If you are really interested in modifying these drivers then
There are two ways of going about it - 1) Modify the drivers 2) Make new drivers
1) Drivers Modify
Prior opening the drivers for modify - test x max at your power listing level and temperature rise of the pole piece over about 4 to 6 hours
A - Open up the drivers
B- Demagnetize the motor structure
C- Undercut the pole piece - these drivers concentrating on mid production are not even sfg , machine them to get an undercut sfg pole
D- Fix and inductance stabilising ring under the undercut
E - Fit a copper cup shorting the top plate and the Pole piece
F- Plate or laminate the pole piece with copper
G- Voice coil - Increase the length of the voice coil to your measured x-max (when ure driver was in use) bose s coils are very short
Voice coil - to maintain 0.9 ohms draw silver wire and have it insulated
I - Voice coil material - highest quality craft paper
F - Choose latest generation hi quality (fabric) spider
G - If you found the pole heating up in your temperature measurements
J - Make cooling holes on the voice coil former , under the dust cap & on the back plate around the pole
K - Basically there should not be any cavities
L - Assemble back driver
Actually bose making a killing selling these units should have at least done a few of the above - but then profit margins will be down , you cannot source from China (can name the supplier ...)
2) Make your own driver
Under-hung voice coil (type) design incorporating all of the above
suranjan dasgupta
There are two ways of going about it - 1) Modify the drivers 2) Make new drivers
1) Drivers Modify
Prior opening the drivers for modify - test x max at your power listing level and temperature rise of the pole piece over about 4 to 6 hours
A - Open up the drivers
B- Demagnetize the motor structure
C- Undercut the pole piece - these drivers concentrating on mid production are not even sfg , machine them to get an undercut sfg pole
D- Fix and inductance stabilising ring under the undercut
E - Fit a copper cup shorting the top plate and the Pole piece
F- Plate or laminate the pole piece with copper
G- Voice coil - Increase the length of the voice coil to your measured x-max (when ure driver was in use) bose s coils are very short
Voice coil - to maintain 0.9 ohms draw silver wire and have it insulated
I - Voice coil material - highest quality craft paper
F - Choose latest generation hi quality (fabric) spider
G - If you found the pole heating up in your temperature measurements
J - Make cooling holes on the voice coil former , under the dust cap & on the back plate around the pole
K - Basically there should not be any cavities
L - Assemble back driver
Actually bose making a killing selling these units should have at least done a few of the above - but then profit margins will be down , you cannot source from China (can name the supplier ...)
2) Make your own driver
Under-hung voice coil (type) design incorporating all of the above
suranjan dasgupta
Sorry, but what mean "SFG"?
Interesting advice.
But modifying the driver by this way, we'll get something completely different. A driver, with different characteristics and sound. The use of the EQ will be controversial question. The size of speaker chambers too.
Interesting advice.
But modifying the driver by this way, we'll get something completely different. A driver, with different characteristics and sound. The use of the EQ will be controversial question. The size of speaker chambers too.
SFG - Symmetrical Field Geometry - when the magnetic field acting on a voice coil is not symmetrical , the top half & bottom half of a sine wave will be distorted (not be the same)
I have not advised to go for neo mag structure , ive advised on using the same magnet and magnet pole piece ms plates with various corrections (machining & fitting of copper rings etc) which bose should have done in the first place when attempting to make a high end driver .
The cone & body is same - the magnet motor structure , the spider if well selected will not change the ts parameters at all much
the same cab can be easily retained - with better performance from increased x max and cooling
well for the st.... equalizer , less i speak the better
take care
suranjan
I have not advised to go for neo mag structure , ive advised on using the same magnet and magnet pole piece ms plates with various corrections (machining & fitting of copper rings etc) which bose should have done in the first place when attempting to make a high end driver .
The cone & body is same - the magnet motor structure , the spider if well selected will not change the ts parameters at all much
the same cab can be easily retained - with better performance from increased x max and cooling
well for the st.... equalizer , less i speak the better
take care
suranjan
Good luck getting a driver apart without destroying it. Good luck getting a magnet seperated from the plates without destroying it.
David S.
I admit it is not that simple - but no modification is
You will need an impulse de-magnetiser , or you will have to go to a local driver manufacturer and use theirs (and pay them for demagnetizing & magnetizing again after the mods)
after you having the motor structure demagnetized , attach the photos here i or others here can advise you on how to go about opening the top & bottom plates (this part is easy getting hold of a magnet charger capable of demagnetizing is a bit difficult).
suranjan
You will need an impulse de-magnetiser , or you will have to go to a local driver manufacturer and use theirs (and pay them for demagnetizing & magnetizing again after the mods)
after you having the motor structure demagnetized , attach the photos here i or others here can advise you on how to go about opening the top & bottom plates (this part is easy getting hold of a magnet charger capable of demagnetizing is a bit difficult).
suranjan
Thanks Suranjan,
If the magnetic field and position of the voice coil are not symmetrical, it is not a good new. Are You sure in it, did You check it for this drivers?
But if we increase the length of the voice coil, what about the sensitivity? Isn't decrease? Don't You think, to increase the length of center pole is better and easier?
Adding a copper cup is good for killing Foucault currents.
In some cases removing the dust cap is for better. What do You think about? And testing to add a center phase-thumb, of course with correct high and shape. This all are easy steps, which we may try.
And I think, the better place to debate this is the neighbours discussion about Bose 901 Modifications: http://www.diyaudio.com/forums/full-range/137079-bose-901-modifications.html
And also, Bose 901 are not high end drivers 🙂
If the magnetic field and position of the voice coil are not symmetrical, it is not a good new. Are You sure in it, did You check it for this drivers?
But if we increase the length of the voice coil, what about the sensitivity? Isn't decrease? Don't You think, to increase the length of center pole is better and easier?
Adding a copper cup is good for killing Foucault currents.
In some cases removing the dust cap is for better. What do You think about? And testing to add a center phase-thumb, of course with correct high and shape. This all are easy steps, which we may try.
And I think, the better place to debate this is the neighbours discussion about Bose 901 Modifications: http://www.diyaudio.com/forums/full-range/137079-bose-901-modifications.html
And also, Bose 901 are not high end drivers 🙂
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bama. bama...
They don't need to, they were pretty impressive in small (closed) venues in the 70's.😉 You should compare their age with size and quality PA for the above mentioned.😉 Now it's not fair to say that, just for the intrinsic value of them or the value for a vintage audiophile classic.
I am sure the pole piece is a regular T yoke ,
regarding sensitivity , playing distortion free loud pure performance is far more precious than a little bit more power requirement to drive the speakers
suranjan
regarding sensitivity , playing distortion free loud pure performance is far more precious than a little bit more power requirement to drive the speakers
suranjan
Check out the screen name & city for post #389 on another forum discussing the 901 magazine review. Could it be that Bryston? Also, an employee of Bose posted there too (scroll up a bit to 386).
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