Driver ratings

I have bought a pair of unbranded drivers, the guy I bought them from told me they are rated at 600 watts. I have put them in some cabs and tested them for a short time with a C-mark 2650, 1 cab per channel. They sounded fine and there was no sign of clipping from the amp.

How can I test, to be sure, what the exact rating is before I start using them for long periods of time?

Keep turning them up a bit at a time and when they blow that was too much.

But in reality stick a photo up on here and see if anyone can recognise them.

Tony

Thats the way I didnt want to find out!

Bit of a long shot with the photo's, look like pretty standard cheap jobbies.

s18.postimage.org/8u3o91eu1/DSCF9172.jpg

s14.postimage.org/n1fj4lxwh/DSCF9173.jpg

Thanks.

I doubt there 600W continuous, the magnet is too small. But they'll probably handle peaks of 600W.

Based on very quick look, looks like 2.5" voice coil so i wouldn't feed more than 400W continuous power into these drivers. It's not about the magnet size how much power driver can take, it's down to voice coil size and cooling for it.

where is most of the heat dissapted? In the magnet.... Bigger magnet cooler voice coil.

No no. Before ferrite magnet gets even warm, voice coil could be melting. Cooling comes from the plate set at the air gap and from possible shorting rings. Also the airflow around the voice coil and through the pole piece creates cooling, but big magnet lump which isn't even close to voice coil will not have any meaningful effect in cooling.

Most heat is dissipated directly in the voice coil, into surrounding air. Situation is slightly different in compression drivers are designed to use ferrofluid.

Yep 200-300 absolute tops I would have said.

I also completely agree with Pasi about he voice coil doing most of the heat transfer itself.
Thermal transfer is so slow across the magnet assembly that this has no appreciable effect on the cooling of the motor, airflow will be the principle cooling agent. However on longish gigs the whole enclosure can heat up to such an extent that even this method of cooling is severely compromised.

I remember putting my hand on the top of a Hog* bass bin after a 5 hr bash and being really surprised at just how hot the wood had become, lord only knows what the peak temperature of the voice coil had been.

Tony

* Magnet assembly is very close to the top

So how do you explain mounting heat sinks to the magnet? Just look at most of the Neo drivers... The air flow is pushed out of the back of the driver through the magnet assembly acting as a heatsink, look at the beyma 15G450 for instance they have drilled 4 extra holes through the magnet assembly to aid with cooling.

Heatsinks at neo motors are there for two reasons. They look cool and they keep temperatures for Neodymium under control as it is much more temperature sensitive than ferrite material is. AlNiCo or Samarium magnets would have the best stability over the temperature changes but they have their own drawbacks which is why they are not really used in Pro Audio drives.

Purpose of those holes in the back plate and the big one in pole piece is to allow venting through the back plate and maximize the air circulation around the voice coil. They also serve on purpose to have equal pressure for cone movement in both directions. If that hole in the pole piece wouldn't exist, it would cause lot of pressure for behind the dust cap to build up in the driver and cause distortion and non linear cone movement. Air gap where voice coil is, isn't large enough to allow that much air to flow through it without restricting it.

Of course the plate set and magnet gets warm over the time as the voice coil heats them up, but as such, they are not (especially the magnet itself) a significant method of cooling the voice coil. Only the bit of top plate and pole piece are, which create the air gap. + any shorting rings close to voice coil. But majority of the cooling is done with air and that is why size of the magnet is irrelevant for cooling.