titanium diaphragm. I'm guessing that the ribs, while stengthening the diaphragm at high output, create phase anomalies of their own due to the ridges in the otherwise spherical surface. It was probably not felt to be an issue in pro applications, but became a concern in hi-fi use. FYI, JBL was using the aquaplas coating on their ribbed pro titanium diaphragms for a time, but I don't think they are now. I'm not sure why they stopped.

[Robh3606]

Not sure about those ribs being a concern or not. Figure the 044,035,046 all have them to stiffen the diaphram. So does the very large 093ti dome.

[4313B]

Oops, it appears there are a few pages missing from this:

http://lansingheritage.org/html/jbl/specs/home-speakers/1984-ti.htm

[Don McRitchie]

Personally, I remain to be convinced that they make an audible difference. Nonetheless, JBL went out of their way to develop a specialized diaphragm for the 475ND that removed the ribs from its pro counterpart.

[scott fitlin]

Originally posted by Don McRitchie
Personally, I remain to be convinced that they make an audible difference. Nonetheless, JBL went out of their way to develop a specialized diaphragm for the 475ND that removed the ribs from its pro counterpart. But that JBL did take the time, and invest the money, into making a differing diaphragm says to me JBL felt it made an audible difference, and did what they may have felt was more suitable for each diaphragms intended application.

I am of the opinion that minute design changes in both driver assemblies, and diaphragms and materials and shapes and ribs, etc, do make audible differences.

[Maron Horonzakz]

Yes and now try to get a 475nd diaphram.

[scott fitlin]

Are the 475nd diaphragms hard to get?

[4313B]

No, they are in stock.

[Maron Horonzakz]

HMMMMM....So now here is the punch line question... What is the difference between the diaphrams of the 475nd coated units and the 2450SL coated aquaplaz diaphrams ???? IS one smooth faced? Is the other embossed ribbed? Or are both smooth faced and coated. We do need a JBL engineer here to give us the details. A chart would help. AS you have figured out I love to swap diaphrams & tweek for any sonic improvements . (if any) Too bad TAD diaphrams won,t fit large JBL drivers. But with a little machineing they might fit. (probably waste of time)

[Robh3606]

Heres a 475nd

[Robh3606]

Here's a ribbed

[4313B]

Originally posted by Maron Horonzakz
We do need a JBL engineer here to give us the details. A chart would help.The chart is in the works with input from at least four people from JBL but it will be awhile. Everyone is very busy.

[spkrman57]

Reading older threads and trying to learn(old dog-new tricks). Thought this thread needed to be brought back to the present.
Ron

[tomt]

any chart yet?

or is this a dud deal?

[Maron Horonzakz]

I,m still holding my breath, but I,m turning blue.:(

[whgeiger]

But that JBL did take the time, and invest the money, into making a differing diaphragm says to me JBL felt it made an audible difference, and did what they may have felt was more suitable for each diaphragms intended application.

I am of the opinion that minute design changes in both driver assemblies, and diaphragms and materials and shapes and ribs, etc, do make audible differences.
SF,

The motivation totem for driver design changes looks something like this:

1) Reduce field returns, particularly for those units still under warrantee. Diaphragm fracture, surround fatigue, voice coil failure (due to heat dissipation problem) are typical causes.

2) Reduce manufacturing cost (acoustics enhanced or otherwise 'negligibly' affected).

3) Design has nasty resonances (response irregularities) that need to be suppressed, or unit drifts out of specifications during the warrantee period.

4) Match driver to new horn (or enclosure) design. These changes result in new driver models rather than variants to those already existing.

Note that 'how it sounds' is at the change totem bottom.

Regards,

WHG

[Mr. Widget]

Hey, for them it's a business not a hobby. ;)

Widget

[whgeiger]

To All,

There is sufficient evidence to suggest that different magnet materials will yield different sounding drivers, since design of the entire magnetic circuit is dependant on the magnet material used. The proposition, that two drivers are identical in all respects, except for the use of different magnetic materials, is at best, an oxymoron.

