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Old 22nd June 2013, 09:37 PM   #1
Ronion is offline Ronion  United States
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Default Parallel Baffle step filter?

Is it possible to build a parallel baffle step filter using a capacitor?

I have a ton of caps and a need to build a light weight baffle step--well actually a shelving filter.

It seems to me this should be a simple thing, but Google turns up nothing.

Thoughts?
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Old 22nd June 2013, 11:25 PM   #2
Ronion is offline Ronion  United States
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Default Linkwitz to the rescue

Active Filters


Equalizer (passive).


Now if someone could help me make sense of them... I'm a bit thick when it comes to circuits. The drivers I'm using are 40Ohm. I can't really get the exact reactance, but even a generic filter should be simple enough to experiment with and get right. I need a 5dB cut centered around 1500Hz.

Thanks for any reply! I'm a bit anxious about trying it.
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Old 23rd June 2013, 03:43 AM   #3
sregor is offline sregor  United States
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These filters are designed to go between the preamp and the power amp, or in a tape deck loop. A little easier to digest is ESP description at Baffle Step Compensation.
It also can be done at the speaker level - i.e. 2.5 or 3.5 way designs. It also can be done with passive components, but loose efficiency (I believe a parallel RL circuit of the right values in series with the speaker can do this).

Parallel capacitor works only with an in line resistance, and still need a resistance in series with the capacitor. - you loose a lot of efficiency, and load down amplifier. In your case, with a 4 ohm speaker, need a 2 ohm resistor in series with your speaker, then a cap and a 4 ohm resistor in parallel with your speaker. If they are 40 ohm ?? then would be 20 ohm in series with the speaker , and a 40 ohm in series with the capacitor in parallel to to speaker. These are for 6 db drops - would require some calculation (or trial and error to figure out 5 db drops - slightly higher value resistor in series with the cap, and should be lower value on the series resistor.with the speaker. My 2 cents.
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Last edited by sregor; 23rd June 2013 at 03:46 AM.
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Old 24th June 2013, 10:56 PM   #4
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It would have the same circuit topology as a Zobel, a resistor & cap in series,
you'd need to ensure that the R wasn't so low as to cause problems with the amp...
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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 25th June 2013, 12:15 AM   #5
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A zobel topology doesn't change response - the circuit just draws more current. You'd have to add series resistance first, like sgregor said.
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Old 25th June 2013, 02:45 AM   #6
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re:"A zobel topology doesn't change response " - I can't agree with that...
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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 25th June 2013, 03:31 AM   #7
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Well it's not a subjective issue. counterexample?
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Old 25th June 2013, 04:41 AM   #8
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think about how a simple treble cut tone control (e.g. as used in gutars) works - same topology
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Old 25th June 2013, 03:05 PM   #9
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Well sure, with 1MΩ impedance it works, but we're talking about changing the response of a speaker/driver.
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Old 25th June 2013, 06:28 PM   #10
Paul W is offline Paul W  United States
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Are you working external to an existing speaker? Your first post asks about BS compensation with a shelving filter while your second post mentions a cut "centered about 1500" which sounds like a notch filter. Assuming you are working externally, the hi-cut shelving filter (BS comp) would be a parallel RL in series with the speaker, a notch filter would be a parallel RLC in series with the speaker.
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