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"The floating cone driver"

Discussion in 'Speakers, Headphones and Room Acoustics' started by oivavoi, Jan 10, 2018.

  1. Thomas savage

    Thomas savage Moderator Moderator Patreon Donor The Watchman

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    I’d rather celebrate good engineering than give publicity to what some might call bad engineering practice ( in the way suggested, obviously we highlight bad practice when we find it in the testing). Being smart folk you will know that having a forum like this slag off a brand ( like say Wilson) really only reinforces the audiophools misconceptions and intrenches their way of thinking with more resolve than ever before.

    Let’s be positive and celebrate go looking for the good and the great , celebrate that.
     
  2. Cosmik

    Cosmik Major Contributor

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    Could you expand on that a little?
     
  3. DonH56

    DonH56 Major Contributor Patreon Donor Technical Expert

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    I had forgotten about that CR case. I did not hear (of) Bose 901's until the mid-70's or so, but CR's review matched my impressions (not a given; I am very mixed on CR reviews in general despite getting the magazines for decades).

    I am not sure the forum can be sued for comments made by its members (not in the time or two it has been tried previously on forums I have been involved with) but individual members could be. At least that's how it went down in a case years ago.
     
  4. sergeauckland

    sergeauckland Member

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    Thanks for the reply. Do you know of any papers that have analysed this effect? I'm not interested so much in what happens to drivers when brand new, but I'm very interested in an stiction when a driver is well past any break-in period. Similarly, I'm very interested if the same effect can be attributed to microphones, and are dynamic microphones any better or worse than condenser mics?

    S.
     
  5. svart-hvitt

    svart-hvitt Senior Member

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    Wayne,

    As I have no theoretical or practical background in speaker design I need to parrot other designers.

    Here’s a good example of a discussion of active vs passive, by AES Fellow John Watkinson:

    https://www.thebroadcastbridge.com/...echnology-part-8-crossover-networks?cat_id=63

    I see no valid argument for passive speakers, except for higher cost. I’d be happy to be corrected, though, if people can make a valid argument for passive.
     
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  6. Frank Dernie

    Frank Dernie Senior Member

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    Where does this stiction come from? There are no rubbing parts in a non-broken conventinal driver from which stiction could possibly originate.
    Since pretty well all cone suspensions are polymers their stiffness will be temperature dependant and batch dependant, +/- 10% is good manufacturing.
    Stiction? Nah.
     
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  7. DonH56

    DonH56 Major Contributor Patreon Donor Technical Expert

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    There is hysteresis in most inductors but I am not sure how much stiction there is from the surround and spyder. I am not sure how it would come about; stiction in say car tires comes about from well-known physics (static friction coefficient is larger than dynamic) but I do not know if the same sort of thing applies to a surround (and/or spydr) assembly. Not my field.

    Dynamic microphones are essentially small speakers in reverse, whilst condenser mics use a charged membrane more akin to an ESL. Ribbon mics use, well, ribbons! Condenser mics tend to be more sensitive than dynamics and generally are not as rugged. They tend to have wider frequency response but other things influence that as well. Not sure there is stiction in any of them.
     
  8. Frank Dernie

    Frank Dernie Senior Member

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    Stiction is caused by rubbing. It causes the moving parts of a dynamic system not to necessarily always return to the same static position due to the point where the returning force of the spring is no longer greater than the friction force doesn't always happen at the same point.
     
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  9. fas42

    fas42 Major Contributor

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    Unfortunately, I can't point to specific papers - it's generally thrown in to refer to the fact that suspensions do not behave in a linear manner, for a variety of reasons. Just Googling, found these two efforts:

    https://www.klippel.de/fileadmin/klippel/Files/Know_How/Literature/Papers/Aging of loudspeaker suspension_Klippel.pdf

    http://www.woofertester.com/getcode/wtpro/wtpro_userguide.pdf

    The first discusses changes in suspension behaviour, without mentioning stiction. The second specifically relates the term to the fact that TS parameters are variable, depending upon how the driver is driven.

    Personal experience made me aware that something was going on. And then came upon discussions that mentioned the term, and connected the dots. At one stage I used a test signal, designed for acoustics testing, on repeat for warming up a driver - subjectively, one hears certain characteristics when listening to this - and over the period of an hour there were very clear changes in the perception of this repeated pattern.
     
