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Neodymium heat question

Discussion in 'Amps and Cabs [BG]' started by Eric Moesle, Sep 10, 2004.


  1. Eric Moesle

    Eric Moesle Supporting Member

    Sep 21, 2001
    Columbus OH
    I'm seriously considering switching over to all-neodymium cabs for the convenience factor alone. I'm aware that neo's have heat issues, namely that the magnets will lose strength if they get overheated to a certain extent.

    The problem is that I don't understand how much heat a typical speaker sees when it is driven hard with lots of power, for example: two 4x10 cabs driven loudly when getting about 1500 watts each. How hot do they get inside, and if I run them hard on a large stage at that wattage, will neo's approach the kind of heat that will damage them? Are neo's better suited for people who don't stress their gear at high volume and wattages?
     
  2. Yes, Neo is subjective to DBOH (death by over heating).

    Other drivers are subject to death by various causes, all of which are severe. Used with adult supervision, Neo drivers should last just as long as any other driver.

    Neo drivers come in all sizes and flavors. Some are better suited than others for specific bass needs.
     
  3. slinkp

    slinkp

    Aug 29, 2003
    brooklyn, NY, USA
    otoh, if a magnet loses strength, a recone can't fix it - you'd have to replace the magnet, and I don't know if it's possible to do that short of buying a whole new speaker.
     
  4. B String

    B String Supporting Member

    Apr 11, 2002
    Los Angeles
    I'm not quite sure how to take some of this information.
    Nick Epifani has assured me that "heat aging" is simply
    not an issue in the top end boxes, using the newest
    designs. Are epifani and euphonic audio just plain lying
    to us to get our money? I may be very gulable here, but
    I believe what these top manufacturers are telling me.
    Is there someone who really has a definitive answer here?
     
  5. McHack

    McHack

    Jul 29, 2003
    Central Ohio!
    Being a cab n00b, I gotta say,, this thread is kinda freaking me out... I understand electronics to a certain degree. It makes perfect sense that drivers heat up when pushed hard. After all, that's what fries voice coils.

    But, if I'm perceiving this right & I may not be, it sounds like these Neo Driver'd cabs, may be rated at a certain power handling capacity, but still the neo drivers may not tolerate heat that well,, & are subject to damage, anyway?
     
  6. inazone

    inazone

    Apr 20, 2003
    Colorado
    Ive tought about this as well. Other top cab people have said there will be problems down the road with neo drivers. Dont know what to think.
     
  7. Eric Moesle

    Eric Moesle Supporting Member

    Sep 21, 2001
    Columbus OH
    There's no question that voice coils heat up. But can they heat up SO MUCH that the heat would transfer to the magnet, and even COME REMOTELY CLOSE to the temperature where the neo's would lost strength? What kind of temp are we looking at here?
     
  8. McHack

    McHack

    Jul 29, 2003
    Central Ohio!
    Is it the assumption that Neodymium drivers are more prone to this weakening, than traditional drivers?
     
  9. Tim__x

    Tim__x

    Aug 13, 2002
    Alberta, Canada
    Lee Valley Tools reccomends using them below 150ºC.
    I have no idea how hot they actualy get in a speaker cabinet.

    Edit: Yes, according to Lee Valley standard AlNiCo magnets can be safely used at up to 550ºC.
     
  10. The Neodymium magnets (Neodymium-iron-boron, NdFeB) magnets are quite interesting. They have a much higher energy density than typical ferrite (barium or strontium) however the trade off is that the Curie temperature is at about 370C rather than 730C for the ferrite magnets. The Curie temperature has to do with how the magnetic properties of a material change with temperature. At the Curie temperature the magnetic domains achieve a random orientation; thus the material will no longer exhibit a macroscopic magnetic field. That is it is no longer a permanent magnet. Obviously ferrite is better suited to high temperature applications.

    This isn't the only thing of interest to temperature and magnets. It is also important how the magnet will change as it is heated and cooled. As all permanent magnets are heated they loose their strength to some degree. The magnetic domains begin to point more and more in random directions as the temperature increases. What is important is how much magnetic field strength is lost and how much will return as it is cooled back to room temperature. Ferrite magnets are quite good in this respect, they will pretty much return to normal for heats up to 450C. Neodymium is not quite as good in this respect. A poor quality Neodymium magnet could irreversibly lose up to 5% of its strength if heated to 80C. A good quality one could go up to about 200C before this happened. Typically, the better the heat resistance of the Neodymium magnets, the lower the magnetic field strength achievable.

    I'm not too sure how hot the magnets are getting inside a speaker cabinets from the voice coil, etc.

    I would say that it is certainly conceivable that the "Neo" drivers being used today by Epifani and EA, etc have no heat aging occuring. The only way to tell for sure would be to get one of the cabs, fire it up and hook a thermocouple up to the magnet inside the cabinet. Then you'd need to know what the quality of the "neo" magnets is that is going into the cabs. Neodymium magnets are not really that expensive anymore and I imagine that there are some pretty good quality ones going into these cabs.

    -Geoff
     
  11. Here is an example of how strong these magnets are for anyone who hasn't played with Nd magnets before. These ones are about 1/4" x 3/4" x 3/4" and they can hold themselves up when separated by about 3 inches. If you get one finger between them it is painful. That 6" one I posted would probably crush your hand off (seriously, I can't even imagine how hard two of those things would come together).

