Something like this then (Ceramic 8 to the left, NdFeB42 to the right:
Looking at the simulations there's an even flux density for 15 mm, so with a voice coil of 10 mm it's 2.5 mm Xmax.
So 2 mm for 300 W is on the safe side then.
I think your design is by far better than my attempts with pole pieces.
A gap of 4 mm resulting an a 1 mm clearance is an easier task to accomplish.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
Looking at the simulations there's an even flux density for 15 mm, so with a voice coil of 10 mm it's 2.5 mm Xmax.
So 2 mm for 300 W is on the safe side then.
I think your design is by far better than my attempts with pole pieces.
A gap of 4 mm resulting an a 1 mm clearance is an easier task to accomplish.
Iam using ferrite magnets like these
and I have enough to be able to have a double magnet instead of a single all the way, but I read somewhere that it only would give 1 db
But I am well pleased with the sensitivity that is now and do not think it is the work and money worth switching to neo.
and I have enough to be able to have a double magnet instead of a single all the way, but I read somewhere that it only would give 1 db
But I am well pleased with the sensitivity that is now and do not think it is the work and money worth switching to neo.
I totally agree!
I'm a little puzzled though that you need 300 W for a 93 dB sensitivity Rubanoid when playing really loud.
That would mean that you are listening at more 117 dB at 1 meter and 111 dB at your sweet-spot if it is at 4 meters. 🎧
By the way, the formula to calculate the relation between two magnet's strengths is really simple.
Just take the square root of the division of the MGOe numbers.
For example, the square root of 42/8 is 2.9.
I'm a little puzzled though that you need 300 W for a 93 dB sensitivity Rubanoid when playing really loud.
That would mean that you are listening at more 117 dB at 1 meter and 111 dB at your sweet-spot if it is at 4 meters. 🎧
By the way, the formula to calculate the relation between two magnet's strengths is really simple.
Just take the square root of the division of the MGOe numbers.
For example, the square root of 42/8 is 2.9.
Late answer 
I´am not listening at 300 watt input, its just to try to se how the voicecoil and membrane was acting and to see how much the speakers could handle.
A guess would be under 50 watt when i am listening.
Another thing is; have anybody tried to use Aramid/Kevlar as membrane and voice coil ?
Heres a link, but its to a Danish site
Aramid vaev 61 g/m2 (Aero, plain) 100 cm godkendt til luftfart
Its a bit expensive but if it is good, so
I $ its about 52 $ for a m2
I´am not listening at 300 watt input, its just to try to se how the voicecoil and membrane was acting and to see how much the speakers could handle.
A guess would be under 50 watt when i am listening.
Another thing is; have anybody tried to use Aramid/Kevlar as membrane and voice coil ?
Heres a link, but its to a Danish site
Aramid vaev 61 g/m2 (Aero, plain) 100 cm godkendt til luftfart
Its a bit expensive but if it is good, so
I $ its about 52 $ for a m2
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