For example, the operating point for ferrite magnets, with their steep sloped demagnetization curves, is radically shifted as the voice coil moves back and forth through the magnetic gap. This shifting is manifested as a modulation to the magnetic flux ‘seen’ by the voice coil when it is in motion. To counter this effect, a flux-stabilizing (copper or aluminum) ring is wrapped around the pole piece body to suppress such action. This design, under these circumstances, will not be functionally or physically identical to a driver motor designed around an AlNICo V magnet nor any other magnetic material.

Regards,

WHG

[frank23]

To All,

There is sufficient evidence to suggest that different magnet materials will yield different sounding drivers, since design of the entire magnetic circuit is dependant on the magnet material used. The proposition, that two drivers are identical in all respects, except for the use of different magnetic materials, is at best, an oxymoron.


Regards,

WHG

That's what I heard once someone telling me, that the magnetic gap properties of an alnico magnet driver were different from those of a ferrite magnet driver

isn't is also so that the magnet itself is in a whole different location in an alnico driver [in front?] than in a ferrite driver [around?]

or am I typing nonsense right now?

does someone have a cut through picture of a ferrite magnet compression driver? to compare with this alnico driver?

frank

[Dave Zan]

For example, the operating point for ferrite magnets, with their steep sloped demagnetization curves
I'm reasonably sure that the common view of this is incorrect so I'll state my idea here for confirmation or criticism.

The voice coil gap geometry sets the reluctance of the magnetic circuit and the designer's specification sets the flux.
To minimize the size (and cost) of the magnet there is a definite operational condition that specifies both B and H. This is the point at which the BH product is maximum. There must be a match between the magnet and the gap -similar to the way impedance is matched to maximizes power. The optimum magnet dimensions are matched to the gap with the field return structure.
The magnet thickness and area will vary for different materials but the B/H relation as seen by the voice coil should be the same. The material properties will vary but the actual magnets will be equivalent because they both must match the same gap.
So it's not because ferrite material has a steeper slope that it had more flux modulation problems (at least to first order).

I believe the main reason is that there are flux stabilizing current flows in Alnico drivers. These are much lower in ferrite drivers due to the lower conductivity of ferrite and possibly the different field return structure required by the ferrite's different magnet proportions is also less able to support stabilizing currents.



is radically shifted as the voice coil moves back and forth through the magnetic gap. This shifting is manifested as a modulation to the magnetic flux ‘seen’ by the voice coil when it is in motion.

I don't think that the motion of the voice coil is a factor here. Flux modulation would still happen if the VC was blocked. Of course it wouldn't matter as muchhttp://audioheritage.org/vbulletin/images/smilies/smile.gif

Dave

[whgeiger]

[/size][/font]
I'm reasonably sure that the common view of this is incorrect so I'll state my idea here for confirmation or criticism.

The voice coil gap geometry sets the reluctance of the magnetic circuit and the designer's specification sets the flux.
To minimize the size (and cost) of the magnet there is a definite operational condition that specifies both B and H. This is the point at which the BH product is maximum. There must be a match between the magnet and the gap -similar to the way impedance is matched to maximizes power. The optimum magnet dimensions are matched to the gap with the field return structure.
The magnet thickness and area will vary for different materials but the B/H relation as seen by the voice coil should be the same. The material properties will vary but the actual magnets will be equivalent because they both must match the same gap.
So it's not because ferrite material has a steeper slope that it had more flux modulation problems (at least to first order).

I believe the main reason is that there are flux stabilizing current flows in Alnico drivers. These are much lower in ferrite drivers due to the lower conductivity of ferrite and possibly the different field return structure required by the ferrite's different magnet proportions is also less able to support stabilizing currents.



is radically shifted as the voice coil moves back and forth through the magnetic gap. This shifting is manifested as a modulation to the magnetic flux ‘seen’ by the voice coil when it is in motion.

I don't think that the motion of the voice coil is a factor here. Flux modulation would still happen if the VC was blocked. Of course it wouldn't matter as muchhttp://audioheritage.org/vbulletin/images/smilies/smile.gif

Dave

DZ,

These statements, while mostly true for static conditions, obfuscate, deny or otherwise ignore what takes place within the magnetic circuit under dynamic conditions when the voice coil wire ‘cuts’ through that magnetic gap. So, the claim remains that the acoustic signal so generated, contains distortion products whose signature is unique to each circuit configuration and that such signatures are audible to a discriminating listener.

