It all depends what variables you change, also I was talking about drivers with relatively large Xmax. For short coil drivers the optimum diameter will be larger than for long-coil ones because the coil weighs less, for example the best 8" mid driver I know off (RCF MR8N301) has a 3" coil with tiny inductance and weight in an 8" driver.
If the smaller-diameter long coil drivers have more layers and/or turns (which is often the case) then they will have higher inductance. With the same number of layers and turns the bigger diameter coil will have more inductance, and will be heavier for the same Xmax. But this is more in theory, in practice the picture is usually differnent.
Bigger coil drivers usually also have higher power handling and heavier coils, also often longer Xmax because the top plate can be made thicker and the coil longer. The modern trend is towards bigger coil higher Xmax drivers with higher Pe, higher BL and heavier cones but often less efficiency; there are few drivers nowadays like the B&C 18PS76 which had a 3" coil on an 18" driver and was higher efficiency in a reflex than any of the newer drivers.
And the other point is that for all these reasons (and other things being equal) bigger coil drivers tend to cost more...
tricky
I thought high inductance was equal to a 'strong' drive
but from what you say, only because the designer have 'compensated' with equally bigger magnets
this is completely new to me
and interesting could you explain further ?
could this be one reason why Faital is 'reviving' ferrite designs, despite being neo design experts
PrecisionDevices's neo designs also appear to go obsolete very fast
tricky
I thought high inductance was equal to a 'strong' drive
but from what you say, only because the designer have 'compensated' with equally bigger magnets
this is completely new to me
could you explain further ?
Inductance (Le) isn't directly linked to "drive strength" (BL), you can have drivers with high BL and relatively low Le and vice versa.
Usually high BL and low Le means a driver with a big magnet and a larger diameter coil (expensive). Cheaper subwoofer drivers often use smaller coils (and magnets) with more turns (to get BL back up) and end up with high inductance as a consequence.
I could give you all the equations but you probably don't want me to
Faital (and everyone else) are reviving ferrite magnets because China has cornered the world supply of neodymium and has put the price up by about 400% in the last year.
This is really bad news for the new "uber-drivers" (B&C, 18Sound, Faital...) which have all been using neo magnets to get enough flux for these big diameter tall high-power voicecoils -- you don't want to know how big and heavy the equivalent ferrite magnet would be for a driver like the B&C 21SW152...
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sounds like you are 'linked' to the industry, since you have this huge insight ?
well, I don't know, but from looking at the ferrite Faital drivers, this new situation with neo magnet issues(price/delivery) seems like a 'strike of luck' to them
btw, my older mentor once asked me if there would be any reason why many preferred the sound of ferrite drivers, over neo drivers
but a very long time ago, and could have been 'early designs'
or all sorts of other reasons, along with the ones you mention
I guess some are just better designers than others
well, I don't know, but from looking at the ferrite Faital drivers, this new situation with neo magnet issues(price/delivery) seems like a 'strike of luck' to them
btw, my older mentor once asked me if there would be any reason why many preferred the sound of ferrite drivers, over neo drivers
but a very long time ago, and could have been 'early designs'
or all sorts of other reasons, along with the ones you mention
I guess some are just better designers than others
sounds like you are 'linked' to the industry, since you have this huge insight ?
well, I don't know, but from looking at the ferrite Faital drivers, this new situation with neo magnet issues(price/delivery) seems like a 'strike of luck' to them
btw, my older mentor once asked me if there would be any reason why many preferred the sound of ferrite drivers, over neo drivers
but a very long time ago, and could have been 'early designs'
or all sorts of other reasons, along with the ones you mention
I guess some are just better designers than others
The massive cost increase for neo is well known in the industry. The problem is that all of the new big-coil "super-drivers" are neo partly because an exactly equivalent ferrite driver typically weigh twice as much (much bigger top/bottom plates as well as magnet):
Precision Devices PDN.2151=16kg, PD.2150=32kg
Ciare 12.00SWDC-NdW=5.5kg, 12.00SW=11kg
(the new Faital ferrite drivers are lower-spec more "normal" drivers, not "super" ones -- same with 18Sound and B&C)
So here are a few guesses for ferrite "super-driver" weights:
18NLW9600 12.5kg ==> 25kg
18SW115 12kg ==> 24kg
21SW152 18.5kg ==> 37kg
Not easy to handle or mount, or to stop them breaking the cabinet (or the driver) if you drop it.
-- the TC Sounds LMS Ultra 5400 is an example of a ferrite "super-driver", it weighs 39kg and has crushed many fingers...
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