Increase cone mass to rid cone resonance; worth it? - diyAudio
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Old 30th July 2010, 03:25 AM   #1
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Default Increase cone mass to rid cone resonance; worth it?

Due to cone resonance of a driver (scan 18w/4), I'm considering ways of adding mass to the cone itself.
I've tried raising/lowering qts via series resistors and AP mat tuning, but the problem always rears it's head with lower bass guitar and I've narrowed it down to ~71hz notes. I'm considering adding mass to the cone and hopefully bring the resonance to a point outside the passband (60hz).
I am aware that adding mass will raise qts (a benefit in my install) and decreases sensitivity (not a problem; plenty of power on tap and actively processed).

Driver is pretty much a 'throw away' and I figure it's a good chance to experiment with adding mass to the cone to see if it breaks up the resonance.
I've seen mention of using epoxy/resin combos, lead weights with glue, etc. Not sure of the effect on various types of glue on a paper cone, though.

I've got viscoelastic material (sound deadener) laying around. Was even considering cutting 4 very small pieces of equal size and attaching that to the back of the cone, symmetrically.


I typically try crap anyway and learn as I go, but in this case, I'm open to suggestions. So, any 'hey, DON'T do this:' suggestions?
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Old 30th July 2010, 03:40 AM   #2
sreten is offline sreten  United Kingdom
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Hi,

71Hz is an issue ? Far more likely a room issue than a driver issue.
Room mode analysis and then optimum placement are better bets.

Most drivers are optimised for purpose, mods only change the purpose.

/Sreten.
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Old 30th July 2010, 03:50 AM   #3
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it's a cone resonance issue; no doubt. After nearly a year of trying to figure it out I'm 100% sure that's the issue.

You can hear it pull straight to the floor and can feel the floor resonate. Not an enclosure issue. Nothing in the floor is causing the resonance (ie: no rattles).

FWIW, this is a car audio install.
I understand changing the mms means changing the FR. This driver's puprose is for midbass and is playing 60-250. As I said, it's pretty much a throw away driver at this point (beat up and won't sell anyway) so it's an option I want to explore.

I understand trying to get to the root of the problem, but I've gotten to it. Short of buying new drivers to fit the bill (no $$$) this is kind of my last option.

Thanks

Last edited by bikinpunk; 30th July 2010 at 03:54 AM.
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Old 30th July 2010, 07:10 AM   #4
rabbitz is offline rabbitz  Australia
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I know Legend Acoustics in Australia used strips of balsa on the back of the the older 18W8545 drivers.
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Old 30th July 2010, 09:50 AM   #5
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"You can hear it pull straight to the floor and can feel the floor resonate."

Then you hit the floors resonant frequency. You can't really blame the driver for that.

If you have a mass coupling between the enclosure ant cone that the easiest to change is the enclosure. Add a big weight on top of it and check what happens.

Any measurements would be useful, can't really tell what's going on from your description. And guessing isn't the way to solve a problem like this.
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Old 30th July 2010, 11:43 AM   #6
AndrewT is offline AndrewT  Scotland
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cone resonance due to breakup modes is more likely up in the low kHz region.
A low frequency resonance cannot be due to cone breakup modes.

Altering the moving mass of the driver will alter the way it is tuned.
Listen to what they are telling you.
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Old 30th July 2010, 05:08 PM   #7
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the floors are COVERED in clay+lead shot as well as multiple layers of viscoelastic material. COVERED. I'm talking 8 lbs to each side. The enclosure's baffle has about 2lbs on it. The problem didn't go away with that.

Thanks. I'll consider other options.
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