Forced air cooling subwoofer driver?

So I've been dabbling with the idea after hearing a sound system recently that definitely used forced air cooling within their subwoofer drivers. So I'm used b&c tbw100 drivers and they have ventilated voice coils, I found an old post regarding cooling drivers using a copper/aluminium plug machines to fit tightly into the pole piece which is something I'm curious about. But also would it be possible to duct air into the drivers around the voice coil to help shift some of the heat actively out in order to lower power compression and push the drivers a little harder. In the keystone cabinets I'm using your limited to 750w aes of the total 1500w, so figured with some active cooling I might be able to eek a little more out of the cabinets!
 
Quite possibly, there was talk on another forum about it though it depends on which direction you sent air in, if you ducted it via cone side via the vent holes on the backside of the magnet then it might not be so bad, going in from the back of the magnet vent on the other hand would put pressure on the dust cap and change the ts parameters maybe? I just figure a combination of this and essentially heatsinking the pole piece would help to some extent!

Having heard and read about rc1's subwoofers it definitely works and allows them to push their drivers wide open. I know John was saying more than anything he was running out of power on a 32 amp supply with 4 cabs running crest ca18's. For context, you couldn't swallow your drink due to the excessive bass at the event
 
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Sounds interesting, always wondered about high power subwoofers temperature, even more in the case of sealed ones
Wouldn't the turbulence of the air moved by the sub driver break the fan in a short time?
How much power we will need to send to a driver to start thinking about forced cooling?
Is not like we are running 2000W sinewaves for hours
 
Well I know mine have over heated several times, voice coils can hit over 200degrees pretty rapidly in certain conditions at war volumes. Depending on the cabinet it can be a lot lower than you think hence why I'm interested in this! There are various cabinets including those by void that run heatsinks on the sealed chambers that are not coupled to the drivers but must have some effect in order to help reduce heat build up. I can't see why a combination of pole mounted heatsinks and a high volume air pump feeding small tubes into the voice coil wouldn't make a significant difference.
 
Thanks for the link, I had some of the information there but nothing quite as full featured as that! So forced air cooling of the gap looks like a solid no but creating the plug and machining a heatsink up is definitely within the realms of my abilities!
 
The fundamental problem (or challenge) is that the voice coil is surrounded by air, and that is the medium via and thru which you must cool a hot piece of metal via conduction or radiation. Air is a relatively poor conductor of heat. One possibility is to increase the temperature difference between the hot VC and nearby parts by using cold air or other fluid. Cold air tends to also be wet which could be a problem, but for example, if you could bleed a liquid nitrogen tank through the gap you would be using a very, very cold fluid that would also cool all the other motor parts at the same time. Not cheap or very practical, but it would definitely work. Sublimated CO2 could also work in this way but is not nearly as cold as LN2!
 
The fundamental problem (or challenge) is that the voice coil is surrounded by air, and that is the medium via and thru which you must cool a hot piece of metal via conduction or radiation. Air is a relatively poor conductor of heat.
Static air? Sure!

But this is not static by any means.
Air between VC and pole piece and gap walls is incredibly turbulent, so it conducts heat away very well.
Fane measured that in the late 60s early 70s and found it was equivalent to "solid silver" 😲
Their words in a Wireless World article.


VC heat goes to the magnetic structure which is the heat sink coupled to it, that's why magnetic structures become unbearably hot at high power, also why speakers have different power rating whether in a sealed or an open back cabinet.
Only EV mentions that in their brochures.
Also why finned heatsinks are attached to magnet structures.

A perforated polepiece allows some hot air to exit the enclosure under high internal pressure.

FWIW all my MI speakers have a lathe turned perforated polepiece, every bit helps..

Not sure a copper plug will prove cooling, I'd rather leave that hole open.
A through and through hole, of course..

Some JBL woofers have axial slots milled into polepieces.
 
Another reason why I hate sealed enclosures.
When designing an enclosure, the back of driver should be mounted at least the distance equal to the voicecoil vent diameter from the back wall of the enclosure. I try to design my BP4 or FLH enclosures with driver's basket in the vented chamber of the enclosure. I've never blown a driver in a BP enclosure, but blown drivers in sealed enclosures.
 
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Thanks for the link, I had some of the information there but nothing quite as full featured as that! So forced air cooling of the gap looks like a solid no but creating the plug and machining a heatsink up is definitely within the realms of my abilities!
Wayne made the vent plugs for LAB 12s used in small sealed chambers to get the pole piece heat out of the box.

1) The driver's vents in the Keystone are within a few centimeters of open air.
2) The (~24year old) LAB12 design lacks vent holes around it's 2.5" (63.5mm) voice coil, it's cooling is not nearly as effective as the 100mm (4") B&C TBW100.
Screen Shot 2024-05-31 at 4.03.23 PM.png


3) Adding heat sinks to the TBW100 magnet structure could reduce it's heat, but a plug in it's center vent probably won't.
 
Yes, I remember heat pipe technology it works well in a passive way

Heat pipe on wikipedia

Due to the very high heat transfer coefficients for boiling and condensation, heat pipes are highly effective thermal conductors. The effective thermal conductivity varies with heat pipe length and can approach 100 kW/(m⋅K) for long heat pipes, in comparison with approximately 0.4 kW/(m⋅K) for copper.[2]
 
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The eminence kilomax PRO 18A has some sort of heat sink mounted onto the front pole piece, to help get heat away from the motor assembly.
https://eminence.com/products/kilomax_pro_18a#description

I've worked on a few Nexo speakers and the woofer for the PS15 has an air flow restrictor plate fitted to the rear basket vent to make the air flow more turbulent, which increases heat transfer, though I imagine it would make the driver more noisier.
https://www.fullcompass.com/prod/149244-yamaha-n1560p-8-woofer-for-ps15u-and-nexo-b1-alpha
 
Adding a "buck" magnet of neodyme on the back plate increases the efficiency of the driver without increasing heat. You can easy increase efficiency with 3 dB.
And that is a lot less heat that has to be dissipated from the voice coil. The extra magnet will also contribute to a slightly larger heat dissipation surface as well.
There is also paint Pyromark 2500 that can be used to increase the heat radiation from a surface that can be painted on the basket and magnet assembly.