# "Bass Blocker" Calculation help please..



## s60rguy (Feb 14, 2007)

Hey all. 

I just can't seem to understand the Formula you use to figure out the correct Capacitance to see what one you need for Bass Blockers. 

I got all my interior speakers installed in the car, but I don't have all my amps yet, so I can't use the x-overs on them yet. Still looking around for them.

So everything is still powered off the stock amp & deck.

Can someone that understands the forumula  let me know what size capacitor I need?? 

What I am looking for is to block out everything from *150hz & lower*. They will be used on a *4ohm speaker*. 

If they don't make one dead on at 150hz, a little higher cut-off is ok, just not lower.

TIA!!


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## legend94 (Mar 15, 2006)

265 uf is the calculation with the 6db per oct 
so you may want to go with a 225 or 250 uf to be safe  
check out:

http://www.bcae1.com/
scroll on the right to the number 54 on passive xovers and there is a calculator inside that link 

also what size speakers are you using? you may not need to go down to 150hz


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## s60rguy (Feb 14, 2007)

legend94 said:


> 265 uf is the calculation with the 6db per oct
> so you may want to go with a 225 or 250 uf to be safe
> check out:
> 
> ...



Nice!! Thank you..that's what I needed. Now how many Volts should they be?? 100v??


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## legend94 (Mar 15, 2006)

that would be fine in my experience, but maybe someone else could say for certain. many passive xovers use 50v so i think 100v would be great.


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## Whiterabbit (May 26, 2006)

either way, 50 or 100 is fine.


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## Fast Hot Rod (Apr 19, 2007)

For a 6dB high pass filter, use this equation:

Capacitor value = 1 / ((2 pi) * driver impedance * desired frequency) 

In your case, it would look like this:

==> 1 / (6.2832) * (4 ohms) * (150 Hz)

==> 1 / 3769.911

==> 2.65258 * 10 ^ -4

==> 265.258 * 10 ^ -6

==> 265.258 micro Farad.


The voltage requirement is another interesting equation... you can calculate the amp's voltage using the following equation:

Power output per channel = Voltage ^ 2 / driver impedance

Example: 100 watts at 4 ohms:

==> 100 = V ^2 / 4 ohms.

==> 100 (4 ohms) = V ^2

==> 400 = V ^2

==> Square Root of (400) = V

==> V = 20 volts

*Understand* that this is a _very_ rough estimate, not a design number. A 50 volt capacitor would be okay in your case. 

Hope this helps.

Mark


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