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Item found inside my RB-75


Guest davidness

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Guest davidness

This weekend, I upgraded the binding posts on my RB-75 speakers. As I was reconnecting the leads, I noticed something stuck to the HF horn magnet. It was a round, black metal disk a little larger and thicker than a quarter. It was highly magnetic, but I'm NOT ruling out that the long-term exposure to the tweeter magnet caused it to become magnetized. It looks like it's probably a 'donut-hole' that came from some metal punching process, but I'm not certain.

I, of course, removed it. It's at home so I can't post a picture from here at work. I suspect it's nothing to worry about, but thought I'd post my find here in case anybody had any additional experiences like this or could explain if this is something more important that come loose or come out of one of my drivers.

Any thoughts?

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Guest davidness

Bucking magnet for the compression driver, should be glued to the back of the HF driver. Polarity to push out when gluing it on.

Thanks for the reply. Your response caused me to remove both RB-75 front panels, to which the HF horns are attached, and yes, it's obvious that the mystery disk detached from the backside of one of the horns. I can even see the previous glue marks where it came apart.

That leads me to the observation that the detached magnet appears to need to be re-glued the opposite than the way I read your response; one way the disk is attracted to the backside, the other way it is push away. According to the glue marks, it clearly used to be attached 'drawn together', not pushing away (which would also make gluing very difficult). I suspect I'm just misreading your response. Can you clarify?

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It must be glued on in pushing away mode to cancel the stray magnetic field.

If not using near a CRT monitor or television, the bucking magnet is not needed.

The magnets are attached to the diaphragm cover before it is assembled to the driver. If you disassemble the driver to do this be careful to not damage the diaphragm assembly, you will need something to set it on so the voice-coil doesn't touch anything. Be careful, or figure out how to do it without disassembly.

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