Metal Speaker Cone Design

Discussion in 'Amps and Cabs [BG]' started by zac2944, Apr 22, 2005.

  1. zac2944

    zac2944 Supporting Member

    Dec 28, 2004
    Rochester, NY
    I hope this isn't off topic, but I would like to learn about speaker driver design and could use some help getting started.

    I am a mechanical engineer by day and a bassist by night. I am interested in investigating the feasibility of creating a one piece metal speaker cone/dustcap/surrond using a process called electroforming. I know everything about electroforming, but nothing about speaker cone design. I have been able to find tons of info on box/enclosure design, but very little on the design of the actual driver.

    Any help would be greatly appreciated.

    P.S. If you're wondering what the hell electroforming is you can check out an explanation on my company's web site .
  2. zac2944

    zac2944 Supporting Member

    Dec 28, 2004
    Rochester, NY
  3. BassIan

    BassIan Supporting Member

    Apr 27, 2003
    Cupertino, California
    This sounds pretty interesting. As a studying mechanical engineer, I want to come in and say a few things.

    Firstly, what do you think would be the benefits of such a design? In terms of manufacturing ease, consider the costs of tooling to create multi-piece paper/fabric cones relative to those for creating an electroformed cone. In terms of sound, do you think you would be able to improve a certain characteristic of driver sound? Would you be able to control cone breakup accurately? Would your cones be lower in mass and higher in strength than current paper cones? You also need to consider perhaps the most difficult aspect of designs with metal: fatigue. For typical structures, load cycles are low-frequency. For a speaker driver, you're talking millions of cycles within perhaps a few minutes. To distribute the strain over such a small area as the surround would be nearly impossible. Acousound (search for this as a keyword on this forum and you'll find a thread with a link) has developed a spider for their subwoofer drivers made of thin laminated sheets of various metals. The spider is larger in area and still had to utilize some serious shaping to control strain evenly along the spider. So, the surround would be your biggest hurdle, clearly, since it would have to endure so many cycles and cannot utilize as significant an area of the speaker driver as even the spider.

    I guess the biggest question any product developer should ask is the following: "What am I trying to improve with my product?"
  4. Happy MurphDay

    Happy MurphDay

    Mar 9, 2004
    While a mass producer asks that question, a hobbist might also do it for the sheer satisfaction, how many people can build there own enclosure, a lot, and every one is happy that they made the cab, however, to make a working speaker would, IMHO, be the ultimate satisfaction.

    but yeah, BasIan, I totally agree with you too

    good luck!
  5. BassIan

    BassIan Supporting Member

    Apr 27, 2003
    Cupertino, California
    *If* the hobbyist has the machinery to produce electroformed metal this precisely in his garage, then I agree with you.

    I know I'd be doing silly amounts of CNC production out of my garage if I had the machinery for it. I'd certainly be studying friction stir welding and its automation for complex joints. :D

    As it were, I always like new ideas and I don't mean to shoot anything down. I just think that any potentially good idea deserves a good long thinking session and answers to many of the typical questions. :bassist:
  6. zac2944

    zac2944 Supporting Member

    Dec 28, 2004
    Rochester, NY

    I don't know enough about speaker design at this point to nail down goals. I just see something that hasn't been done, and could have potential. For instance, combining multiple components into one piece, improving/controling mass and stiffness peramiters. I hope to determine what goal could be realistic once I learn more about speaker design.

    I'm not considering cost at the moment because I'm not interested in volume manufacturing. I have all the necessary tools to create an electroformed cone. I have full access to a very advanced electrforming facility, as well as a CNC shop. It's what I do for a living.

    At this point I'm not concerned about improving the sound. I just don't know enough about speaker design at this point. I would like to get to that point if it looks feasible.

    The material I would be using is a proprietary NiCo alloy that my company developed. I do believe that it would indeed be higher in strength and stiffness and lower in mass than a paper cone.

    I think that I can deal with the fatigue issue. I design electroformed bellows for infinate fatigue under similar conditions. I have created my own design software and even have custom test equipment. This is one of the main reasons I think it is worth looking into.