So that there is no further equivocation on the matter, the following excerpts from Douglas Button’s paper [1] and John Eargle’s book [2] are provided forthwith. For those that want to persue magnetic circuit design for loudspeaker drivers, an additional reference to Eric Guarin’s work [3] is also provided.

Regards,

WHG

Quotations:

“3. The Magnetic Assembly” ([1], p. 9)

“The magnetic assembly is probably the most taken for granted part of a loudspeaker assembly. It is this author's opinion that it happens to the most exciting part of the design. The magnetic structure is in fact not a simple static field that is merrily supplying the voice coil with needed flux lines to modulate the cone. The materials used and geometry of the magnetic structure can radically alter the impedance curve and completely dominate the 2nd. and 3rd. harmonic distortion products in mid and lower frequencies. The interaction of the voice coil and it's surrounding is very complex and can change the sound of a driver dramatically.”

“3.4.1 Flux Modulation” ([2], p. 52)

“This occurs when the magnet is alternatively over-magnetized and reversely magnetized by the cyclic signal current in the voice coil itself. This effectively amounts to shifting of the instantaneous operating point up and down the demagnetization curve. It is minimal when the demagnetization curve itself is fairly flat, as in the upper portion of a typical AlNiCo V demagnetization curve.”

“However, in the case of a ferrite magnet, with its high-sloped demagnetization curve, no such solution is available. When JBL, like all other manufacturers, was forced to develop a new ferrite motor structure when cobalt became too expensive, they added a large conductive ring, made of aluminum, at the base of the pole piece. Through transformer action, the voice coil signals that are induced into the magnet structure will set up a countercurrent in the aluminum ring. The ring, a single turn with a cross-sectional area of about 1 cm^2, has an extremely low resistance; consequently, there is substantial current flow through the ring at high signal levels. As in all induction phenomena, the action of the induced current is to counter the effect that produced it in the first place, thus the tendency for flux modulation is greatly reduced at the price about 1 dB of overall magnetic efficiency”

References:

[1] File: AESP3192.pdf
Title: Design Parameters and Trade-Offs in Large Diameter Transducers
Author: Douglas J. Button
Affiliation: JBL/Harmon Loudspeaker Manufacturing, Northridge, CA
Publication: AES-P, No. 3192, Cnv. 91, Sep-1991
Abstract (1): In the design of high level large format transducers, a variety of interactive parameters define how a loudspeaker will sound at different power levels; voice coil diameter, former and wire material; cone material, geometry and mass; magnet size and material; magnetic gap geometry; dome geometry and material; cone surround linearity and damping; spider linearity; and the mechanical integrity of the entire moving system.
Abstract (2): These factors define; inductance; hysteresis and eddy current losses; spectral response and high frequency extension; cone break-up and modal behavior; power compression; flux modulation; low frequency linearity; and of course, sensitivity. This paper will investigate the trade-offs and design elements that influence the sound of modern high-level transducers by evaluating current designs.
Abstract (3): The purpose of the paper is to shed light into some commonly held preconceptions as to why a given engineer may have made the design choices he or she has made.

[2] Title: Loudspeaker Handbook
Author: John M. Eargle
Affiliation: JBL/Harmon International
Publication: Book, Kluwer Academic Publishers, Norwell, MA, 1996
ISBN: 0-412-09721-4
Abstract: A well-balanced treatment covering both the technological and practical aspects of the basic component design and construction of loudspeakers is presented. Rigorous mathematical/graphical explanations concerning the function of loudspeakers are provided and insight into modern testing methods is reviewed.

[3] File: AESP2979.pdf
Title: Design and Optimization Considerations for Speaker Magnets
Author: Eric Guarin
Affiliation: Armadillo Audio, Anaheim, CA
Publication: AES-P, No. 2979, Cnv. 89, Aug-1990
Abstract: A production ceramic magnet needs to be downsized for possible automotive use. Simultaneously, high energy magnet materials are to be evaluated as alternatives. Magnet design basics, pole and plate shaping, and production feasibility considerations combine to yield more efficient designs. Computer software implementation aids in the design process.

