Alnico Drivers

[Don Richard]

On ‎10‎/‎7‎/‎2003 at 7:24 PM, JohnA said:

"3. If the speakers are better, which I doubt, there's some reason other than 'Alniconess'."

For me this is the closest to the truth. I prefer the K-55-V squawker primarily because of the crossover. The ferrite K-55-M is supposed to be +/- 3dB vs +/- 5dB for the -V. However, there is a difference in their sound, even when both are played through Al K's networks. I prefer the -V and I *think* it is because of the sound or performance down low near the 400 Hz crossover point.

Whatever it is, I have never thought AlNiCo had anything to do with it. There is no reason a ferrite magnet cannot duplicate the magnetic field of an AlNiCo magnet. It will be larger doing it, though.

 

Ferrite does not conduct electricity, so drivers made from ferrite often use shorting rings to reduce distortion. Alnico is a conductor and naturally does what a shorting ring does:

 

http://www.htguide.com/forum/showthread.php?23768-What-exactly-do-shorting-rings-do

[glens]

I didn't quite get that in my research this morning.  The patent link inside your link doesn't work today but it can easily be found elsewhere.  I perused it and didn't notice anything about "alnico conducting thus not benefiting from a shorting ring."  The paper "Feyz" mentions is also not available any longer at the link in that thread, but can be found at http://www.diy-audio.narod.ru/litr/FaradayRingsVoiceCoilImpedance.pdf (it's quite an interesting read, but doesn't mention magnet material).

 

Probably the most-pertinent-to-this-thread thing I found was http://www.cieri.net/Documenti/JBL/Documenti tecnici/JBL - The Great Alnico-Ferrite Debat.pdf

 

In everything I looked at this morning, nothing lead me to believe that alnico magnet speakers wouldn't benefit from shorting rings too.

[Don Richard]

20 hours ago, glens said:

obably the most-pertinent-to-this-thread thing I found was http://www.cieri.net/Documenti/JBL/Documenti tecnici/JBL - The Great Alnico-Ferrite Debat.pdf

 

In everything I looked at this morning, nothing lead me to believe that alnico magnet speakers wouldn't benefit from shorting rings too.

 

From the JBL PDF:

"Now to factual differences, There are three main advantages of alnico over ferrite: 

 

1) Greater immunity to flux modulation

 

Shorting rings are used to reduce flux modulation, which reduces distortion. Which alnico magnet structures use shorting rings?

[glens]

The shorting rings aren't so much for flux modulation as for the changing inductance of the coil as more or less of it has metal inside as it moves in and out.  There may be some flux modulation benefit as well but it's secondary.  That's what I gleaned at any rate.  The main difference is the alnico magnet typically occupies the position of the "pole piece" required by the mud magnet, which piece is typically larger in diameter, thus acts more as a core for the coil (also thus gleaned).

 

I always liked the magnet structures of JBL alnico drivers and was saddened to see what I'd thought was a cheapening when they went to mud.  Now I know "the rest of the story" as Paul Harvey would say.  Drop back to the root at that cieri site and have a look around.  They've got a slew of JBL tech. docs there.  Some very interesting stuff!

[Don Richard]

38 minutes ago, glens said:

The main difference is the alnico magnet typically occupies the position of the "pole piece" required by the mud magnet, which piece is typically larger in diameter, thus acts more as a core for the coil (also thus gleaned).

 

Yes, and the rest of the magnet assembly is also metal in speakers with alnico.

[glens]

Isn't there usually more overhang (outerhang?) from a central alnico magnet to the inner diameter of the voice coil gap than with an outer mud magnet and its pole piece?  Even if not, I surmise that a coil generating a magnetic field surround something metallic would influence magnetic energy within that "whatever" more if that thing were merely acting as a conductor of external magnetic energy as opposed to producing it (if that notion is sensibly expressed).  And perhaps it's in that way the mud magnet assembly is more susceptible to flux variation?

 

Though if I properly recall the content of the "JBL" pdf I linked earlier, the overall tone of it was that alnico assemblies are not inherently better in the final analysis.

[glens]

25 minutes ago, Don Richard said:

 

Yes, and the rest of the magnet assembly is also metal in speakers with alnico.

 

It's only the metal inside the coil that matters.

[glens]

One other thing I think has to be said.  I'm just talking about this with you, not fighting over anything.

[glens]

One last thing before I go to bed: have a look at http://www.cieri.net/Documenti/JBL/Technical Notes/JBL Technical Note - Vol.1, No.9.pdf

 

Inquiring minds would like to know, does Klipsch make use of shorting rings in any way in their mud-magnet drivers?

[Don Richard]

1 hour ago, glens said:

It's only the metal inside the coil that matters.

 

Having electrically conductive metal in the magnetic circuit of an alnico driver forms a complete electric circuit that serves the same function as a shorting ring.

 

Ferrite does not conduct electricity, therefore the separate shorting coils sometimes seen in those drivers.

 

It seems that magnetic field modulation by the voice coil would show a greater effect at higher power levels?

[glens]

Yeah I understood the effect to be greater as power levels rise.

 

7 hours ago, Don Richard said:

Ferrite does not conduct electricity, therefore the separate shorting coils sometimes seen in those drivers.