    I'm just tinkering at this point, trying to find ideas and educate myself on speaker design.
  7. zac2944

    zac2944 Supporting Member

    Dec 28, 2004
    Rochester, NY
    BTW, great questions BassIAN.
  8. BassIan

    BassIan Supporting Member

    Apr 27, 2003
    Cupertino, California
    Well you're several steps ahead of the game then. :) It sounds like your next step then is to do some serious research on driver design, since clearly you have the tools and resources available to you.

    What's been happening mostly with drivers lately, at least that has been apparent to the public, is the development of stronger, more linear, and lighter magnetic structures using neodymium magnets. As a product of this, manufacturers have needed to be more aware of cooling the magnet/voice coil structure with cast aluminum frames and other heat-sinking measures (aluminum phase plugs as seen on some Eminence neodymium drivers).

    This Nickel/Cobalt alloy, if it is high-strength, and stiff, what is its modulus like? Will it endure infinite fatigue cycles? If this is what you used in the bellows you designed, then you are well on your way.

    If you are really serious about doing some development, you've come to the right place. There are many representatives from a variety of manufacturers here. I won't list names since I know I'll miss people, but you may be able to make some connections here that will help you.

    One idea I'm sure you've thought of is starting out by creating a "recone" for an existing driver. Using its existing frame, you could build a new cone, and perhaps voice coil/suspension structure for it to match/mimmick the old parameters.

    At any rate, keep us updated.
  9. fdeck

    fdeck Supporting Member Commercial User

    Mar 20, 2004
    Madison WI
    HPF Technology LLC
    Zac, one possible concern is that the Ni-Co is probably ferromagnetic. This would have to be considered in any design.

    Don't overlook the possibility of using this technology for tweeters.
  10. msquared


    Sep 19, 2004
    Kansas City
    A company called Velodyne was doing a full cone/dustcap driver that was one piece of metal back in the '90s. I'm not sure if they still do it or not but supposedly they sounded great (at the time).
  11. billfitzmaurice

    billfitzmaurice Commercial User

    Sep 15, 2004
    New Hampshire
    Owner, Bill Fitzmaurice Loudspeaker Design
    A cone/dustcap combination might not be an improvement. Most cone drivers purposely use a different density material for the dustcap to extend frequency response. Then there's the matter of assembling the driver. When the cone assembly is added to the motor structure a spacer is used to properly align the voice coil over the pole piece; after the adhesive has set the spacer is removed and then the dustcover is installed. A one piece cone/dustcover would not allow this, which would complicate the assembly process. You might want to touch base with someone at Eminence to see if they're interested in any event.
  12. zac2944

    zac2944 Supporting Member

    Dec 28, 2004
    Rochester, NY
    Since the Ni-Co alloy I would be using is an electrodeposited alloy, I have control over the composition of the alloy as well as other factors that will affect physical properties of the material. I can also a “sandwich” of multiple layers of different materials like copper and pure nickel. Heat treating can also be used to the change the properties of the material. I have used techniques like this along with proper design to develop bellows with infinite life. I believe that it might be possible to use the same techniques to develop a surround for the one piece design.

    I think that designing a re-cone would be a good place to start. I also like the idea of looking into tweeters.

    The Ni-Co alloy is slightly magnetic. Will this be a problem?

    I’m not too concerned with incorporating the dust cap at this point. I have read a little about the dampening effects that a dust cap can provide. I’m more interested in a one piece cone-surround design. If I can incorporate the dust cap too it would be a bonus.

    Before I contact anyone at Eminence, or any other professionals for that matter, I need to do my home work. I don’t want to waste anyone’s time asking questions that could be easily answered with a little research.