[Dave Zan]

As someone once said "What we have here is a failure to communicate" so I'll expand my thesis - somewhat tediously!
Proposition 1.
I think most people have read statements like the one in Eargles book and conceive the demagnetization curve mentioned, and hence the flux modulation, is inherently a property of Alnico - similar to the way the conductivity of copper alters with temperature -essentially the same (percent) for any copper voice coil.
They therefore expect the flux modulation to be much the same for any Alnico magnet.
(To be pedantic this is actually an opinion about what people think. It's really by way of introduction rather than essential to the thesis.)

Proposition 2.
I believe this is a misconception and that what determines the response to flux modulation is a property of the entire component - very similar to the _resistance_ of the voice coil - and therefore that this can be built to practically any value.
(This is a statement of physics.)
If Prop. 2 is true then it raises an obvious question. If the "magnetic resistance" (in fact called the reluctance) can be built to specification then why were ferrite magnets initially specified that had more flux modulation than Alnico and that required a new structure? The obvious comparison is between ferrite and Alnico magnets where both are "equivalent" in the sense that they are the cheapest (minimum amount of magnetic material) that will create the same flux in the same gap. This leads to

Proposition 3.
A ferrite magnet "equivalent" to an Alnico magnet will have the same reluctance and hence incremental sensitivity to flux modulation - to first order and small values of delta.

Now I realize there are complications beyond this. The curves of Alnico and ferrite are non linear and different. I just want to establish the basics before I consider the complexities because I don't think even the basics are well known and I want to understand what the physics really are.
If the propositon is true then we can better understand what _really_ causes the differences (Which I don't deny - JBL didn't reengineer the transducers just for fun). The two most obvious explanations are -
1. That the magnets are operated dynamically so far from the static conditions that the distinctive shape of the BH curves does indeed matter.
This is most people's intuitive expectation but I don't think it likely to be a major factor. A magnet operated significantly into the non linear zone will tend to be irreversably demagnetized.
2. That the _conductivity_ of the Alnico meant that significant currents flowed in these tranducers that stabilized the flux. This is less obvious but I believe that this is actually the case for several reasons.
First of all is that it seems that the JBL engineers were a bit surprised by the differences. The shape of the BH curve is their daily bread so I expect it was the less obvious.
Secondly, one of Don's comments about the Alnico/ferrite work practically stated as much (I meant ask him to confirm this but now can't find the quote - hello Don?).
Thirdly is that (as Button says in his quote) the magnetic distortion is most present at lower frequencies. The magnetic curve of ferrite doesn't alter much over this frequency span. If the slope of the BH curve doesn't alter then nonlinearities dominated by this source would not decrease with frequency. But eddy currents do increase with frequency so a frequency dependent decrease in flux modulation would be expected.
Finally. The MMF from the voice coil in a woofer is quite substantial. I calculate it would be sufficient to significantly demagnetize the Alnico if there were not substantial flux stabilization currents. This is substantiated by the discussion of the development of the 1500AL woofer which needed the Aluminium flux stabilization coil in addition to internal currents.

Do we have any competent physicists or Elec.E.s to comment on the thesis? Because if I'm correct then I would say the Eargles book is not as clear as it could be.(by coincidence I ordered a copy of the 2nd Edition a few weeks back but it hasn't arrived yet so I can't comment on the full text).



Quote:
Originally Posted by whgeiger

These statements, while mostly true

What of the _mostly_ true bits aren't true?

for static conditions,


It's precisely the dynamic flux modulation that I modelled.


obfuscate, deny or otherwise ignore what takes place within the magnetic circuit under dynamic conditions when the voice coil wire ‘cuts’ through that magnetic gap.

