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Thread: Diaphragm Damping Agents

  1. #1
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    Lightbulb Diaphragm Damping Agents

    Hello All,

    Hope all is well for you. I am interested in your experiences or thoughts around the idea of applying damping agents to compression driver diaphrams. Certainly Acquaplas is used and has been tried- anyone tried anything else? I do not have a specific project in mind, but I thought it might prove an interesting topic for discussion.

    I have known of some audiophiles that have applied vaseline (petroleum jelly) to Dynaudio dust caps. Not sure that is so clever with a plastic, but food for thought anyway. Something like a 3M spray adhesive, latex or gum might be OK and even peel straight off if you didn't like it ??? Any before and after damping application, frequency responses or better yet cumulative decay spectra.

    Of course this stuff will add some mass to the diaphragm, but probably no more than a few %.


    Thoughts,

    Best
    JA
    Have Fun - >>> Nessun Dorma - 12 years old <<<
    Best, Joe Alesi

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    Administrator Robh3606's Avatar
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    Hello Joe

    The only material I have tried is aquaplas. I took some before and after measurements using an 035Ti tweeter. Will be doing some after market 2425 diaphrams when I get a chance. You can try anything however with cost of these diaphrams you have to be careful what you put on. In case you have not seen this thread

    http://www.audioheritage.org/vbullet...t=14236&page=2


    Rob

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    Hi, Joe,

    If you think about it, you likely already know the answer to your question.

    Does the diaphragm(s) you have in mind perform as if it's underdamped (exhibits ringing)? If not, adding mass will create a problem instead of fixing one.

    It seems the instruction "if it moves, coat it" has been grossly misinterpreted by many.

    (Add/edit) The pot life of most viscoelastic damping compounds is 6 months...

  4. #4
    Administrator Robh3606's Avatar
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    "if it moves, coat it"
    More like if it's metal coat it. Although it seems JBL likes their cones well damped. The only metal domes that are not damped in some way are the compression driver domes. Tweeter domes have a foam pad. That said looking at the new JBL pro stuff if the tweeter dome is not fabric it's aquaplased.

    Rob

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    Administrator Mr. Widget's Avatar
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    Quote Originally Posted by Joe Alesi View Post
    I am interested in your experiences or thoughts around the idea of applying damping agents to compression driver diaphrams.

    I have known of some audiophiles that have applied vaseline (petroleum jelly) to Dynaudio dust caps.
    JBL has had very good results using aquaplas on their titanium, aluminum, and beryllium diaphragms... TAD doesn't seem to use anything on their 4001/4002 beryllium diaphragms, however on the lighter 4003 beryllium diaphragms they have a very light oil on the surface of the diaphragm. I doubt they are using this because they are unaware of aquaplas... as they use aquaplas or a similar product on some of their cone woofers.

    Quote Originally Posted by Robh3606 View Post
    You can try anything however with cost of these diaphrams you have to be careful what you put on.
    Absolutely!

    I personally wouldn't try anything... without far more knowledge and better test gear, any experimenting would be a simple trial and error crap shoot. I suppose duplicating what JBL does on their diaphragms is fine, but outside of that I wouldn't go messing around with random chemicals on other diaphragms.


    Widget

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    Quote Originally Posted by Robh3606 View Post
    Hello Joe

    The only material I have tried is aquaplas. I took some before and after measurements using an 035Ti tweeter. Will be doing some after market 2425 diaphrams when I get a chance. You can try anything however with cost of these diaphrams you have to be careful what you put on. In case you have not seen this thread

    http://www.audioheritage.org/vbullet...t=14236&page=2


    Rob
    Thanks for that Rob, I am interested to see the before and after curves, but the link doesn't work for me-it say report it to the administrator- so I've got the right guy.

    Best
    JA
    Have Fun - >>> Nessun Dorma - 12 years old <<<
    Best, Joe Alesi

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    Quote Originally Posted by moldyoldy View Post
    Hi, Joe,

    Does the diaphragm(s) you have in mind perform as if it's underdamped (exhibits ringing)? If not, adding mass will create a problem instead of fixing one.
    Haven't decided to use it on a particular driver yet, really just wanted to stimulate discussion on possible damping agents. Come to think of it maybe some aftermarket(can I say that here? ) 2425 diaphragms I have may benefit from something.