    Does anyone know of any good books that would address speaker design? I’d like to learn more about the physics behind that design, and test procedures for evaluating a design.
  13. Plain Old Me

    Plain Old Me

    Dec 14, 2004
    If it is magnetic, won't it go in/out further on part of the cycle? I'm no expert, but I think think that the magnetic property is going to be an obsticle.
  14. lhoward


    Apr 27, 2003
    Western NY State
    I think the magnetism of the cone/dustcap assembly could be a major obstacle. The two things that came to mind are:

    1) The field of the cone/dustcap will interact with the magnetic field generated by the magnetic field of the driver motor. One effect might be the cone being offset from what would normally be the rest position of cone assembly were it non-magnetic with no signal applied to the voice coil terminals. The possibility also of magnetic deformation of the cone/dustcap assembly raises additional questions for such concerns as cone linear motion, pistionic motion and maybe others.

    2) The other question is what happens when an electrical signal is input to the voice coil. The voice coil generates its own varying magnetic field from the input signal which inter-reacts with the field of the driver motor and causes motion of the cone. Does the magnetism of the cone assembly cause inter-reaction with its own moving assembly when a signal is applied to the voice coil terminals?

    Since a loudspeaker is basically a transformer of electrical energy to acoustic energy via magnetic interaction, it seems that one of the properties of the cone/dustcap/voice coil, or moving assembly, is that it be non-magnetic to prevent any interaction with the motor magnetic field and the varying field of the voice coil. Such interaction could introduce additional distortion and may discount the idea of using the NiCo alloy. There may be other concerns, but that's what struck me.

    It would interesting if there is anyone on Talkbass who is currently working or has engineering experience in the field of magnetics who'd like to comment? I don't consider myself an expert, just some thoughts and questions on this. Beyond the magnetic question and the comments of Bill Fitzmaurice, it sounds like a challenging project.
  15. Petebass


    Dec 22, 2002
    QLD Australia
    Some more things to consider. Firstly the dust cap. As Bill mentioned, it is not only a tweakable part of the speakers overall sound, in many cases it is often porus as well, allowing air to travel through it and help cool down the voice coil. I assume the a metal dust cap would'nt allow this. The alternative is a speaker which dispells hot air from around the voice coil via a vent in the middle of the magnet at the rear of the speaker. Your design may have to take this approach.

    Also I'm struggling to imagine a metal based surround. The word "stiffness" has been used a lot in this thread and I see that as a disadvantage for the design of the surround. As part of the suspension system it will have to have the ability to let the speaker move freely. I don't know anything about metal engineering or fabrication so if I'm of the mark with this one, let me know.

    Next point - recones! If I was getting a speaker reconed and someone offered me a new metal based option, my first question would be "How does this new proceedure affect the speakers T/S parameters?". the chances of the T/s parameters remaining unchanged are virtually nill. It may very well improve the speaker but if the cabinet is now wrong for it, the results could be disappointing. I'd concentrate on offering new drivers only.
  16. Passinwind

    Passinwind I Know Nothing Supporting Member

    I'm just tinkering at this point, trying to find ideas and educate myself on speaker design.

    Maybe you could pick up some good info from a few of the big dogs in reconing:,, and Waldom/Image Communications, who run a reconing school and franchise arrangement.
  17. zac2944

    zac2944 Supporting Member

    Dec 28, 2004
    Rochester, NY
    Thanks for the links. And thanks everyone for all the questions.

    I am quite concerned that the surrond will be too stiff. It's too early for me to say if this will be a problem or not. I know how to design metal bellows for desired spring rate, max displacement, and infinate fatigue life (with in a certain range of course). A souround and a bellows seem very simlar in function to me. Untill I find out things like necessary Xmax and spring rate for a "standard" surround I will not be sure.

    I plan on researching this idea through out the summer. If i reach any interesting milestones I will be sure to post the results.

    Thanks again for all the ideas.

    Any more sources for speaker design info would be awesome.

  18. Petebass


    Dec 22, 2002
    QLD Australia
    Try this!

    It's basically the part of the Eminence website that promotes their custom speaker business, the point of which is to let you design your own speaker with the help of Eminence technicians. In effect that's what youre doing, only outside the square. It'll give you a good idea of the parts of a speaker and how they interact.

    It's good to see people thinking up new ideas. Keep it up!