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Aluminum voice coils? Why?

Discussion in 'Sound Science' started by grapefruit, Apr 7, 2012.
  1. grapefruit
    I've recently been checking out some higher end cans and some (I can't remember which) contain aluminum voice coils.  This seems slightly strange, since aluminum is definitely not as good of a conductor as copper or silver, and given that the voice coil is designed to create and respond to a magnetic field, it seems like an aluminum voice coil would do a poorer job, even after considering its inherent lightness.  Is it used in conjunction with copper to create a more rigid and light voice coil?  or am I totally off?  This question's purely out of curiosity. 
     
  2. stv014
    Copper is a somewhat (~1.7x) better conductor than aluminum, but is much (~3.3x) heavier. So, the latter is a better choice overall, since minimizing the mass of the voice coil is important. Silver is not used for the same reason.
     
     
  3. Mauricio
    Right.  Al has as little as one third the mass of Cu, but retains two thirds of its conductivity.  You lose a little to gain a lot more.  What matters more is the conductivity-to-mass ratio, and on that score alone, Al is superior.
     
  4. grapefruit


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    Thanks guys that clears things up.  That's kinda cool, I never thought of aluminum as being used for electrical purposes other than heat sinks.  Just out of further curiousity is there a metal out there with a better conductivity/mass ratio than aluminum?
     
     
     
  5. Mauricio
    I don't know, but I would probably look to Beryllium.  Maybe you can get the data, figure it out and post the result here.
     
  6. Anaxilus


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    Beryllium must be made as an alloy otherwise it's carcinogenic.  Banned by the FIA in Formula 1.
     
     
     
  7. RexAeterna
    aluminum has far greater power handling. that's why it's used. lot of massive,expensive subwoofers uses dual to quad aluminum voice coils with a special alloy coating to prevent oxidation. sometimes it uses OFC coating on some speakers but i never seen much do so. aluminum also dissipates heat much faster so you can drive more power for longer times without the risk of melting or burning the voice coil. aluminum is as well as a conductor as copper can be, but it requires overall more power to reach the same given sensitivity of the speaker. they're usually more pain to drive due to them naturally being current gobblers.
     
  8. Mauricio
    Yes, Aluminum's thermal conductivity is also lower relative to copper and silver.  Beryllium is even lower.
     
    Some speakers use Beryllium tweeters so its use in audio equipment is not necessarily proscribed.  When saying something is carcinogenic, one must also specify the amount and route of ingestion.  Hard to ingest or inhale the wire in the speaker/headphone coil.  The temperatures and conditions in formula racing (e.g. fuel fire, collisions, shock/pressure from power tools) are hardly comparable to listening conditions in the home or studio.
     
  9. Anaxilus


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    Yes, Focal Utopia Be's. It's used for weight and stiffness.  Are you sure they are pure and not in alloy form?  Plus a rigid tweeter isn't what we are talking about, it's voice coils.  Focal doesn't use Beryllium in the voice coils despite making a tweeter w/ it.  That should tell you something. 
     
    I guess speakers don't blow do they? [​IMG]  Whether you feel good about having a carcinogen around you is irrelevant to whether a company would be interested in manufacturing the material and exposing it's workers and customers to it.  Plus exposing themselves to potential liability and environmental regulation.  Hardly comparable is it?
     
    I do believe it is particulate levels that are the issue btw, not slugs.
     
    http://www.elcosh.org/en/document/560/d000542/beryllium-fact-sheet.html?utm_source=adwords&utm_medium=adwords&utm_campaign=adwords&gclid=CLnYtJbmqq8CFQJ9hwodUy-jaQ
     
     
  10. Mauricio
    Let's see the progression of the issue.  I said that Be could perhaps have a better conductiviy-to-mass ratio.  To which you replied that Be is carcinogenic.  The fact is that, unlike F1 racing, Be or Be alloys are in fact already used in audio equipment sold and manufactured in countries with more or less stringent environmental and health standards (U.S. and France, for example).  Focal does it.
     
  11. Anaxilus


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    I don't think you read my post very closely and you are just parroting your first post.  
     
    Edit - Find someone who makes a Be voice-coil if you want to progress upon your point and remain topical to the thread.
     
     
  12. RexAeterna

    i think silver is not used cause it's much softer than copper and aluminum. since it's a better conductor it will heat up faster and i don't think silver can dissipate heat nearly as quick as copper and aluminum. that's why it's only used as a thermal paste or heatsink plate. while it will conduct the heat faster, the other metals(aluminum) say like the fins will dissipate the heat as quickly as it's been absorbed. i think silver has less of thermal threshold compared to copper and aluminum as well. i am not sure. never took chemistry before and only remember basic science and only know basic things when i use to work on computers in the past. actual silver as well is very expensive compared to copper so it is used in very little ways.
     
  13. DaBomb77766
    I'm pretty sure that copper is a far better thermal conductor than aluminum, and will dissipate the heat far faster, since it has a much lower specific heat capacity than aluminum.  However, it is very expensive in large quantities which is why it isn't used in heatsinks much, and it's also more difficult to manufacture into heatsinks.  Silver only has a slightly lower specific heat capacity and is yet again far more expensive, which is why, I guess, it isn't used much in applications which require high thermal dissipation and conductivity.
     
    But all things considered, I guess the number one limiting factor for the voice coil must be the weight of it, which is why they tend to use aluminum for them.  If conductivity were really such a concern then aluminum would hardly even be considered since it isn't a great conductor, and considering how anal retentive some audiophiles are over the absolute purity of their cables...
     
  14. Yoga Flame
    Aluminum can be anodized fairly easily too. Improves durability and heat dissipation by thermal radiation. Copper would eventually turn green under all that heat I suppose.
     
    Does all this apply to planars too? The HE-6 uses gold, I think.
     
     
  15. obobskivich

    Doesn't the Technics SB-10000 use Be in the actual CD stage? (I don't know this for certain, it's just the only speaker I'm aware of that uses Be and it doesn't use it as a cone/diaphram - they're rare enough that they might've well not ever been produced though). 
     
    Regarding conductivity in general, since someone asked:
    http://www.roger-russell.com/wire/wire.htm#silverwire There's an IACS table for you.
     
    That doesn't get into things like specific heat or density/mass though (for that we go here: http://en.wikipedia.org/wiki/Specific_heat#Table_of_specific_heat_capacities). And that's an important consideration, as explained in earlier posts. You can look all that up on a periodic table or Wikipedia if you're really curious. Aluminum is cheaper, lighter, and so on. Silver is a pain because it oxidizes and costs a fortune for minimal gains over copper (and again, it really does cost a lot). Copper is expensive and heavy by comparison (to Aluminum).  
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