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Thread: First Time JBL 128H Refoaming Help

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    First Time JBL 128H Refoaming Help

    Hello, I picked up a pair of JBL L112 speakers and the 128Hís needed new foam. I refoamed both of the 128H drivers using a 30hz tone generator on both and followed the same steps. I ended up using Simply Speakers surrounds and Aleeneís Tacky Glue. I didnít hear any rubbing during the process, but after the glue dried I hear some distortion in one as I tested on very low volume, no bass. Also, when I push in various places on the cone to test, one half of the cone has some rubbing and makes a scratching type noise. Does this mean the voice coil on this driver is not centered? Could it be anything else? Thanks

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    Administrator Mr. Widget's Avatar
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    Quote Originally Posted by VintageUT View Post
    I didnít hear any rubbing during the process, but after the glue dried I hear some distortion in one as I tested on very low volume, no bass. Also, when I push in various places on the cone to test, one half of the cone has some rubbing and makes a scratching type noise. Does this mean the voice coil on this driver is not centered? Could it be anything else? Thanks
    Either not centered or there is debris in the gap.



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    Senior Member SEAWOLF97's Avatar
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    I've done a handful of those. Remember them as pretty much "self centering".

    IF it was OK when you worked it in & out, then something went wrong, obviously.

    you've gotta strip the new foam off anyway. "crap in the gap" seems likely, so dustcap needs to come off too.

    IN the past I've refoamed drivers w/o testing them and wasted the time/supplies on bad ones. Now all drivers get tested before refoams. Just lay them on their backs on the floor (so gravity does not put them off center) and apply low signal.
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    Senior Member RMC's Avatar
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    Hi vintageUT,

    RE "when I push in various places on the cone to test, one half of the cone has some rubbing and makes a scratching type noise."

    When you push on a cone you should be pushing at the center of the cone, not at various places.

    Pushing elsewhere may lead to a little sideway displacement which in turn may aggravate your issue.

    Remember, the natural movement of a cone is from the middle of it, in or out, so that's where you ought to push.

    Clever idea btw to use clothespins. Regards,

    Richard

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    Quote Originally Posted by VintageUT View Post
    Hello, I picked up a pair of JBL L112 speakers and the 128Hís needed new foam. I refoamed both of the 128H drivers using a 30hz tone generator on both and followed the same steps. I ended up using Simply Speakers surrounds and Aleeneís Tacky Glue. I didnít hear any rubbing during the process, but after the glue dried I hear some distortion in one as I tested on very low volume, no bass. Also, when I push in various places on the cone to test, one half of the cone has some rubbing and makes a scratching type noise. Does this mean the voice coil on this driver is not centered? Could it be anything else? Thanks
    Is the spider centered on the top plate? It's possible it may not be. If it isn't, you need to follow that same asymmetry to the basket flange. The gap on those drivers and other 3" vc drivers is very tight ime. You definitely need to find center by shifting it around with the test tone first.

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    Quote Originally Posted by Mr. Widget View Post
    Either not centered or there is debris in the gap.



    Widget

    Thatís what it seems. I guess Iíll have to remove the surround and start from scratch.

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    Quote Originally Posted by SEAWOLF97 View Post
    I've done a handful of those. Remember them as pretty much "self centering".

    IF it was OK when you worked it in & out, then something went wrong, obviously.

    you've gotta strip the new foam off anyway. "crap in the gap" seems likely, so dustcap needs to come off too.

    IN the past I've refoamed drivers w/o testing them and wasted the time/supplies on bad ones. Now all drivers get tested before refoams. Just lay them on their backs on the floor (so gravity does not put them off center) and apply low signal.
    Thanks for the info. Now I think if it, I did press the center of the cone before and there was a slight rub. Wonder if there is the foam parts in the gap? Is it easy to remove the dust cap or should I leave it to a pro?

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    Quote Originally Posted by RMC View Post
    Hi vintageUT,

    RE "when I push in various places on the cone to test, one half of the cone has some rubbing and makes a scratching type noise."

    When you push on a cone you should be pushing at the center of the cone, not at various places.

    Pushing elsewhere may lead to a little sideway displacement which in turn may aggravate your issue.

    Remember, the natural movement of a cone is from the middle of it, in or out, so that's where you ought to push.

