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Old 30th December 2006, 04:38 PM   #1
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Default Bandpass Filter on a Subwoofer

Hello, This is my first post in the Subwoofer forum!

I ran into an unbelievable deal on a pair of Magneplanar SMGs a few days ago, with the Maggies, I got two 8-inch passive subwoofers for use with the SMGs to take some of the bass load away from them. The subs were homade in gorgeous boxes (ones that I could never personaly construct). The reason I am posting is because I found something perplexing in the crossover.

The two sets of terminals (one for in, and one for out) have the two red nodes shorted by a capacitor, this makes perfect sense to me, as It acts as a high pass filter to keep some of the bass frequencies from getting to the SMGs. Then the signal line going to the sub goes through and inductor, this would make a low-pass filter (once again something I completly understand). After this inductor, the wire then goes through a capacitor before going into the woofer, making the inductor, and the capacitor together a bandpass filter. Is this a common practice in subwoofers? is there any need for a low-end roll off in a subwoofer?

In any event, I guess what sounds the best is the most important thing, so I may try shunting the second capacitor to ground (making it another low-pass filter), and see how that sounds.

Thanks alot, any comments would be greatly appreciated\

-Moose
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Old 30th December 2006, 06:34 PM   #2
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It's possibly a high pass filter to protect the drivers from over excursion at low frequencies. In that case, bypassing would be a bad idea.
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Old 30th December 2006, 07:10 PM   #3
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What size is the cap?
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Old 31st December 2006, 01:54 AM   #4
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Many car audio amps have a built in subsonic filter to block the really low frequencies (set usually around 15-25 hz). It is there to prevent the sub from bottoming out at high volumes in ported enclosures.
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Old 31st December 2006, 04:05 AM   #5
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all of these explainations make sense to me, i'll look at the cap once I return home tomorrow afternoon, and run it through the equation to see where the 6db point is
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