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Speaker Foam

Discussion in 'Electronic Design' started by Mark, Mar 15, 2013.

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  1. Mark

    Mark Guest

    I have four infinity speakers.
    they all need new foam (maybe).
    infinity say they have no replacement speakers (what?) and offered no
    repair kits.
    i do have a few local places that refoam but have not called for prices
    yet.
    the speakers still sound fine to me except when there is some low
    frequency music that cause the speakers to rattle.

    1) what is the purpose of the foam? dirt? rattle?
    2) how do I measure the speaker to buy a foam kit?
    speaker diameter? cone diameter? what?
    3) if I can live with it, does it further damage the speakers without
    the foam?
    4) what destroys the foam?

    If i just want to replace the speakers, what is recommended. Mine are
    9 inches outside diameter so should be easy to find replacements.
    Want good enough sound not expensive.
     
  2. Bill Sloman

    Bill Sloman Guest

    As far as I know, it prevents the compression and rarefaction of the
    air within the speaker from making the air marginally hotter or colder
    - the foam doesn't have much thermal mass, but it has quite a bit more
    than the air itself. There's also an element of damping, which may be
    what you are missing, though the "rattle" may be the speaker cone
    running into the end of the hole in the foam that it has dug for
    itself over the years.
    It's suppposed to fill the internal volume of the speaker cabinet The
    outside dimensions of the cabinet are probably what you want.
    I'd be surprised if it did any serious damage. The "rattle" sounds
    ominous, but the foam isn't stiff, and having the speaker cone slam
    into what's left of it probably isn't going to break anything.
    Oxidation? Insects? Maybe the components weren't properly mixed in the
    first place and you always had patches of duff foam within the cabinet
    that broke up more rapidly than thye should have done.
    How deep is your pocket? And how golden are your ears? Manufacturers
    like KEF have always had a good reputation, and everything they sell
    is good, but you are paying about 50% extra for that reputation. You
    need to go to one of the audio groups to get this kind of advice, but
    many of them are dominated by the golden-eared boys who think that
    valve amplifiers are better than transistor-based amplifiers because
    they like a bit of third harmonic distortion, so any advice you get
    has to be taken with a large grain of salt.

    If Phil Alison posts a response to this post, take his advice
    seriously. He's famously irritable, but knows more about audio than
    anybody else who posts here regularly - much more than I do.
     
  3. Gib Bogle

    Gib Bogle Guest

    A quick google will tell you all you need to know (and more).
    E.g. http://www.audionote.co.uk/downloads/speaker_foam_replace.pdf

    "(Material) for loudspeaker suspension is compressed foam, it is evenly
    compliant across a wide range of movement and affect the sound of the
    driver far less than rubber and other less perishable materials, so it
    is an unavoidable part of a quality loudspeaker, it only down side is
    that, depending on environment and climate, it will perish and start
    hardening after 8 – 12 years."

    The surround has multiple functions - maintaining cone alignment is one.
     
  4. gregz

    gregz Guest

    The outer foam band seals the inner/outer enclosure. It also is part of the
    mechanical assembly which plays a role in the Q of the speaker. It also
    helps keep the cone centered.
    Some drivers are different. I would look into model number replacements.

    They either rot, or dry out and crack. Or just break down over time. With
    good foam you can manipulate it with your finger without tearing it apart.
    too many variables. Boxes are designed to work with the drivers parameters.

    You can search Internet for model number foam replacements. There are sites
    that specialize in foam replacements or others that also include selling
    them
    If you screw up, your screwed.

    Greg
     
  5. gregz

    gregz Guest

    I don't think he is talking about interior foam. Foam usually not used,
    mostly because it's expensive, and depending on enclosure type, polyester,
    might be better. I often use foam myself, again depending on the situation.
    Interior foam does not break up as fast as driver foam. Also, sometimes
    rubber is the replacement outer flexor. As long as it does not change the
    driver parameters.

    Greg
     
  6. gregz

    gregz Guest

    Foam breaks down the fastest from what I've seen. I try to avoid foam
    drivers.
    When switching surround types, you can get unexpected results for another
    reason. The surround is part of the cone surface. It radiates. Sometimes
    the surround phase will cause peaks or mulls in the centerline response.
    Foam and folded paper or hardened cloth will radiate upper frequencies
    better. Rubber does not couple well at higher freqs. If the woofer is not
    used at upper freqs., it's not going to be an issue. Another good old
    surround type was treated cloth, which except for the drying out or flow of
    the gook, lasted a very long time. Many still going good.