    Thanks & Best
    JA
    Have Fun - >>> Nessun Dorma - 12 years old <<<
    Best, Joe Alesi

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    Quote Originally Posted by Mr. Widget View Post
    JBL has had very good results using aquaplas on their titanium, aluminum, and beryllium diaphragms... TAD doesn't seem to use anything on their 4001/4002 beryllium diaphragms, however on the lighter 4003 beryllium diaphragms they have a very light oil on the surface of the diaphragm. I doubt they are using this because they are unaware of aquaplas... as they use aquaplas or a similar product on some of their cone woofers.
    Hello Mr W,

    Interesting- The light oil on the TAD sounds like a similar treatment to the dynaudio dust cap vaseline treatment.

    Thanks and Best
    JA
    Have Fun - >>> Nessun Dorma - 12 years old <<<
    Best, Joe Alesi

  9. #9
    pocketchange
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    If petro jelly is used, maybe LPS 3 would be useful.
    pc

  10. #10
    Senior Member Steve Schell's Avatar
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    Damping compounds such as Aquaplas are apparently applied to help tame misbehavior in the metal diaphragm. This may work to an extent, but I think a better approach is to begin with a better behaved diaphragm material. Composite diaphragms made from phenolic and cloth work great; they sound very clean and open, and lack the high frequency breakups typical of many metal diaphragms. Problem is that most phenolic diaphragms lack high frequencies altogether, having been designed rather thick and heavy for high power applications. If one finds a driver with a reasonably light composite diaphragm, it may provide just the sound one has been hoping for.

  11. #11
    Administrator Mr. Widget's Avatar
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    Quote Originally Posted by Steve Schell View Post
    Damping compounds such as Aquaplas are apparently applied to help tame misbehavior in the metal diaphragm. This may work to an extent, but I think a better approach is to begin with a better behaved diaphragm material.
    I agree... that said, the approach I prefer is to use bandwidth limiting... i.e. don't try to make a two-way out of a driver exhibiting break-up. With care, adding the tweeter allows you to preserve the clarity and detail of the lower frequencies and if the tweeter does exhibit break-up it will only piss off the neighbor's dog or the unfortunate bat who flies by.


    Widget

  12. #12
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    Quote Originally Posted by Robh3606 View Post
    More like if it's metal coat it.
    The original statement was "If it's metal, coat it." It was later changed to "If it moves, coat it."

    I need to stop posting these kinds of things.

  13. #13
    vince
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    Hi guys, interesting question, like some of you, I'd be dubitative about applying something on the diaph itself (mostly because I don't know what I will want out of it...because for ringing problems I solved that simply in modifying my crossover ,ringing came , in my case, from fs around 500hz when I used a crossover that underdamped the system...) some resistors divider, put in a certain way(cf Pi crossover from Wayne' website) helped much in that way...althought I was convinced that it was only a diaphragm issue...(and it is of course , but can be solved many other way, electronically I mean...)
    I'll be glad anyway to have inputs on what could be done to that diaph...but I also wonder if anyone tried modifying the damping material beside the diaph, in theory the rear charge of the diaph should be in adequation with the front(horn), did anyone tried to modify it? or damping it differently? for sure it has an influence on the cone motion, any input?
    Vince

  14. #14
    pocketchange
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    Cool for consideration ....

    per diaphgram(s) and info from outside reading, notice was given concerning improved material and processing technique. Heat treating the typical material prior to forming the diaphragm. I have not noted anything added. Since [Al] in whatever spec is the choice for most diaphragm material, I'm wondering if there is a process after the stress generated in the forming of the diaphragm?

    NOTE: I know nothing on how diaphragms are produced ...

    There has been a great deal of headway made in post production processing including heat treatment of material(s) other than ferrous and non ferrous metal.
    I'm talking stress relief here if there is any confusion.
    pc

  15. #15
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    Quote Originally Posted by pocketchange View Post
    There has been a great deal of headway made in post production processing including heat treatment of material(s) other than ferrous and non ferrous metal.
    I'm talking stress relief here if there is any confusion.
    pc
    Hello Pocketcahnge,

    Yes I could easily imagine a stress relieving processes like annealing or heat soaking being used. Although, if the orginal forming process created any assymetrical residual stresses in the diaphragm, the relief of such stresses can result in a distorted part.

    Come to think of it the diaphragm isn't all that deep compared to its diameter- It may even be formed and just let be.

    Best
    JA
    Have Fun - >>> Nessun Dorma - 12 years old <<<
    Best, Joe Alesi

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