Has anybody here tried to drill a venting hole through the pole piece of a larger driver?
A few of my drivers need to have the surrounds replaced if I am going to re-use them in a new project and if it was worthwhile doing it could be done then.
However does having ventilation holes at the base of the cone mean that centre venting the pole piece is not needed?
During the re-foaming process are there any other modifications that people may have done that are both effective and not to expensive?
Wooden phase plugs etc.
Such modifications may or may not be done as the drivers are acceptable in the current form and funds may not become available.
A few of my drivers need to have the surrounds replaced if I am going to re-use them in a new project and if it was worthwhile doing it could be done then.
However does having ventilation holes at the base of the cone mean that centre venting the pole piece is not needed?
During the re-foaming process are there any other modifications that people may have done that are both effective and not to expensive?
Wooden phase plugs etc.
Such modifications may or may not be done as the drivers are acceptable in the current form and funds may not become available.
Sincerelly I didn't but you can destroy it definitivelly if some particles of the metal goes into the magnetic gap. Thought about this point.
I did that, but with tweeters: SEAS tweeter pole piece drilling
If you can remove magnet or voice coil it might work similarly with woofers. I would not drill the assembled speaker from behind, that will get iron particles into the magnet gap.
If you can remove magnet or voice coil it might work similarly with woofers. I would not drill the assembled speaker from behind, that will get iron particles into the magnet gap.
I have watched the video where the magnetic gap was filled with bluetack and than taped over, if I was to drill out I thought that would be the technique to use.
The drivers have a tapped hole centered on the pole piece to take a protective plastic shroud so finding the centre-line wouldn't be a problem
The drivers have a tapped hole centered on the pole piece to take a protective plastic shroud so finding the centre-line wouldn't be a problem
As mentioned above, possible but very dangerous and doable only on a disassembled speaker (moving parts removed) so you can tightly tape over the magnetic gap, wich WILL collect all kinds of magnetic debris over tape, which then are glued/taped over so you guarantee removal down to the last bit.
You can not do that with voice coil present in the gap then stays exposed.
You can not do that with voice coil present in the gap then stays exposed.
That is understood and what probably makes this sort of project worth asking questions about.
Is cone venting equal to pole piece venting as far as reducing heat and compression effects?
There are 4 equally spaced ~4mm diametre holes set at the top of the voicecoil, that's only about half the area of a 6mm hole in a pole piece, I can only assume that as I think the driver performs reasonably well that the designers did their work correctly
Thought experiments and dumb questions mean that costly mistakes can be avoided
Is cone venting equal to pole piece venting as far as reducing heat and compression effects?
There are 4 equally spaced ~4mm diametre holes set at the top of the voicecoil, that's only about half the area of a 6mm hole in a pole piece, I can only assume that as I think the driver performs reasonably well that the designers did their work correctly
Thought experiments and dumb questions mean that costly mistakes can be avoided
There was an old article (think late 60's early 70's) by Fane where they measured voice coil temperature rise.
One thing they found is that, counter intuitively, most VC dissipation (heat transmission was from VC to top plate and polepice.
But ...but ... you have at least 0.15 mm space (so air layer) both inside and outside!!!
And air is a TERRIBLE heat conductor!!!!
TRUE.
But that´s STATIC air.
They discovered (of course measured) that **turbulent** air had way better heat conductivity, and turbulent it becomes so by VC movement.
They discovered that under those circunstances, "air conductivity became as good as solid silver" 😱 which was nothing short of amazing, and stuck to my mind ever since.
How did they measure voice coil Rth? (thermal resistance):
* Power dissipated was easily measurable.
* polepiece and top plate temperature was measurable: just drill a couple small holes on each, near the gap, and insert thermocouples there.
* the problem to be solved was to accurately measure VC temperature, and in real time.
Easier said than done, huh?
Just quoting from my feeble memory stuff read 50 years ago:
* they discovered that at certain frequency, typically between 250Hz and 400Hz, speaker phase shift was zero, meaning it *behaved* like a pure resistance, what certainly makes things easier.
* so they could use a Wheatstone bridge to accurately measure VC resistance.
Impedance you mean? IT´s a speaker!!!!
No, no, resistance, at a *single* critical frequency speaker behaves as a pure resistance. Go figure.
There is also another frequency at which VC does the same, which is DC conditions, but of course this trivial solution is useless for us.
Back to that very clever Fane test:
* knowing copper voice coil resistance increase relative to 20C and its temperature coefficient we know it temperature, real time,and with precision.
* knowing Power + Temperature differential relative to pole piece and plate, we have Rth, again with precision.
* in fact, they had designed that experiment to find TRUE VC/Speaker RMS power handling, with no need for destructive tests (increase power until speaker self destroys), they simply increased power drive until VC almost reached self destruct temperature, typically by adhesive of former thermal failure.
Pretty clever these Fane chaps.
FWIW they were the first to produce a true 100W RMS speaker; they also invented the fiberglass voice coil former in the process.
One thing they found is that, counter intuitively, most VC dissipation (heat transmission was from VC to top plate and polepice.
But ...but ... you have at least 0.15 mm space (so air layer) both inside and outside!!!
And air is a TERRIBLE heat conductor!!!!
TRUE.
But that´s STATIC air.
They discovered (of course measured) that **turbulent** air had way better heat conductivity, and turbulent it becomes so by VC movement.
They discovered that under those circunstances, "air conductivity became as good as solid silver" 😱 which was nothing short of amazing, and stuck to my mind ever since.
How did they measure voice coil Rth? (thermal resistance):
* Power dissipated was easily measurable.
* polepiece and top plate temperature was measurable: just drill a couple small holes on each, near the gap, and insert thermocouples there.
* the problem to be solved was to accurately measure VC temperature, and in real time.
Easier said than done, huh?
Just quoting from my feeble memory stuff read 50 years ago:
* they discovered that at certain frequency, typically between 250Hz and 400Hz, speaker phase shift was zero, meaning it *behaved* like a pure resistance, what certainly makes things easier.
* so they could use a Wheatstone bridge to accurately measure VC resistance.
Impedance you mean? IT´s a speaker!!!!
No, no, resistance, at a *single* critical frequency speaker behaves as a pure resistance. Go figure.
There is also another frequency at which VC does the same, which is DC conditions, but of course this trivial solution is useless for us.
Back to that very clever Fane test:
* knowing copper voice coil resistance increase relative to 20C and its temperature coefficient we know it temperature, real time,and with precision.
* knowing Power + Temperature differential relative to pole piece and plate, we have Rth, again with precision.
* in fact, they had designed that experiment to find TRUE VC/Speaker RMS power handling, with no need for destructive tests (increase power until speaker self destroys), they simply increased power drive until VC almost reached self destruct temperature, typically by adhesive of former thermal failure.
Pretty clever these Fane chaps.
FWIW they were the first to produce a true 100W RMS speaker; they also invented the fiberglass voice coil former in the process.
Are you suggesting that VC cooling via pole piece vent holes and/or vent holes in the cone are not needed??
Good news if so but why then is such a design feature heavily pushed when describing a drivers use.
Good news if so but why then is such a design feature heavily pushed when describing a drivers use.
as far as I remember having read, having no pole piece hole or similar increases the cooling effect of air circulating around the voice coil.
pole piece hole or ventilating holes of voice coil former/cone affect thiele small parameters and eventually reduce turbulence induced distortion/noise, afaik.
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