    Clever idea btw to use clothespins. Regards,

    Richard
    Very helpful, thanks. Iím new to this hobby and will definitely follow this guidance. Appreciate it!

    I stole that idea from someone else.

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    Quote Originally Posted by gasfan View Post
    Is the spider centered on the top plate? It's possible it may not be. If it isn't, you need to follow that same asymmetry to the basket flange. The gap on those drivers and other 3" vc drivers is very tight ime. You definitely need to find center by shifting it around with the test tone first.
    Yes, the spider looks centered, just like the other speaker. I really wonder if there is crap in the gap as mentioned below.

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    Senior Member RMC's Avatar
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    Hi VintageUT,

    RE "I stole that idea from someone else." Then I may steal it from you for future use, fair game: robber robbed, lol.

    RE "Wonder if there is the foam parts in the gap? Is it easy to remove the dust cap or should I leave it to a pro?"

    Removing the dustcap isn't rocket science. If you have a stable non-shaky hand and can do detail work you pretty much have what it takes.

    From the driver pics seen on the Web, 128H white cone has a screen on driver back vent and 128H-1 black cone has a bare hole on the back presumably with some foam in it. Yours may also be a "hybrid" 128H-1 with 128H white cone??

    First check the driver's back vent to see if you have a screen there. JBL mentioned drivers have a screen or a foam plug to cover the back vent hole. If its a screen still try to look through it with a good flashlight to confirm the absence of some foam. If no foam, that reduces the possibility of rotten foam having migrated in the gap. If your model has no screen then it probably has foam in the back vent hole and that foam could have desintegrated and migrated in the gap. Btw a screen with no foam seen doesn't guarantee there's nothing in the gap, it may be something else, or other issue.

    Cut the dustcap in a way to save it (see below), clean the Gap and to use shims for the refoam. You need to be careful doing this, just take your time.

    You don't have to cut dustcap all around like for taking it off completely. You can cut ALMOST around it but STOP cutting just a bit before the wires covered with black glue. That means there's about 3/4" of UNCUT dustcap left still holding it in place, this way you can reuse the original dustcap.

    You need cutting cap HORIZONTALLY and straight, ALWAYS just above the black glue line to avoid damaging the round voice coil under cap. Cut delicately with a very sharp blade using a back and forth movement, after initially piercing the cap (I use scalpels, but a sharp exacto should do).

    When that is done, lift up the dustcap SLOWLY and make it hold upwards at a right angle (no more) with a piece of not too sticky tape from cap edge to driver frame. I typically use 3M Blue painter's tape for that purpose since its made for easy removal. Some lower cost beige color masking tapes are often too sticky to be removed easily, so prudence re damaging cap. At this point you should see inside the driver: the vent hole, voice coil and gap.

    This is the worst part, other than refoaming. Knowing what the job entails, we'll see if you plan to do it yourself or let someone else do it for you. If need be we can discuss further steps based on your decision. Regards,

    Richard

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    Here's a pic of the internal foam filter ( that's a 2235H woofer ).



    To the best of my knowledge all JBL woofers with ceramic magnets, having a single back vent, sport this internal foam filter.

    If one looks through the back vent ( looking past the foilcal screen if present ) and doesn't see the internal filter, one should still assume bits of it are present ( until proven otherwise ).



    PS; Removing the rear foilcal ( with a hair-dryer and putty knife > with patience ) will allow one to vacuum out the foam bits ( avoiding dustcap implosion by using a tiny attachment meant for computer keyboards ).
    - This is best done with the woofer facing done ( + elevated on 4 temporary legs ) while playing low frequency tones to loosen up the foam bits so that they congregate to the center of the dustcap .


    Here's a pic of one of my 2245H woofers ( after the foilcal was removed ).
    - Notice the detached internal foam filter sitting inside the dustcap.



    That leads me to my statement that no-one should bother refoaming their surrounds until the internal foam filter ( issue ) has been addressed ( & cleared ).

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    Quote Originally Posted by RMC View Post
    Hi VintageUT,

    RE "I stole that idea from someone else." Then I may steal it from you for future use, fair game: robber robbed, lol.

    Lol, well played.

    Removing the dustcap isn't rocket science. If you have a stable non-shaky hand and can do detail work you pretty much have what it takes.

    I am sure I have what it takes to successfully remove the caps and clean the VC gap.