    Greg
     
  7. You can get Foam replacements online, jus match your speaker size.
    FYI, I've replaced the foam on my drivers and used Elmers Rubber cement.
    It will hold up well, and also allows you to do it over if your
    alignment is off.
    The voice coil should move freely. I did the foam replacement over 5
    years ago and it's still sticking.

    Cheers
     
  8. gregz

    gregz Guest

    Good to hear. The usual glue is the flexible form of white glue, a
    copolymer, such as Air flex 400 . I once got a gallon of it. Regular white
    glue is a mono polymer.

    Greg
     
  9. gregz

    gregz Guest

    I thought wrong. stiff glue is homopolymer. ! Not monopolymer.

    Greg
     
  10. Phil Allison

    Phil Allison Guest

    "Bill Sloman"
    As far as I know, it prevents the compression and rarefaction of the
    air within the speaker from making the air marginally hotter or colder
    - the foam doesn't have much thermal mass,

    ** The OP is asking about annular foam surrounds for his woofers.

    They famously perish and need to be replaced.


    If Phil Alison posts a response to this post, take his advice
    seriously. He's famously irritable, but knows more about audio than
    anybody else who posts here regularly - much more than I do.


    ** Nice of you to say so.

    BTW:

    are you still living in Centennial Park or some other part of Sydney now ?


    .... Phil
     
  11. Phil Allison

    Phil Allison Guest

    "Martin Riddle"

    ** A couple of questions:

    When replacing a surround, it is necessary ( or a good idea ) to remove the
    dust cap and shim the voice coil tightly in the gap first ? Or can you
    just wing it and rely on slow setting adhesives ( like Silastic) to let you
    fiddle with the new surround till there is no sign of poling?

    And do you glue the surround to the cone first or the frame ?



    ..... Phil
     
  12. Phil Allison

    Phil Allison Guest

    "gregz"

    ** Isn't long haired sheep's wool supposed to be the best ??

    That was THE recommended filling for " transmission line" bass boxes.

    I have used " bonded acetate" fibre or white polyester pillow material in
    the past.

    They seem to work OK.

    Sheep's wool is a tad exotic.



    ..... Phil
     
  13. No, I didn't remove the dust cap. The drivers weren't anything special,
    so I just winged it and made sure there wasn't any binding.
    I did the frame first then the cone. I think I tacked the cone in 3 or 4
    spots checked for voice coil movement then pressed the rest of the
    surround down. I did have to do it twice on one of the drives, the
    voice coil was not centered the first time.

    There is a 3/16 thk paper ring that sits on top of the surround, that
    tends to fall off every couple of years using the rubber cement.
    But the surrounds are still stuck to the cones and frames.

    Cheers
     
  14. Bill Sloman

    Bill Sloman Guest

    In theory, yes - I've even got a NSW driving licence - but right now
    I'm Christchurch, New Zealand, and will be here for almost another
    fortnight before we go back to Darlinghurst.
     
  15. Bill Sloman

    Bill Sloman Guest

    And perhaps a bit labour-intensive. The only hi-fi enthusiast I've
    known who went to that much trouble with his speaker supported the
    sheep's wool on nylon fishing line that he strung from side to side
    every few inches.

    I'd have thought that aerogel might have been better, but it might hae
    been a bit hi-tech for the golden-eared boys.

    http://en.wikipedia.org/wiki/Aerogel
     
  16. gregz

    gregz Guest

    I only did a couple surrounds. Shimming voice coil by removing dust cap.
    I'm pretty sure you do first the foam to cone, but I just followed
    instructions.

    Greg
     
  17. gregz

    gregz Guest

    I have fixed more surrounds than I have replaced them. Using silicone rtv
    or Airflex 400. Its often a tricky situation. I have probably treated a few
    dozen drivers, mostly small 4 1/2 inch type. If the foam is completely
    missing, can't do.

    Greg
     
  18. Phil Allison

    Phil Allison Guest

    "gregz"
    ** Richard Small ( of Theile and Small ) made that same observation back in
    the 1970s.

    Seems he and I were at the University of Sydney in 1972 - though he is a
    few years older than me.

    ** Have you done any testing to verify results ?

    I have tried 4 cycle sine wave tone bursts and close micing with some
    success - you may need to be outdoors or far from walls to eliminate
    extraneous reflections in the scope trace.



    .... Phil
     
  19. Phil Allison

    Phil Allison Guest

    "gregz"

    ** Those 41/2 inch drivers were not Bose by any chance ?


    ..... Phil
     
  20. Phil Allison

    Phil Allison Guest

    "gregz"
    ** Shimming sounds like the proper way to do it.

    Same as when re-coning.


    .... Phil
     
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