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Old 9th March 2011, 02:58 AM   #1
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Default Do you need a crossover/filter for a sub?

Hi,

You might know I'm working on an LM3886 Stereo amp. I'm a bit antsy you see...

While I'm in the amplifier/speaker building mode. Does anyone actually use a filter for a subwoofer? Is it worth it I mean?

EVENTUALLY, I'd like to get one of those nice 8" HiVi M8a's. Eventually...that is.

Also, is there a special type of amp required? Are 2x bridged LM3886s not good?


Thanks a bunch. Just out of curiosity.

Last edited by TheLaw117; 9th March 2011 at 03:00 AM.
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Old 9th March 2011, 03:12 AM   #2
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yes, you need one; the easiest way: TLS.org | Passive Line-Level Crossover
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Impedance varies with frequency, use impedance plots of your drivers and make crossover calculations using the actual impedance of the driver at the crossover frequency
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Old 9th March 2011, 03:14 AM   #3
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Quote:
Originally Posted by PeteMcK View Post
yes, you need one; the easiest way: TLS.org | Passive Line-Level Crossover
I mean only a subwoofer. Just a subwoofer in a box...no other speaker.

Still?
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Old 9th March 2011, 03:21 AM   #4
N Brock is offline N Brock  United States
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Yes, still. if not the sub will sound poor.

You could use a PLLXO, a passive crossover (more expensive), or an active crossover 9even more $$)

If in doubt you can try it without a crossover, shouldn't hurt anything, but most subs are designed to only play on the lower end.

N-Brock
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Old 9th March 2011, 07:30 AM   #5
AllenB is offline AllenB  Australia
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Do you want your sub/s to be reproducing midrange? Apart from hearing it, if it/they are not close to your mains then you may end up with cancellations (comb filtering).

Unless you build bandpass subs which have inherent physical low pass filtering.
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Old 9th March 2011, 11:39 AM   #6
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You may be able to use a sub without a filter if it's strictly used for a Home Theater ".1" channel, with all the other speakers set for full range operation. For any other setup, no way, a sub without a filter sounds horrid.
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Last edited by audiobomber; 9th March 2011 at 11:42 AM.
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Old 9th March 2011, 09:26 PM   #7
AllenB is offline AllenB  Australia
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If I assume by your reply that you are keen to get on with it, a simple inductor with the speaker lead will get you started, and maybe a well chosen electrolytic capacitor across the speaker terminals to go with it. No big deal until you want to start getting exact.
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Old 10th March 2011, 12:18 AM   #8
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Thanks. I won't be building the sub for a while, but I was just curious...

And would I need to use a different type of amp? Or...?
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