    From the driver pics seen on the Web, 128H white cone has a screen on driver back vent and 128H-1 black cone has a bare hole on the back presumably with some foam in it. Yours may also be a "hybrid" 128H-1 with 128H white cone?? Mine are the 128H white cones with back vent.

    First check the driver's back vent to see if you have a screen there. JBL mentioned drivers have a screen or a foam plug to cover the back vent hole. If its a screen still try to look through it with a good flashlight to confirm the absence of some foam. If no foam, that reduces the possibility of rotten foam having migrated in the gap. If your model has no screen then it probably has foam in the back vent hole and that foam could have desintegrated and migrated in the gap. Btw a screen with no foam seen doesn't guarantee there's nothing in the gap, it may be something else, or other issue.

    I used a bright flashlight and can see there is a foam vent still attached. It looks to be in place, but with the age of the foam, it would make sense there could possibly be bits of foam in the VC gap. Itís just strange the other driver works well when this one doesnít.

    Cut the dustcap in a way to save it (see below), clean the Gap and to use shims for the refoam. You need to be careful doing this, just take your time.

    You don't have to cut dustcap all around like for taking it off completely. You can cut ALMOST around it but STOP cutting just a bit before the wires covered with black glue. That means there's about 3/4" of UNCUT dustcap left still holding it in place, this way you can reuse the original dustcap.

    This makes sense! Love the idea of using the original cap.

    You need cutting cap HORIZONTALLY and straight, ALWAYS just above the black glue line to avoid damaging the round voice coil under cap. Cut delicately with a very sharp blade using a back and forth movement, after initially piercing the cap (I use scalpels, but a sharp exacto should do).

    When that is done, lift up the dustcap SLOWLY and make it hold upwards at a right angle (no more) with a piece of not too sticky tape from cap edge to driver frame. I typically use 3M Blue painter's tape for that purpose since its made for easy removal. Some lower cost beige color masking tapes are often too sticky to be removed easily, so prudence re damaging cap. At this point you should see inside the driver: the vent hole, voice coil and gap.

    This is the worst part, other than refoaming. Knowing what the job entails, we'll see if you plan to do it yourself or let someone else do it for you. If need be we can discuss further steps based on your decision. Regards,

    Richard
    Really appreciate this solid info. If you have additional instructions, I am definitely interested. Iíll give this a shot later this morning.

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    You haven't got enough cloth pegs :

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    Best regards!

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    Hi Vintage UT,

    RE "Itís just strange the other driver works well when this one doesnít."

    I would still check the other driver. One may be at a more advanced "cancer" stage than the other re foam rot, but chances are the other driver will get there too. So I'd do both.

    RE "If you have additional instructions, I am definitely interested."

    If there's foam inside vent, first I would start by cleaning that from the back of driver, using a flashlight and small vacuum to get the most out. Remember, down at the end of vent hole its the fragile dustcap covering the even more fragile voice coil. I use a small 12 volt portable vacuum (don't want Shop Vac force succion there) and I've extended the nozzle at the end of vacuum, to go deep inside vent hole, with a larger plastic straw.

    Work carefully and keep in mind Earl's notes too. Pics to follow shortly re nozzle and note the end of straw isn't round but rather oval, not an accident. Have different size straws I can use taping them to little vacuum's black nozzle. When you're done removing the "rough" from back vent hole, then you can attack the dustcap.

    cleaning gap

    I typically use single or double copier paper strips about 1"W X 3"L (sometimes softer business cards) to clean the gap. Some business cards are too thick/rigid don't like those here re fear of damaging voice coil wire. So I basically "sink" the paper strip(s) in gap and using a cicular motion go around gap to loosen dirt and lift the paper strips often for the small vacuum close by to suck the dirt with its black nozzle. No metal or sharp objects near coil/gap! Repeat this process many times and replace paper strips with new ones.

    Based on what you want to do, e.g. refoam again at the same time or not, an open dustcap is an opportunity to use shims for a refoam job. You decide.

    glueing dustcap

    Naturally you'll need some black glue, or at least clear one, to seal the original cap back on when all is done.

    back vent hole

    Depending on exact driver model you have (with screen or bare hole) glue foil cal back on or cover the back hole with a glued, slightly stretched, little larger than hole piece of speaker grille cloth to prevent future dust and others from going inside driver. Regards,

    Richard

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