  10. fas42

    fas42 Major Contributor

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    Remember a suspension also means the spider, and if you examine the latter they do not have a homogeneous structure, sometimes having a woven characteristic. Any non-uniformity could easily mean non-linearity effects, etc.
     
    Last edited: Jan 13, 2018
  11. fas42

    fas42 Major Contributor

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    In another discussion of speaker behaviours, http://greenmountainaudio.com/speaker-math-and-physics/, the relevance is noted:
     
  12. RayDunzl

    RayDunzl Major Contributor Central Scrutinizer

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    Blow a tone at the driver in-air.

    Observe the output voltage at the speaker leads.

    Stiction will show up there if it exists.
     
  13. sergeauckland

    sergeauckland Member

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    That's the essence of my question, stiction, or limiting friction I understand. Is there any comparable mechanism in a polymer suspension? I'm not asking about non-linearity, more is there a minimum force required to start a cone moving at all? I've never seen any scientific papers on this.
    S
     
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  14. Wombat

    Wombat Senior Member

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    As the cone and assembly is a mechanical system there will be stiction. As Ray notes it can be measured.

    I think that audiophile overthinking is more of an issue re this characteristic than audible effect on loudspeaker performance. Happy to be proved wrong.
     
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  15. fas42

    fas42 Major Contributor

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    I noted that speakers using conventional drivers always altered over time, depending upon what source material and volumes were used - of course, not so easy to distinguish the precise cause in a system context. A simple expression to describe this is "that one can hear deeper into the mix" - one reason I take no notice of how a rig comes across when it first starts playing; the lack of depth and flatness of sound is not an indicator of potential.
     
  16. jhaider

    jhaider Member

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    Nor is spiderless new. NEAR has long eschewed a spider for a ferrofluid bath of sorts.

    NEAR is now part of Bogen and doing outdoor speakers, but they were a boutique home brand.

    I've heard of two new-tech drivers recently that look more interesting to me than this one.

    The first is a subwoofer driver from Pioneer that they've termed HVT. The patent is discussed in this month's Voice Coil. To summarize, it's basically a scissor jack with diaphragms on one or two sides.

    The only current use I know of is in an inexpensive shallow subwoofer.

    The second one is a pulsating column out of Hungary. Here are two patents:
    https://patents.justia.com/patent/20140321692
    https://patents.justia.com/patent/20140321692
     
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  17. Wombat

    Wombat Senior Member

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    Re the Bogen video: Until now I haven't seen any 'golden-ears' complaining about spider distortion. This could be about to change. ;)
     
  18. Frank Dernie

    Frank Dernie Senior Member

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    Stiction is a non-proportional non-linearity.
    Polymer suspensions will be non linear, but not very non-linear. They may have more damping than ideal.
    They do not have stiction.
    I think the only thing we are disagreeing about is the meaning of the word. Stiction, from my experience in vibration research, is the word used to describe sticking between motor and stator parts due to friction. There won't be any in a loudspeaker which isn't damaged. There is always some in an automotove damper, for example, because of the seals.
    There are plenty of other non-linearities in moving coil drivers due to magnetic circuit design (few older bass drivers have linear motor systems, it seems). Modern computer methods for looking at magnetic circuits have shone a bright light on these shortcomings. An efficient linear bass driver motor system for high level sound is very difficult to design and make and very, very expensive because of the big displacements.
    Linear motors and suspensions are much easier for tweeters and mid units. They have other difficulties :)
    The biggest shortcoming of cone drive units is breakup in the working frequency band. Pistonic drivers are made but have big resonances which, to be never excited, must be very cleverly engineered into a speaker system.
    Paper drivers are not very good at being pistonic, but they aren't too hideous when resonating, so are the most idiot-proof to use.
    This is certainly true. Pretty well all polymers change their mechanical properties with time, temperature and environment, meaning neither their stiffness nor damping will stay constant with age. Older edge solutions like corrugating the paper and doped corrugated fabric will change with use and run in but probably age much more gracefully than foam or rubber.
     
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