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Old 24th June 2010, 10:53 PM   #1
Boscoe is offline Boscoe  United Kingdom
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Default What do I need to filter bass to a sub?

Basically just building my sub and have got a single channel amp which is the complete frequency range but i only want 500Hz and below what do I need to do this for a 4ohm speaker? Can I use a crossover calculator and then use a crossover without the tweet or mid-rand outputs?

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Old 24th June 2010, 11:06 PM   #2
Boscoe is offline Boscoe  United Kingdom
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Okay so I just found the butterworth 3rd order low pass and it says to use a cap with a certain polarity (late i can't think of the name!) so can I just use electrolytic caps or is ther e a certain type needed?
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Old 25th June 2010, 01:51 AM   #3
tinitus is online now tinitus  Europe
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Quote:
Originally Posted by Boscoe View Post

i only want 500Hz and below
then its basicly considered as a common 3way
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Old 25th June 2010, 07:25 AM   #4
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Does seem very high for a subwoofer. What are you crossing it over to? (some bookshelf speakers, other drivers in that cabinet...?)

Which driver are you using - you need the impedance curve so you can select the impedance for the frequency you want.
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Old 25th June 2010, 08:50 AM   #5
Xoc1 is offline Xoc1  United Kingdom
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500 Hz is just below middle C on a piano.
That is a high note for a sub.
Go get a feel for frequencies, listen to some test tones!
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Old 25th June 2010, 09:42 AM   #6
Boscoe is offline Boscoe  United Kingdom
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Okay the driver is one I have just lying around and I'm going to change the frequency to 200Hz.

This is what I'm going to use (in the highlighted area)

Click the image to open in full size.

I am using two 8ohm drivers with both inphase for a sub woofer.
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Old 25th June 2010, 10:26 AM   #7
AndrewT is offline AndrewT  Scotland
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3pole filter and 200Hz will pass a lot of mid range to the bass only drivers.
Turning off the satellites, you will clearly recognise the low passed music & songs with all that mid range content.

The filter components will almost certainly be unavailable in 1% values.

5% values are getting a bit wide for a 3pole filter. The tolerance must be tighter for higher pole filters.

4m7H or [4m7H + 100uH] for 4.77
270uF or [220uF+47uF] for 265
1m5H or 1m6H or [1m5+75uH] for 1.59

You may need to add a Zobel correction across the driver terminals to bring the driver load closer to the assumed 8ohms that your calculator uses.

Personally, I would add an active filter in front of the power amp and drive each 8ohm speaker with one half of a stereo amplifier. The active filter could be a CFP which inverts the signal and also capable of summing two (or many) channels to a mono channel.
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Old 25th June 2010, 01:38 PM   #8
Xoc1 is offline Xoc1  United Kingdom
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Quote:
I would add an active filter in front of the power amp and drive each 8ohm speaker with one half of a stereo amplifier.
If you use an active filter and a separate amplifier you are far more likely to get a satifactory result.
Also if you are not happy with the frequency response, you will be able to modify it with a few pence worth of components.
At the moment if you build this passive filter, and your not happy with the result (which is very likely) you will end up with a expensive load of junk!
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Old 26th July 2010, 01:39 PM   #9
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Paradigm x30 sells used for under $100.
Infiniti makes a similar device.
Or get a 2/3 way stereo active crossover from Behringer for $99.00usd. Being adjustable is a major plus with any project. I have just ordered a CX3400. Or get a costlier digital unit such as the dcx2496 for $299.00

BTW A subwoofer will want a frequency cut-off at 50 or 80Hz. Not 200Hz.
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