    -Geoff
     
  12. McHack

    McHack

    Jul 29, 2003
    Central Ohio!
    I'm envisioning some serious heat sinks attached to the backs of the magnet structures, to help dissapate excessive heat.
     
  13. Squidfinger

    Squidfinger I wish I could sing like Rick Danko.

    Jan 7, 2004
    Shreveport LA
    Fascinating stuff Geoff.


    Interesting thread too. I'm planning on buying a GK NEO 2X12 cab in the future and this has given me something to chew on.


    Do cabs heat up more as they're pushed closer to their rating or is it uniform?


    ie---->Does a 12" NEO sub rated at 100W running at 100W heat up more than a 12" Neo sub rated at 200W running at 100w? :confused:
     
  14. McHack

    McHack

    Jul 29, 2003
    Central Ohio!
    I could be wrong, BUT, seems to me that the more current you push, the more heat will be generated... Regardless of what type of driver. That's why I'm scratching my head... Seems there might be a ceiling as to how much power these Neo drivers could handle... potentially.

    Maybe that's an really high number, but still... As Geoff pointed it, that temperature is alot more attainable on a Neo driver than a traditional ferrite driver.

    I think this also explains why were only seeing Neo driver cabs trickle into the market place, rather than them flooding it.
     
  15. B String

    B String Supporting Member

    Apr 11, 2002
    Los Angeles
    Epifani says, the more power, the better. Is it possible that
    some of these high end speaker box guys have spent enough
    time with specs and testing to say that heat is not a problem
    with their boxes? Again, i'm just having a problem with.....
    are these companies bald face lying to us to make a buck,
    or are they telling us the truth about their products?
    Some of us have spent alot of money to lighten our load.
    It would be a shame to have it all to turn to crap in a few
    years.
     
  16. Jerrold Tiers

    Jerrold Tiers

    Nov 14, 2003
    St Louis
    It is perfectly possible and normal for the voice coils themselves to get to 150 deg C, or higher.

    You can count on the vast majority of the power entering a speaker to be dissipated as heat. Speakers are only a few percent efficient.

    If you assumed that a speaker was 5% efficient (that is a high efficiency), and that it actually converted 5% of the input power into sound, that would leave 95% lost as heat. All of that loss is in the voice coil, for practical purposes.

    Therefore, a 200 watt speaker of 5% efficiency, presented with 200 watts input power, will have to dissipate 190 watts of power.

    A resistor capable of about 200 watts of dissipation is typically made of high temperature material. A usual construction is of ceramic and special wire. It is common for such a resistor to be large, perhaps 40mm diameter and 100 to 200mm long. Even so, it usually gets very hot.

    A speaker voice coil weighs about 100 times less than a 200W resistor. It is merely a coil of wire wound on a special lightweight tube of high temperature plastic or special paper. Nomex is common, which is also used in fireproof clothing for race car drivers. Sometimes coated metal is used.

    Obviously it cannot handle the 190 watts of power on its own. It would quickly overheat, and so must have a heat sink.

    The magnet structure is the main heat sink for the voice coil. Even coils wound on metal must have heatsinking to the magnet structure.

    Heat passes across the narrow gap between the voice coil and the pole pieces, by radiation.

    It seems that this would be inadequate, but it is effective enough to work. The problem is, there must be a difference of temperature for heat to move from the coil to the magnet structure. So the coil gets rather hot, even if the magnet is cooler.

    With neo, the overall magnet structure is smaller and lighter. Heat capacity is less, and dissipation capability is less. So it will get hotter than a traditional ferrite magnet structure. And, it will get hot faster, because it has less mass.

    Unfortunately, this is the wrong direction. Neo must be kept cooler.

    With the voice coil reaching 150 deg C or more, it is not unreasonable to expect the small magnet structure to easily reach the 80 deg C area, and perhaps more. You may need to use better grade, higher priced neo to withstand that. You may need to add cooling fins and some thermal mass to avoid "spiking" the temperature too high over short term high power inputs.

    There is the "neo problem". The small, light, powerful magnet is great, but it often requires additional cost, weight and volume for high power performance.

    By the time you are done, using better neo magnets, cooling fins, etc, the weight and cost of adequate power handling has a hard time competing against plain old ferrite magnets. Performance may even be better in some cases with the ceramic.

    Neo can still be good, I am not blasting it universally. But it isn't the obvious no-brainer "better " material that it often is touted to be.

    We've used it, but we are no longer using it for some products. For those products, we got better performance with more conventional speakers, with a very small and acceptable penalty in weight. We may use neo again, it just depends on what the tradeoffs are.
     
  17. How do they mean? Better sound? Better cooling of the magnet?

    -Geoff
     
  18. Ozzyman

    Ozzyman

    Jul 21, 2004
    Can the voice coil be seperated from the magnet by like maybe a ceramic wall (ceramic heats VERY slowly) to stop heat dissipating into the magnet?
     
  19. B String

    B String Supporting Member

    Apr 11, 2002
    Los Angeles
    Everyone i've spoken with, as well as the company say that
    the more power you have, the better the epifani boxes
    sound. When i used a woods ultra with a 112UL, the louder
    it went, the better it sounded. Its almost wierd in that i've
    never used a box so small that sounded better the more it
    was pushed. If it means anything, i had the same experience
    with the regular epi 112. They both sound very similar.

    Ampeg insider. Can you bottom line it for me? Are these
    other companies full of crap and being dishonest. or are
    they honestly able to say "heat aging" is not a problem
    with their products??