Hoping this is the right forum for this, because it seems to fall in between categories... plus the wealth of woofer knowledge here...
Given the immense amount of knowledge and experience I've seen in this thread, I think here is the best place to ask.
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In preparation for an upcoming OB project, I have a pair of 15" woofers that had trashed cones/coils when I acquired them, but are cosmetically pristine and have Huge alnico magnets and cast baskets...
They were not originally intended for OB use, and were of limited excursion capability.
It's NOT desirable to rebuild them to original specs...
Indeed replacement parts of that type are harder to get now, than more contemporary stuff anyway...
So, it's desirable to rebuild them in a way that will make them better suited for OB as a true woofer (up to ~75hz and down as low as possible).
The main question I have at this juncture is:
What degree of stiffness/compliance is desirable in replacement spiders, to make them suitable for OB... and why?
My understanding is that spiders are graded for stiffness alphabetically... from A to... not sure but I think F.
The original spiders are C rated.
I can go with the original C stiffness/compliance, or certainly at least one step in either direction... IE: B or D.. Perhaps even more choices but I haven't confirmed that so far.
No point in doing that till I know what and why..
I have purposely not mentioned exactly which vintage woofers these are, so as to not prejudice any potential replies for the time being..
I can and will if anyone thinks it matters....
I already have slightly heavier cones with a high-compliant rubber half-roll surround.
I'm not of the extremely high Q camp, as I prefer very detailed/articulate non "one note" bass.
I'll gladly trade off some db for that...
I should also mention, that I'm not after massive bass output that could compete with box-speaker bass..... since I now live in a small apartment where bass travels easily and neighbors complain.
Really, I just want to fill in below the LF cutoff of the "full-range" (wide-range/midrange) 8-incher.
TIA!!!
Greg
Given the immense amount of knowledge and experience I've seen in this thread, I think here is the best place to ask.
===============================================
In preparation for an upcoming OB project, I have a pair of 15" woofers that had trashed cones/coils when I acquired them, but are cosmetically pristine and have Huge alnico magnets and cast baskets...
They were not originally intended for OB use, and were of limited excursion capability.
It's NOT desirable to rebuild them to original specs...
Indeed replacement parts of that type are harder to get now, than more contemporary stuff anyway...
So, it's desirable to rebuild them in a way that will make them better suited for OB as a true woofer (up to ~75hz and down as low as possible).
The main question I have at this juncture is:
What degree of stiffness/compliance is desirable in replacement spiders, to make them suitable for OB... and why?
My understanding is that spiders are graded for stiffness alphabetically... from A to... not sure but I think F.
The original spiders are C rated.
I can go with the original C stiffness/compliance, or certainly at least one step in either direction... IE: B or D.. Perhaps even more choices but I haven't confirmed that so far.
No point in doing that till I know what and why..
I have purposely not mentioned exactly which vintage woofers these are, so as to not prejudice any potential replies for the time being..
I can and will if anyone thinks it matters....
I already have slightly heavier cones with a high-compliant rubber half-roll surround.
I'm not of the extremely high Q camp, as I prefer very detailed/articulate non "one note" bass.
I'll gladly trade off some db for that...
I should also mention, that I'm not after massive bass output that could compete with box-speaker bass..... since I now live in a small apartment where bass travels easily and neighbors complain.
Really, I just want to fill in below the LF cutoff of the "full-range" (wide-range/midrange) 8-incher.
TIA!!!
Greg
The total suspension compliance should be such that the woofer resonates near the bottom of its desired pass band. That will give maximum efficiency. A low mechanical damping will also help to increase efficiency, while a heavy cone reduces efficiency. An open baffle places close to zero air load on the cone (as compared to the forces due to cone acceleration), so a lightweight cone with a compliant suspension is totally fine.
Q of the woofer is not relevant, assuming you use EQ to shape the amplitude response to a desired target response. A [woofer + baffle + EQ] is a minimum phase system at low frequencies, so its impulse response can be calculated from its amplitude response, which is fixed as it is the target response.
Q of the woofer is not relevant, assuming you use EQ to shape the amplitude response to a desired target response. A [woofer + baffle + EQ] is a minimum phase system at low frequencies, so its impulse response can be calculated from its amplitude response, which is fixed as it is the target response.
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This is just the kind of knowledge I was hoping for!
So a "loose" (compliant) suspension tends to cause a lower resonance? Or do I have that reversed?
Would you consider 45 grams a lightweight cone?
(just the cone... not including surround/cap/etc)
This part, I need to think on for a while....
Thanks!
Exactly! Resonance frequency is 2*pi times the square root of (stiffness divided by moving mass), if using SI units.
I think so, most 15" woofers have a higher moving mass of > 100 grams.
Another point to optimize for is low harmonic distortion. A low suspension stiffness reduces harmonic distortion from suspension non-linearity, because the suspension does not contribute much to the forces acting on the cone. On the other hand it increases inductance related distortion, because more current has to flow through the voice coil. I don't know what effect is stronger. I would forget about harmonic distortion with vintage drivers.
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It is GREAT to know that formula! Thanks for that!
The whole moving-assembly is 135 grams...
Would that be considered on the lighter side?
Raises an interesting question... makes me wonder.
This is intended for use with a tube amp... so I'm not sure what that would mean regarding current flow...
Sorry I made a mistake, it is 1/(2*pi) * sqrt(k/m). Mechanical resonance - Wikipedia
I do not know whether 135 grams is light in the absolute sense. Compared to a few PA woofers it is average. It will be OK for your application.
Tube amps typically have a higher output impedance than solid state amps. A higher output impedance means that inductance related distortion is lessened, because the amplifier is closer to a current source (as opposed to a voltage source). With driven by a current source, the non-constant inductance of a voice coil does not influence the current flow any more, which is good. Le(x) and Le(i) are reduced: https://www.klippel.de/fileadmin/kl...rature/Papers/Klippel_Nonlinearity_Poster.pdf
I do not know whether 135 grams is light in the absolute sense. Compared to a few PA woofers it is average. It will be OK for your application.
Tube amps typically have a higher output impedance than solid state amps. A higher output impedance means that inductance related distortion is lessened, because the amplifier is closer to a current source (as opposed to a voltage source). With driven by a current source, the non-constant inductance of a voice coil does not influence the current flow any more, which is good. Le(x) and Le(i) are reduced: https://www.klippel.de/fileadmin/kl...rature/Papers/Klippel_Nonlinearity_Poster.pdf
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Maybe out of date by now, but shows what's possible: 15 inch woofers: which have low moving mass?
GM
GM
Thank you again for all the excellent information!!!!
And for the formula correction; I'll write it down..
Also for that PDF.... I'll study it when I have a moment..
All this knowledge is wonderful!
I seem to be in pretty good shape!
Particularly since the plan is to drive it with a tube amp..
Great reading... thanks for the links!
But a lot of reading.... particularly since the links have further links in them lol... haven't worked my way through it all yet...
There's also a lot of references to particular models I'm not familiar with...
Do you think you might summarize the conclusions?
I think the time has come to "let the cat out of the bag".. 
and state which woofer this is for:
It's the vintage University C15W..
It's a modification rebuild, not just a restoration to original specs (as stated in the OP)..
Huge Alnico magnet..... 15 pounds I've read...
Wondering how this affects the overall question?
Hoping to hear thoughts on this!
and state which woofer this is for:
It's the vintage University C15W..
It's a modification rebuild, not just a restoration to original specs (as stated in the OP)..
Huge Alnico magnet..... 15 pounds I've read...
Wondering how this affects the overall question?
Hoping to hear thoughts on this!
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