I didn't think I obfuscated! As I said - There will be dynamic (time variable) flux modulation even if the voice coil is stationary. The effect of the voice coil wire as it cuts the magnetic field is reflected in the back EMF. This is usually modelled as a linear circuit element and it is other circuit elements that reflect the nonlinear magnetic properties (frequency dependent resistive losses and inductances) Do you have a reference for this idea?

So, the claim remains that the acoustic signal so generated, contains distortion products whose signature is unique to each circuit configuration and that such signatures are audible to a discriminating listener.
So that there is no further equivocation on the matter

I'm an equivocator and an indiscriminate listener too?! In fact, as I said above, this is not my position at all.

“3. The Magnetic Assembly” ([1], p. 9)

“The magnetic assembly is probably the most taken for granted part of a loudspeaker assembly. It is this author's opinion that it happens to the most exciting part of the design. The magnetic structure is in fact not a simple static field that is merrily supplying the voice coil with needed flux lines to modulate the cone. The materials used and geometry of the magnetic structure can radically alter the impedance curve and completely dominate the 2nd. and 3rd. harmonic distortion products in mid and lower frequencies. The interaction of the voice coil and it's surrounding is very complex and can change the sound of a driver dramatically.”

No dispute here! This is why I want to analyze dynamic flux modulation.
I don't understand the 3rd harmonics yet.
Structure is so important it can even trump materials.

“3.4.1 Flux Modulation” ([2], p. 52)

“This occurs when the magnet is alternatively over-magnetized and reversely magnetized by the cyclic signal current in the voice coil itself. This effectively amounts to shifting of the instantaneous operating point up and down the demagnetization curve. It is minimal when the demagnetization curve itself is fairly flat, as in the upper portion of a typical AlNiCo V demagnetization curve.”

“However, in the case of a ferrite magnet, with its high-sloped demagnetization curve, no such solution is available. When JBL, like all other manufacturers, was forced to develop a new ferrite motor structure when cobalt became too expensive, they added a large conductive ring, made of aluminum, at the base of the pole piece. Through transformer action, the voice coil signals that are induced into the magnet structure will set up a countercurrent in the aluminum ring.

I think this duplicates the situation that tends to occur in the conductive Alnico itself.

[Dave Zan]

Looks like everyone's lost interest in this but just for the archive.
I've had a look at John Eargle's book and there are definitely mistakes in the chapter on magnetics. I'm finally sure that the analysis I posted above is correct - which is a relief, because at first I couldn't believe that it was his mistake rather than mine!
That's all unless anyone wants the tedious details.

David

[whgeiger]

Looks like everyone's lost interest in this but just for the archive.
I've had a look at John Eargle's book and there are definitely mistakes in the chapter on magnetics. I'm finally sure that the analysis I posted above is correct - which is a relief, because at first I couldn't believe that it was his mistake rather than mine!
That's all unless anyone wants the tedious details.

David

DZ,



When considering the differences between pros of the author and that of the critic, suspect that what follows this post will constitute yet another inept exercise in ‘nit-picking’ an example rather than dealing with the issue at hand. When doing so, see if you can be as brief as the author you criticize. Irrespective of allegations to the contrary, the previous submission remains flawed and not worthy of the effort that would be required to correct the sophomoric errors it contains.



WHG

[Ian Mackenzie]

There shouldn't be a significant difference, if any, assuming that the throat and phase plug geometry is the same in both the ferrite and Alnico versions. I believe this is the case with the 2420/2425 and 2440/2445, but this is worth checking. Of course the big issue that will have to be checked is whether an Alnico, used for comparison, still meets the factory specs for flux density.

In bass drivers, there is a difference is sonic character because of differences in flux modulation and temperature curves of the different magnetic materials. In a compression driver, the coils are generally underhung so that flux modulation is mitigated to low levels. The lower power handling of compression drivers results in lower operating temperatures so that the temperature curve difference has minimal effect. Nonetheless, I would be interested in the results of any experiments.

I think Don's explanation says it better than any faded white paper.

Ian

[whgeiger]

I think Don's explanation says it better than any faded white paper.

Ian

IM,

The reference is to a book, now available in a most recently published edition. So, the characterization "faded white paper" remains a fallacious attribution of no consequence.

Regards,

WHG