coils/capacitors for crossovers?

Printed From: the12volt.com
Forum Name: Car Audio
Forum Discription: Car Stereos, Amplifiers, Crossovers, Processors, Speakers, Subwoofers, etc.
URL: https://www.the12volt.com/installbay/forum_posts.asp?tid=128634
Printed Date: May 13, 2025 at 12:32 AM

Topic: coils/capacitors for crossovers?

Posted By: carrfamilynj
Subject: coils/capacitors for crossovers?
Date Posted: September 26, 2011 at 8:09 PM

I have a pair of 8" MTX subwoofers. I am building a box for them and I am trying to find the correct coils and capacitors to create a 100-350 hz band-pass crossover network. I am not understanding the calculator on this site. Can anyone help?

Replies:

Posted By: i am an idiot
Date Posted: September 26, 2011 at 8:57 PM

What is the impedance of the driver?

Posted By: carrfamilynj
Date Posted: September 27, 2011 at 4:04 AM

4 ohm

Posted By: haemphyst
Date Posted: September 27, 2011 at 8:46 AM

Select the coil for 350Hz and down at 4-ohms - 2.5mH
Select the cap for 100Hz and up at 4-ohms - 285uF
Wire them in series with the woofer load, coil closest to the amplifier.

Ta daaaa.... 100-350Hz bandpass crossover at 4 ohms!

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It all reminds me of something that Molière once said to Guy de Maupassant at a café in Vienna: "That's nice. You should write it down."

Posted By: carrfamilynj
Date Posted: September 27, 2011 at 6:52 PM

Awesome, thanks man.

Posted By: i am an idiot
Date Posted: September 27, 2011 at 8:02 PM

The above mentioned crossover network will provide a 6dB/Octave roll off. If you need 12dB/Octave, it will take a couple more components per driver. Let us know if you are interested in the component values for said crossover.

Second order band pass filters consist of a 12 dB high pass filter followed by a 12 dB low pass filter. Either the high pass or low pass filter may be first in line. This combination of high pass and low pass filters allow a band of frequencies between the two crossover frequencies to pass with a steeper rate of cut-off than a first order filter. The high pass crossover frequency point must be lower than the low pass crossover frequency point.

As with the second order low pass and high pass filters, power above and below the respective crossover frequncies will be reduced by 93.75.% or 12 dB. Remember if the low pass frequency is less than 20 times the high pass frequency use this calculator for narrow band pass filters. For all others, use this calculator or the appropriate chart.

Posted By: i am an idiot
Date Posted: September 27, 2011 at 8:06 PM

Should the diagram in my above post have L1, C1 and L2 and C2???

Posted By: haemphyst
Date Posted: September 28, 2011 at 2:00 AM

i am an idiot wrote:

Should the diagram in my above post have L1, C1 and L2 and C2???

Yep.

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It all reminds me of something that Molière once said to Guy de Maupassant at a café in Vienna: "That's nice. You should write it down."

Posted By: i am an idiot
Date Posted: September 28, 2011 at 6:07 AM

Higher ups, let me know that you see this so I can not lose sleep worrying about whether or not it gets fixed.

Posted By: the12volt
Date Posted: September 28, 2011 at 6:57 AM

12 dB band pass filter... no, they are the same values.

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Posted By: i am an idiot
Date Posted: September 28, 2011 at 8:13 AM

So which frequency should we use to figure the values? 100Hz or 350Hz?

My logic tells me that same values in both places = high and low pass of the same frequency. But that's just my logic.

This calculator has the components in a slightly different configuration. This may have been the basis for my logic. It has been many years since I have used any of this type of a crossover.

https://archive.pac-audio.com/crossover/crossoverbp.asp

Posted By: the12volt
Date Posted: September 28, 2011 at 9:01 AM

The coil values are the same and the cap values are the same in that filter. You will use whichever band of frequencies you want to pass. The coils are low pass filters at the upper end of the band of frequencies you choose. The caps are high pass filters at the lowered end of that band.

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