I have started my search for 18” sub drivers for my future basement system. I’m looking at all kinds of drivers from BMS, B&C, Beyma, Faital, Fane and Eminence. Sensitivity and low Fs is imperative. Same with die cast frames. But what about magnets? Are there any real benefit to a neo type other than weight/space? To me weight is a plus so should I just ignore all neo types due to the fact it seems only to increase price? Or are there sound quality benefits as well, alternatively if the price increase is because the whole motor is better, not just the more expensive material. What about life cycle perspectives and environmental foot print? Ferrite seems to be durable and made of common compounds and recyclable but what about neos?
As an example I’m compering the following Beyma drivers and I really see no benefit off going neo for home use:
18LEX1600FE: 97dB Fs 34 Hz
18LEX1600ND: 96dB Fs 33 Hz
These are probably way out of price range anyway but I’m just interested in discussing neo magnets for subs in general before I narrow down my search. I understand neo magnets have higher flux pr kg/cm3 but are neo speakers therefore “better”?
As an example I’m compering the following Beyma drivers and I really see no benefit off going neo for home use:
18LEX1600FE: 97dB Fs 34 Hz
18LEX1600ND: 96dB Fs 33 Hz
These are probably way out of price range anyway but I’m just interested in discussing neo magnets for subs in general before I narrow down my search. I understand neo magnets have higher flux pr kg/cm3 but are neo speakers therefore “better”?
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If weight is a plus to you you may as well ignore neodymium.
Neither neodymium or ferrite/ceramic slab magnets are readily recyclable in the usual consumer streams.
For portable use, neodymium is "better" in terms of really high flux density potential when using very large voice coils that would require so much ferrite/ceramic material that the structure would not be road-worthy, increasing original shipping/packaging costs as well as any subsequent transportation and storage costs.
Neither neodymium or ferrite/ceramic slab magnets are readily recyclable in the usual consumer streams.
For portable use, neodymium is "better" in terms of really high flux density potential when using very large voice coils that would require so much ferrite/ceramic material that the structure would not be road-worthy, increasing original shipping/packaging costs as well as any subsequent transportation and storage costs.
It is a lot easier to saturate the iron near the gap with a Nd magnet than it is with a ferrite magnet. If the iron is saturated, its magnetization can no longer be modulated by the field of the voice coil. You can forego a shorting ring or copper sleeve which is what many Nd motors do, e.g. the 12M revelator. When there is a ferrite and a Nd version of the same driver, sometimes only the ferrite version will have a shorting ring.
Next thing, a ferrite magnet has Barkhausen domains
Barkhausen effect - Wikipedia
Nd magnets are said not to exhibit this effect, maybe because they retain their magnetization better.
That being said, it is also possible to design a poor motor with Nd. As a general trend from distortion tests in HobbyHifi magazine, Hifi compass and Audioexpress, Nd motors do not systematically exhibit lower distortion. One of the best motors today, Purifi, uses a ferrite magnet and plenty of copper shielding.
Next thing, a ferrite magnet has Barkhausen domains
Barkhausen effect - Wikipedia
Nd magnets are said not to exhibit this effect, maybe because they retain their magnetization better.
That being said, it is also possible to design a poor motor with Nd. As a general trend from distortion tests in HobbyHifi magazine, Hifi compass and Audioexpress, Nd motors do not systematically exhibit lower distortion. One of the best motors today, Purifi, uses a ferrite magnet and plenty of copper shielding.
That has more to do with marketing, than anything else.
Adding proper demodulation rings to a design costs close to nothing.
Same goes for progressive spiders and all these other nice things.
Unfortunately I think we will never get the best price-performance ratio because of this.
In general, use whatever you want if weight is not a main constraint.
Just look at all those tests out there and find what fits best in your specific project.
If that is Nd than it's Nd, if that is Ferrite, also fine.
From a manufacturer point of view, not using Nd is pure a price point thing, or just saving money on the design.
Even the main PA brands have now Nd all over, without heavily failing (because of heat etc)
The shorting rings themselves may cost next to nothing, but even if they only sit below and above the actual gap, it still means tighter mechanical tolerances because the coil has to run exactly parallel to the gap in order not to rub on the rings. And a sleeve means a trade-off between loss of field strength or very tight tolerances.
That really depends I think.
There are plenty of demodulation constructions out there that don't require a lot of tight tolerances.
Otherwise, if there is so much rocking going on, one has much bigger issues. Even with just a simple straight pole plate.
From a practical point of view, I have seen plenty of manufactures putting in demodulation rings in 3 inch and sometimes even 2 inch drivers without any issues. Even for extremely affordable drivers.
So it doesn't seem to be an excuse these days anymore.
neodymium production seems to be problematic regarding enviromental impact:
"the manufacture of neodymium magnets, particularly the mining phase of the material, is incredibly energy-intensive"
(Neodymium – Anthony Kuntz – A blog on materials, energy, and the environment for CMU 99-238)
"Mining interests clash with native populations at those sites, due to release of radioactive substances during the mining process"
(Neodymium - Wikipedia)
The October 2021 issue of voice coil magazine (free subscription) discusses woofer magnet tech. Nd magnet recycling isn't quite there yet but is expected to be an important source of magnets in the future. If weight is a plus just go with ceramic magnets as only the very largest woofers need Nd magnets.