 

You lose me there.  There is no ferrite anywhere inside the voice coil in my admittedly dated experience.  The ferrite is outside the coil with the magnetic circuit being completed to the inside of the coil gap through a central hunk of material which in all likelihood conducts electricity even better than would AlNiCo.

[Don Richard]

Ferrite magnet assemblies are sandwiched between iron plates, with an iron slug inside the voice coil. There is no electrical continuity through the ferrite.

 

Alnico magnet assemblies have the magnet itself inside the voice coil. The magnetic circuit and an electrical circuit are formed by iron pieces that wrap around the voice coil and form a gap on the outside of the voice coil. This configuration acts similarly to a shorting ring WRT controlling magnetic flux variations.

 

[glens]

4 minutes ago, Don Richard said:

(Annotated by GS)

Ferrite magnet assemblies are sandwiched between iron plates, with an iron slug inside the voice coil (the "pole piece"). The ferrite magnet completes (generates) the magnetic circuit (it's the inner pole piece that completes it). The only electrical continuity is through the screws that hold the sandwich together (electrical continuity is immaterial - this is not an electrical circuit).

 

Alnico magnet assemblies have the magnet itself inside the voice coil. The magnetic circuit and an electrical circuit are formed by iron pieces that wrap around the voice coil and form a gap on the outside of the voice coil. This configuration acts similarly to a shorting ring WRT controlling magnetic flux variations.

 

Electrical continuity in the assembly is immaterial.  Shorting rings, when used, are inside the voice coil, correct?  Same as the pole piece, where (aside from the presence of any [electrically insulative?] adhesives in either type) there would be no benefit towards completing any electrical circuit across said outer ferrite magnet anyway.

 

My understanding of the shorting rings is that they basically kill off the magnetic flux being generated within (inside of) the voice coil, in the areas they perform no useful (motive) function - areas outside the voice coil gap proper.

[Don Richard]

Shorting rings don't "kill off" anything. They act as the secondary of a transformer which causes a magnetic field to be generated and which subsequently opposes (shapes) the magnetic field generated by the voice coil in such a way that it stays within the VC gap. This lowers distortion.

 

Speakers that use alnico magnets have less of this problem to begin with, as detailed in the JBL PDFs you referenced.

[glens]

1 hour ago, glens said:

My understanding of the shorting rings is that they basically kill off the magnetic flux being generated within (inside of) the voice coil, in the areas they perform no useful (motive) function - areas outside the voice coil gap proper.

 

19 minutes ago, Don Richard said:

They act as the secondary of a transformer which causes a magnetic field to be generated and which subsequently opposes (shapes) the magnetic field generated by the voice coil in such a way that it stays within the VC gap.

 

Here it seems we're saying much the same thing from different angles.  Why is it that I get the feeling you're disagreeing with me in this respect?

 

I very well understand transformers.  I've made quite a fair amount of money field testing such equipment.

 

You've claimed that an internal hunk of alnico somehow performs the same function as a shorting ring but you've either not tried to explain that or have failed to adequately communicate your thoughts to me.  Is this pigeon chess?

[Don Richard]

50 minutes ago, glens said:

Is this pigeon chess?

 

I had to google pigeon chess, lol. No, it isn't, but we are discussing a subject with a lot of incomplete information available online. What we know is that alnico speakers have performance advantages over ferrite speakers, and the performance of ferrite speakers can be improved with the use of shorting rings, which can introduce other issues, such as requiring larger magnets. At this point I'm honestly not sure exactly why alnico drivers don't need shorting rings but a design engineer I met at an audio show told me that it was because alnico was a conductor of electricity and ferrite wasn't. I'll make some calls and check into this further.

 

 

[glens]

Great, thanks.

[glens]

10 hours ago, Don Richard said:

What we know is that alnico speakers have performance advantages over ferrite speakers

 

And, that ferrite speakers have performance advantages over alnico (ref. the "JBL" pdf I linked earlier).

 

10 hours ago, Don Richard said:

At this point I'm honestly not sure exactly why alnico drivers don't need shorting rings

 

"Don't need" and "don't (wouldn't) benefit from" are perhaps separate issues.  For now I'll stick with the notion I'd suggested earlier where the magnetic flux is modulated more so in an exterior-ferrite-magnet-with-interior-pole-piece because the interior piece in that case is merely a magnetic flux carrier instead of a producer.  But in retrospect... the magnetic flux of an exterior magnet (I'd bet either ferrite or alnico if it were so used) is temporarily modified (without use of shorting rings) whereas the magnetic flux of an interior alnico can be permanently (without later outside intervention) modified!

 

I believe either that engineer was mistaken or that you misunderstood what he'd said in respect to "electrical continuity" of the magnetic structure.

[Don Richard]

9 hours ago, glens said:

I believe either that engineer was mistaken or that you misunderstood what he'd said in respect to "electrical continuity" of the magnetic structure.

 

He said that alnico was a conductor of electricity and ferrite wasn't. That is an accurate statement.

[glens]

I don't have any reason to doubt it's an accurate (factual) statement.  I just fail to see the pertinence.  Like I said earlier, a central pole piece is undoubtedly as good a conductor of electricity as a central alnico magnet.