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Adding cone mass
Adding cone mass
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Old 17th June 2009, 02:09 AM   #1
fdeck is offline fdeck  United States
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Default Adding cone mass

Is there a safe / correct / preferable way of adding mass to a woofer cone? I want to add roughly 10 grams to a 10" musical instrument driver.
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Old 17th June 2009, 02:45 AM   #2
dave_gerecke is offline dave_gerecke  United States
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I haven't personally tried it, but I have read that others have glued either solder or fishing weights around the perimeter of the dustcap, on the cone, where the dustcap glues to the cone.
The most important things I can think of are to use multiple small weights spaced evenly around the dustcap, and use an adhesive that is strong enough to hold the weights onto the cone, but also allow you to remove them if desired.

Peace,

Dave
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Old 17th June 2009, 02:47 AM   #3
infinia is offline infinia  United States
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Default Re: Adding cone mass

Quote:
Is there a safe / correct / preferable way of adding mass to a woofer cone? I want to add roughly 10 grams to a 10" musical instrument driver.



Glue small lead fishing weights symetrically around the junction of the dust cap/cone. There are otherways, but this seems to be most reasonable ie least side effects IMO.
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Old 17th June 2009, 02:54 AM   #4
fdeck is offline fdeck  United States
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Thanks! Is any particular kind of glue favored?
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Old 17th June 2009, 03:09 AM   #5
Moondog55 is offline Moondog55  Australia
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I have been told to use epoxy resin mixed with a heavy filler, lead shot would do, 10 grams isn't much mass plain epoxy mixed with dry sand about 2 teaspoons full of each should work.
1 tspn on each woofer set it on a horizontal surface and pour over dustcap; let it settle where dustcap meets cone and dry for 24 hours
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Old 17th June 2009, 07:16 AM   #6
Circlotron is offline Circlotron  Australia
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I did it once using coins.

http://www.diyaudio.com/forums/showt...714&highlight=

Interesting thing about those coins: in 5, 10 and 20 cent denomination the weight of the coin is proportional to it's value. Makes it easy to find the total value of a big pile of mixed coins just by weighing them.
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Old 17th June 2009, 02:29 PM   #7
Patrick Bateman is offline Patrick Bateman  United States
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I increased the QMS on a set of MCM 55-2421 woofers using polyurethane glue. The other methods mentioned will work, but the use of polyurethane has the advantage of strengthening the cone, waterproofing it, and damping it.

Be sure to measure the t/s parameters before and after, to insure both woofers are consistent.

Back in the day I tried to do it with fiberglass and resin, and it disintegrated the wooofer's surround. So don't do that
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Old 17th June 2009, 02:34 PM   #8
badman is offline badman  United States
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I used coating to stiffen and increase mass in a cone. Shellac works very nicely.
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Old 17th June 2009, 03:35 PM   #9
GM is offline GM  United States
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Normally, MI drivers are used well up into its break-up BW, so any diaphragm mods such as adding mass in any form can have an audible affect and IME not in a pleasant way, though the least offensive have been with Dammar and the aforementioned shellac coatings and/or replacing the dust cap with a heavier DIY aluminum one.

GM
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Old 17th June 2009, 04:00 PM   #10
AndrewT is offline AndrewT  Scotland
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I would not add lumps of weight to specific locations of the cone.
I think that may promote asymmetrical flexure and premature "breakup".

I used lead sheet beaten out to a thin foil. Secured it with double sided tape. The fresh adhesive could easily cope with 100g accelerations.
I have no idea how long the adhesive will retain the weights in place.

If it does not need to be reversible then painted on coatings are far more likely to do the job better. One could vary the thickness of the coating from edge to centre and even double coat (both sides) in some areas.
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