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What's up with this speaker!

Hey folks!

I'm building an fk617 amp kit, and am using a salvaged thrift store speaker. When I took it out of its enclosure, I found this:

The hot wire goes through what I think (I know nothing about electronics) is a big capacitor before it hooks into both the positive speaker terminal and a piezo.

I'm guessing the piezo is there for high-frequency response, but what is the other do-dad doing? Is it necessary? I'm guessing it wont hurt to leave it there, but it bugs me not knowing why it's there....

Many thanks.

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Permalink Reply by Doc Oakroot on April 15, 2009 at 4:01am

I would guess that the cap is splitting the freqs between the speaker and the piezo, but I don't know enough to explain how it's doing it.

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Permalink Reply by BT Cohosh on April 15, 2009 at 4:10am

That's kind of what I initially thought, too, except that the capacitor isn't between the speaker and the piezo. The hot line goes through it, and *then* to both of them.

Could this have functioned as some sort of buffer to prevent speaker damage?

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Permalink Reply by JUJU on April 15, 2009 at 5:08am

it's like Doc says a cap to split the high and low freq - so it's a two way speker

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Permalink Reply by Doc Oakroot on April 15, 2009 at 5:25am

There's a complication in that the piezo is both a cap and a MOhm resistor. Like, I said, I don't know enough to understand what the interaction between that and the cap does. It may very well protect the speaker - or even protect the amp by keeping the overall impedance under control.

BT Cohosh said:

That's kind of what I initially thought, too, except that the capacitor isn't between the speaker and the piezo. The hot line goes through it, and *then* to both of them.

Could this have functioned as some sort of buffer to prevent speaker damage?

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Permalink Reply by rodney fruits on April 15, 2009 at 7:15am

you have a two way speaker here. the piezo is being used as a tweeter. the black thing is a capacitor.

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Permalink Reply by BT Cohosh on April 15, 2009 at 9:59am

Thanks for the info. I guess I'll leave everything be.

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Permalink Reply by BLY on April 16, 2009 at 12:46am

That's just a very simple "first order" (one component) passive crossover filter. It will attenuate the lows or pass the higher frequencies at a "slope" or rate of 6db per octave. So the big speaker acts like a woofer and the little speaker acts like a tweeter. By adding a coil to the filter you can increase the slope to 12db per octave which would give it a much "sharper" cut over point. It would be a "second order" filter. More details than you will ever want or need here. http://www.termpro.com/articles/xover2.html